WorldWideScience

Sample records for gan based metal

  1. GaN Micromechanical Resonators with Meshed Metal Bottom Electrode.

    Science.gov (United States)

    Ansari, Azadeh; Liu, Che-Yu; Lin, Chien-Chung; Kuo, Hao-Chung; Ku, Pei-Cheng; Rais-Zadeh, Mina

    2015-03-17

    This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO₂) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient ( d 33 ) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF₂) etch and therefore eliminating the need for backside lithography and etching.

  2. Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process

    Energy Technology Data Exchange (ETDEWEB)

    Swain, Basudev, E-mail: Swain@iae.re.kr [Institute for Advanced Engineering (IAE), Advanced Materials & Processing Center, Yongin-Si 449-863 (Korea, Republic of); Mishra, Chinmayee; Lee, Chan Gi; Park, Kyung-Soo [Institute for Advanced Engineering (IAE), Advanced Materials & Processing Center, Yongin-Si 449-863 (Korea, Republic of); Lee, Kun-Jae [Department of Energy Engineering, Dankook University, Cheonan 330-714 (Korea, Republic of)

    2015-07-15

    Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga{sub 0.97}N{sub 0.9}O{sub 0.09} is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga{sub 0.97}N{sub 0.9}O{sub 0.09} of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4 M HCl, 100 °C and pulp density of 100 kg/m{sup 3,} respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition. - Highlights: • Waste MOCVD dust is treated through mechanochemical leaching. • GaN is hardly leached, and converted to NaGaO{sub 2} through ball milling and annealing. • Process for gallium recovery from waste MOCVD dust has been developed. • Thermal analysis and phase properties of GaN to Ga{sub 2}O{sub 3} and GaN to NaGaO{sub 2} is revealed. • Solid-state chemistry involved in this process is reported.

  3. Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process.

    Science.gov (United States)

    Swain, Basudev; Mishra, Chinmayee; Lee, Chan Gi; Park, Kyung-Soo; Lee, Kun-Jae

    2015-07-01

    Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga0.97N0.9O0.09 is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga0.97N0.9O0.09 of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4M HCl, 100°C and pulp density of 100 kg/m(3,) respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. Metal contacts on ZnSe and GaN

    Energy Technology Data Exchange (ETDEWEB)

    Duxstad, Kristin Joy [Univ. of California, Berkeley, CA (United States). Materials Science and Mineral Engineering

    1997-05-01

    Recently, considerable interest has been focused on the development of blue light emitting materials and devices. The focus has been on GaN and ZnSe, direct band gap semiconductors with bands gaps of 3.4 and 2.6 eV, respectively. To have efficient, reliable devices it is necessary to have thermally and electrically stable Ohmic contacts. This requires knowledge of the metal-semiconductor reaction behavior. To date few studies have investigated this behavior. Much information has accumulated over the years on the behavior of metals on Si and GaAs. This thesis provides new knowledge for the more ionic wide band gap semiconductors. The initial reaction temperatures, first phases formed, and phase stability of Pt, Pd, and Ni on both semiconductors were investigated. The reactions of these metals on ZnSe and GaN are discussed in detail and correlated with predicted behavior. In addition, comparisons are made between these highly ionic semiconductors and Si and GaAs. The trends observed here should also be applicable to other II-VI and III-Nitride semiconductor systems, while the information on phase formation and stability should be useful in the development of contacts for ZnSe and GaN devices.

  5. GaN based nanorods for solid state lighting

    Energy Technology Data Exchange (ETDEWEB)

    Li Shunfeng; Waag, Andreas [Institute of Semiconductor Technology, Braunschweig University of Technology, 38106 Braunschweig (Germany)

    2012-04-01

    In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

  6. Synthesis, optical properties and residual strain effect of GaN nanowires generated via metal-assisted photochemical electroless etching

    KAUST Repository

    Najar, Adel

    2017-04-18

    Herein, we report on the studies of GaN nanowires (GaN NWs) prepared via a metal-assisted photochemical electroless etching method with Pt as the catalyst. It has been found that etching time greatly influences the growth of GaN NWs. The density and the length of nanowires increased with longer etching time, and excellent substrate coverage was observed. The average nanowire width and length are around 35 nm and 10 μm, respectively. Transmission electron microscopy (TEM) shows a single-crystalline wurtzite structure and is confirmed by X-ray measurements. The synthesis mechanism of GaN NWs using the metal-assisted photochemical electroless etching method was presented. Photoluminescence (PL) measurements of GaN NWs show red-shift PL peaks compared to the as-grown sample associated with the relaxation of compressive stress. Furthermore, a shift of the E2 peak to the lower frequency in the Raman spectra for the samples etched for a longer time confirms such a stress relaxation. Based on Raman measurements, the compressive stress σxx and the residual strain εxx were evaluated to be 0.23 GPa and 2.6 × 10−4, respectively. GaN NW synthesis using a low cost method might be used for the fabrication of power optoelectronic devices and gas sensors.

  7. Effects of radiation and temperature on gallium nitride (GaN) metal-semiconductor-metal ultraviolet photodetectors

    Science.gov (United States)

    Chiamori, Heather C.; Angadi, Chetan; Suria, Ateeq; Shankar, Ashwin; Hou, Minmin; Bhattacharya, Sharmila; Senesky, Debbie G.

    2014-06-01

    The development of radiation-hardened, temperature-tolerant materials, sensors and electronics will enable lightweight space sub-systems (reduced packaging requirements) with increased operation lifetimes in extreme harsh environments such as those encountered during space exploration. Gallium nitride (GaN) is a ceramic, semiconductor material stable within high-radiation, high-temperature and chemically corrosive environments due to its wide bandgap (3.4 eV). These material properties can be leveraged for ultraviolet (UV) wavelength photodetection. In this paper, current results of GaN metal-semiconductor-metal (MSM) UV photodetectors behavior after irradiation up to 50 krad and temperatures of 15°C to 150°C is presented. These initial results indicate that GaN-based sensors can provide robust operation within extreme harsh environments. Future directions for GaN-based photodetector technology for down-hole, automotive and space exploration applications are also discussed.

  8. Ab initio-based approach to reconstruction, adsorption and incorporation on GaN surfaces

    International Nuclear Information System (INIS)

    Ito, T; Akiyama, T; Nakamura, K

    2012-01-01

    Reconstruction, adsorption and incorporation on various GaN surfaces are systematically investigated using an ab initio-based approach that predicts the surface phase diagram as functions of temperature and beam-equivalent pressure (BEP). The calculated results for GaN surface reconstructions with polar (0 0 0 1), nonpolar (1 1 −2 0), semipolar (1 −1 0 1) and semipolar (1 1 −2 2) orientations imply that reconstructions on GaN surfaces with Ga adlayers generally appear on the polar and the semipolar surfaces, while the stable ideal surface without Ga adsorption is found on the nonpolar GaN(1 1 −2 0) surface because it satisfies the electron counting rule. The hydrogen adsorption on GaN(0 0 0 1) and GaN(1 1 −2 0) realizes several surface structures forming N–H and Ga–NH 2 bonds on their surfaces that depend on temperature and Ga BEP during metal-organic vapor-phase epitaxy (MOVPE). In contrast, the stable structures due to hydrogen adsorption on the semipolar GaN(1 −1 0 1) and GaN(1 1 −2 2) surfaces are not varied over the wide range of temperature and Ga BEP. This implies that the hydrogen adsorbed stable structures are expected to emerge on the semipolar surfaces during MOVPE regardless of the growth conditions. Furthermore, we clarify that Mg incorporation on GaN(1 −1 0 1) surfaces is enhanced by hydrogen adsorption consistent with experimental findings

  9. Synthesis, optical properties and residual strain effect of GaN nanowires generated via metal-assisted photochemical electroless etching

    KAUST Repository

    Najar, Adel; Shafa, Muhammad; Anjum, Dalaver H.

    2017-01-01

    Herein, we report on the studies of GaN nanowires (GaN NWs) prepared via a metal-assisted photochemical electroless etching method with Pt as the catalyst. It has been found that etching time greatly influences the growth of GaN NWs. The density

  10. Crystal Structures of GaN Nanodots by Nitrogen Plasma Treatment on Ga Metal Droplets

    Directory of Open Access Journals (Sweden)

    Yang-Zhe Su

    2018-06-01

    Full Text Available Gallium nitride (GaN is one of important functional materials for optoelectronics and electronics. GaN exists both in equilibrium wurtzite and metastable zinc-blende structural phases. The zinc-blende GaN has superior electronic and optical properties over wurtzite one. In this report, GaN nanodots can be fabricated by Ga metal droplets in ultra-high vacuum and then nitridation by nitrogen plasma. The size, shape, density, and crystal structure of GaN nanodots can be characterized by transmission electron microscopy. The growth parameters, such as pre-nitridation treatment on Si surface, substrate temperature, and plasma nitridation time, affect the crystal structure of GaN nanodots. Higher thermal energy could provide the driving force for the phase transformation of GaN nanodots from zinc-blende to wurtzite structures. Metastable zinc-blende GaN nanodots can be synthesized by the surface modification of Si (111 by nitrogen plasma, i.e., the pre-nitridation treatment is done at a lower growth temperature. This is because the pre-nitridation process can provide a nitrogen-terminal surface for the following Ga droplet formation and a nitrogen-rich condition for the formation of GaN nanodots during droplet epitaxy. The pre-nitridation of Si substrates, the formation of a thin SiNx layer, could inhibit the phase transformation of GaN nanodots from zinc-blende to wurtzite phases. The pre-nitridation treatment also affects the dot size, density, and surface roughness of samples.

  11. Epitaxial Gd2O3 on GaN and AlGaN: a potential candidate for metal oxide semiconductor based transistors on Si for high power application

    Science.gov (United States)

    Ghosh, Kankat; Das, S.; Khiangte, K. R.; Choudhury, N.; Laha, Apurba

    2017-11-01

    We report structural and electrical properties of hexagonal Gd2O3 grown epitaxially on GaN/Si (1 1 1) and AlGaN/GaN/Si(1 1 1) virtual substrates. GaN and AlGaN/GaN heterostructures were grown on Si(1 1 1) substrates by plasma assisted molecular beam epitaxy (PA-MBE), whereas the Gd2O3 layer was grown by the pulsed laser ablation (PLA) technique. Initial structural characterizations show that Gd2O3 grown on III-nitride layers by PLA, exhibit a hexagonal structure with an epitaxial relationship as {{≤ft[ 0 0 0 1 \\right]}G{{d2}{{O}3}}}||{{≤ft[ 0 0 0 1 \\right]}GaN} and {{≤ft[ 1 \\bar{1} 0 0 \\right]}G{{d2}{{O}3}}}||{{≤ft[ 1 \\bar{1} 0 0 \\right]}GaN} . X-ray photoelectron measurements of the valence bands revealed that Gd2O3 exhibits band offsets of 0.97 eV and 0.4 eV, for GaN and Al0.3Ga0.7N, respectively. Electrical measurements such as capacitance-voltage and leakage current characteristics further confirm that epi-Gd2O3 on III-nitrides could be a potential candidate for future metal-oxide-semiconductor (MOS)-based transistors also for high power applications in radio frequency range.

  12. Determination of the nitrogen vacancy as a shallow compensating center in GaN doped with divalent metals.

    Science.gov (United States)

    Buckeridge, J; Catlow, C R A; Scanlon, D O; Keal, T W; Sherwood, P; Miskufova, M; Walsh, A; Woodley, S M; Sokol, A A

    2015-01-09

    We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p-type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

  13. Determination of the Nitrogen Vacancy as a Shallow Compensating Center in GaN Doped with Divalent Metals

    Science.gov (United States)

    Buckeridge, J.; Catlow, C. R. A.; Scanlon, D. O.; Keal, T. W.; Sherwood, P.; Miskufova, M.; Walsh, A.; Woodley, S. M.; Sokol, A. A.

    2015-01-01

    We report accurate energetics of defects introduced in GaN on doping with divalent metals, focusing on the technologically important case of Mg doping, using a model that takes into consideration both the effect of hole localization and dipolar polarization of the host material, and includes a well-defined reference level. Defect formation and ionization energies show that divalent dopants are counterbalanced in GaN by nitrogen vacancies and not by holes, which explains both the difficulty in achieving p -type conductivity in GaN and the associated major spectroscopic features, including the ubiquitous 3.46 eV photoluminescence line, a characteristic of all lightly divalent-metal-doped GaN materials that has also been shown to occur in pure GaN samples. Our results give a comprehensive explanation for the observed behavior of GaN doped with low concentrations of divalent metals in good agreement with relevant experiment.

  14. Improved crystal quality of a-plane GaN with high- temperature 3-dimensional GaN buffer layers deposited by using metal-organic chemical vapor deposition

    International Nuclear Information System (INIS)

    Park, Sung Hyun; Moon, Dae Young; Kim, Bum Ho; Kim, Dong Uk; Chang, Ho Jun; Jeon, Heon Su; Yoon, Eui Joon; Joo, Ki Su; You, Duck Jae; Nanishi, Yasushi

    2012-01-01

    a-plane GaN on r-plane sapphire substrates suffers from high density defects and rough surfaces. To obtain pit-free a-plane GaN by metal-organic chemical vapor deposition, we intentionally grew high-temperature (HT) 3-dimensional (3D) GaN buffer layers on a GaN nucleation layer. The effects of the HT 3D GaN buffer layers on crystal quality and the surface morphology of a-plane GaN were studied. The insertion of a 3D GaN buffer layer with an optimum thickness was found to be an effective method to obtain pit-free a-plane GaN with improved crystalline quality on r-plane sapphire substrates. An a-plane GaN light emitting diode (LED) at an emission wavelength around 480 nm with negligible peak shift was successfully fabricated.

  15. Electronic and optical device applications of hollow cathode plasma assisted atomic layer deposition based GaN thin films

    International Nuclear Information System (INIS)

    Bolat, Sami; Tekcan, Burak; Ozgit-Akgun, Cagla; Biyikli, Necmi; Okyay, Ali Kemal

    2015-01-01

    Electronic and optoelectronic devices, namely, thin film transistors (TFTs) and metal–semiconductor–metal (MSM) photodetectors, based on GaN films grown by hollow cathode plasma-assisted atomic layer deposition (PA-ALD) are demonstrated. Resistivity of GaN thin films and metal-GaN contact resistance are investigated as a function of annealing temperature. Effect of the plasma gas and postmetallization annealing on the performances of the TFTs as well as the effect of the annealing on the performance of MSM photodetectors are studied. Dark current to voltage and responsivity behavior of MSM devices are investigated as well. TFTs with the N 2 /H 2 PA-ALD based GaN channels are observed to have improved stability and transfer characteristics with respect to NH 3 PA-ALD based transistors. Dark current of the MSM photodetectors is suppressed strongly after high-temperature annealing in N 2 :H 2 ambient

  16. Electronic structures and valence band splittings of transition metals doped GaNs

    International Nuclear Information System (INIS)

    Lee, Seung-Cheol; Lee, Kwang-Ryeol; Lee, Kyu-Hwan

    2007-01-01

    For a practical viewpoint, presence of spin splitting of valence band in host semiconductors by the doping of transition metal (TM) ions is an essential property when designing a diluted magnetic semiconductors (DMS) material. The first principle calculations were performed on the electronic and magnetic structure of 3d transition metal doped GaN. V, Cr, and Mn doped GaNs could not be candidates for DMS materials since most of their magnetic moments is concentrated on the TM ions and the splittings of valence band were negligible. In the cases of Fe, Co, Ni, and Cu doped GaNs, on the contrary, long-ranged spin splitting of valence band was found, which could be candidates for DMS materials

  17. Conductivity based on selective etch for GaN devices and applications thereof

    Science.gov (United States)

    Zhang, Yu; Sun, Qian; Han, Jung

    2015-12-08

    This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm.sup.2) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

  18. Fast Growth of GaN Epilayers via Laser-Assisted Metal-Organic Chemical Vapor Deposition for Ultraviolet Photodetector Applications.

    Science.gov (United States)

    Rabiee Golgir, Hossein; Li, Da Wei; Keramatnejad, Kamran; Zou, Qi Ming; Xiao, Jun; Wang, Fei; Jiang, Lan; Silvain, Jean-François; Lu, Yong Feng

    2017-06-28

    In this study, we successfully developed a carbon dioxide (CO 2 )-laser-assisted metal-organic chemical vapor deposition (LMOCVD) approach to fast synthesis of high-quality gallium nitride (GaN) epilayers on Al 2 O 3 [sapphire(0001)] substrates. By employing a two-step growth procedure, high crystallinity and smooth GaN epilayers with a fast growth rate of 25.8 μm/h were obtained. The high crystallinity was confirmed by a combination of techniques, including X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and atomic force microscopy. By optimizing growth parameters, the ∼4.3-μm-thick GaN films grown at 990 °C for 10 min showed a smooth surface with a root-mean-square surface roughness of ∼1.9 nm and excellent thickness uniformity with sharp GaN/substrate interfaces. The full-width at half-maximum values of the GaN(0002) X-ray rocking curve of 313 arcsec and the GaN(101̅2) X-ray rocking curve of 390 arcsec further confirmed the high crystallinity of the GaN epilayers. We also fabricated ultraviolet (UV) photodetectors based on the as-grown GaN layers, which exhibited a high responsivity of 0.108 A W -1 at 367 nm and a fast response time of ∼125 ns, demonstrating its high optical quality with potential in optoelectronic applications. Our strategy thus provides a simple and cost-effective means toward fast and high-quality GaN heteroepitaxy growth suitable for fabricating high-performance GaN-based UV detectors.

  19. Radiation sensors based on GaN microwires

    Science.gov (United States)

    Verheij, D.; Peres, M.; Cardoso, S.; Alves, L. C.; Alves, E.; Durand, C.; Eymery, J.; Lorenz, K.

    2018-05-01

    GaN microwires were shown to possess promising characteristics as building blocks for radiation resistant particle detectors. They were grown by metal organic vapour phase epitaxy with diameters between 1 and 2 μm and lengths around 20 μm. Devices were fabricated by depositing gold contacts at the extremities of the wires using photolithography. The response of these single wire radiation sensors was then studied under irradiation with 2 MeV protons. Severe degradation of the majority of devices only sets in for fluences above protons cm‑2 revealing good radiation resistance. During proton irradiation, a clear albeit small current gain was observed with a corresponding decay time below 1 s. Photoconductivity measurements upon irradiation with UV light were carried out before and after the proton irradiation. Despite a relatively low gain, attributed to significant dark currents caused by a high dopant concentration, fast response times of a few seconds were achieved comparable to state-of-the-art GaN nanowire photodetectors. Irradiation and subsequent annealing resulted in an overall improvement of the devices regarding their response to UV radiation. The photocurrent gain increased compared to the values that were obtained prior to the irradiation, without compromising the decay times. The results indicate the possibility of using GaN microwires not only as UV detectors, but also as particle detectors.

  20. Thermodynamic analysis of trimethylgallium decomposition during GaN metal organic vapor phase epitaxy

    Science.gov (United States)

    Sekiguchi, Kazuki; Shirakawa, Hiroki; Chokawa, Kenta; Araidai, Masaaki; Kangawa, Yoshihiro; Kakimoto, Koichi; Shiraishi, Kenji

    2018-04-01

    We analyzed the decomposition of Ga(CH3)3 (TMG) during the metal organic vapor phase epitaxy (MOVPE) of GaN on the basis of first-principles calculations and thermodynamic analysis. We performed activation energy calculations of TMG decomposition and determined the main reaction processes of TMG during GaN MOVPE. We found that TMG reacts with the H2 carrier gas and that (CH3)2GaH is generated after the desorption of the methyl group. Next, (CH3)2GaH decomposes into (CH3)GaH2 and this decomposes into GaH3. Finally, GaH3 becomes GaH. In the MOVPE growth of GaN, TMG decomposes into GaH by the successive desorption of its methyl groups. The results presented here concur with recent high-resolution mass spectroscopy results.

  1. Electronic structure and magnetic properties of substitutional transition-metal atoms in GaN nanotubes

    International Nuclear Information System (INIS)

    Zhang Min; Shi Jun-Jie

    2014-01-01

    The electronic structure and magnetic properties of the transition-metal (TM) atoms (Sc—Zn, Pt and Au) doped zigzag GaN single-walled nanotubes (NTs) are investigated using first-principles spin-polarized density functional calculations. Our results show that the bindings of all TM atoms are stable with the binding energy in the range of 6–16 eV. The Sc- and V-doped GaN NTs exhibit a nonmagnetic behavior. The GaN NTs doped with Ti, Mn, Ni, Cu and Pt are antiferromagnetic. On the contrary, the Cr-, Fe-, Co-, Zn- and Au-doped GaN NTs show the ferromagnetic characteristics. The Mn- and Co-doped GaN NTs induce the largest local moment of 4μ B among these TM atoms. The local magnetic moment is dominated by the contribution from the substitutional TM atom and the N atoms bonded with it. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  2. Beryllium doped p-type GaN grown by metal-organic chemical vapor depostion

    International Nuclear Information System (INIS)

    Al-Tahtamouni, T.M.; Sedhain, A.; Lin, J.Y.; Jiang, H.X.

    2010-01-01

    The authors report on the growth of Be-doped p-type GaN epilayers by metal-organic chmical vapor deposition (MOCVD). The electrical and optical properties of the Be-doped GaN epilayers were studied by Hall-effect measurements and photoluminescence (PL) spectroscopy. The PL spectra of Be-doped GaN epilayers ethibited two emission lines at 3.36 and 2.71 eV, which were obsent in undoped epilayers. The transition at 3.36 eV was at 3.36 and 2.71eV, which were absent in undoped epilayers. The transition at 3.36 eV was assigned to the transition of free electrons to the neutral Be acceptor Be d eg.. The transition at 2.71 eV was assigned to the transition of electrons bound to deep level donors to the Be d eg. acceptors. Three independent measurements: (a) resistivity vs. temperature, (b) PL peak positions between Be doped and undoped GaN and (c) activation energy of 2.71 eV transition all indicate that the Be energy level is between 120 and 140 meV above the valence band. This is about 20-40 meV shallower than the Mg energy level (160 meV) in GaN. It is thus concluded that Be could be an excellent acceptor dopant in nitride materials. (authors).

  3. GaN MOSFET with Boron Trichloride-Based Dry Recess Process

    International Nuclear Information System (INIS)

    Jiang, Y; Wang, Q P; Tamai, K; Ao, J P; Ohno, Y; Miyashita, T; Motoyama, S; Wang, D J

    2013-01-01

    The dry recessed-gate GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure using boron trichloride (BCl 3 ) as etching gas were fabricated and characterized. Etching with different etching power was conducted. Devices with silicon tetrachloride (SiCl 4 ) etching gas were also prepared for comparison. Field-effect mobility and interface state density were extracted from current-voltage (I-V) characteristics. GaN MOSFETs on AlGaN/GaN heterostructure with BCl 3 based dry recess achieved a high maximum electron mobility of 141.5 cm 2 V −1 s −1 and a low interface state density.

  4. High sensitivity hydrogen sensors based on GaN

    Czech Academy of Sciences Publication Activity Database

    Yatskiv, Roman; Grym, Jan; Žďánský, Karel

    2012-01-01

    Roč. 7, č. 9 (2012), s. 1661-1663 ISSN 1610-1642. [16th International Semiconducting and Insulating Materials Conference (SIMC-XVI). Stockholm, 19.06.2011-23.06.2011] R&D Projects: GA MŠk(CZ) OC10021 Institutional support: RVO:67985882 Keywords : Pt nanoparticles * Graphite based Schottky diodes * Hydrogen sensor * GaN Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  5. The structural and optical properties of metal ion-implanted GaN

    Czech Academy of Sciences Publication Activity Database

    Macková, Anna; Malinský, Petr; Sofer, Z.; Šimek, P.; Sedmidubský, D.; Veselý, M.; Bottger, R.

    2016-01-01

    Roč. 371, MAR (2016), s. 254-257 ISSN 0168-583X. [22nd International conference on Ion Beam Analysis (IBA). Opatija, 14.06.2015-19.06.2015] R&D Projects: GA MŠk(CZ) LM2011019; GA ČR GA15-01602S Institutional support: RVO:61389005 Keywords : RBS channelling * metal-implanted GaN * structural changes Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.109, year: 2016

  6. Catalyst and processing effects on metal-assisted chemical etching for the production of highly porous GaN

    International Nuclear Information System (INIS)

    Geng, Xuewen; Grismer, Dane A; Bohn, Paul W; Duan, Barrett K; Zhao, Liancheng

    2013-01-01

    Metal-assisted chemical etching is a facile method to produce micro-/nanostructures in the near-surface region of gallium nitride (GaN) and other semiconductors. Detailed studies of the production of porous GaN (PGaN) using different metal catalysts and GaN doping conditions have been performed in order to understand the mechanism by which metal-assisted chemical etching is accomplished in GaN. Patterned catalysts show increasing metal-assisted chemical etching activity to n-GaN in the order Ag < Au < Ir < Pt. In addition, the catalytic behavior of continuous films is compared to discontinuous island films. Continuous metal films strongly shield the surface, hindering metal-assisted chemical etching, an effect which can be overcome by using discontinuous films or increasing the irradiance of the light source. With increasing etch time or irradiance, PGaN morphologies change from uniform porous structures to ridge and valley structures. The doping type plays an important role, with metal-assisted chemical etching activity increasing in the order p-GaN < intrinsic GaN < n-GaN. Both the catalyst identity and the doping type effects are explained by the work functions and the related band offsets that affect the metal-assisted chemical etching process through a combination of different barriers to hole injection and the formation of hole accumulation/depletion layers at the metal–semiconductor interface. (paper)

  7. Broadband nanophotonic waveguides and resonators based on epitaxial GaN thin films

    Energy Technology Data Exchange (ETDEWEB)

    Bruch, Alexander W.; Xiong, Chi; Leung, Benjamin; Poot, Menno; Han, Jung; Tang, Hong X., E-mail: hong.tang@yale.edu [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06511 (United States)

    2015-10-05

    We demonstrate broadband, low loss optical waveguiding in single crystalline GaN grown epitaxially on c-plane sapphire wafers through a buffered metal-organic chemical vapor phase deposition process. High Q optical microring resonators are realized in near infrared, infrared, and near visible regimes with intrinsic quality factors exceeding 50 000 at all the wavelengths we studied. TEM analysis of etched waveguide reveals growth and etch-induced defects. Reduction of these defects through improved material and device processing could lead to even lower optical losses and enable a wideband photonic platform based on GaN-on-sapphire material system.

  8. Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination

    Science.gov (United States)

    2016-06-01

    Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination Distribution Statement A. Approved for public release; distribution is...Final Technical Report BRBAA08-Per5-Y-1-2-0030 Title: “Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination ” Grant...Analysis  .............................................................................................  23   6.   Gamma-ray Discrimination

  9. Polycrystalline GaN layer recrystallization by metal-induced method during the baking process

    Energy Technology Data Exchange (ETDEWEB)

    Jagoda, A.; Stanczyk, B.; Dobrzanski, L.; Diduszko, R. [Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw 118 (Poland)

    2007-04-15

    Radio frequency reactive sputtering was used to produce gallium nitride films on thermally oxidized silicon substrates at room temperature. Metallic Ga (purity 6N) was used as the target, N{sub 2} and Ar were utilized as sputtering gases. Amorphous GaN was obtained by metal-induced crystallization with a Ni assistance. The nickel particles were scattered onto the surface by rf sputtering and their density was 2 x 10{sup 14} atoms/cm{sup 2} or 4 x 10{sup 14} atoms/cm{sup 2}, which corresponds to 0.02 nm and 0.04 nm thick layer. These values are less than a monolayer thickness, so they are not continuous. Samples were annealed at 700 C for 3 h and at 900 C for 5 min in a RTP furnace. The 2.5 {mu}m GaN layers grown on the Ni-coated SiO{sub 2} surface recrystallized during annealing forming crystals of (002) orientation. The catalytic regrowth mechanism of GaN is discussed on the basis of experimental results. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

    International Nuclear Information System (INIS)

    Burnham, Shawn D.; Doolittle, W. Alan; Namkoong, Gon; Look, David C.; Clafin, Bruce

    2008-01-01

    The metal modulated epitaxy (MME) growth technique is reported as a reliable approach to obtain reproducible large hole concentrations in Mg-doped GaN grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates. An extremely Ga-rich flux was used, and modulated with the Mg source according to the MME growth technique. The shutter modulation approach of the MME technique allows optimal Mg surface coverage to build between MME cycles and Mg to incorporate at efficient levels in GaN films. The maximum sustained concentration of Mg obtained in GaN films using the MME technique was above 7x10 20 cm -3 , leading to a hole concentration as high as 4.5x10 18 cm -3 at room temperature, with a mobility of 1.1 cm 2 V -1 s -1 and a resistivity of 1.3 Ω cm. At 580 K, the corresponding values were 2.6x10 19 cm -3 , 1.2 cm 2 V -1 s -1 , and 0.21 Ω cm, respectively. Even under strong white light, the sample remained p-type with little change in the electrical parameters

  11. Reproducible increased Mg incorporation and large hole concentration in GaN using metal modulated epitaxy

    Science.gov (United States)

    Burnham, Shawn D.; Namkoong, Gon; Look, David C.; Clafin, Bruce; Doolittle, W. Alan

    2008-07-01

    The metal modulated epitaxy (MME) growth technique is reported as a reliable approach to obtain reproducible large hole concentrations in Mg-doped GaN grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates. An extremely Ga-rich flux was used, and modulated with the Mg source according to the MME growth technique. The shutter modulation approach of the MME technique allows optimal Mg surface coverage to build between MME cycles and Mg to incorporate at efficient levels in GaN films. The maximum sustained concentration of Mg obtained in GaN films using the MME technique was above 7×1020cm-3, leading to a hole concentration as high as 4.5×1018cm-3 at room temperature, with a mobility of 1.1cm2V-1s-1 and a resistivity of 1.3Ωcm. At 580K, the corresponding values were 2.6×1019cm-3, 1.2cm2V-1s-1, and 0.21Ωcm, respectively. Even under strong white light, the sample remained p-type with little change in the electrical parameters.

  12. Transmission electron microscopy of GaN based, doped semiconductor heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Pretorius, A.

    2006-07-01

    This thesis addresses the analysis of GaN based heterostructures with transmission electron microscopy (TEM). Basic properties of the material of interest are introduced in chapter 2. These include the structural and optical properties as well as an introduction to the growth methods used for the samples analysed in this work. In chapter 3 a brief theoretical treatment of TEM is given. As one main topic of this work is the determination of the In concentration in InGaN islands using strain state analysis, a detailed description of the method is given. Chapter 4 describes the results obtained for pyramidal defects present in metalorganic vapour phase epitaxy grown GaN:Mg with high dopant concentration. Based on the experimental results and the well established knowledge that GaN of inverted polarity is present inside the pyramidal defects, a variety of basal plane inversion domain boundary models was set up. From these models, HRTEM images were simulated using the multislice approach, followed by a quantitative comparison to experimentally obtained HRTEM images. Another focus of this work is the analysis of In{sub x}Ga{sub 1-x}N islands grown on GaN presented in chapter 5. Following a literature survey which describes different methods used to obtain In{sub x}Ga{sub 1-x}N islands, the first topic is the distinction of In{sub x}Ga{sub 1-x}N islands and metal droplets, which can form during growth. This is followed by the experimental results of molecular beam epitaxy and metalorganic vapour phase epitaxy grown In{sub x}Ga{sub 1-x}N island and quantum dot samples. (orig.)

  13. Design and simulation of GaN based Schottky betavoltaic nuclear micro-battery

    International Nuclear Information System (INIS)

    San, Haisheng; Yao, Shulin; Wang, Xiang; Cheng, Zaijun; Chen, Xuyuan

    2013-01-01

    The current paper presents a theoretical analysis of Ni-63 nuclear micro-battery based on a wide-band gap semiconductor GaN thin-film covered with thin Ni/Au films to form Schottky barrier for carrier separation. The total energy deposition in GaN was calculated using Monte Carlo methods by taking into account the full beta spectral energy, which provided an optimal design on Schottky barrier width. The calculated results show that an 8 μm thick Schottky barrier can collect about 95% of the incident beta particle energy. Considering the actual limitations of current GaN growth technique, a Fe-doped compensation technique by MOCVD method can be used to realize the n-type GaN with a carrier concentration of 1×10 15 cm −3 , by which a GaN based Schottky betavoltaic micro-battery can achieve an energy conversion efficiency of 2.25% based on the theoretical calculations of semiconductor device physics. - Highlights: • Ni-63 is employed as the pure beta radioisotope source. • The Schottky junction betavoltaic battery is based on the wide-band gap semiconductor GaN. • The total energy deposition of incident beta particles in GaN was simulated by the Monte Carlo method. • A Fe-doped compensation technique is suggested to increase the energy conversion efficiency

  14. Emission channeling studies on transition-metal doped GaN and ZnO: Cation versus anion substitution

    CERN Document Server

    AUTHOR|(CDS)2070176; Wahl, Ulrich; Martins Correia, Joao; Amorim, Lígia; Silva, Daniel; Decoster, Stefan; Castro Ribeiro Da Silva, Manuel; Temst, Kristiaan; Vantomme, André

    2014-01-01

    The magnetic and electric properties of impurities in semiconductors are strongly dependent on the lattice sites which they occupy. While the majority site can often be predicted based on chemical similarities with the host elements and is usually simple to confirm experimentally, minority sites are far more complicated to predict, detect and identify. We have carried out extensive beta− emission channeling studies on the lattice location of transition metal impurities in wide-gap dilute magnetic semiconductors, namely Co and Mn in GaN and ZnO, making use of radioactive 61Co and 56Mn implanted at the ISOLDE facility at CERN. In addition to the majority occupation of cation (Ga, Zn) sites, we located significant fractions (of the order of 20%) of the Co and Mn impurities in anion (N, O) sites, which are virtually unaffected by thermal annealing up to 900 °C. Here, we present the beta− emission channeling experiments on 61Co-implanted GaN. We discuss these results in the context of our recent reports of mi...

  15. Design of Low Inductance Switching Power Cell for GaN HEMT Based Inverter

    DEFF Research Database (Denmark)

    Gurpinar, Emre; Iannuzzo, Francesco; Yang, Yongheng

    2018-01-01

    . The design of gate drivers for the GaN HEMT devices is presented. Parasitic inductance and resistance of the proposed design are extracted with finite element analysis and discussed. Common-mode behaviours based on the SPICE model of the converter are analyzed. Experimental results on the designed 3L......In this paper, an ultra-low inductance power cell is designed for a three-Level Active Neutral Point Clamped (3LANPC) based on 650 V gallium nitride (GaN) HEMT devices. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices...... are presented. The commutation loops, which mainly contribute to voltage overshoots and increase of switching losses, are discussed. The ultra-low inductance power cell design based on a four-layer Printed Circuit Board (PCB) with the aim to maximize the switching performance of GaN HEMTs is explained...

  16. Metal modulation epitaxy growth for extremely high hole concentrations above 1019 cm-3 in GaN

    Science.gov (United States)

    Namkoong, Gon; Trybus, Elaissa; Lee, Kyung Keun; Moseley, Michael; Doolittle, W. Alan; Look, David C.

    2008-10-01

    The free hole carriers in GaN have been limited to concentrations in the low 1018cm-3 range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ˜10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ˜1.5×1019cm-3.

  17. Metal modulation epitaxy growth for extremely high hole concentrations above 1019 cm-3 in GaN

    International Nuclear Information System (INIS)

    Namkoong, Gon; Trybus, Elaissa; Lee, Kyung Keun; Moseley, Michael; Doolittle, W. Alan; Look, David C.

    2008-01-01

    The free hole carriers in GaN have been limited to concentrations in the low 10 18 cm -3 range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ∼10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ∼1.5x10 19 cm -3

  18. Control of residual carbon concentration in GaN high electron mobility transistor and realization of high-resistance GaN grown by metal-organic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    He, X.G. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhao, D.G., E-mail: dgzhao@red.semi.ac.cn [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Jiang, D.S.; Liu, Z.S.; Chen, P.; Le, L.C.; Yang, J.; Li, X.J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang, S.M.; Zhu, J.J.; Wang, H.; Yang, H. [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China)

    2014-08-01

    GaN films were grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions. The influences of MOCVD growth parameters, i.e., growth pressure, ammonia (NH{sub 3}) flux, growth temperature, trimethyl-gallium flux and H{sub 2} flux, on residual carbon concentration ([C]) were systematically investigated. Secondary ion mass spectroscopy measurements show that [C] can be effectively modulated by growth conditions. Especially, it can increase by reducing growth pressure up to two orders of magnitude. High-resistance (HR) GaN epilayer with a resistivity over 1.0 × 10{sup 9} Ω·cm is achieved by reducing growth pressure. The mechanism of the formation of HR GaN epilayer is discussed. An Al{sub x}Ga{sub 1−x}N/GaN high electron mobility transistor structure with a HR GaN buffer layer and an additional low-carbon GaN channel layer is presented, exhibiting a high two dimensional electron gas mobility of 1815 cm{sup 2}/Vs. - Highlights: • Influence of MOCVD parameters on residual carbon concentration in GaN is studied. • GaN layer with a resistivity over 1 × 10{sup 9} Ω·cm is achieved by reducing growth pressure. • High electron mobility transistor (HEMT) structures were prepared. • Control of residual carbon content results in HEMT with high 2-D electron gas mobility.

  19. In0.15Ga0.85N visible-light metal-semiconductor-metal photodetector with GaN interlayers deposited by pulsed NH3

    Science.gov (United States)

    Wang, Hongxia; Zhang, Xiaohan; Wang, Hailong; Lv, Zesheng; Li, Yongxian; Li, Bin; Yan, Huan; Qiu, Xinjia; Jiang, Hao

    2018-05-01

    InGaN visible-light metal-semiconductor-metal photodetectors with GaN interlayers deposited by pulsed NH3 were fabricated and characterized. By periodically inserting the GaN thin interlayers, the surface morphology of InGaN active layer is improved and the phase separation is suppressed. At 5 V bias, the dark current reduced from 7.0 × 10-11 A to 7.0 × 10-13 A by inserting the interlayers. A peak responsivity of 85.0 mA/W was measured at 420 nm and 5 V bias, corresponding to an external quantum efficiency of 25.1%. The insertion of GaN interlayers also lead to a sharper spectral response cutoff.

  20. High growth rate GaN on 200 mm silicon by metal-organic vapor phase epitaxy for high electron mobility transistors

    Science.gov (United States)

    Charles, M.; Baines, Y.; Bavard, A.; Bouveyron, R.

    2018-02-01

    It is increasingly important to reduce the cycle time of epitaxial growth, in order to reduce the costs of device fabrication, especially for GaN based structures which typically have growth cycles of several hours. We have performed a comprehensive study using metal-organic vapor phase epitaxy (MOVPE) investigating the effects of changing GaN growth rates from 0.9 to 14.5 μm/h. Although there is no significant effect on the strain incorporated in the layers, we have seen changes in the surface morphology which can be related to the change in dislocation behaviour and surface diffusion effects. At the small scale, as seen by AFM, increased dislocation density for higher growth rates leads to increased pinning of growth terraces, resulting in more closely spaced terraces. At a larger scale of hundreds of μm observed by optical profiling, we have related the formation of grains to the rate of surface diffusion of adatoms using a random walk model, implying diffusion distances from 30 μm for the highest growth rates up to 100 μm for the lowest. The increased growth rate also increases the intrinsic carbon incorporation which can increase the breakdown voltage of GaN films. Despite an increased threading dislocation density, these very high growth rates of 14.5 μm/hr by MOVPE have been shown to be appealing for reducing epitaxial growth cycle times and therefore costs in High Electron Mobility Transistor (HEMT) structures.

  1. Influence of AlGaN Buffer Growth Temperature on GaN Epilayer based on Si(lll) Substrate

    International Nuclear Information System (INIS)

    Wei Meng; Wang Xiaoliang; Pan Xu; Xiao Hongling; Wang Cuimei; Zhang Minglan; Wang Zhanguo

    2011-01-01

    This paper investigated the influence of AlGaN buffer growth temperature on strain status and crystal quality of the GaN film on Si(111) sbustrates by metal organic chemical vapor deposition. It was demonstrated by the optical microscopy that AlGaN buffer gorwth temperature had a remarkable effect on compensating tensil stress in top GaN layer and preventing the formation of cracks. X-ray diffraction and atomic force microscopy analysis showed crystal quality and surface morphology of the GaN epilayer could be improved through increasing AlGaN buffer growth temperature. 1μm crack-free GaN epilayer on Si (111) substrates was obtained with graded AlGaN buffer layer at optimized temperature of 1050 deg. C. Transmission electron microscopy analysis revealed that a significant reduction in threading dislocations was achieved in GaN epilayer.

  2. RADIATION PERFORMANCE OF GAN AND INAS/GAAS QUANTUM DOT BASED DEVICES SUBJECTED TO NEUTRON RADIATION

    Directory of Open Access Journals (Sweden)

    Dhiyauddin Ahmad Fauzi

    2017-05-01

    Full Text Available In addition to their useful optoelectronics functions, gallium nitride (GaN and quantum dots (QDs based structures are also known for their radiation hardness properties. With demands on such semiconductor material structures, it is important to investigate the differences in reliability and radiation hardness properties of these two devices. For this purpose, three sets of GaN light-emitting diode (LED and InAs/GaAs dot-in-a well (DWELL samples were irradiated with thermal neutron of fluence ranging from 3×1013 to 6×1014 neutron/cm2 in PUSPATI TRIGA research reactor. The radiation performances for each device were evaluated based on the current-voltage (I-V and capacitance-voltage (C-V electrical characterisation method. Results suggested that the GaN based sample is less susceptible to electrical changes due to the thermal neutron radiation effects compared to the QD based sample.

  3. Thermoelastic Stress Field Investigation of GaN Material for Laser Lift-off Technique based on Finite Element Method

    International Nuclear Information System (INIS)

    Ting, Wang; Zhan-Zhong, Cui; Li-Xin, Xu

    2009-01-01

    The transient thermoelastic stress fields of GaN films is analyzed by the finite element method for the laser lift-off (LLO) technique. Stress distributions in GaN films irradiated by pulse laser with different energy densities as functions of time and depth are simulated. The results show that the high thermoelastic stress distributions in GaN films localize within about 1 μm below the GaN/Al 2 O 3 interface using proper laser parameters. It is also found that GaN films can avoid the thermal deformation because the maximum thermoelastic stress 4.28 GPa is much smaller than the yield strength of GaN 15GPa. The effects of laser beam dimension and the thickness of GaN films on stress distribution are also analyzed. The variation range of laser beam dimension as a function of the thickness of GaN films is simulated to keep the GaN films free of thermal deformation. LLO experiments are also carried out. GaN-based light-emitting diodes (LEDs) are separated from sapphire substrates using the parameters obtained from the simulation. Compared with devices before LLO, P–I–V measurements of GaN-based LEDs after LLO show that the electrical and optical characteristics improve greatly, indicating that no stress damage is brought to GaN films using proper parameters obtained by calculation during LLO

  4. Analysis and modelling of GaN Schottky-based circuits at millimeter wavelengths

    International Nuclear Information System (INIS)

    Pardo, D; Grajal, J

    2015-01-01

    This work presents an analysis of the capabilities of GaN Schottky diodes for frequency multipliers and mixers at millimeter wavelengths. By using a Monte Carlo (MC) model of the diode coupled to a harmonic balance technique, the electrical and noise performances of these circuits are investigated. Despite the lower electron mobility of GaN compared to GaAs, multipliers based on GaN Schottky diodes can be competitive in the first stages of multiplier chains, due to the excellent power handling capabilities of this material. The performance of these circuits can be improved by taking advantage of the lateral Schottky diode structures based on AlGaN/GaN HEMT technology. (paper)

  5. Interface gap states and Schottky barrier inhomogeneity at metal/n-type GaN Schottky contacts

    International Nuclear Information System (INIS)

    Mamor, M

    2009-01-01

    The barrier heights (BH) of various metals including Pd, Pt and Ni on n-type GaN (M/n-GaN) have been measured in the temperature range 80-400 K with using a current-voltage (I-V) technique. The temperature dependence of the I-V characteristics of M/n-GaN have shown non-ideal behaviors and indicate the presence of a non-uniform distribution of surface gap states, resulting from the residual defects in the as grown GaN. The surface gap states density N ss , as well as its temperature dependence were obtained from the bias and temperature dependence of the ideality factor n(V,T) and the barrier height Φ Bn (V,T). Further, a dependence of zero-bias BH Φ 0Bn on the metal work function (Φ m ) with an interface parameter coefficient of proportionality of 0.47 is found. This result indicates that the Fermi level at the M/n-GaN interface is unpinned. Additionally, the presence of lateral inhomogeneities of the BH, with two Gaussian distributions of the BH values is seen. However, the non-homogeneous SBH is found to be correlated to the surface gap states density, in that Φ 0Bn becomes smaller with increasing N ss . These findings suggest that the lateral inhomogeneity of the SBH is connected to the non-uniform distribution of the density of surface gap states at metal/GaN which is attributed to the presence of native defects in the as grown GaN. Deep level transient spectroscopy confirms the presence of native defects with discrete energy levels at GaN and provides support to this interpretation.

  6. High-voltage vertical GaN Schottky diode enabled by low-carbon metal-organic chemical vapor deposition growth

    Science.gov (United States)

    Cao, Y.; Chu, R.; Li, R.; Chen, M.; Chang, R.; Hughes, B.

    2016-02-01

    Vertical GaN Schottky barrier diode (SBD) structures were grown by metal-organic chemical vapor deposition on free-standing GaN substrates. The carbon doping effect on SBD performance was studied by adjusting the growth conditions and spanning the carbon doping concentration between ≤3 × 1015 cm-3 and 3 × 1019 cm-3. Using the optimized growth conditions that resulted in the lowest carbon incorporation, a vertical GaN SBD with a 6-μm drift layer was fabricated. A low turn-on voltage of 0.77 V with a breakdown voltage over 800 V was obtained from the device.

  7. Modeling of radiation damage recovery in particle detectors based on GaN

    Energy Technology Data Exchange (ETDEWEB)

    Gaubas, E., E-mail: eugenijus.gaubas@ff.vu.lt; Ceponis, T.; Pavlov, J.

    2015-12-15

    The pulsed characteristics of the capacitor-type and PIN diode type detectors based on GaN have been simulated using the dynamic and drift–diffusion models. The drift–diffusion current simulations have been implemented by employing the commercial software package Synopsys TCAD Sentaurus. The bipolar drift regime has been analyzed. The possible internal gain in charge collection through carrier multiplication processes determined by impact ionization has been considered in order to compensate carrier lifetime reduction due to radiation defects introduced into GaN material of detector.

  8. Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

    Science.gov (United States)

    Wang, Xue; Hartmann, Jana; Mandl, Martin; Sadat Mohajerani, Matin; Wehmann, Hergo-H.; Strassburg, Martin; Waag, Andreas

    2014-04-01

    Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

  9. Closed-loop MBE growth of droplet-free GaN with very metal rich conditions using Metal Modulated Epitaxy with Mg and In

    Energy Technology Data Exchange (ETDEWEB)

    Burnham, S.D.; Henderson, W.; Doolittle, W.A. [School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

    2008-07-01

    Improvements to the Metal Modulated Epitaxy (MME) technique are achieved through computer controlled shutter transitions based on feedback from RHEED transients (S. D. Burnham and W. A. Doolittle, J. Vac. Sci. Technol. B 24, 2100 (2006)), thus creating a closed-loop control system for nitride MBE, the first of its kind. A high-sensitivity 22 bit camera is used to determine when RHEED transients have subsided, upon which a shutter transition is initiated allowing the efficient buildup and depletion of the metal bilayer, which improves surface morphology and growth rate compared to the standard MME technique. RMS surface roughness was reduced by 41% by using this 'Smart Shuttering' improvement to MME. A substantially higher peak concentration of Mg, approaching 2% atomic concentration, was achieved using the MME technique. As expected, a negligible amount of In was incorporated into the very Ga-rich films. Using the new closed loop control system developed for MBE, the surface morphology was improved for GaN films while highly repeatable holes concentrations as high as 4.7 x 10{sup 18} cm{sup -3} with 1.07 cm{sup 2}/V-sec mobility was obtained. This approach offers great promise for improved reproducibility and improved material quality. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Design of Low Inductance Switching Power Cell for GaN HEMT Based Inverter

    Energy Technology Data Exchange (ETDEWEB)

    Gurpinar, Emre [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Power Electronics and Electric Machinery Research Group; Iannuzzo, Francesco [Aalborg Univ., Aalborg (Denmark). Dept. of Energy Technology; Yang, Yongheng [Aalborg Univ., Aalborg (Denmark). Dept. of Energy Technology; Castellazzi, Alberto [Univ. of Nottingham (United Kingdom). Power Electronics, Machines and Control (PEMC); Blaabjerg, Frede [Aalborg Univ., Aalborg (Denmark). Dept. of Energy Technology

    2017-11-23

    Here in this paper, an ultra-low inductance power cell is designed for a three-Level Active Neutral Point Clamped (3LANPC) based on 650 V gallium nitride (GaN) HEMT devices. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which mainly contribute to voltage overshoots and increase of switching losses, are discussed. The ultra-low inductance power cell design based on a fourlayer Printed Circuit Board (PCB) with the aim to maximize the switching performance of GaN HEMTs is explained. The design of gate drivers for the GaN HEMT devices is presented. Parasitic inductance and resistance of the proposed design are extracted with finite element analysis and discussed. Common mode behaviours based on the SPICE model of the converter are analyzed. Experimental results on the designed 3L-ANPC with the output power of up to 1 kW are presented, which verifies the performance of the proposed design in terms of ultra-low inductance.

  11. Design of Low Inductance Switching Power Cell for GaN HEMT Based Inverter

    International Nuclear Information System (INIS)

    Gurpinar, Emre; Iannuzzo, Francesco; Yang, Yongheng; Castellazzi, Alberto; Blaabjerg, Frede

    2017-01-01

    Here in this paper, an ultra-low inductance power cell is designed for a three-Level Active Neutral Point Clamped (3LANPC) based on 650 V gallium nitride (GaN) HEMT devices. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which mainly contribute to voltage overshoots and increase of switching losses, are discussed. The ultra-low inductance power cell design based on a fourlayer Printed Circuit Board (PCB) with the aim to maximize the switching performance of GaN HEMTs is explained. The design of gate drivers for the GaN HEMT devices is presented. Parasitic inductance and resistance of the proposed design are extracted with finite element analysis and discussed. Common mode behaviours based on the SPICE model of the converter are analyzed. Experimental results on the designed 3L-ANPC with the output power of up to 1 kW are presented, which verifies the performance of the proposed design in terms of ultra-low inductance.

  12. Structure guided GANs

    Science.gov (United States)

    Cao, Feidao; Zhao, Huaici; Liu, Pengfei

    2017-11-01

    Generative adversarial networks (GANs) has achieved success in many fields. However, there are some samples generated by many GAN-based works, whose structure is ambiguous. In this work, we propose Structure Guided GANs that introduce structural similar into GANs to overcome the problem. In order to achieve our goal, we introduce an encoder and a decoder into a generator to design a new generator and take real samples as part of the input of a generator. And we modify the loss function of the generator accordingly. By comparison with WGAN, experimental results show that our proposed method overcomes largely sample structure ambiguous and can generate higher quality samples.

  13. GaN Based Electronics And Their Applications

    Science.gov (United States)

    Ren, Fan

    2002-03-01

    The Group III-nitrides were initially researched for their promise to fill the void for a blue solid state light emitter. Electronic devices from III-nitrides have been a more recent phenomenon. The thermal conductivity of GaN is three times that of GaAs. For high power or high temperature applications, good thermal conductivity is imperative for heat removal or sustained operation at elevated temperatures. The development of III-N and other wide bandgap technologies for high temperature applications will likely take place at the expense of competing technologies, such as silicon-on-insulator (SOI), at moderate temperatures. At higher temperatures (>300°C), novel devices and components will become possible. The automotive industry will likely be one of the largest markets for such high temperature electronics. One of the most noteworthy advantages for III-N materials over other wide bandgap semiconductors is the availability of AlGaN/GaN and InGaN/GaN heterostructures. A 2-dimensional electron gas (2DEG) has been shown to exist at the AlGaN/GaN interface, and heterostructure field effect transistors (HFETs) from these materials can exhibit 2DEG mobilities approaching 2000 cm2 / V?s at 300K. Power handling capabilities of 12 W/mm appear feasible, and extraordinary large signal performance has already been demonstrated, with a current state-of-the-art of >10W/mm at X-band. In this talk, high speed and high temperature AlGaN/GaN HEMTs as well as MOSHEMTs, high breakdown voltage GaN (>6KV) and AlGaN (9.7 KV) Schottky diodes, and their applications will be presented.

  14. Design and simulation of a novel GaN based resonant tunneling high electron mobility transistor on a silicon substrate

    International Nuclear Information System (INIS)

    Chowdhury, Subhra; Biswas, Dhrubes; Chattaraj, Swarnabha

    2015-01-01

    For the first time, we have introduced a novel GaN based resonant tunneling high electron mobility transistor (RTHEMT) on a silicon substrate. A monolithically integrated GaN based inverted high electron mobility transistor (HEMT) and a resonant tunneling diode (RTD) are designed and simulated using the ATLAS simulator and MATLAB in this study. The 10% Al composition in the barrier layer of the GaN based RTD structure provides a peak-to-valley current ratio of 2.66 which controls the GaN based HEMT performance. Thus the results indicate an improvement in the current–voltage characteristics of the RTHEMT by controlling the gate voltage in this structure. The introduction of silicon as a substrate is a unique step taken by us for this type of RTHEMT structure. (paper)

  15. Self-assembled growth and structural analysis of inclined GaN nanorods on nanoimprinted m-sapphire using catalyst-free metal-organic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kyuseung; Chae, Sooryong; Jang, Jongjin; Min, Daehong; Kim, Jaehwan; Nam, Okhyun, E-mail: ohnam@kpu.ac.kr [Convergence Center for Advanced Nano Semiconductor (CANS), Department of Nano-Optical Engineering, Korea Polytechnic University, Siheung, 15073 (Korea, Republic of)

    2016-04-15

    In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ∼57.5° to the [10-10]{sub sapp} direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]{sub sapp}. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to be mostly free of stacking fault-related defects using high-resolution transmission electron microscopy.

  16. Ultra-Low Inductance Design for a GaN HEMT Based 3L-ANPC Inverter

    DEFF Research Database (Denmark)

    Gurpinar, Emre; Castellazzi, Alberto; Iannuzzo, Francesco

    2016-01-01

    contributors to voltage overshoots and increase of switching losses, are discussed. The ultra-low inductance power cell design based on a four layer PCB with the aim to maximise the switching performance of GaN HEMTs is explained. Gate driver design for GaN HEMT devices is presented. Common-mode behaviours......In this paper, an ultra-low inductance power cell design for a 3L-ANPC based on 650 V GaN HEMT devices is presented. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which are the main...

  17. Barrier inhomogeneities limited current and 1/f noise transport in GaN based nanoscale Schottky barrier diodes

    Science.gov (United States)

    Kumar, Ashutosh; Heilmann, M.; Latzel, Michael; Kapoor, Raman; Sharma, Intu; Göbelt, M.; Christiansen, Silke H.; Kumar, Vikram; Singh, Rajendra

    2016-01-01

    The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained. PMID:27282258

  18. Vertical architecture for enhancement mode power transistors based on GaN nanowires

    Science.gov (United States)

    Yu, F.; Rümmler, D.; Hartmann, J.; Caccamo, L.; Schimpke, T.; Strassburg, M.; Gad, A. E.; Bakin, A.; Wehmann, H.-H.; Witzigmann, B.; Wasisto, H. S.; Waag, A.

    2016-05-01

    The demonstration of vertical GaN wrap-around gated field-effect transistors using GaN nanowires is reported. The nanowires with smooth a-plane sidewalls have hexagonal geometry made by top-down etching. A 7-nanowire transistor exhibits enhancement mode operation with threshold voltage of 1.2 V, on/off current ratio as high as 108, and subthreshold slope as small as 68 mV/dec. Although there is space charge limited current behavior at small source-drain voltages (Vds), the drain current (Id) and transconductance (gm) reach up to 314 mA/mm and 125 mS/mm, respectively, when normalized with hexagonal nanowire circumference. The measured breakdown voltage is around 140 V. This vertical approach provides a way to next-generation GaN-based power devices.

  19. GaN light-emitting device based on ionic liquid electrolyte

    Science.gov (United States)

    Hirai, Tomoaki; Sakanoue, Tomo; Takenobu, Taishi

    2018-06-01

    Ionic liquids (ILs) are attractive materials for fabricating unique hybrid devices based on electronics and electrochemistry; thus, IL-gated transistors and organic light-emitting devices of light-emitting electrochemical cells (LECs) are investigated for future low-voltage and high-performance devices. In LECs, voltage application induces the formation of electrochemically doped p–n homojunctions owing to ion rearrangements in composites of semiconductors and electrolytes, and achieves electron–hole recombination for light emission at the homojunctions. In this work, we applied this concept of IL-induced electrochemical doping to the fabrication of GaN-based light-emitting devices. We found that voltage application to the layered IL/GaN structure accumulated electrons on the GaN surface owing to ion rearrangements and improved the conductivity of GaN. The ion rearrangement also enabled holes to be injected by the strong electric field of electric double layers on hole injection contacts. This simultaneous injection of holes and electrons into GaN mediated by ions achieves light emission at a low voltage of around 3.4 V. The light emission from the simple IL/GaN structure indicates the usefulness of an electrochemical technique in generating light emission with great ease of fabrication.

  20. High-electron-mobility GaN grown on free-standing GaN templates by ammonia-based molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kyle, Erin C. H., E-mail: erinkyle@umail.ucsb.edu; Kaun, Stephen W.; Burke, Peter G.; Wu, Feng; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Wu, Yuh-Renn [Institute of Photonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei City 10617, Taiwan (China)

    2014-05-21

    The dependence of electron mobility on growth conditions and threading dislocation density (TDD) was studied for n{sup −}-GaN layers grown by ammonia-based molecular beam epitaxy. Electron mobility was found to strongly depend on TDD, growth temperature, and Si-doping concentration. Temperature-dependent Hall data were fit to established transport and charge-balance equations. Dislocation scattering was analyzed over a wide range of TDDs (∼2 × 10{sup 6} cm{sup −2} to ∼2 × 10{sup 10} cm{sup −2}) on GaN films grown under similar conditions. A correlation between TDD and fitted acceptor states was observed, corresponding to an acceptor state for almost every c lattice translation along each threading dislocation. Optimized GaN growth on free-standing GaN templates with a low TDD (∼2 × 10{sup 6} cm{sup −2}) resulted in electron mobilities of 1265 cm{sup 2}/Vs at 296 K and 3327 cm{sup 2}/Vs at 113 K.

  1. The structural and optical properties of metal ion-implanted GaN

    Energy Technology Data Exchange (ETDEWEB)

    Macková, A.; Malinský, P. [Nuclear Physics Institute of the Academy of Sciences of the Czech Republic, v.v.i., 250 68 Řež (Czech Republic); Department of Physics, Faculty of Science, J.E. Purkinje University, České Mládeže 8, 400 96 Ústí nad Labem (Czech Republic); Sofer, Z.; Šimek, P.; Sedmidubský, D. [Department of Inorganic Chemistry, Institute of Chemical Technology, 166 28 Prague (Czech Republic); Veselý, M. [Dept. of Organic Technology, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6 (Czech Republic); Böttger, R. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden – Rossendorf, 01328 Dresden (Germany)

    2016-03-15

    The practical development of novel optoelectronic materials with appropriate optical properties is strongly connected to the structural properties of the prepared doped structures. We present GaN layers oriented along the (0 0 0 1) crystallographic direction that have been grown by low-pressure metal–organic vapour-phase epitaxy (MOVPE) on sapphire substrates implanted with 200 keV Co{sup +}, Fe{sup +} and Ni{sup +} ions. The structural properties of the ion-implanted layers have been characterised by RBS-channelling and Raman spectroscopy to obtain a comprehensive insight into the structural modification of implanted GaN layers and to study the subsequent influence of annealing on crystalline-matrix recovery. Photoluminescence was measured to control the desired optical properties. The post-implantation annealing induced the structural recovery of the modified GaN layer depending on the introduced disorder level, e.g. depending on the ion implantation fluence, which was followed by structural characterisation and by the study of the surface morphology by AFM.

  2. Growth of (20 anti 21)AlGaN, GaN and InGaN by metal organic vapor phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ploch, S.; Wernicke, T.; Rass, J.; Pristovsek, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

    2012-07-01

    Green InGaN-based laser diodes on (20 anti 21)GaN substrates have recently demonstrated performances exceeding those of conventional (0001) oriented devices. However little is known regarding the growth parameters. We have investigated growth of AlGaN, GaN and InGaN on (20 anti 21)GaN substrates by MOVPE. Smooth GaN layers with a rms roughness <0.5 nm were obtained by low growth temperatures and reactor pressures. The layers exhibit undulations along [10 anti 14] similar to the GaN substrate. AlGaN and InGaN layers exhibit an increased surface roughness. Undulation bunching was observed and attributed to reduced adatom surface mobility due to the binding energy of Al and the low growth temperature for InGaN respectively or strain relaxation. AlGaN and InGaN heterostructures on (20 anti 21)GaN relax by layer tilt accompanied by formation of misfit dislocations, due to shear strain of the unit cell. This relaxation mechanism leads to a reduced critical layer thickness of (20 anti 21)AlGaN layers and InGaN multi quantum wells (MQW) in comparison to (0001). PL spectral broadening of 230 meV of (20 anti 21)InGaN single QWs emitting at 415 nm can be reduced by increased growth temperature or increased number of QWs with reduced thickness.

  3. The nucleation of HCl and Cl{sub 2}-based HVPE GaN on mis-oriented sapphire substrates

    Energy Technology Data Exchange (ETDEWEB)

    Bohnen, Tim; Dreumel, Gerbe W.G. van; Enckevort, Willem J.P. van; Ashraf, Hina; Jong, Aryan E.F. de; Hageman, Paul R.; Vlieg, Elias [IMM, Radboud University, Nijmegen (Netherlands); Weyher, Jan L. [Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw (Poland)

    2010-07-15

    The nucleation of both classic HCl-based and novel Cl{sub 2{sup -}} based HVPE GaN on mis-oriented sapphire substrates was investigated. The use of Cl{sub 2}in HVPE increases the growth rate by a factor of 4-5 and strongly reduces the parasitic deposition, allowing for the growth of much thicker wafers than HCl-based HVPE. Morphological SEM surface studies of the HCl-based HVPE sample surface show that at 600 C a nanocrystalline layer is deposited on the sapphire. During the subsequent annealing phase, the morphology changes to a {mu}m-sized island structure. During overgrowth at 1080 C, the islands coalesce. Small voids or pinholes are then formed in between the coalescing GaN islands. These pinholes lead to numerous pits on the surface of the GaN at thicknesses of 5 {mu}m. The pits disappear during continued overgrowth and can no longer be found on the surface, when the GaN film reaches a thickness of 45 {mu}m. This particular coalescence mechanism also applies to Cl{sub 2}-based HVPE GaN on sapphire (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Molten Salt-Based Growth of Bulk GaN and InN for Substrates

    Energy Technology Data Exchange (ETDEWEB)

    Waldrip, Karen Elizabeth [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Advanced Power Sources Technology Dept.; Tsao, Jeffrey Yeenien [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Energy Sciences Dept.; Kerley, Thomas M. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Advanced Materials Sciences Dept.

    2006-09-01

    An atmospheric pressure approach to growth of bulk group III-nitrides is outlined. Native III-nitride substrates for optoelectronic and high power, high frequency electronics are desirable to enhance performance and reliability of these devices; currently, these materials are available in research quantities only for GaN, and are unavailable in the case of InN. The thermodynamics and kinetics of the reactions associated with traditional crystal growth techniques place these activities on the extreme edges of experimental physics. The technique described herein relies on the production of the nitride precursor (N3-) by chemical and/or electrochemical methods in a molten halide salt. This nitride ion is then reacted with group III metals in such a manner as to form the bulk nitride material. The work performed during the period of funding (July 2004-September 2005) focused on the initial measurement of the solubility of GaN in molten LiCl as a function of temperature, the construction of electrochemical cells, the modification of a commercial glove box (required for handling very hygroscopic LiCl), and on securing intellectual property for the technique.

  5. Surface Preparation and Deposited Gate Oxides for Gallium Nitride Based Metal Oxide Semiconductor Devices

    Directory of Open Access Journals (Sweden)

    Paul C. McIntyre

    2012-07-01

    Full Text Available The literature on polar Gallium Nitride (GaN surfaces, surface treatments and gate dielectrics relevant to metal oxide semiconductor devices is reviewed. The significance of the GaN growth technique and growth parameters on the properties of GaN epilayers, the ability to modify GaN surface properties using in situ and ex situ processes and progress on the understanding and performance of GaN metal oxide semiconductor (MOS devices are presented and discussed. Although a reasonably consistent picture is emerging from focused studies on issues covered in each of these topics, future research can achieve a better understanding of the critical oxide-semiconductor interface by probing the connections between these topics. The challenges in analyzing defect concentrations and energies in GaN MOS gate stacks are discussed. Promising gate dielectric deposition techniques such as atomic layer deposition, which is already accepted by the semiconductor industry for silicon CMOS device fabrication, coupled with more advanced physical and electrical characterization methods will likely accelerate the pace of learning required to develop future GaN-based MOS technology.

  6. Steps towards a GaN nanowire based light emitting diode and its integration with Si-MOS technology

    Energy Technology Data Exchange (ETDEWEB)

    Limbach, Friederich

    2012-06-22

    This work is concerned with the realization and investigation of a light emitting diode (LED) structure within single GaN nanowires (NWs) and its integration with Si technology. To this end first a general understanding of the GaN NW growth is given. This is followed by investigations of the influence which doping species, such as Mg and Si, have on the growth of the NWs. The experience gathered in these studies set the basis for the synthesis of nominal p-i-n and n-i-p junctions in GaN NWs. Investigations of these structures resulted in the technologically important insight, that p-type doping with Mg is achieved best if it is done in the later NW growth stage. This implies that it is beneficial for a NW LED to place the p-type segment on the NW top. Another important component of an LED is the active zone where electron-hole recombination takes place. In the case of planar GaN LEDs, this is usually achieved by alloying Ga and In to form InGaN. In order to be able to control the growth under a variety of conditions, we investigate the growth of InGaN in the form of extended segments on top of GaN NWs, as well as multi quantum wells (MQWs) in GaN NWs. All the knowledge gained during these preliminary studies is harnessed to reach the overall goal: The realization of a GaN NW LED. Such structures are fabricated, investigated and processed into working LEDs. Finally, a report on the efforts of integrating III-nitride NW LEDs and Si based metaloxide-semiconductor field effect transistor (MOSFET) technology is given. This demonstrates the feasibility of the monolithic integration of both devices on the same wafer at the same time.

  7. MOCVD growth of GaN layer on InN interlayer and relaxation of residual strain

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Keon-Hun; Park, Sung Hyun; Kim, Jong Hack; Kim, Nam Hyuk; Kim, Min Hwa [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Na, Hyunseok [Department of Advanced Materials Science and Engineering, Daejin University, Pocheon, 487-711 (Korea, Republic of); Yoon, Euijoon, E-mail: eyoon@snu.ac.k [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Department of Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University, Suwon 433-270 (Korea, Republic of)

    2010-09-01

    100 nm InN layer was grown on sapphire c-plane using a metal-organic chemical vapor deposition (MOCVD) system. Low temperature (LT) GaN layer was grown on InN layer to protect InN layer from direct exposure to hydrogen flow during high temperature (HT) GaN growth and/or abrupt decomposition. Subsequently, thick HT GaN layer (2.5 {mu}m thick) was grown at 1000 {sup o}C on LT GaN/InN/sapphire template. Microstructure of epilayer-substrate interface was investigated by transmission electron microscopy (TEM). From the high angle annular dark field TEM image, the growth of columnar structured LT GaN and HT GaN with good crystallinity was observed. Though thickness of InN interlayer is assumed to be about 100 nm based on growth rate, it was not clearly shown in TEM image due to the InN decomposition. The lattice parameters of GaN layers were measured by XRD measurement, which shows that InN interlayer reduces the compressive strain in GaN layer. The relaxation of compressive strain in GaN layer was also confirmed by photoluminescence (PL) measurement. As shown in the PL spectra, red shift of GaN band edge peak was observed, which indicates the reduction of compressive strain in GaN epilayer.

  8. Improved performance of GaN based light emitting diodes with ex-situ sputtered AlN nucleation layers

    Directory of Open Access Journals (Sweden)

    Shuo-Wei Chen

    2016-04-01

    Full Text Available The crystal quality, electrical and optical properties of GaN based light emitting diodes (LEDs with ex-situ sputtered physical vapor deposition (PVD aluminum nitride (AlN nucleation layers were investigated. It was found that the crystal quality in terms of defect density and x-ray diffraction linewidth was greatly improved in comparison to LEDs with in-situ low temperature GaN nucleation layer. The light output power was 3.7% increased and the reverse bias voltage of leakage current was twice on LEDs with ex-situ PVD AlN nucleation layers. However, larger compressive strain was discovered in LEDs with ex-situ PVD AlN nucleation layers. The study shows the potential and constrain in applying ex-situ PVD AlN nucleation layers to fabricate high quality GaN crystals in various optoelectronics.

  9. New surface plasmon polariton waveguide based on GaN nanowires

    Directory of Open Access Journals (Sweden)

    Jun Zhu

    Full Text Available Lasers are nowadays widely used in industry, in hospitals and in many devices that we have at home. Random laser development is challenging given its high threshold and low integration. Surface plasmon polariton (SPP can improve random laser characteristics because of its ability to control diffraction. In this study, we establish a random laser structural model with silicon-based parcel GaN nanowires. The GaN nanowire gain and enhanced surface plasmon increase population inversion level. Our laser model is based on random particle scattering feedback mechanism, nanowire use, and surface plasmon enhancement effect, which causes stochastic laser emergence. Analysis shows that the SPP mode and nanowire waveguides coupled in the dielectric layer of low refractive index can store light energy like a capacitor under low refractive index clearance. The waveguide mode field area and limiting factors show that the modeled laser can achieve sub-wavelength constraints of the output light field. We also investigate emergent laser performance for a more limited light field capacity and lower threshold. Keywords: Random laser, Surface plasmon polariton, Feedback mechanism, Low threshold, Subwavelength constraints

  10. Highly aligned vertical GaN nanowires using submonolayer metal catalysts

    Science.gov (United States)

    Wang, George T [Albuquerque, NM; Li, Qiming [Albuquerque, NM; Creighton, J Randall [Albuquerque, NM

    2010-06-29

    A method for forming vertically oriented, crystallographically aligned nanowires (nanocolumns) using monolayer or submonolayer quantities of metal atoms to form uniformly sized metal islands that serve as catalysts for MOCVD growth of Group III nitride nanowires.

  11. A High-Efficiency 100-W GaN Three-Way Doherty Amplifier for Base-Station Applications

    NARCIS (Netherlands)

    Pelk, M.J.; Neo, W.C.E.; Gajadharsing, J.R.; Pengelly, R.S.; De Vreede, L.C.N.

    2008-01-01

    A three-way Doherty 100-W GaN base-station power amplifier at 2.14 GHz is presented. Simple, but accurate design equations for the output power combiner of the amplifier are introduced. Mixed-signal techniques are utilized for uncompromised control of the amplifier stages to optimize efficiency, as

  12. Effect of III/V ratio on the polarity of AlN and GaN layers grown in the metal rich growth regime on Si(111) by plasma assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    Agrawal, Manvi; Dharmarasu, Nethaji; Radhakrishnan, K.; Pramana, Stevin Snellius

    2015-01-01

    Wet chemical etching, reflection high energy electron diffraction, scanning electron microscope and convergent beam electron diffraction have been employed to study the polarities of AlN and the subsequently grown GaN as a function of metal flux in the metal rich growth regime. Both AlN and GaN exhibited metal polarity in the intermediate growth conditions. However, in the droplet growth regime, the polarity of AlN and GaN were N polar and Ga polar, respectively. It was observed that Ga polar GaN could be obtained on both Al and N polar AlN. AlGaN/GaN high electron mobility transistor (HEMT) heterostructure exhibiting hall mobility of 900 cm 2 V -1 s -1 and sheet carrier density of 1.2 × 10 13 cm -2 was demonstrated using N polar AlN which confirmed Ga polarity of GaN. Al metal flux was likely to play an important role in controlling the polarity of AlN and determining the polarity of the subsequent GaN grown on Si(111) by plasma assisted molecular beam epitaxy (PA-MBE). (author)

  13. Fabrication and characterization of GaN-based light-emitting diodes without pre-activation of p-type GaN.

    Science.gov (United States)

    Hu, Xiao-Long; Wang, Hong; Zhang, Xi-Chun

    2015-01-01

    We fabricated GaN-based light-emitting diodes (LEDs) without pre-activation of p-type GaN. During the fabrication process, a 100-nm-thick indium tin oxide film was served as the p-type contact layer and annealed at 500°C in N2 ambient for 20 min to increase its transparency as well as to activate the p-type GaN. The electrical measurements showed that the LEDs were featured by a lower forward voltage and higher wall-plug efficiency in comparison with LEDs using pre-activation of p-type GaN. We discussed the mechanism of activation of p-type GaN at 500°C in N2 ambient. Furthermore, x-ray photoemission spectroscopy examinations were carried out to study the improved electrical performances of the LEDs without pre-activation of p-type GaN.

  14. GaN Nanowires Synthesized by Electroless Etching Method

    KAUST Repository

    Najar, Adel; Anjum, Dalaver H.; Ng, Tien Khee; Ooi, Boon S.; Ben Slimane, Ahmed

    2012-01-01

    Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

  15. Fabrication of p-type porous GaN on silicon and epitaxial GaN

    OpenAIRE

    Bilousov, Oleksandr V.; Geaney, Hugh; Carvajal, Joan J.; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Giguere, A.; Drouin, D.; Diaz, Francesc; Aguilo, Magdalena; O'Dwyer, Colm

    2013-01-01

    Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurem...

  16. First-principle-based full-dispersion Monte Carlo simulation of the anisotropic phonon transport in the wurtzite GaN thin film

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Ruikang; Hu, Run, E-mail: hurun@hust.edu.cn, E-mail: luoxb@hust.edu.cn; Luo, Xiaobing, E-mail: hurun@hust.edu.cn, E-mail: luoxb@hust.edu.cn [State Key Laboratory of Coal Combustion and Thermal Packaging Laboratory, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2016-04-14

    In this study, we developed a first-principle-based full-dispersion Monte Carlo simulation method to study the anisotropic phonon transport in wurtzite GaN thin film. The input data of thermal properties in MC simulations were calculated based on the first-principle method. The anisotropy of thermal conductivity in bulk wurtzite GaN is found to be strengthened by isotopic scatterings and reduced temperature, and the anisotropy reaches 40.08% for natural bulk GaN at 100 K. With the GaN thin film thickness decreasing, the anisotropy of the out-of-plane thermal conductivity is heavily reduced due to both the ballistic transport and the less importance of the low-frequency phonons with anisotropic group velocities. On the contrary, it is observed that the in-plane thermal conductivity anisotropy of the GaN thin film is strengthened by reducing the film thickness. And the anisotropy reaches 35.63% when the natural GaN thin film thickness reduces to 50 nm at 300 K with the degree of specularity being zero. The anisotropy is also improved by increasing the surface roughness of the GaN thin film.

  17. GaN MOSHEMT employing HfO2 as a gate dielectric with partially etched barrier

    Science.gov (United States)

    Han, Kefeng; Zhu, Lin

    2017-09-01

    In order to suppress the gate leakage current of a GaN high electron mobility transistor (GaN HEMT), a GaN metal-oxide-semiconductor high electron mobility transistor (MOSHEMT) is proposed, in which a metal-oxide-semiconductor gate with high-dielectric-constant HfO2 as an insulating dielectric is employed to replace the traditional GaN HEMT Schottky gate. A 0.5 μm gate length GaN MOSHEMT was fabricated based on the proposed structure, the {{{Al}}}0.28{{{Ga}}}0.72{{N}} barrier layer is partially etched to produce a higher transconductance without deteriorating the transport characteristics of the two-dimensional electron gas in the channel, the gate dielectric is HfO2 deposited by atomic layer deposition. Current-voltage characteristics and radio frequency characteristics are obtained after device preparation, the maximum current density of the device is 900 mA mm-1, the source-drain breakdown voltage is 75 V, gate current is significantly suppressed and the forward gate voltage swing range is about ten times higher than traditional GaN HEMTs, the GaN MOSHEMT also demonstrates radio frequency characteristics comparable to traditional GaN HEMTs with the same gate length.

  18. High-resistivity unintentionally carbon-doped GaN layers with nitrogen as nucleation layer carrier gas grown by metal-organic chemical vapor deposition

    Directory of Open Access Journals (Sweden)

    Fu Chen

    2017-12-01

    Full Text Available In this letter, high-resistivity unintentionally carbon-doped GaN layers with sheet resistivity greater than 106 Ω/□ have been grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD. We have observed that the growth of GaN nucleation layers (NLs under N2 ambient leads to a large full width at half maximum (FWHM of (102 X-ray diffraction (XRD line in the rocking curve about 1576 arc sec. Unintentional carbon incorporation can be observed in the secondary ion mass spectroscopy (SIMS measurements. The results demonstrate the self-compensation mechanism is attributed to the increased density of edge-type threading dislocations and carbon impurities. The AlGaN/GaN HEMT grown on the high-resistivity GaN template has also been fabricated, exhibiting a maximum drain current of 478 mA/mm, a peak transconductance of 60.0 mS/mm, an ON/OFF ratio of 0.96×108 and a breakdown voltage of 621 V.

  19. As-grown deep-level defects in n-GaN grown by metal-organic chemical vapor deposition on freestanding GaN

    International Nuclear Information System (INIS)

    Chen Shang; Ishikawa, Kenji; Hori, Masaru; Honda, Unhi; Shibata, Tatsunari; Matsumura, Toshiya; Tokuda, Yutaka; Ueda, Hiroyuki; Uesugi, Tsutomu; Kachi, Tetsu

    2012-01-01

    Traps of energy levels E c -0.26 and E c -0.61 eV have been identified as as-grown traps in n-GaN grown by metal-organic chemical vapor deposition by using deep level transient spectroscopy of the Schottky contacts fabricated by resistive evaporation. The additional traps of E c -0.13 and E c -0.65 eV have been observed in samples whose contacts are deposited by electron-beam evaporation. An increase in concentration of the E c -0.13 and E c -0.65 eV traps when approaching the interface between the contact and the GaN film supports our argument that these traps are induced by electron-beam irradiation. Conversely, the depth profiles of as-grown traps show different profiles between several samples with increased or uniform distribution in the near surface below 50 nm. Similar profiles are observed in GaN grown on a sapphire substrate. We conclude that the growth process causes these large concentrations of as-grown traps in the near-surface region. It is speculated that the finishing step in the growth process should be an essential issue in the investigation of the surface state of GaN.

  20. Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

    Science.gov (United States)

    Shirazi-HD, M.; Diaz, R. E.; Nguyen, T.; Jian, J.; Gardner, G. C.; Wang, H.; Manfra, M. J.; Malis, O.

    2018-04-01

    AlxGa1-xN layers with Al-composition above 0.6 (0.6 < x < 0.9) grown under metal-rich conditions by plasma-assisted molecular beam epitaxy on m-plane GaN miscut towards the -c axis are kinetically unstable. Even under excess Ga flux, the effective growth rate of AlGaN is drastically reduced, likely due to suppression of Ga-N dimer incorporation. The defect structure generated during these growth conditions is studied with energy dispersive x-ray spectroscopy scanning transmission electron microscopy as a function of Al flux. The AlGaN growth results in the formation of thin Al(Ga)N layers with Al-composition higher than expected and lower Al-composition AlGaN islands. The AlGaN islands have a flat top and are elongated along the c-axis (i.e., stripe-like shape). Possible mechanisms for the observed experimental results are discussed. Our data are consistent with a model in which Al-N dimers promote release of Ga-N dimers from the m-plane surface.

  1. High-resistivity unintentionally carbon-doped GaN layers with nitrogen as nucleation layer carrier gas grown by metal-organic chemical vapor deposition

    Science.gov (United States)

    Chen, Fu; Sun, Shichuang; Deng, Xuguang; Fu, Kai; Yu, Guohao; Song, Liang; Hao, Ronghui; Fan, Yaming; Cai, Yong; Zhang, Baoshun

    2017-12-01

    In this letter, high-resistivity unintentionally carbon-doped GaN layers with sheet resistivity greater than 106 Ω/□ have been grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). We have observed that the growth of GaN nucleation layers (NLs) under N2 ambient leads to a large full width at half maximum (FWHM) of (102) X-ray diffraction (XRD) line in the rocking curve about 1576 arc sec. Unintentional carbon incorporation can be observed in the secondary ion mass spectroscopy (SIMS) measurements. The results demonstrate the self-compensation mechanism is attributed to the increased density of edge-type threading dislocations and carbon impurities. The AlGaN/GaN HEMT grown on the high-resistivity GaN template has also been fabricated, exhibiting a maximum drain current of 478 mA/mm, a peak transconductance of 60.0 mS/mm, an ON/OFF ratio of 0.96×108 and a breakdown voltage of 621 V.

  2. Kinetic-limited etching of magnesium doping nitrogen polar GaN in potassium hydroxide solution

    International Nuclear Information System (INIS)

    Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Yang, Fan; Li, Pengchong; Zhao, Degang; Zhang, Baolin; Du, Guotong

    2016-01-01

    Graphical abstract: - Highlights: • Effects of Mg doping on wet etching of N-polar GaN are illustrated and analysed. • Etching process model of Mg-doped N-polar GaN in KOH solution is purposed. • It is found that Mg doping can induce tensile strain in N-polar GaN film. • N-polar p-GaN film with a hole concentration of 2.4 × 10"1"7 cm"−"3 is obtained. - Abstract: KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 × 10"1"7 cm"−"3 was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

  3. Kinetic-limited etching of magnesium doping nitrogen polar GaN in potassium hydroxide solution

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Yang, Fan; Li, Pengchong [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Qianjin Street 2699, Changchun 130012 (China); Zhao, Degang [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Science, PO Box 912, Beijing 100083 (China); Zhang, Baolin; Du, Guotong [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Qianjin Street 2699, Changchun 130012 (China)

    2016-01-01

    Graphical abstract: - Highlights: • Effects of Mg doping on wet etching of N-polar GaN are illustrated and analysed. • Etching process model of Mg-doped N-polar GaN in KOH solution is purposed. • It is found that Mg doping can induce tensile strain in N-polar GaN film. • N-polar p-GaN film with a hole concentration of 2.4 × 10{sup 17} cm{sup −3} is obtained. - Abstract: KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 × 10{sup 17} cm{sup −3} was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

  4. Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

    International Nuclear Information System (INIS)

    Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok; Jeon, In-Jun; Ahn, Hyung Soo; Yi, Sam Nyung; Ha, Dong Han

    2015-01-01

    Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices

  5. Hybrid device based on GaN nanoneedles and MEH-PPV/PEDOT:PSS polymer

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Min Jeong; Gwon, Dong-Oh; Lee, Chan-Mi; Lee, Gang Seok [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Jeon, In-Jun [Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Ahn, Hyung Soo [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Yi, Sam Nyung, E-mail: snyi@kmou.ac.kr [Department of Applied Science, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Department of Nano-semiconductor Engineering, Korea Maritime and Ocean University, Busan 606-791 (Korea, Republic of); Ha, Dong Han [Division of Convergence Technology, Korea Research Institute of Standards and Science, Daejeon 305-340 (Korea, Republic of)

    2015-08-15

    Highlights: • A hybrid device was demonstrated by using MEH-PPV, PEDOT:PSS, and GaN nanoneedles. • I–V curve of the hybrid device showed its rectification behaviour, similar to a diode. • EL peak originated by the different potential barriers at MEH-PPV and GaN interface. - Abstract: A hybrid device that combines the properties of organic and inorganic semiconductors was fabricated and studied. It incorporated poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as organic polymers and GaN nanoneedles as an inorganic semiconductor. Layers of the two polymers were spin coated on to the GaN nanoneedles. The one peak in the electroluminescence spectrum originated from the MEH-PPV layer owing to the different potential barriers of electrons and holes at its interface with the GaN nanoneedles. However, the photoluminescence spectrum showed peaks due to both GaN nanoneedles and MEH-PPV. Such hybrid structures, suitably developed, might be able to improve the efficiency of optoelectronic devices.

  6. Theoretical investigation of electronic, magnetic and optical properties of Fe doped GaN thin films

    International Nuclear Information System (INIS)

    Salmani, E.; Mounkachi, O.; Ez-Zahraouy, H.; Benyoussef, A.; Hamedoun, M.; Hlil, E.K.

    2013-01-01

    Highlights: •Magnetic and optical properties Fe-doped GaN thin films are studied using DFT. •The band gaps of GaN thin films are larger than the one of the bulk. •The layer thickness and acceptor defect can switch the magnetic ordering. -- Abstract: Using first principles calculations based on spin-polarized density functional theory, the magnetic and optical properties of GaN and Fe-doped GaN thin films with and without acceptor defect is studied. The band structure calculations show that the band gaps of GaN thin films with 2, 4 and 6 layers are larger than the one of the bulk with wurtzite structure and decreases with increasing the film thickness. In Fe doped GaN thin films, we show that layer of thickness and acceptor defect can switch the magnetic ordering from disorder local moment (DLM) to ferromagnetic (FM) order. Without acceptor defect Fe doped GaN exhibits spin glass phase in 4 layers form and ferromagnetic state for 2 layers form of the thin films, while it exhibits ferromagnetic phase with acceptor defect such as vacancies defect for 2 and 4 layers. In the FM ordering, the thin films is half-metallic and is therefore ideal for spin application. The different energy between ferromagnetic state and disorder local moment state was evaluated. Moreover, the optical absorption spectra obtained by ab initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities

  7. Properties of TiO2-based transparent conducting oxide thin films on GaN(0001) surfaces

    International Nuclear Information System (INIS)

    Kasai, J.; Nakao, S.; Yamada, N.; Hitosugi, T.; Moriyama, M.; Goshonoo, K.; Hoang, N. L. H.; Hasegawa, T.

    2010-01-01

    Anatase Nb-doped TiO 2 transparent conducting oxide has been formed on GaN(0001) surfaces using a sputtering method. Amorphous films deposited at room temperature were annealed at a substrate temperature of 500 deg. C in vacuum to form single-phase anatase films. Films with a thickness of 170 nm exhibited a resistivity of 8x10 -4 Ω cm with absorptance less than 5% at a wavelength of 460 nm. Furthermore, the refractive index of the Nb-doped TiO 2 was well matched to that of GaN. These findings indicate that Nb-doped TiO 2 is a promising material for use as transparent electrodes in GaN-based light emitting diodes (LEDs), particularly since reflection at the electrode/GaN boundary can be suppressed, enhancing the external quantum efficiency of blue LEDs.

  8. Advances in Hydrogen, Carbon Dioxide, and Hydrocarbon Gas Sensor Technology Using GaN and ZnO-Based Devices

    Directory of Open Access Journals (Sweden)

    Jenshan Lin

    2009-06-01

    Full Text Available In this paper, we review our recent results in developing gas sensors for hydrogen using various device structures, including ZnO nanowires and GaN High Electron Mobility Transistors (HEMTs. ZnO nanowires are particularly interesting because they have a large surface area to volume ratio, which will improve sensitivity, and because they operate at low current levels, will have low power requirements in a sensor module. GaN-based devices offer the advantage of the HEMT structure, high temperature operation, and simple integration with existing fabrication technology and sensing systems. Improvements in sensitivity, recoverability, and reliability are presented. Also reported are demonstrations of detection of other gases, including CO2 and C2H4 using functionalized GaN HEMTs. This is critical for the development of lab-on-a-chip type systems and can provide a significant advance towards a market-ready sensor application.

  9. Advances in Hydrogen, Carbon Dioxide, and Hydrocarbon Gas Sensor Technology Using GaN and ZnO-Based Devices.

    Science.gov (United States)

    Anderson, Travis; Ren, Fan; Pearton, Stephen; Kang, Byoung Sam; Wang, Hung-Ta; Chang, Chih-Yang; Lin, Jenshan

    2009-01-01

    In this paper, we review our recent results in developing gas sensors for hydrogen using various device structures, including ZnO nanowires and GaN High Electron Mobility Transistors (HEMTs). ZnO nanowires are particularly interesting because they have a large surface area to volume ratio, which will improve sensitivity, and because they operate at low current levels, will have low power requirements in a sensor module. GaN-based devices offer the advantage of the HEMT structure, high temperature operation, and simple integration with existing fabrication technology and sensing systems. Improvements in sensitivity, recoverability, and reliability are presented. Also reported are demonstrations of detection of other gases, including CO(2) and C(2)H(4) using functionalized GaN HEMTs. This is critical for the development of lab-on-a-chip type systems and can provide a significant advance towards a market-ready sensor application.

  10. Kinetic-limited etching of magnesium doping nitrogen polar GaN in potassium hydroxide solution

    Science.gov (United States)

    Jiang, Junyan; Zhang, Yuantao; Chi, Chen; Yang, Fan; Li, Pengchong; Zhao, Degang; Zhang, Baolin; Du, Guotong

    2016-01-01

    KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 ÿ 1017 cm⿿3 was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

  11. Heteroepitaxial growth of basal plane stacking fault free a-plane GaN

    Energy Technology Data Exchange (ETDEWEB)

    Wieneke, Matthias; Hempel, Thomas; Noltemeyer, Martin; Witte, Hartmut; Dadgar, Armin; Blaesing, Juergen; Christen, Juergen; Krost, Alois [Otto-von-Guericke Universitaet Magdeburg, FNW/IEP, Magdeburg (Germany)

    2010-07-01

    Growth of light emitting quantum-wells based on a-plane GaN is a possibility to reduce or even to avoid polarization correlated luminescence red shift and reduction of radiative recombination efficiency. But until now heteroepitaxially grown a-plane GaN films are characterized by a poor crystalline quality expressed by a high density of basal plane stacking faults (BSF) and partial dislocations. We present Si doped a-plane GaN films grown on r-plane sapphire substrates by metal organic vapor phase epitaxy using high temperature AlGaN nucleation layers. FE-SEM images revealed three dimensionally grown GaN crystallites sized up to tenth micrometer in the basal plane and a few tenth micrometers along the c-axes. Though, the full width at half maxima of the X-ray diffraction {omega}-scans of the in-plane GaN(1 anti 100) and GaN(0002) Bragg reflections exhibited a very high crystal quality. Furthermore, luminescence spectra were dominated by near band gap emission, while there was no separated peak of the basal plane stacking fault. In summary we present heteroepitaxially grown a-plane GaN without an evidence of basal plane stacking faults in X-ray diffraction measurements and luminescence spectra.

  12. Methanol, ethanol and hydrogen sensing using metal oxide and metal (TiO2–Pt) composite nanoclusters on GaN nanowires: a new route towards tailoring the selectivity of nanowire/nanocluster chemical sensors

    International Nuclear Information System (INIS)

    Aluri, Geetha S; Motayed, Abhishek; Davydov, Albert V; Oleshko, Vladimir P; Bertness, Kris A; Sanford, Norman A; Mulpuri, Rao V

    2012-01-01

    We demonstrate a new method for tailoring the selectivity of chemical sensors using semiconductor nanowires (NWs) decorated with metal and metal oxide multicomponent nanoclusters (NCs). Here we present the change of selectivity of titanium dioxide (TiO 2 ) nanocluster-coated gallium nitride (GaN) nanowire sensor devices on the addition of platinum (Pt) nanoclusters. The hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN NWs followed by the deposition of TiO 2 and/or Pt nanoclusters (NCs) using the sputtering technique. This paper present the sensing characteristics of GaN/(TiO 2 –Pt) nanowire–nanocluster (NWNC) hybrids and GaN/(Pt) NWNC hybrids, and compare their selectivity with that of the previously reported GaN/TiO 2 sensors. The GaN/TiO 2 NWNC hybrids showed remarkable selectivity to benzene and related aromatic compounds, with no measurable response for other analytes. Addition of Pt NCs to GaN/TiO 2 sensors dramatically altered their sensing behavior, making them sensitive only to methanol, ethanol and hydrogen, but not to any other chemicals we tested. The GaN/(TiO 2 –Pt) hybrids were able to detect ethanol and methanol concentrations as low as 100 nmol mol −1 (ppb) in air in approximately 100 s, and hydrogen concentrations from 1 µmol mol −1 (ppm) to 1% in nitrogen in less than 60 s. However, GaN/Pt NWNC hybrids showed limited sensitivity only towards hydrogen and not towards any alcohols. All these hybrid sensors worked at room temperature and are photomodulated, i.e. they responded to analytes only in the presence of ultraviolet (UV) light. We propose a qualitative explanation based on the heat of adsorption, ionization energy and solvent polarity to explain the observed selectivity of the different hybrids. These results are significant from the standpoint of applications requiring room-temperature hydrogen sensing and sensitive alcohol monitoring. These results demonstrate the tremendous potential

  13. Methanol, ethanol and hydrogen sensing using metal oxide and metal (TiO(2)-Pt) composite nanoclusters on GaN nanowires: a new route towards tailoring the selectivity of nanowire/nanocluster chemical sensors.

    Science.gov (United States)

    Aluri, Geetha S; Motayed, Abhishek; Davydov, Albert V; Oleshko, Vladimir P; Bertness, Kris A; Sanford, Norman A; Mulpuri, Rao V

    2012-05-04

    We demonstrate a new method for tailoring the selectivity of chemical sensors using semiconductor nanowires (NWs) decorated with metal and metal oxide multicomponent nanoclusters (NCs). Here we present the change of selectivity of titanium dioxide (TiO(2)) nanocluster-coated gallium nitride (GaN) nanowire sensor devices on the addition of platinum (Pt) nanoclusters. The hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN NWs followed by the deposition of TiO(2) and/or Pt nanoclusters (NCs) using the sputtering technique. This paper present the sensing characteristics of GaN/(TiO(2)-Pt) nanowire-nanocluster (NWNC) hybrids and GaN/(Pt) NWNC hybrids, and compare their selectivity with that of the previously reported GaN/TiO(2) sensors. The GaN/TiO(2) NWNC hybrids showed remarkable selectivity to benzene and related aromatic compounds, with no measurable response for other analytes. Addition of Pt NCs to GaN/TiO(2) sensors dramatically altered their sensing behavior, making them sensitive only to methanol, ethanol and hydrogen, but not to any other chemicals we tested. The GaN/(TiO(2)-Pt) hybrids were able to detect ethanol and methanol concentrations as low as 100 nmol mol(-1) (ppb) in air in approximately 100 s, and hydrogen concentrations from 1 µmol mol(-1) (ppm) to 1% in nitrogen in less than 60 s. However, GaN/Pt NWNC hybrids showed limited sensitivity only towards hydrogen and not towards any alcohols. All these hybrid sensors worked at room temperature and are photomodulated, i.e. they responded to analytes only in the presence of ultraviolet (UV) light. We propose a qualitative explanation based on the heat of adsorption, ionization energy and solvent polarity to explain the observed selectivity of the different hybrids. These results are significant from the standpoint of applications requiring room-temperature hydrogen sensing and sensitive alcohol monitoring. These results demonstrate the tremendous potential for

  14. GaN nanorods and LED structures grown on patterned Si and AlN/Si substrates by selective area growth

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shunfeng; Fuendling, Soenke; Soekmen, Uensal; Neumann, Richard; Merzsch, Stephan; Peiner, Erwin; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig (Germany); Hinze, Peter; Weimann, Thomas [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany); Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

    2010-07-15

    GaN nanorods (NRs) show promising applications in high-efficiency light emitting diodes, monolithic white light emission and optical interconnection due to their superior properties. In this work, we performed GaN nanostructures growth by pre-patterning the Si and AlN/Si substrates. The pattern was transferred to Si and AlN/Si substrates by photolithography and inductively-coupled plasma etching. GaN NRs were grown on these templates by metal-organic vapour phase epitaxy (MOVPE). GaN grown on Si pillar templates show a truncated pyramidal structure. Transmission electron microscopy measurements demonstrated clearly that the threading dislocations bend to the side facets of the GaN nanostructures and terminate. GaN growth can also be observed on the sidewalls and bottom surface between the Si pillars. A simple phenomenological model is proposed to explain the GaN nanostructure growth on Si pillar templates. Based on this model, we developed another growth method, by which we grow GaN rod structures on pre-patterned AlN/Si templates. By in-situ nitridation and decreasing of the V/III ratio, we found that GaN rods only grew on the patterned AlN/Si dots with an aspect ratio of about 1.5 - 2. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Characteristics of Mg-doped and In-Mg co-doped p-type GaN epitaxial layers grown by metal organic chemical vapour deposition

    International Nuclear Information System (INIS)

    Chung, S J; Lee, Y S; Suh, E-K; Senthil Kumar, M; An, M H

    2010-01-01

    Mg-doped and In-Mg co-doped p-type GaN epilayers were grown using the metal organic chemical vapour deposition technique. The effect of In co-doping on the physical properties of p-GaN layer was examined by high resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), Hall effect, photoluminescence (PL) and persistent photoconductivity (PPC) at room temperature. An improved crystalline quality and a reduction in threading dislocation density are evidenced upon In doping in p-GaN from HRXRD and TEM images. Hole conductivity, mobility and carrier density also significantly improved by In co-doping. PL studies of the In-Mg co-doped sample revealed that the peak position is blue shifted to 3.2 eV from 2.95 eV of conventional p-GaN and the PL intensity is increased by about 25%. In addition, In co-doping significantly reduced the PPC effect in p-type GaN layers. The improved electrical and optical properties are believed to be associated with the active participation of isolated Mg impurities.

  16. High-Temperature Growth of GaN and Al x Ga1- x N via Ammonia-Based Metalorganic Molecular-Beam Epitaxy

    Science.gov (United States)

    Billingsley, Daniel; Henderson, Walter; Doolittle, W. Alan

    2010-05-01

    The effect of high-temperature growth on the crystalline quality and surface morphology of GaN and Al x Ga1- x N grown by ammonia-based metalorganic molecular-beam epitaxy (NH3-MOMBE) has been investigated as a means of producing atomically smooth films suitable for device structures. The effects of V/III ratio on the growth rate and surface morphology are described herein. The crystalline quality of both GaN and AlGaN was found to mimic that of the GaN templates, with (002) x-ray diffraction (XRD) full-widths at half- maximum (FWHMs) of ~350 arcsec. Nitrogen-rich growth conditions have been found to provide optimal surface morphologies with a root-mean-square (RMS) roughness of ~0.8 nm, yet excessive N-rich environments have been found to reduce the growth rate and result in the formation of faceted surface pitting. AlGaN exhibits a decreased growth rate, as compared with GaN, due to increased N recombination as a result of the increased pyrolysis of NH3 in the presence of Al. AlGaN films grown directly on GaN templates exhibited Pendellösung x-ray fringes, indicating an abrupt interface and a planar AlGaN film. AlGaN films grown for this study resulted in an optimal RMS roughness of ~0.85 nm with visible atomic steps.

  17. GaN Bulk Growth and Epitaxy from Ca-Ga-N Solutions, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR proposal addresses the liquid phase epitaxy (LPE) of gallium nitride (GaN) films using nitrogen-enriched metal solutions. Growth of GaN from solutions...

  18. GaN and ZnO nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Fuendling, Soenke; Soekmen, Uensal; Behrends, Arne; Al-Suleiman, Mohamed Aid Mansur; Merzsch, Stephan; Li, Shunfeng; Bakin, Andrey; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, Technische Universitaet Braunschweig, Braunschweig (Germany); Laehnemann, Jonas; Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

    2010-10-15

    GaN and ZnO are both wide band gap semiconductors with interesting properties concerning optoelectronic and sensor device applications. Due to the lack or the high costs of native substrates, alternatives like sapphire, silicon, or silicon carbide are taken, but the resulting lattice and thermal mismatches lead to increased defect densities which reduce the material quality. In contrast, nanostructures with high aspect ratio have lower defect densities as compared to layers. In this work, we give an overview on our results achieved on both ZnO as well as GaN based nanorods. ZnO nanostructures were grown by a wet chemical approach as well as by VPT on different substrates - even on flexible polymers. To compare the growth results we analyzed the structures by XRD and PL and show possible device applications. The GaN nano- and microstructures were grown by metal organic vapor phase epitaxy either in a self-organized process or by selective area growth for a better control of shape and material composition. Finally we take a look onto possible device applications, presenting our attempts, e.g., to build LEDs based on GaN nanostructures. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  19. Refractory metal based superalloys

    International Nuclear Information System (INIS)

    Alonso, Paula R.; Vicente, Eduardo E.; Rubiolo, Gerardo H.

    1999-01-01

    Refractory metals are looked as promising materials for primary circuits in fission reactors and even as fusion reactor components. Indeed, superalloys could be developed which take advantage of their high temperature properties together with the benefits of a two- phase (intermetallic compound-refractory metal matrix) coherent structure. In 1993, researchers of the Office National d'Etudes et de Recherches Aerospatiales of France reported the observation of such a coherent structure in the Ta-Ti-Zr-Al-Nb-Mo system although the exact composition is not reported. The intermetallic compound would be Ti 2 AlMo based. However, the formation of this compound and its possible coexistence with a disordered bcc phase in the ternary system Ti-Al-Mo is a controversial subject in the related literature. In this work we develop a technique to obtain homogeneous alloys samples with 50 Ti-25 Al-25 Mo composition. The resulting specimens were characterized by optical and electronic metallography (SEM), microprobe composition measurements (EPMA) and X-ray diffraction (XRD) analyses. The results show the evidence for a bcc (A2→B2) ordering reaction in the Ti-Al-Mo system in the 50 Ti-25 Al-25 Mo composition. (author)

  20. Geometric contribution leading to anomalous estimation of two-dimensional electron gas density in GaN based heterostructures

    Science.gov (United States)

    Upadhyay, Bhanu B.; Jha, Jaya; Takhar, Kuldeep; Ganguly, Swaroop; Saha, Dipankar

    2018-05-01

    We have observed that the estimation of two-dimensional electron gas density is dependent on the device geometry. The geometric contribution leads to the anomalous estimation of the GaN based heterostructure properties. The observed discrepancy is found to originate from the anomalous area dependent capacitance of GaN based Schottky diodes, which is an integral part of the high electron mobility transistors. The areal capacitance density is found to increase for smaller radii Schottky diodes, contrary to a constant as expected intuitively. The capacitance is found to follow a second order polynomial on the radius of all the bias voltages and frequencies considered here. In addition to the quadratic dependency corresponding to the areal component, the linear dependency indicates a peripheral component. It is further observed that the peripheral to areal contribution is inversely proportional to the radius confirming the periphery as the location of the additional capacitance. The peripheral component is found to be frequency dependent and tends to saturate to a lower value for measurements at a high frequency. In addition, the peripheral component is found to vanish when the surface is passivated by a combination of N2 and O2 plasma treatments. The cumulative surface state density per unit length of the perimeter of the Schottky diodes as obtained by the integrated response over the distance between the ohmic and Schottky contacts is found to be 2.75 × 1010 cm-1.

  1. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

    Unknown

    of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the .... Considerable research is being carried out on GaN HEMTs at present. ... by InGaN/GaN multiquantum well in MOVPE was first.

  2. Improving the Efficiency Enhancement of Photonic Crystal Based InGaN Solar Cell by Using a GaN Cap Layer

    Directory of Open Access Journals (Sweden)

    T. F. Gundogdu

    2014-01-01

    Full Text Available We studied a high indium content (0.8 InGaN based solar cell design where the active InGaN layer is sandwiched between a GaN cap layer and a GaN spacer layer. The incorporation of the sacrificial cap layer allows for the etching of the front surface without removing the active InGaN resulting in a 50% enhancement of the short-circuit current density for a 15 nm-thick InGaN layer.

  3. Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

    International Nuclear Information System (INIS)

    Zhao, Qian; Xiong, Zhihua; Luo, Lan; Sun, Zhenhui; Qin, Zhenzhen; Chen, Lanli; Wu, Ning

    2017-01-01

    Highlights: • It is found nonmagnetic GaN ML exhibits half-metallic FM behavior by Mn doping due to double exchange mechanism. • Interestingly, the FM coupling is enhanced with the increasing tensile strain due to stronger interaction between Mn-3d and N-2p state. • While, the FM interaction is weakened with the increasing compressive strain until it transforms into AFM under strain of −9.5%. • These results provide a feasible approach for the fabrication of 2D DMS based GaN ML. - Abstract: To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

  4. Design of a new two-dimensional diluted magnetic semiconductor: Mn-doped GaN monolayer

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Qian [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Xiong, Zhihua, E-mail: xiong_zhihua@126.com [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Luo, Lan [School of Materials Science and Engineering, Nanchang University, Nanchang 330031 (China); Sun, Zhenhui [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China); Qin, Zhenzhen [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Chen, Lanli [Materials Genome Institute, Shanghai University, Shanghai 200444 (China); Wu, Ning [Key Laboratory for Optoelectronics and Communication of Jiangxi Province, Jiangxi Science & Technology Normal University, Nanchang 330038 (China)

    2017-02-28

    Highlights: • It is found nonmagnetic GaN ML exhibits half-metallic FM behavior by Mn doping due to double exchange mechanism. • Interestingly, the FM coupling is enhanced with the increasing tensile strain due to stronger interaction between Mn-3d and N-2p state. • While, the FM interaction is weakened with the increasing compressive strain until it transforms into AFM under strain of −9.5%. • These results provide a feasible approach for the fabrication of 2D DMS based GaN ML. - Abstract: To meet the need of low-dimensional spintronic devices, we investigate the electronic structure and magnetic properties of Mn-doped GaN monolayer using first-principles method. We find the nonmagnetic GaN monolayer exhibits half-metallic ferromagnetism by Mn doping due to double-exchange mechanism. Interestingly, the ferromagnetic coupling in Mn-doped GaN monolayer is enhanced with tensile strain and weakened with compressive strain. What is more, the ferromagnetic–antiferromagnetic transformation occurs under compressive strain of −9.5%. These results provide a feasible approach for fabrication of a new GaN monolayer based diluted magnetic semiconductor.

  5. Fabrication of full-color GaN-based light-emitting diodes on nearly lattice-matched flexible metal foils.

    Science.gov (United States)

    Kim, Hyeryun; Ohta, Jitsuo; Ueno, Kohei; Kobayashi, Atsushi; Morita, Mari; Tokumoto, Yuki; Fujioka, Hiroshi

    2017-05-18

    GaN-based light-emitting diodes (LEDs) have been widely accepted as highly efficient solid-state light sources capable of replacing conventional incandescent and fluorescent lamps. However, their applications are limited to small devices because their fabrication process is expensive as it involves epitaxial growth of GaN by metal-organic chemical vapor deposition (MOCVD) on single crystalline sapphire wafers. If a low-cost epitaxial growth process such as sputtering on a metal foil can be used, it will be possible to fabricate large-area and flexible GaN-based light-emitting displays. Here we report preparation of GaN films on nearly lattice-matched flexible Hf foils using pulsed sputtering deposition (PSD) and demonstrate feasibility of fabricating full-color GaN-based LEDs. It was found that introduction of low-temperature (LT) grown layers suppressed the interfacial reaction between GaN and Hf, allowing the growth of high-quality GaN films on Hf foils. We fabricated blue, green, and red LEDs on Hf foils and confirmed their normal operation. The present results indicate that GaN films on Hf foils have potential applications in fabrication of future large-area flexible GaN-based optoelectronics.

  6. First-principles and thermodynamic analysis of trimethylgallium (TMG) decomposition during MOVPE growth of GaN

    Science.gov (United States)

    Sekiguchi, K.; Shirakawa, H.; Yamamoto, Y.; Araidai, M.; Kangawa, Y.; Kakimoto, K.; Shiraishi, K.

    2017-06-01

    We analyzed the decomposition mechanisms of trimethylgallium (TMG) used for the gallium source of GaN fabrication based on first-principles calculations and thermodynamic analysis. We considered two conditions. One condition is under the total pressure of 1 atm and the other one is under metal organic vapor phase epitaxy (MOVPE) growth of GaN. Our calculated results show that H2 is indispensable for TMG decomposition under both conditions. In GaN MOVPE, TMG with H2 spontaneously decomposes into Ga(CH3) and Ga(CH3) decomposes into Ga atom gas when temperature is higher than 440 K. From these calculations, we confirmed that TMG surely becomes Ga atom gas near the GaN substrate surfaces.

  7. GaN Power Stage for Switch-mode Audio Amplification

    DEFF Research Database (Denmark)

    Ploug, Rasmus Overgaard; Knott, Arnold; Poulsen, Søren Bang

    2015-01-01

    Gallium Nitride (GaN) based power transistors are gaining more and more attention since the introduction of the enhancement mode eGaN Field Effect Transistor (FET) which makes an adaptation from Metal-Oxide Semiconductor (MOSFET) to eGaN based technology less complex than by using depletion mode Ga......N FETs. This project seeks to investigate the possibilities of using eGaN FETs as the power switching device in a full bridge power stage intended for switch mode audio amplification. A 50 W 1 MHz power stage was built and provided promising audio performance. Future work includes optimization of dead...

  8. Electronic Transport Mechanism for Schottky Diodes Formed by Au/HVPE a-Plane GaN Templates Grown via In Situ GaN Nanodot Formation

    Directory of Open Access Journals (Sweden)

    Moonsang Lee

    2018-06-01

    Full Text Available We investigate the electrical characteristics of Schottky contacts for an Au/hydride vapor phase epitaxy (HVPE a-plane GaN template grown via in situ GaN nanodot formation. Although the Schottky diodes present excellent rectifying characteristics, their Schottky barrier height and ideality factor are highly dependent upon temperature variation. The relationship between the barrier height, ideality factor, and conventional Richardson plot reveals that the Schottky diodes exhibit an inhomogeneous barrier height, attributed to the interface states between the metal and a-plane GaN film and to point defects within the a-plane GaN layers grown via in situ nanodot formation. Also, we confirm that the current transport mechanism of HVPE a-plane GaN Schottky diodes grown via in situ nanodot formation prefers a thermionic field emission model rather than a thermionic emission (TE one, implying that Poole–Frenkel emission dominates the conduction mechanism over the entire range of measured temperatures. The deep-level transient spectroscopy (DLTS results prove the presence of noninteracting point-defect-assisted tunneling, which plays an important role in the transport mechanism. These electrical characteristics indicate that this method possesses a great throughput advantage for various applications, compared with Schottky contact to a-plane GaN grown using other methods. We expect that HVPE a-plane GaN Schottky diodes supported by in situ nanodot formation will open further opportunities for the development of nonpolar GaN-based high-performance devices.

  9. Continuous-Wave Operation of GaN Based Multi-Quantum-Well Laser Diode at Room Temperature

    International Nuclear Information System (INIS)

    Li-Qun, Zhang; Shu-Ming, Zhang; Hui, Yang; Lian, Ji; Jian-Jun, Zhu; Zong-Shun, Liu; De-Gang, Zhao; De-Sheng, Jiang; Li-Hong, Duan; Hai, Wang; Yong-Sheng, Shi; Su-Ying, Liu; Jun-Wu, Liang; Qing, Cao; Liang-Hui, Chen

    2008-01-01

    Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5μm × 800μm ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110 mA and 10.5 V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12° and 32°, respectively

  10. Effects of Mg doping in the quantum barriers on the efficiency droop of GaN based light emitting diodes

    International Nuclear Information System (INIS)

    Liu Yang; Yang Yongchun

    2016-01-01

    The effects of Mg doping in the quantum barriers (QBs) on the efficiency droop of GaN based light emitting diodes (LEDs) were investigated through a duel wavelength method. Barrier Mg doping would lead to the enhanced hole transportation and reduced polarization field in the quantum wells (QWs), both may reduce the efficiency droop. However, heavy Mg doping in the QBs would strongly deteriorate the crystal quality of the QWs grown after the doped QB. When increasing the injection current, the carriers would escape from the QWs between n-GaN and the doped QB and recombine non-radiatively in the QWs grown after the doped QB, leading to a serious efficiency droop. (paper)

  11. Vectorial near-field imaging of a GaN based photonic crystal cavity

    International Nuclear Information System (INIS)

    La China, F.; Intonti, F.; Caselli, N.; Lotti, F.; Vinattieri, A.; Gurioli, M.; Vico Triviño, N.; Carlin, J.-F.; Butté, R.; Grandjean, N.

    2015-01-01

    We report a full optical deep sub-wavelength imaging of the vectorial components of the electric local density of states for the confined modes of a modified GaN L3 photonic crystal nanocavity. The mode mapping is obtained with a scanning near-field optical microscope operating in a resonant forward scattering configuration, allowing the vectorial characterization of optical passive samples. The optical modes of the investigated cavity emerge as Fano resonances and can be probed without the need of embedded light emitters or evanescent light coupling into the nanocavity. The experimental maps, independently measured in the two in-plane polarizations, turn out to be in excellent agreement with numerical predictions

  12. Zirconium based bulk metallic glasses

    International Nuclear Information System (INIS)

    Dey, G.K.; Neogy, S.; Savalia, R.T.; Tewari, R.; Srivastava, D.; Banerjee, S.

    2006-01-01

    Metallic glasses have come into prominence in recent times because their nanocrystalline atomic arrangement imparts many useful and unusual properties to these metallic solids. In this study, bulk glasses have been obtained in Zr based multicomponent alloy by induction melting these alloys in silica crucibles and casting these in form of rods 3 and 6 mm in diameter in a copper mould

  13. Ultrafast, superhigh gain visible-blind UV detector and optical logic gates based on nonpolar a-axial GaN nanowire

    Science.gov (United States)

    Wang, Xingfu; Zhang, Yong; Chen, Xinman; He, Miao; Liu, Chao; Yin, Yian; Zou, Xianshao; Li, Shuti

    2014-09-01

    Nonpolar a-axial GaN nanowire (NW) was first used to construct the MSM (metal-semiconductor-metal) symmetrical Schottky contact device for application as visible-blind ultraviolet (UV) detector. Without any surface or composition modifications, the fabricated device demonstrated a superior performance through a combination of its high sensitivity (up to 104 A W-1) and EQE value (up to 105), as well as ultrafast (memory storage.Nonpolar a-axial GaN nanowire (NW) was first used to construct the MSM (metal-semiconductor-metal) symmetrical Schottky contact device for application as visible-blind ultraviolet (UV) detector. Without any surface or composition modifications, the fabricated device demonstrated a superior performance through a combination of its high sensitivity (up to 104 A W-1) and EQE value (up to 105), as well as ultrafast (memory storage. Electronic supplementary information (ESI) available: Details of the EDS and SAED data, supplementary results of the UV detector, and the discussion of the transport properties of the MSM Schottky contact devices. See DOI: 10.1039/c4nr03581j

  14. Steps towards a GaN nanowire based light emitting diode and its integration with Si-MOS technology

    OpenAIRE

    Limbach, Friederich

    2012-01-01

    In dieser Arbeit wird die Machbarkeit der Herstellung von Leuchtdioden Strukturen (LEDs) in einzelnen GaN Nanodrähten (ND) und deren Integration mit herkömmlicher Si Technologie untersucht. Hierzu wird zunächst ein generelles Verständnis des Wachstums von GaN ND erarbeitet und dargestellt. Es folgen Untersuchungen zum Einfluss von Dotierstoffen, wie z.B. Mg und Si, auf das Wachstum der ND. Dieses Wissen wird anschließend angewandt um Dotierübergänge in GaN ND herzustellen die nominell n-i-p ...

  15. Optical properties of photodetectors based on single GaN nanowires with a transparent graphene contact

    Energy Technology Data Exchange (ETDEWEB)

    Babichev, A. V., E-mail: A.Babichev@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Institute (Russian Federation); Zhang, H.; Guan, N. [University Paris Saclay, Institut d’Electronique Fondamentale, UMR 8622 CNRS (France); Egorov, A. Yu. [ITMO University (Russian Federation); Julien, F. H.; Messanvi, A. [University Paris Saclay, Institut d’Electronique Fondamentale, UMR 8622 CNRS (France); Durand, C.; Eymery, J. [University Grenoble Alpes (France); Tchernycheva, M. [University Paris Saclay, Institut d’Electronique Fondamentale, UMR 8622 CNRS (France)

    2016-08-15

    We report the fabrication and optical and electrical characterization of photodetectors for the UV spectral range based on single p–n junction nanowires with a transparent contact of a new type. The contact is based on CVD-grown (chemical-vapor deposition) graphene. The active region of the nitride nanowires contains a set of 30 radial In{sub 0.18}Ga{sub 0.82}N/GaN quantum wells. The structure is grown by metal-organic vaporphase epitaxy. The photodetectors are fabricated using electron-beam lithography. The current–voltage characteristics exhibit a rectifying behavior. The spectral sensitivity of the photodetector is recorded starting from 3 eV and extending far in the UV range. The maximal photoresponse is observed at a wavelength of 367 nm (sensitivity 1.9 mA/W). The response switching time of the photodetector is less than 0.1 s.

  16. Influence of growth conditions and surface reaction byproducts on GaN grown via metal organic molecular beam epitaxy: Toward an understanding of surface reaction chemistry

    Science.gov (United States)

    Pritchett, David; Henderson, Walter; Burnham, Shawn D.; Doolittle, W. Alan

    2006-04-01

    The surface reaction byproducts during the growth of GaN films via metal organic molecular beam epitaxy (MOMBE) were investigated as a means to optimize material properties. Ethylene and ethane were identified as the dominant surface reaction hydrocarbon byproducts, averaging 27.63% and 7.15% of the total gas content present during growth. Intense ultraviolet (UV) photoexcitation during growth was found to significantly increase the abundance of ethylene and ethane while reducing the presence of H2 and N2. At 920°C, UV excitation was shown to enhance growth rate and crystalline quality while reducing carbon incorporation. Over a limited growth condition range, a 4.5×1019-3.4×1020 cm-3 variation in carbon incorporation was achieved at constant high vacuum. Coupled with growth rate gains, UV excitation yielded films with ˜58% less integrated carbon content. Structural material property variations are reported for various ammonia flows and growth temperatures. The results suggest that high carbon incorporation can be achieved and regulated during MOMBE growth and that in-situ optimization through hydrocarbon analysis may provide further enhancement in the allowable carbon concentration range.

  17. Low-leakage-current AlGaN/GaN HEMTs on Si substrates with partially Mg-doped GaN buffer layer by metal organic chemical vapor deposition

    International Nuclear Information System (INIS)

    Li Ming; Wang Yong; Wong Kai-Ming; Lau Kei-May

    2014-01-01

    High-performance low-leakage-current AlGaN/GaN high electron mobility transistors (HEMTs) on silicon (111) substrates grown by metal organic chemical vapor deposition (MOCVD) with a novel partially Magnesium (Mg)-doped GaN buffer scheme have been fabricated successfully. The growth and DC results were compared between Mg-doped GaN buffer layer and a unintentionally one. A 1-μm gate-length transistor with Mg-doped buffer layer exhibited an OFF-state drain leakage current of 8.3 × 10 −8 A/mm, to our best knowledge, which is the lowest value reported for MOCVD-grown AlGaN/GaN HEMTs on Si featuring the same dimension and structure. The RF characteristics of 0.25-μm gate length T-shaped gate HEMTs were also investigated

  18. Demonstration of an RF front-end based on GaN HEMT technology

    Science.gov (United States)

    Ture, Erdin; Musser, Markus; Hülsmann, Axel; Quay, Rüdiger; Ambacher, Oliver

    2017-05-01

    The effectiveness of the developed front-end on blocking the communication link of a commercial drone vehicle has been demonstrated in this work. A jamming approach has been taken in a broadband fashion by using GaN HEMT technology. Equipped with a modulated-signal generator, a broadband power amplifier, and an omni-directional antenna, the proposed system is capable of producing jamming signals in a very wide frequency range between 0.1 - 3 GHz. The maximum RF output power of the amplifier module has been software-limited to 27 dBm (500 mW), complying to the legal spectral regulations of the 2.4 GHz ISM band. In order to test the proof of concept, a real-world scenario has been prepared in which a commercially-available quadcopter UAV is flown in a controlled environment while the jammer system has been placed in a distance of about 10 m from the drone. It has been proven that the drone of interest can be neutralized as soon as it falls within the range of coverage (˜3 m) which endorses the promising potential of the broadband jamming approach.

  19. Nitride-based quantum structures and devices on modified GaN substrates

    International Nuclear Information System (INIS)

    Perlin, Piotr; Leszczynski, Mike; Grzegory, Izabella; Franssen, Gijs; Targowski, Grzegorz; Krysko, Marcin; Nowak, Grzegorz; Litwin-Staszewska, Elzbieta; Piotrzkowski, Ryszard; Lucznik, Bolek; Suski, Tadek; Szeszko, Justyna; Czernecki, R.; Grzanka, Szymon; Jakiela, Rafal; Albrecht, Martin

    2009-01-01

    We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c-axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 C and 820 C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p-type GaN layers. With increasing misorientation, the free hole density drastically increases above 10 18 cm -3 . This improvement in p-type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics

    OpenAIRE

    Kusaba, Akira; Li, Guanchen; von Spakovsky, Michael R.; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-01-01

    Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and Nad-H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict...

  1. Taevo Gans / Ene Ammer

    Index Scriptorium Estoniae

    Ammer, Ene

    1998-01-01

    Sisearhitekt Taevo Gansist. Tudengipõlvest, selle aja projektidest, sõpruskonnast, tandemist Summatavet & Gans, Venemaa tellimustest, kaastöölistest. Üksinda Hommilkumaal vene tarbekunsti näitusega 1974. a. 1988. a. loodud perefirmast "GaDis" (omanikud Taevo, Helle Gans, Riia Oja), mis nõustab ka "Wermot" mööbli osas. "GaDise" sisekujundusprojektidest, millega Taevo ja Helle Gans tegelevad üheskoos

  2. Simultaneously Enhancing Light Emission and Suppressing Efficiency Droop in GaN Microwire-Based Ultraviolet Light-Emitting Diode by the Piezo-Phototronic Effect.

    Science.gov (United States)

    Wang, Xingfu; Peng, Wenbo; Yu, Ruomeng; Zou, Haiyang; Dai, Yejing; Zi, Yunlong; Wu, Changsheng; Li, Shuti; Wang, Zhong Lin

    2017-06-14

    Achievement of p-n homojuncted GaN enables the birth of III-nitride light emitters. Owing to the wurtzite-structure of GaN, piezoelectric polarization charges present at the interface can effectively control/tune the optoelectric behaviors of local charge-carriers (i.e., the piezo-phototronic effect). Here, we demonstrate the significantly enhanced light-output efficiency and suppressed efficiency droop in GaN microwire (MW)-based p-n junction ultraviolet light-emitting diode (UV LED) by the piezo-phototronic effect. By applying a -0.12% static compressive strain perpendicular to the p-n junction interface, the relative external quantum efficiency of the LED is enhanced by over 600%. Furthermore, efficiency droop is markedly reduced from 46.6% to 7.5% and corresponding droop onset current density shifts from 10 to 26.7 A cm -2 . Enhanced electrons confinement and improved holes injection efficiency by the piezo-phototronic effect are revealed and theoretically confirmed as the physical mechanisms. This study offers an unconventional path to develop high efficiency, strong brightness and high power III-nitride light sources.

  3. Z L GAN

    Indian Academy of Sciences (India)

    Z L GAN. Articles written in Sadhana. Volume 43 Issue 4 April 2018 pp 59. Effect of scale size, orientation type and dispensing method on void formation in the CUF encapsulation of BGA · AIZAT ABAS FEI CHONG NG Z L GAN M H H ISHAK M Z ABDULLAH GEAN YUEN CHONG · More Details Abstract Fulltext PDF.

  4. Electrically active point defects in Mg implanted n-type GaN grown by metal-organic chemical vapor deposition

    Science.gov (United States)

    Alfieri, G.; Sundaramoorthy, V. K.; Micheletto, R.

    2018-05-01

    Magnesium (Mg) is the p-type doping of choice for GaN, and selective area doping by ion implantation is a routine technique employed during device processing. While electrically active defects have been thoroughly studied in as-grown GaN, not much is known about defects generated by ion implantation. This is especially true for the case of Mg. In this study, we carried out an electrical characterization investigation of point defects generated by Mg implantation in GaN. We have found at least nine electrically active levels in the 0.2-1.2 eV energy range, below the conduction band. The isochronal annealing behavior of these levels showed that most of them are thermally stable up to 1000 °C. The nature of the detected defects is then discussed in the light of the results found in the literature.

  5. Transport mechanisms in Schottky diodes realized on GaN

    Science.gov (United States)

    Amor, Sarrah; Ahaitouf, Ali; Ahaitouf, Abdelaziz; Salvestrini, Jean Paul; Ougazzaden, Abdellah

    2017-03-01

    This work is focused on the conducted transport mechanisms involved on devices based in gallium nitride GaN and its alloys. With considering all conduction mechanisms of current, its possible to understanded these transport phenomena. Thanks to this methodology the current-voltage characteristics of structures with unusual behaviour are further understood and explain. Actually, the barrier height (SBH) is a complex problem since it depends on several parameters like the quality of the metal-semiconductor interface. This study is particularly interesting as solar cells are made on this material and their qualification is closely linked to their transport properties.

  6. Impact of GaN cap on charges in Al₂O₃/(GaN/)AlGaN/GaN metal-oxide-semiconductor heterostructures analyzed by means of capacitance measurements and simulations

    Energy Technology Data Exchange (ETDEWEB)

    Ťapajna, M., E-mail: milan.tapajna@savba.sk; Jurkovič, M.; Válik, L.; Haščík, Š.; Gregušová, D.; Kuzmík, J. [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Brunner, F.; Cho, E.-M. [Ferdinand-Braun-Institut, Leibniz Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Hashizume, T. [Research Center for Integrated Quantum Electronics (RCIQE), Hokkaido University, 060-0814 Sapporo, Japan and JST-CREST, 102-0075 Tokyo (Japan)

    2014-09-14

    Oxide/semiconductor interface trap density (D{sub it}) and net charge of Al₂O₃/(GaN)/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with and without GaN cap were comparatively analyzed using comprehensive capacitance measurements and simulations. D{sub it} distribution was determined in full band gap of the barrier using combination of three complementary capacitance techniques. A remarkably higher D{sub it} (∼5–8 × 10¹²eV⁻¹ cm⁻²) was found at trap energies ranging from EC-0.5 to 1 eV for structure with GaN cap compared to that (D{sub it} ∼ 2–3 × 10¹²eV⁻¹ cm⁻²) where the GaN cap was selectively etched away. D{sub it} distributions were then used for simulation of capacitance-voltage characteristics. A good agreement between experimental and simulated capacitance-voltage characteristics affected by interface traps suggests (i) that very high D{sub it} (>10¹³eV⁻¹ cm⁻²) close to the barrier conduction band edge hampers accumulation of free electron in the barrier layer and (ii) the higher D{sub it} centered about EC-0.6 eV can solely account for the increased C-V hysteresis observed for MOS-HEMT structure with GaN cap. Analysis of the threshold voltage dependence on Al₂O₃ thickness for both MOS-HEMT structures suggests that (i) positive charge, which compensates the surface polarization, is not necessarily formed during the growth of III-N heterostructure, and (ii) its density is similar to the total surface polarization charge of the GaN/AlGaN barrier, rather than surface polarization of the top GaN layer only. Some constraints for the positive surface compensating charge are discussed.

  7. Understanding the Room Temperature Ferromagnetism in GaN Nanowires with Pd Doping

    International Nuclear Information System (INIS)

    Manna, S; De, S K

    2011-01-01

    We report the first synthesis and characterization of 4d transition metal palladium-doped GaN nanowires (NWs). Room temperature ferromagnetism has been observed in high quality Vapor Liquid Solid (VLS) epitaxy grown undoped n-type GaN nanowires. It was proposed that this type of magnetism is due to defects which are not observed in Bulk GaN because of large formation energy of defects in bulk GaN. Here we have successfully doped 4d transition metal Pd in GaN NWs. We find fairly strong and long-range ferromagnetic coupling between Pd substituted for Ga in GaN . The results suggest that 4d metals such as Pd may also be considered as candidates for ferromagnetic dopants in semiconductors.

  8. Pt-decorated GaN nanowires with significant improvement in H2 gas-sensing performance at room temperature.

    Science.gov (United States)

    Abdullah, Q N; Yam, F K; Hassan, Z; Bououdina, M

    2015-12-15

    Superior sensitivity towards H2 gas was successfully achieved with Pt-decorated GaN nanowires (NWs) gas sensor. GaN NWs were fabricated via chemical vapor deposition (CVD) route. Morphology (field emission scanning electron microscopy and transmission electron microscopy) and crystal structure (high resolution X-ray diffraction) characterizations of the as-synthesized nanostructures demonstrated the formation of GaN NWs having a wurtzite structure, zigzaged shape and an average diameter of 30-166nm. The Pt-decorated GaN NWs sensor shows a high response of 250-2650% upon exposure to H2 gas concentration from 7 to 1000ppm respectively at room temperature (RT), and then increases to about 650-4100% when increasing the operating temperature up to 75°C. The gas-sensing measurements indicated that the Pt-decorated GaN NWs based sensor exhibited efficient detection of H2 at low concentration with excellent sensitivity, repeatability, and free hysteresis phenomena over a period of time of 100min. The large surface-to-volume ratio of GaN NWs and the catalytic activity of Pt metal are the most influential factors leading to the enhancement of H2 gas-sensing performances through the improvement of the interaction between the target molecules (H2) and the sensing NWs surface. The attractive low-cost, low power consumption and high-performance of the resultant decorated GaN NWs gas sensor assure their uppermost potential for H2 gas sensor working at low operating temperature. Copyright © 2015 Elsevier Inc. All rights reserved.

  9. Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

    Energy Technology Data Exchange (ETDEWEB)

    Choudhary, B. S. [CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India); Rajasthan Technical University, Rawatbhata Road, Kota 324010 (India); Singh, A.; Tyagi, P. K. [Department of Applied Physics, Delhi Technological University, Delhi 110042 (India); Tanwar, S. [Rajasthan Technical University, Rawatbhata Road, Kota 324010 (India); Kumar, M. Senthil; Kushvaha, S. S., E-mail: kushvahas@nplindia.org [CSIR-National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India)

    2016-04-13

    We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.

  10. GaN epitaxial layers grown on multilayer graphene by MOCVD

    Science.gov (United States)

    Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe

    2018-04-01

    In this study, GaN epitaxial layers were successfully deposited on a multilayer graphene (MLG) by using metal-organic chemical vapor deposition (MOCVD). Highly crystalline orientations of the GaN films were confirmed through electron backscatter diffraction (EBSD). An epitaxial relationship between GaN films and MLG is unambiguously established by transmission electron microscope (TEM) analysis. The Raman spectra was used to analyze the internal stress of GaN films, and the spectrum shows residual tensile stress in the GaN films. Moreover, the results of the TEM analysis and Raman spectra indicate that the high quality of the MLG substrate is maintained even after the growth of the GaN film. This high-quality MLG makes it possible to easily remove epitaxial layers from the supporting substrate by micro-mechanical exfoliation technology. This work can aid in the development of transferable devices using GaN films.

  11. Fabrications and application of single crystalline GaN for high-performance deep UV photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Velazquez, R.; Rivera, M.; Feng, P., E-mail: p.feng@upr.edu [Department of Physics, College of Natural Sciences, University of Puerto Rico, San Juan, 00936-8377, PR/USA (Puerto Rico); Aldalbahi, A. [Department of Chemistry, College of Science, King Saud University, Riyadh 11451 (Saudi Arabia)

    2016-08-15

    High-quality single crystalline Gallium Nitride (GaN) semiconductor has been synthesized using molecule beam epitaxy (MBE) technique for development of high-performance deep ultraviolet (UV) photodetectors. Thickness of the films was estimated by using surface profile meter and scanning electron microscope. Electronic states and elemental composition of the films were obtained using Raman scattering spectroscopy. The orientation, crystal structure and phase purity of the films were examined using a Siemens x-ray diffractometer radiation. The surface microstructure was studied using high resolution scanning electron microscopy (SEM). Two types of metal pairs: Al-Al, Al-Cu or Cu-Cu were used for interdigital electrodes on GaN film in order to examine the Schottky properties of the GaN based photodetector. The characterizations of the fabricated prototype include the stability, responsivity, response and recovery times. Typical time dependent photoresponsivity by switching different UV light source on and off five times for each 240 seconds at a bias of 2V, respectively, have been obtained. The detector appears to be highly sensitive to various UV wavelengths of light with very stable baseline and repeatability. The obtained photoresponsivity was up to 354 mA/W at the bias 2V. Higher photoresponsivity could be obtained if higher bias was applied but it would unavoidably result in a higher dark current. Thermal effect on the fabricated GaN based prototype was discussed.

  12. StackGAN++: Realistic Image Synthesis with Stacked Generative Adversarial Networks

    OpenAIRE

    Zhang, Han; Xu, Tao; Li, Hongsheng; Zhang, Shaoting; Wang, Xiaogang; Huang, Xiaolei; Metaxas, Dimitris

    2017-01-01

    Although Generative Adversarial Networks (GANs) have shown remarkable success in various tasks, they still face challenges in generating high quality images. In this paper, we propose Stacked Generative Adversarial Networks (StackGAN) aiming at generating high-resolution photo-realistic images. First, we propose a two-stage generative adversarial network architecture, StackGAN-v1, for text-to-image synthesis. The Stage-I GAN sketches the primitive shape and colors of the object based on given...

  13. Enhanced piezoelectric output of NiO/nanoporous GaN by suppression of internal carrier screening

    Science.gov (United States)

    Waseem, Aadil; Jeong, Dae Kyung; Johar, Muhammad Ali; Kang, Jin-Ho; Ha, Jun-Seok; Key Lee, June; Ryu, Sang-Wan

    2018-06-01

    The efficiency of piezoelectric nanogenerators (PNGs) significantly depends on the free carrier concentration of semiconductors. In the presence of a mechanical stress, piezoelectric charges are generated at both ends of the PNG, which are rapidly screened by the free carriers. The screening effect rapidly decreases the piezoelectric output within fractions of a second. In this study, the piezoelectric outputs of bulk- and nanoporous GaN-based heterojunction PNGs are compared. GaN thin films were epitaxially grown on sapphire substrates using metal organic chemical vapor deposition. Nanoporous GaN was fabricated using electrochemical etching, depleted of free carriers owing to the surface Fermi-level pinning. A highly resistive NiO thin film was deposited on bulk- and nanoporous GaN using radio frequency magnetron sputter. The NiO/nanoporous GaN PNG (NPNG) under a periodic compressive stress of 4 MPa exhibited an output voltage and current of 0.32 V and 1.48 μA cm‑2, respectively. The output voltage and current of the NiO/thin film-GaN PNG (TPNG) were three and five times smaller than those of the NPNG, respectively. Therefore, the high-resistivity of NiO and nanoporous GaN depleted by the Fermi-level pinning are advantageous and provide a better piezoelectric performance of the NPNG, compared with that of the TPNG.

  14. Amorphous metal based nanoelectromechanical switch

    KAUST Repository

    Mayet, Abdulilah M.; Smith, Casey; Hussain, Muhammad Mustafa

    2013-01-01

    Nanoelectromechanical (NEM) switch is an interesting ultra-low power option which can operate in the harsh environment and can be a complementary element in complex digital circuitry. Although significant advancement is happening in this field, report on ultra-low voltage (pull-in) switch which offers high switching speed and area efficiency is yet to be made. One key challenge to achieve such characteristics is to fabricate nano-scale switches with amorphous metal so the shape and dimensional integrity are maintained to achieve the desired performance. Therefore, we report a tungsten alloy based amorphous metal with fabrication process development of laterally actuated dual gated NEM switches with 100 nm width and 200 nm air-gap to result in <5 volts of actuation voltage (Vpull-in). © 2013 IEEE.

  15. Amorphous metal based nanoelectromechanical switch

    KAUST Repository

    Mayet, Abdulilah M.

    2013-04-01

    Nanoelectromechanical (NEM) switch is an interesting ultra-low power option which can operate in the harsh environment and can be a complementary element in complex digital circuitry. Although significant advancement is happening in this field, report on ultra-low voltage (pull-in) switch which offers high switching speed and area efficiency is yet to be made. One key challenge to achieve such characteristics is to fabricate nano-scale switches with amorphous metal so the shape and dimensional integrity are maintained to achieve the desired performance. Therefore, we report a tungsten alloy based amorphous metal with fabrication process development of laterally actuated dual gated NEM switches with 100 nm width and 200 nm air-gap to result in <5 volts of actuation voltage (Vpull-in). © 2013 IEEE.

  16. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p-n diodes and InGaN LEDs

    Science.gov (United States)

    Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

    2017-12-01

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal-organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p-n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm-3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10-3-3.4 × 10-3 Ω·cm2, and the turn-on voltages of the diodes.

  17. The controlled growth of GaN microrods on Si(111) substrates by MOCVD

    Science.gov (United States)

    Foltynski, Bartosz; Garro, Nuria; Vallo, Martin; Finken, Matthias; Giesen, Christoph; Kalisch, Holger; Vescan, Andrei; Cantarero, Andrés; Heuken, Michael

    2015-03-01

    In this paper, a selective area growth (SAG) approach for growing GaN microrods on patterned SiNx/Si(111) substrates by metal-organic chemical vapor deposition (MOCVD) is studied. The surface morphology, optical and structural properties of vertical GaN microrods terminated by pyramidal shaped facets (six { 10 1 bar 1} planes) were characterized using scanning electron microscopy (SEM), room temperature photoluminescence (PL) and Raman spectroscopy, respectively. Measurements revealed high-quality GaN microcolumns grown with silane support. Characterized structures were grown nearly strain-free (central frequency of Raman peak of 567±1 cm-1) with crystal quality comparable to bulk crystals (FWHM=4.2±1 cm-1). Such GaN microrods might be used as a next-generation device concept for solid-state lighting (SSL) applications by realizing core-shell InGaN/GaN multi-quantum wells (MQWs) on the n-GaN rod base.

  18. Mn doped GaN thin films and nanoparticles

    Czech Academy of Sciences Publication Activity Database

    Šofer, Z.; Sedmidubský, D.; Huber, Š.; Hejtmánek, Jiří; Macková, Anna; Fiala, R.

    2012-01-01

    Roč. 9, 8-9 (2012), s. 809-824 ISSN 1475-7435 R&D Projects: GA ČR GA104/09/0621 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10480505 Keywords : GaN nanoparticles * GaN thin films * manganese * transition metals * MOVPE * ion implantations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.087, year: 2012

  19. Simulation based comparative analysis of photoresponse in front- and back-illuminated GaN P-I-N ultraviolet photodetectors

    Science.gov (United States)

    Wang, Jun; Guo, Jin; Xie, Feng; Wang, Guosheng; Wu, Haoran; Song, Man; Yi, Yuanyuan

    2016-10-01

    This paper presents the comparative analysis of influence of doping level and doping profile of the active region on zero bias photoresponse characteristics of GaN-based p-i-n ultraviolet (UV) photodetectors operating at front- and back-illuminated. A two dimensional physically-based computer simulation of GaN-based p-i-n UV photodetectors is presented. We implemented GaN material properties and physical models taken from the literature. It is shown that absorption layer doping profile has notable impacts on the photoresponse of the device. Especially, the effect of doping concentration and distribution of the absorption layer on photoresponse is discussed in detail. In the case of front illumination, comparative to uniform n-type doping, the device with n-type Gaussian doping profiles at absorption layer has higher responsivity. Comparative to front illumination, back illuminated detector with p-type doping profiles at absorption layer has higher maximum photoresponse, while the Gaussian doping profiles have a weaker ability to enhance the device responsivity. It is demonstrated that electric field distribution, mobility degradation, and recombinations are jointly responsible for the variance of photoresponse. Our work enriches the understanding and utilization of GaN based p-i-n UV photodetectors.

  20. X-parameter Based GaN Device Modeling and its Application to a High-efficiency PA Design

    DEFF Research Database (Denmark)

    Wang, Yelin; Nielsen, Troels Studsgaard; Jensen, Ole Kiel

    2014-01-01

    X-parameters are supersets of S-parameters and applicable to both linear and nonlinear system modeling. In this paper, a packaged 6 W Gallium Nitride (GaN) RF power transistor is modeled using load-dependent X-parameters by simulations. During the device characterization the load impedance is tuned...... to decrease the complexity of a harmonic load-pull measurement setup. A high-efficiency 2 GHz power amplifier is also designed for further validation of the concept....

  1. The compositional, structural, and magnetic properties of a Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN spin injecting hetero-structure grown by metal-organic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Zhonghua; Huang, Shimin [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Tang, Kun, E-mail: ktang@nju.edu.cn [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Gu, Shulin, E-mail: slgu@nju.edu.cn [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Zhu, Shunming [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Ye, Jiandong [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Nanjing University Institute of Optoelectronics at Yangzhou, Yangzhou 225009 (China); Xu, Mingxiang [Department of Physics, Southeast University, Nanjing 210096 (China); Wang, Wei; Zheng, Youdou [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China)

    2016-12-01

    Highlights: • The Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN hetero-structure has been fabricated by MOCVD successfully. • The formation mechanism of different layers in sample was revealed in details. • The properties of the hetero-structure have been presented and discussed extensively. • The effect of Ga diffusion on the magnetic properties of Fe{sub 3}O{sub 4} film has been shown. - Abstract: In this article, the authors have designed and fabricated a Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN spin injecting hetero-structure by metal-organic chemical vapor deposition. The compositional, structural, and magnetic properties of the hetero-structure have been characterized and discussed. From the characterizations, the hetero-structure has been successfully grown generally. However, due to the unintentional diffusion of Ga ions from Ga{sub 2}O{sub 3}/GaN layers, the most part of the nominal Fe{sub 3}O{sub 4} layer is actually in the form of Ga{sub x}Fe{sub 3−x}O{sub 4} with gradually decreased x values from the Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3} interface to the Fe{sub 3}O{sub 4} surface. Post-annealing process can further aggravate the diffusion. Due to the similar ionic radius of Ga and Fe, the structural configuration of the Ga{sub x}Fe{sub 3−x}O{sub 4} does not differ from that of pure Fe{sub 3}O{sub 4}. However, the ferromagnetism has been reduced with the incorporation of Ga into Fe{sub 3}O{sub 4}, which has been explained by the increased Yafet-Kittel angles in presence of considerable amount of Ga incorporation. A different behavior of the magnetoresistance has been found on the as-grown and annealed samples, which could be modelled and explained by the competition between the spin-dependent and spin-independent conduction channels. This work has provided detailed information on the interfacial properties of the Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN spin injecting hetero-structure, which is the solid basis for further improvement and application of

  2. Optical properties of metastable shallow acceptors in Mg-doped GaN layers grown by metal-organic vapor phase epitaxy

    OpenAIRE

    Pozina, Galia; Hemmingsson, Carl; Bergman, Peder; Kawashima, T.; Amano, H.; Akasaki, I.; Usui, A.; Monemar, Bo

    2010-01-01

    GaN layers doped by Mg show a metastable behavior of the near-band-gap luminescence caused by electron irradiation or UV excitation. At low temperatures < 30 K the changes in luminescence are permanent. Heating to room temperature recovers the initial low temperature spectrum shape completely. Two acceptors are involved in the recombination process as confirmed by transient PL. In as-grown samples a possible candidate for the metastable acceptor is C-N, while after annealing a second m...

  3. Characterization of 380nm UV-LEDs grown on free-standing GaN by atmospheric-pressure metal-organic chemical vapor deposition

    Science.gov (United States)

    Shieh, C. Y.; Li, Z. Y.; Kuo, H. C.; Chang, J. Y.; Chi, G. C.

    2014-03-01

    We reported the defects and optical characterizations of the ultraviolet light-emitting diodes grown on free-standing GaN substrate (FS-GaN) and sapphire. Cross-sectional transmission electron microscopy (TEM) images showed that the total defect densities of grown UV LEDs on FS-GaN and sapphire including edge, screw and mixed type were 3.6×106 cm-2 and 5.5×108 cm-2. When substrate of UV LEDs was changed from sapphire to FS-GaN, it can be clearly found that the crystallography of GaN epilayers was drastically different from that GaN epilayers on sapphire. Besides, the microstructures or indium clustering can be not observed at UV LEDs on FS-GaN from TEM measurement. The internal quantum efficiency of UVLEDs on FS-GaN and sapphire were 34.8 % and 39.4 % respectively, which attributed to indium clustering in multi-layers quantum wells (MQWs) of UV LEDs on sapphire. The relationship between indiumclustering and efficiency droop were investigated by temperature-dependent electroluminescence (TDEL) measurements.

  4. Determination of carrier diffusion length in GaN

    Science.gov (United States)

    Hafiz, Shopan; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit; Metzner, Sebastian; Bertram, Frank; Christen, Jürgen; Gil, Bernard

    2015-01-01

    Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) and cross-sectional cathodoluminescence (CL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p-GaN or 1500 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photo-generation near the surface region by above bandgap excitation. Taking into consideration the absorption in the top GaN layer as well as active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be 93 ± 7 nm and 70 ± 7 nm for Mg-doped p-type GaN and 432 ± 30 nm and 316 ± 30 nm for unintentionally doped n-type GaN, respectively, at photogenerated carrier densities of 4.2 × 1018 cm-3 using PL spectroscopy. CL measurements of the unintentionally doped n-type GaN layer at much lower carrier densities of 1017 cm-3 revealed a longer diffusion length of 525 ± 11 nm at 6 K.

  5. Polarization Raman spectroscopy of GaN nanorod bundles

    International Nuclear Information System (INIS)

    Tite, T.; Lee, C. J.; Chang, Y.-M.

    2010-01-01

    We performed polarization Raman spectroscopy on single wurtzite GaN nanorod bundles grown by plasma-assisted molecular beam epitaxy. The obtained Raman spectra were compared with those of GaN epilayer. The spectral difference between the GaN nanorod bundles and epilayer reveals the relaxation of Raman selection rules in these GaN nanorod bundles. The deviation of polarization-dependent Raman spectroscopy from the prediction of Raman selection rules is attributed to both the orientation of the crystal axis with respect to the polarization vectors of incident and scattered light and the structural defects in the merging boundary of GaN nanorods. The presence of high defect density induced by local strain at the merging boundary was further confirmed by transmission electron microscopy. The averaged defect interspacing was estimated to be around 3 nm based on the spatial correlation model.

  6. Speciation in Metal Toxicity and Metal-Based Therapeutics

    Directory of Open Access Journals (Sweden)

    Douglas M. Templeton

    2015-04-01

    Full Text Available Metallic elements, ions and compounds produce varying degrees of toxicity in organisms with which they come into contact. Metal speciation is critical to understanding these adverse effects; the adjectives “heavy” and “toxic” are not helpful in describing the biological properties of individual elements, but detailed chemical structures are. As a broad generalization, the metallic form of an element is inert, and the ionic salts are the species that show more significant bioavailability. Yet the salts and other chelates of a metal ion can give rise to quite different toxicities, as exemplified by a range of carcinogenic potential for various nickel species. Another important distinction comes when a metallic element is organified, increasing its lipophilicity and hence its ability to penetrate the blood brain barrier, as is seen, for example, with organic mercury and tin species. Some metallic elements, such as gold and platinum, are themselves useful therapeutic agents in some forms, while other species of the same element can be toxic, thus focusing attention on species interconversions in evaluating metal-based drugs. The therapeutic use of metal-chelating agents introduces new species of the target metal in vivo, and this can affect not only its desired detoxification, but also introduce a potential for further mechanisms of toxicity. Examples of therapeutic iron chelator species are discussed in this context, as well as the more recent aspects of development of chelation therapy for uranium exposure.

  7. Strain management of AlGaN-based distributed Bragg reflectors with GaN interlayer grown by metalorganic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yuh-Shiuan; Kao, Tsung-Ting; Mehta, Karan; Jia, Xiao Jia; Shen, Shyh-Chiang; Yoder, P. Douglas; Detchprohm, Theeradetch; Dupuis, Russell D., E-mail: dupuis@gatech.edu [Center for Compound Semiconductors and School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr. NW, Atlanta, Georgia 30332-0250 (United States); Wang, Shuo; Xie, Hongen; Ponce, Fernando A. [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)

    2016-08-22

    We report the crack-free growth of a 45-pair Al{sub 0.30}Ga{sub 0.70}N/Al{sub 0.04}Ga{sub 0.96}N distributed Bragg reflector (DBR) on 2 in. diameter AlN/sapphire template by metalorganic chemical vapor deposition. To mitigate the cracking issue originating from the tensile strain of Al{sub 0.30}Ga{sub 0.70}N on GaN, an AlN template was employed in this work. On the other hand, strong compressive strain experienced by Al{sub 0.04}Ga{sub 0.96}N favors 3D island growth, which is undesired. We found that inserting an 11 nm thick GaN interlayer upon the completion of AlN template layer properly managed the strain such that the Al{sub 0.30}Ga{sub 0.70}N/Al{sub 0.04}Ga{sub 0.96}N DBR was able to be grown with an atomically smooth surface morphology. Smooth surfaces and sharp interfaces were observed throughout the structure using high-angle annular dark-field imaging in the STEM. The 45-pair AlGaN-based DBR provided a peak reflectivity of 95.4% at λ = 368 nm with a bandwidth of 15 nm.

  8. Integrated luminescent chemical microsensors based on GaN LEDs for security applications using smartphones

    Science.gov (United States)

    Orellana, Guillermo; Muñoz, Elias; Gil-Herrera, Luz K.; Muñoz, Pablo; Lopez-Gejo, Juan; Palacio, Carlos

    2012-09-01

    Development of PCB-integrateable microsensors for monitoring chemical species is a goal in areas such as lab-on-a-chip analytical devices, diagnostics medicine and electronics for hand-held instruments where the device size is a major issue. Cellular phones have pervaded the world inhabitants and their usefulness has dramatically increased with the introduction of smartphones due to a combination of amazing processing power in a confined space, geolocalization and manifold telecommunication features. Therefore, a number of physical and chemical sensors that add value to the terminal for health monitoring, personal safety (at home, at work) and, eventually, national security have started to be developed, capitalizing also on the huge number of circulating cell phones. The chemical sensor-enabled "super" smartphone provides a unique (bio)sensing platform for monitoring airborne or waterborne hazardous chemicals or microorganisms for both single user and crowdsourcing security applications. Some of the latest ones are illustrated by a few examples. Moreover, we have recently achieved for the first time (covalent) functionalization of p- and n-GaN semiconductor surfaces with tuneable luminescent indicator dyes of the Ru-polypyridyl family, as a key step in the development of innovative microsensors for smartphone applications. Chemical "sensoring" of GaN-based blue LED chips with those indicators has also been achieved by plasma treatment of their surface, and the micrometer-sized devices have been tested to monitor O2 in the gas phase to show their full functionality. Novel strategies to enhance the sensor sensitivity such as changing the length and nature of the siloxane buffer layer are discussed in this paper.

  9. Role of Ag-alloy in the thermal stability of Ag-based ohmic contact to GaN(0 0 0 1) surface

    International Nuclear Information System (INIS)

    Xiong, Zhihua; Qin, Zhenzhen; Zhao, Qian; Chen, Lanli

    2015-01-01

    First-principles calculations are performed to study Ag and Ag-alloy adsorption stability on GaN(0 0 0 1) surface. We find Ag only contact to GaN surface is unstable under high temperature. While Ag-alloy adsorption exhibits better adsorption stability and electronic properties than that of the Ag only contact,due to the enhanced interaction between Ag-alloy and GaN(0 0 0 1) surface. The Ag-alloy, particularly AgNi, is proposed to be used as very promising ohmic contact to GaN for practical applications

  10. Alignment control and atomically-scaled heteroepitaxial interface study of GaN nanowires.

    Science.gov (United States)

    Liu, Qingyun; Liu, Baodan; Yang, Wenjin; Yang, Bing; Zhang, Xinglai; Labbé, Christophe; Portier, Xavier; An, Vladimir; Jiang, Xin

    2017-04-20

    Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH 3 flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001) GaN ∥(0001) sapphire and (101[combining macron]0) GaN ∥(112[combining macron]0) sapphire . Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of "type I" stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.

  11. 15 Gb/s OFDM-based VLC using direct modulation of 450 GaN laser diode

    Science.gov (United States)

    Viola, Shaun; Islim, Mohamed Sufyan; Watson, Scott; Videv, Stefan; Haas, Harald; Kelly, Anthony E.

    2017-10-01

    A record data rate for visible light communications (VLC) using a transistor outline (TO) packaged Gallium Nitride (GaN) laser diode is reported. Using a system 3 dB bandwidth of 1.4 GHz data transmission at 15 Gb/s is reported. This is achieved due to the use of orthogonal frequency division multiplexing (OFDM) in combination with a high system signal to noise ratio (SNR) and adaptive bit loading extending the effective bandwidth to 2.5 GHz. To the best of authors knowledge this is the highest reported data rate for single channel VLC.

  12. Low modulation bias InGaN-based integrated EA-modulator-laser on semipolar GaN substrate

    KAUST Repository

    Shen, Chao; Leonard, John; Pourhashemi, Arash; Oubei, Hassan M.; Alias, Mohd Sharizal; Ng, Tien Khee; Nakamura, Shuji; DenBaars, Steven P.; Speck, James S.; Alyamani, Ahmed Y.; Eldesouki, Munir M.; Ooi, Boon S.

    2015-01-01

    In summary, we demonstrated the monolithic integration of electroabsorption modulator with laser diode and measured DC and AC modulation characteristics of the device, which is grown on (2021̅) plane GaN substrate. By alternating the modulation voltage at −3.5 V and 0 V, we achieve the laser output power of < 1.5 mW to > 9 mW, respectively, leading to ∼8.1 dB On/Off ratio. Our results clearly show that a low power consumption modulator can be achieved with semipolar EA-modulator compared to that of the c-plane devices.

  13. Low modulation bias InGaN-based integrated EA-modulator-laser on semipolar GaN substrate

    KAUST Repository

    Shen, Chao

    2015-10-06

    In summary, we demonstrated the monolithic integration of electroabsorption modulator with laser diode and measured DC and AC modulation characteristics of the device, which is grown on (2021̅) plane GaN substrate. By alternating the modulation voltage at −3.5 V and 0 V, we achieve the laser output power of < 1.5 mW to > 9 mW, respectively, leading to ∼8.1 dB On/Off ratio. Our results clearly show that a low power consumption modulator can be achieved with semipolar EA-modulator compared to that of the c-plane devices.

  14. Investigation into the use of molecular hydrogen on the growth of gallium nitride via metal-organic molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Billingsley, Daniel; Pritchett, David; Henderson, Walter; Carver, Alexander G.; Burnham, Shawn D.; Doolittle, W.A. [Georgia Institute of Technology, School of Electrical and Computer Engineering, 777 Atlantic Dr., Atlanta, GA 30332 (United States)

    2008-07-01

    Molecular hydrogen (H{sub 2}) has been investigated as a means to improve ammonia nitridation efficiency and attempts to reduce carbon contamination in ammonia-based metal-organic molecular beam epitaxy (MOMBE). A 30% improvement in crystalline quality, inferred from XRD, as well as an increase in subsequent GaN bulk growth rate was observed when bare sapphire was subject to H{sub 2} annealing before nitridation. However, the use of H{sub 2} during GaN homoepitaxy on GaN templates resulted in increased carbon contamination and decreased growth rate of GaN. The results demonstrate promise and proper uses of H{sub 2} during GaN growth under certain conditions. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Chemical lift-off of (11-22) semipolar GaN using periodic triangular cavities

    Science.gov (United States)

    Jeon, Dae-Woo; Lee, Seung-Jae; Jeong, Tak; Baek, Jong Hyeob; Park, Jae-Woo; Jang, Lee-Woon; Kim, Myoung; Lee, In-Hwan; Ju, Jin-Woo

    2012-01-01

    Chemical lift-off of (11-22) semipolar GaN using triangular cavities was investigated. The (11-22) semipolar GaN was grown using epitaxial lateral overgrowth by metal-organic chemical vapor deposition on m-plane sapphire, in such a way as to keep N terminated surface of c-plane GaN exposed in the cavities. After regrowing 300 μm thick (11-22) semipolar GaN by hydride vapor phase epitaxy for a free-standing (11-22) semipolar GaN substrate, the triangular cavities of the templates were chemically etched in molten KOH. The (000-2) plane in the triangular cavities can be etched in the [0002] direction with the high lateral etching rate of 196 μm/min. The resulting free-standing (11-22) semipolar GaN substrate was confirmed to be strain-free by the Raman analysis.

  16. Understanding of surface pit formation mechanism of GaN grown in MOCVD based on local thermodynamic equilibrium assumption

    International Nuclear Information System (INIS)

    Gao Zhi-Yuan; Xue Xiao-Wei; Li Jiang-Jiang; Wang Xun; Xing Yan-Hui; Cui Bi-Feng; Zou De-Shu

    2016-01-01

    Frank’s theory describes that a screw dislocation will produce a pit on the surface, and has been evidenced in many material systems including GaN. However, the size of the pit calculated from the theory deviates significantly from experimental result. Through a careful observation of the variations of surface pits and local surface morphology with growing temperature and V/III ratio for c -plane GaN, we believe that Frank’s model is valid only in a small local surface area where thermodynamic equilibrium state can be assumed to stay the same. If the kinetic process is too vigorous or too slow to reach a balance, the local equilibrium range will be too small for the center and edge of the screw dislocation spiral to be kept in the same equilibrium state. When the curvature at the center of the dislocation core reaches the critical value 1/ r 0 , at the edge of the spiral, the accelerating rate of the curvature may not fall to zero, so the pit cannot reach a stationary shape and will keep enlarging under the control of minimization of surface energy to result in a large-sized surface pit. (paper)

  17. Understanding of surface pit formation mechanism of GaN grown in MOCVD based on local thermodynamic equilibrium assumption

    Science.gov (United States)

    Zhi-Yuan, Gao; Xiao-Wei, Xue; Jiang-Jiang, Li; Xun, Wang; Yan-Hui, Xing; Bi-Feng, Cui; De-Shu, Zou

    2016-06-01

    Frank’s theory describes that a screw dislocation will produce a pit on the surface, and has been evidenced in many material systems including GaN. However, the size of the pit calculated from the theory deviates significantly from experimental result. Through a careful observation of the variations of surface pits and local surface morphology with growing temperature and V/III ratio for c-plane GaN, we believe that Frank’s model is valid only in a small local surface area where thermodynamic equilibrium state can be assumed to stay the same. If the kinetic process is too vigorous or too slow to reach a balance, the local equilibrium range will be too small for the center and edge of the screw dislocation spiral to be kept in the same equilibrium state. When the curvature at the center of the dislocation core reaches the critical value 1/r 0, at the edge of the spiral, the accelerating rate of the curvature may not fall to zero, so the pit cannot reach a stationary shape and will keep enlarging under the control of minimization of surface energy to result in a large-sized surface pit. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204009 and 61204011) and the Beijing Municipal Natural Science Foundation, China (Grant No. 4142005).

  18. GaN membrane MSM ultraviolet photodetectors

    Science.gov (United States)

    Muller, A.; Konstantinidis, G.; Kostopoulos, A.; Dragoman, M.; Neculoiu, D.; Androulidaki, M.; Kayambaki, M.; Vasilache, D.; Buiculescu, C.; Petrini, I.

    2006-12-01

    GaN exhibits unique physical properties, which make this material very attractive for wide range of applications and among them ultraviolet detection. For the first time a MSM type UV photodetector structure was manufactured on a 2.2 μm. thick GaN membrane obtained using micromachining techniques. The low unintentionally doped GaN layer structure was grown by MOCVD on high resistivity (ρ>10kΩcm) oriented silicon wafers, 500μm thick. The epitaxially grown layers include a thin AlN layer in order to reduce the stress in the GaN layer and avoid cracking. Conventional contact lithography, e-gun Ni/Au (10nm /200nm) evaporation and lift-off techniques were used to define the interdigitated Schottky metalization on the top of the wafer. Ten digits with a width of 1μm and a length of 100μm were defined for each electrode. The distance between the digits was also 1μm. After the backside lapping of the wafer to a thickness of approximately 150μm, a 400nm thick Al layer was patterned and deposited on the backside, to be used as mask for the selective reactive ion etching of silicon. The backside mask, for the membrane formation, was patterned using double side alignment techniques and silicon was etched down to the 2.2μm thin GaN layer using SF 6 plasma. A very low dark current (30ρA at 3V) was obtained. Optical responsivity measurements were performed at 1.5V. A maximum responsivity of 18mA/W was obtained at a wavelength of 370nm. This value is very good and can be further improved using transparent contacts for the interdigitated structure.

  19. Lateral epitaxial overgrowth of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Wang, Yongjin; Hu, Fangren; Hane, Kazuhiro

    2011-01-01

    We report here the lateral epitaxial overgrowth (LEO) of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy (MBE) growth with radio frequency nitrogen plasma as a gas source. Two kinds of GaN nanostructures are defined by electron beam lithography and realized on a GaN substrate by fast atom beam etching. The epitaxial growth of GaN by MBE is performed on the prepared GaN template, and the selective growth of GaN takes place with the assistance of GaN nanostructures. The LEO of GaN produces novel GaN epitaxial structures which are dependent on the shape and the size of the processed GaN nanostructures. Periodic GaN hexagonal pyramids are generated inside the air holes, and GaN epitaxial strips with triangular section are formed in the grating region. This work provides a promising way for producing novel GaN-based devices by the LEO of GaN using the MBE technique

  20. Knowledge-based metals & materials

    OpenAIRE

    Sasson, Amir

    2011-01-01

    This study presents the Norwegian metal and material industry (defined as all metal and material related firms located in Norway, regardless of ownership) and evaluates the industry according to the underlying dimensions of a global knowledge hub - cluster attractiveness, education attractiveness, talent attractiveness, R&D and innovation attractiveness, ownership attractiveness, environmental attractiveness and cluster dynamics.

  1. Metallic Nanostructures Based on DNA Nanoshapes

    Directory of Open Access Journals (Sweden)

    Boxuan Shen

    2016-08-01

    Full Text Available Metallic nanostructures have inspired extensive research over several decades, particularly within the field of nanoelectronics and increasingly in plasmonics. Due to the limitations of conventional lithography methods, the development of bottom-up fabricated metallic nanostructures has become more and more in demand. The remarkable development of DNA-based nanostructures has provided many successful methods and realizations for these needs, such as chemical DNA metallization via seeding or ionization, as well as DNA-guided lithography and casting of metallic nanoparticles by DNA molds. These methods offer high resolution, versatility and throughput and could enable the fabrication of arbitrarily-shaped structures with a 10-nm feature size, thus bringing novel applications into view. In this review, we cover the evolution of DNA-based metallic nanostructures, starting from the metallized double-stranded DNA for electronics and progress to sophisticated plasmonic structures based on DNA origami objects.

  2. Demonstration of high-responsivity epitaxial β-Ga2O3/GaN metal–heterojunction-metal broadband UV-A/UV-C detector

    Science.gov (United States)

    Kalra, Anisha; Vura, Sandeep; Rathkanthiwar, Shashwat; Muralidharan, Rangarajan; Raghavan, Srinivasan; Nath, Digbijoy N.

    2018-06-01

    We demonstrate epitaxial β-Ga2O3/GaN-based vertical metal–heterojunction-metal (MHM) broadband UV-A/UV-C photodetectors with high responsivity (3.7 A/W) at 256 and 365 nm, UV-to-visible rejection >103, and a photo-to-dark current ratio of ∼100. A small (large) conduction (valence) band offset at the heterojunction of pulsed laser deposition (PLD)-grown β-Ga2O3 on metal organic chemical vapor deposition (MOCVD)-grown GaN-on-silicon with epitaxial registry, as confirmed by X-ray diffraction (XRD) azimuthal scanning, is exploited to realize detectors with an asymmetric photoresponse and is explained with one-dimensional (1D) band diagram simulations. The demonstrated novel vertical MHM detectors on silicon are fully scalable and promising for enabling focal plane arrays for broadband ultraviolet sensing.

  3. Super high-power AlGaInN-based laser diodes with a single broad-area stripe emitter fabricated on a GaN substrate

    Energy Technology Data Exchange (ETDEWEB)

    Goto, Shu; Ohta, Makoto; Yabuki, Yoshifumi; Hoshina, Yukio; Hashizu, Toshihiro; Ikeda, Masao [Development Center, Sony Shiroishi Semiconductor, Inc., 3-53-2 Shiratori, Shiroishi, Miyagi, 989-0734 (Japan); Naganuma, Kaori; Tamamura, Koshi [Core Technology Development Group, Micro Systems Network Company, Sony Corporation, 4-14-1 Asahi-cho, Atsugi-shi Kanagawa, 243-0041 (Japan)

    2003-11-01

    AlGaInN-based blue-violet laser diodes with a single broad-area stripe emitter were successfully fabricated on GaN substrates. Three stripe widths were examined; 10, 50, and 100 {mu}m, and the maximum light output power of 0.94 W under cw operation at 20 C was achieved for the sample with a stripe width of 10 {mu}m. A super high-power laser diode array was fabricated using 11 of these high-performance laser chips, with a resultant output power of 6.1 W under cw operation at 20 C. This result represents the highest reported output power for blue-violet laser diodes. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Metal detector technology data base

    Energy Technology Data Exchange (ETDEWEB)

    Porter, L.K.; Gallo, L.R.; Murray, D.W.

    1990-08-01

    The tests described in this report were conducted to obtain information on the effects target characteristics have on portal type metal detector response. A second purpose of the tests was to determine the effect of detector type and settings on the detection of the targets. Although in some cases comparison performance of different types and makes of metal detectors is found herein, that is not the primary purpose of the report. Further, because of the many variables that affect metal detector performance, the information presented can be used only in a general way. The results of these tests can show general trends in metal detection, but do little for making accurate predictions as to metal detector response to a target with a complex shape such as a handgun. The shape of an object and its specific metal content (both type and treatment) can have a significant influence on detection. Thus it should not be surprising that levels of detection for a small 100g stainless steel handgun are considerably different than for detection of the 100g stainless steel right circular cylinder that was used in these tests. 7 figs., 1 tab.

  5. Laser-based additive manufacturing of metals

    CSIR Research Space (South Africa)

    Kumar, S

    2010-11-01

    Full Text Available For making metallic products through Additive Manufacturing (AM) processes, laser-based systems play very significant roles. Laser-based processes such as Selective Laser Melting (SLM) and Laser Engineered Net Shaping (LENS) are dominating processes...

  6. High hole mobility p-type GaN with low residual hydrogen concentration prepared by pulsed sputtering

    Science.gov (United States)

    Arakawa, Yasuaki; Ueno, Kohei; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2016-08-01

    We have grown Mg-doped GaN films with low residual hydrogen concentration using a low-temperature pulsed sputtering deposition (PSD) process. The growth system is inherently hydrogen-free, allowing us to obtain high-purity Mg-doped GaN films with residual hydrogen concentrations below 5 × 1016 cm-3, which is the detection limit of secondary ion mass spectroscopy. In the Mg profile, no memory effect or serious dopant diffusion was detected. The as-deposited Mg-doped GaN films showed clear p-type conductivity at room temperature (RT) without thermal activation. The GaN film doped with a low concentration of Mg (7.9 × 1017 cm-3) deposited by PSD showed hole mobilities of 34 and 62 cm2 V-1 s-1 at RT and 175 K, respectively, which are as high as those of films grown by a state-of-the-art metal-organic chemical vapor deposition apparatus. These results indicate that PSD is a powerful tool for the fabrication of GaN-based vertical power devices.

  7. Influence of V/III growth flux ratio on trap states in m-plane GaN grown by ammonia-based molecular beam epitaxy

    International Nuclear Information System (INIS)

    Zhang, Z.; Arehart, A. R.; Hurni, C. A.; Speck, J. S.; Ringel, S. A.

    2012-01-01

    Deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) were utilized to investigate the behavior of deep states in m-plane, n-type GaN grown by ammonia-based molecular beam epitaxy (NH 3 -MBE) as a function of systematically varied V/III growth flux ratios. Levels were detected at E C - 0.14 eV, E C - 0.21 eV, E C - 0.26 eV, E C - 0.62 eV, E C - 0.67 eV, E C - 2.65 eV, and E C - 3.31 eV, with the concentrations of several traps exhibiting systematic dependencies on V/III ratio. The DLTS spectra are dominated by traps at E C - 0.14 eV and E C - 0.67 eV, whose concentrations decreased monotonically with increasing V/III ratio and decreasing oxygen impurity concentration, and by a trap at E C - 0.21 eV that revealed no dependence of its concentration on growth conditions, suggestive of different physical origins. Higher concentrations of deeper trap states detected by DLOS with activation energies of E C - 2.65 eV and E C - 3.31 eV in each sample did not display measureable sensitivity to the intentionally varied V/III ratio, necessitating further study on reducing these deep traps through growth optimization for maximizing material quality of NH 3 -MBE grown m-plane GaN.

  8. Dislocation-induced nanoparticle decoration on a GaN nanowire.

    Science.gov (United States)

    Yang, Bing; Yuan, Fang; Liu, Qingyun; Huang, Nan; Qiu, Jianhang; Staedler, Thorsten; Liu, Baodan; Jiang, Xin

    2015-02-04

    GaN nanowires with homoepitaxial decorated GaN nanoparticles on their surface along the radial direction have been synthesized by means of a chemical vapor deposition method. The growth of GaN nanowires is catalyzed by Au particles via the vapor-liquid-solid (VLS) mechanism. Screw dislocations are generated along the radial direction of the nanowires under slight Zn doping. In contrast to the metal-catalyst-assisted VLS growth, GaN nanoparticles are found to prefer to nucleate and grow at these dislocation sites. High-resolution transmission electron microscopy (HRTEM) analysis demonstrates that the GaN nanoparticles possess two types of epitaxial orientation with respect to the corresponding GaN nanowire: (I) [1̅21̅0]np//[1̅21̅0]nw, (0001)np//(0001)nw; (II) [1̅21̅3]np//[12̅10]nw, (101̅0)np//(101̅0)nw. An increased Ga signal in the energy-dispersive spectroscopy (EDS) profile lines of the nanowires suggests GaN nanoparticle growth at the edge surface of the wires. All the crystallographic results confirm the importance of the dislocations with respect to the homoepitaxial growth of the GaN nanoparticles. Here, screw dislocations situated on the (0001) plane provide the self-step source to enable nucleation of the GaN nanoparticles.

  9. Transient atomic behavior and surface kinetics of GaN

    International Nuclear Information System (INIS)

    Moseley, Michael; Billingsley, Daniel; Henderson, Walter; Trybus, Elaissa; Doolittle, W. Alan

    2009-01-01

    An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.

  10. Transient atomic behavior and surface kinetics of GaN

    Science.gov (United States)

    Moseley, Michael; Billingsley, Daniel; Henderson, Walter; Trybus, Elaissa; Doolittle, W. Alan

    2009-07-01

    An in-depth model for the transient behavior of metal atoms adsorbed on the surface of GaN is developed. This model is developed by qualitatively analyzing transient reflection high energy electron diffraction (RHEED) signals, which were recorded for a variety of growth conditions of GaN grown by molecular-beam epitaxy (MBE) using metal-modulated epitaxy (MME). Details such as the initial desorption of a nitrogen adlayer and the formation of the Ga monolayer, bilayer, and droplets are monitored using RHEED and related to Ga flux and shutter cycles. The suggested model increases the understanding of the surface kinetics of GaN, provides an indirect method of monitoring the kinetic evolution of these surfaces, and introduces a novel method of in situ growth rate determination.

  11. Implantation doping of GaN

    International Nuclear Information System (INIS)

    Zolper, J.C.

    1996-01-01

    Ion implantation has played an enabling role in the realization of many high performance photonic and electronic devices in mature semiconductor materials systems such as Si and GaAs. This can also be expected to be the case in III-Nitride based devices as the material quality continues to improve. This paper reviews the progress in ion implantation processing of the III-Nitride materials, namely, GaN, AlN, InN and their alloys. Details are presented of the successful demonstrations of implant isolation as well as n- and p-type implantation doping of GaN. Implant doping has required activation annealing at temperatures in excess of 1,000 C. The nature of the implantation induced damage and its response to annealing is addressed using Rutherford Backscattering. Finally, results are given for the first demonstration of a GaN device fabricated using ion implantation doping, a GaN junction field effect transistor (JFET)

  12. Thermal analysis and improvement of cascode GaN device package for totem-pole bridgeless PFC rectifier

    International Nuclear Information System (INIS)

    She, Shuojie; Zhang, Wenli; Liu, Zhengyang; Lee, Fred C.; Huang, Xiucheng; Du, Weijing; Li, Qiang

    2015-01-01

    The totem-pole bridgeless power factor correction (PFC) rectifier has a simpler topology and higher efficiency than other boost-type bridgeless PFC rectifiers. Its promising performance is enabled by using high-voltage gallium nitride (GaN) high-electron-mobility transistors, which have considerably better figures of merit (e.g., lower reverse recovery charges and less switching losses) than the state-of-the-art silicon metal-oxide-semiconductor field-effect transistors. Cascode GaN devices in traditional packages, i.e., the TO-220 and power quad flat no-lead, are used in the totem-pole PFC boost rectifier. But the parasitic inductances induced by the traditional packages not only significantly deteriorate the switching characteristics of the discrete GaN device but also adversely affect the performance of the built PFC rectifier. A new stack-die packaging structure with an embedded capacitor has been introduced and proven to be efficient in reducing parasitic ringing at the turn-off transition and achieving true zero-voltage-switching turn-on. However, the thermal dissipation capability of the device packaged in this configuration becomes a limitation on further pushing the operating frequency and the output current level for high-efficiency power conversion. This paper focuses on the thermal analysis of the cascode GaN devices in different packages and the GaN-based multichip module used in a two-phase totem-pole bridgeless PFC boost rectifier. A series of thermal models are built based on the actual structures and materials of the packaged devices to evaluate their thermal performance. Finite element analysis (FEA) simulation results of the cascode GaN device in a flip-chip format demonstrate the possibility of increasing the device switching speed while maintaining the peak temperature of the device below 125 °C. Thermal analysis of the GaN-based power module in a very similar structure is also conducted using the FEA method. Experimental data measured using

  13. Model Based Metal Transfer Control

    DEFF Research Database (Denmark)

    Thomsen, Jesper Sandberg

    2006-01-01

    In pulsed gas metal arc welding (pulsed GMAW) current pulses are used for detaching drops at the tip of the electrode. To obtain a high weld quality one drop should be detached for every pulse, and moreover, the amount of energy used for detachment should be kept at a minimum. Thus, each pulse must...

  14. Tuning electronic and magnetic properties of GaN nanosheets by surface modifications and nanosheet thickness.

    Science.gov (United States)

    Xiao, Meixia; Yao, Tingzhen; Ao, Zhimin; Wei, Peng; Wang, Danghui; Song, Haiyang

    2015-04-14

    Density-functional theory calculations are performed to investigate the effects of surface modifications and nanosheet thickness on the electronic and magnetic properties of gallium nitride (GaN) nanosheets (NSs). Unlike the bare GaN NSs terminating with polar surfaces, the systems with hydrogenated Ga (H-GaN), fluorinated Ga (F-GaN), and chlorinated Ga (Cl-GaN) preserve their initial wurtzite structures and exhibit ferromagnetic states. The abovementioned three different decorations on Ga atoms are energetically more favorable for thicker GaN NSs. Moreover, as the thickness increases, H-GaN and F-GaN NSs undergo semiconductor to metal and half-metal to metal transition, respectively, while Cl-GaN NSs remain completely metallic. The predicted diverse and tunable electronic and magnetic properties highlight the potential of GaN NSs for novel electronic and spintronic nanodevices.

  15. Fabrication of a Lateral Polarity GaN MESFET: An Exploratory Study

    National Research Council Canada - National Science Library

    Sitar, Zlatko; Collazo, Ramon

    2007-01-01

    This report describes exploratory studies in the fabrication of the GaN LPH structures and their application in the fabrication of a depletion-mode metal semiconductor field effect transistors (MESFETs...

  16. Surface States Effect on the Large Photoluminescence Redshift in GaN Nanostructures

    KAUST Repository

    Ben Slimane, Ahmed; Najar, Adel; Ooi, Boon S.; Shen, Chao; Anjum, Dalaver H.; San-Romá n-Alerigi, Damiá n P.; Ng, Tien Khee

    2013-01-01

    We report on the large photoluminescence redshift observed in nanostructures fabricated using n-type GaN by ultraviolet (UV) metal-assisted electroless chemical-etching method. The scanning electron microscopy (SEM) characterization showed

  17. Hydrogen Sensors Using Nitride-Based Semiconductor Diodes: The Role of Metal/Semiconductor Interfaces

    Directory of Open Access Journals (Sweden)

    Yoshihiro Irokawa

    2011-01-01

    Full Text Available In this paper, I review my recent results in investigating hydrogen sensors using nitride-based semiconductor diodes, focusing on the interaction mechanism of hydrogen with the devices. Firstly, effects of interfacial modification in the devices on hydrogen detection sensitivity are discussed. Surface defects of GaN under Schottky electrodes do not play a critical role in hydrogen sensing characteristics. However, dielectric layers inserted in metal/semiconductor interfaces are found to cause dramatic changes in hydrogen sensing performance, implying that chemical selectivity to hydrogen could be realized. The capacitance-voltage (C-V characteristics reveal that the work function change in the Schottky metal is not responsible mechanism for hydrogen sensitivity. The interface between the metal and the semiconductor plays a critical role in the interaction of hydrogen with semiconductor devises. Secondly, low-frequency C-V characterization is employed to investigate the interaction mechanism of hydrogen with diodes. As a result, it is suggested that the formation of a metal/semiconductor interfacial polarization could be attributed to hydrogen-related dipoles. In addition, using low-frequency C-V characterization leads to clear detection of 100 ppm hydrogen even at room temperature where it is hard to detect hydrogen by using conventional current-voltage (I-V characterization, suggesting that low-frequency C-V method would be effective in detecting very low hydrogen concentrations.

  18. Growth of GaN micro/nanolaser arrays by chemical vapor deposition.

    Science.gov (United States)

    Liu, Haitao; Zhang, Hanlu; Dong, Lin; Zhang, Yingjiu; Pan, Caofeng

    2016-09-02

    Optically pumped ultraviolet lasing at room temperature based on GaN microwire arrays with Fabry-Perot cavities is demonstrated. GaN microwires have been grown perpendicularly on c-GaN/sapphire substrates through simple catalyst-free chemical vapor deposition. The GaN microwires are [0001] oriented single-crystal structures with hexagonal cross sections, each with a diameter of ∼1 μm and a length of ∼15 μm. A possible growth mechanism of the vertical GaN microwire arrays is proposed. Furthermore, we report room-temperature lasing in optically pumped GaN microwire arrays based on the Fabry-Perot cavity. Photoluminescence spectra exhibit lasing typically at 372 nm with an excitation threshold of 410 kW cm(-2). The result indicates that these aligned GaN microwire arrays may offer promising prospects for ultraviolet-emitting micro/nanodevices.

  19. Zn doped GaN for single-photon emission

    Energy Technology Data Exchange (ETDEWEB)

    Behrends, Arne; Ledig, Johannes; Al-Suleiman, Mohamed Aid Mansur; Bakin, Andrey; Waag, Andreas [Institute of Semiconductor Technology, University of Technology Braunschweig, Hans-Sommer-Str. 66, 38106 Braunschweig (Germany); Peters, Silke; Racu, Ana Maria; Schmunk, Waldemar; Hofer, Helmut; Kueck, Stefan [Physikalisch Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig (Germany)

    2012-03-15

    In this work we report on the optical investigation of Zn doped GaN films fabricated by metal organic chemical vapor deposition. The samples show bright emission in the blue spectral range around 2.9 eV when Si codoping is provided. This emission is suggested to be used for single-photon emission, thus the density of the Zn-Si pairs was drastically reduced leading to a decrease of the blue luminescence. For electrically excited single-photon sources these Zn-Si pairs have to be incorporated into LEDs, therefore we fabricated GaN-based nano-LEDs which show electroluminescence at 430 nm (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Application of Generative Adversarial Networks (GANs) to jet images

    CERN Multimedia

    CERN. Geneva

    2017-01-01

    https://arxiv.org/abs/1701.05927 We provide a bridge between generative modeling in the Machine Learning community and simulated physical processes in High Energy Particle Physics by applying a novel Generative Adversarial Network (GAN) architecture to the production of jet images -- 2D representations of energy depositions from particles interacting with a calorimeter. We propose a simple architecture, the Location-Aware Generative Adversarial Network, that learns to produce realistic radiation patterns from simulated high energy particle collisions. The pixel intensities of GAN-generated images faithfully span over many orders of magnitude and exhibit the desired low-dimensional physical properties (i.e., jet mass, n-subjettiness, etc.). We shed light on limitations, and provide a novel empirical validation of image quality and validity of GAN-produced simulations of the natural world. This work provides a base for further explorations of GANs for use in faster simulation in High Energy Particle Physics.

  1. Energetics of Mg incorporation at GaN(0001) and GaN(0001¯) surfaces

    Science.gov (United States)

    Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan

    2006-04-01

    By using density functional calculations in the generalized gradient approximation, we investigate the energetics of Mg adsorption and incorporation at GaN(0001) and GaN(0001¯) surfaces under various Ga and Mg coverage conditions as well as in presence of light or electron beam-induced electronic excitation. We find significant differences in Mg incorporation between Ga- and N-polar surfaces. Mg incorporation is easier at the Ga-polar surface, but high Mg coverages are found to cause important distortions which locally change the polarity from Ga to N polar. At the N-rich and moderately Ga-rich GaN(0001) surface, 0.25 ML of Mg substituting Ga in the top bilayer strongly reduce the surface diffusion barriers of Ga and N adatoms, in agreement with the surfactant effect observed in experiments. As the Mg coverage exceeds 0.5 ML, partial incorporation in the subsurface region (second bilayer) becomes favorable. A surface structure with 0.5 ML of incorporated Mg in the top bilayer and 0.25 ML in the second bilayer is found to be stable over a wide range of Ga chemical potential. At the Ga bilayer-terminated GaN(0001) surface, corresponding to Ga-rich conditions, configurations where Mg is incorporated in the interface region between the metallic Ga bilayer and the underlying GaN bilayer appear to be favored. At the N-polar surface, Mg is not incorporated under N-rich or moderately Ga-rich conditions, whereas incorporation in the adlayer may take place under Ga-rich conditions. In the presence of light or electron beam induced excitation, energy differences between Mg incorporated at the surface and in deeper layers are reduced so that the tendency toward surface segregation is also reduced.

  2. Epitaxial Single-Layer MoS2 on GaN with Enhanced Valley Helicity

    KAUST Repository

    Wan, Yi

    2017-12-19

    Engineering the substrate of 2D transition metal dichalcogenides can couple the quasiparticle interaction between the 2D material and substrate, providing an additional route to realize conceptual quantum phenomena and novel device functionalities, such as realization of a 12-time increased valley spitting in single-layer WSe2 through the interfacial magnetic exchange field from a ferromagnetic EuS substrate, and band-to-band tunnel field-effect transistors with a subthreshold swing below 60 mV dec−1 at room temperature based on bilayer n-MoS2 and heavily doped p-germanium, etc. Here, it is demonstrated that epitaxially grown single-layer MoS2 on a lattice-matched GaN substrate, possessing a type-I band alignment, exhibits strong substrate-induced interactions. The phonons in GaN quickly dissipate the energy of photogenerated carriers through electron–phonon interaction, resulting in a short exciton lifetime in the MoS2/GaN heterostructure. This interaction enables an enhanced valley helicity at room temperature (0.33 ± 0.05) observed in both steady-state and time-resolved circularly polarized photoluminescence measurements. The findings highlight the importance of substrate engineering for modulating the intrinsic valley carriers in ultrathin 2D materials and potentially open new paths for valleytronics and valley-optoelectronic device applications.

  3. Dry etching of MgCaO gate dielectric and passivation layers on GaN

    International Nuclear Information System (INIS)

    Hlad, M.; Voss, L.; Gila, B.P.; Abernathy, C.R.; Pearton, S.J.; Ren, F.

    2006-01-01

    MgCaO films grown by rf plasma-assisted molecular beam epitaxy and capped with Sc 2 O 3 are promising candidates as surface passivation layers and gate dielectrics on GaN-based high electron mobility transistors (HEMTs) and metal-oxide semiconductor HEMTs (MOS-HEMTs), respectively. Two different plasma chemistries were examined for etching these thin films on GaN. Inductively coupled plasmas of CH 4 /H 2 /Ar produced etch rates only in the range 20-70 A/min, comparable to the Ar sputter rates under the same conditions. Similarly slow MgCaO etch rates (∼100 A/min) were obtained with Cl 2 /Ar discharges under the same conditions, but GaN showed rates almost an order of magnitude higher. The MgCaO removal rates are limited by the low volatilities of the respective etch products. The CH 4 /H 2 /Ar plasma chemistry produced a selectivity of around 2 for etching the MgCaO with respect to GaN

  4. Epitaxial Single-Layer MoS2 on GaN with Enhanced Valley Helicity

    KAUST Repository

    Wan, Yi; Xiao, Jun; Li, Jingzhen; Fang, Xin; Zhang, Kun; Fu, Lei; Li, Pan; Song, Zhigang; Zhang, Hui; Wang, Yilun; Zhao, Mervin; Lu, Jing; Tang, Ning; Ran, Guangzhao; Zhang, Xiang; Ye, Yu; Dai, Lun

    2017-01-01

    Engineering the substrate of 2D transition metal dichalcogenides can couple the quasiparticle interaction between the 2D material and substrate, providing an additional route to realize conceptual quantum phenomena and novel device functionalities, such as realization of a 12-time increased valley spitting in single-layer WSe2 through the interfacial magnetic exchange field from a ferromagnetic EuS substrate, and band-to-band tunnel field-effect transistors with a subthreshold swing below 60 mV dec−1 at room temperature based on bilayer n-MoS2 and heavily doped p-germanium, etc. Here, it is demonstrated that epitaxially grown single-layer MoS2 on a lattice-matched GaN substrate, possessing a type-I band alignment, exhibits strong substrate-induced interactions. The phonons in GaN quickly dissipate the energy of photogenerated carriers through electron–phonon interaction, resulting in a short exciton lifetime in the MoS2/GaN heterostructure. This interaction enables an enhanced valley helicity at room temperature (0.33 ± 0.05) observed in both steady-state and time-resolved circularly polarized photoluminescence measurements. The findings highlight the importance of substrate engineering for modulating the intrinsic valley carriers in ultrathin 2D materials and potentially open new paths for valleytronics and valley-optoelectronic device applications.

  5. Inert anode containing base metal and noble metal useful for the electrolytic production of aluminum

    Science.gov (United States)

    Ray, Siba P.; Liu, Xinghua

    2000-01-01

    An inert anode for production of metals such as aluminum is disclosed. The inert anode comprises a base metal selected from Cu and Ag, and at least one noble metal selected from Ag, Pd, Pt, Au, Rh, Ru, Ir and Os. The inert anode may optionally be formed of sintered particles having interior portions containing more base metal than noble metal and exterior portions containing more noble metal than base metal. In a preferred embodiment, the base metal comprises Cu, and the noble metal comprises Ag, Pd or a combination thereof.

  6. Thermodynamic data-base for metal fluorides

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Jae Hyung; Lee, Byung Gik; Kang, Young Ho and others

    2001-05-01

    This study is aimed at collecting useful data of thermodynamic properties of various metal fluorides. Many thermodynamic data for metal fluorides are needed for the effective development, but no report of data-base was published. Accordingly, the objective of this report is to rearrange systematically the existing thermodynamic data based on metal fluorides and is to use it as basic data for the development of pyrochemical process. The physicochemical properties of various metal fluorides and metals were collected from literature and such existing data base as HSC code, TAPP code, FACT code, JANAF table, NEA data-base, CRC handbook. As major contents of the thermodynamic data-base, the physicochemical properties such as formation energy, viscosity, density, vapor pressure, etc. were collected. Especially, some phase diagrams of eutectic molten fluorides are plotted and thermodynamic data of liquid metals are also compiled. In the future, the technical report is to be used as basic data for the development of the pyrochemical process which is being carried out as a long-term nuclear R and D project.

  7. Thermodynamic data-base for metal fluorides

    International Nuclear Information System (INIS)

    Yoo, Jae Hyung; Lee, Byung Gik; Kang, Young Ho and others

    2001-05-01

    This study is aimed at collecting useful data of thermodynamic properties of various metal fluorides. Many thermodynamic data for metal fluorides are needed for the effective development, but no report of data-base was published. Accordingly, the objective of this report is to rearrange systematically the existing thermodynamic data based on metal fluorides and is to use it as basic data for the development of pyrochemical process. The physicochemical properties of various metal fluorides and metals were collected from literature and such existing data base as HSC code, TAPP code, FACT code, JANAF table, NEA data-base, CRC handbook. As major contents of the thermodynamic data-base, the physicochemical properties such as formation energy, viscosity, density, vapor pressure, etc. were collected. Especially, some phase diagrams of eutectic molten fluorides are plotted and thermodynamic data of liquid metals are also compiled. In the future, the technical report is to be used as basic data for the development of the pyrochemical process which is being carried out as a long-term nuclear R and D project

  8. Spin injection in epitaxial MnGa(111)/GaN(0001) heterostructures

    Science.gov (United States)

    Zube, Christian; Malindretos, Joerg; Watschke, Lars; Zamani, Reza R.; Disterheft, David; Ulbrich, Rainer G.; Rizzi, Angela; Iza, Michael; Keller, Stacia; DenBaars, Steven P.

    2018-01-01

    Ferromagnetic MnGa(111) layers were grown on GaN(0001) by molecular beam epitaxy. MnGa/GaN Schottky diodes with a doping level of around n = 7 × 1018 cm-3 were fabricated to achieve single step tunneling across the metal/semiconductor junction. Below the GaN layer, a thin InGaN quantum well served as optical spin detector ("spin-LED"). For electron spin injection from MnGa into GaN and subsequent spin transport through a 45 nm (70 nm) thick GaN layer, we observe a circular polarization of 0.3% (0.2%) in the electroluminescence at 80 K. Interface mixing, spin polarization losses during electrical transport in the GaN layer, and spin relaxation in the InGaN quantum well are discussed in relation with the low value of the optically detected spin polarization.

  9. A density functional theory study of the TMG adsorption on the GaN surface

    Energy Technology Data Exchange (ETDEWEB)

    Ptasinska, Maria; Soltys, Jakub; Piechota, Jacek [Interdisciplinary Centre for Materials Modelling, University of Warsaw, ul. Pawinskiego 5a, 02-106 Warszawa (Poland); Krukowski, Stanislaw [Interdisciplinary Centre for Materials Modelling, University of Warsaw, ul. Pawinskiego 5a, 02-106 Warszawa (Poland); Institute of High Pressure Physics, Polish Academy of Sciences, ul. Sokolowska 29/37, 01-142 Warsaw (Poland)

    2011-07-01

    TMG (trimetylogallium) and NH{sub 3} (ammonia) are widely used reactants in the metal organic chemical vapor deposition (MOCVD) technique used in the growth of the GaN thin films. We have recently examined theoretically, with the help of the density functional theory (DFT), TMG adsorption on the GaN(0001) surface in order to study formation of bonds between Ga and N. Dangling bonds on the GaN(0001) surface were saturated with the hydrogen atoms. The slab polarization, which is due to the dangling bonds present on the GaN(0001) surface, and energy of the system in the vicinity of TMG was computed for different distances between the surface atoms and TMG. We also studied TMG diffusion on the GaN surface. As a result, the energy path for diffusion from Top N to Hollow was obtained.

  10. Increase the threshold voltage of high voltage GaN transistors by low temperature atomic hydrogen treatment

    Energy Technology Data Exchange (ETDEWEB)

    Erofeev, E. V., E-mail: erofeev@micran.ru [Tomsk State University of Control Systems and Radioelectronics, Research Institute of Electrical-Communication Systems (Russian Federation); Fedin, I. V.; Kutkov, I. V. [Research and Production Company “Micran” (Russian Federation); Yuryev, Yu. N. [National Research Tomsk Polytechnic University, Institute of Physics and Technology (Russian Federation)

    2017-02-15

    High-electron-mobility transistors (HEMTs) based on AlGaN/GaN epitaxial heterostructures are a promising element base for the fabrication of high voltage electronic devices of the next generation. This is caused by both the high mobility of charge carriers in the transistor channel and the high electric strength of the material, which makes it possible to attain high breakdown voltages. For use in high-power switches, normally off-mode GaN transistors operating under enhancement conditions are required. To fabricate normally off GaN transistors, one most frequently uses a subgate region based on magnesium-doped p-GaN. However, optimization of the p-GaN epitaxial-layer thickness and the doping level makes it possible to attain a threshold voltage of GaN transistors close to V{sub th} = +2 V. In this study, it is shown that the use of low temperature treatment in an atomic hydrogen flow for the p-GaN-based subgate region before the deposition of gate-metallization layers makes it possible to increase the transistor threshold voltage to V{sub th} = +3.5 V. The effects under observation can be caused by the formation of a dipole layer on the p-GaN surface induced by the effect of atomic hydrogen. The heat treatment of hydrogen-treated GaN transistors in a nitrogen environment at a temperature of T = 250°C for 12 h reveals no degradation of the transistor’s electrical parameters, which can be caused by the formation of a thermally stable dipole layer at the metal/p-GaN interface as a result of hydrogenation.

  11. Increase the threshold voltage of high voltage GaN transistors by low temperature atomic hydrogen treatment

    International Nuclear Information System (INIS)

    Erofeev, E. V.; Fedin, I. V.; Kutkov, I. V.; Yuryev, Yu. N.

    2017-01-01

    High-electron-mobility transistors (HEMTs) based on AlGaN/GaN epitaxial heterostructures are a promising element base for the fabrication of high voltage electronic devices of the next generation. This is caused by both the high mobility of charge carriers in the transistor channel and the high electric strength of the material, which makes it possible to attain high breakdown voltages. For use in high-power switches, normally off-mode GaN transistors operating under enhancement conditions are required. To fabricate normally off GaN transistors, one most frequently uses a subgate region based on magnesium-doped p-GaN. However, optimization of the p-GaN epitaxial-layer thickness and the doping level makes it possible to attain a threshold voltage of GaN transistors close to V_t_h = +2 V. In this study, it is shown that the use of low temperature treatment in an atomic hydrogen flow for the p-GaN-based subgate region before the deposition of gate-metallization layers makes it possible to increase the transistor threshold voltage to V_t_h = +3.5 V. The effects under observation can be caused by the formation of a dipole layer on the p-GaN surface induced by the effect of atomic hydrogen. The heat treatment of hydrogen-treated GaN transistors in a nitrogen environment at a temperature of T = 250°C for 12 h reveals no degradation of the transistor’s electrical parameters, which can be caused by the formation of a thermally stable dipole layer at the metal/p-GaN interface as a result of hydrogenation.

  12. High-Quality GaN Epilayers Achieved by Facet-Controlled Epitaxial Lateral Overgrowth on Sputtered AlN/PSS Templates.

    Science.gov (United States)

    He, Chenguang; Zhao, Wei; Zhang, Kang; He, Longfei; Wu, Hualong; Liu, Ningyang; Zhang, Shan; Liu, Xiaoyan; Chen, Zhitao

    2017-12-13

    It is widely believed that the lack of high-quality GaN wafers severely hinders the progress in GaN-based devices, especially for defect-sensitive devices. Here, low-cost AlN buffer layers were sputtered on cone-shaped patterned sapphire substrates (PSSs) to obtain high-quality GaN epilayers. Without any mask or regrowth, facet-controlled epitaxial lateral overgrowth was realized by metal-organic chemical vapor deposition. The uniform coating of the sputtered AlN buffer layer and the optimized multiple modulation guaranteed high growth selectivity and uniformity of the GaN epilayer. As a result, an extremely smooth surface was achieved with an average roughness of 0.17 nm over 3 × 3 μm 2 . It was found that the sputtered AlN buffer layer could significantly suppress dislocations on the cones. Moreover, the optimized three-dimensional growth process could effectively promote dislocation bending. Therefore, the threading dislocation density (TDD) of the GaN epilayer was reduced to 4.6 × 10 7 cm -2 , which is about an order of magnitude lower than the case of two-step GaN on the PSS. In addition, contamination and crack in the light-emitting diode fabricated on the obtained GaN were also effectively suppressed by using the sputtered AlN buffer layer. All of these advantages led to a high output power of 116 mW at 500 mA with an emission wavelength of 375 nm. This simple, yet effective growth technique is believed to have great application prospects in high-performance TDD-sensitive optoelectronic and electronic devices.

  13. The feasibility of tunable p-type Mg doping in a GaN monolayer nanosheet

    International Nuclear Information System (INIS)

    Xia, Congxin; Peng, Yuting; Wei, Shuyi; Jia, Yu

    2013-01-01

    Based on density functional theory, the electronic structures, formation energy and transition energy level of a p-type Mg-doped GaN nanosheet are investigated. Numerical results show that the transition energy level decreases monotonously with increasing Mg doping concentration in Mg-doped GaN nanosheet systems, which is lower than that of the Mg-doped bulk GaN case. Moreover, the formation energy calculations indicate that Mg-doped GaN nanosheet structures can be realized under N-rich experimental growth conditions

  14. Fabrication of GaN with buried tungsten (W) structures using epitaxial lateral overgrowth (ELO) via LP-MOVPE

    International Nuclear Information System (INIS)

    Miyake, Hideto; Yamaguchi, Motoo; Haino, Masahiro

    2000-01-01

    A buried tungsten (W) mask structure with GaN is successfully obtained by epitaxial lateral overgrowth (ELO) technique via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The selectivity of GaN growth on the window region vs. the mask region is good. An underlying GaN with a striped W metal mask is easily decomposed above 500 C by the W catalytic effect, by which radical hydrogen is reacted with GaN. It is difficult to bury the W mask because severe damage occurs in the GaN epilayer under the mask. It is found that an underlying AlGaN/GaN layer with a narrow W stripe mask width (mask/window - 2/2 microm) leads the ELO GaN layer to be free from damage, resulting in an excellent W-buried structure

  15. Influence of in-situ deposited SiNx interlayer on crystal quality of GaN epitaxial films

    Science.gov (United States)

    Fan, Teng; Jia, Wei; Tong, Guangyun; Zhai, Guangmei; Li, Tianbao; Dong, Hailiang; Xu, Bingshe

    2018-05-01

    GaN epitaxial films with SiNx interlayers were prepared by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. The influences of deposition times and locations of SiNx interlayers on crystal quality of GaN epitaxial films were studied. Under the optimal growth time of 120 s for the SiNx interlayer, the dislocation density of GaN film is reduced to 4.05 × 108 cm-2 proved by high resolution X-ray diffraction results. It is found that when the SiNx interlayer deposits on the GaN nucleation islands, the subsequent GaN film has the lowest dislocation density of only 2.89 × 108 cm-2. Moreover, a model is proposed to illustrate the morphological evolution and associated propagation processes of TDs in GaN epi-layers with SiNx interlayers for different deposition times and locations.

  16. Polarity Control of Heteroepitaxial GaN Nanowires on Diamond.

    Science.gov (United States)

    Hetzl, Martin; Kraut, Max; Hoffmann, Theresa; Stutzmann, Martin

    2017-06-14

    Group III-nitride materials such as GaN nanowires are characterized by a spontaneous polarization within the crystal. The sign of the resulting sheet charge at the top and bottom facet of a GaN nanowire is determined by the orientation of the wurtzite bilayer of the different atomic species, called N and Ga polarity. We investigate the polarity distribution of heteroepitaxial GaN nanowires on different substrates and demonstrate polarity control of GaN nanowires on diamond. Kelvin Probe Force Microscopy is used to determine the polarity of individual selective area-grown and self-assembled nanowires over a large scale. At standard growth conditions, mixed polarity occurs for selective GaN nanowires on various substrates, namely on silicon, on sapphire and on diamond. To obtain control over the growth orientation on diamond, the substrate surface is modified by nitrogen and oxygen plasma exposure prior to growth, and the growth parameters are adjusted simultaneously. We find that the surface chemistry and the substrate temperature are the decisive factors for obtaining control of up to 93% for both polarity types, whereas the growth mode, namely selective area or self-assembled growth, does not influence the polarity distribution significantly. The experimental results are discussed by a model based on the interfacial bonds between the GaN nanowires, the termination layer, and the substrate.

  17. Epitaxial GaN around ZnO nanopillars

    Energy Technology Data Exchange (ETDEWEB)

    Fikry, Mohamed; Scholz, Ferdinand [Institut fuer Optoelektronik, Universitaet Ulm, Albert-Einstein-Allee 45, 89081 Ulm (Germany); Madel, Manfred; Tischer, Ingo; Thonke, Klaus [Institut fuer Quantenmaterie, Universitaet Ulm, Albert-Einstein-Allee 45, 89081 Ulm (Germany)

    2011-07-01

    We report on an investigation of the epitaxial quality of GaN layers overgrown coaxially around ZnO nanopillars. In a first step, regularly arranged ZnO nanopillars were grown using pre-patterning by e-beam lithography or self-organized hexagonal polystyrene sphere masks. Alternatively, ZnO pillars were also successfully grown on top of GaN pyramids. In a second step, GaN layers were grown around the ZnO pillars by Metal Organic Vapor Phase Epitaxy. At growth temperatures above 800 C, the ZnO pillars are dissolved by the hydrogen carrier gas leaving hollow GaN nanotubes. Characterization involved photoluminescence (PL), scanning electron microscopy and cathodoluminescence. The fair quality of the deposited GaN layers is confirmed by a sharp low temperature PL peak at 3.48 eV attributed to the donor bound exciton emission. Further peaks at 3.42 eV and 3.29 eV show the possible existence of basal plane and prismatic stacking faults.

  18. Hole-induced d"0 ferromagnetism enhanced by Na-doping in GaN

    International Nuclear Information System (INIS)

    Zhang, Yong; Li, Feng

    2017-01-01

    The d"0 ferromagnetism in wurtzite GaN is investigated by the first-principle calculations. It is found that spontaneous magnetization occurs if sufficient holes are injected in GaN. Both Ga vacancy and Na doping can introduce holes into GaN. However, Ga vacancy has a high formation energy, and is thus unlikely to occur in a significant concentration. In contrast, Na doping has relatively low formation energy. Under N-rich growth condition, Na doping with a sufficient concentration can be achieved, which can induce half-metallic ferromagnetism in GaN. Moreover, the estimated Curie temperature of Na-doped GaN is well above the room temperature. - Highlights: • Hole-induced ferromagnetism in GaN is confirmed. • Both Ga Vacancy and Na-doping can introduce hole into GaN. • The concentration of Ga vacancy is too low to induce detectable ferromagnetism. • Na-doped GaN is a possible ferromagnet with a high curie-temperature.

  19. GaN and LED structures grown on pre-patterned silicon pillar arrays

    Energy Technology Data Exchange (ETDEWEB)

    Li, Shunfeng; Fuendling, Soenke; Soekmen, Uensal; Merzsch, Stephan; Neumann, Richard; Peiner, Erwin; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig, Hans-Sommer-Strasse 66, 38106 Braunschweig (Germany); Hinze, Peter; Weimann, Thomas [Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig (Germany); Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvoigteiplatz 5-7, 10117 Berlin (Germany)

    2010-01-15

    GaN nanorods (or nanowires) have attracted great interest in a variety of applications, e.g. high-efficiency light emitting diodes, monolithic white light emission and optical interconnection due to their superior properties. In contrast to the mostly investigated self-assembled growth of GaN nanorods, we performed GaN nanorod growth by pre-patterning of the Si substrates. The pattern was transferred to Si substrates by photolithography and cryo-temperature inductively-coupled plasma etching. These Si templates then were used for further GaN nanorod growth by metal-organic vapour phase epitaxy (MOVPE). The low temperature AlN nucleation layer had to be optimized since it differs from its 2D layer counterpart on the surface area and orientations. We found a strong influence of diffusion processes, i.e. the GaN grown on top of the Si nanopillars can deplete the GaN around the Si pillars. Transmission electron microscopy measurements demonstrated clearly that the threading dislocations bend to the side facets of the pyramidal GaN nanostructures and terminate. Cathodoluminescence measurements reveal a difference of In composition and/or thickness of InGaN quantum wells on the different facets of the pyramidal GaN nanostructures. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Precious-metal-base advanced materials

    International Nuclear Information System (INIS)

    Nowicki, T.; Carbonnaux, C.

    1993-01-01

    Precious metals constitute also the base of several advanced materials used in the industry in hundreds of metric tons. Platinum alloys have been used as structural materials for equipments in the glass industry. The essential reason for this is the excellent resistance of platinum alloys to oxidation and electrolytical corrosion in molten glasses at temperatures as high as 1200-1500 C. The major drawback is a weak creep resistance. The unique way for significant improvement of platinum base materials creep resistance is a strengthening by an oxide dispersion (ODS). In the case of CLAL's patented ''Plativer'' materials, 0.05 wt% of Y 2 O 3 is incorporated within the alloy matrix by the flame spraying process. Further improvement of platinum base materials is related, in the authors opinion, to the development of precious metals base intermetallics. Another interesting applications of precious metals are silver base electrical contacts. They are in fact silver matrix composites containing varying amounts of well-dispersed particles of constituents such as CdO, SnO 2 , Ni, WC or C. In the case of such materials, particular properties are required and tested : resistance to arc erosion, resistance to welding and contact resistance. Many other technically fascinating precious metals base materials exist: brazing alloys for assembling metals, superconductors and ceramics; dental materials including magnetic biocompatible alloys; silver composites for superconductor wire jackets. The observation of current evolution indicates very clearly that precious metals cannot be replaced by common metals because of their unique characteristics due to their atomic level properties

  1. Base Metal Co-Fired Multilayer Piezoelectrics

    Directory of Open Access Journals (Sweden)

    Lisheng Gao

    2016-03-01

    Full Text Available Piezoelectrics have been widely used in different kinds of applications, from the automobile industry to consumer electronics. The novel multilayer piezoelectrics, which are inspired by multilayer ceramic capacitors, not only minimize the size of the functional parts, but also maximize energy efficiency. Development of multilayer piezoelectric devices is at a significant crossroads on the way to achieving low costs, high efficiency, and excellent reliability. Concerning the costs of manufacturing multilayer piezoelectrics, the trend is to replace the costly noble metal internal electrodes with base metal materials. This paper discusses the materials development of metal co-firing and the progress of integrating current base metal chemistries. There are some significant considerations in metal co-firing multilayer piezoelectrics: retaining stoichiometry with volatile Pb and alkaline elements in ceramics, the selection of appropriate sintering agents to lower the sintering temperature with minimum impact on piezoelectric performance, and designing effective binder formulation for low pO2 burnout to prevent oxidation of Ni and Cu base metal.

  2. Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics.

    Science.gov (United States)

    Kusaba, Akira; Li, Guanchen; von Spakovsky, Michael R; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-08-15

    Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and N ad -H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium where the state evolution is a combination of reversible and irreversible dynamics. SEAQT is an ideal choice to handle this problem on a first-principles basis since the chemical adsorption process starts from a highly non-equilibrium state. A result of the analysis shows that the probability of adsorption on 3Ga-H is significantly higher than that on N ad -H + Ga-H. Additionally, the growth temperature dependence of these adsorption probabilities and the temperature increase due to the heat of reaction is determined. The non-equilibrium thermodynamic modeling applied can lead to better control of the MOVPE process through the selection of preferable reconstructed surfaces. The modeling also demonstrates the efficacy of DFT-SEAQT coupling for determining detailed non-equilibrium process characteristics with a much smaller computational burden than would be entailed with mechanics-based, microscopic-mesoscopic approaches.

  3. Base metals in the new economic environment

    International Nuclear Information System (INIS)

    Lennon, J.

    2002-01-01

    The focus of this paper was on the demand side of the base metals industry. It is expected that in the next decade more than 50 per cent of global demand growth will come from China and other countries of the former Eastern block. Following the large decline in base metals demand in 2001, it is expected that a large growth in metals supply will be needed over the next decade and there is a real possibility that the mining industry will struggle to meet demand growth. While industry performance is usually driven by economic growth and its impact on metals demand, analysts realize that every cycle is different and it can be easily affected by unpredicted, economic and geopolitical events. The author suggests that the while next few years will be a period of slower growth in the traditional consuming countries, this will be offset by the significant rise in the importance of China and the possible resurgence in demand growth in the Former Soviet Union and Eastern Europe. The paper presented a brief historical overview of the different growth phases for metals over the past 50 years. Strong metal demand in the 1990s was driven by the telecommunications and computer revolutions. Stainless steel/nickel, zinc/galvanized applications and aluminium were used to save on maintenance costs and to improve energy efficiency. The paper also discussed the shifting pattern of copper and aluminium demand by decade. 2 tabs., 7 figs

  4. Optical and field emission properties of layer-structure GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Cui, Zhen [Science School, Xi’an University of Technology, Xi’an 710048 (China); School of automation and Information Engineering, Xi’an University of Technology, Xi’an 710048 (China); Li, Enling, E-mail: Lienling@xaut.edu.cn [Science School, Xi’an University of Technology, Xi’an 710048 (China); Shi, Wei; Ma, Deming [Science School, Xi’an University of Technology, Xi’an 710048 (China)

    2014-08-15

    Highlights: • The layer-structure GaN nanowires with hexagonal-shaped cross-sections are produced via a process based on the CVD method. • The diameter of the layer-structure GaN nanowire gradually decreases from ∼500 nm to ∼200 nm along the wire axis. • The layer-structure GaN nanowire film possesses good field emission property. - Abstract: A layer-structure gallium nitride (GaN) nanowires, grown on Pt-coated n-type Si (1 1 1) substrate, have been synthesized using chemical vapor deposition (CVD). The results show: (1) SEM indicates that the geometry structure is layer-structure. HRTEM indicates that GaN nanowire’s preferential growth direction is along [0 0 1] direction. (2) The room temperature PL emission spectrum of the layer-structure GaN nanowires has a peak at 375 nm, which proves that GaN nanowires have potential application in light-emitting nano-devices. (3) Field-emission measurements show that the layer-structure GaN nanowires film has a low turn-on field of 4.39 V/μm (at room temperature), which is sufficient for electron emission devices, field emission displays and vacuum nano-electronic devices. The growth mechanism for GaN nanowires has also been discussed briefly.

  5. Thermal degradation of ohmic contacts on semipolar (11-22) GaN films grown on m-plane (1-100) sapphire substrates

    International Nuclear Information System (INIS)

    Kim, Doo Soo; Kim, Deuk Young; Seo, Yong Gon; Kim, Ji Hoon; Hwang, Sung Min; Baik, Kwang Hyeon

    2012-01-01

    Semipolar (11-22) GaN films were grown on m-plane (1-100) sapphire substrates by using metalorganic chemical vapor deposition. The line widths of the omega rocking curves of the semipolar GaN films were 498 arcsec along the [11-23] GaN direction and 908 arcsec along the [10-10] GaN direction. The properties of the Ti/Al/Ni/Au metal contact were investigated using transmission-line-method patterns oriented in both the [11-23] GaN and the [10-10] GaN directions of semipolar (11-22) GaN. The minimum specific contact resistance of ∼3.6 x 10 -4 Ω·cm -2 was obtained on as-deposited metal contacts. The Ohmic contact properties of semipolar (11-22) GaN became degraded with increasing annealing temperature above 400 .deg. C. The thermal degradation of the metal contacts may be attributed to the surface property of N-polarity on the semipolar (11-22) GaN films. Also, the semipolar (11-22) GaN films did not show clear anisotropic behavior of the electrical properties for different azimuthal angles.

  6. The thickness design of unintentionally doped GaN interlayer matched with background doping level for InGaN-based laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, P.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.; Zhu, J. J.; Liu, Z. S.; Yang, J.; Li, X.; Le, L. C.; He, X. G.; Liu, W.; Li, X. J.; Liang, F. [State Key Laboratory of Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Zhang, B. S.; Yang, H. [Key Laboratory of Nano-devices and Applications of CAS, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Zhang, Y. T.; Du, G. T. [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130023 (China)

    2016-03-15

    In order to reduce the internal optical loss of InGaN laser diodes, an unintentionally doped GaN (u-GaN) interlayer is inserted between InGaN/GaN multiple quantum well active region and Al{sub 0.2}Ga{sub 0.8}N electron blocking layer. The thickness design of u-GaN interlayer matching up with background doping level for improving laser performance is studied. It is found that a suitably chosen u-GaN interlayer can well modulate the optical absorption loss and optical confinement factor. However, if the value of background doping concentration of u-GaN interlayer is too large, the output light power may decrease. The analysis of energy band diagram of a LD structure with 100 nm u-GaN interlayer shows that the width of n-side depletion region decreases when the background concentration increases, and may become even too small to cover whole MQW, resulting in a serious decrease of the output light power. It means that a suitable interlayer thickness design matching with the background doping level of u-GaN interlayer is significant for InGaN-based laser diodes.

  7. The thickness design of unintentionally doped GaN interlayer matched with background doping level for InGaN-based laser diodes

    Directory of Open Access Journals (Sweden)

    P. Chen

    2016-03-01

    Full Text Available In order to reduce the internal optical loss of InGaN laser diodes, an unintentionally doped GaN (u-GaN interlayer is inserted between InGaN/GaN multiple quantum well active region and Al0.2Ga0.8N electron blocking layer. The thickness design of u-GaN interlayer matching up with background doping level for improving laser performance is studied. It is found that a suitably chosen u-GaN interlayer can well modulate the optical absorption loss and optical confinement factor. However, if the value of background doping concentration of u-GaN interlayer is too large, the output light power may decrease. The analysis of energy band diagram of a LD structure with 100 nm u-GaN interlayer shows that the width of n-side depletion region decreases when the background concentration increases, and may become even too small to cover whole MQW, resulting in a serious decrease of the output light power. It means that a suitable interlayer thickness design matching with the background doping level of u-GaN interlayer is significant for InGaN-based laser diodes.

  8. Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

    Science.gov (United States)

    Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

    2017-01-01

    For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap

  9. Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals

    Directory of Open Access Journals (Sweden)

    Hongbo Qin

    2017-12-01

    Full Text Available For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100 and (111 are isotropic, while the Poisson’s ratio at plane (110 exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger

  10. Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals.

    Science.gov (United States)

    Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, Guoqi

    2017-12-12

    For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and , respectively, while they are in the orientations and for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson's ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson's ratios at planes (100) and (111) are isotropic, while the Poisson's ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol -1 K -1 , respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of

  11. Thulium-based bulk metallic glass

    International Nuclear Information System (INIS)

    Yu, H. B.; Yu, P.; Wang, W. H.; Bai, H. Y.

    2008-01-01

    We report the formation and properties of a thulium-based bulk metallic glass (BMG). Compared with other known rare-earth (RE) based BMGs, Tm-based BMGs show features of excellent glass formation ability, considerable higher elastic modulus, smaller Poisson's ratio, high mechanical strength, and intrinsic brittleness. The reasons for the different properties between the Tm-based and other RE-based BMGs are discussed. It is expected that the Tm-based glasses with the unique properties are appropriate candidates for studying some important issues in BMGs

  12. Interface and transport properties of metallization contacts to flat and wet-etching roughed N-polar n-type GaN.

    Science.gov (United States)

    Wang, Liancheng; Liu, Zhiqiang; Guo, Enqing; Yang, Hua; Yi, Xiaoyan; Wang, Guohong

    2013-06-26

    The electrical characteristics of metallization contacts to flat (F-sample, without wet-etching roughed) and wet-etching roughed (R-sample) N-polar (Nitrogen-polar) n-GaN have been investigated. R-sample shows higher contact resistance (Rc) to Al/Ti/Au (~2.5 × 10(-5) Ω·cm(2)) and higher Schottky barriers height (SBH, ~0.386 eV) to Ni/Au, compared with that of F-sample (~1.3 × 10(-6) Ω·cm(2), ~0.154 eV). Reasons accounting for this discrepancy has been detail investigated and discussed: for R-sample, wet-etching process caused surface state and spontaneous polarization variation will degraded its electrical characteristics. Metal on R-sample shows smoother morphology, however, the effect of metal deposition state on electrical characteristics is negligible. Metallization contact area for both samples has also been further considered. Electrical characteristics of metallization contact to both samples show degradation upon annealing. The VLED chip (1 mm × 1 mm), which was fabricated on the basis of a hybrid scheme, coupling the advantage of F- and R-sample, shows the lowest forward voltage (2.75 V@350 mA) and the highest light output power.

  13. Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

    International Nuclear Information System (INIS)

    Puybaret, Renaud; Jordan, Matthew B.; Voss, Paul L.; Ougazzaden, Abdallah; Patriarche, Gilles; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean-Paul; Heer, Walt A. de; Berger, Claire

    2016-01-01

    We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5–8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

  14. Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

    Energy Technology Data Exchange (ETDEWEB)

    Puybaret, Renaud; Jordan, Matthew B.; Voss, Paul L.; Ougazzaden, Abdallah, E-mail: aougazza@georgiatech-metz.fr [School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); CNRS UMI 2958, Georgia Institute of Technology, 2 Rue Marconi, 57070 Metz (France); Patriarche, Gilles [CNRS, Laboratoire de Photonique et de Nanostructures, Route de Nozay, 91460 Marcoussis (France); Sundaram, Suresh; El Gmili, Youssef [CNRS UMI 2958, Georgia Institute of Technology, 2 Rue Marconi, 57070 Metz (France); Salvestrini, Jean-Paul [Université de Lorraine, CentraleSupélec, LMOPS, EA4423, 57070 Metz (France); Heer, Walt A. de [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Berger, Claire [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); CNRS, Institut Néel, BP166, 38042 Grenoble Cedex 9 (France)

    2016-03-07

    We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5–8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

  15. Structural and optical properties of Si-doped GaN

    OpenAIRE

    Cremades Rodríguez, Ana Isabel; Gorgens, L.; Ambacher, O.; Stutzmann, M.; Scholz, F.

    2000-01-01

    Structural and optical properties of Si-doped GaN thin films grown by metal-organic chemical vapor deposition have been studied by means of high resolution x-ray diffraction (XRD), atomic force microscopy, photoluminescence, photothermal deflection spectroscopy, and optical transmission measurements. The incorporation of silicon in the GaN films leads to pronounced tensile stress. The energy position of the neutral donor bound excitonic emission correlates with the measured stress. The stress...

  16. Chemoelectronic circuits based on metal nanoparticles

    Science.gov (United States)

    Yan, Yong; Warren, Scott C.; Fuller, Patrick; Grzybowski, Bartosz A.

    2016-07-01

    To develop electronic devices with novel functionalities and applications, various non-silicon-based materials are currently being explored. Nanoparticles have unique characteristics due to their small size, which can impart functions that are distinct from those of their bulk counterparts. The use of semiconductor nanoparticles has already led to improvements in the efficiency of solar cells, the processability of transistors and the sensitivity of photodetectors, and the optical and catalytic properties of metal nanoparticles have led to similar advances in plasmonics and energy conversion. However, metals screen electric fields and this has, so far, prevented their use in the design of all-metal nanoparticle circuitry. Here, we show that simple electronic circuits can be made exclusively from metal nanoparticles functionalized with charged organic ligands. In these materials, electronic currents are controlled by the ionic gradients of mobile counterions surrounding the ‘jammed’ nanoparticles. The nanoparticle-based electronic elements of the circuitry can be interfaced with metal nanoparticles capable of sensing various environmental changes (humidity, gas, the presence of various cations), creating electronic devices in which metal nanoparticles sense, process and ultimately report chemical signals. Because the constituent nanoparticles combine electronic and chemical sensing functions, we term these systems ‘chemoelectronic’. The circuits have switching times comparable to those of polymer electronics, selectively transduce parts-per-trillion chemical changes into electrical signals, perform logic operations, consume little power (on the scale of microwatts), and are mechanically flexible. They are also ‘green’, in the sense that they comprise non-toxic nanoparticles cast at room temperature from alcohol solutions.

  17. Growth and characterization of GaN nanostructures under various ammoniating time with fabricated Schottky gas sensor based on Si substrate

    Science.gov (United States)

    Abdullah, Q. N.; Ahmed, A. R.; Ali, A. M.; Yam, F. K.; Hassan, Z.; Bououdina, M.; Almessiere, M. A.

    2018-05-01

    This paper presents the investigation of the influence of the ammoniating time of GaN nanowires (NWs) on the crystalline structure, surface morphology, and optical characteristics. Morphological analysis indicates the growth of good quality and high density of NWs with diameters around 50 nm and lengths up to tens of microns after ammoniating for 30 min. Structural analysis shows that GaN NWs have a typical hexagonal wurtzite crystal structure. Raman spectroscopy confirms the formation of GaN compound with the presence of compressive stress. Photoluminescence (PL) measurements revealed two band emissions, an UV and a broad visible emission. Hydrogen sensor was subsequently fabricated by depositing Pt Schottky contact onto GaN NWs film. The sensor response was measured at various H2 concentrations ranged from 200 up to 1200 ppm at room temperature. It was found that the response increases significantly for low H2 concentration (200-300 ppm) to reach about 50% then increases smoothly to reach 60% at 1200 ppm. The as-fabricated sensor possesses higher performances as compared to similar devices reported in the literature.

  18. Synchrotron-based XPS studies of AlGaN and GaN surface chemistry and its relationship to ion sensor behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Khir, Farah Liyana Muhammad, E-mail: 21001899@student.uwa.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Myers, Matthew, E-mail: Matt.Myers@csiro.au [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); CSIRO Earth Science and Resource Engineering, Kensington, Western Australia 6151 (Australia); Podolska, Anna [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Department of Exploration Geophysics, Curtin University of Technology, 26 Dick Perry Avenue, ARRC, Kensington, Western Australia 6151 (Australia); Sanders, Tarun Maruthi [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Baker, Murray V., E-mail: murray.baker@uwa.edu.au [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Nener, Brett D., E-mail: brett.nener@uwa.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Parish, Giacinta, E-mail: giacinta.parish@uwa.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia)

    2014-09-30

    Highlights: • Soft X-ray was used to study the surface chemistry of GaN and AlGaN. • The surface chemistry and sensor behaviour were investigated. • The oxide of aluminum is significantly more reactive than gallium. • The Cl{sup −} ions are greater in GaN samples compared to AlGaN samples. - Abstract: Soft X-ray photoelectron spectroscopy was used to investigate the fundamental surface chemistry of both AlGaN and GaN surfaces in the context of understanding the behaviour of AlGaN/GaN heterostructures as chemical field-effect transistor (CHEMFET) ion sensors. AlGaN and GaN samples were subjected to different methods of oxide growth (native oxide and thermally grown oxide) and chemical treatment conditions. Our investigations indicate that the etching of the oxide layer is more pronounced with AlGaN compared to GaN. Also, we observed that chloride ions have a greater tendency to attach to the GaN surface relative to the AlGaN surface. Furthermore, chloride ions are comparatively more prevalent on surfaces treated with 5% HCl acid solution. The concentration of chloride ions is even higher on the HCl treated native oxide surface resulting in a very clear deconvolution of the Cl 2p{sub 1/2} and Cl 2p{sub 3/2} peaks. For GaN and AlGaN surfaces, a linear response (e.g. source-drain current) is typically seen with variation in pH of buffered solutions with constant reference electrode voltage at the surface gate; however, an inverted bath-tub type response (e.g. a maximum at neutral pH and lower values at pH values away from neutral) and a general tendency to negative charge selectivity has been also widely reported. We have shown that our XPS investigations are consistent with the different sensor response reported in the literature for these CHEMFET devices and may help to explain the differing response of these materials.

  19. Effect of 60Co γ-irradiation on the nature of electronic transport in heavily doped n-type GaN based Schottky photodetectors

    Science.gov (United States)

    Chatterjee, Abhishek; Khamari, Shailesh K.; Porwal, S.; Kher, S.; Sharma, T. K.

    2018-04-01

    GaN Schottky photodetectors are fabricated on heavily doped n-type GaN epitaxial layers grown by the hydride vapour phase epitaxy technique. The effect of 60Co γ-radiation on the electronic transport in GaN epilayers and Schottky detectors is studied. In contrast to earlier observations, a steady rise in the carrier concentration with increasing irradiation dose is clearly seen. By considering a two layer model, the contribution of interfacial dislocations in carrier transport is isolated from that of the bulk layer for both the pristine and irradiated samples. The bulk carrier concentration is fitted by using the charge balance equation which indicates that no new electrically active defects are generated by γ-radiation even at 500 kGy dose. The irradiation induced rise in the bulk carrier concentration is attributed to the activation of native Si impurities that are already present in an electrically inert form in the pristine sample. Further, the rise in interfacial contribution in the carrier concentration is governed by the enhanced rate of formation of nitrogen vacancies by irradiation, which leads to a larger diffusion of oxygen impurities. A large value of the characteristic tunnelling energy for both the pristine and irradiated Au/Ni/GaN Schottky devices confirms that the dislocation-assisted tunnelling dominates the low temperature current transport even after irradiation. The advantage of higher displacement energy and larger bandgap of GaN as compared to GaAs is evident from the change in leakage current after irradiation. Further, a fast recovery of the photoresponse of GaN photodetectors after irradiation signifies their compatibility to operate in high radiation zones. The results presented here are found to be crucial in understanding the interaction of 60Co γ-irradiation with n+-GaN epilayers.

  20. Determination of carrier diffusion length in p- and n-type GaN

    Science.gov (United States)

    Hafiz, Shopan; Metzner, Sebastian; Zhang, Fan; Monavarian, Morteza; Avrutin, Vitaliy; Morkoç, Hadis; Karbaum, Christopher; Bertram, Frank; Christen, Jürgen; Gil, Bernard; Özgür, Ümit

    2014-03-01

    Diffusion lengths of photo-excited carriers along the c-direction were determined from photoluminescence (PL) measurements in p- and n-type GaN epitaxial layers grown on c-plane sapphire by metal-organic chemical vapor deposition. The investigated samples incorporate a 6 nm thick In0.15Ga0.85N active layer capped with either 500 nm p- GaN or 1300 nm n-GaN. The top GaN layers were etched in steps and PL from the InGaN active region and the underlying layers was monitored as a function of the top GaN thickness upon photogeneration near the surface region by above bandgap excitation. Taking into consideration the absorption in the active and underlying layers, the diffusion lengths at 295 K and at 15 K were measured to be about 92 ± 7 nm and 68 ± 7 nm for Mg-doped p-type GaN and 432 ± 30 nm and 316 ± 30 nm for unintentionally doped n-type GaN, respectively. Cross-sectional cathodoluminescence line-scan measurement was performed on a separate sample and the diffusion length in n-type GaN was measured to be 280 nm.

  1. Polarity analysis of GaN nanorods by photo-assisted Kelvin probe force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Jiandong; Neumann, Richard; Wang, Xue; Li, Shunfeng; Fuendling, Soenke; Merzsch, Stephan; Al-Suleiman, Mohamed A.M.; Soekmen, Uensal; Wehmann, Hergo-H.; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig (Germany)

    2011-07-15

    Polarity dependence (N-polar (000-1) and Ga-polar (0001)) of surface photovoltage of epitaxially grown, vertically aligned GaN nanorods has been investigated by photo-assisted Kelvin probe force microscopy (KPFM). Commercial GaN substrates with known polarities are taken as reference samples. The polarity of GaN substrates can be well distinguished by the change in surface photovoltage upon UV illumination in air ambient. These different behaviors of Ga- and N-polar surfaces are attributed to the polarity-related surface-bound charges and photochemical reactivity. GaN nanorods were grown on patterned SiO{sub 2}/sapphire templates by metal-organic vapor phase epitaxy (MOVPE). In order to analyze the bottom surface of the grown GaN nanorods, a technique known from high power electronics and joining techniques is applied to remove the substrate. The top and bottom surfaces of the GaN nanorods are identified to be N-polar and Ga-polar according to the KPFM results, respectively. Our experiments demonstrate that KPFM is a simple and suitable method capable to identify the polarity of GaN nanorods. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Nanoscratch Characterization of GaN Epilayers on c- and a-Axis Sapphire Substrates

    Directory of Open Access Journals (Sweden)

    Wen Hua-Chiang

    2010-01-01

    Full Text Available Abstract In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

  3. The 2018 GaN power electronics roadmap

    Science.gov (United States)

    Amano, H.; Baines, Y.; Beam, E.; Borga, Matteo; Bouchet, T.; Chalker, Paul R.; Charles, M.; Chen, Kevin J.; Chowdhury, Nadim; Chu, Rongming; De Santi, Carlo; Merlyne De Souza, Maria; Decoutere, Stefaan; Di Cioccio, L.; Eckardt, Bernd; Egawa, Takashi; Fay, P.; Freedsman, Joseph J.; Guido, L.; Häberlen, Oliver; Haynes, Geoff; Heckel, Thomas; Hemakumara, Dilini; Houston, Peter; Hu, Jie; Hua, Mengyuan; Huang, Qingyun; Huang, Alex; Jiang, Sheng; Kawai, H.; Kinzer, Dan; Kuball, Martin; Kumar, Ashwani; Boon Lee, Kean; Li, Xu; Marcon, Denis; März, Martin; McCarthy, R.; Meneghesso, Gaudenzio; Meneghini, Matteo; Morvan, E.; Nakajima, A.; Narayanan, E. M. S.; Oliver, Stephen; Palacios, Tomás; Piedra, Daniel; Plissonnier, M.; Reddy, R.; Sun, Min; Thayne, Iain; Torres, A.; Trivellin, Nicola; Unni, V.; Uren, Michael J.; Van Hove, Marleen; Wallis, David J.; Wang, J.; Xie, J.; Yagi, S.; Yang, Shu; Youtsey, C.; Yu, Ruiyang; Zanoni, Enrico; Zeltner, Stefan; Zhang, Yuhao

    2018-04-01

    Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

  4. Electronic and Optical Properties of Two-Dimensional GaN from First-Principles.

    Science.gov (United States)

    Sanders, Nocona; Bayerl, Dylan; Shi, Guangsha; Mengle, Kelsey A; Kioupakis, Emmanouil

    2017-12-13

    Gallium nitride (GaN) is an important commercial semiconductor for solid-state lighting applications. Atomically thin GaN, a recently synthesized two-dimensional material, is of particular interest because the extreme quantum confinement enables additional control of its light-emitting properties. We performed first-principles calculations based on density functional and many-body perturbation theory to investigate the electronic, optical, and excitonic properties of monolayer and bilayer two-dimensional (2D) GaN as a function of strain. Our results demonstrate that light emission from monolayer 2D GaN is blueshifted into the deep ultraviolet range, which is promising for sterilization and water-purification applications. Light emission from bilayer 2D GaN occurs at a similar wavelength to its bulk counterpart due to the cancellation of the effect of quantum confinement on the optical gap by the quantum-confined Stark shift. Polarized light emission at room temperature is possible via uniaxial in-plane strain, which is desirable for energy-efficient display applications. We compare the electronic and optical properties of freestanding two-dimensional GaN to atomically thin GaN wells embedded within AlN barriers in order to understand how the functional properties are influenced by the presence of barriers. Our results provide microscopic understanding of the electronic and optical characteristics of GaN at the few-layer regime.

  5. Study of Charge Carrier Transport in GaN Sensors

    Science.gov (United States)

    Gaubas, Eugenijus; Ceponis, Tomas; Kuokstis, Edmundas; Meskauskaite, Dovile; Pavlov, Jevgenij; Reklaitis, Ignas

    2016-01-01

    Capacitor and Schottky diode sensors were fabricated on GaN material grown by hydride vapor phase epitaxy and metal-organic chemical vapor deposition techniques using plasma etching and metal deposition. The operational characteristics of these devices have been investigated by profiling current transients and by comparing the experimental regimes of the perpendicular and parallel injection of excess carrier domains. Profiling of the carrier injection location allows for the separation of the bipolar and the monopolar charge drift components. Carrier mobility values attributed to the hydride vapor phase epitaxy (HVPE) GaN material have been estimated as μe = 1000 ± 200 cm2/Vs for electrons, and μh = 400 ± 80 cm2/Vs for holes, respectively. Current transients under injection of the localized and bulk packets of excess carriers have been examined in order to determine the surface charge formation and polarization effects. PMID:28773418

  6. Benefits and Drawbacks of A High Frequency Gan Zvzcps Converter

    Directory of Open Access Journals (Sweden)

    Blanes J. M.

    2017-01-01

    Full Text Available This paper presents the benefits and drawbacks of replacing the traditional Si Mosfets transistors with enhancement mode GaN transistors in a Half-Bridge Zero Voltage and Zero Current Switching Power Switching (ZVZCPS converter. This type of converters is usually used as Electronic Power Converters (EPC for telecommunication satellites travelling-wave tube amplifiers (TWTAs. In this study, firstly the converter is theoretically analysed, obtaining its operation, losses and efficiency equations. From these equations, optimizations maps based on the main system parameters are obtained. These optimization maps are the key to quantify the potential benefits of GaN transistors in this type of converters. Theoretical results show that using GaN transistors, the frequency of the converter can be pushed from 125kHz to 830kHz without sacrificing the converter efficiency. This frequency increase is directly related to reduction on the EPC size and weight.

  7. Computational chemistry and metal-based radiopharmaceuticals

    International Nuclear Information System (INIS)

    Neves, M.; Fausto, R.

    1998-01-01

    Computer-assisted techniques have found extensive use in the design of organic pharmaceuticals but have not been widely applied on metal complexes, particularly on radiopharmaceuticals. Some examples of computer generated structures of complexes of In, Ga and Tc with N, S, O and P donor ligands are referred. Besides parameters directly related with molecular geometries, molecular properties of the predicted structures, as ionic charges or dipole moments, are considered to be related with biodistribution studies. The structure of a series of oxo neutral Tc-biguanide complexes are predicted by molecular mechanics calculations, and their interactions with water molecules or peptide chains correlated with experimental data of partition coefficients and percentage of human protein binding. The results stress the interest of using molecular modelling to predict molecular properties of metal-based radiopharmaceuticals, which can be successfully correlated with results of in vitro studies. (author)

  8. Structural and magnetic investigation of dilute magnetic semiconductors based on GaN and ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Kammermeier, Tom

    2010-01-19

    -ray absorption near edge spectroscopy (XANES) and XMCD at the Co K-edge support an increased fraction of Co atoms with metallic character in these samples. A reduced XLD signal indicates less substitutional Co-atoms. These samples were subject to annealing procedures either conducted under O{sub 2} atmosphere or high vacuum (HV) conditions. While the latter strongly enhances ferromagnetic-like properties, they vanish upon O{sub 2} annealing. XANES and XLD analyses show that non-substitutional Co atoms are oxidized to Co{sub 3}O{sub 4} by annealing in an O{sub 2} atmosphere, whereas HV annealing increases the fraction of a metallic Co phase. ESR measurements consistently show signatures of superparamagnetic ensembles at elevated temperatures (>60 K) and isotropic spectra of blocked magnetic moments of nanoparticles at low temperatures. Samples of high structural quality, i.e. with a large fraction of substitutional Co, are inert to annealing procedures. (orig.)

  9. Base metal dehydrogenation of amine-boranes

    Science.gov (United States)

    Blacquiere, Johanna Marie [Ottawa, CA; Keaton, Richard Jeffrey [Pearland, TX; Baker, Ralph Thomas [Los Alamos, NM

    2009-06-09

    A method of dehydrogenating an amine-borane having the formula R.sup.1H.sub.2N--BH.sub.2R.sup.2 using base metal catalyst. The method generates hydrogen and produces at least one of a [R.sup.1HN--BHR.sup.2].sub.m oligomer and a [R.sup.1N--BR.sup.2].sub.n oligomer. The method of dehydrogenating amine-boranes may be used to generate H.sub.2 for portable power sources, such as, but not limited to, fuel cells.

  10. Influencing factors of GaN growth uniformity through orthogonal test analysis

    International Nuclear Information System (INIS)

    Zhang, Zhi; Fang, Haisheng; Yan, Han; Jiang, Zhimin; Zheng, Jiang; Gan, Zhiyin

    2015-01-01

    Gallium nitride (GaN) is widely used in light-emitting diode (LED) devices due to its wide bandgap and excellently optoelectronic performance. The efficiency and lifetime of LEDs are critically determined by quality of GaN, for example, growth uniformity. Metal-organic chemical vapor deposition (MOCVD) is the most popular technique to grow high-quality GaN epitaxial layers. Growth uniformity is influenced by fluid flow, heat transfer and chemical reactions in the reactor. In this paper, the growth process in a close-coupled showerhead (CCS) MOCVD reactor is investigated based on 3D numerical simulation. Influences of the operating parameters on the growth uniformity are presented. To evaluate the role of the parameters systematically and efficiently on the growth uniformity, orthogonal test method is introduced. The results reveal that the growth rate and uniformity are strongly related to the total gas flow rate, the showerhead height and the inlet gas temperature, but are weakly affected by the isothermal wall temperature, the rotating speed and the susceptor temperature under the ranges of the current study. The optimized combination of the parameters is further proposed as a useful reference for obtaining the LED layers with a balance between the growth rate and the growth uniformity in industry. - Highlights: • Fluid flow, heat transfer, chemical reactions are calculated for a 3D CCS reactor. • The effects of process parameters on growth rate and uniformity are investigated. • Orthogonal test method is introduced to analyze the effect of multi-factors. • Optimal combinations can be obtained for the best growth rate and uniformity.

  11. THERMAL IMAGING OF Si, GaAs AND GaN -BASED DEVICES WITHIN THE MICROTHERM PROJECT

    OpenAIRE

    Pavageau , S.; Tessier , G.; Filloy , C.; Jerosolimski , G.; Fournier , D.; Polignano , M.-L.; Mica , I.; Cassette , S.; Aubry , R.; Durand , O.

    2005-01-01

    Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/5920); International audience; Within the european project Microtherm, we have developed a CCD-based thermoreflectance system which delivers thermal images of working integrated circuits with high spatial and thermal resolutions (down to 350 nm and 0.1 K respectively). We illustrate the performances of this set-up on several classes of semiconductor devices including high power transistors and transistor ar...

  12. ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

    Energy Technology Data Exchange (ETDEWEB)

    Long, CL; Del Genio, A; Deng, M; Fu, X; Gustafson, W; Houze, R; Jakob, C; Jensen, M; Johnson, R; Liu, X; Luke, E; May, P; McFarlane, S; Minnis, P; Schumacher, C; Vogelmann, A; Wang, Y; Webster, P; Xie, S; Zhang, C

    2011-04-11

    The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJO initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde

  13. Chemical Sensors Based on Metal Oxide Nanostructures

    Science.gov (United States)

    Hunter, Gary W.; Xu, Jennifer C.; Evans, Laura J.; VanderWal, Randy L.; Berger, Gordon M.; Kulis, Mike J.; Liu, Chung-Chiun

    2006-01-01

    This paper is an overview of sensor development based on metal oxide nanostructures. While nanostructures such as nanorods show significan t potential as enabling materials for chemical sensors, a number of s ignificant technical challenges remain. The major issues addressed in this work revolve around the ability to make workable sensors. This paper discusses efforts to address three technical barriers related t o the application of nanostructures into sensor systems: 1) Improving contact of the nanostructured materials with electrodes in a microse nsor structure; 2) Controling nanostructure crystallinity to allow co ntrol of the detection mechanism; and 3) Widening the range of gases that can be detected by using different nanostructured materials. It is concluded that while this work demonstrates useful tools for furt her development, these are just the beginning steps towards realizati on of repeatable, controlled sensor systems using oxide based nanostr uctures.

  14. Efficient waveguide coupler based on metal materials

    Science.gov (United States)

    Wu, Wenjun; Yang, Junbo; Chang, Shengli; Zhang, Jingjing; Lu, Huanyu

    2015-10-01

    Because of the diffraction limit of light, the scale of optical element stays in the order of wavelength, which makes the interface optics and nano-electronic components cannot be directly matched, thus the development of photonics technology encounters a bottleneck. In order to solve the problem that coupling of light into the subwavelength waveguide, this paper proposes a model of coupler based on metal materials. By using Surface Plasmon Polaritons (SPPs) wave, incident light can be efficiently coupled into waveguide of diameter less than 100 nm. This paper mainly aims at near infrared wave band, and tests a variety of the combination of metal materials, and by changing the structural parameters to get the maximum coupling efficiency. This structure splits the plane incident light with wavelength of 864 nm, the width of 600 nm into two uniform beams, and separately coupled into the waveguide layer whose width is only about 80 nm, and the highest coupling efficiency can reach above 95%. Using SPPs structure will be an effective method to break through the diffraction limit and implement photonics device high-performance miniaturization. We can further compress the light into small scale fiber or waveguide by using the metal coupler, and to save the space to hold more fiber or waveguide layer, so that we can greatly improve the capacity of optical communication. In addition, high-performance miniaturization of the optical transmission medium can improve the integration of optical devices, also provide a feasible solution for the photon computer research and development in the future.

  15. Impact of substrate off-angle on the m-plane GaN Schottky diodes

    Science.gov (United States)

    Yamada, Hisashi; Chonan, Hiroshi; Takahashi, Tokio; Shimizu, Mitsuaki

    2018-04-01

    We investigated the effects of the substrate off-angle on the m-plane GaN Schottky diodes. GaN epitaxial layers were grown by metal-organic chemical vapor deposition on m-plane GaN substrates having an off-angle of 0.1, 1.1, 1.7, or 5.1° toward [000\\bar{1}]. The surface of the GaN epitaxial layers on the 0.1°-off substrate consisted of pyramidal hillocks and contained oxygen (>1017 cm-3) and carbon (>1016 cm-3) impurities. The residual carbon and oxygen impurities decreased to current of the 0.1°-off m-plane GaN Schottky diodes originated from the +c facet of the pyramidal hillocks. The leakage current was efficiently suppressed through the use of an off-angle that was observed to be greater than 1.1°. The off-angle of the m-plane GaN substrate is critical in obtaining high-performance Schottky diodes.

  16. Shape dependent electronic properties of wurzite GaN nanowire

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Pankaj, E-mail: pankajs@iiitm.ac.in; Kumar, Avaneesh, E-mail: avaneeshk7@ymail.com; Sharma, Varun, E-mail: sunny2013@gmail.com [Nanomaterials Research Group, ABV-Indian Institute of Information Technology and Management (IIITM), Gwalior-474015 (India); Jaiswal, Neeraj K., E-mail: neerajkumar.phd@gmail.com [Discipline of Physics, PDPM-Indian Institute of Information Technology, Design and Manufacturing (IIITDM), Jabalpur-482005 (India)

    2016-05-06

    In the present work, energetic stability and electronic behavior of triangular and square shaped wurzite GaN NW oriented along [1100] and [11 2 0] direction has been investigated by employing ab-initio DFT calculation. Structural analysis suggests that triangular shaped NW undergoes strong surface reconstruction compared to square shaped NW. However, binding energy reveals that square shaped NW is energetically more feasible than triangular NW. Further, from electronic band structure we observe that both structures are metallic with higher metallicity for triangular shaped NW.

  17. Theoretical study for heterojunction surface of NEA GaN photocathode dispensed with Cs activation

    Science.gov (United States)

    Xia, Sihao; Liu, Lei; Wang, Honggang; Wang, Meishan; Kong, Yike

    2016-09-01

    For the disadvantages of conventional negative electron affinity (NEA) GaN photocathodes activated by Cs or Cs/O, new-type NEA GaN photocathodes with heterojunction surface dispensed with Cs activation are investigated based on first-principle study with density functional theory. Through the growth of an ultrathin n-type GaN cap layer on p-type GaN emission layer, a p-n heterojunction is formed on the surface. According to the calculation results, it is found that Si atoms tend to replace Ga atoms to result in an n-type doped cap layer which contributes to the decreasing of work function. After the growth of n-type GaN cap layer, the atom structure near the p-type emission layer is changed while that away from the surface has no obvious variations. By analyzing the E-Mulliken charge distribution of emission surface with and without cap layer, it is found that the positive charge of Ga and Mg atoms in the emission layer decrease caused by the cap layer, while the negative charge of N atom increases. The conduction band moves downwards after the growth of cap layer. Si atom produces donor levels around the valence band maximum. The absorption coefficient of GaN emission layer decreases and the reflectivity increases caused by n-type GaN cap layer.

  18. Defect formation and magnetic properties of Co-doped GaN crystal and nanowire

    International Nuclear Information System (INIS)

    Shi, Li-Bin; Liu, Jing-Jing; Fei, Ying

    2013-01-01

    Theoretical calculation based on density functional theory (DFT) and generalized gradient approximation (GGA) has been carried out in studying defect formation and magnetic properties of Co doped GaN crystal and nanowire (NW). Co does not exhibit site preference in GaN crystal. However, Co occupies preferably surface sites in GaN NW. Transition level of the defect is also investigated in GaN crystal. We also find that Co Ga (S) in NW does not produce spin polarization and Co Ga (B) produces spontaneous spin polarization. Ferromagnetic (FM) and antiferromagnetic (AFM) couplings are analyzed by six different configurations. The results show that AFM coupling is more stable than FM coupling for Co doped GaN crystal. It is also found from Co doped GaN NW calculation that the system remains FM stability for majority of the configurations. Magnetic properties in Co doped GaN crystal can be mediated by N and Ga vacancies. The FM and AFM stability can be explained by Co 3d energy level coupling

  19. High-quality GaN epitaxially grown on Si substrate with serpentine channels

    Science.gov (United States)

    Wei, Tiantian; Zong, Hua; Jiang, Shengxiang; Yang, Yue; Liao, Hui; Xie, Yahong; Wang, Wenjie; Li, Junze; Tang, Jun; Hu, Xiaodong

    2018-06-01

    A novel serpentine-channeled mask was introduced to Si substrate for low-dislocation GaN epitaxial growth and the fully coalesced GaN film on the masked Si substrate was achieved for the first time. Compared with the epitaxial lateral overgrowth (ELOG) growth method, this innovative mask only requires one-step epitaxial growth of GaN which has only one high-dislocation region per mask opening. This new growth method can effectively reduce dislocation density, thus improving the quality of GaN significantly. High-quality GaN with low dislocation density ∼2.4 × 107 cm-2 was obtained, which accounted for about eighty percent of the GaN film in area. This innovative technique is promising for the growth of high-quality GaN templates and the subsequent fabrication of high-performance GaN-based devices like transistors, laser diodes (LDs), and light-emitting diodes (LEDs) on Si substrate.

  20. Evidence for moving of threading dislocations during the VPE growth in GaN thin layers

    Energy Technology Data Exchange (ETDEWEB)

    Kuwano, Noriyuki [Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Miyake, Hideto; Hiramatsu, Kazumasa [Department of Electrical and Electronic Engineering, Mie University, Tsu, Mie 514-8507 (Japan); Amano, Hiroshi [Graduate School of Engineering, Akasaki Research Center, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603 (Japan); Akasaki, Isamu [Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi, Tempaku, Nagoya 468-8502 (Japan)

    2011-05-15

    Cross-sectional transmission electron microscope (TEM) observation was performed in detail to analyze the morphology of threading dislocations (TDs) in GaN thin layers with various thicknesses. The GaN layers were overgrown on an Al{sub 0.28}Ga{sub 0.72}N layer by the metal-organic vapor-phase epitaxy (MOVPE) method. In a GaN layer about 50 nm in thickness, TDs running up in the AlGaN layer pass into the GaN layer and most of them reach the top surface without bending. In thicker GaN layers, on the other hand, many of TDs form a hairpin-configuration on or above the interface of GaN and AlGaN to be annihilated. This difference in morphology of TDs indicates that the TDs have moved down inside the GaN layer. Since the formation of hairpins is attributed to a stress-relief, there should be an extra half-plane between the paired TDs. Therefore, the movement of TDs should be of ''climb motion''. Another example of possible TD movement inside a GaN layer is also described. It is emphasized that the possibility of TD-movements inside the thin film crystal during the growth should be taken into account in analysis of thin-layer growth through the behavior of TDs (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  1. Photo-assisted local oxidation of GaN using an atomic force microscope

    International Nuclear Information System (INIS)

    Hwang, J S; Hu, Z S; Lu, T Y; Chen, L W; Chen, S W; Lin, T Y; Hsiao, C-L; Chen, K-H; Chen, L-C

    2006-01-01

    This paper introduces a photo-assisted atomic force microscope (AFM) local oxidation technique which is capable of producing highly smooth oxide patterns with heights reaching several tens of nanometres on both n- and p-types of GaN (and in principle on most semiconductors) without the use of chemicals. The novel methodology relies on UV illumination of the surface of the substrate during conventional AFM local oxidation. A low 1.2 V threshold voltage for n-type GaN was obtained, which can be explained by UV photo-generation of excess electron-hole pairs in the substrate near the junction, thereby reducing the electric field required to drive carrier flow through the tip-sample Schottky barrier. It was demonstrated that the presence or absence of light alone was sufficient to switch the growth of the oxide on or off. The photo-assisted AFM oxidation technique is of immediate interest to the semiconductor industry for the fabrication of GaN-based complementary metal-oxide-semiconductor devices and nanodevices, improves chances for AFM-type data storage, and presents new degrees of freedom for process control technique

  2. Assembly of phosphonic acids on GaN and AlGaN

    Energy Technology Data Exchange (ETDEWEB)

    Simpkins, B S; Stine, R; Theodore, N D; Pehrsson, P E [Chemistry Division, Naval Research Laboratory, Washington DC (United States); Hong, S [Thomas Jefferson High School, McClean, VA (United States); Maekinen, A J [Optical Sciences Division, Naval Research Laboratory, Washington, DC (United States); Mastro, M A; Eddy, C R Jr [Electronics Science and Technology Division, Naval Research Laboratory, Washington, DC (United States)

    2010-01-13

    Self-assembled monolayers of octadecylphosphonic acid and 16-phosphonohexadecanoic acid (PHDA) were formed on the semiconductor substrates gallium nitride (GaN) and aluminium gallium nitride (AlGaN). The presence of the molecular layers was verified through x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Structural information was acquired with infrared spectroscopy which verified the bonding orientation of the carboxyl-containing PHDA. The impact of the molecular layers on the channel conductivity and the surface electronic structure of an AlGaN/GaN heterostructure was measured. Our results indicate that pinning of the surface Fermi level prohibits modification of the channel conductivity by the layer. However, a surface dipole of {approx}0.8 eV is present and associated with both phosphonic acid layers. These results are of direct relevance to field-effect-based biochemical sensors and metal-semiconductor contact formation for this system and provide a fundamental basis for further applications of GaN and AlGaN technology in the fields of biosensing and microelectronics.

  3. Effect of annealing on metastable shallow acceptors in Mg-doped GaN layers grown on GaN substrates

    OpenAIRE

    Pozina, Galia; Hemmingsson, Carl; Paskov, Plamen P.; Bergman, Peder; Monemar, Bo; Kawashima, T.; Amano, H.; Akasaki, I.; Usui, A.

    2008-01-01

    Mg-doped GaN layers grown by metal-organic vapor phase epitaxy on GaN substrates produced by the halide vapor phase technique demonstrate metastability of the near-band-gap photoluminescence (PL). The acceptor bound exciton (ABE) line possibly related to the C acceptor vanishes in as-grown samples within a few minutes under UV laser illumination. Annealing activates the more stable Mg acceptors and passivates C acceptors. Consequently, only the ABE line related to Mg is dominant in PL spectra...

  4. Design and testing of a phantom and instrumented gynecological applicator based on GaN dosimeter for use in high dose rate brachytherapy quality assurance

    Energy Technology Data Exchange (ETDEWEB)

    Guiral, P.; Ribouton, J.; Jalade, P. [Service de Physique Médicale et Radioprotection, Centre Hospitalier Lyon Sud, Pierre-Bénite F-69495 (France); Wang, R.; Galvan, J.-M.; Lu, G.-N.; Pittet, P., E-mail: patrick.pittet@univ-lyon1.fr [Institut des Nanotechnologies de Lyon, University Lyon, Université Claude Bernard Lyon 1, CNRS, INL UMR5270, F-69622 Villeurbanne (France); Rivoire, A.; Gindraux, L. [DOSILAB, 66 Boulevard Niels Bohr, Villeurbanne F-69100 (France)

    2016-09-15

    Purpose: High dose rate brachytherapy (HDR-BT) is widely used to treat gynecologic, anal, prostate, head, neck, and breast cancers. These treatments are typically administered in large dose per fraction (>5 Gy) and with high-gradient-dose-distributions, with serious consequences in case of a treatment delivery error (e.g., on dwell position and dwell time). Thus, quality assurance (QA) or quality control (QC) should be systematically and independently implemented. This paper describes the design and testing of a phantom and an instrumented gynecological applicator for pretreatment QA and in vivo QC, respectively. Methods: The authors have designed a HDR-BT phantom equipped with four GaN-based dosimeters. The authors have also instrumented a commercial multichannel HDR-BT gynecological applicator by rigid incorporation of four GaN-based dosimeters in four channels. Specific methods based on the four GaN dosimeter responses are proposed for accurate determination of dwell time and dwell position inside phantom or applicator. The phantom and the applicator have been tested for HDR-BT QA in routine over two different periods: 29 and 15 days, respectively. Measurements in dwell position and time are compared to the treatment plan. A modified position–time gamma index is used to monitor the quality of treatment delivery. Results: The HDR-BT phantom and the instrumented applicator have been used to determine more than 900 dwell positions over the different testing periods. The errors between the planned and measured dwell positions are 0.11 ± 0.70 mm (1σ) and 0.01 ± 0.42 mm (1σ), with the phantom and the applicator, respectively. The dwell time errors for these positions do not exhibit significant bias, with a standard deviation of less than 100 ms for both systems. The modified position–time gamma index sets a threshold, determining whether the treatment run passes or fails. The error detectability of their systems has been evaluated through tests on

  5. Saccharide-based Approach to Green Metallic Nanostructure Synthesis

    DEFF Research Database (Denmark)

    Engelbrekt, Christian; Sørensen, Karsten Holm; Jensen, Palle Skovhus

    A green approach to solution synthesis of metallic nanoparticles has been developed using harmless and bioapplicable chemicals as well as moderate temperatures. Metal precursors are reduced by glucose/buffers and sterically stabilized by starch. The saccharide based procedure is highly diverse pr...... producing specifically a wide range of spherical, anisotropic, metallic, semi - conductor and core-shell nanostructures....

  6. Economical characteristics of base types of minerals. 1. Metallic minerals

    International Nuclear Information System (INIS)

    Khasanov, A.Kh.

    1990-01-01

    Metallic minerals is raw materials base of black and colour metallurgy. In this article of book author describes the group of black metals (iron, manganese, chromium), group of tempers (titanium, vanadium, nickel, cobalt, molybdenum, tungsten), colour metals (copper, lead, zinc, aluminium, tin, mercury, antimony, bismuth) and etc.

  7. The structure of InAlGaN layers grown by metal organic vapour phase epitaxy: effects of threading dislocations and inversion domains from the GaN template.

    Science.gov (United States)

    Ben Ammar, H; Minj, A; Chauvat, M-P; Gamarra, P; Lacam, C; Morales, M; Ruterana, P

    2017-12-01

    Defects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morphology have been studied. In addition to growth conditions, the quality of the GaN template may play an important role in the formation of defects in the barrier. Therefore, this work is focused on effects caused by threading dislocations (TDs) and inversion domains (IDs) originating from the underlying GaN. The effects are observed on the crystalline quality of the barrier and characteristic surface morphologies. Each type of TDs is shown to affect the surface morphology in a different way. Depending on the size of the corresponding hillock for a given pinhole, it was possible to determine the dislocation type. It is pointed out that the smallest pinholes are not connected to TDs whereas the large ones terminate either mixed type or edge type TDs. At sufficiently large layer thickness, the IDs originating from the GaN template lead to the formation of concentric trenches at the layer surface, and this is related to the change in growth kinetics on top and at the immediate surroundings of the ID. © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society.

  8. Surface morphology of homoepitaxial GaN grown on non- and semipolar GaN substrates

    Energy Technology Data Exchange (ETDEWEB)

    Wernicke, Tim; Ploch, Simon [Institute of Solid State Physics, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Hoffmann, Veit; Knauer, Arne; Weyers, Markus [Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, Michael [Institute of Solid State Physics, Technische Universitaet Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

    2011-03-15

    GaN layers on bulk m-plane, (11 anti 22), (10 anti 12) and (10 anti 11) GaN substrates were grown by metal organic vapor phase epitaxy. XRD rocking curves have a FWHM of less than 150'', indicating excellent crystalline quality. However in many cases surface morphology exhibits hillocks with a height of 1-2 {mu}m and a lateral extension of 50-200 {mu}m whereas a smooth surface would be desirable for optoelectronic devices. The influence of growth parameters on the surface morphology was studied. The goal was, to constrain the material redistribution, that is necessary to form large hillocks. This was achieved by lowering the adatom diffusion length by a reduction of temperature and an increased reactor pressure. In the case of the (10 anti 11) and (10 anti 12) semipolar planes a reduction of the adatom diffusion length leads to a reduction of hillock density, hillock size and a smoother surface between hillocks. However, the m-plane surface does not react to a reduction of adatom mobility. Even at 890 C and 400 mbar rectangular pyramids cover the surface. In contrast to the other planes, the (11 anti 22) becomes instable, when the adatom diffusion length is reduced. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. GaN epilayers on nanopatterned GaN/Si(1 1 1) templates: Structural and optical characterization

    International Nuclear Information System (INIS)

    Wang, L.S.; Tripathy, S.; Wang, B.Z.; Chua, S.J.

    2006-01-01

    Template-based nanoscale epitaxy has been explored to realize high-quality GaN on Si(1 1 1) substrates. We have employed polystyrene-based nanosphere lithography to form the nano-hole array patterns on GaN/Si(1 1 1) template and then, subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition (MOCVD). During the initial growth stage of GaN on such nanopatterned substrates, we have observed formation of nanoislands with hexagonal pyramid shape due to selective area epitaxy. With further epitaxial regrowth, these nanoislands coalesce and form continuous GaN film. The overgrown GaN on patterned and non-patterned regions is characterized by high-resolution X-ray diffraction (HRXRD) and high-spatial resolution optical spectroscopic methods. Micro-photoluminescence (PL), micro-Raman scattering and scanning electron microscopy (SEM) have been used to assess the microstructural and optical properties of GaN. Combined PL and Raman data analyses show improved optical quality when compared to GaN simultaneously grown on non-patterned bulk Si(1 1 1). Such thicker GaN templates would be useful to achieve III-nitride-based opto- and electronic devices integrated on Si substrates

  10. Flexible Self-Powered GaN Ultraviolet Photoswitch with Piezo-Phototronic Effect Enhanced On/Off Ratio.

    Science.gov (United States)

    Peng, Mingzeng; Liu, Yudong; Yu, Aifang; Zhang, Yang; Liu, Caihong; Liu, Jingyu; Wu, Wei; Zhang, Ke; Shi, Xieqing; Kou, Jinzong; Zhai, Junyi; Wang, Zhong Lin

    2016-01-26

    Flexible self-powered sensing is urgently needed for wearable, portable, sustainable, maintenance-free and long-term applications. Here, we developed a flexible and self-powered GaN membrane-based ultraviolet (UV) photoswitch with high on/off ratio and excellent sensitivity. Even without any power supply, the driving force of UV photogenerated carriers can be well boosted by the combination of both built-in electric field and piezoelectric polarization field. The asymmetric metal-semiconductor-metal structure has been elaborately utilized to enhance the carrier separation and transport for highly sensitive UV photoresponse. Its UV on/off ratio and detection sensitivity reach to 4.67 × 10(5) and 1.78 × 10(12) cm·Hz(0.5) W(1-), respectively. Due to its excellent mechanical flexibility, the piezoelectric polarization field in GaN membrane can be easily tuned/controlled based on piezo-phototronic effect. Under 1% strain, a stronger and broader depletion region can be obtained to further enhance UV on/off ratio up to 154%. As a result, our research can not only provide a deep understanding of local electric field effects on self-powered optoelectronic detection, but also promote the development of self-powered flexible optoelectronic devices and integrated systems.

  11. Gallium adsorption on (0001) GaN surfaces

    International Nuclear Information System (INIS)

    Adelmann, Christoph; Brault, Julien; Mula, Guido; Daudin, Bruno; Lymperakis, Liverios; Neugebauer, Joerg

    2003-01-01

    We study the adsorption behavior of Ga on (0001) GaN surfaces combining experimental specular reflection high-energy electron diffraction with theoretical investigations in the framework of a kinetic model for adsorption and ab initio calculations of energy parameters. Based on the experimental results we find that for substrate temperatures and Ga fluxes typically used in molecular-beam epitaxy of GaN, finite equilibrium Ga surface coverages can be obtained. The measurement of a Ga/GaN adsorption isotherm allows the quantification of the equilibrium Ga surface coverage as a function of the impinging Ga flux. In particular, we show that a large range of Ga fluxes exists, where 2.5±0.2 monolayers (in terms of the GaN surface site density) of Ga are adsorbed on the GaN surface. We further demonstrate that the structure of this adsorbed Ga film is in good agreement with the laterally contracted Ga bilayer model predicted to be most stable for strongly Ga-rich surfaces [Northrup et al., Phys. Rev. B 61, 9932 (2000)]. For lower Ga fluxes, a discontinuous transition to Ga monolayer equilibrium coverage is found, followed by a continuous decrease towards zero coverage; for higher Ga fluxes, Ga droplet formation is found, similar to what has been observed during Ga-rich GaN growth. The boundary fluxes limiting the region of 2.5 monolayers equilibrium Ga adsorption have been measured as a function of the GaN substrate temperature giving rise to a Ga/GaN adsorption phase diagram. The temperature dependence is discussed within an ab initio based growth model for adsorption taking into account the nucleation of Ga clusters. This model consistently explains recent contradictory results of the activation energy describing the critical Ga flux for the onset of Ga droplet formation during Ga-rich GaN growth [Heying et al., J. Appl. Phys. 88, 1855 (2000); Adelmann et al., J. Appl. Phys. 91, 9638 (2002).

  12. Electrical transport in GaN and InN nanowires; Elektrischer Transport in GaN- und InN-Nanodraehten

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Thomas Fabian

    2008-12-19

    This thesis discusses the analysis of the electrical transport in GaN and InN nanowires at room temperature and deep temperatures. From those measurements two different transport models for those two in matter of the band banding completely different materials have been found. In the investigation of the GaN nanowires the main focus was the electrical transport in dependence of the diameter and the n-doping. With the use of IV-measurements on those MBE grown nanowires with different diameters at dark and under UV illumination as well as the decay of the persistent photocurrent, it was possible to find an for GaN untypical behaviour. The electrical transport in those wires is extremely diameter dependent. The dark current shows space charged limited current. With the help of those cognitions a diameter dependent transport model could be found. The transport phenomena in those wires is based on the diameter depending band bending at the edge of the wires caused by the Fermi level pinning inside the forbidden band. This model can be fit to the data with the three parameter doping, fermi level pinning and wire diameter. On the base of those effects a method to determine the doping concentration inside those wires without field effect measurements and contact resistance has been developed. The defect structure inside those wires has been analysed with the help of spectral photoluminescence measurements. Here several defect bands have been found and it was possible with help of several contacts on one single wire to determine different defect regions along the wire and to explain them by the lattice mismatch between nanowire and substrate. Further temperature depending measurements and investigations on Schottky contacted wires as well as on GaN wires with AlN tunnel structures complete the work on GaN. The electrical characterisation on a large scale of undoped and doped InN nanowires shows linear growth of the dark current with the diameter up to wires of around 100 nm

  13. Fabrication of high quality GaN nanopillar arrays by dry and wet chemical etching

    OpenAIRE

    Paramanik, Dipak; Motayed, Abhishek; King, Matthew; Ha, Jong-Yoon; Kryluk, Sergi; Davydov, Albert V.; Talin, Alec

    2013-01-01

    We study strain relaxation and surface damage of GaN nanopillar arrays fabricated using inductively coupled plasma (ICP) etching and post etch wet chemical treatment. We controlled the shape and surface damage of such nanopillar structures through selection of etching parameters. We compared different substrate temperatures and different chlorine-based etch chemistries to fabricate high quality GaN nanopillars. Room temperature photoluminescence and Raman scattering measurements were carried ...

  14. Emission spectra from AlN and GaN doped with rare earth elements

    International Nuclear Information System (INIS)

    Choi, Sung Woo; Emura, Shuichi; Kimura, Shigeya; Kim, Moo Seong; Zhou Yikai; Teraguchi, Nobuaki; Suzuki, Akira; Yanase, Akira; Asahi, Hajime

    2006-01-01

    Luminescent properties of GaN and AlN based semiconductors containing rare earth metals of Gd and Dy are studied. Cathodoluminescent spectra from AlGdN show a clear and sharp peak at 318 nm following LO phonon satellites. Photoluminescence spectra from GaDyN by the above-gap excitation also show several peaks in addition to the broad luminescence band emission. For GaGdN, the sharp PL peaks are also observed at 650 and 670 nm, and they are assigned to the intra-f orbital transitions by their time decay measurements. The broad band at around 365 nm for AlGdN, 505 nm for GaGdN and GaDyN are commonly observed. The origin of these broad bands is discussed

  15. GaN Initiative for Grid Applications (GIGA)

    Energy Technology Data Exchange (ETDEWEB)

    Turner, George [MIT Lincoln Lab., Lexington, MA (United States)

    2015-07-03

    For nearly 4 ½ years, MIT Lincoln Laboratory (MIT/LL) led a very successful, DoE-funded team effort to develop GaN-on-Si materials and devices, targeting high-voltage (>1 kV), high-power, cost-effective electronics for grid applications. This effort, called the GaN Initiative for Grid Applications (GIGA) program, was initially made up of MIT/LL, the MIT campus group of Prof. Tomas Palacios (MIT), and the industrial partner M/A Com Technology Solutions (MTS). Later in the program a 4th team member was added (IQE MA) to provide commercial-scale GaN-on-Si epitaxial materials. A basic premise of the GIGA program was that power electronics, for ubiquitous utilization -even for grid applications - should be closer in cost structure to more conventional Si-based power electronics. For a number of reasons, more established GaN-on-SiC or even SiC-based power electronics are not likely to reach theses cost structures, even in higher manufacturing volumes. An additional premise of the GIGA program was that the technical focus would be on materials and devices suitable for operating at voltages > 1 kV, even though there is also significant commercial interest in developing lower voltage (< 1 kV), cost effective GaN-on-Si devices for higher volume applications, like consumer products. Remarkable technical progress was made during the course of this program. Advances in materials included the growth of high-quality, crack-free epitaxial GaN layers on large-diameter Si substrates with thicknesses up to ~5 μm, overcoming significant challenges in lattice mismatch and thermal expansion differences between Si and GaN in the actual epitaxial growth process. Such thick epilayers are crucial for high voltage operation of lateral geometry devices such as Schottky barrier (SB) diodes and high electron mobility transistors (HEMTs). New “Normally-Off” device architectures were demonstrated – for safe operation of power electronics circuits. The trade-offs between lateral and

  16. Reduced MLH3 Expression in the Syndrome of Gan-Shen Yin Deficiency in Patients with Different Diseases.

    Science.gov (United States)

    Du, Juan; Zhong, Maofeng; Liu, Dong; Liang, Shufang; Liu, Xiaolin; Cheng, Binbin; Zhang, Yani; Yin, Zifei; Wang, Yuan; Ling, Changquan

    2017-01-01

    Traditional Chinese medicine formulates treatment according to body constitution (BC) differentiation. Different constitutions have specific metabolic characteristics and different susceptibility to certain diseases. This study aimed to assess the characteristic genes of gan-shen Yin deficiency constitution in different diseases. Fifty primary liver cancer (PLC) patients, 94 hypertension (HBP) patients, and 100 diabetes mellitus (DM) patients were enrolled and classified into gan-shen Yin deficiency group and non-gan-shen Yin deficiency group according to the body constitution questionnaire to assess the clinical manifestation of patients. The mRNA expressions of 17 genes in PLC patients with gan-shen Yin deficiency were different from those without gan-shen Yin deficiency. However, considering all patients with PLC, HBP, and DM, only MLH3 was significantly lower in gan-shen Yin deficiency group than that in non-gen-shen Yin deficiency. By ROC analysis, the relationship between MLH3 and gan-shen Yin deficiency constitution was confirmed. Treatment of MLH3 (-/- and -/+) mice with Liuweidihuang wan, classical prescriptions for Yin deficiency, partly ameliorates the body constitution of Yin deficiency in MLH3 (-/+) mice, but not in MLH3 (-/-) mice. MLH3 might be one of material bases of gan-shen Yin deficiency constitution.

  17. Above room-temperature ferromagnetism of Mn delta-doped GaN nanorods

    International Nuclear Information System (INIS)

    Lin, Y. T.; Wadekar, P. V.; Kao, H. S.; Chen, T. H.; Chen, Q. Y.; Tu, L. W.; Huang, H. C.; Ho, N. J.

    2014-01-01

    One-dimensional nitride based diluted magnetic semiconductors were grown by plasma-assisted molecular beam epitaxy. Delta-doping technique was adopted to dope GaN nanorods with Mn. The structural and magnetic properties were investigated. The GaMnN nanorods with a single crystalline structure and with Ga sites substituted by Mn atoms were verified by high-resolution x-ray diffraction and Raman scattering, respectively. Secondary phases were not observed by high-resolution x-ray diffraction and high-resolution transmission electron microscopy. In addition, the magnetic hysteresis curves show that the Mn delta-doped GaN nanorods are ferromagnetic above room temperature. The magnetization with magnetic field perpendicular to GaN c-axis saturates easier than the one with field parallel to GaN c-axis

  18. Effects of hydrogen on Mn-doped GaN: A first principles calculation

    International Nuclear Information System (INIS)

    Wu, M.S.; Xu, B.; Liu, G.; Lei, X.L.; Ouyang, C.Y.

    2013-01-01

    First-principles calculations based on spin density functional theory are performed to study the effects of H on the structural, electronic and magnetic properties of the Mn-doped GaN dilute magnetic semiconductors. Our results show that the interstitial H atom prefers to bond with N atom rather than Mn atom, which means that H favors to form the N–H complex rather than Mn–H complex in the Mn-doped GaN. After introducing one H atom in the system, the total magnetic moment of the Mn-doped GaN increases by 25%, from 4.0μ B to 5.0μ B . The physics mechanism of the increase of magnetic moment after hydrogenation in Mn-doped GaN is discussed

  19. Thermodynamic analysis of Mg-doped p-type GaN semiconductor

    International Nuclear Information System (INIS)

    Li Jingbo; Liang Jingkui; Rao Guanghui; Zhang Yi; Liu Guangyao; Chen Jingran; Liu Quanlin; Zhang Weijing

    2006-01-01

    A thermodynamic modeling of Mg-doped p-type GaN was carried out to describe the thermodynamic behaviors of native defects, dopants (Mg and H) and carriers in GaN. The formation energies of charged component compounds in a four-sublattice model were defined as functions of the Fermi-level based on the results of the first-principles calculations and adjusted to fit experimental data. The effect of the solubility of Mg on the low doping efficiency of Mg in GaN and the role of H in the Mg-doping MOCVD process were discussed. The modeling provides a thermodynamic approach to understand the doping process of GaN semiconductors

  20. Semi-polar GaN heteroepitaxy an high index Si-surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Ravash, Roghaiyeh; Blaesing, Juergen; Hempel, Thomas; Dadgar, Armin; Christen, Juergen; Krost, Alois [Otto-von-Guericke-University Magdeburg, FNW/IEP/AHE, Magdeburg (Germany)

    2011-07-01

    Due to the lack of GaN homosubstrates, the growth of GaN-based devices is usually performed on heterosubstrates as sapphire or SiC. These substrates are either insulating or expensive, and both unavailable in large diameters. Meanwhile, silicon can meet the requirements for a low price and thermally well conducting substrate and also enabling the integration of optoelectronic devices with Si-based electronics. Up to now, the good matching of hexagonal GaN with the three-fold symmetry of Si(111) greatly promotes the c-axis orientated growth of GaN on this surface plane. A large spontaneous and piezoelectric polarization oriented along the c-axis exists in such hexagonal structure leading to low efficiencies for thick quantum wells. The attention to the growth of non-polar or semi-polar GaN based epitaxial structures has been increased recently because of reducing the effect of the polarization fields in these growth directions. Therefore we studied semi-polar GaN epilayers grown by metalorganic vapor phase epitaxy on silicon substrates with different orientations from Si(211) to Si(711). We observed that AlN seeding layer growth time play a significant role in obtaining the different GaN texture.

  1. Study on the structural, optical, and electrical properties of the yellow light-emitting diode grown on free-standing (0001) GaN substrate

    Science.gov (United States)

    Deng, Gaoqiang; Zhang, Yuantao; Yu, Ye; Yan, Long; Li, Pengchong; Han, Xu; Chen, Liang; Zhao, Degang; Du, Guotong

    2018-04-01

    In this paper, GaN-based yellow light-emitting diodes (LEDs) were homoepitaxially grown on free-standing (0001) GaN substrates by metal-organic chemical vapor deposition. X-ray diffraction (XRD), photoluminescence (PL), and electroluminescence (EL) measurements were conducted to investigate the structural, optical, and electrical properties of the yellow LED. The XRD measurement results showed that the InGaN/GaN multiple quantum wells (MQWs) in the LED structure have good periodicity because the distinct MQWs related higher order satellite peaks can be clearly observed from the profile of 2θ-ω XRD scan. The low temperature (10 K) and room temperature PL measurement results yield an internal quantum efficiency of 16% for the yellow LED. The EL spectra of the yellow LED present well Gaussian distribution with relatively low linewidth (47-55 nm), indicating the homogeneous In-content in the InGaN quantum well layers in the yellow LED structure. It is believed that this work will aid in the future development of GaN on GaN LEDs with long emission wavelength.

  2. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

    KAUST Repository

    Mughal, Asad J.

    2017-11-27

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

  3. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

    KAUST Repository

    Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

    2017-01-01

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

  4. A High-Voltage Low-Power Switched-Capacitor DC-DC Converter Based on GaN and SiC Devices for LED Drivers

    DEFF Research Database (Denmark)

    Fan, Lin; Knott, Arnold; Jørgensen, Ivan Harald Holger

    2018-01-01

    Previous research on switched-capacitor DC-DC converters has focused on low-voltage and/or high-power ranges where the efficiencies are dominated by conduction loss. Switched-capacitor DC-DC converters at high-voltage (> 100 V) low-power (high efficiency and high power density...... are anticipated to emerge. This paper presents a switched-capacitor converter with an input voltage up to 380 V (compatible with rectified European mains) and a maximum output power of 10 W. GaN switches and SiC diodes are analytically compared and actively combined to properly address the challenges at high......-voltage low-current levels, where switching loss becomes significant. Further trade-off between conduction loss and switching loss is experimentally optimized with switching frequencies. Three variant designs of the proposed converter are implemented, and the trade-off between the efficiency and the power...

  5. Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si.

    Science.gov (United States)

    Tanaka, Atsunori; Choi, Woojin; Chen, Renjie; Dayeh, Shadi A

    2017-10-01

    Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain-relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN-on-Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack-free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10 7 cm -2 achieved to date in GaN-on-Si is demonstrated. With these advances, the first vertical GaN metal-insulator-semiconductor field-effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost-effective high power device paradigm on an Si CMOS platform are demonstrated. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

    International Nuclear Information System (INIS)

    Gao, Qingxue; Liu, Rong; Xiao, Hongdi; Cao, Dezhong; Liu, Jianqiang; Ma, Jin

    2016-01-01

    Highlights: • GaN film with a strong phase-separated InGaN/GaN layer was etched by electrochemical etching. • Vertically aligned nanopores in n-GaN films were buried underneath the InGaN/GaN structures. • The relaxation of compressive stress in the MQW structure was found by PL and Raman spectra. - Abstract: A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

  7. Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Qingxue [School of Physics, Shandong University, Jinan, 250100 (China); Liu, Rong [Department of Fundamental Theories, Shandong Institute of Physical Education and Sports, Jinan 250063 (China); Xiao, Hongdi, E-mail: hdxiao@sdu.edu.cn [School of Physics, Shandong University, Jinan, 250100 (China); Cao, Dezhong; Liu, Jianqiang; Ma, Jin [School of Physics, Shandong University, Jinan, 250100 (China)

    2016-11-30

    Highlights: • GaN film with a strong phase-separated InGaN/GaN layer was etched by electrochemical etching. • Vertically aligned nanopores in n-GaN films were buried underneath the InGaN/GaN structures. • The relaxation of compressive stress in the MQW structure was found by PL and Raman spectra. - Abstract: A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

  8. Electrical properties of cubic InN and GaN epitaxial layers as a function of temperature

    International Nuclear Information System (INIS)

    Fernandez, J.R.L.; Chitta, V.A.; Abramof, E.

    2000-01-01

    Carrier concentration and mobility were measured for intrinsic cubic InN and GaN, and for Si-doped cubic GaN as a function of temperature. Metallic n-type conductivity was found for the InN, while background p-type conductivity was observed for the intrinsic GaN layer. Doping the cubic GaN with Si two regimes were observed. For low Si-doping concentrations, the samples remain p-type. Increasing the Si-doping level, the background acceptors are compensated and the samples became highly degenerated n-type. From the carrier concentration dependence on temperature, the activation energy of the donor and acceptor levels was determined. Attempts were made to determine the scattering mechanisms responsible for the behavior of the mobility as a function of temperature

  9. Simulation of optimum parameters for GaN MSM UV photodetector

    Energy Technology Data Exchange (ETDEWEB)

    Alhelfi, Mohanad A., E-mail: mhad12344@gmail.com; Ahmed, Naser M., E-mail: nas-tiji@yahoo.com; Hashim, M. R., E-mail: roslan@usm.my; Hassan, Z., E-mail: zai@usm.my [Institue of Nano-Optoelectronics Research and Technology (INOR), School of Physics, Universiti Sains Malaysia 11800 Penang (Malaysia); Al-Rawi, Ali Amer, E-mail: aliamer@unimap.edu.my [School of Computer and Communication Eng. 3st Floor, Pauh Putra Main Campus 02600 Arau, Perlis Malaysia (Malaysia)

    2016-07-06

    In this study the optimum parameters of GaN M-S-M photodetector are discussed. The evaluation of the photodetector depends on many parameters, the most of the important parameters the quality of the GaN film and others depend on the geometry of the interdigited electrode. In this simulation work using MATLAB software with consideration of the reflection and absorption on the metal contacts, a detailed study involving various electrode spacings (S) and widths (W) reveals conclusive results in device design. The optimum interelectrode design for interdigitated MSM-PD has been specified and evaluated by effect on quantum efficiency and responsivity.

  10. Structural and optical properties of vanadium ion-implanted GaN

    Czech Academy of Sciences Publication Activity Database

    Macková, Anna; Malinský, Petr; Jagerová, Adéla; Sofer, Z.; Klímová, K.; Sedmidubský, D.; Mikulics, M.; Lorinčík, Jan; Veselá, D.; Bottger, R.; Akhmadaliev, S.

    2017-01-01

    Roč. 406, SEP (2017), s. 53-57 ISSN 0168-583X R&D Projects: GA ČR GA13-20507S; GA ČR GA15-01602S; GA MŠk LM2015056 Institutional support: RVO:61389005 ; RVO:67985882 Keywords : GaN implantation * RBS-channelling * optical properties of metal-implanted GaN Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders; JA - Electronics ; Optoelectronics, Electrical Engineering (URE-Y) OBOR OECD: Nuclear physics; Electrical and electronic engineering (URE-Y) Impact factor: 1.109, year: 2016

  11. Electron beam welding of the dissimilar Zr-based bulk metallic glass and Ti metal

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jonghyun [Department of Material Science, Kumamoto University, Kumamoto 860-8555 (Japan)], E-mail: joindoc@kumamoto-u.ac.jp; Kawamura, Y. [Department of Material Science, Kumamoto University, Kumamoto 860-8555 (Japan)

    2007-04-15

    We successfully welded 3 mm thick Zr{sub 41}Be{sub 23}Ti{sub 14}Cu{sub 12}Ni{sub 10} bulk metallic glass plate to Ti metal by electron beam welding with a beam irradiated 0.4 mm on the BMG side of the interface. There was no crystallization or defects in the weld because changes in the chemical composition of the weld metal were prevented. Bending showed that the welded sample had a higher strength than the Ti base metal. The interface had a 10 {mu}m thick interdiffusion layer of Zr and Ti.

  12. Large scale 2D/3D hybrids based on gallium nitride and transition metal dichalcogenides.

    Science.gov (United States)

    Zhang, Kehao; Jariwala, Bhakti; Li, Jun; Briggs, Natalie C; Wang, Baoming; Ruzmetov, Dmitry; Burke, Robert A; Lerach, Jordan O; Ivanov, Tony G; Haque, Md; Feenstra, Randall M; Robinson, Joshua A

    2017-12-21

    Two and three-dimensional (2D/3D) hybrid materials have the potential to advance communication and sensing technologies by enabling new or improved device functionality. To date, most 2D/3D hybrid devices utilize mechanical exfoliation or post-synthesis transfer, which can be fundamentally different from directly synthesized layers that are compatible with large scale industrial needs. Therefore, understanding the process/property relationship of synthetic heterostructures is priority for industrially relevant material architectures. Here we demonstrate the scalable synthesis of molybdenum disulfide (MoS 2 ) and tungsten diselenide (WSe 2 ) via metal organic chemical vapor deposition (MOCVD) on gallium nitride (GaN), and elucidate the structure, chemistry, and vertical transport properties of the 2D/3D hybrid. We find that the 2D layer thickness and transition metal dichalcogenide (TMD) choice plays an important role in the transport properties of the hybrid structure, where monolayer TMDs exhibit direct tunneling through the layer, while transport in few layer TMDs on GaN is dominated by p-n diode behavior and varies with the 2D/3D hybrid structure. Kelvin probe force microscopy (KPFM), low energy electron microscopy (LEEM) and X-ray photoelectron spectroscopy (XPS) reveal a strong intrinsic dipole and charge transfer between n-MoS 2 and p-GaN, leading to a degraded interface and high p-type leakage current. Finally, we demonstrate integration of heterogeneous 2D layer stacks of MoS 2 /WSe 2 on GaN with atomically sharp interface. Monolayer MoS 2 /WSe 2 /n-GaN stacks lead to near Ohmic transport due to the tunneling and non-degenerated doping, while few layer stacking is Schottky barrier dominated.

  13. Identification of deep levels in GaN associated with dislocations

    International Nuclear Information System (INIS)

    Soh, C B; Chua, S J; Lim, H F; Chi, D Z; Liu, W; Tripathy, S

    2004-01-01

    To establish a correlation between dislocations and deep levels in GaN, a deep-level transient spectroscopy study has been carried out on GaN samples grown by metalorganic chemical vapour deposition. In addition to typical undoped and Si-doped GaN samples, high-quality crack-free undoped GaN film grown intentionally on heavily doped cracked Si-doped GaN and cracked AlGaN templates are also chosen for this study. The purpose of growth of such continuous GaN layers on top of the cracked templates is to reduce the screw dislocation density by an order of magnitude. Deep levels in these layers have been characterized and compared with emphasis on their thermal stabilities and capture kinetics. Three electron traps at E c -E T ∼0.10-0.11, 0.24-0.27 and 0.59-0.63 eV are detected common to all the samples while additional levels at E c -E T ∼0.18 and 0.37-0.40 eV are also observed in the Si-doped GaN. The trap levels exhibit considerably different stabilities under rapid thermal annealing. Based on the observations, the trap levels at E c -E T ∼0.18 and 0.24-0.27 eV can be associated with screw dislocations, whereas the level at E c -E T ∼0.59-0.63 eV can be associated with edge dislocations. This is also in agreement with the transmission electron microscopy measurements conducted on the GaN samples

  14. Single phase semipolar (11 anti 22) GaN on (10 anti 10) sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Ploch, S.; Stellmach, J.; Schwaner, T.; Frentrup, M.; Wernicke, T.; Pristovsek, M.; Kneissl, M. [Institute of Solid States Physics, (Germany); Park, J.B.; Niermann, T.; Lehmann, M. [Institute of Optics and Atomic Physics, TU Berlin, Hardenbergstr. 36, 10623 Berlin (Germany)

    2011-07-01

    InGaN quantum well based light emitters grown on (0001) GaN suffer from poor quantum efficiencies with increasing indium mole fraction due to strong polarization fields along the polar crystal orientation. This effect can be greatly reduced by growing on semi- and non-polar GaN orientations. Semipolar (11 anti 22) GaN layers were deposited by metalorganic vapour phase epitaxy on (10 anti 10) sapphire. After sapphire substrate nitridation at 1000 C, a GaN nucleation layer was deposited at high temperature, followed by the deposition of 1.5 nm thick GaN buffer layers. The samples show predominantly (11 anti 22) orientation with a small fraction of (10 anti 13) oriented domains. With increasing nitridation layer thickness the (10 anti 13) phase is suppressed leading to a very smooth surface morphology (rms roughness < 4nm). PL measurements show dominant basel plane stacking fault (BSF) I{sub 1} luminescence without any other defects. Transmission electron microscopy measurements reveal a high BSF density. The FWHM of the X-ray diffraction rocking curve measurements of the (1122) reflection decreases to 1193 arcsec and 739 arcsec along [1 anti 100] and [11 anti 23] respectively with increasing nucleation temperature. Using high temperature nucleation smooth and homogeneous (11 anti 22) phase GaN layers have been obtained.

  15. Infrared reflectance of GaN films grown on Si(001) substrates

    International Nuclear Information System (INIS)

    Zhang, Xiong; Hou, Yong-Tian; Feng, Zhe-Chuan; Chen, Jin-Li

    2001-01-01

    GaN thin films on Si(001) substrates are studied by infrared reflectance (IRR) spectroscopy at room temperature (RT). Variations in the IRR spectral line shape with the microstructure of GaN/Si(011) film are quantitatively explained in terms of a three-component effective medium model. In this model, the nominally undoped GaN film is considered to consist of three elementary components, i.e., single crystalline GaN grains, pores (voids), and inter-granulated materials (amorphous GaN clusters). Such a polycrystalline nature of the GaN/Si(001) films was confirmed by scanning electron microscopy measurements. It was demonstrated that based on the proposed three-component effective medium model, excellent overall simulation of the RT-IRR spectra can be achieved, and the fine structures of the GaN reststrahlen band in the measured RT-IRR spectra can also be interpreted very well. Furthermore, the volume fraction for each component in the GaN/Si(001) film was accurately determined by fitting the experimental RT-IRR spectra with the theoretical simulation. These results indicate that IRR spectroscopy can offer a sensitive and convenient tool to probe the microstructure of GaN films grown on silicon. [copyright] 2001 American Institute of Physics

  16. Understanding the Growth Mechanism of GaN Epitaxial Layers on Mechanically Exfoliated Graphite.

    Science.gov (United States)

    Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Gan, Lin; Xu, Bingshe; Jiang, Haiwei

    2018-04-27

    The growth mechanism of GaN epitaxial layers on mechanically exfoliated graphite is explained in detail based on classic nucleation theory. The number of defects on the graphite surface can be increased via O-plasma treatment, leading to increased nucleation density on the graphite surface. The addition of elemental Al can effectively improve the nucleation rate, which can promote the formation of dense nucleation layers and the lateral growth of GaN epitaxial layers. The surface morphologies of the nucleation layers, annealed layers and epitaxial layers were characterized by field-emission scanning electron microscopy, where the evolution of the surface morphology coincided with a 3D-to-2D growth mechanism. High-resolution transmission electron microscopy was used to characterize the microstructure of GaN. Fast Fourier transform diffraction patterns showed that cubic phase (zinc-blend structure) GaN grains were obtained using conventional GaN nucleation layers, while the hexagonal phase (wurtzite structure) GaN films were formed using AlGaN nucleation layers. Our work opens new avenues for using highly oriented pyrolytic graphite as a substrate to fabricate transferable optoelectronic devices.

  17. On the phenomenon of large photoluminescence red shift in GaN nanoparticles

    KAUST Repository

    Ben Slimane, Ahmed

    2013-07-01

    We report on the observation of broad photoluminescence wavelength tunability from n-type gallium nitride nanoparticles (GaN NPs) fabricated using the ultraviolet metal-assisted electroless etching method. Transmission and scanning electron microscopy measurements performed on the nanoparticles revealed large size dispersion ranging from 10 to 100 nm. Nanoparticles with broad tunable emission wavelength from 362 to 440 nm have been achieved by exciting the samples using the excitation power-dependent method. We attribute this large wavelength tunability to the localized potential fluctuations present within the GaN matrix and to vacancy-related surface states. Our results show that GaN NPs fabricated using this technique are promising for tunable-color-temperature white light-emitting diode applications. © 2013 Slimane et al.; licensee Springer.

  18. Unstable behaviour of normally-off GaN E-HEMT under short-circuit

    Science.gov (United States)

    Martínez, P. J.; Maset, E.; Sanchis-Kilders, E.; Esteve, V.; Jordán, J.; Bta Ejea, J.; Ferreres, A.

    2018-04-01

    The short-circuit capability of power switching devices plays an important role in fault detection and the protection of power circuits. In this work, an experimental study on the short-circuit (SC) capability of commercial 600 V Gallium Nitride enhancement-mode high-electron-mobility transistors (E-HEMT) is presented. A different failure mechanism has been identified for commercial p-doped GaN gate (p-GaN) HEMT and metal-insulator-semiconductor (MIS) HEMT. In addition to the well known thermal breakdown, a premature breakdown is shown on both GaN HEMTs, triggered by hot electron trapping at the surface, which demonstrates that current commercial GaN HEMTs has requirements for improving their SC ruggedness.

  19. On the phenomenon of large photoluminescence red shift in GaN nanoparticles

    KAUST Repository

    Ben Slimane, Ahmed; Anjum, Dalaver H.; Elafandy, Rami T.; Najar, Adel; Ng, Tien Khee; San Roman Alerigi, Damian; Ooi, Boon S.

    2013-01-01

    We report on the observation of broad photoluminescence wavelength tunability from n-type gallium nitride nanoparticles (GaN NPs) fabricated using the ultraviolet metal-assisted electroless etching method. Transmission and scanning electron microscopy measurements performed on the nanoparticles revealed large size dispersion ranging from 10 to 100 nm. Nanoparticles with broad tunable emission wavelength from 362 to 440 nm have been achieved by exciting the samples using the excitation power-dependent method. We attribute this large wavelength tunability to the localized potential fluctuations present within the GaN matrix and to vacancy-related surface states. Our results show that GaN NPs fabricated using this technique are promising for tunable-color-temperature white light-emitting diode applications. © 2013 Slimane et al.; licensee Springer.

  20. Influence of Si-doping on heteroepitaxially grown a-plane GaN

    Energy Technology Data Exchange (ETDEWEB)

    Wieneke, Matthias; Bastek, Barbara; Noltemeyer, Martin; Hempel, Thomas; Rohrbeck, Antje; Witte, Hartmut; Veit, Peter; Blaesing, Juergen; Dadgar, Armin; Christen, Juergen; Krost, Alois [Otto-von-Guericke-Universitaet Magdeburg, FNW/IEP, Universitaetsplatz 2, 39106 Magdeburg (Germany)

    2011-07-01

    Si-doped a-plane GaN samples with nominal doping levels up to 10{sup 20} cm{sup -3} were grown on r-plane sapphire by metal organic vapor phase epitaxy. Silane flow rates higher than 59 nmol/min lead to three dimensional grown crystallites as revealed by scanning electron microscopy. High resolution X-ray diffraction, photoluminescence and cathodoluminescence suggest considerably reduced defect densities in the large micrometer-sized GaN crystallites. Especially, transmission electron microscopy images verify a very low density of basal plane stacking faults less than 10{sup 4} cm{sup -1} in these crystallites consisting of heteroepitaxially grown a-plane GaN. In our presentation the influence of the Si doping on the basal plane stacking faults will be discussed.

  1. Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

    Science.gov (United States)

    Sharma, Venus; Srivastava, Sunita

    2018-04-01

    Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

  2. Influence of different aspect ratios on the structural and electrical properties of GaN thin films grown on nanoscale-patterned sapphire substrates

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Fang-Wei [Department of Electrophysics, National Chiao-Tung University, Hsinchu 300, Taiwan (China); Ke, Wen-Cheng, E-mail: wcke@mail.ntust.edu.tw [Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Cheng, Chun-Hong; Liao, Bo-Wei; Chen, Wei-Kuo [Department of Electrophysics, National Chiao-Tung University, Hsinchu 300, Taiwan (China)

    2016-07-01

    Highlights: • Nanoscale patterned sapphire substrate was prepared by anodic-aluminum-oxide etching mask. • Influence of aspect ratio of NPSS on structural and electrical properties of GaN films was studied. • Low dislocation density and high carrier mobility of GaN films were grown on high aspect ratio NPSS. - Abstract: This study presents GaN thin films grown on nanoscale-patterned sapphire substrates (NPSSs) with different aspect ratios (ARs) using a homemade metal-organic chemical vapor deposition system. The anodic aluminum oxide (AAO) technique is used to prepare the dry etching mask. The cross-sectional view of the scanning electron microscope image shows that voids exist between the interface of the GaN thin film and the high-AR (i.e. ∼2) NPSS. In contrast, patterns on the low-AR (∼0.7) NPSS are filled full of GaN. The formation of voids on the high-AR NPSS is believed to be due to the enhancement of the lateral growth in the initial growth stage, and the quick-merging GaN thin film blocks the precursors from continuing to supply the bottom of the pattern. The atomic force microscopy images of GaN on bare sapphire show a layer-by-layer surface morphology, which becomes a step-flow surface morphology for GaN on a high-AR NPSS. The edge-type threading dislocation density can be reduced from 7.1 × 10{sup 8} cm{sup −2} for GaN on bare sapphire to 4.9 × 10{sup 8} cm{sup −2} for GaN on a high-AR NPSS. In addition, the carrier mobility increases from 85 cm{sup 2}/Vs for GaN on bare sapphire to 199 cm{sup 2}/Vs for GaN on a high-AR NPSS. However, the increased screw-type threading dislocation density for GaN on a low-AR NPSS is due to the competition of lateral growth on the flat-top patterns and vertical growth on the bottom of the patterns that causes the material quality of the GaN thin film to degenerate. Thus, the experimental results indicate that the AR of the particular patterning of a NPSS plays a crucial role in achieving GaN thin film with

  3. Surface/structure functionalization of copper-based catalysts by metal-support and/or metal-metal interactions

    Science.gov (United States)

    Konsolakis, Michalis; Ioakeimidis, Zisis

    2014-11-01

    Cu-based catalysts have recently attracted great attention both in catalysis and electro-catalysis fields due to their excellent catalytic performance and low cost. Given that their performance is determined, to a great extent, by Cu sites local environment, considerable efforts have been devoted on the strategic modifications of the electronic and structural properties of Cu sites. In this regard, the feasibility of tuning the local structure of Cu entities by means of metal-support or metal-metal interactions is investigated. More specifically, the physicochemical properties of Cu entities are modified by employing: (i) different oxides (CeO2, La2O3, Sm2O3), or (ii) ceria-based mixed oxides (Ce1-xSmxOδ) as supporting carriers, and (iii) a second metal (Cobalt) adjacent to Cu (bimetallic Cu-Co/CeO2). A characterization study, involving BET, XRD, TPR, and XPS, reveal that significant modifications on structural, redox and electronic properties of Cu sites can be induced by adopting either different oxide carriers or bimetallic complexes. Fundamental insights into the tuning of Cu local environment by metal-support or metal-metal interactions are provided, paving the way for real-life industrial applications.

  4. Microfluidic paper-based analytical device for particulate metals.

    Science.gov (United States)

    Mentele, Mallory M; Cunningham, Josephine; Koehler, Kirsten; Volckens, John; Henry, Charles S

    2012-05-15

    A microfluidic paper-based analytical device (μPAD) fabricated by wax printing was designed to assess occupational exposure to metal-containing aerosols. This method employs rapid digestion of particulate metals using microliters of acid added directly to a punch taken from an air sampling filter. Punches were then placed on a μPAD, and digested metals were transported to detection reservoirs upon addition of water. These reservoirs contained reagents for colorimetric detection of Fe, Cu, and Ni. Dried buffer components were used to set the optimal pH in each detection reservoir, while precomplexation agents were deposited in the channels between the sample and detection zones to minimize interferences from competing metals. Metal concentrations were quantified from color intensity images using a scanner in conjunction with image processing software. Reproducible, log-linear calibration curves were generated for each metal, with method detection limits ranging from 1.0 to 1.5 μg for each metal (i.e., total mass present on the μPAD). Finally, a standard incineration ash sample was aerosolized, collected on filters, and analyzed for the three metals of interest. Analysis of this collected aerosol sample using a μPAD showed good correlation with known amounts of the metals present in the sample. This technology can provide rapid assessment of particulate metal concentrations at or below current regulatory limits and at dramatically reduced cost.

  5. Proton irradiation effects on deep level states in Mg-doped p-type GaN grown by ammonia-based molecular beam epitaxy

    Science.gov (United States)

    Zhang, Z.; Arehart, A. R.; Kyle, E. C. H.; Chen, J.; Zhang, E. X.; Fleetwood, D. M.; Schrimpf, R. D.; Speck, J. S.; Ringel, S. A.

    2015-01-01

    The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 1013 cm-2 and 3 × 1013 cm-2 fluences not only introduces a trap with an EV + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at EV + 0.48 eV, EV + 2.42 eV, EV + 3.00 eV, and EV + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment.

  6. Ultralow threading dislocation density in GaN epilayer on near-strain-free GaN compliant buffer layer and its applications in hetero-epitaxial LEDs.

    Science.gov (United States)

    Shih, Huan-Yu; Shiojiri, Makoto; Chen, Ching-Hsiang; Yu, Sheng-Fu; Ko, Chung-Ting; Yang, Jer-Ren; Lin, Ray-Ming; Chen, Miin-Jang

    2015-09-02

    High threading dislocation (TD) density in GaN-based devices is a long unresolved problem because of the large lattice mismatch between GaN and the substrate, which causes a major obstacle for the further improvement of next-generation high-efficiency solid-state lighting and high-power electronics. Here, we report InGaN/GaN LEDs with ultralow TD density and improved efficiency on a sapphire substrate, on which a near strain-free GaN compliant buffer layer was grown by remote plasma atomic layer deposition. This "compliant" buffer layer is capable of relaxing strain due to the absorption of misfit dislocations in a region within ~10 nm from the interface, leading to a high-quality overlying GaN epilayer with an unusual TD density as low as 2.2 × 10(5) cm(-2). In addition, this GaN compliant buffer layer exhibits excellent uniformity up to a 6" wafer, revealing a promising means to realize large-area GaN hetero-epitaxy for efficient LEDs and high-power transistors.

  7. CARBON-CONTAINING COMPOSITES BASED ON METALS

    Directory of Open Access Journals (Sweden)

    VAGANOV V. E.

    2015-10-01

    Full Text Available Problem statement Among the developed technologies metal-composites production,a special place takes powder metallurgy, having fundamental differences from conventionally used foundry technologies. The main advantages of this technology are: the possibility of sensitive control, the structure and phase composition of the starting components, and ultimately the possibility of obtaining of bulk material in nanostructured state with a minimum of processing steps. The potential reinforcers metals include micro and nano-sized oxides, carbides, nitrides, whiskers. The special position is occupied with carbon nanostructures (CNS: С60 fullerenes, single-layer and multi-layer nanotubes, onions (spherical "bulbs", nano-diamonds and graphite,their properties are being intensively studied in recent years. These objects have a high thermal and electrical conductivity values, superelasticity, and have a strength approximate to the theoretical value, which can provide an obtaining composite nanomaterial with a unique set of physical and mechanical properties. In creation of a metal matrix composite nanomaterials (CM, reinforced by various CNS, a special attention should be given to mechanical activation processes (MA already at the stage of preparation of the starting components affecting the structure, phase composition and properties of aluminum-matrix composites. Purpose. To investigate the influence of mechanical activation on the structure and phase composition of aluminum-matrix composites. Conclusion. The results of the study of the structure and phase composition of the initial and mechanically activated powders and bulk-modified metal-composites are shown, depending on the type and concentration of modifying varieties CNS, regimes of MA and parameters of compaction. The study is conducted of tribological properties of Al-CNS OF nanostructured materials.

  8. The base metal of the oxide-coated cathode

    International Nuclear Information System (INIS)

    Poret, F.; Roquais, J.M.

    2005-01-01

    The oxide-coated cathode has been the most widely used electron emitter in vacuum electronic devices. From one manufacturing company to another the emissive oxide is either a double-Ba, Sr-or a triple-Ba, Sr, Ca-oxide, having always the same respective compositions. Conversely, the base metal composition is very often proprietary because of its importance in the cathode emission performances. The present paper aims at explaining the operation of the base metal through a review. After a brief introduction, the notion of activator is detailed along with their diffusivities and their associated interfacial compounds. Then, the different cathode life models are described prior to few comments on the composition choice of a base metal. Finally, the specificities of the RCA/Thomson 'bimetal' base metal are presented with a discussion on the optimized composition choice illustrated by a long-term life-test of five different melts

  9. Fracture toughness measurements of WC-based hard metals

    International Nuclear Information System (INIS)

    Prakash, L.; Albert, B.

    1983-01-01

    The fracture toughness of WC-based cemented carbides was determined by different methods. The values obtained are dependent on the procedure of measurement. Each method thoughness of hard metals mutually. (orig.) [de

  10. GaN thin films growth and their application in photocatalytic removal of sulforhodamine B from aqueous solution under UV pulsed laser irradiation.

    Science.gov (United States)

    Gondal, Mohammed A; Chang, Xiao F; Yamani, Zain H; Yang, Guo F; Ji, Guang B

    2011-01-01

    Single-crystalline Gallium Nitride (GaN) thin films were fabricated and grown by metal organic chemical vapor deposition (MOCVD) method on c-plane sapphire substrates and then characterized by high resolution-X-ray diffraction (HR-XRD) and photoluminescence (PL) measurements. The photocatalytic decomposition of Sulforhodamine B (SRB) molecules on GaN thin films was investigated under 355 nm pulsed UV laser irradiation. The results demonstrate that as-grown GaN thin films exhibited efficient degradation of SRB molecules and exhibited an excellent photocatalytic-activity-stability under UV pulsed laser exposure.

  11. Exploration of the catalytic use of alkali metal bases

    OpenAIRE

    Bao, Wei

    2017-01-01

    This PhD thesis project was concerned with the use of alkali metal amide Brønsted bases and alkali metal alkoxide Lewis bases in (asymmetric) catalysis. The first chapter deals with formal allylic C(sp3)–H bond activation of aromatic and functionalized alkenes for subsequent C–C and C–H bond formations. The second chapter is focused on C(sp3)–Si bond activation of fluorinated pro-nucleophiles in view of C–C bond formations. In the first chapter, a screening of various metal amides...

  12. Transition-Metal-Free Biomolecule-Based Flexible Asymmetric Supercapacitors.

    Science.gov (United States)

    Yang, Yun; Wang, Hua; Hao, Rui; Guo, Lin

    2016-09-01

    A transition-metal-free asymmetric supercapacitor (ASC) is successfully fabricated based on an earth-abundant biomass derived redox-active biomolecule, named lawsone. Such an ASC exhibits comparable or even higher energy densities than most of the recently reported transition-metal-based ASCs, and this green ASC generation from renewable resources is promising for addressing current issues of electronic hazard processing, high cost, and unsustainability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Yi-gan san restores behavioral alterations and a decrease of brain glutathione level in a mouse model of schizophrenia.

    Science.gov (United States)

    Makinodan, Manabu; Yamauchi, Takahira; Tatsumi, Kouko; Okuda, Hiroaki; Noriyama, Yoshinobu; Sadamatsu, Miyuki; Kishimoto, Toshifumi; Wanaka, Akio

    2009-01-01

    The traditional Chinese herbal medicine yi-gan san has been used to cure neuropsychological disorders. Schizophrenia can be one of the target diseases of yi-gan san. We aimed at evaluating the possible use of yi-gan san in improving the schizophrenic symptoms of an animal model. Yi-gan san or distilled water was administered to mice born from pregnant mice injected with polyinosinic-polycytidilic acid or phosphate buffered saline. The former is a model of schizophrenia based on the epidemiological data that maternal infection leads to psychotic disorders including schizophrenia in the offspring. Prepulse inhibition and sensitivity to methamphetamine in open field tests were analyzed and the total glutathione content of whole brains was measured. Yi-gan san reversed the decrease in prepulse inhibition, hypersensitivity to methamphetamine and cognitive deficits found in the model mice to the level of control mice. Total glutathione content in whole brains was reduced in the model mice but was restored to normal levels by yi-gan san treatment. These results suggest that yi-gan san may have ameliorating effects on the pathological symptoms of schizophrenia.

  14. Yi-Gan San Restores Behavioral Alterations and a Decrease of Brain Glutathione Level in a Mouse Model of Schizophrenia

    Directory of Open Access Journals (Sweden)

    Manabu Makinodan M.D.

    2009-01-01

    Full Text Available The traditional Chinese herbal medicine yi-gan san has been used to cure neuropsychological disorders. Schizophrenia can be one of the target diseases of yi-gan san. We aimed at evaluating the possible use of yi-gan san in improving the schizophrenic symptoms of an animal model. Yi-gan san or distilled water was administered to mice born from pregnant mice injected with polyinosinic-polycytidilic acid or phosphate buffered saline. The former is a model of schizophrenia based on the epidemiological data that maternal infection leads to psychotic disorders including schizophrenia in the offspring. Prepulse inhibition and sensitivity to methamphetamine in open field tests were analyzed and the total glutathione content of whole brains was measured. Yi-gan san reversed the decrease in prepulse inhibition, hypersensitivity to methamphetamine and cognitive deficits found in the model mice to the level of control mice. Total glutathione content in whole brains was reduced in the model mice but was restored to normal levels by yi-gan san treatment. These results suggest that yi-gan san may have ameliorating effects on the pathological symptoms of schizophrenia.

  15. Influence of growth temperature and temperature ramps on deep level defect incorporation in m-plane GaN

    International Nuclear Information System (INIS)

    Armstrong, A. M.; Kelchner, K.; Nakamura, S.; DenBaars, S. P.; Speck, J. S.

    2013-01-01

    The dependence of deep level defect incorporation in m-plane GaN films grown by metal-organic chemical vapor deposition on bulk m-plane GaN substrates as a function of growth temperature (T g ) and T g ramping method was investigated using deep level optical spectroscopy. Understanding the influence of T g on GaN deep level incorporation is important for InGaN/GaN multi-quantum well (MQW) light emitting diodes (LEDs) and laser diodes (LDs) because GaN quantum barrier (QB) layers are grown much colder than thin film GaN to accommodate InGaN QW growth. Deep level spectra of low T g (800 °C) GaN films grown under QB conditions were compared to deep level spectra of high T g (1150 °C) GaN. Reducing T g , increased the defect density significantly (>50×) through introduction of emergent deep level defects at 2.09 eV and 2.9 eV below the conduction band minimum. However, optimizing growth conditions during the temperature ramp when transitioning from high to low T g substantially reduced the density of these emergent deep levels by approximately 40%. The results suggest that it is important to consider the potential for non-radiative recombination in QBs of LED or LD active regions, and tailoring the transition from high T g GaN growth to active layer growth can mitigate such non-radiative channels

  16. Growth and characterizations of GaN micro-rods on graphene films for flexible light emitting diodes

    Directory of Open Access Journals (Sweden)

    Kunook Chung

    2014-09-01

    Full Text Available We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto SiO2/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metal–organic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance light-emitting diodes (LEDs, were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, InxGa1–xN/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation.

  17. Photoconductive GaN UV Detectors

    National Research Council Canada - National Science Library

    Baranowski, Jacek

    1999-01-01

    This report results from a contract tasking University of Warsaw as follows: The contractor will investigate the growth of GaN material using atmospheric pressure metalorganic chemical vapor deposition method (MOCVD...

  18. High current density 2D/3D MoS2/GaN Esaki tunnel diodes

    Science.gov (United States)

    Krishnamoorthy, Sriram; Lee, Edwin W.; Lee, Choong Hee; Zhang, Yuewei; McCulloch, William D.; Johnson, Jared M.; Hwang, Jinwoo; Wu, Yiying; Rajan, Siddharth

    2016-10-01

    The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current density of 446 A/cm2 with repeatable room temperature negative differential resistance, peak to valley current ratio of 1.2, and minimal hysteresis was measured in the MoS2/GaN non-epitaxial tunnel diode. A high current density of 1 kA/cm2 was measured in the Zener mode (reverse bias) at -1 V bias. The GaN/MoS2 tunnel junction was also modeled by treating MoS2 as a bulk semiconductor, and the electrostatics at the 2D/3D interface was found to be crucial in explaining the experimentally observed device characteristics.

  19. A new kind of metal detector based on chaotic oscillator

    Science.gov (United States)

    Hu, Wenjing

    2017-12-01

    The sensitivity of a metal detector greatly depends on the identification ability to weak signals from the probe. In order to improve the sensitivity of metal detectors, this paper applies the Duffing chaotic oscillator to metal detectors based on its characteristic which is very sensitive to weak periodic signals. To make a suitable Duffing system for detectors, this paper computes two Lyapunov characteristics exponents of the Duffing oscillator, which help to obtain the threshold of the Duffing system in the critical state accurately and give quantitative criteria for chaos. Meanwhile, a corresponding simulation model of the chaotic oscillator is made by the Simulink tool box of Matlab. Simulation results shows that Duffing oscillator is very sensitive to sinusoidal signals in high frequency cases. And experimental results show that the measurable diameter of metal particles is about 1.5mm. It indicates that this new method can feasibly and effectively improve the metal detector sensitivity.

  20. Rare earth point defects in GaN

    Energy Technology Data Exchange (ETDEWEB)

    Sanna, S.

    2007-12-14

    In this work we investigate rare earth doped GaN, by means of theoretical simulations. The huge unit cells necessary to model the experimental system, where dilute amount of rare earth ions are used, are handled with the charge self consistent density-functional based-tight binding (SCC-DFTB) calculational scheme. The method has been extended to include LDA+U and simplified self interaction corrected (SIC)-like potentials for the simulation of systems with localised and strongly correlated electrons. A set of tight-binding parameters has been created to model the interaction of GaN with some dopants, including a selection of lanthanide ions interesting due to their optical or magnetic properties (Pr, Eu, Gd, Er and Tm). The f-electrons were treated as valence electrons. A qualitatively correct description of the band gap is crucial for the simulation of rare earth doped GaN, because the luminescence intensity of the implanted samples depends on the size of the host band gap and because the rare earths could introduce charge transition levels near the conduction band. In this work these levels are calculated with the Slater-Janak (SJ) transition state model, which allows an approximate calculation of the charge transition levels by analysing the Kohn-Sham eigenvalues of the DFT. (orig.)

  1. Metallic ion release from biocompatible cobalt-based alloy

    Directory of Open Access Journals (Sweden)

    Dimić Ivana D.

    2014-01-01

    Full Text Available Metallic biomaterials, which are mainly used for the damaged hard tissue replacements, are materials with high strength, excellent toughness and good wear resistance. The disadvantages of metals as implant materials are their susceptibility to corrosion, the elastic modulus mismatch between metals and human hard tissues, relatively high density and metallic ion release which can cause serious health problems. The aim of this study was to examine metallic ion release from Co-Cr-Mo alloy in artificial saliva. In that purpose, alloy samples were immersed into artificial saliva with different pH values (4.0, 5.5 and 7.5. After a certain immersion period (1, 3 and 6 weeks the concentrations of released ions were determined using Inductively Coupled Plasma - Mass Spectrophotometer (ICP-MS. The research findings were used in order to define the dependence between the concentration of released metallic ions, artificial saliva pH values and immersion time. The determined released metallic ions concentrations were compared with literature data in order to describe and better understand the phenomenon of metallic ion release from the biocompatible cobalt-based alloy. [Projekat Ministarstva nauke Republike Srbije, br. III 46010 i br. ON 174004

  2. Doping of GaN by ion implantation: Does It Work?

    International Nuclear Information System (INIS)

    Suvkhanov, A.; Wu, W.; Price, K.; Parikh, N.; Irene, E.; Hunn, J.; Thomson, D.; Davis, R.F.; Krasnobaev, L.

    1998-04-01

    Epitaxially grown GaN by metal organic chemical vapor deposition (MOCVD) on SiC were implanted with 100 keV Si + (for n-type) and 80 keV Mg + (for p-type) with various fluences from 1 x 10 12 to 7 x 10 15 ions/cm 2 at liquid nitrogen temperature (LT), room temperature (RT), and 700 C (HT). High temperature (1,200 C and 1,500 C) annealing was carried out after capping the GaN with epitaxial AlN by MOCVD to study damage recovery. Samples were capped by a layer of AlN in order to protect the GaN surface during annealing. Effects of implant temperature, damage and dopant activation are critically studied to evaluate a role of ion implantation in doping of GaN. The damage was studied by Rutherford Backscattering/Channeling, spectroscopic ellipsometry and photoluminescence. Results show dependence of radiation damage level on temperature of the substrate during implantation: implantations at elevated temperatures up to 550 C decrease the lattice disorder; hot implants above 550 C can not be useful in doping of GaN due to nitrogen loss from the surface. SE measurements have indicated very high sensitivity to the implantation damage. PL measurements at LT of 80 keV Mg + (5 x 10 14 cm 2 ) implanted and annealed GaN showed two peaks: one ∼ 100 meV and another ∼ 140 meV away from the band edge

  3. Hydrogen-surfactant-assisted coherent growth of GaN on ZnO substrate

    Science.gov (United States)

    Zhang, Jingzhao; Zhang, Yiou; Tse, Kinfai; Zhu, Junyi

    2018-01-01

    Heterostructures of wurtzite based devices have attracted great research interest because of the tremendous success of GaN in light emitting diodes (LED) industry. High-quality GaN thin films on inexpensive and lattice matched ZnO substrates are both commercially and technologically desirable. Intrinsic wetting conditions, however, forbid such heterostructures as the energy of ZnO polar surfaces is much lower than that of GaN polar surfaces, resulting in 3D growth mode and poor crystal quality. Based on first-principles calculations, we propose the use of surfactant hydrogen to dramatically alter the growth mode of the heterostructures. Stable H-involved surface configurations and interfaces are investigated with the help of our newly developed modelling techniques. The temperature and chemical potential dependence of our proposed strategy, which is critical in experiments, is predicted by applying the experimental Gibbs free energy of H2. Our thermodynamic wetting condition analysis is a crucial step for the growth of GaN on ZnO, and we find that introducing H will not degrade the stability of ZnO substrate. This approach will allow the growth of high-quality GaN thin films on ZnO substrates. We believe that our new strategy may reduce the manufactory cost, improve the crystal quality, and improve the efficiency of GaN-based devices.

  4. Piezo-generator integrating a vertical array of GaN nanowires.

    Science.gov (United States)

    Jamond, N; Chrétien, P; Houzé, F; Lu, L; Largeau, L; Maugain, O; Travers, L; Harmand, J C; Glas, F; Lefeuvre, E; Tchernycheva, M; Gogneau, N

    2016-08-12

    We demonstrate the first piezo-generator integrating a vertical array of GaN nanowires (NWs). We perform a systematic multi-scale analysis, going from single wire properties to macroscopic device fabrication and characterization, which allows us to establish for GaN NWs the relationship between the material properties and the piezo-generation, and to propose an efficient piezo-generator design. The piezo-conversion of individual MBE-grown p-doped GaN NWs in a dense array is assessed by atomic force microscopy (AFM) equipped with a Resiscope module yielding an average output voltage of 228 ± 120 mV and a maximum value of 350 mV generated per NW. In the case of p-doped GaN NWs, the piezo-generation is achieved when a positive piezo-potential is created inside the nanostructures, i.e. when the NWs are submitted to compressive deformation. The understanding of the piezo-generation mechanism in our GaN NWs, gained from AFM analyses, is applied to design a piezo-generator operated under compressive strain. The device consists of NW arrays of several square millimeters in size embedded into spin-on glass with a Schottky contact for rectification and collection of piezo-generated carriers. The generator delivers a maximum power density of ∼12.7 mW cm(-3). This value sets the new state of the art for piezo-generators based on GaN NWs and more generally on nitride NWs, and offers promising prospects for the use of GaN NWs as high-efficiency ultra-compact energy harvesters.

  5. Structure and properties of transition metal-metalloid glasses based on refractory metals

    International Nuclear Information System (INIS)

    Johnson, W.L.; Williams, A.R.

    1979-01-01

    The structure and properties of several new transition metal-metalloid (TM/sub 1-x/M/sub x/) metallic glasses based on refractory transition metals (e.g. Mo, W, Ru etc.) have been systemically investigated as a function of composition. The structure of the alloys has been investigated by x-ray diffraction methods and measurements of superconducting properties, electrical resistivity, density, hardness, and mechanical behavior were made. These data are used in developing a novel description of the structure of TM/sub 1-x/M/sub x/ glasses. The experimental evidence suggests that an ideal amorphous phase forms at a specific composition x/sub c/ and that this phase has a well defined atomic short range order. For metallic glasses having x x/sub c/. This novel picture can explain the variation of many properties of these glasses with metalloid concentration

  6. Effects of Mn Ion Implantation on XPS Spectroscopy of GaN Thin Films

    Science.gov (United States)

    Majid, Abdul; Ahmad, Naeem; Rizwan, Muhammad; Khan, Salah Ud-Din; Ali, Fekri Abdulraqeb Ahmed; Zhu, Jianjun

    2018-02-01

    Gallium nitride (GaN) thin film was deposited onto a sapphire substrate and then implanted with 250 keV Mn ions at two different doses of 2 × 1016 ions/cm2 and 5 × 1016 ions/cm2. The as-grown and post-implantation-thermally-annealed samples were studied in detail using x-ray photoelectron spectroscopy (XPS). The XPS peaks of Ga 3 d, Ga 2 p, N 1 s, Mn 2 p and C 1 s were recorded in addition to a full survey of the samples. The doublet peaks of Ga 2 p for pure GaN were observed blue-shifted when compared with elemental Ga, and appeared further shifted to higher energies for the implanted samples. These observations point to changes in the bonds and the chemical environment of the host as a result of ion implantation. The results revealed broadening of the N 1 s peak after implantation, which is interpreted in terms of the presence of N-Mn bonds in addition to N-Ga bonds. The XPS spectra of Mn 2 p recorded for ion-implanted samples indicated splitting of Mn 2 p 1/2 and Mn 2 p 3/2 peaks higher than that for metallic Mn, which helps rule out the possibility of clustering and points to substitutional doping of Mn. These observations provide a framework that sheds light on the local environment of the material for understanding the mechanism of magnetic exchange interactions in Mn:GaN based diluted magnetic semiconductors.

  7. All-Metallic Vertical Transistors Based on Stacked Dirac Materials

    OpenAIRE

    Wang, Yangyang; Ni, Zeyuan; Liu, Qihang; Quhe, Ruge; Zheng, Jiaxin; Ye, Meng; Yu, Dapeng; Shi, Junjie; Yang, Jinbo; Lu, Jing

    2014-01-01

    It is an ongoing pursuit to use metal as a channel material in a field effect transistor. All metallic transistor can be fabricated from pristine semimetallic Dirac materials (such as graphene, silicene, and germanene), but the on/off current ratio is very low. In a vertical heterostructure composed by two Dirac materials, the Dirac cones of the two materials survive the weak interlayer van der Waals interaction based on density functional theory method, and electron transport from the Dirac ...

  8. Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing of GaN

    Science.gov (United States)

    Wang, Jie; Wang, Tongqing; Pan, Guoshun; Lu, Xinchun

    2016-08-01

    Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing (CMP) of GaN were deeply investigated in this paper. Working as an ideal homogeneous substrate material in LED industry, GaN ought to be equipped with a smooth and flat surface. Taking the strong chemical stability of GaN into account, photocatalytic oxidation technology was adopted in GaN CMP process to realize efficient removal. It was found that, because of the improved reaction rate of photocatalytic oxidation, GaN material removal rate (MRR) increases by a certain extent with catalyst concentration increasing. Cross single line analysis on the surface after polishing by Phase Shift MicroXAM-3D was carried out to prove the better removal effect with higher catalyst concentration. Ultraviolet intensity field in H2O2-SiO2-based polishing system was established and simulated, revealing the variation trend of ultraviolet intensity around the outlet of the slurry. It could be concluded that, owing to the higher planarization efficiency and lower energy damage, the UV lamp of 125 W is the most appropriate lamp in this system. Based on the analysis, defects removal model of this work was proposed to describe the effects of higher catalyst concentration and higher power of UV lamp.

  9. Individual GaN nanowires exhibit strong piezoelectricity in 3D.

    Science.gov (United States)

    Minary-Jolandan, Majid; Bernal, Rodrigo A; Kuljanishvili, Irma; Parpoil, Victor; Espinosa, Horacio D

    2012-02-08

    Semiconductor GaN NWs are promising components in next generation nano- and optoelectronic systems. In addition to their direct band gap, they exhibit piezoelectricity, which renders them particularly attractive in energy harvesting applications for self-powered devices. Nanowires are often considered as one-dimensional nanostructures; however, the electromechanical coupling leads to a third rank tensor that for wurtzite crystals (GaN NWs) possesses three independent coefficients, d(33), d(13), and d(15). Therefore, the full piezoelectric characterization of individual GaN NWs requires application of electric fields in different directions and measurements of associated displacements on the order of several picometers. In this Letter, we present an experimental approach based on scanning probe microscopy to directly quantify the three-dimensional piezoelectric response of individual GaN NWs. Experimental results reveal that GaN NWs exhibit strong piezoelectricity in three dimensions, with up to six times the effect in bulk. Based on finite element modeling, this finding has major implication on the design of energy harvesting systems exhibiting unprecedented levels of power density production. The presented method is applicable to other piezoelectric NW materials as well as wires manufactured along different crystallographic orientations. © 2011 American Chemical Society

  10. Microstructures and growth mechanisms of GaN films epitaxially grown on AlN/Si hetero-structures by pulsed laser deposition at different temperatures.

    Science.gov (United States)

    Wang, Wenliang; Yang, Weijia; Lin, Yunhao; Zhou, Shizhong; Li, Guoqiang

    2015-11-13

    2 inch-diameter GaN films with homogeneous thickness distribution have been grown on AlN/Si(111) hetero-structures by pulsed laser deposition (PLD) with laser rastering technique. The surface morphology, crystalline quality, and interfacial property of as-grown GaN films are characterized in detail. By optimizing the laser rastering program, the ~300 nm-thick GaN films grown at 750 °C show a root-mean-square (RMS) thickness inhomogeneity of 3.0%, very smooth surface with a RMS surface roughness of 3.0 nm, full-width at half-maximums (FWHMs) for GaN(0002) and GaN(102) X-ray rocking curves of 0.7° and 0.8°, respectively, and sharp and abrupt AlN/GaN hetero-interfaces. With the increase in the growth temperature from 550 to 850 °C, the surface morphology, crystalline quality, and interfacial property of as-grown ~300 nm-thick GaN films are gradually improved at first and then decreased. Based on the characterizations, the corresponding growth mechanisms of GaN films grown on AlN/Si hetero-structures by PLD with various growth temperatures are hence proposed. This work would be beneficial to understanding the further insight of the GaN films grown on Si(111) substrates by PLD for the application of GaN-based devices.

  11. The Formation and Characterization of GaN Hexagonal Pyramids

    Science.gov (United States)

    Zhang, Shi-Ying; Xiu, Xiang-Qian; Lin, Zeng-Qin; Hua, Xue-Mei; Xie, Zi-Li; Zhang, Rong; Zheng, You-Dou

    2013-05-01

    GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method. Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination, producing submicron-sized pyramids. Hexagonal pyramids on the etched GaN with well-defined {101¯1¯} facets and very sharp tips are formed. High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality, and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN. The cathodoluminescence intensity of GaN after etching is significantly increased by three times, which is attributed to the reduction in the internal reflection, high-quality GaN with pyramids and the Bragg effect.

  12. A Frontal Attack on Limiting Defects in GaN

    National Research Council Canada - National Science Library

    Morkoc, Hadis

    2002-01-01

    GaN community, particularly under the leadership of Drs. Wood, Win, and Litton, recognized that it is imperative that the extended, and point defects in GaN and related materials, and the mechanisms for their formation are understood...

  13. Synthetic Strategies and Applications of GaN Nanowires

    Directory of Open Access Journals (Sweden)

    Guoquan Suo

    2014-01-01

    Full Text Available GaN is an important III-V semiconductor material with a direct band gap of 3.4 eV at 300 K. The wide direct band gap makes GaN an attractive material for various applications. GaN nanowires have demonstrated significant potential as fundamental building blocks for nanoelectronic and nanophotonic devices and also offer substantial promise for integrated nanosystems. In this paper, we provide a comprehensive review on the general synthetic strategies, characterizations, and applications of GaN nanowires. We first summarize several growth techniques of GaN nanowires. Subsequently, we discuss mechanisms involved to generate GaN nanowires from different synthetic schemes and conditions. Then we review some characterization methods of GaN nanowires. Finally, several kinds of main applications of GaN nanowires are discussed.

  14. Effect of annealing time and NH3 flow on GaN films deposited on amorphous SiO2 by MOCVD

    Science.gov (United States)

    Li, Tianbao; Liu, Chenyang; Zhang, Zhe; Yu, Bin; Dong, Hailiang; Jia, Wei; Jia, Zhigang; Yu, Chunyan; Xu, Bingshe

    2018-05-01

    GaN polycrystalline films were successfully grown on amorphous SiO2 by metal-organic chemical vapour deposition to fabricate transferable devices using inorganic films. Field-emission scanning electron microscopy images show that by prolonging the annealing time, re-evaporation is enhanced, which reduced the uniformity of the nucleation layer and GaN films. X-ray diffraction patterns indicate that the decomposition rate of the nucleation layer increases when the annealing flow rate of NH3 is 500 sccm, which makes the unstable plane and amorphous domains decompose rapidly, thereby improving the crystallinity of the GaN films. Photoluminescence spectra also indicate the presence of fewer defects when the annealing flow rate of NH3 is 500 sccm. The excellent crystal structure of the GaN films grown under optimized conditions was revealed by transmission electron microscopy analysis. More importantly, the crystal structure and orientation of GaN grown on SiO2 are the same as that of GaN grown on conventional sapphire substrate when a buffer layer is used. This work can aid in the development of transferable devices using GaN films.

  15. Improved linearity and reliability in GaN metal-oxide-semiconductor high-electron-mobility transistors using nanolaminate La2O3/SiO2 gate dielectric

    Science.gov (United States)

    Hsu, Ching-Hsiang; Shih, Wang-Cheng; Lin, Yueh-Chin; Hsu, Heng-Tung; Hsu, Hisang-Hua; Huang, Yu-Xiang; Lin, Tai-Wei; Wu, Chia-Hsun; Wu, Wen-Hao; Maa, Jer-Shen; Iwai, Hiroshi; Kakushima, Kuniyuki; Chang, Edward Yi

    2016-04-01

    Improved device performance to enable high-linearity power applications has been discussed in this study. We have compared the La2O3/SiO2 AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) with other La2O3-based (La2O3/HfO2, La2O3/CeO2 and single La2O3) MOS-HEMTs. It was found that forming lanthanum silicate films can not only improve the dielectric quality but also can improve the device characteristics. The improved gate insulation, reliability, and linearity of the 8 nm La2O3/SiO2 MOS-HEMT were demonstrated.

  16. Surface plasmons based terahertz modulator consisting of silicon-air-metal-dielectric-metal layers

    Science.gov (United States)

    Wang, Wei; Yang, Dongxiao; Qian, Zhenhai

    2018-05-01

    An optically controlled modulator of the terahertz wave, which is composed of a metal-dielectric-metal structure etched with circular loop arrays on both the metal layers and a photoexcited silicon wafer separated by an air layer, is proposed. Simulation results based on experimentally measured complex permittivities predict that modification of complex permittivity of the silicon wafer through excitation laser leads to a significant tuning of transmission characteristics of the modulator, forming the modulation depths of 59.62% and 96.64% based on localized surface plasmon peak and propagating surface plasmon peak, respectively. The influences of the complex permittivity of the silicon wafer and the thicknesses of both the air layer and the silicon wafer are numerically studied for better understanding the modulation mechanism. This study proposes a feasible methodology to design an optically controlled terahertz modulator with large modulation depth, high speed and suitable insertion loss, which is useful for terahertz applications in the future.

  17. Graphite-based extinguishants for liquid metal fires

    International Nuclear Information System (INIS)

    Simpson, J.M.; Gardener, N.J.L.

    1987-01-01

    Effective extinguishants for liquid alkali metal fires must be provided for all LMFBRs. Traditional sodium salt based extinguishants have disadvantages. An intercalation compound of graphite was identified as a possible alternative. Following successful tests on fires of up to 25 m 2 area the graphite based extinguishant has been introduced by the UKAEA at Dounreay. (author)

  18. Artificial tongue based on metal-biomolecule coordination polymer nanoparticles.

    Science.gov (United States)

    Pu, Fang; Ran, Xiang; Ren, Jinsong; Qu, Xiaogang

    2016-02-25

    We construct an array-based recognition system (the so-called artificial tongue) through the self-assembly of nucleotides, dyes and lanthanide ions. Metal ions are selected as model analytes for verifying its discrimination ability. The work provides valuable insights into the application and development of biomolecule-based materials.

  19. Metal hydride-based thermal energy storage systems

    Science.gov (United States)

    Vajo, John J.; Fang, Zhigang

    2017-10-03

    The invention provides a thermal energy storage system comprising a metal-containing first material with a thermal energy storage density of about 1300 kJ/kg to about 2200 kJ/kg based on hydrogenation; a metal-containing second material with a thermal energy storage density of about 200 kJ/kg to about 1000 kJ/kg based on hydrogenation; and a hydrogen conduit for reversibly transporting hydrogen between the first material and the second material. At a temperature of 20.degree. C. and in 1 hour, at least 90% of the metal is converted to the hydride. At a temperature of 0.degree. C. and in 1 hour, at least 90% of the metal hydride is converted to the metal and hydrogen. The disclosed metal hydride materials have a combination of thermodynamic energy storage densities and kinetic power capabilities that previously have not been demonstrated. This performance enables practical use of thermal energy storage systems for electric vehicle heating and cooling.

  20. The study of electronic structures and optical properties of Al-doped GaN

    International Nuclear Information System (INIS)

    Li Enling; Hou Liping; Liu Mancang; Xi Meng; Wang Xiqiang; Dai Yuanbin; Li Lisha

    2011-01-01

    The electronic structures and optical properties of undoped and Al-doped GaN (Al x Ga 1-x N, x=0.0625, 0.125, 0.25) have been studied based on generalized gradient approximation (GGA) method of density functional theory (DFT). The differences of the electronic structures and optical properties of undoped and Al-doped GaN have been discussed in detail. The result shows: according to total density of state of undoped and Al-doped GaN, the conduction band becomes width and moves to high energy level with gradual increase concentration of Al impurity. Impurity energy band isn't found in energy band structures of Al x Ga 1-x N, the same as energy band structures of undoped GaN, but the band gaps gradually become wide with increase of Al impurity. Absorption spectra of undoped and Al-doped GaN of main absorption peak moves to high energy level with increase of Al impurity.

  1. Nanoscale imaging of surface piezoresponse on GaN epitaxial layers

    International Nuclear Information System (INIS)

    Stoica, T.; Calarco, R.; Meijers, R.; Lueth, H.

    2007-01-01

    Surfaces of GaN films were investigated by atomic force microscopy (AFM) with implemented piezoelectric force microscopy technique. A model of PFM based on the surface depletion region in GaN films is discussed. The local piezoelectric effect of the low frequency regime was found to be in phase with the applied voltage on large domains, corresponding to a Ga-face of the GaN layer. Low piezoresponse is obtained within the inter-domain regions. The use of frequencies near a resonance frequency enhances very much the resolution of piezo-imaging, but only for very low scanning speed the piezo-imaging can follow the local piezoelectric effect. An inversion of the PFM image contrast is obtained for frequencies higher than the resonance frequencies. The effect of a chemical surface treatment on the topography and the piezoresponse of the GaN films was also investigated. Textured surfaces with very small domains were observed after the chemical treatment. For this kind of surfaces, piezo-induced torsion rather than bending of the AFM cantilever dominates the contrast of the PFM images. A small memory effect was observed, and explained by surface charging and confinement of the piezoelectric effect within the carrier depletion region at the GaN surface

  2. Mechanisms of current flow in metal-semiconductor ohmic contacts

    International Nuclear Information System (INIS)

    Blank, T. V.; Gol'dberg, Yu. A.

    2007-01-01

    Published data on the properties of metal-semiconductor ohmic contacts and mechanisms of current flow in these contacts (thermionic emission, field emission, thermal-field emission, and also current flow through metal shunts) are reviewed. Theoretical dependences of the resistance of an ohmic contact on temperature and the charge-carrier concentration in a semiconductor were compared with experimental data on ohmic contacts to II-VI semiconductors (ZnSe, ZnO), III-V semiconductors (GaN, AlN, InN, GaAs, GaP, InP), Group IV semiconductors (SiC, diamond), and alloys of these semiconductors. In ohmic contacts based on lightly doped semiconductors, the main mechanism of current flow is thermionic emission with the metal-semiconductor potential barrier height equal to 0.1-0.2 eV. In ohmic contacts based on heavily doped semiconductors, the current flow is effected owing to the field emission, while the metal-semiconductor potential barrier height is equal to 0.3-0.5 eV. In alloyed In contacts to GaP and GaN, a mechanism of current flow that is not characteristic of Schottky diodes (current flow through metal shunts formed by deposition of metal atoms onto dislocations or other imperfections in semiconductors) is observed

  3. Simulations of Operation Dynamics of Different Type GaN Particle Sensors

    Science.gov (United States)

    Gaubas, Eugenijus; Ceponis, Tomas; Kalesinskas, Vidas; Pavlov, Jevgenij; Vysniauskas, Juozas

    2015-01-01

    The operation dynamics of the capacitor-type and PIN diode type detectors based on GaN have been simulated using the dynamic and drift-diffusion models. The drift-diffusion current simulations have been implemented by employing the software package Synopsys TCAD Sentaurus. The monopolar and bipolar drift regimes have been analyzed by using dynamic models based on the Shockley-Ramo theorem. The carrier multiplication processes determined by impact ionization have been considered in order to compensate carrier lifetime reduction due to introduction of radiation defects into GaN detector material. PMID:25751080

  4. Selectively Enhanced UV-A Photoresponsivity of a GaN MSM UV Photodetector with a Step-Graded AlxGa1-xN Buffer Layer.

    Science.gov (United States)

    Lee, Chang-Ju; Won, Chul-Ho; Lee, Jung-Hee; Hahm, Sung-Ho; Park, Hongsik

    2017-07-21

    The UV-to-visible rejection ratio is one of the important figure of merits of GaN-based UV photodetectors. For cost-effectiveness and large-scale fabrication of GaN devices, we tried to grow a GaN epitaxial layer on silicon substrate with complicated buffer layers for a stress-release. It is known that the structure of the buffer layers affects the performance of devices fabricated on the GaN epitaxial layers. In this study, we show that the design of a buffer layer structure can make effect on the UV-to-visible rejection ratio of GaN UV photodetectors. The GaN photodetector fabricated on GaN-on-silicon substrate with a step-graded Al x Ga -x N buffer layer has a highly-selective photoresponse at 365-nm wavelength. The UV-to-visible rejection ratio of the GaN UV photodetector with the step-graded Al x Ga 1-x N buffer layer was an order-of-magnitude higher than that of a photodetector with a conventional GaN/AlN multi buffer layer. The maximum photoresponsivity was as high as 5 × 10 - ² A/W. This result implies that the design of buffer layer is important for photoresponse characteristics of GaN UV photodetectors as well as the crystal quality of the GaN epitaxial layers.

  5. First-Principle Study of the Optical Properties of Dilute-P GaN1-xPx Alloys.

    Science.gov (United States)

    Borovac, Damir; Tan, Chee-Keong; Tansu, Nelson

    2018-04-16

    An investigation on the optical properties of dilute-P GaN 1-x P x alloys by First-Principle Density Functional Theory (DFT) methods is presented, for phosphorus (P) content varying from 0% up to 12.5%. Findings on the imaginary and real part of the dielectric function are analyzed and the results are compared with previously reported theoretical works on GaN. The complex refractive index, normal-incidence reflectivity and birefringence are presented and a difference in the refractive index in the visible regime between GaN and GaNP alloys of ~0.3 can be engineered by adding minute amounts of phosphorus, indicating strong potential for refractive index tunability. The optical properties of the GaN 1-x P x alloys indicate their strong potential for implementation in various III-nitride-based photonic waveguide applications and Distributed Bragg Reflectors (DBR).

  6. Efficient photoelectrochemical water splitting by a doping-controlled GaN photoanode coated with NiO cocatalyst

    International Nuclear Information System (INIS)

    Kang, Jin-Ho; Kim, Soo Hee; Ebaid, Mohamed; Lee, June Key; Ryu, Sang-Wan

    2014-01-01

    Efficient photoelectrochemical (PEC) water splitting was demonstrated by a doping-controlled GaN photoanode coated with NiO cocatalyst. Highly doped n-GaN was sandwiched between undoped GaN layers to effectively collect electrons through ohmic contact. With zero external bias, the photocurrent density of the optimized doping profile was ∼3.5 times higher than that of the undoped GaN reference. However, the increased doping concentration degraded the photoanode stability, which was attributed to crystalline defects generated in the highly doped n-GaN. NiO cocatalyst improved the long-term stability of the photoanode because of GaN/NiO band alignment, enhancing hole transport into NiO and suppressing PEC corrosion mediated by hole crowding in GaN. This work established a design strategy for increasing the photocurrent as well as improving stability during water splitting with a GaN-based photoanode

  7. Free-standing GaN grating couplers and rib waveguide for planar photonics at telecommunication wavelength

    Science.gov (United States)

    Liu, Qifa; Wang, Wei

    2018-01-01

    Gallium Nitride (GaN) free-standing planar photonic device at telecommunication wavelength based on GaN-on-silicon platform was presented. The free-standing structure was realized by particular double-side fabrication process, which combining GaN front patterning, Si substrate back releasing and GaN slab etching. The actual device parameters were identified via the physical characterizations employing scanning electron microscope (SEM), atomic force microscope (AFM) and reflectance spectra testing. High coupling efficiency and good light confinement properties of the gratings and rib waveguide at telecommunication wavelength range were verified by finite element method (FEM) simulation. This work illustrates the potential of new GaN photonic structure which will enable new functions for planar photonics in communication and sensing applications, and is favorable for the realization of integrated optical circuit.

  8. Epitaxial condition and polarity in GaN grown on a HfN-buffered Si(111) wafer

    Science.gov (United States)

    Xu, X.; Armitage, R.; Shinkai, Satoko; Sasaki, Katsutaka; Kisielowski, C.; Weber, E. R.

    2005-05-01

    Single-crystal GaN thin films have been deposited epitaxially on a HfN-buffered Si(111) substrates by molecular-beam epitaxy. The microstructural and compositional characteristics of the films were studied in detail by transmission electron microscopy (TEMs). Cross-sectional TEM investigations have revealed the crystallographic orientation relationship in different GaN /HfN/Si layers. GaN film polarity is studied by conventional TEM and convergent beam electron diffraction simulations, and the results show that the GaN film has a Ga polarity with relatively high density of inversion domains. Based on our observations, growth mechanisms related to the structural properties are discussed.

  9. Photoluminescence enhancement from GaN by beryllium doping

    Science.gov (United States)

    García-Gutiérrez, R.; Ramos-Carrazco, A.; Berman-Mendoza, D.; Hirata, G. A.; Contreras, O. E.; Barboza-Flores, M.

    2016-10-01

    High quality Be-doped (Be = 0.19 at.%) GaN powder has been grown by reacting high purity Ga diluted alloys (Be-Ga) with ultra high purity ammonia in a horizontal quartz tube reactor at 1200 °C. An initial low-temperature treatment to dissolve ammonia into the Ga melt produced GaN powders with 100% reaction efficiency. Doping was achieved by dissolving beryllium into the gallium metal. The powders synthesized by this method regularly consist of two particle size distributions: large hollow columns with lengths between 5 and 10 μm and small platelets in a range of diameters among 1 and 3 μm. The GaN:Be powders present a high quality polycrystalline profile with preferential growth on the [10 1 bar 1] plane, observed by means of X-ray diffraction. The three characteristics growth planes of the GaN crystalline phase were found by using high resolution TEM microscopy. The optical enhancing of the emission in the GaN powder is attributed to defects created with the beryllium doping. The room temperature photoluminescence emission spectra of GaN:Be powders, revealed the presence of beryllium on a shoulder peak at 3.39 eV and an unusual Y6 emission at 3.32eV related to surface donor-acceptor pairs. Also, a donor-acceptor-pair transition at 3.17 eV and a phonon replica transition at 3.1 eV were observed at low temperature (10 K). The well-known yellow luminescence band coming from defects was observed in both spectra at room and low temperature. Cathodoluminescence emission from GaN:Be powders presents two main peaks associated with an ultraviolet band emission and the yellow emission known from defects. To study the trapping levels related with the defects formed in the GaN:Be, thermoluminescence glow curves were obtained using UV and β radiation in the range of 50 and 150 °C.

  10. Plasmonic modulator based on thin metal-semiconductor-metal waveguide with gain core

    DEFF Research Database (Denmark)

    Babicheva, Viktoriia; Malureanu, Radu; Lavrinenko, Andrei

    2013-01-01

    We focus on plasmonic modulators with a gain core to be implemented as active nanodevices in photonic integrated circuits. In particular, we analyze metal–semiconductor–metal (MSM) waveguides with InGaAsP-based active material layers. A MSM waveguide enables high field localization and therefore...

  11. Biomaterial based novel polyurethane adhesives for wood to wood and metal to metal bonding

    Directory of Open Access Journals (Sweden)

    Mitesh Ramanlal Patel

    2009-01-01

    Full Text Available Polyurethane adhesives made from synthetic chemicals are non-biodegradable, costly and difficult to find raw materials from local market. To avoid solid pollution problem, cost effectiveness and easy availability of raw materials, biomaterials based polyurethane adhesives are used in current industrial interest. Direct use of castor oil in polyurethane adhesive gives limited hardness. Modification on active sites of castor oil to utilize double bond of unsaturated fatty acid and carboxyl group yields new modified or activated polyols, which can be utilized for polyurethane adhesive formulation. In view of this, we have synthesized polyurethane adhesives from polyester polyols, castor oil based polyols and epoxy based polyols with Isocyanate adducts based on castor oil and trimethylolpropane. To study the effects of polyurethane adhesive strength (i.e. lap shear strength on wood-to-wood and metal-to-metal bonding through various types of polyols, cross-linking density, isocyanate adducts and also to compare adhesive strength between wood to wood and metal to metal surface. These polyols and polyurethanes were characterized through GPC, NMR and IR-spectroscopy, gel and surface drying time. Thermal stability of PU adhesives was determined under the effect of cross-linking density (NCO/OH ratio. The NCO/OH ratio (1.5 was optimized for adhesives as the higher NCO/OH ratio (2.0 increasing cross-linking density and decreases adhesion. Lower NCO/OH ratio (1.0 provideslow cross-linking density and low strength of adhesives.

  12. Thermal behaviors of liquid La-based bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, D. W.; Wang, X. D., E-mail: wangxd@zju.edu.cn, E-mail: jiangjz@zju.edu.cn; Lou, H. B.; Cao, Q. P.; Jiang, J. Z., E-mail: wangxd@zju.edu.cn, E-mail: jiangjz@zju.edu.cn [International Center for New-Structured Materials (ICNSM), Laboratory of New-Structured Materials, State Key Laboratory of Silicon Materials, and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Wang, L. W. [Institute of Materials Science and Engineering, Lanzhou University, Lanzhou 730000 (China); Zhang, D. X. [State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027 (China)

    2014-12-14

    Thermal behaviors of liquid La-based bulk metallic glasses have been measured by using the dilatometer with a self-sealed sample cell. It is demonstrated that the strong glass forming liquid not only has the small thermal expansion coefficient but also shows the slow variation rate. Moreover, the strong glass former has relatively dense atomic packing and also small density change in the liquid state. The results suggest that the high glass forming ability of La-based metallic glasses would be closely related to the slow atomic rearrangements in liquid melts.

  13. Incorporation of Mg in Free-Standing HVPE GaN Substrates

    Science.gov (United States)

    Zvanut, M. E.; Dashdorj, J.; Freitas, J. A.; Glaser, E. R.; Willoughby, W. R.; Leach, J. H.; Udwary, K.

    2016-06-01

    Mg, the only effective p-type dopant for nitrides, is well studied in thin films due to the important role of the impurity in light-emitting diodes and high-power electronics. However, there are few reports of Mg in thick free-standing GaN substrates. Here, we demonstrate successful incorporation of Mg into GaN grown by hydride vapor-phase epitaxy (HVPE) using metallic Mg as the doping source. The concentration of Mg obtained from four separate growth runs ranged between 1016 cm-3 and 1019 cm-3. Raman spectroscopy and x-ray diffraction revealed that Mg did not induce stress or perturb the crystalline quality of the HVPE GaN substrates. Photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies were performed to investigate the types of point defects in the crystals. The near-band-edge excitonic and shallow donor-shallow acceptor radiative recombination processes involving shallow Mg acceptors were prominent in the PL spectrum of a sample doped to 3 × 1018 cm-3, while the EPR signal was also thought to represent a shallow Mg acceptor. Detection of this signal reflects minimization of nonuniform strain obtained in the thick free-standing HVPE GaN compared with heteroepitaxial thin films.

  14. Investigations on 40 MeV Li3+ ions irradiated GaN epilayers

    International Nuclear Information System (INIS)

    Suresh Kumar, V.; Kumar, J.; Kanjilal, D.; Asokan, K.; Mohanty, T.; Tripathi, A.; Rossi, Francisca; Zappettini, A.; Lazzarani, L.; Ferrari, C.

    2008-01-01

    The Metal Organic Chemical Vapour Deposition (MOCVD) grown n-type Gallium nitride (GaN) layers on sapphire (0 0 0 1) substrates have been irradiated at low and room temperatures with 40 MeV Li 3+ ions at the fluence of 1 x 10 13 ions cm -2 . Irradiated samples were characterised by using X-ray diffraction (XRD), photoluminescence (PL), Raman spectroscopy and atomic force microscopy (AFM). XRD results show that the formation of Ga 2 O 3 has been observed upon irradiation. This is due to interface mixing of GaN/Al 2 O 3 , at both temperatures. Also the GaN (0 0 0 2) peak splits into two at low temperature irradiation. PL measurements show a yellow emission band shift towards blue band side upon irradiation at 77 K. Raman studies indicate that the lattice disorder is high at room temperature irradiation compared to low temperature irradiation. AFM images indicate the increasing surface roughness after ion irradiation at room temperature when compared to pristine GaN and low temperature irradiated GaN. These observations are discussed in detail with the use of complementary techniques

  15. Epitaxy of GaN on silicon-impact of symmetry and surface reconstruction

    International Nuclear Information System (INIS)

    Dadgar, A; Schulze, F; Wienecke, M; Gadanecz, A; Blaesing, J; Veit, P; Hempel, T; Diez, A; Christen, J; Krost, A

    2007-01-01

    GaN-on-silicon is a low-cost alternative to growth on sapphire or SiC. Today epitaxial growth is usually performed on Si(111), which has a threefold symmetry. The growth of single crystalline GaN on Si(001), the material of the complementary metal oxide semiconductor (CMOS) industry, is more difficult due to the fourfold symmetry of this Si surface leading to two differently aligned domains. We show that breaking the symmetry to achieve single crystalline growth can be performed, e.g. by off-oriented substrates to achieve single crystalline device quality GaN layers. Furthermore, an exotic Si orientation for GaN growth is Si(110), which we show is even better suited as compared to Si(111) for the growth of high quality GaN-on-silicon with a nearly threefold reduction in the full width at half maximum (FWHM) of the (1 1-bar 0 0)ω-scan. It is found that a twofold surface symmetry is in principal suitable for the growth of single crystalline GaN on Si

  16. Production and properties of light-metal base amorphous alloys

    International Nuclear Information System (INIS)

    Inoue, Akihisa; Masumoto, Tsuyoshi

    1993-01-01

    Light-metal base alloys with high specific strength and good corrosion resistance were produced through amorphization of Al and Mg-based alloys. The amorphous phase is formed in rapidly solidified Al-TM-Ln and Mg-TM-Ln (TM=transition metal, Ln=lanthanide metal) alloys. The highest tensile strength (σ f ) reaches 1,330 MPa for the Al base and 830 MPa for the Mg base. Furthermore, the Mg-based alloys have a large glass-forming capacity which enables to produce an amorphous phase by a metallic mold casting method. The extrusion of the Al-based amorphous powders at temperatures above crystallization temperature caused the formation of high strength materials with finely mixed structure consisting of dispersed intermetallic compounds in an Al matrix. The highest values of σ f and fatigue limit are as high as 940 and 313 MPa, respectively, at room temperature and 520 and 165 MPa at 473 K. The extruded Al-Ni-Mm alloy has already been used as machine parts and subsequent further development as practical materials is expected by taking these advantages

  17. Antimicrobial resistance challenged with metal-based antimicrobial macromolecules.

    Science.gov (United States)

    Abd-El-Aziz, Alaa S; Agatemor, Christian; Etkin, Nola

    2017-02-01

    Antimicrobial resistance threatens the achievements of science and medicine, as it deactivates conventional antimicrobial therapeutics. Scientists respond to the threat by developing new antimicrobial platforms to prevent and treat infections from these resistant strains. Metal-based antimicrobial macromolecules are emerging as an alternative to conventional platforms because they combine multiple mechanisms of action into one platform due to the distinctive properties of metals. For example, metals interact with intracellular proteins and enzymes, and catalyse various intracellular processes. The macromolecular architecture offers a means to enhance antimicrobial activity since several antimicrobial moieties can be conjugated to the scaffold. Further, these macromolecules can be fabricated into antimicrobial materials for contact-killing medical implants, fabrics, and devices. As volatilization or leaching out of the antimicrobial moieties from the macromolecular scaffold is reduced, these medical implants, fabrics, and devices can retain their antimicrobial activity over an extended period. Recent advances demonstrate the potential of metal-based antimicrobial macromolecules as effective platforms that prevent and treat infections from resistant strains. In this review these advances are thoroughly discussed within the context of examples of metal-based antimicrobial macromolecules, their mechanisms of action and biocompatibility. Copyright © 2016 Elsevier Ltd. All rights reserved.

  18. Charge transport in metal oxide nanocrystal-based materials

    Science.gov (United States)

    Runnerstrom, Evan Lars

    There is probably no class of materials more varied, more widely used, or more ubiquitous than metal oxides. Depending on their composition, metal oxides can exhibit almost any number of properties. Of particular interest are the ways in which charge is transported in metal oxides: devices such as displays, touch screens, and smart windows rely on the ability of certain metal oxides to conduct electricity while maintaining visible transparency. Smart windows, fuel cells, and other electrochemical devices additionally rely on efficient transport of ionic charge in and around metal oxides. Colloidal synthesis has enabled metal oxide nanocrystals to emerge as a relatively new but highly tunable class of materials. Certain metal oxide nanocrystals, particularly highly doped metal oxides, have been enjoying rapid development in the last decade. As in myriad other materials systems, structure dictates the properties of metal oxide nanocrystals, but a full understanding of how nanocrystal synthesis, the processing of nanocrystal-based materials, and the structure of nanocrystals relate to the resulting properties of nanocrystal-based materials is still nascent. Gaining a fundamental understanding of and control over these structure-property relationships is crucial to developing a holistic understanding of metal oxide nanocrystals. The unique ability to tune metal oxide nanocrystals by changing composition through the introduction of dopants or by changing size and shape affords a way to study the interplay between structure, processing, and properties. This overall goal of this work is to chemically synthesize colloidal metal oxide nanocrystals, process them into useful materials, characterize charge transport in materials based on colloidal metal oxide nanocrystals, and develop ways to manipulate charge transport. In particular, this dissertation characterizes how the charge transport properties of metal oxide nanocrystal-based materials depend on their processing and

  19. Three-dimensionally structured silicon as a substrate for the MOVPE growth of GaN nanoLEDs

    Energy Technology Data Exchange (ETDEWEB)

    Fuendling, Soenke; Li, Shunfeng; Soekmen, Uensal; Merzsch, Stephan; Peiner, Erwin; Wehmann, Hergo-Heinrich; Waag, Andreas [Institut fuer Halbleitertechnik, TU Braunschweig, Braunschweig (Germany); Hinze, Peter; Weimann, Thomas [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany); Jahn, Uwe; Trampert, Achim; Riechert, Henning [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany)

    2009-06-15

    Three-dimensionally patterned Si(111) substrates are used to grow GaN based heterostructures by metalorganic vapour phase epitaxy, with the goal of fabricating well controlled, defect reduced GaN-based nanoLEDs. In contrast to other approaches to achieve GaN nanorods, we employed silicon substrates with deep etched nanopillars to control the GaN nanorods growth by varying the size and distance of the Si pillars. The small footprint of GaN nanorods grown on Si pillars minimise the influence of the lattice mismatched substrate and improve the material quality. For the Si pillars an inductively coupled plasma dry-etching process at cryogenic temperature has been developed. An InGaN/GaN multi quantum well (MQW) structure has been incorporated into the GaN nanorods. We found GaN nanostructures grown on top of the silicon pillars with a pyramidal shape. This shape results from a competitive growth on different facets as well as from surface diffusion of the growth species. Spatially resolved optical properties of the structures are analysed by cathodoluminescence. Strongly spatial-dependent MQW emission spectra indicate the growth rate differences on top of the rods. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Study of the dosimetric response of Gallium Nitride (GaN): modeling, simulation and characterization on radiotherapy

    International Nuclear Information System (INIS)

    Wang, Ruoxi

    2015-01-01

    The work in this thesis has the objective to increase the measurement precision of the dosimetry based on the Gallium Nitride (GaN) transducer and develop its applications on radiotherapy. The study includes the aspects of modeling, simulation and characterization of this response in external radiotherapy and brachytherapy. In modeling, we have proposed two approaches to model the GaN transducer's response in external radiotherapy. For the first approach, a model has been built based on experimental data, while separating the primary and scattering component of the beam. For the second approach, we have adopted a response model initially developed for the silicon diodes for the GaN radioluminescent transducer. We have also proposed an original concept of bi-media dosimetry which evaluates the dose in tissue according to different responses from two media without prior information on the conditions of irradiation. This concept has been shown by Monte Carlo simulation. Moreover, for High Dose Rate brachytherapy, the response of GaN transducer irradiated by iridium 192 and cobalt 60 sources has been evaluated by Monte Carlo simulation and confirmed by the measurements. Studies on the property characterization of GaN radioluminescent transducer has been carried out with these sources as well. An instrumented phantom prototype with GaN probe has been developed for the HDR brachytherapy quality control. It allows a real-time verification of the physics parameters of a treatment (source dwell position, source dwell time, source activity). (author) [fr

  1. Photophysics of GaN single-photon emitters in the visible spectral range

    Science.gov (United States)

    Berhane, Amanuel M.; Jeong, Kwang-Yong; Bradac, Carlo; Walsh, Michael; Englund, Dirk; Toth, Milos; Aharonovich, Igor

    2018-04-01

    In this work, we present a detailed photophysical analysis of recently discovered, optically stable single-photon emitters (SPEs) in gallium nitride (GaN). Temperature-resolved photoluminescence measurements reveal that the emission lines at 4 K are three orders of magnitude broader than the transform-limited width expected from excited-state lifetime measurements. The broadening is ascribed to ultrafast spectral diffusion. The photophysical study on several emitters at room temperature (RT) reveals an average brightness of (427 ±215 )kCounts /s . Finally, polarization measurements from 14 emitters are used to determine visibility as well as dipole orientation of defect systems within the GaN crystal. Our results underpin some of the fundamental properties of SPEs in GaN both at cryogenic and RT, and define the benchmark for future work in GaN-based single-photon technologies.

  2. Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

    Science.gov (United States)

    Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

    2008-12-01

    Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

  3. Spintronic materials and devices based on antiferromagnetic metals

    OpenAIRE

    Wang, Y.Y.; Song, C.; Zhang, J.Y.; Pan, F.

    2017-01-01

    In this paper, we review our recent experimental developments on antiferromagnet (AFM) spintronics mainly comprising Mn-based noncollinear AFM metals. IrMn-based tunnel junctions and Hall devices have been investigated to explore the manipulation of AFM moments by magnetic fields, ferromagnetic materials and electric fields. Room-temperature tunneling anisotropic magnetoresistance based on IrMn as well as FeMn has been successfully achieved, and electrical control of the AFM exchange spring i...

  4. DFT study on metal-mediated uracil base pair complexes

    Directory of Open Access Journals (Sweden)

    Ayhan Üngördü

    2017-11-01

    Full Text Available The most stable of metal-mediated uracil base pair complexes were determined. Method was used density functional theory, B3LYP. The calculations of systems containing C, H, N, O were described by 6-311++G(d,p and cc-PVTZ basis sets and LANL2DZ and SDD basis sets was used for transition metals. Then Egap values of complexes were calculated and the electrical conductivity of the complexes for single nanowires was studied by band theory. Metal-mediated uracil base pair complexes which will be used as conductive wires in nanotechnology were predicted. In nanoworld, this study is expected to show a way for practical applications.

  5. GaN microring waveguide resonators bonded to silicon substrate by a two-step polymer process.

    Science.gov (United States)

    Hashida, Ryohei; Sasaki, Takashi; Hane, Kazuhiro

    2018-03-20

    Using a polymer bonding technique, GaN microring waveguide resonators were fabricated on a Si substrate for future hybrid integration of GaN and Si photonic devices. The designed GaN microring consisted of a rib waveguide having a core of 510 nm in thickness, 1000 nm in width, and a clad of 240 nm in thickness. A GaN crystalline layer of 1000 nm in thickness was grown on a Si(111) substrate by metal organic chemical vapor deposition using a buffer layer of 300 nm in thickness for the compensation of lattice constant mismatch between GaN and Si crystals. The GaN/Si wafer was bonded to a Si(100) wafer by a two-step polymer process to prevent it from trapping air bubbles. The bonded GaN layer was thinned from the backside by a fast atom beam etching to remove the buffer layer and to generate the rib waveguides. The transmission characteristics of the GaN microring waveguide resonators were measured. The losses of the straight waveguides were measured to be 4.0±1.7  dB/mm around a wavelength of 1.55 μm. The microring radii ranged from 30 to 60 μm, where the measured free-spectral ranges varied from 2.58 to 5.30 nm. The quality factors of the microring waveguide resonators were from 1710 to 2820.

  6. Halide based MBE of crystalline metals and oxides

    Energy Technology Data Exchange (ETDEWEB)

    Greenlee, Jordan D.; Calley, W. Laws; Henderson, Walter; Doolittle, W. Alan [Georgia Institute of Technology, School of Electrical and Computer Engineering, Atlanta, Georgia (United States)

    2012-02-15

    A halide based growth chemistry has been demonstrated which can deliver a range of transition metals using low to moderate effusion cell temperatures (30-700 C) even for high melting point metals. Previously, growth with transition metal species required difficult to control electron beam or impurity inducing metal organic sources. Both crystalline oxide and metal films exhibiting excellent crystal quality are grown using this halide-based growth chemistry. Films are grown using a plasma assisted Molecular Beam Epitaxy (MBE) system with metal-chloride precursors. Crystalline niobium, cobalt, iron, and nickel were grown using this chemistry but the technology can be generalized to almost any metal for which a chloride precursor is available. Additionally, the oxides LiNbO{sub 3} and LiNbO{sub 2} were grown with films exhibiting X-ray diffraction (XRD) rocking curve full-widths at half maximum of 150 and 190 arcseconds respectively. LiNbO{sub 2} films demonstrate a memristive response due to the rapid movement of lithium in the layered crystal structure. The rapid movement of lithium ions in LiNbO{sub 2} memristors is characterized using impedance spectroscopy measurements. The impedance spectroscopy measurements suggest an ionic current of.1 mA for a small drive voltage of 5 mV AC or equivalently an ionic current density of {proportional_to}87 A/cm{sup 2}. This high ionic current density coupled with low charge transfer resistance of {proportional_to}16.5 {omega} and a high relaxation frequency (6.6 MHz) makes this single crystal material appealing for battery applications in addition to memristors. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. RenderGAN: Generating Realistic Labeled Data

    Directory of Open Access Journals (Sweden)

    Leon Sixt

    2018-06-01

    Full Text Available Deep Convolutional Neuronal Networks (DCNNs are showing remarkable performance on many computer vision tasks. Due to their large parameter space, they require many labeled samples when trained in a supervised setting. The costs of annotating data manually can render the use of DCNNs infeasible. We present a novel framework called RenderGAN that can generate large amounts of realistic, labeled images by combining a 3D model and the Generative Adversarial Network framework. In our approach, image augmentations (e.g., lighting, background, and detail are learned from unlabeled data such that the generated images are strikingly realistic while preserving the labels known from the 3D model. We apply the RenderGAN framework to generate images of barcode-like markers that are attached to honeybees. Training a DCNN on data generated by the RenderGAN yields considerably better performance than training it on various baselines.

  8. A transparent electrode based on a metal nanotrough network.

    Science.gov (United States)

    Wu, Hui; Kong, Desheng; Ruan, Zhichao; Hsu, Po-Chun; Wang, Shuang; Yu, Zongfu; Carney, Thomas J; Hu, Liangbing; Fan, Shanhui; Cui, Yi

    2013-06-01

    Transparent conducting electrodes are essential components for numerous flexible optoelectronic devices, including touch screens and interactive electronics. Thin films of indium tin oxide-the prototypical transparent electrode material-demonstrate excellent electronic performances, but film brittleness, low infrared transmittance and low abundance limit suitability for certain industrial applications. Alternatives to indium tin oxide have recently been reported and include conducting polymers, carbon nanotubes and graphene. However, although flexibility is greatly improved, the optoelectronic performance of these carbon-based materials is limited by low conductivity. Other examples include metal nanowire-based electrodes, which can achieve sheet resistances of less than 10Ω □(-1) at 90% transmission because of the high conductivity of the metals. To achieve these performances, however, metal nanowires must be defect-free, have conductivities close to their values in bulk, be as long as possible to minimize the number of wire-to-wire junctions, and exhibit small junction resistance. Here, we present a facile fabrication process that allows us to satisfy all these requirements and fabricate a new kind of transparent conducting electrode that exhibits both superior optoelectronic performances (sheet resistance of ~2Ω □(-1) at 90% transmission) and remarkable mechanical flexibility under both stretching and bending stresses. The electrode is composed of a free-standing metallic nanotrough network and is produced with a process involving electrospinning and metal deposition. We demonstrate the practical suitability of our transparent conducting electrode by fabricating a flexible touch-screen device and a transparent conducting tape.

  9. Schiff base transition metal complexes for Suzuki–Miyaura cross

    Indian Academy of Sciences (India)

    Schiff base ligand and its complex with iron (Fe), cobalt (Co), nickel (Ni) and copper (Cu) ions were synthesized using 4-aminoacetophenone and salicylaldehyde and characterized. FTIR spectrum shows that bidentate coordination of metal ions with ligand where O, N are electron donating sites of azomethine group.

  10. Indicator minerals as guides to base metal sulphide mineralisation ...

    Indian Academy of Sciences (India)

    Zn-bearing minerals that act as indicator minerals for base metal sulphide mineralization from the Proterozoic Betul Belt,central India with special emphasis on their genetic significance have been discussed.Sulphide mineralisation is hosted by the felsic volcanic rocks and has similarities with volcanic-hosted massive ...

  11. Hydrometallurgical Approach for Leaching of Metals from Copper Rich Side Stream Originating from Base Metal Production

    Directory of Open Access Journals (Sweden)

    Udit Surya Mohanty

    2018-01-01

    Full Text Available Pyrometallurgical metal production results in side streams, such as dusts and slags, which are carriers of metals, though commonly containing lower metal concentrations compared to the main process stream. In order to improve the circular economy of metals, selective leaching of copper from an intermediate raw material originating from primary base metal production plant was investigated. The raw material investigated was rich in Cu (12.5%, Ni (2.6%, Zn (1.6%, and Fe (23.6% with the particle size D80 of 124 µm. The main compounds present were nickel ferrite (NiFe2O4, fayalite (Fe2SiO4, cuprite (Cu2O, and metallic copper. Leaching was studied in 16 different solutions. The results revealed that copper phases could be dissolved with high yield (>90% and selectivity towards nickel (Cu/Ni > 7 already at room temperature with the following solutions: 0.5 M HCl, 1.5 M HCl, 4 M NaOH, and 2 M HNO3. A concentration of 4 M NaOH provided a superior selectivity between Cu/Ni (340 and Cu/Zn (51. In addition, 1–2 M HNO3 and 0.5 M HCl solutions were shown to result in high Pb dissolution (>98%. Consequently, 0.5 M HCl leaching is suggested to provide a low temperature, low chemical consumption method for selective copper removal from the investigated side stream, resulting in PLS (pregnant leach solution which is a rich in Cu and lead free residue, also rich in Ni and Fe.

  12. White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates

    Science.gov (United States)

    Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

    2017-06-01

    We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

  13. White light emission of monolithic InGaN/GaN grown on morphology-controlled, nanostructured GaN templates.

    Science.gov (United States)

    Song, Keun Man; Kim, Do-Hyun; Kim, Jong-Min; Cho, Chu-Young; Choi, Jehyuk; Kim, Kahee; Park, Jinsup; Kim, Hogyoug

    2017-06-02

    We demonstrated an InGaN/GaN-based, monolithic, white light-emitting diode (LED) without phosphors by using morphology-controlled active layers formed on multi-facet GaN templates containing polar and semipolar surfaces. The nanostructured surface morphology was controlled by changing the growth time, and distinct multiple photoluminescence peaks were observed at 360, 460, and 560 nm; these features were caused by InGaN/GaN-based multiple quantum wells (MQWs) on the nanostructured facets. The origin of each multi-peak was related to the different indium (In) compositions in the different planes of the quantum wells grown on the nanostructured GaN. The emitting units of MQWs in the LED structures were continuously connected, which is different from other GaN-based nanorod or nanowire LEDs. Therefore, the suggested structure had a larger active area. From the electroluminescence spectrum of the fabricated LED, monolithic white light emission with CIE color coordinates of x = 0.306 and y = 0.333 was achieved via multi-facet control combined with morphology control of the metal organic chemical vapor deposition-selective area growth of InGaN/GaN MQWs.

  14. Gan-Hang tectonic belt and its geologic significance

    International Nuclear Information System (INIS)

    Deng Jiarui; Zhang Zhiping.

    1989-01-01

    Gan-Hang tectonic belt is predominantly controlled by Gan-Hang fracture zone. It is mainly composed of Yongfeng-Zhuji downwarping zone, Gan-Hang volcanic activity structural belt and Gan-Hang red basin downfaulted zone. Gan-Hang fracture zone is derived from evolution and development of Shaoxing-Jiangshan deep fracture. It is mainly composed of three deep and large fracture and Fuzhou-Yongfeng large fracture. The fracture zone is a long active belt, but in each active period the geologic structural patterns intensity, depth and forming time were not same. Gan-Hang tectonic belt possesses obvious inheritance. It has always maintained the character of the relative depression or low land since the Caledonian movement. This specific structural environment is favourable for uranium mineralization. At any rate, the formation of this uranium minerogenetic zone has been experiencing a long and complicated processes which were closely associated with long activity of Gan-Hang fracture zone

  15. Piezotronic Effect in Polarity-Controlled GaN Nanowires.

    Science.gov (United States)

    Zhao, Zhenfu; Pu, Xiong; Han, Changbao; Du, Chunhua; Li, Linxuan; Jiang, Chunyan; Hu, Weiguo; Wang, Zhong Lin

    2015-08-25

    Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.

  16. Chemical sensors based on molecularly modified metallic nanoparticles

    International Nuclear Information System (INIS)

    Haick, Hossam

    2007-01-01

    This paper presents a concise, although admittedly non-exhaustive, didactic review of some of the main concepts and approaches related to the use of molecularly modified metal nanoparticles in or as chemical sensors. This paper attempts to pull together different views and terminologies used in sensors based on molecularly modified metal nanoparticles, including those established upon electrochemical, optical, surface Plasmon resonance, piezoelectric and electrical transduction approaches. Finally, this paper discusses briefly the main advantages and disadvantages of each of the presented class of sensors. (review article)

  17. Additively manufactured metallic porous biomaterials based on minimal surfaces

    DEFF Research Database (Denmark)

    Bobbert, F. S. L.; Lietaert, K.; Eftekhari, Ali Akbar

    2017-01-01

    Porous biomaterials that simultaneously mimic the topological, mechanical, and mass transport properties of bone are in great demand but are rarely found in the literature. In this study, we rationally designed and additively manufactured (AM) porous metallic biomaterials based on four different...... of bone properties is feasible, biomaterials that could simultaneously mimic all or most of the relevant bone properties are rare. We used rational design and additive manufacturing to develop porous metallic biomaterials that exhibit an interesting combination of topological, mechanical, and mass...

  18. Energy reversible switching from amorphous metal based nanoelectromechanical switch

    KAUST Repository

    Mayet, Abdulilah M.; Smith, Casey; Hussain, Muhammad Mustafa

    2013-01-01

    We report observation of energy reversible switching from amorphous metal based nanoelectromechanical (NEM) switch. For ultra-low power electronics, NEM switches can be used as a complementary switching element in many nanoelectronic system applications. Its inherent zero power consumption because of mechanical detachment is an attractive feature. However, its operating voltage needs to be in the realm of 1 volt or lower. Appropriate design and lower Young's modulus can contribute achieving lower operating voltage. Therefore, we have developed amorphous metal with low Young's modulus and in this paper reporting the energy reversible switching from a laterally actuated double electrode NEM switch. © 2013 IEEE.

  19. Energy reversible switching from amorphous metal based nanoelectromechanical switch

    KAUST Repository

    Mayet, Abdulilah M.

    2013-08-01

    We report observation of energy reversible switching from amorphous metal based nanoelectromechanical (NEM) switch. For ultra-low power electronics, NEM switches can be used as a complementary switching element in many nanoelectronic system applications. Its inherent zero power consumption because of mechanical detachment is an attractive feature. However, its operating voltage needs to be in the realm of 1 volt or lower. Appropriate design and lower Young\\'s modulus can contribute achieving lower operating voltage. Therefore, we have developed amorphous metal with low Young\\'s modulus and in this paper reporting the energy reversible switching from a laterally actuated double electrode NEM switch. © 2013 IEEE.

  20. Mechanism of nucleation and growth of catalyst-free self-organized GaN columns by MOVPE

    Science.gov (United States)

    Wang, Xue; Li, Shunfeng; Fündling, Sönke; Wehmann, Hergo-H.; Strassburg, Martin; Lugauer, Hans-Jürgen; Steegmüller, Ulrich; Waag, Andreas

    2013-05-01

    The growth mechanism of catalyst-free self-organized GaN nuclei and three-dimensional columns on sapphire by metal organic vapour phase epitaxy (MOVPE) is investigated. Temperature- and time-dependent growth is performed. The growth behaviour can be characterized by two different kinetic regimes: mass-transport-limited growth and thermodynamically limited growth. The sum of activation energies for thermodynamic barrier of nucleation and for surface diffusion/mass-transport limitation, i.e. Whet +Ed, is 0.57 eV in the ‘low’-temperature region and 2.43 eV in the ‘high’-temperature region. GaN columns grown under the same conditions have very comparable height, which is not dependent on their diameter or the distance to other columns. Therefore, the growth rate is presumably limited by the incorporation rate on the top surface of columns. The height and diameter at the top of the GaN columns increase linearly with time and no height limit is observed. The GaN columns can reach more than 40 µm in height. Moreover, the investigated GaN columns are Ga-polar.

  1. Atomic-scale structure of irradiated GaN compared to amorphised GaP and GaAs

    International Nuclear Information System (INIS)

    Ridgway, M.C.; Everett, S.E.; Glover, C.J.; Kluth, S.M.; Kluth, P.; Johannessen, B.; Hussain, Z.S.; Llewellyn, D.J.; Foran, G.J.; Azevedo, G. de M.

    2006-01-01

    We have compared the atomic-scale structure of ion irradiated GaN to that of amorphised GaP and GaAs. While continuous and homogenous amorphised layers were easily achieved in GaP and GaAs, ion irradiation of GaN yielded both structural and chemical inhomogeneities. Transmission electron microscopy revealed GaN crystallites and N 2 bubbles were interspersed within an amorphous GaN matrix. The crystallite orientation was random relative to the unirradiated epitaxial structure, suggesting their formation was irradiation-induced, while the crystallite fraction was approximately constant for all ion fluences beyond the amorphisation threshold, consistent with a balance between amorphisation and recrystallisation processes. Extended X-ray absorption fine structure measurements at the Ga K-edge showed short-range order was retained in the amorphous phase for all three binary compounds. For ion irradiated GaN, the stoichiometric imbalance due to N 2 bubble formation was not accommodated by Ga-Ga bonding in the amorphous phase or precipitation of metallic Ga but instead by a greater reduction in Ga coordination number

  2. Stress engineering in GaN structures grown on Si(111) substrates by SiN masking layer application

    Energy Technology Data Exchange (ETDEWEB)

    Szymański, Tomasz, E-mail: tomasz.szymanski@pwr.edu.pl; Wośko, Mateusz; Paszkiewicz, Bogdan; Paszkiewicz, Regina [The Faculty of Microsystem Electronics and Photonics, Wrocaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw (Poland); Drzik, Milan [International Laser Center, Ilkovicova 3, 841-04 Bratislava 4 (Slovakia)

    2015-07-15

    GaN layers without and with an in-situ SiN mask were grown by using metal organic vapor phase epitaxy for three different approaches used in GaN on silicon(111) growth, and the physical and optical properties of the GaN layers were studied. For each approach applied, GaN layers of 1.4 μm total thickness were grown, using silan SiH{sub 4} as Si source in order to grow Si{sub x}N{sub x} masking layer. The optical micrographs, scanning electron microscope images, and atomic force microscope images of the grown samples revealed cracks for samples without SiN mask, and micropits, which were characteristic for the samples grown with SiN mask. In situ reflectance signal traces were studied showing a decrease of layer coalescence time and higher degree of 3D growth mode for samples with SiN masking layer. Stress measurements were conducted by two methods—by recording micro-Raman spectra and ex-situ curvature radius measurement—additionally PLs spectra were obtained revealing blueshift of PL peak positions with increasing stress. The authors have shown that a SiN mask significantly improves physical and optical properties of GaN multilayer systems reducing stress in comparison to samples grown applying the same approaches but without SiN masking layer.

  3. Metal hydrides based high energy density thermal battery

    International Nuclear Information System (INIS)

    Fang, Zhigang Zak; Zhou, Chengshang; Fan, Peng; Udell, Kent S.; Bowman, Robert C.; Vajo, John J.; Purewal, Justin J.; Kekelia, Bidzina

    2015-01-01

    Highlights: • The principle of the thermal battery using advanced metal hydrides was demonstrated. • The thermal battery used MgH 2 and TiMnV as a working pair. • High energy density can be achieved by the use of MgH 2 to store thermal energy. - Abstract: A concept of thermal battery based on advanced metal hydrides was studied for heating and cooling of cabins in electric vehicles. The system utilized a pair of thermodynamically matched metal hydrides as energy storage media. The pair of hydrides that was identified and developed was: (1) catalyzed MgH 2 as the high temperature hydride material, due to its high energy density and enhanced kinetics; and (2) TiV 0.62 Mn 1.5 alloy as the matching low temperature hydride. Further, a proof-of-concept prototype was built and tested, demonstrating the potential of the system as HVAC for transportation vehicles

  4. Quantum-based Atomistic Simulation of Transition Metals

    International Nuclear Information System (INIS)

    Moriarty, J A; Benedict, L X; Glosli, J N; Hood, R Q; Orlikowski, D A; Patel, M V; Soderlind, P; Streitz, F H; Tang, M; Yang, L H

    2005-01-01

    First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in d-electron transition metals within density-functional quantum mechanics. In mid-period bcc metals, where multi-ion angular forces are important to structural properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions of pressure and temperature. Recent algorithm improvements have also led to a more general matrix representation of MGPT beyond canonical bands allowing increased accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed, and the current development of temperature-dependent potentials

  5. Towards Flexible Transparent Electrodes Based on Carbon and Metallic Materials

    Directory of Open Access Journals (Sweden)

    Minghui Luo

    2017-01-01

    Full Text Available Flexible transparent electrodes (FTEs with high stability and scalability are in high demand for the extremely widespread applications in flexible optoelectronic devices. Traditionally, thin films of indium thin oxide (ITO served the role of FTEs, but film brittleness and scarcity of materials limit its further application. This review provides a summary of recent advances in emerging transparent electrodes and related flexible devices (e.g., touch panels, organic light-emitting diodes, sensors, supercapacitors, and solar cells. Mainly focusing on the FTEs based on carbon nanomaterials (e.g., carbon nanotubes and graphene and metal materials (e.g., metal grid and metal nanowires, we discuss the fabrication techniques, the performance improvement, and the representative applications of these highly transparent and flexible electrodes. Finally, the challenges and prospects of flexible transparent electrodes will be summarized.

  6. Axial p-n junction and space charge limited current in single GaN nanowire

    Science.gov (United States)

    Fang, Zhihua; Donatini, Fabrice; Daudin, Bruno; Pernot, Julien

    2018-01-01

    The electrical characterizations of individual basic GaN nanostructures, such as axial nanowire (NW) p-n junctions, are becoming indispensable and crucial for the fully controlled realization of GaN NW based devices. In this study, electron beam induced current (EBIC) measurements were performed on two single axial GaN p-n junction NWs grown by plasma-assisted molecular beam epitaxy. I-V characteristics revealed that both ohmic and space charge limited current (SCLC) regimes occur in GaN p-n junction NW. Thanks to an improved contact process, both the electric field induced by the p-n junction and the SCLC in the p-part of GaN NW were disclosed and delineated by EBIC signals under different biases. Analyzing the EBIC profiles in the vicinity of the p-n junction under 0 V and reverse bias, we deduced a depletion width in the range of 116-125 nm. Following our previous work, the acceptor N a doping level was estimated to be 2-3 × 1017 at cm-3 assuming a donor level N d of 2-3 × 1018 at cm-3. The hole diffusion length in n-GaN was determined to be 75 nm for NW #1 and 43 nm for NW #2, demonstrating a low surface recombination velocity at the m-plane facet of n-GaN NW. Under forward bias, EBIC imaging visualized the electric field induced by the SCLC close to p-side contact, in agreement with unusual SCLC previously reported in GaN NWs.

  7. Axial p-n junction and space charge limited current in single GaN nanowire.

    Science.gov (United States)

    Fang, Zhihua; Donatini, Fabrice; Daudin, Bruno; Pernot, Julien

    2018-01-05

    The electrical characterizations of individual basic GaN nanostructures, such as axial nanowire (NW) p-n junctions, are becoming indispensable and crucial for the fully controlled realization of GaN NW based devices. In this study, electron beam induced current (EBIC) measurements were performed on two single axial GaN p-n junction NWs grown by plasma-assisted molecular beam epitaxy. I-V characteristics revealed that both ohmic and space charge limited current (SCLC) regimes occur in GaN p-n junction NW. Thanks to an improved contact process, both the electric field induced by the p-n junction and the SCLC in the p-part of GaN NW were disclosed and delineated by EBIC signals under different biases. Analyzing the EBIC profiles in the vicinity of the p-n junction under 0 V and reverse bias, we deduced a depletion width in the range of 116-125 nm. Following our previous work, the acceptor N a doping level was estimated to be 2-3 × 10 17 at cm -3 assuming a donor level N d of 2-3 × 10 18 at cm -3 . The hole diffusion length in n-GaN was determined to be 75 nm for NW #1 and 43 nm for NW #2, demonstrating a low surface recombination velocity at the m-plane facet of n-GaN NW. Under forward bias, EBIC imaging visualized the electric field induced by the SCLC close to p-side contact, in agreement with unusual SCLC previously reported in GaN NWs.

  8. Terahertz wave manipulation with metamaterials based on metal and graphene

    DEFF Research Database (Denmark)

    Andryieuski, Andrei; Malureanu, Radu; Zalkovskij, Maksim

    2013-01-01

    response. In this presentation we overview our results on theory, fabrication and characterization of metal and graphene based metamaterials for the THz range. We show that the multiple layers of structured graphene can form a hyperbolic dispersion medium lens able to resolve the subwavelength features [2......]. We analyze the limitations and demonstrate numerically and experimentally the chiral and nonchiral thin-film metamaterial based polarization converters [3–5] and graphene total absorbers for THz radiation [6]....

  9. Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

    International Nuclear Information System (INIS)

    Lee, Sung-Nam; Paek, H.S.; Son, J.K.; Sakong, T.; Yoon, E.; Nam, O.H.; Park, Y.

    2006-01-01

    We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1 o . As the surface tilt angle increased to 0.35 o , the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4 o , surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers

  10. Growth and properties of Al-rich InxAl1-xN ternary alloy grown on GaN template by metalorganic chemical vapour deposition

    International Nuclear Information System (INIS)

    Oh, Tae Su; Suh, Eun-Kyung; Kim, Jong Ock; Jeong, Hyun; Lee, Yong Seok; Nagarajan, S; Lim, Kee Young; Hong, Chang-Hee

    2008-01-01

    An Al-rich In x Al 1-x N ternary alloy was grown on a GaN template by metal-organic chemical vapour deposition (MOCVD). The GaN template was fabricated on a c-plane sapphire with a low temperature GaN nucleation layer. The growth of the 300 nm thick In x Al 1-x N layer was carried out under various growth temperatures and pressures. The surface morphology and the InN molar fraction of the In x Al 1-x N layer were assessed by using atomic force microscopy (AFM) and high resolution x-ray diffraction, respectively. The AFM surface images of the In x Al 1-x N ternary alloy exhibited quantum dot-like grains caused by the 3D island growth mode. The grains, however, disappeared rapidly by increasing diffusion length and mobility of the Al adatoms with increasing growth temperature and the full width at half maximum value of ternary peaks in HR-XRD decreased with decreasing growth pressure. The MOCVD growth condition with the increased growth temperature and decreased growth pressure would be effective to grow the In x Al 1-x N ternary alloy with a smooth surface and improved quality. The optical band edge of In x Al 1-x N ternary alloys was estimated by optical absorbance and, based on the results of HR-XRD and optical absorbance measurements, we obtained the bowing parameter of the In x Al 1-x N ternary alloy at b = 5.3 eV, which was slightly larger than that of previous reports

  11. Enzymatic biosensors based on the use of metal oxide nanoparticles

    International Nuclear Information System (INIS)

    Shi, Xinhao; Gu, Wei; Li, Bingyu; Chen, Ningning; Zhao, Kai; Xian, Yuezhong

    2014-01-01

    Over the past decades, various techniques have been developed to obtain materials at a nanoscale level to design biosensors with high sensitivity, selectivity and efficiency. Metal oxide nanoparticles (MONPs) are of particular interests and have received much attention because of their unique physical, chemical and catalytic properties. This review summarizes the progress made in enzymatic biosensors based on the use of MONPs. Synthetic methods, strategies for immobilization, and the functions of MONPs in enzymatic biosensing systems are reviewed and discussed. The article is subdivided into sections on enzymatic biosensors based on (a) zinc oxide nanoparticles, (b) titanium oxide nanoparticles, (c) iron oxide nanoparticles, and (d) other metal oxide nanoparticles. While substantial advances have been made in MONPs-based enzymatic biosensors, their applications to real samples still lie ahead because issues such as reproducibility and sensor stability have to be solved. (author)

  12. Simulation of electrical characteristics of GaN vertical Schottky diodes

    Science.gov (United States)

    Łukasiak, Lidia; Jasiński, Jakub; Jakubowski, Andrzej

    2016-12-01

    Reverse current of GaN vertical Schottky diodes is simulated using Silvaco ATLAS to optimize the geometry for the best performance. Several physical quantities and phenomena, such as carrier mobility and tunneling mechanism are studied to select the most realistic models. Breakdown voltage is qualitatively estimated based on the maximum electric field in the structure.

  13. Mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals

    NARCIS (Netherlands)

    Qin, Hongbo; Luan, Xinghe; Feng, Chuang; Yang, Daoguo; Zhang, G.Q.

    2017-01-01

    For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli,

  14. Diamond-coated three-dimensional GaN micromembranes: effect of nucleation and deposition techniques

    Czech Academy of Sciences Publication Activity Database

    Ižák, Tibor; Vanko, G.; Babchenko, Oleg; Potocký, Štěpán; Marton, M.; Vojs, M.; Choleva, P.; Kromka, Alexander

    2015-01-01

    Roč. 252, č. 11 (2015), s. 2585-2590 ISSN 0370-1972 R&D Projects: GA ČR(CZ) GP14-16549P Institutional support: RVO:68378271 Keywords : diamond film * GaN micromembranes * microwave chemical vapour deposition * polymer-based nucleation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.522, year: 2015

  15. Selective fluorescence sensors for detection of nitroaniline and metal Ions based on ligand-based luminescent metal-organic frameworks

    International Nuclear Information System (INIS)

    Yu, Zongchao; Wang, Fengqin; Lin, Xiangyi; Wang, Chengmiao; Fu, Yiyuan; Wang, Xiaojun; Zhao, Yongnan; Li, Guodong

    2015-01-01

    Metal-organic frameworks (MOFs) are porous crystalline materials with high potential for applications in fluorescence sensors. In this work, two solvent-induced Zn(II)–based metal-organic frameworks, Zn_3L_3(DMF)_2 (1) and Zn_3L_3(DMA)_2(H_2O)_3 (2) (L=4,4′-stilbenedicarboxylic acid), were investigated as selective sensing materials for detection of nitroaromatic compounds and metal ions. The sensing experiments show that 1 and 2 both exhibit selective fluorescence quenching toward nitroaniline with a low detection limit. In addition, 1 exhibits high selectivity for detection of Fe"3"+ and Al"3"+ by significant fluorescence quenching or enhancement effect. While for 2, it only exhibits significant fluorescence quenching effect for Fe"3"+. The results indicate that 1 and 2 are both promising fluorescence sensors for detecting and recognizing nitroaniline and metal ions with high sensitivity and selectivity. - Graphical abstract: Two MOFs have been selected as the fluorescence sensing materials for selectively sensing mitroaromatic compounds and metal ions. The high selectivity makes them promising fluorescence sensors for detecting and recognizing nitroaniline and Fe"3"+ or Al"3"+.

  16. MgNiO-based metal-semiconductor- metal ultraviolet photodetector

    International Nuclear Information System (INIS)

    Zhao Yanmin; Zhang Jiying; Jiang Dayong; Shan Chongxin; Zhang Zhenzhong; Yao Bin; Zhao Dongxu; Shen Dezhen

    2009-01-01

    In this study, we report the growth of Mg x Ni 1-x O thin films on quartz substrates by electron beam evaporation. The absorption edge shows a blue shift from 340 nm to 260 nm with increase in the Mg content from 0.2 to 0.8. A metal-semiconductor-metal structured photodetector is fabricated from the Mg 0.2 Ni 0.8 O film. At a bias of 5 V, the dark current of the photodetector is about 70 nA. The maximum responsivity is about 147.3 μA W -1 at 320 nm. In addition, the ultraviolet (UV) (320 nm) to visible (400 nm) rejection ratio is nearly two orders of magnitude. Based on these results, it is proposed that Mg x Ni 1-x O is a potential candidate for application in UV photodetectors. (fast track communication)

  17. Infrared plasmonic nano-lasers based on Metal Insulator Metal waveguides

    NARCIS (Netherlands)

    Hill, M.T.

    2010-01-01

    We will present our latest results on metal-insulator-metal waveguide devices, in particular reducing the dimensions of devices and distributed feedback lasers. Also we will examine potential useful applications for metal nano-lasers.

  18. Liquid metal-based reconfigurable and stretchable photolithography

    International Nuclear Information System (INIS)

    Kim, Daeyoung; Yoo, Jun Hyeon; Lee, Jeong-Bong

    2016-01-01

    Conventional ultraviolet (UV) lithography typically uses a photomask made of a fused silica plate covered with a layer of UV opaque material such as chromium. The photomask has passive binary patterns of UV opaque and UV transparent regions and the pattern is unalterable. We report a novel real-time dynamically reconfigurable photomask technology using a liquid metal (as a UV opaque material) filled in polydimethylsiloxane (PDMS, as a UV transparent material) microfluidic channels. We found that the gallium-based liquid metal (e.g. Galinstan ® ) is opaque in broad spectrum of light in the wavelength from 325 nm to 850 nm while the PDMS is highly transparent in this wide range of spectrum. We made both bright field and dark field microfluidic photomasks and transferred various patterns onto a positive photoresist. A 7-segment display microfluidic channel photomask was also fabricated and decimal numerals (from ‘0’ to ‘9’) were patterned with one photomask by dynamically reconfiguring decimal numeral shapes with on-demand injection and withdrawal of the liquid metal in specific segment microfluidic channels in the photomask. In addition, utilizing mechanical flexibility of the PDMS and the liquid metal, reconfiguration of the patterns in a microfluidic photomask under stretching was successfully tested. (paper)

  19. Magnetic properties of fcc Ni-based transition metal alloy

    Czech Academy of Sciences Publication Activity Database

    Kudrnovský, Josef; Drchal, Václav

    2009-01-01

    Roč. 100, č. 9 (2009), s. 1193-1196 ISSN 1862-5282 R&D Projects: GA MŠk OC 150; GA AV ČR IAA100100616 Institutional research plan: CEZ:AV0Z10100520 Keywords : transition metal alloys * Ni-based * pair exchange interactions * Curie temperatures * renormalized RPA Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.862, year: 2009

  20. Molecularly Imprinted Polymer/Metal Organic Framework Based Chemical Sensors

    Directory of Open Access Journals (Sweden)

    Zhenzhong Guo

    2016-10-01

    Full Text Available The present review describes recent advances in the concept of molecular imprinting using metal organic frameworks (MOF for development of chemical sensors. Two main strategies regarding the fabrication, performance and applications of recent sensors based on molecularly imprinted polymers associated with MOF are presented: molecularly imprinted MOF films and molecularly imprinted core-shell nanoparticles using MOF as core. The associated transduction modes are also discussed. A brief conclusion and future expectations are described herein.

  1. Development of a thermodynamic data base for selected heavy metals

    International Nuclear Information System (INIS)

    Hageman, Sven; Scharge, Tina; Willms, Thomas

    2015-07-01

    The report on the development of a thermodynamic data base for selected heavy metals covers the description of experimental methods, the thermodynamic model for chromate, the thermodynamic model for dichromate, the thermodynamic model for manganese (II), the thermodynamic model for cobalt, the thermodynamic model for nickel, the thermodynamic model for copper (I), the thermodynamic model for copper(II), the thermodynamic model for mercury (0) and mercury (I), the thermodynamic model for mercury (III), the thermodynamic model for arsenate.

  2. In-situ TEM study of domain switching in GaN thin films

    Science.gov (United States)

    Wang, Baoming; Wang, Tun; Haque, Aman; Snure, Michael; Heller, Eric; Glavin, Nicholas

    2017-09-01

    Microstructural response of gallium nitride (GaN) films, grown by metal-organic chemical vapor deposition, was studied as a function of applied electrical field. In-situ transmission electron microscopy showed sudden change in the electron diffraction pattern reflecting domain switching at around 20 V bias, applied perpendicular to the polarization direction. No such switching was observed for thicker films or for the field applied along the polarization direction. This anomalous behavior is explained by the nanoscale size effects on the piezoelectric coefficients of GaN, which can be 2-3 times larger than the bulk value. As a result, a large amount of internal energy can be imparted in 100 nm thick films to induce domain switching at relatively lower voltages to induce such events at the bulk scale.

  3. Multilayer porous structures of HVPE and MOCVD grown GaN for photonic applications

    Science.gov (United States)

    Braniste, T.; Ciers, Joachim; Monaico, Ed.; Martin, D.; Carlin, J.-F.; Ursaki, V. V.; Sergentu, V. V.; Tiginyanu, I. M.; Grandjean, N.

    2017-02-01

    In this paper we report on a comparative study of electrochemical processes for the preparation of multilayer porous structures in hydride vapor phase epitaxy (HVPE) and metal organic chemical vapor phase deposition (MOCVD) grown GaN. It was found that in HVPE-grown GaN, multilayer porous structures are obtained due to self-organization processes leading to a fine modulation of doping during the crystal growth. However, these processes are not totally under control. Multilayer porous structures with a controlled design have been produced by optimizing the technological process of electrochemical etching in MOCVD-grown samples, consisting of five pairs of thin layers with alternating-doping profiles. The samples have been characterized by SEM imaging, photoluminescence spectroscopy, and micro-reflectivity measurements, accompanied by transfer matrix analysis and simulations by a method developed for the calculation of optical reflection spectra. We demonstrate the applicability of the produced structures for the design of Bragg reflectors.

  4. Surface States Effect on the Large Photoluminescence Redshift in GaN Nanostructures

    KAUST Repository

    Ben Slimane, Ahmed

    2013-01-01

    We report on the large photoluminescence redshift observed in nanostructures fabricated using n-type GaN by ultraviolet (UV) metal-assisted electroless chemical-etching method. The scanning electron microscopy (SEM) characterization showed nanostructures with size dispersion ranging from 10 to 100 nm. We observed the crystalline structure using high resolution transmission electron microscopy (HRTEM) and electron energy loss (EELS) techniques. In contrast to 362 nm UV emission from the GaN epitaxy, the nanostructures emitted violet visible-light in photoluminescence (PL) characterization with increasing optical excitation. An energy band model was presented to shed light on the large PL redshift under the influence of surface states, which resulted in two competing photoluminescence mechanisms depending on excitation conditions.

  5. Morphological and luminescent characteristics of GaN dots deposited on AlN by alternate supply of TMG and NH3

    International Nuclear Information System (INIS)

    Tsai, Y.-L.; Gong, J.-R.; Lin, T.-Y.; Lin, H.-Y.; Chen, Yang-Fang; Lin, K.-M.

    2006-01-01

    GaN dots were deposited on AlN underlayers by alternate supply of trimethylgallium (TMG) and ammonia (NH 3 ) in an inductively heated quartz reactor operated at atmospheric pressure. Various growth parameters including deposition temperature, TMG admittance and pulse time between TMG and NH 3 exposures were proposed to investigate the influence of growth parameters on the size distribution of GaN dots. It appears that GaN dots with uniform size distribution can be achieved under certain growth conditions. Based on the study of atomic force microscopy (AFM), high deposition temperature was found to be in favor of forming large GaN dots with small dot density. Decrement of TMG flow rate or reduction in the number of growth cycle tends to enable the formation of GaN dots with small dot sizes. The results of room temperature (RT) cathodoluminescence (CL) measurements of the GaN dots exhibit an emission peak at 3.735 eV. A remarkable blue shift of GaN dot emission was observed by reduced temperature photoluminescence (PL) measurements

  6. Morphological and luminescent characteristics of GaN dots deposited on AlN by alternate supply of TMG and NH{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Y.-L. [Department of Materials Science and Engineering, Feng Chia University, Taichung 407, Taiwan (China); Gong, J.-R. [Institute of Opto-Mechatronics, National Chung Cheng University, Chiayi 621, Taiwan (China); Lin, T.-Y. [Institute of Optoelectronic Sciences, National Taiwan Ocean University, Keelung 202, Taiwan (China); Lin, H.-Y. [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Chen, Yang-Fang [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Lin, K.-M. [Department of Materials Science and Engineering, Feng Chia University, Taichung 407, Taiwan (China)

    2006-03-15

    GaN dots were deposited on AlN underlayers by alternate supply of trimethylgallium (TMG) and ammonia (NH{sub 3}) in an inductively heated quartz reactor operated at atmospheric pressure. Various growth parameters including deposition temperature, TMG admittance and pulse time between TMG and NH{sub 3} exposures were proposed to investigate the influence of growth parameters on the size distribution of GaN dots. It appears that GaN dots with uniform size distribution can be achieved under certain growth conditions. Based on the study of atomic force microscopy (AFM), high deposition temperature was found to be in favor of forming large GaN dots with small dot density. Decrement of TMG flow rate or reduction in the number of growth cycle tends to enable the formation of GaN dots with small dot sizes. The results of room temperature (RT) cathodoluminescence (CL) measurements of the GaN dots exhibit an emission peak at 3.735 eV. A remarkable blue shift of GaN dot emission was observed by reduced temperature photoluminescence (PL) measurements.

  7. Breaking Through the Multi-Mesa-Channel Width Limited of Normally Off GaN HEMTs Through Modulation of the Via-Hole-Length.

    Science.gov (United States)

    Chien, Cheng-Yen; Wu, Wen-Hsin; You, Yao-Hong; Lin, Jun-Huei; Lee, Chia-Yu; Hsu, Wen-Ching; Kuan, Chieh-Hsiung; Lin, Ray-Ming

    2017-12-01

    We present new normally off GaN high-electron-mobility transistors (HEMTs) that overcome the typical limitations in multi-mesa-channel (MMC) width through modulation of the via-hole-length to regulate the charge neutrality screen effect. We have prepared enhancement-mode (E-mode) GaN HEMTs having widths of up to 300 nm, based on an enhanced surface pinning effect. E-mode GaN HEMTs having MMC structures and widths as well as via-hole-lengths of 100 nm/2 μm and 300 nm/6 μm, respectively, exhibited positive threshold voltages (V th ) of 0.79 and 0.46 V, respectively. The on-resistances of the MMC and via-hole-length structures were lower than those of typical tri-gate nanoribbon GaN HEMTs. In addition, the devices not only achieved the E-mode but also improved the power performance of the GaN HEMTs and effectively mitigated the device thermal effect. We controlled the via-hole-length sidewall surface pinning effect to obtain the E-mode GaN HEMTs. Our findings suggest that via-hole-length normally off GaN HEMTs have great potential for use in next-generation power electronics.

  8. Breaking Through the Multi-Mesa-Channel Width Limited of Normally Off GaN HEMTs Through Modulation of the Via-Hole-Length

    Science.gov (United States)

    Chien, Cheng-Yen; Wu, Wen-Hsin; You, Yao-Hong; Lin, Jun-Huei; Lee, Chia-Yu; Hsu, Wen-Ching; Kuan, Chieh-Hsiung; Lin, Ray-Ming

    2017-06-01

    We present new normally off GaN high-electron-mobility transistors (HEMTs) that overcome the typical limitations in multi-mesa-channel (MMC) width through modulation of the via-hole-length to regulate the charge neutrality screen effect. We have prepared enhancement-mode (E-mode) GaN HEMTs having widths of up to 300 nm, based on an enhanced surface pinning effect. E-mode GaN HEMTs having MMC structures and widths as well as via-hole-lengths of 100 nm/2 μm and 300 nm/6 μm, respectively, exhibited positive threshold voltages ( V th) of 0.79 and 0.46 V, respectively. The on-resistances of the MMC and via-hole-length structures were lower than those of typical tri-gate nanoribbon GaN HEMTs. In addition, the devices not only achieved the E-mode but also improved the power performance of the GaN HEMTs and effectively mitigated the device thermal effect. We controlled the via-hole-length sidewall surface pinning effect to obtain the E-mode GaN HEMTs. Our findings suggest that via-hole-length normally off GaN HEMTs have great potential for use in next-generation power electronics.

  9. Study of using aqueous NH{sub 3} to synthesize GaN nanowires on Si(1 1 1) by thermal chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Saron, K.M.A., E-mail: kamalmohammedabdalla@yahoo.com [Nano-Optoelectronics Research and Technology Laboratory, School of Physics, University Sains Malaysia, Penang 11800 (Malaysia); Hashim, M.R. [Nano-Optoelectronics Research and Technology Laboratory, School of Physics, University Sains Malaysia, Penang 11800 (Malaysia)

    2013-03-20

    Highlights: ► This study presents a facile, low cost and safe method to synthesize high quality GaN NWs, by using NH{sub 3} solution as N source. ► Moderating the N{sub 2} flow rate improved the crystalline quality of the NWs and also produced zigzag shaped NWs. ► Raman spectra showed that the synthesized GaN NWs had hexagonal wurtzite structures as a result of increased tensile stress. ► By moderating N{sub 2} flow, strong NBE emission peaks at about 364 nm and YB is subsided. -- Abstract: High-quality GaN nanowires (NWs) and zigzag-shaped NWs were grown on catalyst-free Si(1 1 1) substrate by thermal chemical vapor deposition (TCVD). Gallium (Ga) metal and aqueous NH{sub 3} solution are used as a source of materials. Ga vapor was directly reacts with gaseous NH{sub 3} under controlled nitrogen flow at 1050 °C. Scanning electron microscopy (SEM) images showed that the morphology of GaN displayed various densities of NWs and zigzag NWs depending on the gas flow rate, and increased nitrogen flow rate caused density reduction. The GaN NWs exhibited clear X-ray diffraction analysis (XRD) peaks that corresponded to GaN with hexagonal wurtzite structures. The photoluminescence spectra showed that the ultraviolet band emission of GaN NWs had a strong near band-edge emission (NBE) at 361–367 nm. Yellow band emissions were observed at low and high flow rates due to nitrogen and Ga vacancies, respectively. Moderate N{sub 2} flow resulted in a strong NBE emission and a high optical quality of the NWs. This study shows the possibility of low-cost synthesis of GaN nanostructures on Si wafers using aqueous NH{sub 3} solution.

  10. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Bajaj, Sanyam, E-mail: bajaj.10@osu.edu; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Reza, Shahed; Chumbes, Eduardo M. [Raytheon Integrated Defense Systems, Andover, Massachusetts 01810 (United States); Khurgin, Jacob [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Material Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)

    2015-10-12

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10{sup 7 }cm/s at a low sheet charge density of 7.8 × 10{sup 11 }cm{sup −2}. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  11. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Bajaj, Sanyam; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang; Reza, Shahed; Chumbes, Eduardo M.; Khurgin, Jacob; Rajan, Siddharth

    2015-01-01

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10 7  cm/s at a low sheet charge density of 7.8 × 10 11  cm −2 . An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs

  12. GRAPHENE BASED METAL AND METAL OXIDE NANOCOMPOSITES: SYNTHESIS, PROPERTIES AND THEIR APPLICATIONS

    KAUST Repository

    Khan, Mujeeb

    2015-06-11

    Graphene, an atomically thin two-dimensional carbonaceous material, has attracted tremendous attention in the scientific community, due to its exceptional electronic, electrical, and mechanical properties. Indeed, with the recent explosion of methods for a large-scale synthesis of graphene, the number of publications related to graphene and other graphene based materials have increased exponentially. Particularly the easy preparation of graphene like materials, such as, highly reduced graphene oxide (HRG) via reduction of graphite oxide (GO), offers a wide range of possibilities for the preparation of graphene based inorganic nanocomposites by the incorporation of various functional nanomaterials for a variety of applications. In this review, we discuss the current development of graphene based metal and metal oxide nanocomposites, with a detailed account of their synthesis and properties. Specifically, much attention has been given to their wide range of applications in various fields, including, electronics, electrochemical and electrical fields. Overall, by the inclusion of various references, this review covers in detail aspects of the graphene-based inorganic nanocomposites.

  13. GRAPHENE BASED METAL AND METAL OXIDE NANOCOMPOSITES: SYNTHESIS, PROPERTIES AND THEIR APPLICATIONS

    KAUST Repository

    Khan, Mujeeb; Tahir, Muhammad Nawaz; Adil, Syed F; Khan, Hadayat Ullah; Siddiqui, Rafiq H; Al-Warthan, Abdulrahman Abdullah; Tremel, Wolfgang

    2015-01-01

    Graphene, an atomically thin two-dimensional carbonaceous material, has attracted tremendous attention in the scientific community, due to its exceptional electronic, electrical, and mechanical properties. Indeed, with the recent explosion of methods for a large-scale synthesis of graphene, the number of publications related to graphene and other graphene based materials have increased exponentially. Particularly the easy preparation of graphene like materials, such as, highly reduced graphene oxide (HRG) via reduction of graphite oxide (GO), offers a wide range of possibilities for the preparation of graphene based inorganic nanocomposites by the incorporation of various functional nanomaterials for a variety of applications. In this review, we discuss the current development of graphene based metal and metal oxide nanocomposites, with a detailed account of their synthesis and properties. Specifically, much attention has been given to their wide range of applications in various fields, including, electronics, electrochemical and electrical fields. Overall, by the inclusion of various references, this review covers in detail aspects of the graphene-based inorganic nanocomposites.

  14. Hydrogen storage evaluation based on investigations of the catalytic properties of metal/metal oxides in electrospun carbon fibers

    Energy Technology Data Exchange (ETDEWEB)

    Im, Ji Sun; Lee, Young-Seak [Department of Fine Chemical Engineering and Chemistry, Chungnam National University, Daejeon 305-764 (Korea); Park, Soo-Jin [Department of Chemistry, Inha University, Incheon 402-751 (Korea); Kim, Taejin [Core Technology Research Center for Fuel Cell, Jeollabuk-do 561-844 (Korea)

    2009-05-15

    In order to investigate the catalytic capacity of metals and metal oxides based on electrospun carbon fibers for improving hydrogen storage, electrospinning and heat treatments were carried out to obtain metal/metal oxide-embedded carbon fibers. Although the fibers were treated with the same activation procedure, they had different pore structures, due to the nature of the metal oxide. When comparing the catalytic capacity of metal and metal oxide, metal exhibits better performance as a catalyst for the improvement of hydrogen storage, when considering the hydrogen storage system. When a metal oxide with an m.p. lower than the temperature of heat treatment was used, the metal oxide was changed to metal during the heat treatment, developing a micropore structure. The activation process produced a high specific surface area of up to 2900 m{sup 2}/g and a pore volume of up to 2.5 cc/g. The amount of hydrogen adsorption reached approximately 3 wt% at 100 bar and room temperature. (author)

  15. Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air

    Science.gov (United States)

    Hou, Minmin; Senesky, Debbie G.

    2014-08-01

    The high-temperature characteristics (at 600 °C) of Ti/Al/Pt/Au multilayer contacts to gallium nitride (GaN) in air are reported. Microfabricated circular-transfer-line-method test structures were subject to 10 h of thermal storage at 600 °C. Intermittent electrical characterization during thermal storage showed minimal variation in the contact resistance after 2 h and that the specific contact resistivity remained on the order of 10-5 Ω-cm2. In addition, the thermally stored multilayer contacts to GaN showed ohmic I-V characteristics when electrically probed at 600 °C. The microstructural analysis with atomic force microscopy showed minimal changes in surface roughness after thermal storage. Observations of the thermochemical reactions after thermal storage using Auger electron spectroscopy chemical depth profiling showed diffusion of Pt and minimal additional Al oxidation. The results support the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.

  16. In-situ potential mapping of space charge layer in GaN nanowires under electrical field by off-axis electron holography

    Directory of Open Access Journals (Sweden)

    Xiao Chen

    2016-04-01

    Full Text Available In situ potential mapping of space charge (SC layer in a single GaN nanowire (NW contacted to the Au metal electrode has been conducted using off-axis electron holography in order to study the space distribution of SC layer under electric biases. Based on the phase image reconstructed from the complex hologram the electrostatic potential at the SC layer was clearly revealed; the SC width was estimated to be about 76 nm under zero bias condition. In order to study dynamic interrelation between the SC layer and bias conditions, the variation of the electrostatic potential due to change of the SC widths respond to the different bias conditions have also been examined. The measured SC layers are found to vary between 68 nm and 91 nm, which correspond to the saturated SC layers at the GaN-Au contact under the forward and reverse bias conditions, respectively. By plotting the square widths of the SC layer against the applied voltages, donor density of GaN NWs was derived to be about 4.3*106 cm−3. Our experiments demonstrate that in-situ electron holography under electric field can be a useful method to investigate SC layers and donor density in single NW and other heterostructures.

  17. Site controlled Red-Yellow-Green light emitting InGaN Quantum Discs on nano-tipped GaN rods

    KAUST Repository

    Conroy, Michele Ann; Li, Haoning; Kusch, Gunnar; Zhao, Chao; Ooi, Boon S.; Paul, Edwards; Martin, Robert; Holmes, Justin D.; Parbrook, Peter

    2016-01-01

    We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive x-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips’ broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD’s confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.

  18. Site controlled Red-Yellow-Green light emitting InGaN Quantum Discs on nano-tipped GaN rods

    KAUST Repository

    Conroy, Michele Ann

    2016-03-10

    We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive x-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips’ broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD’s confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.

  19. Brazing of Cu with Pd-based metallic glass filler

    Energy Technology Data Exchange (ETDEWEB)

    Terajima, Takeshi [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)], E-mail: terajima@jwri.osaka-u.ac.jp; Nakata, Kazuhiro [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Matsumoto, Yuji [Materials and Structures Laboratory, Tokyo Institute of Technology (Japan); Zhang, Wei; Kimura, Hisamichi; Inoue, Akihisa [Institute for Materials Research, Tohoku University (Japan)

    2008-02-25

    Metallic glass has several unique properties, including high mechanical strength, small solidification shrinkage, small elastic modulus and supercooling state, all of which are well suited as a residual stress buffer for metal and ceramic joining. In the present preliminary study, we demonstrated brazing of Cu rods with Pd{sub 40}Cu{sub 30}Ni{sub 10}P{sub 20} metallic glass filler. The brazing was carried out at 873 K for 1 min in a vacuum atmosphere (1 x 10{sup -3} Pa), and then the specimens were quenched at the rate of 30 K/s by blowing He. The metallic glass brazing of Cu using Pd{sub 40}Cu{sub 30}Ni{sub 10}P{sub 20} filler was successful, with the exception that several voids remained in the filler. According to micro-focused X-ray diffraction, no diffraction patterns were observed at both the center of the Pd{sub 40}Cu{sub 30}Ni{sub 10}P{sub 20} filler and the Cu/Pd{sub 40}Cu{sub 30}Ni{sub 10}P{sub 20} interface. The result showed that the Cu specimens were joined with Pd{sub 40}Cu{sub 30}Ni{sub 10}P{sub 20} filler in the glassy state. The tensile fracture strength of the brazed specimens ranged from 20 to 250 MPa. The crack extension from the voids in the Pd{sub 40}Cu{sub 30}Ni{sub 10}P{sub 20} filler may have caused the results to be uneven and very low compared to the strength of Pd-based bulk metallic glass.

  20. Induced defects in neutron irradiated GaN single crystals

    International Nuclear Information System (INIS)

    Park, I. W.; Koh, E. K.; Kim, Y. M.; Choh, S. H.; Park, S. S.; Kim, B. G.; Sohn, J. M.

    2005-01-01

    The local structure of defects in undoped, Si-doped, and neutron irradiated free standing GaN bulk crystals, grown by hydride vapor phase epitaxy, has been investigated by employing Raman scattering and cathodoluminescence. The GaN samples were irradiated to a dose of 2 x 10 17 neutrons in an atomic reactor at Korea Atomic Energy Research Institute. There was no appreciable change in the Raman spectra for undoped GaN samples before and after neutron irradiation. However, a forbidden transition, A 1 (TO) mode, appeared for a neutron irradiated Si-doped GaN crystal. Cathodoluminescence spectrum for the neutron irradiated Si-doped GaN crystal became much more broadened than that for the unirradiated one. The experimental results reveal the generation of defects with locally deformed structure in the wurtzite Si-doped GaN single crystal

  1. GaN Nanowire Arrays for High-Output Nanogenerators

    KAUST Repository

    Huang, Chi-Te

    2010-04-07

    Three-fold symmetrically distributed GaN nanowire (NW) arrays have been epitaxially grown on GaN/sapphire substrates. The GaN NW possesses a triangular cross section enclosed by (0001), (2112), and (2112) planes, and the angle between the GaN NW and the substrate surface is ∼62°. The GaN NW arrays produce negative output voltage pulses when scanned by a conductive atomic force microscope in contact mode. The average of piezoelectric output voltage was about -20 mV, while 5-10% of the NWs had piezoelectric output voltages exceeding -(0.15-0.35) V. The GaN NW arrays are highly stable and highly tolerate to moisture in the atmosphere. The GaN NW arrays demonstrate an outstanding potential to be utilized for piezoelectric energy generation with a performance probably better than that of ZnO NWs. © 2010 American Chemical Society.

  2. Theoretical bases on thermal stability of layered metallic systems

    International Nuclear Information System (INIS)

    Kadyrzhanov, K.K.; Rusakov, V.S.; Turkebaev, T.Eh.; Zhankadamova, A.M.; Ensebaeva, M.Z.

    2003-01-01

    The paper is dedicated to implementation of the theoretical bases for layered metallic systems thermal stabilization. The theory is based on the stabilization mechanism expense of the intermediate two-phase field formation. As parameters of calculated model are coefficients of mutual diffusion and inclusions sizes of generated phases in two-phase fields. The stabilization time dependence for beryllium-iron (Be (1.1 μm)-Fe(5.5 μm)) layered system from iron and beryllium diffusion coefficients, and inclusions sizes is shown as an example. Conclusion about possible mechanisms change at transition from microscopic consideration to the nano-crystal physics level is given

  3. Metal-composite adhesion based on diazonium chemistry.

    Science.gov (United States)

    Oweis, Yara; Alageel, Omar; Kozak, Paige; Abdallah, Mohamed-Nur; Retrouvey, Jean-Marc; Cerruti, Marta; Tamimi, Faleh

    2017-11-01

    Composite resins do not adhere well to dental alloys. This weak bond can result in failure at the composite-metal interface in fixed dental prostheses and orthodontic brackets. The aim of this study was to develop a new adhesive, based on diazonium chemistry, to facilitate chemical bonding between dental alloys and composite resin. Samples of two types of dental alloys, stainless steel and cobalt chromium were primed with a diazonium layer in order to create a surface coating favorable for composite adhesion. Untreated metal samples served as controls. The surface chemical composition of the treated and untreated samples was analyzed by X-ray photoelectron spectroscopy (XPS) and the tensile strength of the bond with composite resin was measured. The diazonium adhesive was also tested for shear bond strength between stainless steel orthodontic brackets and teeth. XPS confirmed the presence of a diazonium coating on the treated metals. The coating significantly increased the tensile and shear bond strengths by three and four folds respectively between the treated alloys and composite resin. diazonium chemistry can be used to develop composite adhesives for dental alloys. Diazonium adhesion can effectively achieve a strong chemical bond between dental alloys and composite resin. This technology can be used for composite repair of fractured crowns, for crown cementation with resin based cements, and for bracket bonding. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  4. Welding of Zr-based bulk metallic glasses

    International Nuclear Information System (INIS)

    Elahi, M.

    2010-01-01

    Recently, many bulk metallic glass (BMG) materials with high specific strength, hardness and superior corrosion resistance have been developed and the maximum thickness of some Zr-based BMGs have reached several tenths of millimeters. Nevertheless, homogeneous glassy BMGs are not thick enough to be used for structural applications. In order to extend the engineering applications of BMG materials, BMG welding technologies needed to be developed. Specifically, the welding technologies of dissimilar materials such as BMG materials to crystalline alloys are to be developed. The functional use of the specific properties of each material in dissimilar material combination provides flexible design possibilities for products. In this project electron beam welding is employed to join BMG with BMG of different composition as well as with different crystalline materials (i.e. Hastealoy C-276, Inconel-625 and pure Ti metal). Defects free weld joint was achieved in BMG-BMG welding. Some cracks were produced in melt zone of BMG-Ti and BMG-Hastealoy C-276 welding while at joint they fuse properly with BMG. Inconel-625 could not properly weld with BMG. In all cases, hardness of melt zone was found to be higher than the base metals and the heat affected zone (HAZ). (author)

  5. High pressure die casting of Fe-based metallic glass

    Science.gov (United States)

    Ramasamy, Parthiban; Szabo, Attila; Borzel, Stefan; Eckert, Jürgen; Stoica, Mihai; Bárdos, András

    2016-01-01

    Soft ferromagnetic Fe-based bulk metallic glass key-shaped specimens with a maximum and minimum width of 25.4 and 5 mm, respectively, were successfully produced using a high pressure die casting (HPDC) method, The influence of die material, alloy temperature and flow rate on the microstructure, thermal stability and soft ferromagnetic properties has been studied. The results suggest that a steel die in which the molten metal flows at low rate and high temperature can be used to produce completely glassy samples. This can be attributed to the laminar filling of the mold and to a lower heat transfer coefficient, which avoids the skin effect in the steel mold. In addition, magnetic measurements reveal that the amorphous structure of the material is maintained throughout the key-shaped samples. Although it is difficult to control the flow and cooling rate of the molten metal in the corners of the key due to different cross sections, this can be overcome by proper tool geometry. The present results confirm that HPDC is a suitable method for the casting of Fe-based bulk glassy alloys even with complex geometries for a broad range of applications. PMID:27725780

  6. High pressure die casting of Fe-based metallic glass.

    Science.gov (United States)

    Ramasamy, Parthiban; Szabo, Attila; Borzel, Stefan; Eckert, Jürgen; Stoica, Mihai; Bárdos, András

    2016-10-11

    Soft ferromagnetic Fe-based bulk metallic glass key-shaped specimens with a maximum and minimum width of 25.4 and 5 mm, respectively, were successfully produced using a high pressure die casting (HPDC) method, The influence of die material, alloy temperature and flow rate on the microstructure, thermal stability and soft ferromagnetic properties has been studied. The results suggest that a steel die in which the molten metal flows at low rate and high temperature can be used to produce completely glassy samples. This can be attributed to the laminar filling of the mold and to a lower heat transfer coefficient, which avoids the skin effect in the steel mold. In addition, magnetic measurements reveal that the amorphous structure of the material is maintained throughout the key-shaped samples. Although it is difficult to control the flow and cooling rate of the molten metal in the corners of the key due to different cross sections, this can be overcome by proper tool geometry. The present results confirm that HPDC is a suitable method for the casting of Fe-based bulk glassy alloys even with complex geometries for a broad range of applications.

  7. High pressure die casting of Fe-based metallic glass

    Science.gov (United States)

    Ramasamy, Parthiban; Szabo, Attila; Borzel, Stefan; Eckert, Jürgen; Stoica, Mihai; Bárdos, András

    2016-10-01

    Soft ferromagnetic Fe-based bulk metallic glass key-shaped specimens with a maximum and minimum width of 25.4 and 5 mm, respectively, were successfully produced using a high pressure die casting (HPDC) method, The influence of die material, alloy temperature and flow rate on the microstructure, thermal stability and soft ferromagnetic properties has been studied. The results suggest that a steel die in which the molten metal flows at low rate and high temperature can be used to produce completely glassy samples. This can be attributed to the laminar filling of the mold and to a lower heat transfer coefficient, which avoids the skin effect in the steel mold. In addition, magnetic measurements reveal that the amorphous structure of the material is maintained throughout the key-shaped samples. Although it is difficult to control the flow and cooling rate of the molten metal in the corners of the key due to different cross sections, this can be overcome by proper tool geometry. The present results confirm that HPDC is a suitable method for the casting of Fe-based bulk glassy alloys even with complex geometries for a broad range of applications.

  8. Heavy metals contamination and their risk assessment around the abandoned base metals and Au-Ag mines in Korea

    Science.gov (United States)

    Chon, Hyo-Taek

    2017-04-01

    Heavy metals contamination in the areas of abandoned Au-Ag and base metal mines in Korea was investigated in order to assess the level of metal pollution, and to draw general summaries about the fate of toxic heavy metals in different environments. Efforts have been made to compare the level of heavy metals, chemical forms, and plant uptake of heavy metals in each mine site. In the base-metals mine areas, significant levels of Cd, Cu, Pb and Zn were found in mine dump soils developed over mine waste materials and tailings. Leafy vegetables tend to accumulate heavy metals(in particular, Cd and Zn) higher than other crop plants, and high metal concentrations in rice crops may affect the local residents' health. In the Au-Ag mining areas, arsenic would be the most characteristic contaminant in the nearby environment. Arsenic and heavy metals were found to be mainly associated with sulfide gangue minerals, and the mobility of these metals would be enhanced by the effect of continuing weathering and oxidation. According to the sequential extraction of metals in soils, most heavy metals were identified as non-residual chemical forms, and those are very susceptible to the change of ambient conditions of a nearby environment. The concept of pollution index(PI) of soils gives important information on the extent and degree of multi-element contamination, and can be applied to the evaluation of mine soils before their agricultural use and remediation. The risk assessment process comprising exposure assessment, dose-response assessment, and risk characterization was discussed, and the results of non-cancer risk of As, Cd, and Zn, and those of cancer risk of As were suggested.

  9. Facet formation and ohmic contacts for laser diodes on non- and semipolar GaN

    Energy Technology Data Exchange (ETDEWEB)

    Rass, Jens; Ploch, Simon; Vogt, Patrick [Technische Universitaet Berlin (Germany). Institute of Solid State Physics; Wernicke, Tim; Redaelli, Luca; Einfeldt, Sven [Ferdinand- Braun-Institut fuer Hoechstfrequenztechnik, Berlin (Germany); Kneissl, Michael [Technische Universitaet Berlin (Germany). Institute of Solid State Physics; Ferdinand- Braun-Institut fuer Hoechstfrequenztechnik, Berlin (Germany)

    2009-07-01

    Group-III-Nitride heterostructures grown on nonpolar and semipolar planes allow the realization of highly efficient devices such as laser diodes and LEDs due to the reduction or elimination of the quantum confined Stark effect. However, the realization of these devices poses a number of challenges, in particular the formation of smooth laser facets and the fabrication of ohmic contacts. In this talk optimized schemes for facet formation and contact resistance reduction for nitride based devices on non- and semipolar planes are presented, and various concepts are discussed. We discuss a laser scribing process that allows the cleaving of facets along the c- and a-plane for devices grown on nonpolar substrates. For semipolar planes there is no low-index cleavage plane in order to form resonators along the projection of the c-axis. Therefore we have investigated etching techniques in order to produce flat facets perpendicular to the plane of growth. For the challenging formation of p-type contacts to GaN we discuss different methods such as chemical treatments, different metallization schemes and capping layers to reduce the contact resistivity.

  10. Metal shell technology based upon hollow jet instability

    International Nuclear Information System (INIS)

    Kendall, J.M.; Lee, M.C.; Wang, T.G.

    1982-01-01

    Spherical shells of submillimeter size are sought as ICF targets. Such shells must be dimensionally precise, smooth, of high strength, and composed of a high atomic number material. We describe a technology for the production of shells based upon the hydrodynamic instability of an annular jet of molten metal. We have produced shells in the 0.7--2.0 mm size range using tin as a test material. Specimens exhibit good sphericity, fair concentricity, and excellent finish over most of the surface. Work involving a gold--lead--antimony alloy is in progress. Droplets of this are amorphous and possess superior surface finish. The flow of tin models that of the alloy well; experiments on both metals show that the technique holds considerable promise

  11. Silicon-based metallic micro grid for electron field emission

    International Nuclear Information System (INIS)

    Kim, Jaehong; Jeon, Seok-Gy; Kim, Jung-Il; Kim, Geun-Ju; Heo, Duchang; Shin, Dong Hoon; Sun, Yuning; Lee, Cheol Jin

    2012-01-01

    A micro-scale metal grid based on a silicon frame for application to electron field emission devices is introduced and experimentally demonstrated. A silicon lattice containing aperture holes with an area of 80 × 80 µm 2 and a thickness of 10 µm is precisely manufactured by dry etching the silicon on one side of a double-polished silicon wafer and by wet etching the opposite side. Because a silicon lattice is more rigid than a pure metal lattice, a thin layer of Au/Ti deposited on the silicon lattice for voltage application can be more resistant to the geometric stress caused by the applied electric field. The micro-fabrication process, the images of the fabricated grid with 88% geometric transparency and the surface profile measurement after thermal feasibility testing up to 700 °C are presented. (paper)

  12. Metal nanoparticle film-based room temperature Coulomb transistor.

    Science.gov (United States)

    Willing, Svenja; Lehmann, Hauke; Volkmann, Mirjam; Klinke, Christian

    2017-07-01

    Single-electron transistors would represent an approach to developing less power-consuming microelectronic devices if room temperature operation and industry-compatible fabrication were possible. We present a concept based on stripes of small, self-assembled, colloidal, metal nanoparticles on a back-gate device architecture, which leads to well-defined and well-controllable transistor characteristics. This Coulomb transistor has three main advantages. By using the scalable Langmuir-Blodgett method, we combine high-quality chemically synthesized metal nanoparticles with standard lithography techniques. The resulting transistors show on/off ratios above 90%, reliable and sinusoidal Coulomb oscillations, and room temperature operation. Furthermore, this concept allows for versatile tuning of the device properties such as Coulomb energy gap and threshold voltage, as well as period, position, and strength of the oscillations.

  13. Metal nanoparticle film–based room temperature Coulomb transistor

    Science.gov (United States)

    Willing, Svenja; Lehmann, Hauke; Volkmann, Mirjam; Klinke, Christian

    2017-01-01

    Single-electron transistors would represent an approach to developing less power–consuming microelectronic devices if room temperature operation and industry-compatible fabrication were possible. We present a concept based on stripes of small, self-assembled, colloidal, metal nanoparticles on a back-gate device architecture, which leads to well-defined and well-controllable transistor characteristics. This Coulomb transistor has three main advantages. By using the scalable Langmuir-Blodgett method, we combine high-quality chemically synthesized metal nanoparticles with standard lithography techniques. The resulting transistors show on/off ratios above 90%, reliable and sinusoidal Coulomb oscillations, and room temperature operation. Furthermore, this concept allows for versatile tuning of the device properties such as Coulomb energy gap and threshold voltage, as well as period, position, and strength of the oscillations. PMID:28740864

  14. Colored cool colorants based on rare earth metal ions

    Energy Technology Data Exchange (ETDEWEB)

    Sreeram, Kalarical Janardhanan; Aby, Cheruvathoor Poulose; Nair, Balachandran Unni; Ramasami, Thirumalachari [Chemical Laboratory, Central Leather Research Institute, Council of Scientific and Industrial Research, Adyar, Chennai 600 020 (India)

    2008-11-15

    Colored pigments with high near infrared reflectance and not based on toxic metal ions like cadmium, lead and cobalt are being sought as cool colorants. Through appropriate doping two pigments Ce-Pr-Mo and Ce-Pr-Fe have been developed to offer a reddish brown and reddish orange color, respectively. These pigments have been characterized and found to be highly crystalline with an average size of 300 nm. A shift in band gap energy from 2.21 to 2.18 eV has been observed when Li{sub 2}CO{sub 3} was used as a mineralizer. Scanning electron microscope-energy dispersive X-ray analysis (SEM-EDAX) measurement indicate a uniform grind shape and distribution of metal ion, with over 65% reflectance in the NIR region, these pigments can well serve as cool colorants. (author)

  15. Metal-mediated DNA base pairing: alternatives to hydrogen-bonded Watson-Crick base pairs.

    Science.gov (United States)

    Takezawa, Yusuke; Shionoya, Mitsuhiko

    2012-12-18

    With its capacity to store and transfer the genetic information within a sequence of monomers, DNA forms its central role in chemical evolution through replication and amplification. This elegant behavior is largely based on highly specific molecular recognition between nucleobases through the specific hydrogen bonds in the Watson-Crick base pairing system. While the native base pairs have been amazingly sophisticated through the long history of evolution, synthetic chemists have devoted considerable efforts to create alternative base pairing systems in recent decades. Most of these new systems were designed based on the shape complementarity of the pairs or the rearrangement of hydrogen-bonding patterns. We wondered whether metal coordination could serve as an alternative driving force for DNA base pairing and why hydrogen bonding was selected on Earth in the course of molecular evolution. Therefore, we envisioned an alternative design strategy: we replaced hydrogen bonding with another important scheme in biological systems, metal-coordination bonding. In this Account, we provide an overview of the chemistry of metal-mediated base pairing including basic concepts, molecular design, characteristic structures and properties, and possible applications of DNA-based molecular systems. We describe several examples of artificial metal-mediated base pairs, such as Cu(2+)-mediated hydroxypyridone base pair, H-Cu(2+)-H (where H denotes a hydroxypyridone-bearing nucleoside), developed by us and other researchers. To design the metallo-base pairs we carefully chose appropriate combinations of ligand-bearing nucleosides and metal ions. As expected from their stronger bonding through metal coordination, DNA duplexes possessing metallo-base pairs exhibited higher thermal stability than natural hydrogen-bonded DNAs. Furthermore, we could also use metal-mediated base pairs to construct or induce other high-order structures. These features could lead to metal-responsive functional

  16. Metal-organic frameworks based membranes for liquid separation.

    Science.gov (United States)

    Li, Xin; Liu, Yuxin; Wang, Jing; Gascon, Jorge; Li, Jiansheng; Van der Bruggen, Bart

    2017-11-27

    Metal-organic frameworks (MOFs) represent a fascinating class of solid crystalline materials which can be self-assembled in a straightforward manner by the coordination of metal ions or clusters with organic ligands. Owing to their intrinsic porous characteristics, unique chemical versatility and abundant functionalities, MOFs have received substantial attention for diverse industrial applications, including membrane separation. Exciting research activities ranging from fabrication strategies to separation applications of MOF-based membranes have appeared. Inspired by the marvelous achievements of MOF-based membranes in gas separations, liquid separations are also being explored for the purpose of constructing continuous MOFs membranes or MOF-based mixed matrix membranes. Although these are in an emerging stage of vigorous development, most efforts are directed towards improving the liquid separation efficiency with well-designed MOF-based membranes. Therefore, as an increasing trend in membrane separation, the field of MOF-based membranes for liquid separation is highlighted in this review. The criteria for judicious selection of MOFs in fabricating MOF-based membranes are given. Special attention is paid to rational design strategies for MOF-based membranes, along with the latest application progress in the area of liquid separations, such as pervaporation, water treatment, and organic solvent nanofiltration. Moreover, some attractive dual-function applications of MOF-based membranes in the removal of micropollutants, degradation, and antibacterial activity are also reviewed. Finally, we define the remaining challenges and future opportunities in this field. This Tutorial Review provides an overview and outlook for MOF-based membranes for liquid separations. Further development of MOF-based membranes for liquid separation must consider the demands of strict separation standards and environmental safety for industrial application.

  17. [The bonding mechanisms of base metals for metal-ceramic crown microstructure analysis of bonding agent and gold bond between porcelain and base metals].

    Science.gov (United States)

    Wang, C C; Hsu, C S

    1996-06-01

    The use of base metal alloys for porcelain fused to a metal crown and bridges has increased recently because of lower price, high hardness, high tensile strength and high elastic modulus. The addition of beryllium to base metal alloys increased fluidity and improved casting fitness. Beryllium also controlled surface oxidation and bonding strength. The bonding agent and gold bonding agent also affected the bonding strength between porcelain and metal alloys. Four commercially available ceramic base alloys were studied (two alloys contained beryllium element, another two did not). The purpose of this investigation was to study the microstructure between porcelain matrix, bonding agent and alloy matrix interfaces. A scanning electron micro-probe analyzer and energy dispersive X-ray spectroscopy (EDXS) were used to study the distribution of elements (Ni, Cr, Mo, Cu, O, Si, Sn, Al) in four base alloys. The following results were obtained: 1. The thickness of the oxidized layer of Rexillium III alloy and Unitbond alloy (contained beryllium) was thinner than Unibond alloy and Wiron 88 alloy (no beryllium). 2. The thickness of the oxidized layer of alloys in air (10 minutes and 30 minutes) was thinner in Unitbond (2.45 microns and 3.80 microns) and thicker in Wiron 88 (4.39 microns and 5.96 microns). 3. The thickness of the oxidized layer occurring for a duration of ten minutes (in vaccum) showed that the Rexillium III alloy was the thinnest (1.93 microns), and Wiron 88 alloy was the thickest (2.30 microns). But in thirty minutes (vacuum), Unitbond alloy was the thinnest (3.37 microns), and Wiron 88 alloy was the thickest (5.51 microns). 4. The intensity of Cr elements was increased obviously near the interface between Unitbond alloy, Wiron 88 alloy (no beryllium) and oxidized layer, but the intensity of Ni and Mo elements was slightly increased. The intensity of Cr element was not increased markedly between Rexillium III alloy, Unitbond alloy (beryllium) and oxidized

  18. Metal-directed topological diversity of three fluorescent metal-organic frameworks based on a new tetracarboxylate strut

    KAUST Repository

    Lou, Xinhua

    2013-01-01

    Three d- or p-block metal ions based metal-organic frameworks (MOFs) were isolated by employing a new tetracarboxylate linker, featuring unusual flu, self-interpenetrated lvt and new (3,5)-c topological nets, respectively. Interesting photoluminescent properties of these solid-state materials were also observed. © 2013 The Royal Society of Chemistry.

  19. Ionic behavior of organic-inorganic metal halide perovskite based metal-oxide-semiconductor capacitors.

    Science.gov (United States)

    Wang, Yucheng; Zhang, Yuming; Pang, Tiqiang; Xu, Jie; Hu, Ziyang; Zhu, Yuejin; Tang, Xiaoyan; Luan, Suzhen; Jia, Renxu

    2017-05-24

    Organic-inorganic metal halide perovskites are promising semiconductors for optoelectronic applications. Despite the achievements in device performance, the electrical properties of perovskites have stagnated. Ion migration is speculated to be the main contributing factor for the many unusual electrical phenomena in perovskite-based devices. Here, to understand the intrinsic electrical behavior of perovskites, we constructed metal-oxide-semiconductor (MOS) capacitors based on perovskite films and performed capacitance-voltage (C-V) and current-voltage (I-V) measurements of the capacitors. The results provide direct evidence for the mixed ionic-electronic transport behavior within perovskite films. In the dark, there is electrical hysteresis in both the C-V and I-V curves because the mobile negative ions take part in charge transport despite frequency modulation. However, under illumination, the large amount of photoexcited free carriers screens the influence of the mobile ions with a low concentration, which is responsible for the normal C-V properties. Validation of ion migration for the gate-control ability of MOS capacitors is also helpful for the investigation of perovskite MOS transistors and other gate-control photovoltaic devices.

  20. Characterization of vertical GaN p-n diodes and junction field-effect transistors on bulk GaN down to cryogenic temperatures

    Science.gov (United States)

    Kizilyalli, I. C.; Aktas, O.

    2015-12-01

    There is great interest in wide-bandgap semiconductor devices and most recently in vertical GaN structures for power electronic applications such as power supplies, solar inverters and motor drives. In this paper the temperature-dependent electrical behavior of vertical GaN p-n diodes and vertical junction field-effect transistors fabricated on bulk GaN substrates of low defect density (104 to 106 cm-2) is described. Homoepitaxial MOCVD growth of GaN on its native substrate and the ability to control the doping in the drift layers in GaN have allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations as low as 1 × 1015 cm-3. This parameter range is suitable for applications requiring breakdown voltages of 1.2 kV to 5 kV. Mg, which is used as a p-type dopant in GaN, is a relatively deep acceptor (E A ≈ 0.18 eV) and susceptible to freeze-out at temperatures below 200 K. The loss of holes in p-GaN has a deleterious effect on p-n junction behavior, p-GaN contacts and channel control in junction field-effect transistors at temperatures below 200 K. Impact ionization-based avalanche breakdown (BV > 1200 V) in GaN p-n junctions is characterized between 77 K and 423 K for the first time. At higher temperatures the p-n junction breakdown voltage improves due to increased phonon scattering. A positive temperature coefficient in the breakdown voltage is demonstrated down to 77 K; however, the device breakdown characteristics are not as abrupt at temperatures below 200 K. On the other hand, contact resistance to p-GaN is reduced dramatically above room temperature, improving the overall device performance in GaN p-n diodes in all cases except where the n-type drift region resistance dominates the total forward resistance. In this case, the electron mobility can be deconvolved and is found to decrease with T -3/2, consistent with a phonon scattering model. Also, normally-on vertical junction

  1. Characterization of vertical GaN p–n diodes and junction field-effect transistors on bulk GaN down to cryogenic temperatures

    International Nuclear Information System (INIS)

    Kizilyalli, I C; Aktas, O

    2015-01-01

    There is great interest in wide-bandgap semiconductor devices and most recently in vertical GaN structures for power electronic applications such as power supplies, solar inverters and motor drives. In this paper the temperature-dependent electrical behavior of vertical GaN p–n diodes and vertical junction field-effect transistors fabricated on bulk GaN substrates of low defect density (10 4 to 10 6 cm −2 ) is described. Homoepitaxial MOCVD growth of GaN on its native substrate and the ability to control the doping in the drift layers in GaN have allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations as low as 1 × 10 15 cm −3 . This parameter range is suitable for applications requiring breakdown voltages of 1.2 kV to 5 kV. Mg, which is used as a p-type dopant in GaN, is a relatively deep acceptor (E A  ≈ 0.18 eV) and susceptible to freeze-out at temperatures below 200 K. The loss of holes in p-GaN has a deleterious effect on p–n junction behavior, p-GaN contacts and channel control in junction field-effect transistors at temperatures below 200 K. Impact ionization-based avalanche breakdown (BV > 1200 V) in GaN p–n junctions is characterized between 77 K and 423 K for the first time. At higher temperatures the p–n junction breakdown voltage improves due to increased phonon scattering. A positive temperature coefficient in the breakdown voltage is demonstrated down to 77 K; however, the device breakdown characteristics are not as abrupt at temperatures below 200 K. On the other hand, contact resistance to p-GaN is reduced dramatically above room temperature, improving the overall device performance in GaN p–n diodes in all cases except where the n-type drift region resistance dominates the total forward resistance. In this case, the electron mobility can be deconvolved and is found to decrease with T −3/2 , consistent with a phonon scattering model. Also

  2. Band alignments and improved leakage properties of (La2O3)0.5(SiO2)0.5/SiO2/GaN stacks for high-temperature metal-oxide-semiconductor field-effect transistor applications

    Science.gov (United States)

    Gao, L. G.; Xu, B.; Guo, H. X.; Xia, Y. D.; Yin, J.; Liu, Z. G.

    2009-06-01

    The band alignments of (La2O3)0.5(SiO2)0.5(LSO)/GaN and LSO/SiO2/GaN gate dielectric stacks were investigated comparatively by using x-ray photoelectron spectroscopy. The valence band offsets for LSO/GaN stack and LSO/SiO2/GaN stack are 0.88 and 1.69 eV, respectively, while the corresponding conduction band offsets are found to be 1.40 and 1.83 eV, respectively. Measurements of the leakage current density as function of temperature revealed that the LSO/SiO2/GaN stack has much lower leakage current density than that of the LSO/GaN stack, especially at high temperature. It is concluded that the presence of a SiO2 buffer layer increases band offsets and reduces the leakage current density effectively.

  3. Topical Review: Development of overgrown semi-polar GaN for high efficiency green/yellow emission

    Science.gov (United States)

    Wang, T.

    2016-09-01

    The most successful example of large lattice-mismatched epitaxial growth of semiconductors is the growth of III-nitrides on sapphire, leading to the award of the Nobel Prize in 2014 and great success in developing InGaN-based blue emitters. However, the majority of achievements in the field of III-nitride optoelectronics are mainly limited to polar GaN grown on c-plane (0001) sapphire. This polar orientation poses a number of fundamental issues, such as reduced quantum efficiency, efficiency droop, green and yellow gap in wavelength coverage, etc. To date, it is still a great challenge to develop longer wavelength devices such as green and yellow emitters. One clear way forward would be to grow III-nitride device structures along a semi-/non-polar direction, in particular, a semi-polar orientation, which potentially leads to both enhanced indium incorporation into GaN and reduced quantum confined Stark effects. This review presents recent progress on developing semi-polar GaN overgrowth technologies on sapphire or Si substrates, the two kinds of major substrates which are cost-effective and thus industry-compatible, and also demonstrates the latest achievements on electrically injected InGaN emitters with long emission wavelengths up to and including amber on overgrown semi-polar GaN. Finally, this review presents a summary and outlook on further developments for semi-polar GaN based optoelectronics.

  4. Spectrophotometric study of some metal ions using some Schiff's bases

    International Nuclear Information System (INIS)

    Elnager, Nawal Mohomed Ibrahim

    2000-05-01

    In this work two schiff bases namely N,N Bis(benzoyl acetone)-o-phenylene diamine (NNBBPD) and N,N Bis(benzoyl acetone)-isopropylene diamine (NNBBAID) were prepared by direct coupling of benzoyl acetone with o-phenylene and isopropylene diamine respectively. The two reagents were identified by IR spectra, thin layer chromatography (TLC) and determination of the percentage of nitrogen contents (N%). It is found that the two reagents form coloured chelates with Fe (II), Fe (III), Cu (II), U (VI), Ni (II) and Co (II). The two reagents were used for the determination of Fe (II), Fe (III) and U (VI). The formulate of these metal ion complexes were obtained using continuous variations, mole ratio and slope ratio methods. Effect of two micelles, namely sodium n-dodecyl sulphate (SDS) and hexadecyl pyridinum broinide monohydrate (HPB) on metal ion complexes were studied. It is found that both of them increase the solubility and the absorbances of the metal ion complexes with variable effects of the absorption maxima. Calibration curves for Fe (II), Fe (II) and U (VI) were obtained in optimum conditions of pH and micelles solutions. (Author)

  5. Metal hydrides based high energy density thermal battery

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Zhigang Zak, E-mail: zak.fang@utah.edu [Department of Metallurgical Engineering, The University of Utah, 135 South 1460 East, Room 412, Salt Lake City, UT 84112-0114 (United States); Zhou, Chengshang; Fan, Peng [Department of Metallurgical Engineering, The University of Utah, 135 South 1460 East, Room 412, Salt Lake City, UT 84112-0114 (United States); Udell, Kent S. [Department of Metallurgical Engineering, The University of Utah, 50 S. Central Campus Dr., Room 2110, Salt Lake City, UT 84112-0114 (United States); Bowman, Robert C. [Department of Metallurgical Engineering, The University of Utah, 135 South 1460 East, Room 412, Salt Lake City, UT 84112-0114 (United States); Vajo, John J.; Purewal, Justin J. [HRL Laboratories, LLC, 3011 Malibu Canyon Road, Malibu, CA 90265 (United States); Kekelia, Bidzina [Department of Metallurgical Engineering, The University of Utah, 50 S. Central Campus Dr., Room 2110, Salt Lake City, UT 84112-0114 (United States)

    2015-10-05

    Highlights: • The principle of the thermal battery using advanced metal hydrides was demonstrated. • The thermal battery used MgH{sub 2} and TiMnV as a working pair. • High energy density can be achieved by the use of MgH{sub 2} to store thermal energy. - Abstract: A concept of thermal battery based on advanced metal hydrides was studied for heating and cooling of cabins in electric vehicles. The system utilized a pair of thermodynamically matched metal hydrides as energy storage media. The pair of hydrides that was identified and developed was: (1) catalyzed MgH{sub 2} as the high temperature hydride material, due to its high energy density and enhanced kinetics; and (2) TiV{sub 0.62}Mn{sub 1.5} alloy as the matching low temperature hydride. Further, a proof-of-concept prototype was built and tested, demonstrating the potential of the system as HVAC for transportation vehicles.

  6. Metallic molybdenum disulfide nanosheet-based electrochemical actuators

    Science.gov (United States)

    Acerce, Muharrem; Akdoğan, E. Koray; Chhowalla, Manish

    2017-09-01

    Actuators that convert electrical energy to mechanical energy are useful in a wide variety of electromechanical systems and in robotics, with applications such as steerable catheters, adaptive wings for aircraft and drag-reducing wind turbines. Actuation systems can be based on various stimuli, such as heat, solvent adsorption/desorption, or electrochemical action (in systems such as carbon nanotube electrodes, graphite electrodes, polymer electrodes and metals). Here we demonstrate that the dynamic expansion and contraction of electrode films formed by restacking chemically exfoliated nanosheets of two-dimensional metallic molybdenum disulfide (MoS2) on thin plastic substrates can generate substantial mechanical forces. These films are capable of lifting masses that are more than 150 times that of the electrode over several millimetres and for hundreds of cycles. Specifically, the MoS2 films are able to generate mechanical stresses of about 17 megapascals—higher than mammalian muscle (about 0.3 megapascals) and comparable to ceramic piezoelectric actuators (about 40 megapascals)—and strains of about 0.6 per cent, operating at frequencies up to 1 hertz. The actuation performance is attributed to the high electrical conductivity of the metallic 1T phase of MoS2 nanosheets, the elastic modulus of restacked MoS2 layers (2 to 4 gigapascals) and fast proton diffusion between the nanosheets. These results could lead to new electrochemical actuators for high-strain and high-frequency applications.

  7. Amphoteric arsenic in GaN

    CERN Document Server

    Wahl, U; Araújo, J P; Rita, E; Soares, JC

    2007-01-01

    We have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive $^{73}$As. We give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As$\\scriptstyle_{Ga}\\,$ " anti-sites ” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called “ miscibility gap ” in ternary GaAs$\\scriptstyle_{1-x}$N$\\scriptstyle_{x}$ compounds, which cannot be grown with a single phase for values of $x$ in the range 0.1<${x}$< 0.99.

  8. Excitonic transitions in homoepitaxial GaN

    Energy Technology Data Exchange (ETDEWEB)

    Martinez-Criado, G.; Cros, A.; Cantarero, A. [Materials Science Inst. and Dept. of Applied Physics, Univ. of Valencia (Spain); Miskys, C.R.; Ambacher, O.; Stutzmann, M. [Technische Univ. Muenchen, Garching (Germany). Walter-Schottky-Inst. fuer Physikalische Grundlagen der Halbleiterelektronik

    2001-11-08

    The photoluminescence spectrum of a high quality homoepitaxial GaN film has been measured as a function of temperature. As temperature increases the recombination of free excitons dominates the spectra. Their energy shift has successfully fitted in that temperature range by means of the Bose-Einstein expression instead of Varshni's relationship. Values for the parameters of both semi-empirical relations describing the energy shift are reported and compared with the literature. (orig.)

  9. Chitosan based metallic nanocomposite scaffolds as antimicrobial wound dressings.

    Science.gov (United States)

    Mohandas, Annapoorna; Deepthi, S; Biswas, Raja; Jayakumar, R

    2018-09-01

    Chitosan based nanocomposite scaffolds have attracted wider applications in medicine, in the area of drug delivery, tissue engineering and wound healing. Chitosan matrix incorporated with nanometallic components has immense potential in the area of wound dressings due to its antimicrobial properties. This review focuses on the different combinations of Chitosan metal nanocomposites such as Chitosan/nAg, Chitosan/nAu, Chitosan/nCu, Chitosan/nZnO and Chitosan/nTiO 2 towards enhancement of healing or infection control with special reference to the antimicrobial mechanism of action and toxicity.

  10. Spintronic materials and devices based on antiferromagnetic metals

    Directory of Open Access Journals (Sweden)

    Y.Y. Wang

    2017-04-01

    Full Text Available In this paper, we review our recent experimental developments on antiferromagnet (AFM spintronics mainly comprising Mn-based noncollinear AFM metals. IrMn-based tunnel junctions and Hall devices have been investigated to explore the manipulation of AFM moments by magnetic fields, ferromagnetic materials and electric fields. Room-temperature tunneling anisotropic magnetoresistance based on IrMn as well as FeMn has been successfully achieved, and electrical control of the AFM exchange spring is realized by adopting ionic liquid. In addition, promising spin-orbit effects in AFM as well as spin transfer via AFM spin waves reported by different groups have also been reviewed, indicating that the AFM can serve as an efficient spin current source. To explore the crucial role of AFM acting as efficient generators, transmitters, and detectors of spin currents is an emerging topic in the field of magnetism today. AFM metals are now ready to join the rapidly developing fields of basic and applied spintronics, enriching this area of solid-state physics and microelectronics.

  11. A resonant force sensor based on ionic polymer metal composites

    International Nuclear Information System (INIS)

    Bonomo, Claudia; Fortuna, Luigi; Giannone, Pietro; Graziani, Salvatore; Strazzeri, Salvatore

    2008-01-01

    In this paper a novel force sensor, based on ionic polymer metal composites (IPMCs), is presented. The system has DC sensing capabilities and is able to work in the range of a few millinewtons. IPMCs are emerging materials used to realize motion actuators and sensors. An IPMC strip is activated in a beam fixed/simply-supported configuration. The beam is tightened at the simply-supported end by a force. This influences the natural resonant frequency of the beam; the value of the resonant frequency is used in the proposed system to estimate the force applied in the axial direction. The performance of the system based on the IPMC material has proved to be comparable with that of sensors based on other sensing mechanisms. This suggests the possibility of using this class of polymeric devices to realize PMEMS (plastic micro electrical mechanical systems) sensors

  12. A resonant force sensor based on ionic polymer metal composites

    Science.gov (United States)

    Bonomo, Claudia; Fortuna, Luigi; Giannone, Pietro; Graziani, Salvatore; Strazzeri, Salvatore

    2008-02-01

    In this paper a novel force sensor, based on ionic polymer metal composites (IPMCs), is presented. The system has DC sensing capabilities and is able to work in the range of a few millinewtons. IPMCs are emerging materials used to realize motion actuators and sensors. An IPMC strip is activated in a beam fixed/simply-supported configuration. The beam is tightened at the simply-supported end by a force. This influences the natural resonant frequency of the beam; the value of the resonant frequency is used in the proposed system to estimate the force applied in the axial direction. The performance of the system based on the IPMC material has proved to be comparable with that of sensors based on other sensing mechanisms. This suggests the possibility of using this class of polymeric devices to realize PMEMS (plastic micro electrical mechanical systems) sensors.

  13. MgNiO-based metal-semiconductor- metal ultraviolet photodetector

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Yanmin; Zhang Jiying; Jiang Dayong; Shan Chongxin; Zhang Zhenzhong; Yao Bin; Zhao Dongxu; Shen Dezhen, E-mail: zhangjy53@yahoo.com.c [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)

    2009-05-07

    In this study, we report the growth of Mg{sub x}Ni{sub 1-x}O thin films on quartz substrates by electron beam evaporation. The absorption edge shows a blue shift from 340 nm to 260 nm with increase in the Mg content from 0.2 to 0.8. A metal-semiconductor-metal structured photodetector is fabricated from the Mg{sub 0.2}Ni{sub 0.8}O film. At a bias of 5 V, the dark current of the photodetector is about 70 nA. The maximum responsivity is about 147.3 {mu}A W{sup -1} at 320 nm. In addition, the ultraviolet (UV) (320 nm) to visible (400 nm) rejection ratio is nearly two orders of magnitude. Based on these results, it is proposed that Mg{sub x}Ni{sub 1-x}O is a potential candidate for application in UV photodetectors. (fast track communication)

  14. Optical excitation of Er centers in GaN epilayers grown by MOCVD

    Science.gov (United States)

    George, D. K.; Hawkins, M. D.; Jiang, H. X.; Lin, J. Y.; Zavada, J. M.; Vinh, N. Q.

    2016-02-01

    In this paper we present results of photoluminescence (PL), photoluminescence excitation (PLE), and time resolved PL spectroscopy of the 4I13/2 → 4I15/2 transition in Er optical centers in GaN epilayers grown by metal-organic chemical vapor deposition. Under resonance excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, the PL and PLE spectra reveal an existence of two types of Er optical centers from isolated and the defect-related Er centers in GaN epilayers. These centers have different PL spectra, local defect environments, decay dynamics, and excitation cross-sections. The isolated Er optical center, which can be excited by either excitation mechanism, has the same decay dynamics, but possesses a much higher cross-section under band-to-band excitation. In contrast, the defect-related Er center can only be observed through band-to-band excitation but has the largest crosssection. Our results indicate pathways for efficient optical excitation of Er-doped GaN semiconductors.

  15. Ultraviolet Laser SQUID Microscope for GaN Blue Light Emitting Diode Testing

    International Nuclear Information System (INIS)

    Daibo, M; Kamiwano, D; Kurosawa, T; Yoshizawa, M; Tayama, N

    2006-01-01

    We carried out non-contacting measurements of photocurrent distributions in GaN blue light emitting diode (LED) chips using our newly developed ultraviolet (UV) laser SQUID microscope. The UV light generates the photocurrent, and then the photocurrent induces small magnetic fields around the chip. An off-axis arranged HTS-SQUID magnetometer is employed to detect a vector magnetic field whose typical amplitude is several hundred femto-tesla. Generally, it is difficult to obtain Ohmic contacts for p-type GaN because of the low hole concentration in the p-type epitaxial layer and the lack of any available metal with a higher work function compared with the p-type GaN. Therefore, a traditional probecontacted electrical test is difficult to conduct for wide band gap semiconductors without an adequately annealed electrode. Using the UV-laser SQUID microscope, the photocurrent can be measured without any electrical contact. We show the photocurrent vector map which was reconstructed from measured magnetic fields data. We also demonstrate how we found the position of a defect of the electrical short circuits in the LED chip

  16. Selectively Enhanced UV-A Photoresponsivity of a GaN MSM UV Photodetector with a Step-Graded AlxGa1−xN Buffer Layer

    Directory of Open Access Journals (Sweden)

    Chang-Ju Lee

    2017-07-01

    Full Text Available The UV-to-visible rejection ratio is one of the important figure of merits of GaN-based UV photodetectors. For cost-effectiveness and large-scale fabrication of GaN devices, we tried to grow a GaN epitaxial layer on silicon substrate with complicated buffer layers for a stress-release. It is known that the structure of the buffer layers affects the performance of devices fabricated on the GaN epitaxial layers. In this study, we show that the design of a buffer layer structure can make effect on the UV-to-visible rejection ratio of GaN UV photodetectors. The GaN photodetector fabricated on GaN-on-silicon substrate with a step-graded AlxGa−xN buffer layer has a highly-selective photoresponse at 365-nm wavelength. The UV-to-visible rejection ratio of the GaN UV photodetector with the step-graded AlxGa1−xN buffer layer was an order-of-magnitude higher than that of a photodetector with a conventional GaN/AlN multi buffer layer. The maximum photoresponsivity was as high as 5 × 10−2 A/W. This result implies that the design of buffer layer is important for photoresponse characteristics of GaN UV photodetectors as well as the crystal quality of the GaN epitaxial layers.

  17. Insulating gallium oxide layer produced by thermal oxidation of gallium-polar GaN: Insulating gallium oxide layer produced by thermal oxidation of gallium-polar GaN

    Energy Technology Data Exchange (ETDEWEB)

    Hossain, T. [Kansas State Univ., Manhattan, KS (United States); Wei, D. [Kansas State Univ., Manhattan, KS (United States); Nepal, N. [Naval Research Lab. (NRL), Washington, DC (United States); Garces, N. Y. [Naval Research Lab. (NRL), Washington, DC (United States); Hite, J. K. [Naval Research Lab. (NRL), Washington, DC (United States); Meyer, H. M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Eddy, C. R. [Naval Research Lab. (NRL), Washington, DC (United States); Baker, Troy [Nitride Solutions, Wichita, KS (United States); Mayo, Ashley [Nitride Solutions, Wichita, KS (United States); Schmitt, Jason [Nitride Solutions, Wichita, KS (United States); Edgar, J. H. [Kansas State Univ., Manhattan, KS (United States)

    2014-02-24

    We report the benefits of dry oxidation of n -GaN for the fabrication of metal-oxide-semiconductor structures. GaN thin films grown on sapphire by MOCVD were thermally oxidized for 30, 45 and 60 minutes in a pure oxygen atmosphere at 850 °C to produce thin, smooth GaOx layers. Moreover, the GaN sample oxidized for 30 minutes had the best properties. Its surface roughness (0.595 nm) as measured by atomic force microscopy (AFM) was the lowest. Capacitance-voltage measurements showed it had the best saturation in accumulation region and the sharpest transition from accumulation to depletion regions. Under gate voltage sweep, capacitance-voltage hysteresis was completely absent. The interface trap density was minimum (Dit = 2.75×1010 cm–2eV–1) for sample oxidized for 30 mins. These results demonstrate a high quality GaOx layer is beneficial for GaN MOSFETs.

  18. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  19. Multifunctional methacrylate-based coatings for glass and metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Pospiech, Doris, E-mail: pospiech@ipfdd.de [Leibniz-Institut für Polymerforschung Dresden e. V., Dresden (Germany); Jehnichen, Dieter [Leibniz-Institut für Polymerforschung Dresden e. V., Dresden (Germany); Starke, Sandra; Müller, Felix [Leibniz-Institut für Polymerforschung Dresden e. V., Dresden (Germany); Technische Universität Dresden, Organic Chemistry of Polymers, Dresden (Germany); Bünker, Tobias [Leibniz-Institut für Polymerforschung Dresden e. V., Dresden (Germany); Wollenberg, Anne [Leibniz-Institut für Polymerforschung Dresden e. V., Dresden (Germany); Technische Universität Dresden, Organic Chemistry of Polymers, Dresden (Germany); Häußler, Liane; Simon, Frank; Grundke, Karina; Oertel, Ulrich [Leibniz-Institut für Polymerforschung Dresden e. V., Dresden (Germany); Opitz, Michael; Kruspe, Rainer [IDUS Biologisch Analytisches Umweltlabor GmbH, Ottendorf-Okrilla (Germany)

    2017-03-31

    Highlights: • New methacrylate-based copolymers synthesized by free radical polymerization. • Comonomer AAMA was able to complex Cu (II) ions in solvent annealing procedure. • Coatings had efficient anti-biofouling efficacy. - Abstract: In order to prevent freshwater biofouling glass and metal surfaces were coated with novel transparent methacrylate-based copolymers. The multifunctionality of the copolymers, such as adhesion to the substrate, surface polarity, mechanical long-term stability in water, and ability to form metal complexes was inserted by the choice of suitable comonomers. The monomer 2-acetoacetoxy ethyl methacrylate (AAMA) was used as complexing unit to produce copper(II) complexes in the coating’s upper surface layer. The semifluorinated monomer 1H,1H,2H,2H-perfluorodecyl methacrylate was employed to adjust the surface polarity and wettability. Comprehensive surface characterization techniques, such as X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that surface compositions and properties can be easily adjusted by varying the concentrations of the comonomers. The formation of copper(II) complexes along the copolymer chains and their stability against washing out with plenty of water was proven by XPS. Copolymers containing semifluorinated comonomers significantly inhibited the growth of Achnanthidium species. Copolymers with copper-loaded AAMA-sequences were able to reduce both the growth of Achnanthidium spec. and Staphylococcus aureus.

  20. Multifunctional methacrylate-based coatings for glass and metal surfaces

    International Nuclear Information System (INIS)

    Pospiech, Doris; Jehnichen, Dieter; Starke, Sandra; Müller, Felix; Bünker, Tobias; Wollenberg, Anne; Häußler, Liane; Simon, Frank; Grundke, Karina; Oertel, Ulrich; Opitz, Michael; Kruspe, Rainer

    2017-01-01

    Highlights: • New methacrylate-based copolymers synthesized by free radical polymerization. • Comonomer AAMA was able to complex Cu (II) ions in solvent annealing procedure. • Coatings had efficient anti-biofouling efficacy. - Abstract: In order to prevent freshwater biofouling glass and metal surfaces were coated with novel transparent methacrylate-based copolymers. The multifunctionality of the copolymers, such as adhesion to the substrate, surface polarity, mechanical long-term stability in water, and ability to form metal complexes was inserted by the choice of suitable comonomers. The monomer 2-acetoacetoxy ethyl methacrylate (AAMA) was used as complexing unit to produce copper(II) complexes in the coating’s upper surface layer. The semifluorinated monomer 1H,1H,2H,2H-perfluorodecyl methacrylate was employed to adjust the surface polarity and wettability. Comprehensive surface characterization techniques, such as X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that surface compositions and properties can be easily adjusted by varying the concentrations of the comonomers. The formation of copper(II) complexes along the copolymer chains and their stability against washing out with plenty of water was proven by XPS. Copolymers containing semifluorinated comonomers significantly inhibited the growth of Achnanthidium species. Copolymers with copper-loaded AAMA-sequences were able to reduce both the growth of Achnanthidium spec. and Staphylococcus aureus.

  1. ACCEPTABILITY ENVELOPE FOR METAL HYDRIDE-BASED HYDROGEN STORAGE SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Hardy, B.; Corgnale, C.; Tamburello, D.; Garrison, S.; Anton, D.

    2011-07-18

    The design and evaluation of media based hydrogen storage systems requires the use of detailed numerical models and experimental studies, with significant amount of time and monetary investment. Thus a scoping tool, referred to as the Acceptability Envelope, was developed to screen preliminary candidate media and storage vessel designs, identifying the range of chemical, physical and geometrical parameters for the coupled media and storage vessel system that allow it to meet performance targets. The model which underpins the analysis allows simplifying the storage system, thus resulting in one input-one output scheme, by grouping of selected quantities. Two cases have been analyzed and results are presented here. In the first application the DOE technical targets (Year 2010, Year 2015 and Ultimate) are used to determine the range of parameters required for the metal hydride media and storage vessel. In the second case the most promising metal hydrides available are compared, highlighting the potential of storage systems, utilizing them, to achieve 40% of the 2010 DOE technical target. Results show that systems based on Li-Mg media have the best potential to attain these performance targets.

  2. GaN transistors on Si for switching and high-frequency applications

    Science.gov (United States)

    Ueda, Tetsuzo; Ishida, Masahiro; Tanaka, Tsuyoshi; Ueda, Daisuke

    2014-10-01

    In this paper, recent advances of GaN transistors on Si for switching and high-frequency applications are reviewed. Novel epitaxial structures including superlattice interlayers grown by metal organic chemical vapor deposition (MOCVD) relieve the strain and eliminate the cracks in the GaN over large-diameter Si substrates up to 8 in. As a new device structure for high-power switching application, Gate Injection Transistors (GITs) with a p-AlGaN gate over an AlGaN/GaN heterostructure successfully achieve normally-off operations maintaining high drain currents and low on-state resistances. Note that the GITs on Si are free from current collapse up to 600 V, by which the drain current would be markedly reduced after the application of high drain voltages. Highly efficient operations of an inverter and DC-DC converters are presented as promising applications of GITs for power switching. The high efficiencies in an inverter, a resonant LLC converter, and a point-of-load (POL) converter demonstrate the superior potential of the GaN transistors on Si. As for high-frequency transistors, AlGaN/GaN heterojuction field-effect transistors (HFETs) on Si designed specifically for microwave and millimeter-wave frequencies demonstrate a sufficiently high output power at these frequencies. Output powers of 203 W at 2.5 GHz and 10.7 W at 26.5 GHz are achieved by the fabricated GaN transistors. These devices for switching and high-frequency applications are very promising as future energy-efficient electronics because of their inherent low fabrication cost and superior device performance.

  3. Field plated 0.15 μm GaN HEMTs for millimeter-wave application

    International Nuclear Information System (INIS)

    Ren Chunjiang; Li Zhonghui; Yu Xuming; Wang Quanhui; Wang Wen; Chen Tangsheng; Zhang Bin

    2013-01-01

    SiN dielectrically-defined 0.15 μm field plated GaN HEMTs for millimeter-wave application have been presented. The AlGaN/GaN hetero-structure epitaxial material for HEMTs fabrication was grown on a 3-inch SiC substrate with an Fe doped GaN buffer layer by metal-organic chemical deposition. Electron beam lithography was used to define both the gate footprint and the cap of the gate with an integrated field plate. Gate recessing was performed to control the threshold voltage of the devices. The fabricated GaN HEMTs exhibited a unit current gain cut-off frequency of 39 GHz and a maximum frequency of oscillation of 63 GHz. Load-pull measurements carried out at 35 GHz showed a power density of 4 W/mm with associated power gain and power added efficiency of 5.3 dB and 35%, respectively, for a 0.15 mm gate width device operated at a 24 V drain bias. The developed 0.15 μm gate length GaN HEMT technology is suitable for Ka band applications and is ready for millimeter-wave power MMICs development. (semiconductor devices)

  4. Impacts of oxidants in atomic layer deposition method on Al2O3/GaN interface properties

    Science.gov (United States)

    Taoka, Noriyuki; Kubo, Toshiharu; Yamada, Toshikazu; Egawa, Takashi; Shimizu, Mitsuaki

    2018-01-01

    The electrical interface properties of GaN metal-oxide-semiconductor (MOS) capacitors with an Al2O3 gate insulator formed by atomic layer deposition method using three kinds of oxidants were investigated by the capacitance-voltage technique, Terman method, and conductance method. We found that O3 and the alternate supply of H2O and O3 (AS-HO) are effective for reducing the interface trap density (D it) at the energy range of 0.15 to 0.30 eV taking from the conduction band minimum. On the other hand, we found that surface potential fluctuation (σs) induced by interface charges for the AS-HO oxidant is much larger than that for a Si MOS capacitor with a SiO2 layer formed by chemical vapor deposition despite the small D it values for the AS-HO oxidant compared with the Si MOS capacitor. This means that the total charged center density including the fixed charge density, charged slow trap density, and charged interface trap density for the GaN MOS capacitor is higher than that for the Si MOS capacitor. Therefore, σs has to be reduced to improve the performances and reliability of GaN devices with the Al2O3/GaN interfaces.

  5. P-type doping of GaN

    International Nuclear Information System (INIS)

    Wong, R.K.

    2000-01-01

    After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C. The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover

  6. P-type doping of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Raechelle Kimberly [Univ. of California, Berkeley, CA (United States)

    2000-04-01

    After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C. The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover.

  7. Stage of GAN (Grupo de Analise do Nucleo) calculus methodology

    International Nuclear Information System (INIS)

    Silva, C.F. da.

    1987-11-01

    This Technical Note presents the stage of GAN Calculus Methodology in areas of Neutronics, Fuel Rod Performance and Fission Products Inventory. Proposals of GAN's members are presented and analyzed for each of these areas and a work schedule is established. (author)

  8. Feasibility Study on 3-D Printing of Metallic Structural Materials with Robotized Laser-Based Metal Additive Manufacturing

    Science.gov (United States)

    Ding, Yaoyu; Kovacevic, Radovan

    2016-07-01

    Metallic structural materials continue to open new avenues in achieving exotic mechanical properties that are naturally unavailable. They hold great potential in developing novel products in diverse industries such as the automotive, aerospace, biomedical, oil and gas, and defense. Currently, the use of metallic structural materials in industry is still limited because of difficulties in their manufacturing. This article studied the feasibility of printing metallic structural materials with robotized laser-based metal additive manufacturing (RLMAM). In this study, two metallic structural materials characterized by an enlarged positive Poisson's ratio and a negative Poisson's ratio were designed and simulated, respectively. An RLMAM system developed at the Research Center for Advanced Manufacturing of Southern Methodist University was used to print them. The results of the tensile tests indicated that the printed samples successfully achieved the corresponding mechanical properties.

  9. Laser spot welding of cobalt-based amorphous metal foils

    International Nuclear Information System (INIS)

    Runchev, Dobre; Dorn, Lutc; Jaferi, Seifolah; Purbst, Detler

    1997-01-01

    The results concerning weldability of amorphous alloy (VAC 6025F) in shape of foils and the quality of laser-spot welded joints are presented in this paper. The aim of the research was the production of a high quality welding joint, by preserving the amorphous structure. The quality of the joint was tested by shear strength analysis and microhardness measuring. The metallographic studies were made by using optical microscope and SEM. The results show that (1) overlapped Co based amorphous metals foils can be welded with high-quality by a pulsed Nd: YAG-Laser, but only within a very narrow laser parameter window; (2) the laser welded spots show comparably high strength as the basic material; (3) the structure of the welded spot remains amorphous, so that the same characteristics as the base material can be achieved. (author)

  10. Biomedical application of hierarchically built structures based on metal oxides

    Science.gov (United States)

    Korovin, M. S.; Fomenko, A. N.

    2017-12-01

    Nowadays, the use of hierarchically built structures in biology and medicine arouses much interest. The aim of this work is to review and summarize the available literature data about hierarchically organized structures in biomedical application. Nanoparticles can serve as an example of such structures. Medicine holds a special place among various application methods of similar systems. Special attention is paid to inorganic nanoparticles based on different metal oxides and hydroxides, such as iron, zinc, copper, and aluminum. Our investigations show that low-dimensional nanostructures based on aluminum oxides and hydroxides have an inhibitory effect on tumor cells and possess an antimicrobial activity. At the same time, it is obvious that the large-scale use of nanoparticles by humans needs to thoroughly study their properties. Special attention should be paid to the study of nanoparticle interaction with living biological objects. The numerous data show that there is no clear understanding of interaction mechanisms between nanoparticles and various cell types.

  11. Ultramicrosensors based on transition metal hexacyanoferrates for scanning electrochemical microscopy

    Directory of Open Access Journals (Sweden)

    Maria A. Komkova

    2013-10-01

    Full Text Available We report here a way for improving the stability of ultramicroelectrodes (UME based on hexacyanoferrate-modified metals for the detection of hydrogen peroxide. The most stable sensors were obtained by electrochemical deposition of six layers of hexacyanoferrates (HCF, more specifically, an alternating pattern of three layers of Prussian Blue and three layers of Ni–HCF. The microelectrodes modified with mixed layers were continuously monitored in 1 mM hydrogen peroxide and proved to be stable for more than 5 h under these conditions. The mixed layer microelectrodes exhibited a stability which is five times as high as the stability of conventional Prussian Blue-modified UMEs. The sensitivity of the mixed layer sensor was 0.32 A·M−1·cm−2, and the detection limit was 10 µM. The mixed layer-based UMEs were used as sensors in scanning electrochemical microscopy (SECM experiments for imaging of hydrogen peroxide evolution.

  12. Graphene oxide-based flexible metal–insulator–metal capacitors

    International Nuclear Information System (INIS)

    Bag, A; Hota, M K; Mallik, S; Maiti, C K

    2013-01-01

    This work explores the fabrication of graphene oxide (GO)-based metal–insulator–metal (MIM) capacitors on flexible polyethylene terephthalate (PET) substrates. Electrical properties are studied in detail. A high capacitance density of ∼4 fF µm −2 measured at 1 MHz and permittivity of ∼6 have been obtained. A low voltage coefficient of capacitance, VCC-α, and a low dielectric loss tangent indicate the potential of GO-based MIM capacitors for RF applications. The constant voltage stressing study has shown a high reliability against degradation up to a projected period of 10 years. Degradation in capacitance of the devices on flexible substrates has been studied by bending radius down to 1 cm even up to 6000 times of repeated bending. (paper)

  13. Highly resistive C-doped hydride vapor phase epitaxy-GaN grown on ammonothermally crystallized GaN seeds

    Science.gov (United States)

    Iwinska, Malgorzata; Piotrzkowski, Ryszard; Litwin-Staszewska, Elzbieta; Sochacki, Tomasz; Amilusik, Mikolaj; Fijalkowski, Michal; Lucznik, Boleslaw; Bockowski, Michal

    2017-01-01

    GaN crystals were grown by hydride vapor phase epitaxy (HVPE) and doped with C. The seeds were high-structural-quality ammonothermally crystallized GaN. The grown crystals were highly resistive at 296 K and of high structural quality. High-temperature Hall effect measurements revealed p-type conductivity and a deep acceptor level in the material with an activation energy of 1 eV. This is in good agreement with density functional theory calculations based on hybrid functionals as presented by the Van de Walle group. They obtained an ionization energy of 0.9 eV when C was substituted for N in GaN and acted as a deep acceptor.

  14. Dispersion and absorption of longitudinal electro-kinetic wave in ion-implanted GaN semiconductor plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Soni, Dilip [Government P G Madhav Science College, Ujjain (M P) (India); Sharma, Giriraj, E-mail: grsharma@gmail.com [SRJ Government Girls’ College, Neemuch (M P) (India); Saxena, Ajay [Government College, Garoth, Dist. Mandsaur (M P) (India); Jadhav, Akhilesh [Government J Yoganandam Chhattisgarh College, Raipur (C G) (India)

    2015-07-31

    An analytical study on propagation characteristics of longitudinal electro-kinetic (LEK) waves is presented. Based on multi-fluid model of plasma, we have derived a dispersion relation for LEK waves in colloid laden GaN semiconductor plasmas. It is assumed that ions are implanted to form colloids in the GaN sample. The colloids are continuously bombarded by the plasma particles and stick on them, but they acquire a net negative charge due to relatively higher mobility of electrons. It is found from the dispersion relation that the presence of charged colloids not only modifies the existing modes but also supports new novel modes of LEKWs. It is hoped that the study would enhance understanding on dispersion and absorption of LEKWs and help in singling out the appropriate configurations in which GaN crystal would be better suited for fabrication of microwave devices.

  15. Cracking of GaN on sapphire from etch-process-induced nonuniformity in residual thermal stress

    International Nuclear Information System (INIS)

    Lacroix, Yves; Chung, Sung-Hoon; Sakai, Shiro

    2001-01-01

    An experiment was performed to explain the appearance of cracks along mesa structures during the processing of GaN device layers grown on sapphire substrates. Micro-Raman spectroscopy was used to measure the position-dependent stress in the GaN layer. We show evidence that the stress at the interface with the substrate may be larger along the mesa structures than that of the as-grown layer, and that this increase in stress can be enough to induce cracks along mesa structures during processing. We report on the formation of cracks that propagate guided by the nonuniformity of the stress induced by the formation of mesa structures in the GaN layer, independent of crystal direction. The understanding of cracking mechanisms has implications in GaN-based device structures that require heteroepitaxial growth of layers with different lattice size and thermal expansion coefficients. [copyright] 2001 American Institute of Physics

  16. Selective heteroepitaxy on deeply grooved substrate: A route to low cost semipolar GaN platforms of bulk quality

    Energy Technology Data Exchange (ETDEWEB)

    Tendille, Florian, E-mail: florian.tendille@crhea.cnrs.fr; Vennéguès, Philippe; De Mierry, Philippe [CRHEA - CNRS (Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications), Rue Bernard Gregory, Parc de Sophia Antipolis, 06560 Valbonne (France); Martin, Denis; Grandjean, Nicolas [Institute of Physics, EPFL, CH-1015 Lausanne (Switzerland)

    2016-08-22

    Semipolar GaN crystal stripes larger than 100 μm with dislocation densities below 5 × 10{sup 6} cm{sup −2} are achieved using a low cost fabrication process. An original sapphire patterning procedure is proposed, enabling selective growth of semipolar oriented GaN stripes while confining the defects to specific areas. Radiative and non-radiative crystalline defects are investigated by cathodoluminescence and can be correlated to the development of crystal microstructure during the growth process. A dislocation reduction mechanism, supported by transmission electron microscopy, is proposed. This method represents a step forward toward low-cost quasi-bulk semipolar GaN epitaxial platforms with an excellent structural quality which will allow for even more efficient III-nitride based devices.

  17. Impact of GaN transition layers in the growth of GaN epitaxial layer on silicon

    International Nuclear Information System (INIS)

    Zhao Danmei; Zhao Degang; Jiang Desheng; Liu Zongshun; Zhu Jianjun; Chen Ping; Liu Wei; Li Xiang; Shi Ming

    2015-01-01

    A method for growing GaN epitaxial layer on Si (111) substrate is investigated. Due to the large lattice mismatch between GaN and AlN, GaN grown directly above an AlN buffer layer on the Si substrate turns out to be of poor quality. In this study, a GaN transition layer is grown additionally on the AlN buffer before the GaN epitaxial growth. By changing the growth conditions of the GaN transition layer, we can control the growth and merging of islands and control the transfer time from 3D to 2D growth mode. With this method, the crystalline quality of the GaN epitaxial layer can be improved and the crack density is reduced. Here, we have investigated the impact of a transition layer on the crystalline quality and stress evolution of a GaN epitaxial layer with methods of X-ray diffraction, optical microscopy and in situ reflectivity trace. With the increasing thickness of transition layer, the crack decreases and the crystalline quality is improved. But when the transition layer exceeds a critical thickness, the crystalline quality of the epilayer becomes lower and the crack density increases. (paper)

  18. Memory phenomenon in a lanthanum based bulk metallic glass

    International Nuclear Information System (INIS)

    Zhou, Ye; Huang, Wei Min; Zhao, Yong; Ding, Zhen; Li, Yan; Tor, Shu Beng; Liu, Erjia

    2016-01-01

    In this paper, we experimentally investigate two memory phenomena in a lanthanum based bulk metallic glass (BMG). While the temperature memory effect (TME) is not found by differential scanning calorimeter (DSC) test, shape recovery is observed in samples indented at both low and high temperatures. In terms of shape memory related characteristics, this BMG shares some features of shape memory alloys (SMAs) due to its metal nature, and some other features of shape memory polymers (SMPs) owing to its glassy–rubbery transition. The formation of protrusion in the polished sample after heating to super-cooled liquid region (SCLR) indicates that surface tension is not a necessarily positive contributor for shape recovery. Release of internal elastic stress is concluded as the major player. Although the amorphous nature of BMGs enables for storing appreciable amount of internal elastic stress upon deformation, without the presence of cross-linker as in typical SMPs, the shape recovery in BMGs is rather limited. - Highlights: • Experimental investigation of shape recovery in BMG. • Surface tension is not the major reason for shape recovery in BMG. • Release of internal stress is the major contributor for shape recovery. • Comparison of shape memory features of BMG with other shape memory materials.

  19. Process for recovering uranium and other base metals

    International Nuclear Information System (INIS)

    Jan, R. J-J.

    1979-01-01

    Uranium and other base metals are leached from their ores with aqueous solutions containing bicarbonate ions that have been generated or reconstituted by converting other non-bicarbonate anions into bicarbonate ions. The conversion is most conveniently effected by contacting solutions containing SO 4 - and Cl - ions with a basic anion exchange resin so that the SO 4 - and Cl - ions are converted into or exhanged for HCO 3 - ions. CO 2 may be dissolved in the solution so it is present during the exhange. The resin is preferably in bicarbonate form prior to contact and CO 2 partial pressure is adjusted so that the resin is not fouled by depositing metal precipitates. In-situ uranium mining is conducted by circulating such solutions through the ore deposit. Oxidizing agents are included in the injected lixiviant. The leaching strength of the circulating bicarbonate lixiviant is maintained by converting the anions generated during leaching or above-ground recovery processes into HCO 3 - ions. The resin may conveniently be eluted and reformed intermittently

  20. Process for recovering uranium and other base metals

    International Nuclear Information System (INIS)

    Jan, R.J.

    1981-01-01

    Uranium and other base metals are leached from their ores with aqueous solutions containing bicarbonate ions that have been generated or reconstituted by converting other non-bicarbonate anions into bicarbonate ions. The conversion is most conveniently effected by contacting solutions containing SO 4 -- and C1 - ions with a basic anion exchange resin so that the SO 4 -- and Cl - ions are converted into or exchanged for HCO 3 - ions. CO 2 may be dissolved in the solution so it is present during the exchange. The resin is preferably in bicarbonate form prior to contact and CO 2 partial pressure is adjusted so that the resin is not fouled by depositing metal precipitates. In-situ uranium mining is conducted by circulating such solutions through the ore deposit. Oxidizing agents are included in the injected lixiviant. The leaching strength of the circulating bicarbonate lixiviant is maintained by converting the anions generated during leaching or above-ground recovery processes into HCO 3 - ions. The resin may conveniently be eluted and performed intermittently. (author)

  1. Welding of CuZr-based metallic glasses on air

    International Nuclear Information System (INIS)

    Batalha, W.; Gargarella, P.; Kiminami, C.S.

    2016-01-01

    Metallic glass alloys have been studied aiming at its exceptional mechanical properties. This alloys processing's requires high cooling rates, which diminishes the sample's size. There by welding these samples without the loss of amorphous structure is a good alternative. The DEMa group has developed a technique based on Joule effect heating. By applying pressure and electric current, reaching temperatures of super cold liquids (the temperature between crystallizing and vitric transition), the vitric metal has it’s viscosity reduced and sample binding occur. The objective of this paper was to weld samples of cylindrical geometry of 2 and 3 mm in diameter and 4 mm in length of the compositions Cu46Zr42Al7Y5 and (Cu47Zr45Al8)98Y2. The process was done using 2 copper electrodes under(over) argon flux. The samples were later analysed by microscopy, differential scanning calorimetry and X ray diffraction. The results showed that this kind of welding process is possible since crystal formation on the welding region did not occur and there were no faults like cracks or porosity. (author)

  2. Compact-Morphology-based poly-metallic Nodule Delineation.

    Science.gov (United States)

    Schoening, Timm; Jones, Daniel O B; Greinert, Jens

    2017-10-17

    Poly-metallic nodules are a marine resource considered for deep sea mining. Assessing nodule abundance is of interest for mining companies and to monitor potential environmental impact. Optical seafloor imaging allows quantifying poly-metallic nodule abundance at spatial scales from centimetres to square kilometres. Towed cameras and diving robots acquire high-resolution imagery that allow detecting individual nodules and measure their sizes. Spatial abundance statistics can be computed from these size measurements, providing e.g. seafloor coverage in percent and the nodule size distribution. Detecting nodules requires segmentation of nodule pixels from pixels showing sediment background. Semi-supervised pattern recognition has been proposed to automate this task. Existing nodule segmentation algorithms employ machine learning that trains a classifier to segment the nodules in a high-dimensional feature space. Here, a rapid nodule segmentation algorithm is presented. It omits computation-intense feature-based classification and employs image processing only. It exploits a nodule compactness heuristic to delineate individual nodules. Complex machine learning methods are avoided to keep the algorithm simple and fast. The algorithm has successfully been applied to different image datasets. These data sets were acquired by different cameras, camera platforms and in varying illumination conditions. Their successful analysis shows the broad applicability of the proposed method.

  3. Evaluation of different finish line designs in base metal alloys

    Directory of Open Access Journals (Sweden)

    Aghandeh R

    1999-06-01

    Full Text Available This investigation was performed according to the widespread application of base metal alloys"nand few articles published about the marginal integrity of restorations fabricated by these metals."nThree standard dies of a maxillary first premolar were prepared with a flat shoulder finish line in buccal"naspect and chamfer in palatal. One of them left with no change. On the buccal aspect of the second and"nthird dies 135?and 1607 bevel were added respectively"nUsing dual wax technique, nine wax patterns were formed on each die and casting procedure of selected"nnon precious alloy was performed by centrifugal method. Marginal gaps of each copping seated on dies"nwere measured by scanning electron microscope (SEM with X500 magnification. Measurements were"ndone on three areas of marked dies on buccal aspect. Measurement son palatal aspect was done on"nmarked midpalatal point as control."nResults and statistical analysis showed no significant difference among marginal gaps in lingual aspect."nBut on the buccal aspect there were statistically significant differences among the groups (P<0.001. Flat"nshoulder had the best marginal integrity (mean 4 micron. Shoulder with 160' bevel had the most marginal"ngap (mean 26.5 micron and shoulder with 1357 bevel was between two other groups (mean 15.7 micron.

  4. Memory phenomenon in a lanthanum based bulk metallic glass

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ye [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Huang, Wei Min, E-mail: mwmhuang@ntu.edu.sg [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Zhao, Yong [School of Chemistry and Chemical Engineering, Jiangsu University, 301 Xuefu Road, Zhenjiang 212013 (China); Ding, Zhen [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Li, Yan [School of Materials Science and Engineering, Beihang University, Beijing 100191 (China); Tor, Shu Beng; Liu, Erjia [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore)

    2016-07-05

    In this paper, we experimentally investigate two memory phenomena in a lanthanum based bulk metallic glass (BMG). While the temperature memory effect (TME) is not found by differential scanning calorimeter (DSC) test, shape recovery is observed in samples indented at both low and high temperatures. In terms of shape memory related characteristics, this BMG shares some features of shape memory alloys (SMAs) due to its metal nature, and some other features of shape memory polymers (SMPs) owing to its glassy–rubbery transition. The formation of protrusion in the polished sample after heating to super-cooled liquid region (SCLR) indicates that surface tension is not a necessarily positive contributor for shape recovery. Release of internal elastic stress is concluded as the major player. Although the amorphous nature of BMGs enables for storing appreciable amount of internal elastic stress upon deformation, without the presence of cross-linker as in typical SMPs, the shape recovery in BMGs is rather limited. - Highlights: • Experimental investigation of shape recovery in BMG. • Surface tension is not the major reason for shape recovery in BMG. • Release of internal stress is the major contributor for shape recovery. • Comparison of shape memory features of BMG with other shape memory materials.

  5. Multifunctional methacrylate-based coatings for glass and metal surfaces

    Science.gov (United States)

    Pospiech, Doris; Jehnichen, Dieter; Starke, Sandra; Müller, Felix; Bünker, Tobias; Wollenberg, Anne; Häußler, Liane; Simon, Frank; Grundke, Karina; Oertel, Ulrich; Opitz, Michael; Kruspe, Rainer

    2017-03-01

    In order to prevent freshwater biofouling glass and metal surfaces were coated with novel transparent methacrylate-based copolymers. The multifunctionality of the copolymers, such as adhesion to the substrate, surface polarity, mechanical long-term stability in water, and ability to form metal complexes was inserted by the choice of suitable comonomers. The monomer 2-acetoacetoxy ethyl methacrylate (AAMA) was used as complexing unit to produce copper(II) complexes in the coating's upper surface layer. The semifluorinated monomer 1H,1H,2H,2H-perfluorodecyl methacrylate was employed to adjust the surface polarity and wettability. Comprehensive surface characterization techniques, such as X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that surface compositions and properties can be easily adjusted by varying the concentrations of the comonomers. The formation of copper(II) complexes along the copolymer chains and their stability against washing out with plenty of water was proven by XPS. Copolymers containing semifluorinated comonomers significantly inhibited the growth of Achnanthidium species. Copolymers with copper-loaded AAMA-sequences were able to reduce both the growth of Achnanthidium spec. and Staphylococcus aureus.

  6. Process for recovering uranium and other base metals

    International Nuclear Information System (INIS)

    Jan, R.J.

    1984-01-01

    Uranium and other base metals are leached from their ores with aqueous solutions containing bicarbonate ions that have been generated or reconstituted by converting other non-bicarbonate anions into bicarbonate ions. The conversion is most conveniently effected by contacting solutions containing SO 4 2- and Cl - ions with a basic anion exchange resin so that the SO 4 2- and Cl - ions are converted into or exchanged for HCO 3 - ions. CO 2 may be dissolved in the solution so it is present during the exchange. The resin is preferably in bicarbonate form prior to contact and CO 2 partial pressure is adjusted so that the resin is not fouled by depositing metal precipitates. In-situ uranium mining is conducted by circulating such solutions through the ore deposit. Oxidizing agents are included in the injected lixiviant. The leaching strength of the circulating bicarbonate lixiviant is maintained by converting the anions generated during leaching or above-ground recovery processes into HCO 3 - ions. The resin may conveniently be eluted and reformed intermittently

  7. Preparation of freestanding GaN wafer by hydride vapor phase epitaxy on porous silicon

    Science.gov (United States)

    Wu, Xian; Li, Peng; Liang, Renrong; Xiao, Lei; Xu, Jun; Wang, Jing

    2018-05-01

    A freestanding GaN wafer was prepared on porous Si (111) substrate using hydride vapor phase epitaxy (HVPE). To avoid undesirable effects of the porous surface on the crystallinity of the GaN, a GaN seed layer was first grown on the Si (111) bare wafer. A pattern with many apertures was fabricated in the GaN seed layer using lithography and etching processes. A porous layer was formed in the Si substrate immediately adjacent to the GaN seed layer by an anodic etching process. A 500-μm-thick GaN film was then grown on the patterned GaN seed layer using HVPE. The GaN film was separated from the Si substrate through the formation of cracks in the porous layer caused by thermal mismatch stress during the cooling stage of the HVPE. Finally, the GaN film was polished to obtain a freestanding GaN wafer.

  8. Designing biocompatible Ti-based metallic glasses for implant applications

    International Nuclear Information System (INIS)

    Calin, Mariana; Gebert, Annett; Ghinea, Andreea Cosmina; Gostin, Petre Flaviu; Abdi, Somayeh; Mickel, Christine; Eckert, Jürgen

    2013-01-01

    Ti-based metallic glasses show high potential for implant applications; they overcome in several crucial respects their well-established biocompatible crystalline counterparts, e.g. improved corrosion properties, higher fracture strength and wear resistance, increased elastic strain range and lower Young's modulus. However, some of the elements required for glass formation (e.g. Cu, Ni) are harmful for the human body. We critically reviewed the biological safety and glass forming tendency in Ti of 27 elements. This can be used as a basis for the future designing of novel amorphous Ti-based implant alloys entirely free of harmful additions. In this paper, two first alloys were developed: Ti 75 Zr 10 Si 15 and Ti 60 Nb 15 Zr 10 Si 15 . The overheating temperature of the melt before casting can be used as the controlling parameter to produce fully amorphous materials or bcc-Ti-phase reinforced metallic glass nano-composites. The beneficial effect of Nb addition on the glass-formation and amorphous phase stability was assessed by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. Crystallization and mechanical behavior of ribbons are influenced by the amount and distribution of the nano-scaled bcc phase existing in the as-cast state. Their electrochemical stability in Ringer's solution at 310 K was found to be significantly better than that of commercial Ti-based biomaterials; no indication for pitting corrosion was recorded. Highlights: ► Link between biocompatibility and glass-forming ability of alloying additions in Ti ► Selection of Ti–Zr–Si and Ti–Zr–Nb–Si glass-forming alloys ► Two novel glassy alloys were developed: Ti 75 Zr 10 Si 15 and Ti 60 Nb 15 Zr 10 Si 15. ► Glass-formation, thermal stability, corrosion and mechanical behavior were studied. ► Assessing the suitability for orthopedic applications.

  9. Tunable light extraction efficiency of GaN light emitting diodes by ZnO nanorod arrays

    International Nuclear Information System (INIS)

    Chao, C H; Lin, W H; Lin, C F; Chen, C H; Changjean, C H

    2009-01-01

    We report the influence of ZnO nanorod arrays (NRAs) on the light extraction efficiency of GaN light emitting diodes (LEDs). Our investigation indicates that the output light intensity of the device exhibits a periodic oscillation as a function of the rod length. The variation of light extraction efficiency is caused by the Fabry–Perot resonance of the film composed of the nanorods. The theoretical analysis shows a good agreement with the measurement results. Our study reveals a method to control the output light extraction efficiency of GaN LEDs via a simple solution-based synthesized ZnO NRAs

  10. Redox switching and oxygen evolution at oxidized metal and metal oxide electrodes: iron in base.

    Science.gov (United States)

    Lyons, Michael E G; Doyle, Richard L; Brandon, Michael P

    2011-12-28

    Outstanding issues regarding the film formation, redox switching characteristics and the oxygen evolution reaction (OER) electrocatalytic behaviour of multicycled iron oxyhydroxide films in aqueous alkaline solution have been revisited. The oxide is grown using a repetitive potential multicycling technique, and the mechanism of the latter hydrous oxide formation process has been discussed. A duplex layer model of the oxide/solution interphase region is proposed. The acid/base behaviour of the hydrous oxide and the microdispersed nature of the latter material has been emphasised. The hydrous oxide is considered as a porous assembly of interlinked octahedrally coordinated anionic metal oxyhydroxide surfaquo complexes which form an open network structure. The latter contains considerable quantities of water molecules which facilitate hydroxide ion discharge at the metal site during active oxygen evolution, and also charge compensating cations. The dynamics of redox switching has been quantified via analysis of the cyclic voltammetry response as a function of potential sweep rate using the Laviron-Aoki electron hopping diffusion model by analogy with redox polymer modified electrodes. Steady state Tafel plot analysis has been used to elucidate the kinetics and mechanism of oxygen evolution. Tafel slope values of ca. 60 mV dec(-1) and ca. 120 mV dec(-1) are found at low and high overpotentials respectively, whereas the reaction order with respect to hydroxide ion activity changes from ca. 3/2 to ca. 1 as the potential is increased. These observations are rationalised in terms of a kinetic scheme involving Temkin adsorption and the rate determining formation of a physisorbed hydrogen peroxide intermediate on the oxide surface. The dual Tafel slope behaviour is ascribed to the potential dependence of the surface coverage of adsorbed intermediates.

  11. Normally-off GaN Transistors for Power Applications

    International Nuclear Information System (INIS)

    Hilt, O; Bahat-Treidel, E; Brunner, F; Knauer, A; Zhytnytska, R; Kotara, P; Wuerfl, J

    2014-01-01

    Normally-off high voltage GaN-HFETs for switching applications are presented. Normally-off operation with threshold voltages of 1 V and more and with 5 V gate swing has been obtained by using p-type GaN as gate. Different GaN-based buffer types using doping and backside potential barriers have been used to obtain blocking strengths up to 1000 V. The increase of the dynamic on-state resistance is analyzed for the different buffer types. The best trade-off between low dispersion and high blocking strength was obtained for a modified carbon-doped GaN-buffer that showed a 2.6x increase of the dynamic on-state resistance for 500 V switching as compared to switching from 20 V off-state drain bias. Device operation up to 200 °C ambient temperature without any threshold voltage shift is demonstrated.

  12. P-type surface effects for thickness variation of 2um and 4um of n-type layer in GaN LED

    Science.gov (United States)

    Halim, N. S. A. Abdul; Wahid, M. H. A.; Hambali, N. A. M. Ahmad; Rashid, S.; Ramli, M. M.; Shahimin, M. M.

    2017-09-01

    The internal quantum efficiency of III-Nitrides group, GaN light-emitting diode (LED) has been considerably limited due to the insufficient hole injection and this is caused by the lack of performance p-type doping and low hole mobility. The low hole mobility makes the hole less energetic, thus reduced the performance operation of GaN LED itself. The internal quantum efficiency of GaN-based LED with surface roughness (texture) can be changed by texture size, density, and thickness of GaN film or by the combined effects of surface shape and thickness of GaN film. Besides, due to lack of p-type GaN, attempts to look forward the potential of GaN LED relied on the thickness of n-type layer and surface shape of p-type GaN layer. This work investigates the characteristics of GaN LED with undoped n-GaN layer of different thickness and the surface shape of p-type layer. The LEDs performance is significantly altered by modifying the thickness and shape. Enhancement of n-GaN layer has led to the annihilation of electrical conductivity of the chip. Different surface geometry governs the emission rate extensively. Internal quantum efficiency is also predominantly affected by the geometry of n-GaN layer which subjected to the current spreading. It is recorded that the IQE droop can be minimized by varying the thickness of the active layer without amplifying the forward voltage. Optimum forward voltage (I-V), total emission rate relationship with the injected current and internal quantum efficiency (IQE) for 2,4 µm on four different surfaces of p-type layer are also reported in this paper.

  13. Investigation of GaN LED with Be-implanted Mg-doped GaN layer

    International Nuclear Information System (INIS)

    Huang, H.-W.; Kao, C.C.; Chu, J.T.; Kuo, H.C.; Wang, S.C.; Yu, C.C.; Lin, C.F.

    2004-01-01

    We report the electrical and optical characteristics of GaN light emitting diode (LED) with beryllium (Be) implanted Mg-doped GaN layer. The p-type layer of Be-implanted GaN LED showed a higher hole carrier concentration of 2.3 x 10 18 cm -3 and low specific contact resistance value of 2.0 x 10 -4 Ωcm 2 than as-grown p-GaN LED samples without Be-implantation. The Be-implanted GaN LEDs with InGaN/GaN MQW show slightly lower light output (about 10%) than the as-grown GaN LEDs, caused by the high RTA temperature annealing process

  14. Investigation of different mechanisms of GaN growth induced on AlN and GaN nucleation layers

    International Nuclear Information System (INIS)

    Tasco, V.; Campa, A.; Tarantini, I.; Passaseo, A.; Gonzalez-Posada, F.; Munoz, E.; Redondo-Cubero, A.; Lorenz, K.; Franco, N.

    2009-01-01

    The evolution of GaN growth on AlN and GaN nucleation layers is compared through morphological and structural analyses, including ion beam analysis. By using AlN nucleation layer grown at high temperature, improved crystalline quality is exhibited by 300 nm thin GaN epilayers. GaN (002) x-ray rocking curve as narrow as 168 arc sec and atomic-step surface morphology characterize such a thin GaN film on AlN. Defects are strongly confined into the first 50 nm of growth, whereas a fast laterally coherent growth is observed when increasing thickness, as an effect of high temperature AlN surface morphology and Ga adatom dynamics over this template

  15. Resistive switching in ZrO{sub 2} based metal-oxide-metal structures

    Energy Technology Data Exchange (ETDEWEB)

    Kaerkkaenen, Irina

    2014-07-01

    detail for 20 nm thick ZrO{sub 2} films grown by an ozone based ALD process and integrated into Pt/ZrO{sub 2}/Ti/Pt cells while the thickness of the electrochemically active electrode (Ti) was varied from 0 nm to 40 nm. Cells with a thin EAE (<20 nm Ti) exhibited a UP-type RS behavior, while cells with thick EAE (>20 nm Ti) showed BP switching characteristics at a lower current compliance as the UP switching cells. A detailed structural analysis of the ozone grown ZrO{sub 2} films revealed a polycrystalline structure of columnar shaped grains with a meta-stable cubic-tetragonal ZrO{sub 2} phase. In the second part of the thesis an empirical model for the polarity dependence of the RS in the ALD ZrO{sub 2} based devices as a function of the EAE thickness was suggested. The model assumed a columnar shaped microstructure and certain impurity content for the ZrO{sub 2} films. In addition, the results of current-voltage behavior, temperature dependency of the resistance states and impedance spectroscopy (IS) measurements of different devices in different RS states were considered. Impedance spectroscopy measurements of UP and BP type switching devices with the same ZrO{sub 2} films but with different EAE thicknesses were carried out for the states prior to electroforming (pristine), after RS into the ON-state and after RS into the OFF-state. The different devices in their pristine states exhibited nearly identical IS characteristics while the ON and OFF states of the UP and BP devices revealed pronounced differences. In the model, the UP switching in ZrO{sub 2} based devices with thin EAE was described as a result of a noncomplete local reduction of the grain boundary cores, which might gave rise to a hard thermal breakdown and the formation of metallic like conduction paths. On the contrary, the suggested idea for BP switching of ZrO{sub 2} based devices with thick EAE based on the formation of local semiconducting oxygen depleted ZrO{sub 2-x} filament-like regions along

  16. Resistive switching in ZrO2 based metal-oxide-metal structures

    International Nuclear Information System (INIS)

    Kaerkkaenen, Irina

    2014-01-01

    The goal of this work is a deeper understanding of the influence of the (i) metal-oxide-metal (MOM) layer stacks configuration, (ii) the oxide films microstructure, (iii) and their defect structure on the appearance of different switching modes, i.e. unipolar (UP) and bipolar (BP). The first part deals with the fabrication of ZrO 2 thin films by an industrial compatible atomic layer deposition (ALD) process, the chemical, structural and morphological characterization of the films, the growth of ZrO 2 /TiO 2 bilayers, the integration of the layers into metal-oxide-metal (MOM) devices and the electrical characterization with focus on the RS behavior. In the second part the effect of the device structure, in particular the thickness of the electrochemical active electrode (EAE) and the ZrO 2 film morphology, on the RS switching polarity of Pt/ZrO 2 /(EAE) cells is discussed. ZrO 2 films and ZrO 2 /TiO 2 bilayers were grown by ALD and were carefully structurally and electrically characterized. The ZrO 2 films grown from Zr[N(CH 3 )C 2 H 5 ] 4 (TEMA-Zr) at 240 C were polycrystalline with a mixture of cubic/tetragonal phases. ALD/H 2 O-ZrO 2 films exhibited a random oriented polycrystalline structure, whereas the ALD/O 3 -ZrO 2 films consisted of preferably oriented cubic shaped grains. Pt/ZrO 2 /Ti/Pt structures with a Ti top electrode (TE) thickness of 5 to 20 nm showed unipolar type RS behavior, while by increasing the Ti TE thickness a gradual change of switching polarity from unipolar to bipolar with a completely bipolar type RS behavior for a Ti TE thickness of 40 nm is found. The switching in Pt/ZrO 2 /TiO 2 /Ti/Pt devices was unipolar, comparable to Pt/ZrO 2 /Ti/Pt cells. In contrast, bilayers with the reverse structure, Pt/TiO 2 /ZrO 2 /Ti/Pt, showed non-switching behavior. The effect of the cells stack structure on the polarity of the RS behavior was studied in detail for 20 nm thick ZrO 2 films grown by an ozone based ALD process and integrated into Pt/ZrO 2

  17. Commercial Implementation of Model-Based Manufacturing of Nanostructured Metals

    Energy Technology Data Exchange (ETDEWEB)

    Lowe, Terry C. [Los Alamos National Laboratory

    2012-07-24

    Computational modeling is an essential tool for commercial production of nanostructured metals. Strength is limited by imperfections at the high strength levels that are achievable in nanostructured metals. Processing to achieve homogeneity at the micro- and nano-scales is critical. Manufacturing of nanostructured metals is intrinsically a multi-scale problem. Manufacturing of nanostructured metal products requires computer control, monitoring and modeling. Large scale manufacturing of bulk nanostructured metals by Severe Plastic Deformation is a multi-scale problem. Computational modeling at all scales is essential. Multiple scales of modeling must be integrated to predict and control nanostructural, microstructural, macrostructural product characteristics and production processes.

  18. High optical and structural quality of GaN epilayers grown on ( 2¯01) β-Ga2O3

    KAUST Repository

    Mumthaz Muhammed, Mufasila; Peres, M.; Yamashita, Y.; Morishima, Y.; Sato, S.; Franco, N.; Lorenz, K.; Kuramata, A.; Roqan, Iman S.

    2014-01-01

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2̄01) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2̄01) oriented β-Ga 2O3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼108cm-2. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2̄01) β-Ga2O3 with in-plane epitaxial orientation relationships between the β-Ga2O3 and the GaN thin film defined by (010) β-Ga2O3 || (112̄0) GaN and (2̄01) β-Ga2O3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high. © 2014 AIP Publishing LLC.

  19. High optical and structural quality of GaN epilayers grown on ( 2¯01) β-Ga2O3

    KAUST Repository

    Mumthaz Muhammed, Mufasila

    2014-07-28

    Producing highly efficient GaN-based optoelectronic devices has been a challenge for a long time due to the large lattice mismatch between III-nitride materials and the most common substrates, which causes a high density of threading dislocations. Therefore, it is essential to obtain alternative substrates with small lattice mismatches, appropriate structural, thermal and electrical properties, and a competitive price. Our results show that (2̄01) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. Photoluminescence spectra of thick GaN layers grown on (2̄01) oriented β-Ga 2O3 are found to be dominated by intense bandedge emission. Atomic force microscopy studies show a modest threading dislocation density of ∼108cm-2. X-ray diffraction studies show the high quality of the single-phase wurtzite GaN thin film on (2̄01) β-Ga2O3 with in-plane epitaxial orientation relationships between the β-Ga2O3 and the GaN thin film defined by (010) β-Ga2O3 || (112̄0) GaN and (2̄01) β-Ga2O3 || (0001) GaN leading to a lattice mismatch of ∼4.7%. Complementary Raman spectroscopy indicates that the quality of the GaN epilayer is high. © 2014 AIP Publishing LLC.

  20. Polarity control of GaN epitaxial films grown on LiGaO2(001) substrates and its mechanism.

    Science.gov (United States)

    Zheng, Yulin; Wang, Wenliang; Li, Xiaochan; Li, Yuan; Huang, Liegen; Li, Guoqiang

    2017-08-16

    The polarity of GaN epitaxial films grown on LiGaO 2 (001) substrates by pulsed laser deposition has been well controlled. It is experimentally proved that the GaN epitaxial films grown on nitrided LiGaO 2 (001) substrates reveal Ga-polarity, while the GaN epitaxial films grown on non-nitrided LiGaO 2 (001) substrates show N-polarity. The growth mechanisms for these two cases are systematically studied by first-principles calculations based on density functional theory. Theoretical calculation presents that the adsorption of a Ga atom preferentially occurs at the center of three N atoms stacked on the nitrided LiGaO 2 (001) substrates, which leads to the formation of Ga-polarity GaN. Whereas the adsorption of a Ga atom preferentially deposits at the top of a N atom stacked on the non-nitrided LiGaO 2 (001) substrates, which results in the formation of N-polarity GaN. This work of controlling the polarity of GaN epitaxial films is of paramount importance for the fabrication of group-III nitride devices for various applications.

  1. Effects of GaN capping on the structural and the optical properties of InN nanostructures grown by using MOCVD

    International Nuclear Information System (INIS)

    Sun, Yuanping; Cho, Yonghoon; Wang, Hui; Wang, Lili; Zhang, Shuming; Yang, Hui

    2010-01-01

    InN nanostructures with and without GaN capping layers were grown by using metal-organic chemical vapor deposition. Morphological, structural, and optical properties were systematically studied by using atomic force microscopy, X-ray diffraction (XRD) and temperature-dependent photoluminescence (PL). XRD results show that an InGaN structure is formed for the sample with a GaN capping layer, which will reduce the quality and the IR PL emission of the InN. The lower emission peak at ∼0.7 eV was theoretically fitted and assigned as the band edge emission of InN. Temperature-dependent PL shows a good quantum efficiency for the sample without a GaN capping layers; this corresponds to a lower density of dislocations and a small activation energy.

  2. Microstructure-Based Counterfeit Detection in Metal Part Manufacturing

    Science.gov (United States)

    Dachowicz, Adam; Chaduvula, Siva Chaitanya; Atallah, Mikhail; Panchal, Jitesh H.

    2017-11-01

    Counterfeiting in metal part manufacturing has become a major global concern. Although significant effort has been made in detecting the implementation of such counterfeits, modern approaches suffer from high expense during production, invasiveness during manufacture, and unreliability in practice if parts are damaged during use. In this paper, a practical microstructure-based counterfeit detection methodology is proposed, which draws on inherent randomness present in the microstructure as a result of the manufacturing process. An optical Physically Unclonable Function (PUF) protocol is developed which takes a micrograph as input and outputs a compact, unique string representation of the micrograph. The uniqueness of the outputs and their robustness to moderate wear and tear is demonstrated by application of the methodology to brass samples. The protocol is shown to have good discriminatory power even between samples manufactured in the same batch, and runs on the order of several seconds per part on inexpensive machines.

  3. A metal-based inhibitor of NEDD8-activating enzyme.

    Directory of Open Access Journals (Sweden)

    Hai-Jing Zhong

    Full Text Available A cyclometallated rhodium(III complex [Rh(ppy(2(dppz](+ (1 (where ppy=2-phenylpyridine and dppz=dipyrido[3,2-a:2',3'-c]phenazine dipyridophenazine has been prepared and identified as an inhibitor of NEDD8-activating enzyme (NAE. The complex inhibited NAE activity in cell-free and cell-based assays, and suppressed the CRL-regulated substrate degradation and NF-κB activation in human cancer cells with potency comparable to known NAE inhibitor MLN4924. Molecular modeling analysis suggested that the overall binding mode of 1 within the binding pocket of the APPBP1/UBA3 heterodimer resembled that for MLN4924. Complex 1 is the first metal complex reported to suppress the NEDDylation pathway via inhibition of the NEDD8-activating enzyme.

  4. Development of a metal-based composite actuator

    Science.gov (United States)

    Asanuma, Hiroshi; Haga, Osamu; Ishii, Toshio; Kurihara, Haruki; Ohira, Junichiro; Hakoda, Genji

    2000-06-01

    This paper describes a basic concept and elemental developments to realize a metal based composite actuator to be used for smart structures. In this study, CFRP prepreg was laminated on aluminum plate to develop an actuator and this laminate could perform unidirectional actuation. SiC continuous fiber/Al composite thin plate could also be used for form a modified type of actuator instead of using CFRP. As sensors to be embedded in this actuator, the following ones wee developed. (1) A pre-notched optical fiber filament could be embedded in aluminum matrix without fracture by the interphase forming/bonding method with copper insert and could be fractured in it at the notch, which enabled forming of an optical interference type strain sensor. (2) Nickel wire could be uniformly oxidized and embedded in aluminum matrix without fracture, which could successfully work as a temperature sensor and a strain sensor.

  5. Study of structure and surface morphology of two-layer contact Ti/Al metallization

    Directory of Open Access Journals (Sweden)

    Kirill D. Vanyukhin

    2016-06-01

    Full Text Available Ti/Al/Ni/Au metallization widely used in the technology of GaN base devices have a very important imperfection i.e. rough surface. There are different opinions about the causes of this imperfection: balling-up of molten aluminum or the appearance of intermetallic melt phases in the Au–Al system. To check the effect of the former cause, we have studied the formation of rough surface after annealing of Ti/Al metallization which is used as a basis of many metallization systems for GaN. The substrates were made from silicon wafers covered with Si3N4 films (0.15 μm. On these substrates we deposited the Ti(12 nm/Al(135 nm metallization system. After the deposition the substrates were annealed in nitrogen for 30 s at 850 °С. The as-annealed specimens were tested for metallization sheet resistivity, appearance and surface morphology. We have shown that during annealing of the Ti/Al metallization system, mutual diffusion of the metals and their active interaction with the formation of intermetallic phases occur. This makes the metallization system more resistant to subsequent annealing, oxidation and chemical etching. After annealing the surface of the Ti/Al metallization system becomes gently matted. However, large hemispherical convex areas (as in the Ti/Al/Ni/Au metallization system do not form. Thus, the hypothesis on the balling-up of molten aluminum on the surface of the Ti/Al metallization system has not been confirmed.

  6. Nonlinear characterization of GaN HEMT

    International Nuclear Information System (INIS)

    Chen Chi; Hao Yue; Yang Ling; Quan Si; Ma Xiaohua; Zhang Jincheng

    2010-01-01

    DC I-V output, small signal and an extensive large signal characterization (load-pull measurements) of a GaN HEMT on a SiC substrate with different gate widths of 100 μm and 1 mm have been carried out. From the small signal data, it has been found that the cutoff frequencies increase with gate width varying from 100 μm to 1mm, owing to the reduced contribution of the parasitic effect. The devices investigated with different gate widths are enough to work in the C band and X band. The large signal measurements include the load-pull measurements and power sweep measurements at the C band (5.5 GHz) and X band (8 GHz). When biasing the gate voltage in class AB and selecting the source impedance, the optimum load impedances seen from the device for output power and PAE were localized in the load-pull map. The results of a power sweep at an 8 GHz biased various drain voltage demonstrate that a GaN HEMT on a SiC substrate has good thermal conductivity and a high breakdown voltage, and the CW power density of 10.16 W/mm was obtained. From the results of the power sweep measurement at 5.5 GHz with different gate widths, the actual scaling rules and heat effect on the large periphery device were analyzed, although the effects are not serious. The measurement results and analyses prove that a GaN HEMT on a SiC substrate is an ideal candidate for high-power amplifier design.

  7. Oxidation behaviour of Zr-based bulk metallic glasses

    International Nuclear Information System (INIS)

    Wang, Bin

    2011-01-01

    The Zr-based bulk metallic glasses, developed since the late 1980's, have very interesting mechanical properties, which can be considered for many applications including working under oxidizing atmosphere conditions at high temperatures. It is therefore interesting to study their oxidation resistance and to characterize the oxide scale formed on alloys surface. The fundamental objective of this thesis is to enhance the understanding of the role of various thermodynamic and chemistry parameters on the oxidation behaviour of the Zr-based bulk metallic glasses at high temperature under dry air, to determine the residual stresses in the oxide layer, in comparison with their crystalline alloys with the same chemical composition after an annealing treatment. The oxidation kinetics of these glasses and the crystalline structure of oxide scale ZrO 2 depend on the temperature and the oxidation duration: for short periods of oxidation or at a temperature below Tg, the kinetics follows a parabolic law, whereas, if the sample is oxidized at T ≥ Tg, the kinetics can be divided into two parts. The crystalline counterparts are oxidized by a parabolic rule whatever the temperature; for long oxidation duration at a temperature close to Tg, the kinetics becomes more complex because of the crystallisation of the glasses during the oxidation tests. Also the crystalline structure of the oxide layers depends on the oxidation temperature: the oxide layer consists only in tetragonal Zirconia at T ≤ Tg, while monoclinic Zirconia was formed at higher temperature. The mechanism of the formation of the oxide scale is due to both the interior diffusion of Oxygen ions and the external diffusion of Zirconium ions. However the diffusion of Zirconium ions slows gradually during the crystallisation process of the glass matrix. When the crystallisation is completed, the formation of Zirconia is controlled by only the internal diffusion of oxygen ions. The corresponding residual stresses

  8. Ground Albedo Neutron Sensing (GANS) method for measurements of soil moisture in cropped fields

    Science.gov (United States)

    Andres Rivera Villarreyes, Carlos; Baroni, Gabriele; Oswald, Sascha E.

    2013-04-01

    Measurement of soil moisture at the plot or hill-slope scale is an important link between local vadose zone hydrology and catchment hydrology. However, so far only few methods are on the way to close this gap between point measurements and remote sensing. This study evaluates the applicability of the Ground Albedo Neutron Sensing (GANS) for integral quantification of seasonal soil moisture in the root zone at the scale of a field or small watershed, making use of the crucial role of hydrogen as neutron moderator relative to other landscape materials. GANS measurements were performed at two locations in Germany under different vegetative situations and seasonal conditions. Ground albedo neutrons were measured at (i) a lowland Bornim farmland (Brandenburg) cropped with sunflower in 2011 and winter rye in 2012, and (ii) a mountainous farmland catchment (Schaefertal, Harz Mountains) since middle 2011. At both sites depth profiles of soil moisture were measured at several locations in parallel by frequency domain reflectometry (FDR) for comparison and calibration. Initially, calibration parameters derived from a previous study with corn cover were tested under sunflower and winter rye periods at the same farmland. GANS soil moisture based on these parameters showed a large discrepancy compared to classical soil moisture measurements. Therefore, two new calibration approaches and four different ways of integration the soil moisture profile to an integral value for GANS were evaluated in this study. This included different sets of calibration parameters based on different growing periods of sunflower. New calibration parameters showed a good agreement with FDR network during sunflower period (RMSE = 0.023 m3 m-3), but they underestimated soil moisture in the winter rye period. The GANS approach resulted to be highly affected by temporal changes of biomass and crop types which suggest the need of neutron corrections for long-term observations with crop rotation. Finally

  9. Leakage current analysis for dislocations in Na-flux GaN bulk single crystals by conductive atomic force microscopy

    Science.gov (United States)

    Hamachi, T.; Takeuchi, S.; Tohei, T.; Imanishi, M.; Imade, M.; Mori, Y.; Sakai, A.

    2018-04-01

    The mechanisms associated with electrical conduction through individual threading dislocations (TDs) in a Na-flux GaN crystal grown with a multipoint-seed-GaN technique were investigated by conductive atomic force microscopy (C-AFM). To focus on individual TDs, dislocation-related etch pits (DREPs) were formed on the Na-flux GaN surface by wet chemical etching, after which microscopic Pt electrodes were locally fabricated on the DREPs to form conformal contacts to the Na-flux GaN crystal, using electron beam assisted deposition. The C-AFM data clearly demonstrate that the leakage current flows through the individual TD sites. It is also evident that the leakage current and the electrical conduction mechanism vary significantly based on the area within the Na-flux GaN crystal where the TDs are formed. These regions include the c-growth sector (cGS) in which the GaN grows in the [0001 ] direction on top of the point-seed with a c-plane growth front, the facet-growth sector (FGS) in which the GaN grows with {10 1 ¯ 1 } facets on the side of the cGS, the boundary region between the cGS and FGS (BR), and the coalescence boundary region between FGSs (CBR). The local current-voltage (I-V) characteristics of the specimen demonstrate space charge limited current conduction and conduction related to band-like trap states associated with TDs in the FGS, BR, and CBR. A detailed analysis of the I-V data indicates that the electrical conduction through TDs in the cGS may proceed via the Poole-Frenkel emission mechanism.

  10. Test-beds for molecular electronics: metal-molecules-metal junctions based on Hg electrodes.

    Science.gov (United States)

    Simeone, Felice Carlo; Rampi, Maria Anita

    2010-01-01

    Junctions based on mesoscopic Hg electrodes are used to characterize the electrical properties of the organic molecules organized in self-assembled monolayers (SAMs). The junctions M-SAM//SAM-Hg are formed by one electrode based on metals (M) such as Hg, Ag, Au, covered by a SAM, and by a second electrode always formed by a Hg drop carrying also a SAM. The electrodes, brought together by using a micromanipulator, sandwich SAMs of different nature at the contact area (approximately = 0.7 microm2). The high versatility of the system allows a series of both electrical and electrochemical junctions to be assembled and characterized: (i) The compliant nature of the Hg electrodes allows incorporation into the junction and measurement of the electrical behavior of a large number of molecular systems and correlation of their electronic structure to the electrical behavior; (ii) by functionalizing both electrodes with SAMs exposing different functional groups, X and Y, it is possible to compare the rate of electron transfer through different X...Y molecular interactions; (iii) when the junction incorporates one of the electrode formed by a semitransparent film of Au, it allows electrical measurements under irradiation of the sandwiched SAMs. In this case the junction behaves as a photoswitch; iv) incorporation of redox centres with low lying, easily reachable energy levels, provides electron stations as indicated by the hopping mechanism dominating the current flow; (v) electrochemical junctions incorporating redox centres by both covalent and electrostatic interactions permit control of the potential of the electrodes with respect to that of the redox state by means of an external reference electrode. Both these junctions show an electrical behavior similar to that of conventional diodes, even though the mechanism generating the current flow is different. These systems, demonstrating high mechanical stability and reproducibility, easy assembly, and a wide variety of

  11. Interaction of GaN epitaxial layers with atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Losurdo, M.; Giangregorio, M.M.; Capezzuto, P.; Bruno, G.; Namkoong, G.; Doolittle, W.A.; Brown, A.S

    2004-08-15

    GaN surface passivation processes are still under development and among others hydrogen treatments are investigated. In this study, we use non-destructive optical and electrical probes such as spectroscopic ellipsometry (SE) and surface potential Kelvin probe microscopy (SP-KPM) in conjunction with non-contact atomic force microscopy (AFM) for the study of the different reactivity of Ga-polar and N-polar GaN epitaxial layers with atomic hydrogen. The GaN epitaxial layers are grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates, and GaN and AlN buffer layers are used to grow N-polar and Ga-polar films, respectively. The atomic hydrogen is produced by a remote rf (13.56 MHz) H{sub 2} plasma in order to rule out any ion bombardment of the GaN surface and make the interaction chemical. It is found that the interaction of GaN surfaces with atomic hydrogen depends on polarity, with N-polar GaN exhibiting greater reactivity. Furthermore, it is found that atomic hydrogen is effective in the passivation of grain boundaries and surface defects states.

  12. Interaction of GaN epitaxial layers with atomic hydrogen

    International Nuclear Information System (INIS)

    Losurdo, M.; Giangregorio, M.M.; Capezzuto, P.; Bruno, G.; Namkoong, G.; Doolittle, W.A.; Brown, A.S.

    2004-01-01

    GaN surface passivation processes are still under development and among others hydrogen treatments are investigated. In this study, we use non-destructive optical and electrical probes such as spectroscopic ellipsometry (SE) and surface potential Kelvin probe microscopy (SP-KPM) in conjunction with non-contact atomic force microscopy (AFM) for the study of the different reactivity of Ga-polar and N-polar GaN epitaxial layers with atomic hydrogen. The GaN epitaxial layers are grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates, and GaN and AlN buffer layers are used to grow N-polar and Ga-polar films, respectively. The atomic hydrogen is produced by a remote rf (13.56 MHz) H 2 plasma in order to rule out any ion bombardment of the GaN surface and make the interaction chemical. It is found that the interaction of GaN surfaces with atomic hydrogen depends on polarity, with N-polar GaN exhibiting greater reactivity. Furthermore, it is found that atomic hydrogen is effective in the passivation of grain boundaries and surface defects states

  13. In situ synthesis and characterization of GaN nanorods through thermal decomposition of pre-grown GaN films

    International Nuclear Information System (INIS)

    Yan, P; Qin, D; An, Y K; Li, G Z; Xing, J; Liu, J J

    2008-01-01

    Herein we describe a thermal treatment route to synthesize gallium nitride (GaN) nanorods. In this method, GaN nanorods were synthesized by thermal treatment of GaN films at a temperature of 800 deg. C. The morphology and structure of GaN nanorods were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that GaN nanorods have a hexagonal wurtzite structure with diameters ranging from 30 to 50 nm. Additionally, GaN nanoplates are also founded in the products. The growth process of GaN nanostructures was investigated and a thermal decomposition mechanism was proposed. Our method provides a cost-effective route to fabricate GaN nanorods, which will benefit the fabrication of one-dimensional nanomaterials and device applications

  14. Improved InGaN/GaN quantum wells on treated GaN template with a Ga-rich GaN interlayer

    International Nuclear Information System (INIS)

    Fang, Zhilai; Shen, Xiyang; Wu, Zhengyuan; Zhang, Tong-Yi

    2015-01-01

    Treated GaN template was achieved by in situ droplet epitaxy of a Ga-rich GaN interlayer on the conventional GaN template. InGaN/GaN quantum wells (QWs) were grown on the conventional and treated GaN templates under the same growth conditions and then comprehensively characterized. The indium homogeneity in the InGaN layers and the interface sharpness between InGaN and GaN layers of the InGaN/GaN QWs on the treated GaN template were significantly improved. The emission intensity from the InGaN/GaN QWs on the treated GaN template was enhanced by 20% than that on the conventional GaN template, which was attributed to the strain reduction and the improvement in crystalline quality. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Enhanced lateral heat dissipation packaging structure for GaN HEMTs on Si substrate

    International Nuclear Information System (INIS)

    Cheng, Stone; Chou, Po-Chien; Chieng, Wei-Hua; Chang, E.Y.

    2013-01-01

    This work presents a technology for packaging AlGaN/GaN high electron mobility transistors (HEMTs) on a Si substrate. The GaN HEMTs are attached to a V-groove copper base and mounted on a TO-3P leadframe. The various thermal paths from the GaN gate junction to the case are carried out for heat dissipation by spreading to protective coating; transferring through the bond wires; spreading in the lateral device structure through the adhesive layer, and vertical heat spreading of silicon chip bottom. Thermal characterization showed a thermal resistance of 13.72 °C/W from the device to the TO-3P package. Experimental tests of a 30 mm gate-periphery single chip packaged in a 5 × 3 mm V-groove Cu base with a 100 V drain bias showed power dissipation of 22 W. -- Highlights: ► An enhanced packaging structure designed for AlGaN/GaN HEMTs on an Si substrate. ► The V-groove copper base is designed on the device periphery surface heat conduction for enhancing Si substrate thermal dissipation. ► The proposed device shows a lower thermal resistance and upgrade in thermal conductivity capability. ► This work provides useful thermal IR imagery information to aid in designing high efficiency package for GaN HEMTs on Si

  16. Effect of metal selection and porcelain firing on the marginal accuracy of titanium-based metal ceramic restorations.

    Science.gov (United States)

    Shokry, Tamer E; Attia, Mazen; Mosleh, Ihab; Elhosary, Mohamed; Hamza, Tamer; Shen, Chiayi

    2010-01-01

    Titanium is the most biocompatible metal used for dental casting; however, there is concern about its marginal accuracy after porcelain application since this aspect has direct influence on marginal fit. The purpose of this study was to determine the effect that metal selection and the porcelain firing procedure have on the marginal accuracy of metal ceramic prostheses. Cast CP Ti, milled CP Ti, cast Ti-6Al-7Nb, and cast Ni-Cr copings (n=5) were fired with compatible porcelains (Triceram for titanium-based metals and VITA VMK 95 for Ni-Cr alloy). The Ni-Cr alloy fired with its porcelain served as the control. Photographs of metal copings placed on a master die were made. Marginal discrepancy was determined on the photographs using an image processing program at 8 predetermined locations before airborne-particle abrasion for porcelain application, after firing of the opaque layer, and after firing of the dentin layer. Repeated-measures 2-way ANOVA was used to investigate the effect of metal selection and firing stage, and paired t tests were used to determine the effect of each firing stage within each material group (alpha=.05). ANOVA showed that both metal selection and firing stage significantly influenced the measured marginal discrepancy (Pcast Ti-6Al-7Nb alloy (P=.003). Titanium copings fabricated by CAD/CAM demonstrated the least marginal discrepancy among all groups, while the base metal (Ni-Cr) groups exhibited the most discrepancy of all groups tested. Copyright 2010 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

  17. Nanofluid based on self-nanoencapsulated metal/metal alloys phase change materials with tuneable crystallisation temperature.

    Science.gov (United States)

    Navarrete, Nuria; Gimeno-Furio, Alexandra; Mondragon, Rosa; Hernandez, Leonor; Cabedo, Luis; Cordoncillo, Eloisa; Julia, J Enrique

    2017-12-14

    Nanofluids using nanoencapsulated Phase Change Materials (nePCM) allow increments in both the thermal conductivity and heat capacity of the base fluid. Incremented heat capacity is produced by the melting enthalpy of the nanoparticles core. In this work two important advances in this nanofluid type are proposed and experimentally tested. It is firstly shown that metal and metal alloy nanoparticles can be used as self-encapsulated nePCM using the metal oxide layer that forms naturally in most commercial synthesis processes as encapsulation. In line with this, Sn/SnOx nanoparticles morphology, size and thermal properties were studied by testing the suitability and performance of encapsulation at high temperatures and thermal cycling using a commercial thermal oil (Therminol 66) as the base fluid. Secondly, a mechanism to control the supercooling effect of this nePCM type based on non-eutectic alloys was developed.

  18. Biocompatibility study on Ni-free Ti-based and Zr-based bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Li, T.H. [Institute of Material Science and Engineering, National Central University, Taoyuan, Taiwan (China); Wong, P.C. [Department of Biomedical Engineering, National Yang-Ming University, Taipei, Taiwan (China); Chang, S.F. [Department of Mechanical Engineering, National Central University, Taoyuan, Taiwan (China); Tsai, P.H. [Institute of Material Science and Engineering, National Central University, Taoyuan, Taiwan (China); Jang, J.S.C., E-mail: jscjang@ncu.edu.tw [Institute of Material Science and Engineering, National Central University, Taoyuan, Taiwan (China); Department of Mechanical Engineering, National Central University, Taoyuan, Taiwan (China); Huang, J.C. [Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan (China)

    2017-06-01

    Safety and reliability are crucial issues for medical instruments and implants. In the past few decays, bulk metallic glasses (BMGs) have drawn attentions due to their superior mechanical properties, good corrosion resistance, antibacterial and good biocompatibility. However, most Zr-based and Ti-based BMGs contain Ni as an important element which is prone to human allergy problem. In this study, the Ni-free Ti-based and Zr-based BMGs, Ti{sub 40}Zr{sub 10}Cu{sub 36}Pd{sub 14}, and Zr{sub 48}Cu{sub 36}Al{sub 8}Ag{sub 8}, were selected for systematical evaluation of their biocompatibility. Several biocompatibility tests, co-cultural with L929 murine fibroblast cell line, were carried out on these two BMGs, as well as the comparison samples of Ti6Al4V and pure Cu. The results in terms of cellular adhesion, cytotoxicity, and metallic ion release affection reveal that the Ti{sub 40}Zr{sub 10}Cu{sub 36}Pd{sub 14} BMG and Ti6Al4V exhibit the optimum biocompatibility; cells still being attached on the petri dish with good adhesion and exhibiting the spindle shape after direct contact test. Furthermore, the Ti{sub 40}Zr{sub 10}Cu{sub 36}Pd{sub 14} BMG showed very low Cu ion release level, in agreement with the MTT results. Based on the current findings, it is believed that Ni-free Ti-based BMG can act as an ideal candidate for medical implant. - Highlight: • Ni-free bulk metallic glass is promising material for medical implants. • Ni-free Ti-based BMG presents similar cellular adhesion as Ti6Al4V. • Ni-free Ti-based BMG shows less cytotoxicity, and metallic ion release than Ti6Al4V.

  19. UMA/GAN network architecture analysis

    Science.gov (United States)

    Yang, Liang; Li, Wensheng; Deng, Chunjian; Lv, Yi

    2009-07-01

    This paper is to critically analyze the architecture of UMA which is one of Fix Mobile Convergence (FMC) solutions, and also included by the third generation partnership project(3GPP). In UMA/GAN network architecture, UMA Network Controller (UNC) is the key equipment which connects with cellular core network and mobile station (MS). UMA network could be easily integrated into the existing cellular networks without influencing mobile core network, and could provides high-quality mobile services with preferentially priced indoor voice and data usage. This helps to improve subscriber's experience. On the other hand, UMA/GAN architecture helps to integrate other radio technique into cellular network which includes WiFi, Bluetooth, and WiMax and so on. This offers the traditional mobile operators an opportunity to integrate WiMax technique into cellular network. In the end of this article, we also give an analysis of potential influence on the cellular core networks ,which is pulled by UMA network.

  20. Facile synthesis and photoluminescence spectroscopy of 3D-triangular GaN nano prism islands.

    Science.gov (United States)

    Kumar, Mukesh; Pasha, S K; Shibin Krishna, T C; Singh, Avanish Pratap; Kumar, Pawan; Gupta, Bipin Kumar; Gupta, Govind

    2014-08-21

    We report a strategy for fabrication of 3D triangular GaN nano prism islands (TGNPI) grown on Ga/Si(553) substrate at low temperature by N2(+) ions implantation using a sputtering gun technique. The annealing of Ga/Si(553) (600 °C) followed by nitridation (2 keV) shows the formation of high quality GaN TGNPI cross-section. TGNPI morphology has been confirmed by atomic force microscopy. Furthermore, these nano prism islands exhibit prominent ultra-violet luminescence peaking at 366 nm upon 325 nm excitation wavelength along with a low intensity yellow luminescence broad peak at 545 nm which characterizes low defects density TGNPI. Furthermore, the time-resolved spectroscopy of luminescent TGNPI in nanoseconds holds promise for its futuristic application in next generation UV-based sensors as well as many portable optoelectronic devices.