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Sample records for teiiteki gan chiryo

  1. GaN nanowire Schottky barrier diodes

    OpenAIRE

    Sabui, Gourab; Zubialevich, Vitaly Z.; White, Mary; Pampili, Pietro; Parbrook, Peter J.; McLaren, Mathew; Arredondo-Arechavala, Miryam; Shen, Z. John

    2017-01-01

    A new concept of vertical gallium nitride (GaN) Schottky barrier diode based on nanowire (NW) structures and the principle of dielectric REduced SURface Field (RESURF) is proposed in this paper. High-threading dislocation density in GaN epitaxy grown on foreign substrates has hindered the development and commercialization of vertical GaN power devices. The proposed NW structure, previously explored for LEDs offers an opportunity to reduce defect density and fabricate low cost vertical GaN pow...

  2. GaN High Power Devices

    Energy Technology Data Exchange (ETDEWEB)

    PEARTON,S.J.; REN,F.; ZHANG,A.P.; DANG,G.; CAO,X.A.; LEE,K.P.; CHO,H.; GILA,B.P.; JOHNSON,J.W.; MONIER,C.; ABERNATHY,C.R.; HAN,JUNG; BACA,ALBERT G.; CHYI,J.-I.; LEE,C.-M.; NEE,T.-E.; CHUO,C.-C.; CHI,G.C.; CHU,S.N.G.

    2000-07-17

    A brief review is given of recent progress in fabrication of high voltage GaN and AlGaN rectifiers, GaN/AlGaN heterojunction bipolar transistors, GaN heterostructure and metal-oxide semiconductor field effect transistors. Improvements in epitaxial layer quality and in fabrication techniques have led to significant advances in device performance.

  3. GaN Nanowires Synthesized by Electroless Etching Method

    KAUST Repository

    Najar, Adel

    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.

  4. 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 first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is compa- rable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on ...

  5. 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

  6. European Frontiers in RF GaN

    NARCIS (Netherlands)

    Vliet, F.E. van; Hek, P. de

    2015-01-01

    In this overview paper, a summary of the European academic and industrial status on RF GaN is given. The roles of EDA and ESA are highlighted, and examples of on-going research activities are presented. A set of HPAs over frequency, representative of today's European status, is discussed. © 2015

  7. 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

    2015-01-01

    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 (d33) 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. PMID:28787997

  8. GaN based nanorods for solid state lighting

    Science.gov (United States)

    Li, Shunfeng; Waag, Andreas

    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.

  9. 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.

  10. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

    In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. This article is a review of the latest developments in GaN based devices on silicon.

  11. Quantum efficiency of GaN photocathode under different illumination

    Science.gov (United States)

    Wang, Xiaohui; Chang, Benkang; Du, Yujie; Qiao, Jianliang

    2011-07-01

    GaN samples are activated by Cs/O under illumination of deuterium lamp, 300 nm monochromatic light with power of 70 μW and 300 nm monochromatic light with power of 35 μW, respectively. Photocurrent is detected before activation under illumination of deuterium lamp. Quantum efficiency (QE) is tested after activation. The results indicate that GaN activated under 300 nm monochromatic light have higher QE than that under deuterium lamp, and no obvious difference is detected between different power 300 nm monochromatic light. The photocurrent before activation inhibits the adsorption of Cs on the GaN surface, which decrease the QE of GaN.

  12. 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.

  13. 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.)

  14. 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.

  15. 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)

  16. GaN: Defect and Device Issues

    Energy Technology Data Exchange (ETDEWEB)

    Pearton, S.J.; Ren, F.; Shul, R.J.; Zolper, J.C.

    1998-11-09

    The role of extended and point defects, and key impurities such as C, O and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

  17. GaN power devices for automotive applications

    Science.gov (United States)

    Uesugi, T.; Kachi, Tetsu

    2013-03-01

    GaN is an attractive material for high performance power devices. Vertical GaN power devices are suitable for high current operation, on the other hand, lateral GaN power devices, namely GaN lateral HEMTs have both low on-resistance and low parasitic capacitance. In addition, the GaN lateral HEMTs can be fabricated on Si substrate. We can get low conduction loss and low switching loss devices with low cost. So the GaN lateral HEMTs are suitable for subsystems like an air conditioner and an electric power steering. Serious technical issues about GaN power devices are a normally-off operation, a current collapse, and a high quality gate insulator. Several normally-off operation techniques have been proposed but there is no decisive method. An NH3 surface treatment and a SiO2 passivation are useful to suppress the current collapse. An Al2O3 deposited by ALD is excellent for gate insulator in breakdown and it has enough TDDB reliability under room temperature and 150°C.

  18. 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.

  19. Synthesis of Single Crystal GaN Nanowires

    Directory of Open Access Journals (Sweden)

    Lining Fang

    2016-05-01

    Full Text Available The straight and curved gallium nitride (GaN nanowires were successfully synthesized by controlling the gallium/ nitrogen reactant ratio via a chemical vapour deposition method. The structure and morphology of nanowires were characterized by X-ray diffraction (XRD, transmission electronic microscopy (TEM, field emission scanning electron microscopy (FESEM, selected area electron diffraction (SAED and high resolution transmission electron microscopy (HRTEM. The straight and curved GaN nanowires are composed of wurtzite and a zinc blende structure, respectively. Photoluminescence (PL spectra of zinc blende GaN nanowires showed a strong UV emission band at 400 nm, indicating potential application in optoe‐ lectronic devices.

  20. GaN transistors for efficient power conversion

    CERN Document Server

    Lidow, Alex; de Rooij, Michael; Reusch, David

    2014-01-01

    The first edition of GaN Transistors for Efficient Power Conversion was self-published by EPC in 2012, and is currently the only other book to discuss GaN transistor technology and specific applications for the technology. More than 1,200 copies of the first edition have been sold through Amazon or distributed to selected university professors, students and potential customers, and a simplified Chinese translation is also available. The second edition has expanded emphasis on applications for GaN transistors and design considerations. This textbook provides technical and application-focused i

  1. Thermal conductivity of bulk GaN single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Jezowski, A.; Stachowiak, P.; Suski, T.; Krukowski, S.; Bockowski, M.; Grzegory, I.; Danilchenko, B

    2003-05-01

    We have measured thermal conductivity, {kappa}, in the wide temperature range 4-300 K of GaN bulk single crystals grown by high-pressure, high-temperature synthesis. Obtained results (1600 W/Km at 45 K) are the highest {kappa} values reported on GaN material. At the room temperature {kappa} is about 210 W/Km. The contributions to the GaN thermal resistance of Umklapp process, mass point defects as well as phonon scattering on dislocations and sample boundary are discussed.

  2. Photoluminescence of Mg-doped m-plane GaN grown by MOCVD on bulk GaN substrates

    OpenAIRE

    Monemar, Bo; Paskov, Plamen; Pozina, Galia; Hemmingsson, Carl; Bergman, Peder; Lindgren, David; Samuelson, Lars; Ni, Xianfeng; Morkoç, Hadis; Paskova, Tanya; Bi, Zhaoxia; Ohlsson, Jonas

    2011-01-01

    Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 1018cm-3 to well above 1019 cm-3. The samples were grown with MOCVD at reduced pressure on low defect density m-plane bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9 eV to 3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependenc...

  3. [The spectral response analysis of activated GaN photocathode].

    Science.gov (United States)

    Wang, Xiao-Hui; Chang, Ben-Kang; Zhang, Yi-Jun; Hou, Rui-Li; Xiong, Ya-Juan

    2011-10-01

    GaN photocathode has a wide applicaion in ultraviolet detection because of the outstanding performance. GaN photocathode was activated in ultrahigh vacuum (UHV) system by Cs/O, and the reflection-mode quantum efficiency (QE) was analyzed. The QE is 30%-10% corresponding to the wavelength 240-350 nm, and the QE curve is flat. The QE reaches the maximum of 30% at 240 nm. Compared with the abroad result, the QE obtained by us is still inadequate at the short wavelength The atom arrangement of GaN (0001) was studied. The atom arrangement on the surface was simulated by 3D, and in this way the adsorption of Cs on the GaN(0001) was speculated.

  4. GaN grown on nano-patterned sapphire substrates

    Science.gov (United States)

    Jing, Kong; Meixin, Feng; Jin, Cai; Hui, Wang; Huaibing, Wang; Hui, Yang

    2015-04-01

    High-quality gallium nitride (GaN) film was grown on nano-patterned sapphire substrates (NPSS) and investigated using XRD and SEM. It was found that the optimum thickness of the GaN buffer layer on the NPSS is 15 nm, which is thinner than that on micro-patterned sapphire substrates (MPSS). An interesting phenomenon was observed for GaN film grown on NPSS:GaN mainly grows on the trench regions and little grows on the sidewalls of the patterns at the initial growth stage, which is dramatically different from GaN grown on MPSS. In addition, the electrical and optical properties of LEDs grown on NPSS were characterized. Project supported by the Suzhou Nanojoin Photonics Co., Ltd and the High-Tech Achievements Transformation of Jiangsu Province, China (No.BA2012010).

  5. 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.

  6. 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

  7. Effect of photocatalytic oxidation technology on GaN CMP

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jie, E-mail: jie-wang11@mails.tsinghua.edu.cn; Wang, Tongqing, E-mail: wtq@mail.tsinghua.edu.cn; Pan, Guoshun, E-mail: pangs@mail.tsinghua.edu.cn; Lu, Xinchun, E-mail: xclu@mail.tsinghua.edu.cn

    2016-01-15

    Graphical abstract: - Highlights: • Photocatalytic oxidation technology was introduced to GaN CMP for the first time and proves to be more efficient than before. • XPS analysis reveals the planarization process by different N-type semiconductor particles. • Analyzing the effect of pH on photocatalytic oxidation in GaN CMP. • Proposing the photocatalytic oxidation model to reveal the removal mechanism. - Abstract: GaN is so hard and so chemically inert that it is difficult to obtain a high material removal rate (MRR) in the chemical mechanical polishing (CMP) process. This paper discusses the application of photocatalytic oxidation technology in GaN planarization. Three N-type semiconductor particles (TiO{sub 2}, SnO{sub 2}, and Fe{sub 2}O{sub 3}) are used as catalysts and added to the H{sub 2}O{sub 2}–SiO{sub 2}-based slurry. By optical excitation, highly reactive photoinduced holes are produced on the surface of the particles, which can oxidize OH{sup −} and H{sub 2}O absorbed on the surface of the catalysts; therefore, more OH* will be generated. As a result, GaN MRRs in an H{sub 2}O{sub 2}–SiO{sub 2}-based polishing system combined with catalysts are improved significantly, especially when using TiO{sub 2}, the MRR of which is 122 nm/h. The X-ray photoelectron spectroscopy (XPS) analysis shows the variation trend of chemical composition on the GaN surface after polishing, revealing the planarization process. Besides, the effect of pH on photocatalytic oxidation combined with TiO{sub 2} is analyzed deeply. Furthermore, the physical model of GaN CMP combined with photocatalytic oxidation technology is proposed to describe the removal mechanism of GaN.

  8. 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

  9. GaN Technology for Power Electronic Applications: A Review

    Science.gov (United States)

    Flack, Tyler J.; Pushpakaran, Bejoy N.; Bayne, Stephen B.

    2016-06-01

    Power semiconductor devices based on silicon (Si) are quickly approaching their limits, set by fundamental material properties. In order to address these limitations, new materials for use in devices must be investigated. Wide bandgap materials, such as silicon carbide (SiC) and gallium nitride (GaN) have suitable properties for power electronic applications; however, fabrication of practical devices from these materials may be challenging. SiC technology has matured to point of commercialized devices, whereas GaN requires further research to realize full material potential. This review covers fundamental material properties of GaN as they relate to Si and SiC. This is followed by a discussion of the contemporary issues involved with bulk GaN substrates and their fabrication and a brief overview of how devices are fabricated, both on native GaN substrate material and non-native substrate material. An overview of current device structures, which are being analyzed for use in power switching applications, is then provided; both vertical and lateral device structures are considered. Finally, a brief discussion of prototypes currently employing GaN devices is given.

  10. Synthesis and field emission properties of GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Li Enling, E-mail: Lienling@xaut.edu.cn [Science School, Xi' an University of Technology, Xi' an 710048 (China); Cui Zhen; Dai Yuanbin; Zhao Danna; Zhao Tao [Science School, Xi' an University of Technology, Xi' an 710048 (China)

    2011-10-01

    Gallium nitride (GaN) nanowires grown on nickel-coated n-type Si (1 0 0) substrates have been synthesized using chemical vapor deposition (CVD), and the field emission properties of GaN nanowires have been studied. The results show that (1) the grown GaN nanowires, which have diameters in the range of 50-100 nm and lengths of several micrometers, are uniformly distributed on Si substrates. The characteristics of the grown GaN nanowires have been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and through these investigations it was found that the GaN nanowires are of a good crystalline quality (2) When the emission current density is 100 {mu}A/cm{sup 2}, the necessary electric field is an open electric field of around 9.1 V/{mu}m (at room temperature). The field enhancement factor is {approx}730. The field emission properties of GaN nanowires films are related both to the surface roughness and the density of the nanowires in the film.

  11. Role of the ganSPQAB Operon in Degradation of Galactan by Bacillus subtilis.

    Science.gov (United States)

    Watzlawick, Hildegard; Morabbi Heravi, Kambiz; Altenbuchner, Josef

    2016-10-15

    Bacillus subtilis possesses different enzymes for the utilization of plant cell wall polysaccharides. This includes a gene cluster containing galactan degradation genes (ganA and ganB), two transporter component genes (ganQ and ganP), and the sugar-binding lipoprotein-encoding gene ganS (previously known as cycB). These genes form an operon that is regulated by GanR. The degradation of galactan by B. subtilis begins with the activity of extracellular GanB. GanB is an endo-β-1,4-galactanase and is a member of glycoside hydrolase (GH) family 53. This enzyme was active on high-molecular-weight arabinose-free galactan and mainly produced galactotetraose as well as galactotriose and galactobiose. These galacto-oligosaccharides may enter the cell via the GanQP transmembrane proteins of the galactan ABC transporter. The specificity of the galactan ABC transporter depends on the sugar-binding lipoprotein, GanS. Purified GanS was shown to bind galactotetraose and galactotriose using thermal shift assay. The energy for this transport is provided by MsmX, an ATP-binding protein. The transported galacto-oligosaccharides are further degraded by GanA. GanA is a β-galactosidase that belongs to GH family 42. The GanA enzyme was able to hydrolyze short-chain β-1,4-galacto-oligosaccharides as well as synthetic β-galactopyranosides into galactose. Thermal shift assay as well as electrophoretic mobility shift assay demonstrated that galactobiose is the inducer of the galactan operon regulated by GanR. DNase I footprinting revealed that the GanR protein binds to an operator overlapping the -35 box of the σ(A)-type promoter of Pgan, which is located upstream of ganS IMPORTANCE: Bacillus subtilis is a Gram-positive soil bacterium that utilizes different types of carbohydrates, such as pectin, as carbon sources. So far, most of the pectin degradation systems and enzymes have been thoroughly studied in B. subtilis Nevertheless, the B. subtilis utilization system of galactan, which is

  12. 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...

  13. Quantum Yield of Reflection Mode Varied Doping GaN Photocathode

    OpenAIRE

    Qiao Jianliang; Li Xiangjiang; Niu Jun; Gao Youtang

    2016-01-01

    Using the NEA photocathode activation and evaluation experiment system, the varied doping GaN photocathode has been activated and evaluated. According to the diffusion and orientation drifting equation, the quantum yield formula of reflection mode varied doping NEA GaN photocathode was gotten. The factors affecting the quantum efficiency of varied doping GaN photocathode were studied. For the varied doping GaN photocathode, the quantum efficiency is mainly decided by the escape probability of...

  14. Synthesis and characterization of silicon-doped polycrystalline GaN ...

    Indian Academy of Sciences (India)

    Administrator

    from its very low-cost production. Among different ... GaN target (99.999%) containing 1 at% Si in argon plasma and a combination of ... ing the substrate temperatures during sputtering of the. GaN target. The SEM images of two representative nano- crystalline GaN films deposited at substrate temperatures at ~ 423 and 623 ...

  15. Activation and evaluation of GaN photocathodes

    Science.gov (United States)

    Qian, Yunsheng; Chang, Benkang; Qiao, Jiangliang; Zhang, Yijun; Fu, Rongguo; Qiu, Yafeng

    2009-09-01

    Gallium Nitride (GaN) photocathodes are potentially attractive as UV detective materials and electron sources. Based on the activation and evaluation system for GaAs photocathode, which consists of ultra-high vacuum (UHV) activation chamber, multi-information measurement system, X-ray photoelectron spectroscopy (XPS), and ultraviolet ray photoelectron spectroscopy (UPS), the control and measurement system for the activation of UV photocathodes was developed. The developed system, which consists of Xenon lamp, monochromator with scanner, signal-processing module, power control unit of Cs and O source, A/D adapter, digital I/O card, computer and software, can control the activation of GaN photocathodes and measure on-line the spectral response curves of GaN photocathodes. GaN materials on sapphire substrate were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with p-type Mg doping. The GaN materials were activated by Cs-O. The spectral response and quantum efficiency (QE) were measured and calculated. The experiment results are discussed.

  16. GaN photocathodes for UV detection and imaging

    Science.gov (United States)

    Siegmund, Oswald H. W.; Tremsin, Anton S.; Martin, Adrian; Malloy, James; Ulmer, Melville P.; Wessels, Bruce

    2003-12-01

    The nitride-III semiconductors, in particular GaN (band gap energy 3.5 eV), AlN (band gap 6.2 eV) and their alloys AlxGa1-xN are attractive as UV photo-convertors with applications as photocathodes for position sensitive detector systems. These can "fill the gap" in the 150-400nm wavelength regime between alkali halide photocathodes (photocathodes (>4000Å, mutlialkali & GaAs). Currently CsTe photocathodes have fairly low efficiency (Fig. 1) in the 100nm to 300nm regime are sensitive to contamination and have no tolerance to gas exposure. We have prepared and measured a number of GaN photocathodes in opaque and semitransparent modes, achieving >50% quantum efficiency in opaque mode and ~35% in semitransparent mode (Fig. 2). The GaN photocathodes are stable over periods of >1 year and are robust enough to be re-activated many times. The cutoff wavelength is sharp, with a rapid decline in quantum efficiency at ~380-400nm. Application of GaN photocathodes in imaging devices should be feasible in the near future. Further performance improvements are also expected as GaN fabrication and processing techniques are refined.

  17. 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.

  18. Unintentional doping in GaN.

    Science.gov (United States)

    Zhu, Tongtong; Oliver, Rachel A

    2012-07-21

    The optimisation of GaN-based electronic and optoelectronic devices requires control over the doping of the material. However, device performance, particular for lateral transport electronic devices, is degraded by the presence of unintentional doping, which for heteroepitaxial GaN layers grown in the polar (0001) orientation is mainly confined to a layer adjacent to the GaN/substrate interface. The use of scanning capacitance microscopy (SCM) has demonstrated that this layer forms due to the high rate of incorporation of gas phase impurities, primarily oxygen, during the early stages of growth, when N-rich semi-polar facets are often present. The presence of such facets leads to additional unintentional doping when defect density reduction strategies involving a three-dimensional growth phase (such as epitaxial lateral overgrowth) are employed. Many semi-polar epitaxial layers, on the other hand, exhibit significant unintentional doping throughout their thickness, except when a three-dimensional growth phase is introduced to aid in defect density reduction resulting in the presence of (0001) and non-polar facets which incorporate less dopant. Non-polar epitaxial samples exhibit behaviour more similar to (0001)-oriented material, but oxygen diffusion from the sapphire substrate along prismatic stacking faults also locally affects the extent of the unintentional doping in this case.

  19. High Voltage GaN Schottky Rectifiers

    Energy Technology Data Exchange (ETDEWEB)

    CAO,X.A.; CHO,H.; CHU,S.N.G.; CHUO,C.-C.; CHYI,J.-I.; DANG,G.T.; HAN,JUNG; LEE,C.-M.; PEARTON,S.J.; REN,F.; WILSON,R.G.; ZHANG,A.P.

    1999-10-25

    Mesa and planar GaN Schottky diode rectifiers with reverse breakdown voltages (V{sub RB}) up to 550V and >2000V, respectively, have been fabricated. The on-state resistance, R{sub ON}, was 6m{Omega}{center_dot} cm{sup 2} and 0.8{Omega}cm{sup 2}, respectively, producing figure-of-merit values for (V{sub RB}){sup 2}/R{sub ON} in the range 5-48 MW{center_dot}cm{sup -2}. At low biases the reverse leakage current was proportional to the size of the rectifying contact perimeter, while at high biases the current was proportional to the area of this contact. These results suggest that at low reverse biases, the leakage is dominated by the surface component, while at higher biases the bulk component dominates. On-state voltages were 3.5V for the 550V diodes and {ge}15 for the 2kV diodes. Reverse recovery times were <0.2{micro}sec for devices switched from a forward current density of {approx}500A{center_dot}cm{sup -2} to a reverse bias of 100V.

  20. 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.

  1. Post-annealing effects on pulsed laser deposition-grown GaN thin films

    International Nuclear Information System (INIS)

    Cheng, Yu-Wen; Wu, Hao-Yu; Lin, Yu-Zhong; Lee, Cheng-Che; Lin, Ching-Fuh

    2015-01-01

    In this work, the post-annealing effects on gallium nitride (GaN) thin films grown from pulsed laser deposition (PLD) are investigated. The as-deposited GaN thin films grown from PLD are annealed at different temperatures in nitrogen ambient. Significant changes of the GaN crystal properties are observed. Raman spectroscopy is used to observe the crystallinity, the change of residual stress, and the thermal decomposition of the annealed GaN thin films. X-ray diffraction is also applied to identify the crystal phase of GaN thin films, and the surface morphology of GaN thin films annealed at different temperatures is observed by scanning electron microscopy. Through the above analyses, the GaN thin films grown by PLD undergo three stages: phase transition, stress alteration, and thermal decomposition. At a low annealing temperature, the rock salt GaN in GaN films is transformed into wurtzite. The rock salt GaN diminishes with increasing annealing temperature. At a medium annealing temperature, the residual stress of the film changes significantly from compressive strain to tensile strain. As the annealing temperature further increases, the GaN undergoes thermal decomposition and the surface becomes granular. By investigating the annealing temperature effects and controlling the optimized annealing temperature of the GaN thin films, we are able to obtain highly crystalline and strain-free GaN thin films by PLD. - Highlights: • The GaN thin film is grown on sapphire by pulsed laser deposition. • The GaN film undergoes three stages with increasing annealing temperature. • In the first stage, the film transfers from rock salt to wurtzite phase. • In the second stage, the stress in film changes from compressive to tensile. • In the final stage, the film thermally decomposes and becomes granular

  2. Curvature and bow of bulk GaN substrates

    Energy Technology Data Exchange (ETDEWEB)

    Foronda, Humberto M.; Young, Erin C.; Robertson, Christian A.; Speck, James S. [Materials Department, UCSB, Santa Barbara, California 93106 (United States); Romanov, Alexey E. [Materials Department, UCSB, Santa Barbara, California 93106 (United States); Ioffe Physico-Technical Institute RAS, St. Petersburg 194021 (Russian Federation); ITMO University, St. Petersburg 197101 (Russian Federation); Beltz, Glenn E. [Mechanical Engineering Department, UCSB, Santa Barbara, California 93106 (United States)

    2016-07-21

    We investigate the bow of free standing (0001) oriented hydride vapor phase epitaxy grown GaN substrates and demonstrate that their curvature is consistent with a compressive to tensile stress gradient (bottom to top) present in the substrates. The origin of the stress gradient and the curvature is attributed to the correlated inclination of edge threading dislocation (TD) lines away from the [0001] direction. A model is proposed and a relation is derived for bulk GaN substrate curvature dependence on the inclination angle and the density of TDs. The model is used to analyze the curvature for commercially available GaN substrates as determined by high resolution x-ray diffraction. The results show a close correlation between the experimentally determined parameters and those predicted from theoretical model.

  3. Optical and Structural Characterizations of GaN Nano structures

    International Nuclear Information System (INIS)

    Shekari, L.; Abu Hassan, H.; Thahab, S.M.

    2011-01-01

    We have grown wurtzite GaN nano wires (NWs) on polished silicon (Si) either with or without Au as catalyst, using commercial GaN powder by thermal evaporation in an atmosphere of argon (Ar) gas. Structural and optical characterizations were performed using high resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), photoluminescence (PL) and energy-dispersive X-ray spectroscopy (EDX) spectroscopy. Results indicate that the nano wires are of single-crystal hexagonal GaN and the nano wires on Si with Au catalyst are more oriented than those without Au catalyst; and using catalyst make the NWs grow much faster and quite well-ordered. The compositional quality of the grown nano wires on the substrates are mostly same, however the nano wires on the Au coated silicon are of low density, while the nano wires on the Si are of high density. (author)

  4. Design and performance of GaN betavoltaic device

    International Nuclear Information System (INIS)

    Jung, H. K.; Lee, N. M.; Lee, S. K.

    2007-01-01

    Semiconductor betavoltaic cell employs a semiconductor pn junction and a radioisotope that emits beta particles. This device can be used for remote applications requiring a long life power and for minimizing the size. In order to obtain a useful beta radiation power from the nuclear waste, Nickel-63 and Carbon-14 radioisotopes were selected. Ni-63 energy source adapted to a wideband GaN p-n junction as well as silicon device but C-14 has the higher energy which affects the extensive degradation of performance in silicon device and can adapt only to a GaN semiconductor showing the radiation tolerance. The experimental results for I- V characteristics were compared and analyzed. This paper also presents the design concepts for high efficiency GaN betavoltaic cell

  5. Studies on electronic structure of GaN(0001) surface

    CERN Document Server

    Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K

    2002-01-01

    An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

  6. 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.

  7. Critical issues for homoepitaxial GaN growth by molecular beam epitaxy on hydride vapor-phase epitaxy-grown GaN substrates

    Science.gov (United States)

    Storm, D. F.; Hardy, M. T.; Katzer, D. S.; Nepal, N.; Downey, B. P.; Meyer, D. J.; McConkie, Thomas O.; Zhou, Lin; Smith, David J.

    2016-12-01

    While the heteroepitaxial growth of gallium nitride-based materials and devices on substrates such as SiC, sapphire, and Si has been well-documented, the lack of a cost-effective source of bulk GaN crystals has hindered similar progress on homoepitaxy. Nevertheless, freestanding GaN wafers are becoming more widely available, and there is great interest in growing GaN films and devices on bulk GaN substrates, in order to take advantage of the greatly reduced density of threading dislocations, particularly for vertical devices. However, homoepitaxial GaN growth is far from a trivial task due to the reactivity and different chemical sensitivities of N-polar (0001) and Ga-polar (0001) GaN surfaces, which can affect the microstructure and concentrations of impurities in homoepitaxial GaN layers. In order to achieve high quality, high purity homoepitaxial GaN, it is necessary to investigate the effect of the ex situ wet chemical clean, the use of in situ cleaning procedures, the sensitivity of the GaN surface to thermal decomposition, and the effect of growth temperature. We review the current understanding of these issues with a focus on homoepitaxial growth of GaN by molecular beam epitaxy (MBE) on c-plane surfaces of freestanding GaN substrates grown by hydride vapor phase epitaxy (HVPE), as HVPE-grown substrates are most widely available. We demonstrate methods for obtaining homoepitaxial GaN layers by plasma-assisted MBE in which no additional threading dislocations are generated from the regrowth interface and impurity concentrations are greatly reduced.

  8. Study of photoemission mechanism for varied doping GaN photocathode

    Science.gov (United States)

    Qiao, Jianliang; Xu, Yuan; Niu, Jun; Gao, Youtang; Chang, Benkang

    2015-10-01

    Negative electron affinity (NEA) GaN photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive threshold and so on. The quantum efficiency is an important parameter for the preparation and evaluation of NEA GaN photocathode. The varied doping GaN photocathode has the directional inside electric field within the material, so the higher quantum efficiency can be obtained. The varied doping NEA GaN photocathode has better photoemission performance. According to the photoemission theory of NEA GaN photocathode, the quantum efficiency formulas for uniform doping and varied doping NEA GaN photocathodes were given. In the certain condition, the quantum efficiency formula for varied doping GaN photocathode consists with the uniform doping. The activation experiment was finished for varied doping GaN photocathode. The cleaning method and technics for varied doping GaN photocathode were given in detail. To get an atom clean surface, the heat cleaning must be done after the chemical cleaning. Using the activation and evaluation system for NEA photocathode, the varied doping GaN photocathode was activated with Cs and O, and the photocurrent curve for varied doping GaN photocathode was gotten.

  9. The influence of Fe doping on the surface topography of GaN epitaxial material

    International Nuclear Information System (INIS)

    Cui Lei; Yin Haibo; Jiang Lijuan; Wang Quan; Feng Chun; Xiao Hongling; Wang Cuimei; Wang Xiaoliang; Gong Jiamin; Zhang Bo; Li Baiquan; Wang Zhanguo

    2015-01-01

    Fe doping is an effective method to obtain high resistivity GaN epitaxial material. But in some cases, Fe doping could result in serious deterioration of the GaN material surface topography, which will affect the electrical properties of two dimensional electron gas (2DEG) in HEMT device. In this paper, the influence of Fe doping on the surface topography of GaN epitaxial material is studied. The results of experiments indicate that the surface topography of Fe-doped GaN epitaxial material can be effectively improved and the resistivity could be increased after increasing the growth rate of GaN materials. The GaN material with good surface topography can be manufactured when the Fe doping concentration is 9 × 10 19 cm −3 . High resistivity GaN epitaxial material which is 1 × 10 9 Ω·cm is achieved. (paper)

  10. Novel Cs-Free GaN Photocathodes

    Science.gov (United States)

    Tripathi, Neeraj; Bell, L. D.; Nikzad, Shouleh; Tungare, Mihir; Suvarna, Puneet H.; Sandvik, Fatemeh Shahedipour

    2011-04-01

    We report on a novel GaN photocathode structure that eliminates the use of Cs for photocathode activation. Development of such a photocathode structure promises reduced cost and complexity of the device, potentially with stable operation for a longer time. Device simulation studies suggest that deposition of Si delta-doped GaN on p-GaN templates induces sharp downward energy band bending at the surface, assisting in achieving effective negative electron affinity for GaN photocathodes without the use of Cs. A series of experiments has been performed to optimize the quality of the Si delta-doped layer to minimize the emission threshold of the device. This report includes significant observations relating the dependence of device properties such as emission threshold, quantum efficiency, and surface morphology on the Si incorporation in the Si delta-doped layer. An optimum Si incorporation has been observed to provide the minimum emission threshold of 4.1 eV for the discussed Cs-free GaN photocathodes. Photoemission (PE), atomic force microscopy (AFM), and secondary-ion mass spectroscopy (SIMS) have been performed to study the effect of growth conditions on device performance.

  11. Template Approach to Crystalline GaN Nanosheets.

    Science.gov (United States)

    Liu, Baodan; Yang, Wenjin; Li, Jing; Zhang, Xinglai; Niu, Pingjuan; Jiang, Xin

    2017-05-10

    Crystalline GaN nanosheets hold great challenge in growth and promising application in optoelectronic nanodevices. In this work, we reported an accessible template approach toward the rational synthesis of GaN nanosheets through the nitridation of metastable γ-Ga 2 O 3 nanosheets synthesized from a hydrothermal reaction. The cubic γ-Ga 2 O 3 nanosheets with smooth surface and decent crystallinity can be directly converted into hexagonal GaN nanosheets with similar morphology framework and comparable crystal quality in NH 3 at 850 °C. UV-vis spectrum measurement reveals that the GaN nanosheets show a band gap of 3.30 eV with strong visible absorption in the range of 370-500 nm. The template synthetic strategy proposed in this work will open up more opportunities for the achievement of a variety of sheetlike nanostructures that can not be obtained through conventional routines and will undoubtedly further promote the fundamental research of newly emerging sheetlike nanostructures and nanotechnology.

  12. Thermal quenching of the yellow luminescence in GaN

    Science.gov (United States)

    Reshchikov, M. A.; Albarakati, N. M.; Monavarian, M.; Avrutin, V.; Morkoç, H.

    2018-04-01

    We observed varying thermal quenching behavior of the yellow luminescence band near 2.2 eV in different GaN samples. In spite of the different behavior, the yellow band in all the samples is caused by the same defect—the YL1 center. In conductive n-type GaN, the YL1 band quenches with exponential law, and the Arrhenius plot reveals an ionization energy of ˜0.9 eV for the YL1 center. In semi-insulating GaN, an abrupt and tunable quenching of the YL1 band is observed, where the apparent activation energy in the Arrhenius plot is not related to the ionization energy of the defect. In this case, the ionization energy can be found by analyzing the shift of the characteristic temperature of PL quenching with excitation intensity. We conclude that only one defect, namely, the YL1 center, is responsible for the yellow band in undoped and doped GaN samples grown by different techniques.

  13. On the magnetic properties of Gd implanted GaN

    Czech Academy of Sciences Publication Activity Database

    Hejtmánek, J.; Knížek, K.; Maryško, M.; Jirák, Z.; Sedmidubský, D.; Sofer, Z.; Peřina, Vratislav; Hardtdegen, H.; Buchal, C.

    2008-01-01

    Roč. 103, č. 7 (2008), 07D107/1-07D107/3 ISSN 0021-8979 Institutional research plan: CEZ:AV0Z10480505 Keywords : GaN * Curie-type * FM Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 2.201, year: 2008

  14. Taevo Gans : särama pandud postmodernism / Kadi Viljak

    Index Scriptorium Estoniae

    Viljak, Kadi

    2004-01-01

    Viking Window ASi büroo ja ekspositsioonisaal 1979. a. Jüri Okase projekteeritud endises Paide KEKi remontmehaanikatöökoja hoones Mäos. Sisearhitekt Taevo Gans, kelle projekteeritud on ka ettevõtte juhi töölaud. T. Gansi kommentaarid. Ill.: 6 värv. sisevaadet

  15. Electrochemical characterization of GaN surface states

    Science.gov (United States)

    Winnerl, Andrea; Garrido, Jose A.; Stutzmann, Martin

    2017-07-01

    In this work, we present a systematic study of the electrochemical properties of metal-organic chemical vapor deposition and hybrid vapor phase epitaxy grown n-type GaN in aqueous electrolytes. For this purpose, we perform cyclic voltammetry and impedance spectroscopy measurements over a wide range of potentials and frequencies, using a pure aqueous electrolyte and adding two different types of redox couples, as well as applying different surface treatments to the GaN electrodes. For Ga-polar GaN electrodes, the charge transfer to an electrolyte is dominated by surface states, which are not related to dislocations and are independent of the specific growth technique. These surface states can be modified by the surface treatment; they are generated by etching in HCl and are passivated by oxidation. Different surface defect states are present on N-polar GaN electrodes which do not significantly contribute to the charge transfer across the GaN/electrolyte interface.

  16. (Gans, 1960; Schmidt and Inger, 1957). Ovoviviparity i

    African Journals Online (AJOL)

    Embryos found in material from three localities are recorded in Table I. The dispropor- tionate amount of yolk relative to the size of the embryo, first described for T. wiegmanni. (Hediger 1935) and subsequently for the South American Amphisbaena manni by Gans and. Alexander (1962), is a feature also of the development ...

  17. Photoluminescence of Mg-doped m-plane GaN grown by MOCVD on bulk GaN substrates

    Energy Technology Data Exchange (ETDEWEB)

    Monemar, Bo [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden); Solid State Physics-The Nanometer Structure Consortium, Lund University, Box 118, 221 00 Lund (Sweden); Paskov, Plamen; Pozina, Galia; Hemmingsson, Carl; Bergman, Peder [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden); Lindgren, David; Samuelson, Lars [Solid State Physics-The Nanometer Structure Consortium, Lund University, Box 118, 221 00 Lund (Sweden); Ni, Xianfeng; Morkoc, Hadis [Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia 23284-3072 (United States); Paskova, Tanya [Kyma Technologies Inc., Raleigh, North Carolina 27617 (United States); Bi, Zhaoxia; Ohlsson, Jonas [Glo AB, Ideon Science Park, Scheelevaegen 17, 223 70 Lund (Sweden)

    2011-07-15

    Photoluminescence (PL) properties are reported for a set of m-plane GaN films with Mg doping varied from mid 10{sup 18} cm{sup -3} to above 10{sup 20} cm{sup -3}. The samples were grown with MOCVD at reduced pressure on low defect density bulk GaN templates. The sharp line near bandgap bound exciton (BE) spectra observed below 50 K, as well as the broader donor-acceptor pair (DAP) PL bands at 2.9-3.3 eV give evidence of several Mg related acceptors, similar to the case of c-plane GaN. The dependence of the BE spectra on excitation intensity as well as the transient decay behaviour demonstrate acoustic phonon assisted transfer between the acceptor BE states. The lower energy donor-acceptor pair spectra suggest the presence of deep acceptors, in addition to the two main shallower ones at about 0.23 eV. Similar spectra from Mg-doped GaN nanowires (NWs) grown by MOCVD are also briefly discussed. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. GaN layer growth by HVPE on m-plane sapphire substrates

    Energy Technology Data Exchange (ETDEWEB)

    Usikov, Alexander; Shapovalov, Lisa; Ivantsov, Vladimir; Kovalenkov, Oleg; Syrkin, Alexander [Technologies and Devices International an Oxford Instruments Company, 12214 Plum Orchard Dr., Silver Spring, MD 20904 (United States); Spiberg, Philippe; Brown, Robert [Ostendo Technologies, Inc., 6185 Paseo del Norte, Suite 200, Carlsbad, CA 92011 (United States)

    2009-06-15

    Semipolar GaN layers were grown on m-plane sapphire substrates by HVPE. Insertion of Al{sub x}Ga{sub 1-x}N (x{proportional_to}0.1-0.6) layer in-between m-plane sapphire substrate and GaN layer promoted to improve crystalline quality and to grow of semipolar (11-22) plane GaN layers. X-ray diffraction (11-22){omega}-scan rocking curve FWHM of 298 arcsec was measured for a 30 {mu}m thick (11-22)GaN layer. Depending on growth conditions, m-plane GaN layer having micro-crystallites of other orientations (mainly of (11-24) plane GaN layer) was also grown. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Energy Technology Data Exchange (ETDEWEB)

    Manna, S; De, S K, E-mail: mannaju@gmail [Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India)

    2011-04-01

    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.

  20. Integrated GaN photonic circuits on silicon (100) for second harmonic generation

    OpenAIRE

    Xiong, Chi; Pernice, Wolfram; Ryu, Kevin K.; Schuck, Carsten; Fong, King Y.; Palacios, Tomas; Tang, Hong X.

    2014-01-01

    We demonstrate second order optical nonlinearity in a silicon architecture through heterogeneous integration of single-crystalline gallium nitride (GaN) on silicon (100) substrates. By engineering GaN microrings for dual resonance around 1560 nm and 780 nm, we achieve efficient, tunable second harmonic generation at 780 nm. The \\{chi}(2) nonlinear susceptibility is measured to be as high as 16 plus minus 7 pm/V. Because GaN has a wideband transparency window covering ultraviolet, visible and ...

  1. Thermal Annealing induced relaxation of compressive strain in porous GaN structures

    KAUST Repository

    Ben Slimane, Ahmed

    2012-01-01

    The effect of annealing on strain relaxation in porous GaN fabricated using electroless chemical etching is presented. The Raman shift of 1 cm-1 in phonon frequency of annealed porous GaN with respect to as-grown GaN corresponds to a relaxation of compressive strain by 0.41 ± 0.04 GPa. The strain relief promises a marked reduction in threading dislocation for subsequent epitaxial growth.

  2. Nucleation control for the growth of vertically aligned GaN nanowires

    OpenAIRE

    Hou, Wen-Chi; Wu, Tung-Hsien; Tang, Wei-Che; Hong, Franklin Chau-Nan

    2012-01-01

    Aligned GaN nanowire arrays have high potentials for applications in future electronic and optoelectronic devices. In this study, the growth of GaN nanowire arrays with high degree of vertical alignment was attempted by plasma-enhanced CVD on the c-plane GaN substrate. We found that the lattice matching between the substrate and the nanowire is essential for the growth of vertically aligned GaN nanowires. In addition, the initial nucleation process is also found to play a key role in creating...

  3. 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

  4. Photoemission of graded-doping GaN photocathode

    International Nuclear Information System (INIS)

    Fu Xiao-Qian; Chang Ben-Kang; Wang Xiao-Hui; Li Biao; Du Yu-Jie; Zhang Jun-Ju

    2011-01-01

    We study the photoemission process of graded-doping GaN photocathode and find that the built-in electric fields can increase the escape probability and the effective diffusion length of photo-generated electrons, which results in the enhancement of quantum efficiency. The intervalley scattering mechanism and the lattice scattering mechanism in high electric fields are also investigated. To prevent negative differential mobility from appearing, the surface doping concentration needs to be optimized, and it is calculated to be 3.19×10 17 cm −3 . The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  5. Photoemission of graded-doping GaN photocathode

    Science.gov (United States)

    Fu, Xiao-Qian; Chang, Ben-Kang; Wang, Xiao-Hui; Li, Biao; Du, Yu-Jie; Zhang, Jun-Ju

    2011-03-01

    We study the photoemission process of graded-doping GaN photocathode and find that the built-in electric fields can increase the escape probability and the effective diffusion length of photo-generated electrons, which results in the enhancement of quantum efficiency. The intervalley scattering mechanism and the lattice scattering mechanism in high electric fields are also investigated. To prevent negative differential mobility from appearing, the surface doping concentration needs to be optimized, and it is calculated to be 3.19×1017 cm-3. The graded-doping GaN photocathode with higher performance can be realized by further optimizing the doping profile. Project supported by the National Natural Science Foundation of China (Grant No. 60871012) and the Research Fund of Nanjing University of Science and Technology (Grant No. 2010ZYTS032).

  6. 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

  7. Dual Motion GAN for Future-Flow Embedded Video Prediction

    OpenAIRE

    Liang, Xiaodan; Lee, Lisa; Dai, Wei; Xing, Eric P.

    2017-01-01

    Future frame prediction in videos is a promising avenue for unsupervised video representation learning. Video frames are naturally generated by the inherent pixel flows from preceding frames based on the appearance and motion dynamics in the video. However, existing methods focus on directly hallucinating pixel values, resulting in blurry predictions. In this paper, we develop a dual motion Generative Adversarial Net (GAN) architecture, which learns to explicitly enforce future-frame predicti...

  8. Room Temperature Ultralow Threshold GaN Nanowire Polariton Laser

    KAUST Repository

    Das, Ayan

    2011-08-01

    We report ultralow threshold polariton lasing from a single GaN nanowire strongly coupled to a large-area dielectric microcavity. The threshold carrier density is 3 orders of magnitude lower than that of photon lasing observed in the same device, and 2 orders of magnitude lower than any existing room-temperature polariton devices. Spectral, polarization, and coherence properties of the emission were measured to confirm polariton lasing. © 2011 American Physical Society.

  9. Annealing of GaN under high pressure of nitrogen

    CERN Document Server

    Porowski, S; Kolesnikov, D; Lojkowski, W; Jager, V; Jäger, W; Bogdanov, V; Suski, T; Krukowski, S

    2002-01-01

    Gallium nitride, aluminum nitride and indium nitride are basic materials for blue optoelectronic devices. The essential part of the technology of these devices is annealing at high temperatures. Thermodynamic properties of the Ga-N system and their consequences to application of high nitrogen pressure for the annealing of GaN based materials are summarized. The diffusion of Zn, Mg and Au in high dislocation density heteroepitaxial GaN/Al sub 2 O sub 3 layers will be compared with the diffusion in dislocation-free GaN single crystals and homoepitaxial layers. It will be shown that high dislocation density can drastically change the diffusion rates, which strongly affects the performance of nitride devices. Inter-diffusion of Al, Ga and In in AlGaN/GaN and InGaN/GaN quantum well (QW) structures will be also considered. It will be shown that in contrast to stability of metal contacts, which is strongly influenced by dislocations, the inter-diffusion of group III atoms in QW structures is not affected strongly by...

  10. Arsenic mediated reconstructions on cubic (001) GaN

    Energy Technology Data Exchange (ETDEWEB)

    Feuillet, G.; Hamaguchi, H.; Ohta, K.; Hacke, P.; Okumura, H.; Yoshida, S. [Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki, 305 (Japan)

    1997-02-01

    The 4{times}1 (respectively 1{times}1) (001) GaN surfaces obtained when molecular-beam-epitaxy (MBE) growth is carried out on (001) cubic SiC were exposed to an As background pressure in the MBE chamber: The reconstructions rapidly and irreversibly changed to 2{times}2 [respectively {ital c}(2{times}2)] as usually observed for GaN growth on (001) GaAs. The usual reversible 2{times}2/{ital c}(2{times}2) transitions were consequently observed when bringing the Ga flux up or down. The respective positions for the 4{times}1/1{times}1 and 2{times}2/{ital c}(2{times}2) transitions were worked out as a function of the growth parameters. These observations indicate that the 2{times}2 and {ital c}(2{times}2) GaN surface reconstructions are mediated by As atoms which we tentatively assign to a surfactant effect. A simple structural model involving As dimers is proposed that accounts for Ga coverages of 0.5 and 1 monolayer for the 2{times}2 and {ital c}(2{times}2) growth regimes, respectively. {copyright} {ital 1997 American Institute of Physics.}

  11. Anisotropic strain and phonon deformation potentials in GaN

    International Nuclear Information System (INIS)

    Darakchieva, V.; Arwin, H.; Paskov, P. P.; Monemar, B.; Paskova, T.; Hommel, D.; Schubert, M.; Heuken, M.; Off, J.; Scholz, F.; Haskell, B. A.; Fini, P. T.; Speck, J. S.; Nakamura, S.

    2007-01-01

    We report optical phonon frequency studies in anisotropically strained c-plane- and a-plane-oriented GaN films by generalized infrared spectroscopic ellipsometry and Raman scattering spectroscopy. The anisotropic strain in the films is obtained from high-resolution x-ray diffraction measurements. Experimental evidence for splitting of the GaN E 1 (TO), E 1 (LO), and E 2 phonons under anisotropic strain in the basal plane is presented, and their phonon deformation potentials c E 1 (TO) , c E 1 (LO) , and c E 2 are determined. A distinct correlation between anisotropic strain and the A 1 (TO) and E 1 (LO) frequencies of a-plane GaN films reveals the a A 1 (TO) , b A 1 (TO) , a E 1 (LO) , and b E 1 (LO) phonon deformation potentials. The a A 1 (TO) and b A 1 (TO) are found to be in very good agreement with previous results from Raman experiments [V. Yu. Davydov et al., J. Appl. Phys. 82, 5097 (1997)]. Our a A 1 (TO) and a E 1 (LO) phonon deformation potentials agree well with recently reported theoretical estimations [J.-M. Wagner and F. Bechstedt, Phys. Rev. B 66, 115202 (2002)], while b A 1 (TO) and b E 1 (LO) are found to be significantly larger than the theoretical values. A discussion of the observed differences is presented

  12. 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.

  13. 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.)

  14. Investigation on the Solubility of GaN in Supercritical Ammonia Containing Acidic, Neutral, and Some Basic Mineralizers

    National Research Council Canada - National Science Library

    Ehrentraut, Dirk

    2009-01-01

    ... material due to the superior structural quality over HVPE GaN. In order to hold up with the progress, not at least provide a scientific platform, the solubility of GaN in supercritical ammonia (NH3...

  15. Cubic crystalline erbium oxide growth on GaN(0001) by atomic layer deposition

    Science.gov (United States)

    Chen, Pei-Yu; Posadas, Agham B.; Kwon, Sunah; Wang, Qingxiao; Kim, Moon J.; Demkov, Alexander A.; Ekerdt, John G.

    2017-12-01

    Growth of crystalline Er2O3, a rare earth sesquioxide, on GaN(0001) is described. Ex situ HCl and NH4OH solutions and an in situ N2 plasma are used to remove impurities on the GaN surface and result in a Ga/N stoichiometry of 1.02. Using atomic layer deposition with erbium tris(isopropylcyclopentadienyl) [Er(iPrCp)3] and water, crystalline cubic Er2O3 (C-Er2O3) is grown on GaN at 250 °C. The orientation relationships between the C-Er2O3 film and the GaN substrate are C-Er2O3(222) ǁ GaN(0001), C-Er2O3⟨-440⟩ ǁ GaN ⟨11-20⟩, and C-Er2O3⟨-211⟩ ǁ GaN ⟨1-100⟩. Scanning transmission electron microscopy and electron energy loss spectroscopy are used to examine the microstructure of C-Er2O3 and its interface with GaN. With post-deposition annealing at 600 °C, a thicker interfacial layer is observed, and two transition layers, crystalline GaNwOz and crystalline GaErxOy, are found between GaN and C-Er2O3. The tensile strain in the C-Er2O3 film is studied with x-ray diffraction by changes in both out-of-plane and in-plane d-spacing. Fully relaxed C-Er2O3 films on GaN are obtained when the film thickness is around 13 nm. Additionally, a valence band offset of 0.7 eV and a conduction band offset of 1.2 eV are obtained using x-ray photoelectron spectroscopy.

  16. Structural characteristics of single crystalline GaN films grown on (111) diamond with AlN buffer

    DEFF Research Database (Denmark)

    Pécz, Béla; Tóth, Lajos; Barna, Árpád

    2013-01-01

    , eliminated the inversion domains and reduced the density of threading dislocations in the GaN epilayers. The films have an in-plane epitaxial relationship [1010]GaN//[110]diamond. Thus GaN (0001) thin films of single epitaxial relationship and of single polarity were realised on diamond with AlN buffer....

  17. Fabrication and characterization of subwavelength nanostructures on freestanding GaN slab.

    Science.gov (United States)

    Wang, Yongjin; Hu, Fangren; Kanamori, Yoshiaki; Sameshima, Hidehisa; Hane, Kazuhiro

    2010-02-01

    We develop a novel way to fabricate subwavelength nanostructures on the freestanding GaN slab using a GaN-on-silicon system by combining self-assemble technique and backside thinning method. Silicon substrate beneath the GaN slab is removed by bulk silicon micromachining, generating the freestanding GaN slab and eliminating silicon absorption of the emitted light. Fast atom beam (FAB) etching is conducted to thin the freestanding GaN slab from the backside, reducing the number of confined modes inside the GaN slab. With self-assembled silica nanospheres acting as an etching mask, subwavelength nanostructures are realized on the GaN surface by FAB etching. The reflection losses at the GaN interfaces are thus suppressed. When the InGaN/GaN multiple quantum wells (MQWs) active layers are excited, the light extraction efficiency is significantly improved for the freestanding nanostructured GaN slab. This work provides a very practical approach to fabricate freestanding nanostructures on the GaN-on-silicon system for further improving the light extraction efficiency.

  18. Controllable process of nanostructured GaN by maskless inductively coupled plasma (ICP) etching

    International Nuclear Information System (INIS)

    Zhao, Yanfei; Wang, Hu; Shen, Yang; Huang, Zengli; Zhang, Jian; Dingsun, An; Zhang, Wei; Li, Jiadong

    2017-01-01

    This work improved the anisotropically etching profile of GaN with Cl 2 ICP by adjusting etching pressure and gas flow. High etching rate is achieved by lowering pressure and gas flow instead of increasing etching power. High etching power is unfavorable because it may cause physical damages on the surface. In addition, it is noticed that the material of the carrier, used for holding samples during etching, has significant effects on the morphology and profile of the etched GaN surface. A smooth and large-area GaN surface was achieved by proper ICP etching with a big piece of Si carrier; whereas, with other kinds of carriers, various nano-structures were formed on the GaN surfaces after etching. In fact, it is the etching resistance of carrier materials that impacts the surface profile of etched GaN. Needle-like and grass-like nanostructures on etched GaN surfaces were observed with Al and sapphire carriers, of which the process is very similar to RIE-grass or black-silicon technology. This controllable maskless dry-etching process for the GaN nanostructured surface may show more potential applications in GaN devices. (paper)

  19. Conduction, reverse conduction and switching characteristics of GaN E-HEMT

    DEFF Research Database (Denmark)

    Sørensen, Charlie; Lindblad Fogsgaard, Martin; Christiansen, Michael Noe

    2015-01-01

    In this paper switching and conduction characterization of the GS66508P-E03 650V enhancement mode gallium nitride (GaN) transistor is described. GaN transistors are leading edge technology and as so, their characteristics are less than well documented. The switching characteristics are found using...

  20. Viability and proliferation of endothelial cells upon exposure to GaN nanoparticles

    Directory of Open Access Journals (Sweden)

    Tudor Braniste

    2016-09-01

    Full Text Available Nanotechnology is a rapidly growing and promising field of interest in medicine; however, nanoparticle–cell interactions are not yet fully understood. The goal of this work was to examine the interaction between endothelial cells and gallium nitride (GaN semiconductor nanoparticles. Cellular viability, adhesion, proliferation, and uptake of nanoparticles by endothelial cells were investigated. The effect of free GaN nanoparticles versus the effect of growing endothelial cells on GaN functionalized surfaces was examined. To functionalize surfaces with GaN, GaN nanoparticles were synthesized on a sacrificial layer of zinc oxide (ZnO nanoparticles using hydride vapor phase epitaxy. The uptake of GaN nanoparticles by porcine endothelial cells was strongly dependent upon whether they were fixed to the substrate surface or free floating in the medium. The endothelial cells grown on surfaces functionalized with GaN nanoparticles demonstrated excellent adhesion and proliferation, suggesting good biocompatibility of the nanostructured GaN.

  1. High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

    DEFF Research Database (Denmark)

    Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong

    2003-01-01

    Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, whi...

  2. Controllable process of nanostructured GaN by maskless inductively coupled plasma (ICP) etching

    Science.gov (United States)

    Zhao, Yanfei; Wang, Hu; Zhang, Wei; Li, Jiadong; Shen, Yang; Huang, Zengli; Zhang, Jian; Dingsun, An

    2017-11-01

    This work improved the anisotropically etching profile of GaN with Cl2 ICP by adjusting etching pressure and gas flow. High etching rate is achieved by lowering pressure and gas flow instead of increasing etching power. High etching power is unfavorable because it may cause physical damages on the surface. In addition, it is noticed that the material of the carrier, used for holding samples during etching, has significant effects on the morphology and profile of the etched GaN surface. A smooth and large-area GaN surface was achieved by proper ICP etching with a big piece of Si carrier; whereas, with other kinds of carriers, various nano-structures were formed on the GaN surfaces after etching. In fact, it is the etching resistance of carrier materials that impacts the surface profile of etched GaN. Needle-like and grass-like nanostructures on etched GaN surfaces were observed with Al and sapphire carriers, of which the process is very similar to RIE-grass or black-silicon technology. This controllable maskless dry-etching process for the GaN nanostructured surface may show more potential applications in GaN devices.

  3. The investigation of stress in freestanding GaN crystals grown from Si substrates by HVPE.

    Science.gov (United States)

    Lee, Moonsang; Mikulik, Dmitry; Yang, Mino; Park, Sungsoo

    2017-08-17

    We investigate the stress evolution of 400 µm-thick freestanding GaN crystals grown from Si substrates by hydride vapour phase epitaxy (HVPE) and the in situ removal of Si substrates. The stress generated in growing GaN can be tuned by varying the thickness of the MOCVD AlGaN/AlN buffer layers. Micro Raman analysis shows the presence of slight tensile stress in the freestanding GaN crystals and no stress accumulation in HVPE GaN layers during the growth. Additionally, it is demonstrated that the residual tensile stress in HVPE GaN is caused only by elastic stress arising from the crystal quality difference between Ga- and N-face GaN. TEM analysis revealed that the dislocations in freestanding GaN crystals have high inclination angles that are attributed to the stress relaxation of the crystals. We believe that the understanding and characterization on the structural properties of the freestanding GaN crystals will help us to use these crystals for high-performance opto-electronic devices.

  4. The optimal thickness of a transmission-mode GaN photocathode

    Science.gov (United States)

    Wang, Xiao-Hui; Shi, Feng; Guo, Hui; Hu, Cang-Lu; Cheng, Hong-Chang; Chang, Ben-Kang; Ren, Ling; Du, Yu-Jie; Zhang, Jun-Ju

    2012-08-01

    A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 1017 cm-3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 × 104 cm·s-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.

  5. Quantum Yield of Reflection Mode Varied Doping GaN Photocathode

    Directory of Open Access Journals (Sweden)

    Qiao Jianliang

    2016-01-01

    Full Text Available Using the NEA photocathode activation and evaluation experiment system, the varied doping GaN photocathode has been activated and evaluated. According to the diffusion and orientation drifting equation, the quantum yield formula of reflection mode varied doping NEA GaN photocathode was gotten. The factors affecting the quantum efficiency of varied doping GaN photocathode were studied. For the varied doping GaN photocathode, the quantum efficiency is mainly decided by the escape probability of electron P, he absorption coefficient α, the electron diffuse length LD, the reflectance of cathode materials for incident light R, emission layer thickness Te and the inside electric field E. The experiment and analysis results show: With the directional inside electric field in the bulk, the varied doping NEA GaN photocathode has better photoemission performance than uniform doping photocathode.

  6. 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.

  7. Characterization of Pb-Doped GaN Thin Films Grown by Thermionic Vacuum Arc

    Science.gov (United States)

    Özen, Soner; Pat, Suat; Korkmaz, Şadan

    2018-03-01

    Undoped and lead (Pb)-doped gallium nitride (GaN) thin films have been deposited by a thermionic vacuum arc (TVA) method. Glass and polyethylene terephthalate were selected as optically transparent substrates. The structural, optical, morphological, and electrical properties of the deposited thin films were investigated. These physical properties were interpreted by comparison with related analysis methods. The crystalline structure of the deposited GaN thin films was hexagonal wurtzite. The optical bandgap energy of the GaN and Pb-doped GaN thin films was found to be 3.45 eV and 3.47 eV, respectively. The surface properties of the deposited thin films were imaged using atomic force microscopy and field-emission scanning electron microscopy, revealing a nanostructured, homogeneous, and granular surface structure. These results confirm that the TVA method is an alternative layer deposition system for Pb-doped GaN thin films.

  8. Nucleation control for the growth of vertically aligned GaN nanowires.

    Science.gov (United States)

    Hou, Wen-Chi; Wu, Tung-Hsien; Tang, Wei-Che; Hong, Franklin Chau-Nan

    2012-07-07

    Aligned GaN nanowire arrays have high potentials for applications in future electronic and optoelectronic devices. In this study, the growth of GaN nanowire arrays with high degree of vertical alignment was attempted by plasma-enhanced CVD on the c-plane GaN substrate. We found that the lattice matching between the substrate and the nanowire is essential for the growth of vertically aligned GaN nanowires. In addition, the initial nucleation process is also found to play a key role in creating the high-quality homoepitaxy at the nanowire-substrate interface. By controlling the nucleation stage, the growth of highly aligned vertical GaN nanowire arrays can be achieved. The reasons for the observed effects are discussed.

  9. Nondestructive measurement of homoepitaxially grown GaN film thickness with Fourier transform infrared spectroscopy

    Science.gov (United States)

    Horikiri, Fumimasa; Narita, Yoshinobu; Yoshida, Takehiro

    2017-12-01

    In vertical devices containing GaN homoepitaxial layers on GaN substrates, the layer thickness is a key parameter that needs to be clarified before starting the device process. We applied Fourier transform infrared spectroscopy (FT-IR) to a homoepitaxially grown GaN film that consisted of an n--GaN layer. The estimated film thickness from the FT-IR spectrum agreed well with the results of cross-sectional scanning electron microscope cathodoluminescence images. This is the first report of nondestructive film thickness measurements for homoepitaxially grown GaN and indicates the applicability of FT-IR to the nondestructive inspection of vertical GaN power devices.

  10. Reduction of dislocations in GaN epilayers using templated three-dimensional coherent nanoislands

    Science.gov (United States)

    Jeganathan, K.; Shimizu, M.; Okumura, H.

    2005-05-01

    Low-dislocation-density GaN layers have been grown on 6H-SiC(0001) substrates by molecular-beam epitaxy using high-density (˜4×1011cm-2) self-assembled Stranski-Krastanov GaN nanoislands buffer. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that the insertion of coherent nanoislands as a buffer reduces the defect migration from the interface to the GaN epitaxial layers. The dislocation density is dramatically dropped to ˜107cm-2 in GaN layers grown on coherent nanoislands as compared to ˜109cm-2 in the typical GaN layers grown on the AIN buffer.

  11. Lattice-Symmetry-Driven Epitaxy of Hierarchical GaN Nanotripods

    KAUST Repository

    Wang, Ping

    2017-01-18

    Lattice-symmetry-driven epitaxy of hierarchical GaN nanotripods is demonstrated. The nanotripods emerge on the top of hexagonal GaN nanowires, which are selectively grown on pillar-patterned GaN templates using molecular beam epitaxy. High-resolution transmission electron microscopy confirms that two kinds of lattice-symmetry, wurtzite (wz) and zinc-blende (zb), coexist in the GaN nanotripods. Periodical transformation between wz and zb drives the epitaxy of the hierarchical nanotripods with N-polarity. The zb-GaN is formed by the poor diffusion of adatoms, and it can be suppressed by improving the ability of the Ga adatoms to migrate as the growth temperature increased. This controllable epitaxy of hierarchical GaN nanotripods allows quantum dots to be located at the phase junctions of the nanotripods and nanowires, suggesting a new recipe for multichannel quantum devices.

  12. GaN MODFET microwave power technology for future generation radar and communications systems

    Science.gov (United States)

    Grider, D. E.; Nguyen, N. X.; Nguyen, C.

    1999-08-01

    In order to gain a better understanding of the role that GaN MODFET technology will play in future generation radar and communications systems, a comparison of the state-of-the-art performance of alternative microwave power technologies will be reviewed. The relative advantages and limitations of each technology will be discussed in relation to system needs. Device results from recent MBE-grown GaN MODFETs will also be presented. In particular, 0.25 μm gate GaN MODFETs grown by MBE have been shown to exhibit less than 5% variation in maximum drain current density ( Idmax) from the center to the edge of a 2 inch wafer. This level of uniformity is a substantially higher than that normally found in MOCVD-grown GaN devices (˜28% variation). In addition, evidence is also presented to demonstrate the excellent reproducibility of MBE-grown GaN MODFETs.

  13. 1.2 kV GaN Schottky barrier diodes on free-standing GaN wafer using a CMOS-compatible contact material

    Science.gov (United States)

    Liu, Xinke; Liu, Qiang; Li, Chao; Wang, Jianfeng; Yu, Wenjie; Xu, Ke; Ao, Jin-Ping

    2017-02-01

    In this paper, we report the formation of vertical GaN Schottky barrier diodes (SBDs) on a 2-in. free-standing (FS) GaN wafer, using CMOS-compatible contact material. By realizing an off-state breakdown voltage V BR of 1200 V and an on-state resistance R on of 7 mΩ·cm2, the FS-GaN SBDs fabricated in this work achieve a power device figure-of-merit V\\text{BR}2/R\\text{on} of 2.1 × 108 V2·Ω-1·cm-2 on a high quality GaN wafer. In addition, the fabricated FS-GaN SBDs show the highest I on/I off current ratio of ˜2.3 × 1010 among the GaN SBDs reported in the literature.

  14. 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 17 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 17 cm −3 was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

  15. Ab initio investigations of the strontium gallium nitride ternaries Sr 3GaN3 and Sr6GaN5: Promising materials for optoelectronic

    KAUST Repository

    Goumri-Said, Souraya

    2013-05-31

    Sr3GaN3 and Sr6GaN5 could be promising potential materials for applications in the microelectronics, optoelectronics and coating materials areas of research. We studied in detail their structural, elastic, electronic, optical as well as the vibrational properties, by means of density functional theory framework. Both of these ternaries are semiconductors, where Sr3GaN3 exhibits a small indirect gap whereas Sr6GaN5 has a large direct gap. Indeed, their optical properties are reported for radiation up to 40 eV. Charge densities contours, Hirshfeld and Mulliken populations, are reported to investigate the role of each element in the bonding. From the mechanical properties calculation, it is found that Sr6GaN5 is harder than Sr3GaN3, and the latter is more anisotropic than the former. The phonon dispersion relation, density of phonon states and the vibrational stability are reported from the density functional perturbation theory calculations. © 2013 IOP Publishing Ltd.

  16. Current steering effect of GaN nanoporous structure

    International Nuclear Information System (INIS)

    Lin, Chia-Feng; Wang, Jing-Hao; Cheng, Po-Fu; Tseng, Wang-Po; Fan, Feng-Hsu; Wu, Kaun-Chun; Lee, Wen-Che; Han, Jung

    2014-01-01

    Current steering effect of InGaN light emitting diode (LED) structure was demonstrated by forming a high resistivity GaN nanoporous structure. Disk-array patterns with current-injection bridge structures were fabricated on InGaN LED devices through a focused ion beam (FIB) system. GaN nanoporous structure was formed around the FIB-drilled holes through a electrochemical (EC) wet-etching process on a n-type GaN:Si layer under the InGaN active layer. High emission intensity and small peak wavelength blueshift phenomenon of the electroluminescence spectra were observed in the EC-treated region compared with the non-treated region. The branch-like nanoporous structure was formed along the lateral etched direction to steer the injection current in 5 μm-width bridge structures. In the FIB-drilled hole structure, high light emission intensity of the central-disk region was observed by enlarging the bridge width to 10 μm, with a 5 μm EC-treated width, that reduced the current steering effect and increased the light scattering effect on the nanoporous structure. The EC-treated GaN:Si nanoporous structure acted as a high light scattering structure and a current steering structure that has potential on the current confinement for vertical cavity surface emitting laser applications. - Highlights: • High resistivity nanoporous-GaN formed in InGaN LED through electrochemical process. • Branch-like nanoporous in 5 μm-width bridge structure can steer the injection current. • Nanoporous GaN acted as s light scattering and current steering structures in InGaN LED

  17. Chlorine-based plasma etching of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Shul, R.J.; Briggs, R.D. [Sandia National Labs., Albuquerque, NM (United States); Pearton, S.J.; Vartuli, C.B.; Abernathy, C.R.; Lee, J.W. [Univ. of Florida, Gainesville, FL (United States). Dept. of Materials Science and Engineering; Constantine, C.; Baratt, C. [Plasma-Therm, Inc., Saint Petersburg, FL (United States)

    1997-02-01

    The wide band gap group-III nitride materials continue to generate interest in the semiconductor community with the fabrication of green, blue, and ultraviolet light emitting diodes (LEDs), blue lasers, and high temperature transistors. Realization of more advanced devices requires pattern transfer processes which are well controlled, smooth, highly anisotropic and have etch rates exceeding 0.5 {micro}m/min. The utilization of high-density chlorine-based plasmas including electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) systems has resulted in improved GaN etch quality over more conventional reactive ion etch (RIE) systems.

  18. Temperature Dependence of GaN HEMT Small Signal Parameters

    OpenAIRE

    Ali M. Darwish; Amr A. Ibrahim; H. Alfred Hung

    2011-01-01

    This study presents the temperature dependence of small signal parameters of GaN/SiC HEMTs across the 0–150°C range. The changes with temperature for transconductance ( m ), output impedance ( d s and d s ), feedback capacitance ( d g ), input capacitance ( g s ), and gate resistance ( g ) are measured. The variations with temperature are established for m , d s , d s , d g , g s , and g in the GaN technology. This information is useful for MMIC designs....

  19. Pressure-induced phase transition in GaN nanocrystals

    CERN Document Server

    Cui, Q; Zhang, W; Wang, X; Zhang, J; Cui, T; Xie, Y; Liu, J; Zou, G

    2002-01-01

    High-pressure in situ energy-dispersive x-ray diffraction experiments on GaN nanocrystals with 50 nm diameter have been carried out using a synchrotron x-ray source and a diamond-anvil cell up to about 79 GPa at room temperature. A pressure-induced first-order structural phase transition from the wurtzite-type structure to the rock-salt-type structure starts at about 48.8 GPa. The rock-salt-type phase persists to the highest pressure in our experimental range.

  20. Demystifying AlphaGo Zero as AlphaGo GAN

    OpenAIRE

    Dong, Xiao; Wu, Jiasong; Zhou, Ling

    2017-01-01

    The astonishing success of AlphaGo Zero\\cite{Silver_AlphaGo} invokes a worldwide discussion of the future of our human society with a mixed mood of hope, anxiousness, excitement and fear. We try to dymystify AlphaGo Zero by a qualitative analysis to indicate that AlphaGo Zero can be understood as a specially structured GAN system which is expected to possess an inherent good convergence property. Thus we deduct the success of AlphaGo Zero may not be a sign of a new generation of AI.

  1. Comparative study of GaN and GaAs photocathodes

    Science.gov (United States)

    Qiao, Jianliang; Chang, Benkang; Yang, Zhi; Tian, Si; Gao, Youtang

    2008-02-01

    Taking GaAs and GaN as representation, negative electron affinity (NEA) photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive long-wave threshold, great potential to extend the long-wave spectral response waveband. Therefore it plays more and more important effect in high performance image intensifiers and polarized electron sources. GaN NEA photocathode and GaAs NEA photocathode are very similar because they all belong to III-V compound. But, GaN photocathode and GaAs photocathode have many difference in such aspects as preparation process, activation manners, stability and application field etc. In this paper, using the multi-information measurement and evaluation system of photocathode, the preparation processes of native reflection-mode GaN photocathode and GaAs photocathode are studied. The different activation manners of GaN photocathode and GaAs photocathode are compared and analyzed. The spectral response and stability of the two kind of photocathode are compared also. The experiments indicate: the atomically clean degree of NEA photocathode surface and the structure of activation layer are the main factors that influence photocathode sensitivity and stability after activation. GaN photocathode and GaAs photocathode have good NEA property and large quantum yield. Compare with GaAs photocathode, GaN photocathode has high stability, and the decay of the quantum yield is comparatively slow.

  2. Study on photoemission surface of varied doping GaN photocathode

    Science.gov (United States)

    Qiao, Jianliang; Du, Ruijuan; Ding, Huan; Gao, Youtang; Chang, Benkang

    2014-09-01

    For varied doping GaN photocathode, from bulk to surface the doping concentrations are distributed from high to low. The varied doping GaN photocathode may produce directional inside electric field within the material, so the higher quantum efficiency can be obtained. The photoemission surface of varied doping GaN photocathode is very important to the high quantum efficiency, but the forming process of the surface state after Cs activation or Cs/O activation has been not known completely. Encircling the photoemission mechanism of varied GaN photocathode, considering the experiment phenomena during the activation and the successful activation results, the varied GaN photocathode surface model [GaN(Mg):Cs]:O-Cs after activation with cesium and oxygen was given. According to GaN photocathode activation process and the change of electronic affinity, the comparatively ideal NEA property can be achieved by Cs or Cs/O activation, and higher quantum efficiency can be obtained. The results show: The effective NEA characteristic of GaN can be gotten only by Cs. [GaN(Mg):Cs] dipoles form the first dipole layer, the positive end is toward the vacuum side. In the activation processing with Cs/O, the second dipole layer is formed by O-Cs dipoles, A O-Cs dipole includes one oxygen atom and two Cs atoms, and the positive end is also toward the vacuum side thus the escape of electrons can be promoted.

  3. Growth of GaN on Ge(111) by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Lieten, R. R.; Degroote, S.; Cheng, K.; Leys, M.; Kuijk, M.; Borghs, G.

    2006-01-01

    The epitaxial growth of GaN on Ge is reported. The authors found that direct growth of GaN performs exceptionally well on Ge(111) with plasma assisted molecular beam epitaxy. A streaky reflection high energy electron diffraction pattern is observed during growth. X-ray diffraction showed a rocking curve full width at half maximum of only 371 arc sec for a 38 nm GaN layer and indicates an abrupt interface between the GaN and Ge. Secondary ion mass spectrometry shows limited diffusion of Ga atoms into the Ge substrate and Ge atoms into the GaN layers. Current-voltage measurements show rectifying behavior for n-GaN on p-Ge. Their results indicate that GaN growth on Ge does not require intermediate layers, allowing the Ge substrate to be used as back contact in vertical devices. A p-n junction formed between GaN and Ge can be used in heterojunction devices

  4. 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.

  5. Research on quantum efficiency of GaN wire photocathode

    Science.gov (United States)

    Xia, Sihao; Liu, Lei; Diao, Yu; Kong, Yike

    2017-02-01

    On the basis of three-dimensional continuity equation in semiconductors and finite difference method, the carrier concentration and the quantum efficiency of GaN wire photocathode as a function of incident photon energy are achieved. Results show that the quantum efficiency of the wire photocathode is largely enhanced compared with the conventional planar photocathode. The superiority of the wire photocathode is reflected in its structure with surrounding surfaces. The quantum efficiency of the wire photocathode largely depends on the wire width, surface reflectivity, surface escape probability and incident angle of light. The back interface recombination rate, however, has little influences on the quantum efficiency of the wire photocathode. The simulation results suggest that the optimal width for photoemission is 150-200 nm. Besides, the quantum efficiency increases and decreases linearly with increasing surface escape probability and surface reflectivity, respectively. With increasing ratio of wire spacing to wire height, the optimal incident angle of light is reduced. These simulations are expected to guide the preparation of a better performing GaN wire photocathode.

  6. Radiotracer Spectroscopy on Group II Acceptors in GaN

    CERN Multimedia

    2002-01-01

    The semiconductor GaN is already used for the production of high power light emitting diodes in the blue and UV spectral range. But the $\\rho$-type doping, which is usually obtained by Mg doping, is still inefficient due to compensation and passivation effects caused by defects present in the material. It is theoretically predicted, that Be is a more promising candidate for $\\rho$-doping with a lower ionization energy of 60meV. It is our goal to investigate the electrical and optical properties of Be- and Mg-related defects in GaN to clarify the problem of compensation and passivation. The used methods are standard spectroscopic methods in semiconductor physics which are improved by using radioactive isotopes. The radioactive decay of $^{7}$Be and $^{28}$Mg is used to clearly correlate different signals with Be or Mg related defects. We intend to use the spectroscopic techniques Deep Level Transient Spectroscopy (DLTS), Thermal Admittance Spectroscopy (TAS), photoluminescence (PL) and additionally Hall-effect...

  7. Optical properties of inversion domain boundaries in GaN

    Energy Technology Data Exchange (ETDEWEB)

    Kure, Thomas; Kirste, Ronny; Callsen, Gordon; Reparaz, Juan Sebastian; Hoffmann, Axel [Technische Universitaet Berlin, Berlin (Germany); Collazo, Ramon; Sitar, Zlatko [North Carolina State University, Raleigh, North Carolina (United States); HexaTech Inc., Raleigh, North Carolina (United States); Rice, Anthony [North Carolina State University, Raleigh, North Carolina (United States); Mita, Seji; Xie, Jinqiao [HexaTech Inc., Raleigh, North Carolina (United States)

    2011-07-01

    Influenced by the growth method and growth parameters the polarity of epitaxial grown GaN films can be manipulated to form pure N- or Ga-polarity or states of mixed polarity. GaN grown on heterosubstrates can even form spatially adjacent areas of different polarities differentiated by an inversion domain boundary (IDB). Besides their structural differences each of the areas has unique optical properties, likewise the IDB itself. Furthermore, due to a polar selective doping behaviour, it is possible to fabricate a lateral p/n junction. Using spatially-resolved photoluminescence spectroscopy ({mu}-PL) we revealed a temperature dependant enhancement of the luminescence by one order of magnitude at the IDB. Thereby, we confirmed an earlier published model. Samples intentionally doped with Mg, which led to a p/n-junction, revealed an unexpected difference of the enhancement compared to the undoped samples. In addition, we used spatially-resolved electroluminescence spectroscopy ({mu}-EL) to investigate the influence of an external electric field.

  8. MARTA GANs: Unsupervised Representation Learning for Remote Sensing Image Classification

    Science.gov (United States)

    Lin, Daoyu; Fu, Kun; Wang, Yang; Xu, Guangluan; Sun, Xian

    2017-11-01

    With the development of deep learning, supervised learning has frequently been adopted to classify remotely sensed images using convolutional networks (CNNs). However, due to the limited amount of labeled data available, supervised learning is often difficult to carry out. Therefore, we proposed an unsupervised model called multiple-layer feature-matching generative adversarial networks (MARTA GANs) to learn a representation using only unlabeled data. MARTA GANs consists of both a generative model $G$ and a discriminative model $D$. We treat $D$ as a feature extractor. To fit the complex properties of remote sensing data, we use a fusion layer to merge the mid-level and global features. $G$ can produce numerous images that are similar to the training data; therefore, $D$ can learn better representations of remotely sensed images using the training data provided by $G$. The classification results on two widely used remote sensing image databases show that the proposed method significantly improves the classification performance compared with other state-of-the-art methods.

  9. GaN nanophosphors for white-light applications

    Science.gov (United States)

    Kumar, Mirgender; Singh, V. P.; Dubey, Sarvesh; Suh, Youngsuk; Park, Si-Hyun

    2018-01-01

    GaN nanoparticles (NPs) were synthesized by carbothermal reduction combined with nitridation, using Ga2O3 powder and graphitic carbon nitride (g-C3N4) as precursors. Characterization of the NPs was performed by X-ray diffraction, scanning electron microscopy, and room-temperature photoluminescence measurements. X-ray photoelectron spectroscopy was also performed to detect the chemical states of the different species. A universal yellow luminescence (YL) band was observed from complexes of Ga vacancies with O anti-sites and of O anti-sites with C. Further increments in the C content were observed with continued growth and induced an additional blue luminescence (BL) band. Tuning of the YL and BL bands resulted in white-light emission under certain experimental conditions, thus offering a new way of employing GaN nanophosphors for solid-state white lighting. Calculations of the correlated color temperature and color-quality scale parameters confirmed the utility of the experimental process for different applications.

  10. 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

  11. Characteristics of GaN material and application in UV detection

    Science.gov (United States)

    Qiao, Jianliang; Xu, Yuan; Wang, Xiaohui; Qian, Yunsheng; Chang, Benkang

    2012-10-01

    For the characteristics such as wide bandgap, low dielectric constant, ability to bear high temperature, ability to resist radiation etc., GaN material can be used for UV solar blind detection in very rigorous environments. But for a long time, the preparation technology for GaN material has been still keeping it from being used extensively. GaN photocathode with good future is developed slowly in the field of UV detection. The key method of obtaining effective photoemission is to reduce the vacuum energy level of GaN emission surface, make it lower than bulk conduction band minimum. Negative electron affinity (NEA) GaN photocathode can convert the light under 365 nm to the photoelectrons that can be sent to the free space. The surface potential of NEA GaN photocathode is made up of two straight line sections with different slope. As the first dipole layer, [GaN(Mg):Cs] dipole brings 3.0 eV decline of the vacuum energy level, make the GaN photocathode surface obtain about -1.0 eV effective negative electron affinity. The second dipole O-Cs makes effective electron affinity reduce further to - 1.2 eV. The results show: near 37% quantum efficiency can be gotten at the wavelength 200 nm for reflection-mode GaN photocathode, and the quantum efficiency reaches up to 13% at 290 nm in transmission mode. The large quantum efficiency and high stability are very good properties for UV detection devices employing GaN photoemitter.

  12. Facet and in-plane crystallographic orientations of GaN nanowires grown on Si(111)

    International Nuclear Information System (INIS)

    Largeau, L; Harmand, J C; Dheeraj, D L; Tchernycheva, M; Cirlin, G E

    2008-01-01

    We have determined the in-plane orientation of GaN nanowires relative to the Si (111) substrate on which they were grown. We used x-ray diffraction pole figure measurements to evidence two types of crystallographic orientation, all the nanowires having {101-bar 0} lateral facets. The proportion of these two orientations was determined and shown to be influenced by the pre-deposition of Al(Ga)N intermediate layers. In the main orientation, the GaN basal directions are aligned with the directions. This orientation corresponds to an in-plane coincidence of GaN and Si lattices

  13. Characterization of plasma etching damage on p -type GaN using Schottky diodes

    OpenAIRE

    Masashi, Kato; K., Mikamo; Masaya, Ichimura; M., Kanechika; O., Ishiguro; T., Kachi

    2008-01-01

    The plasma etching damage in p-type GaN has been characterized. From current-voltage and capacitance-voltage characteristics of Schottky diodes, it was revealed that inductively coupled plasma (ICP) etching causes an increase in series resistance of the Schottky diodes and compensation of acceptors in p-type GaN. We investigated deep levels near the valence band of p-type GaN using current deep level transient spectroscopy (DLTS), and no deep level originating from the ICP etching damage was ...

  14. Analysis of GaN etching damage by capacitively coupled RF Ar plasma exposure

    International Nuclear Information System (INIS)

    Kawakami, Retsuo; Inaoka, Takeshi; Minamoto, Shingo; Kikuhara, Yasuyuki

    2008-01-01

    GaN etching damage by capacitively-coupled RF Ar plasma exposure is significantly dependent on gas pressure and exposure time. At a low gas pressure (10 mTorr), the N/Ga ratio decreases by the physical etching effect with increasing exposure time, while the GaN surface morphology is smooth. At a high gas pressure (50 mTorr), there are other effects such as UV radiation, by which the GaN surface morphology becomes rough as the exposure time increases from ∼ 60 min

  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

    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. Redshift of A 1(longitudinal optical) mode for GaN crystals under strong electric field

    Science.gov (United States)

    Gu, Hong; Wu, Kaijie; Zheng, Shunan; Shi, Lin; Zhang, Min; Liu, Zhenghui; Liu, Xinke; Wang, Jianfeng; Zhou, Taofei; Xu, Ke

    2018-01-01

    We investigated the property of GaN crystals under a strong electric field. The Raman spectra of GaN were measured using an ultraviolet laser, and a remarkable redshift of the A 1(LO) mode was observed. The role of the surface depletion layer was discussed, and the interrelation between the electric field and phonons was revealed. First-principles calculations indicated that, in particular, the phonons that vibrate along the [0001] direction are strongly influenced by the electric field. This effect was confirmed by a surface photovoltage experiment. The results revealed the origin of the redshift and presented the phonon property of GaN under a strong electric field.

  17. Real time ellipsometry for monitoring plasma-assisted epitaxial growth of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Losurdo, Maria [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy)]. E-mail: maria.losurdo@ba.imip.cnr.it; Giangregorio, Maria M. [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Capezzuto, Pio [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Brown, April S. [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Kim, Tong-Ho [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Choi, Soojeong [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States)

    2006-10-31

    GaN is grown on Si-face 4H-SiC(0 0 0 1) substrates using remote plasma-assisted methods including metalorganic chemical vapour deposition (RP-MOCVD) and molecular beam epitaxy (MBE). Real time spectroscopic ellipsometry is used for monitoring all the steps of substrate pre-treatments and the heteroepitaxial growth of GaN on SiC. Our characterization emphasis is on understanding the nucleation mechanism and the GaN growth mode, which depend on the SiC surface preparation.

  18. Characterization of an Mg-implanted GaN p-i-n Diode

    Science.gov (United States)

    2016-03-31

    future power electronic devices. Keywords: GaN, p-i-n diode, ion implantation Introduction III-nitride materials have attracted a continuous interest...unintentionally doped GaN layer was grown by metal organic chemical vapor deposition (MOCVD) on a n+ Ga-face c-oriented GaN substrate. The as-grown MOCVD film...implantation to a concentration of 2x1019 cm-3 following a box profile to a depth of 500nm. A photoresist mask was used for the implantation, aligned to

  19. Linear Distributed GaN MMIC Power Amplifier with Improved Power-added Efficiency

    Science.gov (United States)

    2017-03-01

    MHz ‒ 8 GHz) GaN MMIC nonuniform distributed amplifier (NDPA) with built-in linearization and a gm3 cancellation method in class A and class C...linear power amplifier using GaN HEMT”, European Microwave Conference, p. 488, 2009 [8] G. A. Ellis, J. S. Moon, D . Wong, M. Micovic, A. Kurdoghlian...0.99 1 1.01 1.02 LT E Sp ec tr um ( d B m ) Frequency (GHz) Without linearization W/ linearization Linear GaN MMIC amplifier with gm3

  20. 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.

  1. Bulk GaN Schottky Diodes for Millimeter Wave Frequency Multipliers, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — Within the context of this project, White Light Power Inc. (WLPI) will demonstrate prototype vertical GaN Schottky diodes for high-power rectification at W-band. To...

  2. Time response of GaN Schottky detector for X-ray detection

    International Nuclear Information System (INIS)

    Fu Kai; Yu Guohao; Lu Min

    2010-01-01

    Time response of GaN Schottky detector with a large area to X-ray was studied. Using a Fe-doped GaN high resistive film to make the detector, the time response under different bias was tested. For the measured results, a theoretical model of time response of GaN Schottky detector to X-ray irradiation was proposed, and its internal mechanism was studied with a very good fitting results. It is found, due to the presence of high resistivity layer, the GaN Schottky detector can have a high signal to noise ratio of about 80 at reverse bias of 200 V, even in the possible effects of light quenching. (authors)

  3. Etching and ellipsometry studies on CL-VPE grown GaN epilayer

    Directory of Open Access Journals (Sweden)

    Puviarasu P.

    2017-02-01

    Full Text Available The surface morphological characteristics of wet chemical etched GaN layers grown at different temperatures on (0 0 0 1 sapphire substrates by Chloride-Vapor Phase Epitaxy (Cl-VPE have been studied using optical microscope. Significant surface morphology changes have been observed in correlation to the growth temperature and etching time. Also optical properties of the as grown and high-energy silicon (Si ion irradiated gallium nitride (GaN epilayers were studied using monochromatic ellipsometry. The effect of ion fluences on the refractive index of the GaN has been investigated and it has been found to decrease with an increase of ion fluence. This decrease is attributed to irradiation-induced defects and polycrystallization which plays an important role in determining the optical properties of silicon (Si ion irradiated GaN layers.

  4. Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

    International Nuclear Information System (INIS)

    Horibuchi, Kayo; Yamaguchi, Satoshi; Kimoto, Yasuji; Nishikawa, Koichi; Kachi, Tetsu

    2016-01-01

    GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer. (paper)

  5. FIR Detectors/Cameras Based on GaN and Si Field-Effect Devices Project

    Data.gov (United States)

    National Aeronautics and Space Administration — SETI proposes to develop GaN and Si based multicolor FIR/THz cameras with detector elements and readout, signal processing electronics integrated on a single chip....

  6. Bulk GaN Schottky Diodes for Millimeter Wave Frequency Multipliers, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Within the context of this project, White Light Power Inc. (WLPI) will demonstrate the feasibility of using vertical GaN Schottky diodes for high-power rectification...

  7. Ivestigation of an InGaN - GaN nanowire heterstructure

    Energy Technology Data Exchange (ETDEWEB)

    Limbach, Friederich; Gotschke, Tobias; Stoica, Toma; Calarco, Raffaella; Gruetzmacher, Detlev [Institute of Bio- and Nanosystems (IBN-1), Research Center Juelich GmbH, Juelich (Germany); JARA-Fundamentals of Future Information Technology, Juelich (Germany); Sutter, Eli; Ciston, Jim [Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY (United States); Cusco, Ramon; Artus, Luis [Institut Jaume Almera, Consell Superior d' Investigacions Cientifiques (CSIC), Barcelona, Catalonia (Spain); Kremling, Stefan; Hoefling, Sven; Worschech, Lukas [University Wurzburg, Wilhelm Conrad Rontgen Research Centre Complex Matter Systems, Wuerzburg (Germany)

    2011-07-01

    InGaN/GaN nanowire (NW) heterostructures grown by molecular beam epitaxy were studied in comparison to their GaN and InGaN counterparts. The InGaN/GaN heterostructure NWs are composed of a GaN NW, a thin InGaN shell, and a multi-faceted InGaN cap wrapping the top part of the GaN NW. Transmission electron microscopy images taken from different parts of a InGaN/GaN nanowire show a wurtzite structure of the GaN core and the epitaxial InGaN shell around it. Photoluminescence spectra of these heterostructure NW ensembles show an emission peak at 2.1 eV. However, {mu}-PL spectra measured on single nanowires reveal much sharper luminescence peaks. A Raman analysis reveals a variation of the In content between 20 % and 30 %, in agreement with PL and TEM investigations.

  8. Development of Epitaxial GaN Films for RF Communications, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — The primary objective of this SBIR is to develop epitaxial GaN films with threading dislocation density less than 10^6 cm^-2. We propose an innovative approach...

  9. Efficient light extraction from GaN LEDs using gold-coated ZnO nanoparticles

    KAUST Repository

    Alhadidi, A.

    2015-11-01

    We experimentally demonstrate the effect of depositing gold-coated ZnO nanoparticles on the surface of GaN multi-quantum well LED structures. We show that this method can significantly increase the amount of extracted light.

  10. Robust Visible and Infrared Light Emitting Devices Using Rare-Earth-Doped GaN

    National Research Council Canada - National Science Library

    Steckl, Andrew

    2006-01-01

    Rare earth (RE) dopants (such as Er, Eu, Tm) in the wide bandgap semiconductor (WBGS) GaN are investigated for the fabrication of robust visible and infrared light emitting devices at a variety of wavelengths...

  11. Nanoindentation characterization of GaN epilayers on A-plane sapphire substrates

    International Nuclear Information System (INIS)

    Lin, Meng-Hung; Wen, Hua-Chiang; Huang, Chih-Yung; Jeng, Yeau-Ren; Yau, Wei-Hung; Wu, Wen-Fa; Chou, Chang-Pin

    2010-01-01

    Gallium nitride (GaN) epilayers was deposited on a-axis sapphire substrate by means of metal-organic chemical vapor deposition (MOCVD) method. The GaN epilayers has been investigated in their repetition pressure-induced impairment events from nanoindentation technique and, the relative deformation effect was observed from atomic force microscopy (AFM). From the morphological studies, it is revealed that none of crack and particle was found even after the indentation beyond the critical depth on the residual indentation impression. The 'pop-in' event was explained by the interaction of the deformed region, produced by the indenter tip, with the inner threading dislocations in the GaN films. Pop-in events indicate the generation and motion of individual dislocation, which is measured under critical depth and, no residual deformation of the GaN films is observed.

  12. GaN nano-membrane for optoelectronic and electronic device applications

    KAUST Repository

    Ooi, Boon S.

    2014-01-01

    The ~25nm thick threading dislocation free GaN nanomembrane was prepared using ultraviolet electroless chemical etching method offering the possibility of flexible integration of (Al,In,Ga)N optoelectronic and electronic devices.

  13. Study on Quantum Efficiency Stability of Reflection-Mode GaN Negative Electronic Affinity Photocathode

    OpenAIRE

    Wei Liu; Jiangtao Fu; Guoqiang Zheng

    2014-01-01

    The aim of this study is to analyze the decaying and recovering mechanism of the quantum efficiency for reflection-mode GaN NEA photocathode. One kind of reflection-mode GaN NEA photocathode is designed and grown in the laboratory. The quantum efficiency curves are obtained immediately and six hours later after the sample is fully activated, the quantum efficiency data at different wavelengths are acquired according to the two different quantum efficiency curves, Through the analysis of exper...

  14. 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

  15. Evolution of deep centers in GaN grown by hydride vapor phaseepitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Z.-Q.; Look, D.C.; Jasinski, J.; Benamara, M.; Liliental-Weber, Z.; Molnar, R.J.

    2001-04-18

    Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

  16. Broadband 0.25-um Gallium Nitride (GaN) Power Amplifier Designs

    Science.gov (United States)

    2017-08-14

    ARL-TR-8091 ● AUG 2017 US Army Research Laboratory Broadband 0.25-µm Gallium Nitride (GaN) Power Amplifier Designs by John E...return it to the originator. ARL-TR-8091 ● AUG 2017 US Army Research Laboratory Broadband 0.25-µm Gallium Nitride (GaN) Power ...notwithstanding any other provision of law , no person shall be subject to any penalty for failing to comply with a collection of information if it does not display

  17. GaN quantum dots: from basic understanding to unique applications

    International Nuclear Information System (INIS)

    Pelekanos, N T; Dialynas, G E; Simon, J; Mariette, H; Daudin, B

    2005-01-01

    The GaN self-assembled quantum dots constitute a very special and intriguing type of semiconductor nanostructure, mainly because they carry in their structure a giant internal electric field that can reach a value up to 7 MV/cm. In this report, we review the most important structural and optical properties of GaN quantum dots, and we discuss their advantages and limitations for blue-UV optoelectronic applications. (invited paper)

  18. GaN quantum dot polarity determination by X-ray photoelectron diffraction

    Czech Academy of Sciences Publication Activity Database

    Romanyuk, Olexandr; Bartoš, Igor; Brault, J.; De Mierry, P.; Paskova, T.; Jiříček, Petr

    2016-01-01

    Roč. 389, Dec (2016), s. 1156-1160 ISSN 0169-4332 R&D Projects: GA ČR GA15-01687S; GA MŠk LM2015088 Institutional support: RVO:68378271 Keywords : GaN * semipolar GaN * quantum dots * X-ray photoelectron diffraction * surface polarity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.387, year: 2016

  19. Scanning capacitance microscopy studies of GaN grown by epitaxial layer overgrowth

    International Nuclear Information System (INIS)

    Oliver, R A; Bennett, S E; Sumner, J; Kappers, M J; Humphreys, C J

    2010-01-01

    Epitaxial layer overgrowth (ELOG) is a common technique for dislocation density reduction in GaN heteroepitaxy. Here, scanning capacitance microscopy is used to study the variations in unintentional doping arising from the ELOG process and reveals facet-dependent incorporation of n-type dopants during the initial regrowth of GaN, and then p-type doping arising from the use of bis(cyclopentadienyl)magnesium to enhance lateral growth during the coalescence stage.

  20. Microstructure of laterally overgrown GaN layers

    Energy Technology Data Exchange (ETDEWEB)

    Liliental-Weber, Zuzanna; Cherns, David

    2001-04-03

    Transmission electron microscopy study of plan-view and cross-section samples of epitaxial laterally overgrown (ELOG) GaN samples is described. Two types of dislocation with the same type of Burgers vector but different line direction have been observed. It is shown that threading edge dislocations bend to form dislocation segments in the c-plane as a result of shear stresses developed in the wing material along the stripe direction. It is shown that migration of these dislocations involves both glide and climb. Propagation of threading parts over the wing area is an indication of high density of point defects present in the wing areas on the ELOG samples. This finding might shed new light on the optical properties of such samples.

  1. Potential for normally-off operation from GaN metal oxide semiconductor devices based upon semi-insulating GaN

    Directory of Open Access Journals (Sweden)

    Yusuke Sakai

    2013-08-01

    Full Text Available The conditions for preparing normally-off GaN devices incorporating semi-insulating (SI GaN materials are explored. The properties of SI GaN where carbon behaves as a deep level acceptor are predicted using a Shockley diagram. Metal-oxide-semiconductor (MOS structures based upon these on SI-GaN layers are designed. The bandgap alignment of these structures is analyzed using Poisson equations. Normally-off operation is shown to be possible in devices featuring a thin n-GaN layer and SI-GaN layer, because of a higher conduction band energy. It is also shown that higher threshold voltage can be achieved by reducing the carrier concentration of the n-GaN channel layer.

  2. Real time spectroscopic ellipsometry investigation of homoepitaxial GaN grown by plasma assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Tong-Ho; Choi, Soojeong; Wu, Pae; Brown, April [Department of Electrical and Computer Engineering, Duke University, 128 Hudson Hall, Durham, NC (United States); Losurdo, Maria; Giangregorio, Maria M.; Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM UdR Bari, via Orabona, 4, 70126 Bari (Italy); Moto, Akihiro [Innovation Core SEI, Inc., 3235 Kifer Road, Santa Clara, CA 95051 (United States)

    2006-06-15

    The growth of GaN by plasma assisted molecular beam epitaxy on GaN template substrates (GaN on sapphire) is investigated with in-situ multi-channel spectroscopic ellipsometry. Growth is performed under various Ga/N flux ratios at growth temperatures in the range 710-780 C. The thermal roughening of the GaN template caused by decomposition of the surface is investigated through the temporal variation of the GaN pseudodielectric function over the temperature range of 650 C to 850 C. The structural, morphological, and optical properties are also discussed. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

    Science.gov (United States)

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

    2017-12-01

    We report a systematic investigation of the transport properties of highly degenerate electrons in Ge-doped and Si-doped GaN epilayers prepared using the pulsed sputtering deposition (PSD) technique. Secondary-ion mass spectrometry and Hall-effect measurements revealed that the doping efficiency of PSD n-type GaN is close to unity at electron concentrations as high as 5.1 × 1020 cm-3. A record low resistivity for n-type GaN of 0.16 mΩ cm was achieved with an electron mobility of 100 cm2 V-1 s-1 at a carrier concentration of 3.9 × 1020 cm-3. We explain this unusually high electron mobility of PSD n-type GaN within the framework of conventional scattering theory by modifying a parameter related to nonparabolicity of the conduction band. The Ge-doped GaN films show a slightly lower electron mobility compared with Si-doped films with the same carrier concentrations, which is likely a consequence of the formation of a small number of compensation centers. The excellent electrical properties presented in this letter clearly demonstrate the striking advantages of the low-temperature PSD technique for growing high-quality and highly conductive n-type GaN.

  4. 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

  5. From Stable ZnO and GaN Clusters to Novel Double Bubbles and Frameworks

    Directory of Open Access Journals (Sweden)

    Matthew R. Farrow

    2014-05-01

    Full Text Available A bottom up approach is employed in the design of novel materials: first, gas-phase “double bubble” clusters are constructed from high symmetry, Th, 24 and 96 atom, single bubbles of ZnO and GaN. These are used to construct bulk frameworks. Upon geometry optimization—minimisation of energies and forces computed using density functional theory—the symmetry of the double bubble clusters is reduced to either C1 or C2, and the average bond lengths for the outer bubbles are 1.9 Å, whereas the average bonds for the inner bubble are larger for ZnO than for GaN; 2.0 Å and 1.9 Å, respectively. A careful analysis of the bond distributions reveals that the inter-bubble bonds are bi-modal, and that there is a greater distortion for ZnO. Similar bond distributions are found for the corresponding frameworks. The distortion of the ZnO double bubble is found to be related to the increased flexibility of the outer bubble when composed of ZnO rather than GaN, which is reflected in their bulk moduli. The energetics suggest that (ZnO12@(GaN48 is more stable both in gas phase and bulk frameworks than (ZnO12@(ZnO48 and (GaN12@(GaN48. Formation enthalpies are similar to those found for carbon fullerenes.

  6. Control of dislocation morphology and lattice distortion in Na-flux GaN crystals

    Science.gov (United States)

    Takeuchi, S.; Mizuta, Y.; Imanishi, M.; Imade, M.; Mori, Y.; Sumitani, K.; Imai, Y.; Kimura, S.; Sakai, A.

    2017-09-01

    The dislocation morphology and lattice distortion, including the tilting and twisting of lattice planes, at the Na-flux GaN/seed-GaN interface were investigated using transmission electron microscopy (TEM) and position-dependent nanobeam X-ray diffraction (nanoXRD). The results revealed that the dislocation morphology and lattice distortion in Na-flux GaN at the initial growth stage are strongly influenced by the seed-GaN surface morphology and the growth mode of Na-flux GaN. From the TEM results, one can observe that the formation of dislocation-related etch pits (DREPs) on the seed-GaN surface and the three-dimensional (3D) growth mode for Na-flux GaN give rise to the bending and lateral propagation of dislocations penetrating from the seed-GaN to the Na-flux GaN. This simultaneously results in homogenization of the GaN crystal domain structure as confirmed by nanoXRD. The mechanism responsible for the bending and lateral propagation of dislocations by the formation of DREPs and the 3D growth mode for the Na-flux GaN and the correlation between the dislocation morphology and the lattice distortion are discussed on the basis of TEM and nanoXRD results.

  7. Impact of gallium supersaturation on the growth of N-polar GaN

    Energy Technology Data Exchange (ETDEWEB)

    Mita, Seiji; Xie, Jinqiao; Dalmau, Rafael [HexaTech, Inc., Morrisville, NC (United States); Collazo, Ramon; Rice, Anthony; Tweedie, James; Sitar, Zlatko [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC (United States)

    2011-07-15

    Experimental results on growth morphology in N-polar GaN grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) were analyzed using a thermodynamic supersaturation model for gallium. Smooth N-polar GaN films with 1 nm RMS roughness were always obtained under extremely low Ga supersaturation in the vapor, although the growth conditions were seemingly different. It was found that increasing H{sub 2} partial pressure during the GaN growth played a role in significantly lowering the Ga supersaturation, since H{sub 2} is a product in the formation of GaN. The degree of Ga supersaturation was also controlled by adjusting the partial pressure of Ga species in the vapor. The surface-diffusion theory dealing with step dynamics described by Burton, Cabrera, and Frank (BCF) was also used to relate Ga supersaturation to the observed smooth N-polar GaN growth. These findings showed that a supersaturation model encompassing all major MOCVD growth parameters can be used to predict the smooth N-polar GaN growth conditions. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Synthesis of GaN Nanorods by a Solid-State Reaction

    Directory of Open Access Journals (Sweden)

    Keyan Bao

    2010-01-01

    Full Text Available An atom-economical and eco-friendly chemical synthetic route was developed to synthesize wurtzite GaN nanorods by the reaction of NaNH2 and the as-synthesized orthorhombic GaOOH nanorods in a stainless steel autoclave at 600∘C. The lengths of the GaN nanorods are in the range of 400–600 nm and the diameters are about 80–150 nm. The process of orthorhombic GaOOH nanorods transformation into wurtzite GaN nanorods was investigated by powder X-ray diffraction (XRD and field emission scanning electron microscope (FESEM, indicating that the GaN product retained essentially the same basic topological morphology in contrast to that of the GaOOH precursor. It was found that rhombohedral Ga2O3 was the intermediate between the starting orthorhombic GaOOH precursor and the final wurtzite GaN product. The photoluminescence measurements reveal that the as-prepared wurtzite GaN nanorods showed strong blue emission.

  9. Characterization of plasma etching damage on p-type GaN using Schottky diodes

    International Nuclear Information System (INIS)

    Kato, M.; Mikamo, K.; Ichimura, M.; Kanechika, M.; Ishiguro, O.; Kachi, T.

    2008-01-01

    The plasma etching damage in p-type GaN has been characterized. From current-voltage and capacitance-voltage characteristics of Schottky diodes, it was revealed that inductively coupled plasma (ICP) etching causes an increase in series resistance of the Schottky diodes and compensation of acceptors in p-type GaN. We investigated deep levels near the valence band of p-type GaN using current deep level transient spectroscopy (DLTS), and no deep level originating from the ICP etching damage was observed. On the other hand, by capacitance DLTS measurements for n-type GaN, we observed an increase in concentration of a donor-type defect with an activation energy of 0.25 eV after the ICP etching. The origin of this defect would be due to nitrogen vacancies. We also observed this defect by photocapacitance measurements for ICP-etched p-type GaN. For both n- and p-type GaN, we found that the low bias power ICP etching is effective to reduce the concentration of this defect introduced by the high bias power ICP etching

  10. Light Modulation and Water Splitting Enhancement Using a Composite Porous GaN Structure.

    Science.gov (United States)

    Yang, Chao; Xi, Xin; Yu, Zhiguo; Cao, Haicheng; Li, Jing; Lin, Shan; Ma, Zhanhong; Zhao, Lixia

    2018-02-14

    On the basis of the laterally porous GaN, we designed and fabricated a composite porous GaN structure with both well-ordered lateral and vertical holes. Compared to the plane GaN, the composite porous GaN structure with the combination of the vertical holes can help to reduce UV reflectance and increase the saturation photocurrent during water splitting by a factor of ∼4.5. Furthermore, we investigated the underlying mechanism for the enhancement of the water splitting performance using a finite-difference time-domain method. The results show that the well-ordered vertical holes can not only help to open the embedded pore channels to the electrolyte at both sides and reduce the migration distance of the gas bubbles during the water splitting reactions but also help to modulate the light field. Using this composite porous GaN structure, most of the incident light can be modulated and trapped into the nanoholes, and thus the electric fields localized in the lateral pores can increase dramatically as a result of the strong optical coupling. Our findings pave a new way to develop GaN photoelectrodes for highly efficient solar water splitting.

  11. Progress in the fabrication of GaN photocathodes

    Science.gov (United States)

    Ulmer, Melville P.; Wessels, Bruce W.; Shahedipour, Fatemeh; Korotokov, Roman Y.; Joseph, Charles L.; Nihashi, Tokuaki

    2001-06-01

    Currently, photo-cathodes hold the highest promise in the near term (next few years) of being able to detect low light level UV signals at high QE while being nearly blind to visible wavelengths. We briefly discuss the requirements for UV detection for astronomical applications, and then we describe our work on producing GaN based photo-cathodes. The p-type GaN films were grown on sapphire at Northwestern University. The films were then converted into opaque photo-cathodes inside photo-tubes at Hamamatsu. Hamamatsu tested detective quantum efficiencies (DQE) of these detectors to be as high as 30% at 200 nm. The ratio of peak DQE at 200 nm to the minimum DQE at 500 nm was measured to be about 6 X 103. We found a dramatic increase in the DQE at 200 nm versus the conductivity, with the break point being near 0.13 1/(Ohm-cm). Based on this dramatic increase, we believe that further improvement in photo-cathode quantum efficiencies can be achieved by increasing the conductivity. We have recently achieved more than an order of magnitude increase in conductivity by co-doping techniques. Improvements in the solar blindness of the devices depend both on characteristics of the film and its surface properties. A detailed discussion of decreasing the visible response and producing a sharper wave-length cutoff is beyond the scope of this work, but we briefly discuss the attributes that most likely affect the wavelength dependence of the photo-cathode response.

  12. 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...

  13. High-Speed Gate Driver Using GaN HEMTs for 20-MHz Hard Switching of SiC MOSFETs

    OpenAIRE

    Okuda, Takafumi; Hikihara, Takashi

    2017-01-01

    In this paper, we investigated a gate driver using a GaN HEMT push-pull configuration for the high-frequency hard switching of a SiC power MOSFET. Low on-resistance and low input capacitance of GaN HEMTs are suitable for a high-frequency gate driver from the logic level, and robustness of SiC MOSFET with high avalanche capability is suitable for a valve transistor in power converters. Our proposed gate driver consists of digital isolators, complementary Si MOSFETs, and GaN HEMTs. The GaN HEMT...

  14. Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

    International Nuclear Information System (INIS)

    Chen, Jr-Tai; Hsu, Chih-Wei; Forsberg, Urban; Janzén, Erik

    2015-01-01

    Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H 2 atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm 2 /V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 10 20  cm −3 at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm 2 SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer

  15. RETRACTED: High quality N-polar GaN two-dimensional growth on c-plane sapphire by metalorganic vapor phase epitaxy

    Science.gov (United States)

    Zhang, Yuantao; Dong, Xin; Li, Guoxing; Li, Wancheng; Zhang, Baolin; Du, Guotong

    2013-03-01

    We report the growth of atomically smooth N-polar GaN on c-plane sapphire by metalorganic vapor phase epitaxy. A two-step growth technique was adopted; low-temperature growth of GaN buffer before high-temperature GaN growth. The complete two-dimensional N-polar GaN growth process was recorded by in situ reflectance. The phase composition of the low-temperature GaN was examined by X-ray diffraction pole figure measurements. The thickness of the low-temperature GaN buffer dramatically affected the crystalline and electronic properties of the N-polar GaN. A very small full width at half maximum for the (0 0 0 2) X-ray rocking curve, 51 arcs, was obtained for 700-nm-thick N-polarity GaN by optimizing the buffer thickness.

  16. Rare earths in GaN and ZnO studied with the PAC method

    International Nuclear Information System (INIS)

    Nedelec, R.

    2007-01-01

    The present thesis deals with the implantation and annealing behaviour of two examples of large-band-gap semiconductors GaN and ZnO. The studies begin with the annealing behaviour of GaN after the implantation of 172 Lu. For GaN the annealing process begins at low temperatures with the decreasing of the damping of the lattice frequency. At essentially higher temperatures finally the substitunial contribution increases. This behaviour is also observed for other probe nuclei in GaN. For ZnO the behaviour at low temperature is different. Both for 172 Lu and for 181 Hf the damping is already after the implantation very low. The increasement of the substitutional contribution occurs like in GaN at higher temperatures. Thereafter for GaN and ZnO PAC spectra were token up at different measurement temperatures between 25 and 873 K. For 172 Lu in GaN and in ZnO a strong temperature dependence of the lattice field gradient was observed. Also for 181 Hf in ZnO a strong temperature dependence is observed. For 172 Lu by means of a model for the interaction of quadrupole moments of electronic shells with the nucleus a lattice field gradient of ±5.9.10 15 Vcm -2 could be determined. For 172 Lu in ZnO the model yields at 293 K a lattice field gradient of +14.10 15 Vcm -2 respectively -13.10 15 Vcm -2 . The corrsponding measurement with 181 Hf yields a lattice field gradient of ±5.7.10 15 Vcm -2

  17. GaN thin film deposition on glass and PET substrates by thermionic vacuum arc (TVA)

    Energy Technology Data Exchange (ETDEWEB)

    Pat, Suat, E-mail: suatpat@ogu.edu.tr [Eskisehir Osmangazi University, Physics Department, 26480 (Turkey); Korkmaz, Şadan; Özen, Soner [Eskisehir Osmangazi University, Physics Department, 26480 (Turkey); Şenay, Volkan [Bayburt University, Primary Science Education Department, 69000 (Turkey)

    2015-06-01

    In this paper, GaN thin film production was realized by thermionic vacuum arc (TVA), a plasma deposition technique, for the first time. We present a new deposition mechanism for GaN thin films with a very short production time. Microstructure properties of samples were analyzed by X-ray diffractometry. The peak at 2θ = 72.88° corresponding to GaN (0004) was detected in XRD spectra. The surface morphology of the deposited GaN films was analyzed using field emission scanning electron microscopy and atomic force microscopy. The surface properties of the produced samples are quite different. The average roughness values were determined to be 0.48 nm for GaN/PET and 1.17 nm for GaN/glass. The optical properties (i.e., refractive index and reflection) were determined using an interferometer. Moreover, the obtained optical data were compared with bulk GaN materials. The refractive indexes were measured as 2.2, 3,0 and 2,5 for the GaN/glass, GaN/PET and bulk GaN, respectively. The transparencies of the different GaN-coated substrates are nearly the same. The obtained band gap values were measured in the energy range of 3.3–3.5 eV. TVA is a novel non-reactive plasma technique for the generation of metal organic thin films. The main advantage of this method is its fast deposition rate without any loss in the quality of the films. - Highlights: • A new GaN thin film growth method is introduced. • Microstructure, surface and optical properties were characterized. • GaN/glass and GaN/PET were produced by a different plasma deposition method.

  18. GaN thin film deposition on glass and PET substrates by thermionic vacuum arc (TVA)

    International Nuclear Information System (INIS)

    Pat, Suat; Korkmaz, Şadan; Özen, Soner; Şenay, Volkan

    2015-01-01

    In this paper, GaN thin film production was realized by thermionic vacuum arc (TVA), a plasma deposition technique, for the first time. We present a new deposition mechanism for GaN thin films with a very short production time. Microstructure properties of samples were analyzed by X-ray diffractometry. The peak at 2θ = 72.88° corresponding to GaN (0004) was detected in XRD spectra. The surface morphology of the deposited GaN films was analyzed using field emission scanning electron microscopy and atomic force microscopy. The surface properties of the produced samples are quite different. The average roughness values were determined to be 0.48 nm for GaN/PET and 1.17 nm for GaN/glass. The optical properties (i.e., refractive index and reflection) were determined using an interferometer. Moreover, the obtained optical data were compared with bulk GaN materials. The refractive indexes were measured as 2.2, 3,0 and 2,5 for the GaN/glass, GaN/PET and bulk GaN, respectively. The transparencies of the different GaN-coated substrates are nearly the same. The obtained band gap values were measured in the energy range of 3.3–3.5 eV. TVA is a novel non-reactive plasma technique for the generation of metal organic thin films. The main advantage of this method is its fast deposition rate without any loss in the quality of the films. - Highlights: • A new GaN thin film growth method is introduced. • Microstructure, surface and optical properties were characterized. • GaN/glass and GaN/PET were produced by a different plasma deposition method

  19. 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.

    2016-08-01

    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.

  20. Crystallographically tilted and partially strain relaxed GaN grown on inclined (111) facets etched on Si(100) substrate

    International Nuclear Information System (INIS)

    Ansah Antwi, K. K.; Soh, C. B.; Wee, Q.; Tan, Rayson J. N.; Tan, H. R.; Yang, P.; Sun, L. F.; Shen, Z. X.; Chua, S. J.

    2013-01-01

    High resolution X-ray diffractometry (HR-XRD), Photoluminescence, Raman spectroscopy, and Transmission electron microscope measurements are reported for GaN deposited on a conventional Si(111) substrate and on the (111) facets etched on a Si(100) substrate. HR-XRD reciprocal space mappings showed that the GaN(0002) plane is tilted by about 0.63° ± 0.02° away from the exposed Si(111) growth surface for GaN deposited on the patterned Si(100) substrate, while no observable tilt existed between the GaN(0002) and Si(111) planes for GaN deposited on the conventional Si(111) substrate. The ratio of integrated intensities of the yellow to near band edge (NBE) luminescence (I YL /I NBE ) was determined to be about one order of magnitude lower in the case of GaN deposited on the patterned Si(100) substrate compared with GaN deposited on the conventional Si(111) substrate. The Raman E 2 (high) optical phonon mode at 565.224 ± 0.001 cm −1 with a narrow full width at half maximum of 1.526 ± 0.002 cm −1 was measured, for GaN deposited on the patterned Si(100) indicating high material quality. GaN deposition within the trench etched on the Si(100) substrate occurred via diffusion and mass-transport limited mechanism. This resulted in a differential GaN layer thickness from the top (i.e., 1.8 μm) of the trench to the bottom (i.e., 0.3 μm) of the trench. Mixed-type dislocation constituted about 80% of the total dislocations in the GaN grown on the inclined Si(111) surface etched on Si(100)

  1. 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

  2. The optimal thickness of a transmission-mode GaN photocathode

    International Nuclear Information System (INIS)

    Wang Xiao-Hui; Shi Feng; Guo Hui; Hu Cang-Lu; Cheng Hong-Chang; Chang Ben-Kang; Ren Ling; Du Yu-Jie; Zhang Jun-Ju

    2012-01-01

    A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6 × 10 17 cm −3 is activated by Cs/O in an ultrahigh vacuum chamber, and a quantum efficiency (QE) curve of the negative electron affinity transmission-mode (t-mode) of the GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5 × 10 4 cm·s −1 , and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  3. Growth of GaN on ZnO for solid state lighting applications

    Science.gov (United States)

    Li, Nola; Park, Eun-Hyun; Huang, Yong; Wang, Shenjie; Valencia, Adriana; Nemeth, Bill; Nause, Jeff; Ferguson, Ian

    2006-08-01

    In this work, ZnO has been investigated as a substrate technology for GaN-based devices due to its close lattice match, stacking order match, and similar thermal expansion coefficient. Since MOCVD is the dominant growth technology for GaN-based materials and devices, there is a need to more fully explore this technique for ZnO substrates. Our aim is to grow low defect density GaN for efficient phosphor free white emitters. However, there are a number of issues that need to be addressed for the MOCVD growth of GaN on ZnO. The thermal stability of the ZnO substrate, out-diffusion of Zn from the ZnO into the GaN, and H II back etching into the substrate can cause growth of poor quality GaN. Cracks and pinholes were seen in the epilayers, leading to the epi-layer peeling off in some instances. These issues were addressed by the use of H II free growth and multiple buffer layers to remove the cracking and reduce the pinholes allowing for a high quality GaN growth on ZnO substrate.

  4. 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.

  5. High-quality GaN nanowires grown on Si and porous silicon by thermal evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Shekari, L., E-mail: lsg09_phy089@student.usm.my [Nano-Optoelectronics Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Ramizy, A.; Omar, K.; Hassan, H. Abu; Hassan, Z. [Nano-Optoelectronics Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer A new kind of substrate (porous silicon) was used. Black-Right-Pointing-Pointer Also this research introduces an easy and safe method to grow high quality GaN NWs. Black-Right-Pointing-Pointer This is a new growth process to decrease the cost, complexity of growth of GaN NWs. Black-Right-Pointing-Pointer It is a controllable method to synthesize GaN NWs by thermal evaporation. - Abstract: Nanowires (NWs) of GaN thin films were prepared on as-grown Si (1 1 1) and porous silicon (PS) substrates using thermal evaporation method. The film growth produced high-quality wurtzite GaN NWs. The size, morphology, and nanostructures of the crystals were investigated through scanning electron microscopy, high-resolution X-ray diffraction and photoluminescence spectroscopy. The NWs grown on porous silicon were thinner, longer and denser compared with those on as-grown Si. The energy band gap of the NWs grown on PS was larger than that of NWs on as-grown Si. This is due to the greater quantum confinement effects of the crystalline structure of the NWs grown on PS.

  6. Amphoteric Behavior of Impurities in GaN Film Grown on Si Substrate

    Science.gov (United States)

    Cho, Hyun-Ick; Lee, Dong-Sik; Lee, Heon-Bok; Hahm, Sung-Ho; Lee, Jung-Hee

    2007-05-01

    Hall measurement presented that an unintentionally doped uniform and crack-free GaN film grown on n-type (111)-oriented Si substrate with high temperature-grown relatively thin AlN single and multiple buffer layer shows p-type conductivity. The position of valence band maximum at the surface of the film measured by the synchrotron radiation photoemission spectroscopy is below Fermi level at 1.09 eV due to band bending at the surface, which is indicative for the p-type nature of the grown film. The n-channel metal-oxide-semiconductor field effect transistor (MOSFET) fabricated on the GaN layer exhibited normally-off mode operation. This cannot be achieved if the GaN layer is not p-type. It is believed that the spatial coordination of auto-doped Si atoms, out-diffused from the substrate, or carbon complexes from metal-organic (MO) precursor favorably occupy the substitutional nitrogen site of the GaN film when the film is under tensile strain during the growth, which clearly explains that the p-type conduction is originated from the stress dependent amphoteric nature of Si atom and/or carbon complex in GaN.

  7. Effect of growth temperature on polytype transition of GaN from zincblende to wurtzite

    Energy Technology Data Exchange (ETDEWEB)

    Suandon, Siripen [Department of Physics, Faculty of Science, Chulalongkorn University, Phayathai Rd., Pathumwan, Bangkok 10330 (Thailand); Sanorpim, Sakuntam [Department of Physics, Faculty of Science, Chulalongkorn University, Phayathai Rd., Pathumwan, Bangkok 10330 (Thailand)]. E-mail: Sakuntam.S@chula.ac.th; Yoodee, Kajornyod [Department of Physics, Faculty of Science, Chulalongkorn University, Phayathai Rd., Pathumwan, Bangkok 10330 (Thailand); Onabe, Kentaro [Department of Advanced Materials Science, Graduate Schools of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8561 (Japan)

    2007-03-26

    We have investigated effect of growth temperature on the polytype conversion of cubic GaN (c-GaN) grown on GaAs (001) substrates by MOVPE. It was found that the polytype transition of GaN from zincblende (cubic) to wurtzite (hexagonal) structures is much dependent on the growth temperature. Transmission electron microscopy (TEM) observations demonstrate that the GaN grown layers have the cubic structure (c-GaN) and contain bands of stacking faults (SFs) parallels to {l_brace}111{r_brace} planes. For low growth temperatures ({approx} 900 deg. C), XRD results demonstrate that the GaN grown layers with the cubic phase purity higher than 85% were obtained. No different types of single diffraction spots, indicating the incorporation of single-crystal h-GaN, on the selected area diffraction (SAD) pattern was observed. It is also found that a density of SFs decreases with the distance from the interface of c-GaN/GaAs. On the other hand, GaN layers exhibited a transition from cubic to mixed cubic/hexagonal phase under conditions of increasing growth temperature ({approx} 960 deg. C) as determined using TEM-SAD technique with complementary XRD and PL observations. In addition, the optical characteristics of c-GaN layers are shown to be very sensitive to the presence of the single-crystal h-GaN.

  8. 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

  9. Ultrafast Hot Carrier Dynamics in GaN and Its Impact on the Efficiency Droop.

    Science.gov (United States)

    Jhalani, Vatsal A; Zhou, Jin-Jian; Bernardi, Marco

    2017-08-09

    GaN is a key material for lighting technology. Yet, the carrier transport and ultrafast dynamics that are central in GaN light-emitting devices are not completely understood. We present first-principles calculations of carrier dynamics in GaN, focusing on electron-phonon (e-ph) scattering and the cooling and nanoscale dynamics of hot carriers. We find that e-ph scattering is significantly faster for holes compared to electrons and that for hot carriers with an initial 0.5-1 eV excess energy, holes take a significantly shorter time (∼0.1 ps) to relax to the band edge compared to electrons, which take ∼1 ps. The asymmetry in the hot carrier dynamics is shown to originate from the valence band degeneracy, the heavier effective mass of holes compared to electrons, and the details of the coupling to different phonon modes in the valence and conduction bands. We show that the slow cooling of hot electrons and their long ballistic mean free paths (over 3 nm at room temperature) are a possible cause of efficiency droop in GaN light-emitting diodes. Taken together, our work sheds light on the ultrafast dynamics of hot carriers in GaN and the nanoscale origin of efficiency droop.

  10. Development of a high-sensitivity UV photocathode using GaN film that works in transmission mode

    Science.gov (United States)

    Ishigami, Yoshihiro; Akiyama, Keisuke; Nagata, Takaaki; Kato, Kazumasa; Ihara, Tsuneo; Nakamura, Kimitsugu; Mizuno, Itaru; Matsuo, Tetsuji; Chino, Emiko; Kyushima, Hiroyuki

    2012-06-01

    We developed a high-sensitivity GaN photocathode that works in transmission mode. It has 40.9 % quantum efficiency at 310 nm wavelength. Conventional GaN photocathodes, both transmission mode and reflection mode, are made on a sapphire substrate using metal-organic vapor phase epitaxy (MOVPE). In reflection mode, a GaN photocathode has very high quantum efficiency (QE) of over 50 %. However, in transmission mode, the quantum efficiency of a GaN photocathode was about 25 % at 240 nm with this technique. Therefore, we developed a new GaN photocathode using a glass-bonding technique, where a GaN thin film was bonded to a glass face plate. We found out that constituting an Al- GaN layer on the light incidence side of the photocathode surface provided higher QE than a sole GaN layer type for transmission mode. We focused on the band bending of the photocathode, and analyzed QE for both transmission mode and reflection mode. We then verified the effectiveness of the AlGaN layer using the results from the analysis. The high-sensitivity UV photocathode will be used for flame detection, corona discharge observation, and other UV imaging.

  11. Effect of H, O intentionally doping on photoelectric properties in MOVPE-growth GaN layers

    KAUST Repository

    Ohkawa, Kazuhiro

    2017-10-24

    GaN crystal growth requires higher purity of materials. Some contaminants in NH3 gas could be the causal factor of defects in GaN crystals. These atoms act as donor or acceptor. In order to clearly demonstrate the effect of gaseous impurities such as H2O on the properties of undoped-GaN layer, high purity NH3 (N70) was used as NH3 source. The concentration of H2O in NH3 was varied at 32, 49, 75, 142, 266, 489, and 899 ppb, respectively. Under the same recipe, we deposited undoped-GaN epitaxial layer with purifier, and H2O-doped GaN series layers. As similar to the results of CO and CO2-doped GaN series, the increase tendency of carrier density changing with increasing H2O concentration. The FWHMs of XRC around (0002) remain stable, witnessing that the crystal quality of GaN layer remain good. LT (15K) PL of undoped-GaN and H2O-doped GaN were measured, the D0X emission peak intensity of all H2O-doped GaN are decreased drastically compared with undoped-GaN. H2O impurity was doped into GaN layer, which not only effects electrical properties and but also effects the radiative emission and furthermore effects PL intensity, its mechanism is discussed.

  12. Effect of H2O intentionally doping on photoelectric properties in MOVPE-growth GaN layers

    Science.gov (United States)

    Wang, Yaxin; Ohkawa, Kazuhiro

    2017-10-01

    GaN crystal growth requires higher purity of materials. Some contaminants in NH3 gas could be the causal factor of defects in GaN crystals. These atoms act as donor or acceptor. In order to clearly demonstrate the effect of gaseous impurities such as H2O on the properties of undoped-GaN layer, high purity NH3 (N70) was used as NH3 source. The concentration of H2O in NH3 was varied at 32, 49, 75, 142, 266, 489, and 899 ppb, respectively. Under the same recipe, we deposited undoped-GaN epitaxial layer with purifier, and H2O-doped GaN series layers. As similar to the results of CO and CO2-doped GaN series, the increase tendency of carrier density changing with increasing H2O concentration. The FWHMs of XRC around (0002) remain stable, witnessing that the crystal quality of GaN layer remain good. LT (15K) PL of undoped-GaN and H2O-doped GaN were measured, the D0X emission peak intensity of all H2O-doped GaN are decreased drastically compared with undoped-GaN. H2O impurity was doped into GaN layer, which not only effects electrical properties and but also effects the radiative emission and furthermore effects PL intensity, its mechanism is discussed.

  13. Reliability-Driven Assessment of GaN HEMTs and Si IGBTs in 3L-ANPC PV Inverters

    DEFF Research Database (Denmark)

    Gurpinar, Emre; Yang, Yongheng; Iannuzzo, Francesco

    2016-01-01

    In this paper, thermal loading of the state-of-the-art GaN HEMTs and traditional Si IGBTs in 3L-ANPC PV inverters is presented considering real-field long-term mission profiles (i.e., ambient temperature and solar irradiance). A comparison of Si IGBT against GaN HEMT with three different possibil...

  14. 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.

  15. Interface dipole and band bending in the hybrid p -n heterojunction Mo S2/GaN (0001 )

    Science.gov (United States)

    Henck, Hugo; Ben Aziza, Zeineb; Zill, Olivia; Pierucci, Debora; Naylor, Carl H.; Silly, Mathieu G.; Gogneau, Noelle; Oehler, Fabrice; Collin, Stephane; Brault, Julien; Sirotti, Fausto; Bertran, François; Le Fèvre, Patrick; Berciaud, Stéphane; Johnson, A. T. Charlie; Lhuillier, Emmanuel; Rault, Julien E.; Ouerghi, Abdelkarim

    2017-09-01

    Hybrid heterostructures based on bulk GaN and two-dimensional (2D) materials offer novel paths toward nanoelectronic devices with engineered features. Here, we study the electronic properties of a mixed-dimensional heterostructure composed of intrinsic n -doped Mo S2 flakes transferred on p -doped GaN(0001) layers. Based on angle-resolved photoemission spectroscopy (ARPES) and high resolution x-ray photoemission spectroscopy (HR-XPS), we investigate the electronic structure modification induced by the interlayer interactions in Mo S2/GaN heterostructure. In particular, a shift of the valence band with respect to the Fermi level for Mo S2/GaN heterostructure is observed, which is the signature of a charge transfer from the 2D monolayer Mo S2 to GaN. The ARPES and HR-XPS revealed an interface dipole associated with local charge transfer from the GaN layer to the Mo S2 monolayer. Valence and conduction band offsets between Mo S2 and GaN are determined to be 0.77 and -0.51 eV , respectively. Based on the measured work functions and band bendings, we establish the formation of an interface dipole between GaN and Mo S2 of 0.2 eV.

  16. High pressure annealing of Europium implanted GaN

    KAUST Repository

    Lorenz, K.

    2012-02-09

    GaN epilayers were implanted with Eu to fluences of 1×10^13 Eu/cm2 and 1×10^15 Eu/cm2. Post-implant thermal annealing was performed in ultra-high nitrogen pressures at temperatures up to 1450 ºC. For the lower fluence effective structural recovery of the crystal was observed for annealing at 1000 ºC while optical activation could be further improved at higher annealing temperatures. The higher fluence samples also reveal good optical activation; however, some residual implantation damage remains even for annealing at 1450 ºC which leads to a reduced incorporation of Eu on substitutional sites, a broadening of the Eu luminescence lines and to a strongly reduced fraction of optically active Eu ions. Possibilities for further optimization of implantation and annealing conditions are discussed.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  17. Algan/Gan Hemt By Magnetron Sputtering System

    Science.gov (United States)

    Garcia Perez, Roman

    In this thesis, the growth of the semiconductor materials AlGaN and GaN is achieved by magnetron sputtering for the fabrication of High Electron Mobility Transistors (HEMTs). The study of the deposited nitrides is conducted by spectroscopy, diffraction, and submicron scale microscope methods. The preparation of the materials is performed using different parameters in terms of power, pressure, temperature, gas, and time. Silicon (Si) and Sapphire (Al2O3) wafers are used as substrates. The chemical composition and surface topography of the samples are analyzed to calculate the materials atomic percentages and to observe the devices surface. The instruments used for the semiconductors characterization are X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Atomic Force Microscope (AFM). The project focused its attention on the reduction of impurities during the deposition, the controlled thicknesses of the thin-films, the atomic configuration of the alloy AlxGa1-xN, and the uniformity of the surfaces.

  18. Intermediate Nucleation State of GaN Growth

    Science.gov (United States)

    Zheng, L. X.; Xie, M. H.; Tong, S. Y.

    2001-03-01

    Homoexpitaxial nucleation of GaN during molecular-beam epitaxy is followed by scanning tunneling microcopy (STM). We observe a metastable nucleation state, which manifests as “ghost” islands in STM images. These “ghost” islands can be irreversibly driven into normal islands by continuous STM imaging. It is further established that the “ghost” island formation is related to the presence of excess Ga atoms on the surface: Normal islands are only seen under the N-rich or stoichiometric flux condition, whereas “ghost” islands are observed under Ga-rich conditions. For intermediate excess-Ga coverages, both normal and “ghost” islands are present, however, they show distinctly different sizes, suggesting different nucleation states for the two. A growth model is proposed to account for the formation of metastable, “ghost” islands. Kinetic Monte Carlo simulation is carried out and main features of the surface are reproduced. We acknowledge financial support from HK RGC under grant Nos. 7396/00P, 7142/99P, and 7121/00P.

  19. In-situ measurement of the strain relaxation of GaN nanograins during X-ray irradiation

    International Nuclear Information System (INIS)

    Choe, Hyeokmin; Lee, Sanghwa; Sohn, Yuri; Kim, Chinkyo

    2008-01-01

    GaN nanograins were grown on a c-plane sapphire substrate and their strain relaxation due to X-ray irradiation was investigated in-situ by utilizing synchrotron xray scattering. The GaN nanograins were constantly exposed to the synchrotron X-ray and θ-2θ scans through the (002) Bragg peak of GaN were repeatedly carried out during the irradiation. The Bragg peak of the compressively strained GaN nanograins gradually shifted toward higher angle, which implies that the GaN nanograins in compressive strain experienced strain relaxation during X-ray irradiation. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Effect of Ga seeding layer on formation of epitaxial Y-shaped GaN nanoparticles on silicon

    Science.gov (United States)

    Fedorov, V. V.; Bolshakov, A. D.; Mozharov, A. M.; Sapunov, G. A.; Shtrom, I. V.; Kirilenko, D. A.; Sitnikova, A. A.; Mukhin, I. S.

    2017-11-01

    Silicon and aluminium nitrides, commonly used as buffer layers for GaN growth on Si are wide gap insulators, preventing barrier free charge-carrier transport across the heterojunction and limiting the functionality of GaN-on-silicon technology. In this work we explore possibility of direct growth of GaN on Si nano-heterostructures by PA-MBE with use of Ga-nanodroplets as seeds. It is demonstrated that use of seeding layer can result in formation of Y-shaped planar GaN nanoparticles (GaN tripods) along with commonly observed GaN nanowires. Growth mechanism, morphology and structural characterization of GaN/Si nano-heterostructures is discussed.

  1. One-step fabrication of porous GaN crystal membrane and its application in energy storage.

    Science.gov (United States)

    Zhang, Lei; Wang, Shouzhi; Shao, Yongliang; Wu, Yongzhong; Sun, Changlong; Huo, Qin; Zhang, Baoguo; Hu, Haixiao; Hao, Xiaopeng

    2017-03-10

    Single-crystal gallium nitride (GaN) membranes have great potential for a variety of applications. However, fabrication of single-crystalline GaN membranes remains a challenge owing to its chemical inertness and mechanical hardness. This study prepares large-area, free-standing, and single-crystalline porous GaN membranes using a one-step high-temperature annealing technique for the first time. A promising separation model is proposed through a comprehensive study that combines thermodynamic theories analysis and experiments. Porous GaN crystal membrane is processed into supercapacitors, which exhibit stable cycling life, high-rate capability, and ultrahigh power density, to complete proof-of-concept demonstration of new energy storage application. Our results contribute to the study of GaN crystal membranes into a new stage related to the elelctrochemical energy storage application.

  2. 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.

  3. 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

  4. 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

  5. Development of UV image intensifier tube with GaN photocathode

    Science.gov (United States)

    Mizuno, I.; Nihashi, T.; Nagai, T.; Niigaki, M.; Shimizu, Y.; Shimano, K.; Katoh, K.; Ihara, T.; Okano, K.; Matsumoto, M.; Tachino, M.

    2008-04-01

    We developed an UV image intensifier tube with a GaN photocathode in semi-transparent mode. In UV spectroscopy and low-light-level UV-imaging applications, there are strong demands for improved detectors which have higher quantum efficiency, low dark current, sharper wavelength cut-off response, and stable and robust characteristics. III-Nitrides semiconductor is one of the promising candidate materials to meet these demands. We developed a GaN photocathode which is epitaxially grown by MOCVD method. It has flat and high quantum efficiency from 200 nm to 360 nm. The cathode is incorporated into an image intensifier tube, which shows good gating performance and fine imaging resolution. With these improved performances, the UV image intensifier tube with GaN photocathode will expand its application fields to include UV spectroscopy and UV-imaging in low light.

  6. Porosity-enhanced solar powered hydrogen generation in GaN photoelectrodes

    Science.gov (United States)

    Hou, Y.; Ahmed Syed, Z.; Jiu, L.; Bai, J.; Wang, T.

    2017-11-01

    Two types of GaN based photoelectrodes using either horizontally aligned or vertically aligned nanopores have been fabricated by means of using an electrochemical etching approach. The photoelectrodes based on such nanostructures have demonstrated an up to 5-fold enhancement in applied bias photon-to-current efficiency and incident photon-to-current efficiency in comparison with their planar counterpart, leading to a high Faradaic conversion efficiency which approaches 1. The GaN photoelectrodes with these nanopores also show excellent chemical stability in HBr solution as an electrolyte. The results presented reveal that the gas diffusion in the nanopores plays an important role in water splitting processes, which should be taken into account when designing a GaN photoelectrode with a nanopore structure.

  7. Growth behavior of GaN film along non-polar [1 1 -2 0] directions

    International Nuclear Information System (INIS)

    Gong Xiaojing; Xu Ke; Wang Jianfeng; Yang Hui; Bian Lifeng; Zhang Jingping; Xu Zijian

    2011-01-01

    We studied the atomic assembly mechanisms of non-polar GaN films by the molecular dynamics method as a function of the N:Ga flux ratio at a fixed adatom energy on non-polar planes. Our study revealed that high quality crystal growth occurred only when off-lattice atoms (which are usually associated with amorphous embryos or defect complexes) formed during deposition were able to move to unoccupied lattice sites by thermally activated diffusion processes, which attests to the experimental difficulties in obtaining smooth surfaces due to dense stacking faults lying in non-polar GaN. Furthermore, surface structures on different planes played an important role. We further suggested favorable conditions for growing high quality GaN films and nano-structures along non-polar directions.

  8. Self-induced growth of vertical GaN nanowires on silica

    International Nuclear Information System (INIS)

    Kumaresan, V; Largeau, L; Oehler, F; Mauguin, O; Glas, F; Gogneau, N; Harmand, J-C; Zhang, H; Tchernycheva, M

    2016-01-01

    We study the self-induced growth of GaN nanowires on silica. Although the amorphous structure of this substrate offers no possibility of an epitaxial relationship, the nanowires are remarkably aligned with the substrate normal whereas, as expected, their in-plane orientation is random. Their structural and optical characteristics are compared to those of GaN nanowires grown on standard crystalline Si (111) substrates. The polarity inversion domains are much less frequent, if not totally absent, in the nanowires grown on silica, which we find to be N-polar. This work demonstrates that high-quality vertical GaN nanowires can be elaborated without resorting to bulk crystalline substrates. (paper)

  9. Ultra-high Efficiency DC-DC Converter using GaN Devices

    DEFF Research Database (Denmark)

    Ramachandran, Rakesh

    2016-01-01

    for many decades. However, the rate of improvement slowed as the silicon power materials asymptotically approached its theoretical bounds. Compared to Si, wideband gap materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are promising semiconductors for power devices due to their superior...... properties of GaN devices can be utilized in power converters to make them more compact and highly efficient. This thesis entitled “Ultra-high Efficiency DC-DC Converter using GaN devices” focuses on achieving ultra-high conversion efficiency in an isolated dc-dc converter by the optimal utilization of Ga...... in this thesis. Efficiency measurements from the hardware prototype of both the topologies are also presented in this thesis. Finally, the bidirectional operation of an optimized isolated dc-dc converter is presented. The optimized converter has achieved an ultra-high efficiency of 98.8% in both directions...

  10. 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.

  11. Surface antireflection properties of GaN nanostructures with various effective refractive index profiles.

    Science.gov (United States)

    Han, Lu; Zhao, Hongping

    2014-12-29

    GaN nanostructures with various effective refractive index profiles (Linear, Cubic, and Quintic functions) were numerically studied as broadband omnidirectional antireflection structures for concentrator photovoltaics by using three-dimensional finite difference time domain (3D-FDTD) method. Effective medium theory was used to design the surface structures corresponding to different refractive index profiles. Surface antireflection properties were calculated and analyzed for incident light with wavelength, polarization and angle dependences. The surface antireflection properties of GaN nanostructures based on six-sided pyramid with both uniform and non-uniform patterns were also investigated. Results indicate a significant dependence of the surface antireflection on the refractive index profiles of surface nanostructures as well as their pattern uniformity. The GaN nanostructures with linear refractive index profile show the best performance to be used as broadband omnidirectional antireflection structures.

  12. 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.

  13. Semipolar AlN and GaN on Si(100): HVPE technology and layer properties

    Science.gov (United States)

    Bessolov, V.; Kalmykov, A.; Konenkova, E.; Kukushkin, S.; Myasoedov, A.; Poletaev, N.; Rodin, S.

    2017-01-01

    Hydride vapor phase epitaxy (HVPE) growth of semipolar AlN and GaN layers on planar Si(100) substrates with SiC nanolayer is investigated. It is shown experimentally that the solid-phase epitaxial formation of a specially oriented SiC nucleation layer followed by epitaxy of AlN layer by HVPE at low rates enables growth of aluminum and gallium nitrides in the semipolar direction. For the best GaN(20-23) layers obtained, the full width at half maximum (FWHM) value for the x-ray diffraction rocking curve is 24 arcmin. The photoluminescence spectrum of the semipolar GaN measured at 4 K exhibits bands related to basal-plane and prismatic stacking faults (BSF and PSF).

  14. 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)

  15. 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.

  16. Electrical characterization of ensemble of GaN nanowires grown by the molecular beam epitaxy technique

    International Nuclear Information System (INIS)

    Kolkovsky, Vl.; Zytkiewicz, Z. R.; Sobanska, M.; Klosek, K.

    2013-01-01

    High quality Schottky contacts are formed on GaN nanowires (NWs) structures grown by the molecular beam epitaxy technique on Si(111) substrate. The current-voltage characteristics show the rectification ratio of about 10 3 and the leakage current of about 10 −4 A/cm 2 at room temperature. From the capacitance-voltage measurements the free carrier concentration in GaN NWs is determined as about 10 16 cm −3 . Two deep levels (H200 and E280) are found in the structures containing GaN NWs. H200 is attributed to an extended defect located at the interface between the substrate and SiN x or near the sidewalls at the bottom of the NWs whereas E280 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect

  17. Measurement of the electrostatic edge effect in wurtzite GaN nanowires

    International Nuclear Information System (INIS)

    Henning, Alex; Rosenwaks, Yossi; Klein, Benjamin; Bertness, Kris A.; Blanchard, Paul T.; Sanford, Norman A.

    2014-01-01

    The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference between the nanowire face and the hexagonal vertices, the surface state concentration and band bending of GaN NWs were estimated. The surface band bending is important for an efficient design of high electron mobility transistors and for opto-electronic devices based on GaN NWs. This methodology provides a way to extract NW parameters without making assumptions concerning the electron affinity. We are taking advantage of electrostatic modeling and the high precision that KPFM offers to circumvent a major source of uncertainty in determining the surface band bending

  18. Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

    Science.gov (United States)

    Calabrese, Gabriele; Corfdir, Pierre; Gao, Guanhui; Pfüller, Carsten; Trampert, Achim; Brandt, Oliver; Geelhaar, Lutz; Fernández-Garrido, Sergio

    2016-05-01

    We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.

  19. Neutral anodic etching of GaN for vertical or crystallographic alignment

    Science.gov (United States)

    Schwab, Mark J.; Han, Jung; Pfefferle, Lisa D.

    2015-06-01

    Etching of gallium nitride for various device applications has attracted much attention; however, previous reports have all been performed in acidic or basic etchant solutions. Herein, we demonstrate how neutral electrolytes such as NaNO3 or NaCl can be used to rapidly etch n-GaN electrochemically and achieve a porous structure that is either vertically aligned or faceted according to the GaN crystallography, in NaNO3 and NaCl, respectively. It is demonstrated that the etching properties of NaNO3 and HNO3 are very similar, showing that the etching process in this system is surprisingly insensitive to pH. This neutral-pH process enables safer and greener GaN etching, as well as opening up the possibility of crystallographic etching of GaN using an anodic process.

  20. Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

    International Nuclear Information System (INIS)

    Calabrese, Gabriele; Corfdir, Pierre; Gao, Guanhui; Pfüller, Carsten; Trampert, Achim; Brandt, Oliver; Geelhaar, Lutz; Fernández-Garrido, Sergio

    2016-01-01

    We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit an equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.

  1. The pyroelectric coefficient of free standing GaN grown by HVPE

    Science.gov (United States)

    Jachalke, Sven; Hofmann, Patrick; Leibiger, Gunnar; Habel, Frank S.; Mehner, Erik; Leisegang, Tilmann; Meyer, Dirk C.; Mikolajick, Thomas

    2016-10-01

    The present study reports on the temperature dependent pyroelectric coefficient of free-standing and strain-free gallium nitride (GaN) grown by hydride vapor phase epitaxy (HVPE). The Sharp-Garn method is applied to extract the pyroelectric coefficient from the electrical current response of the crystals subjected to a sinusoidal temperature excitation in a range of 0 °C to 160 °C. To avoid compensation of the pyroelectric response by an internal conductivity, insulating GaN crystals were used by applying C, Mn, and Fe doping during HVPE growth. The different pyroelectric coefficients observed at room temperature due to the doping correlate well with the change of the lattice parameter c. The obtained data are compared to previously published theoretical and experimental values of thin film GaN and discussed in terms of a strained lattice.

  2. High-pressure X-ray diffraction study of bulk- and nanocrystalline GaN

    DEFF Research Database (Denmark)

    Jorgensen, J.E.; Jakobsen, J.M.; Jiang, Jianzhong

    2003-01-01

    Bulk- and nanocrystalline GaN have been studied by high-pressure energy-dispersive X-ray diffraction. Pressure-induced structural phase transitions from the wurtzite to the NaCl phase were observed in both materials. The transition pressure was found to be 40 GPa for the bulk-crystalline GaN, while...... the wurtzite phase was retained up to 60 GPa in the case of nanocrystalline GaN. The bulk moduli for the wurtzite phases were determined to be 187 ( 7) and 319 ( 10) GPa for the bulk- and nanocrystalline phases, respectively, while the respective NaCl phases were found to have very similar bulk moduli [ 208...... ( 28) and 206 ( 44) GPa]....

  3. Elastic strain relief in nitridated Ga metal buffer layers for epitaxial GaN growth

    International Nuclear Information System (INIS)

    Kim, Yihwan; Shapiro, Noad A.; Feick, Henning; Armitage, Robert; Weber, Eicke R.; Yang, Yi; Cerrina, Franco

    2001-01-01

    Gallium nitride epitaxial layers were grown on sapphire by molecular-beam epitaxy using nitridated gallium metal films as buffer layers. The mechanical properties of the buffer layers were investigated and correlated with their chemical composition as determined by synchrotron radiation photoelectron spectroscopy. Biaxial tension experiments were performed by bending the substrates in a pressure cell designed for simultaneous photoluminescence measurements. The shift of the excitonic luminescence peak was used to determine the stress induced in the main GaN epilayer. The fraction of stress transferred from substrate to main layer was as low as 27% for samples grown on nitridated metal buffer layers, compared to nearly 100% for samples on conventional low-temperature GaN buffer layers. The efficiency of stress relief increased in proportion to the fraction of metallic Ga in the nitridated metal buffer layers. These findings suggest GaN films containing residual metallic Ga may serve as compliant buffer layers for heteroepitaxy

  4. Defect reduction in GaN on dome-shaped patterned-sapphire substrates

    Science.gov (United States)

    Chen, Po-Hsun; Su, Vin-Cent; Wu, Shang-Hsuan; Lin, Ray-Ming; Kuan, Chieh-Hsiung

    2018-02-01

    This paper demonstrates the behavior of defect reduction in un-doped GaN (u-GaN) grown on a commercial dome-shaped patterned-sapphire substrate (CDPSS). Residual strain inside the u-GaN grown on the CDPSS have been investigated as well. As verified by the experimentally measured data, the limited growth rate of the u-GaN on the sidewall of the CDPSS enhances the lateral growth of the GaN on the trench region while increasing the growth time. This subsequently contributes to improve the crystalline quality of the GaN on the CDPSS. The more prominent dislocations occur in the u-GaN epilayers on the CDPSS after reaching the summit of the accumulated strain inside the epilayers. Such prominent bent dislocations improve their blocking abilities, followed by the achievement of the better crystalline quality for the growth of the u-GaN on the CDPSS.

  5. 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.

  6. The role of alternating current in photo-assisted electrochemical porosification of GaN

    International Nuclear Information System (INIS)

    Ainorkhilah, Mahmood; Naser, M. Ahmed; Yushamdan, Yusof; Kwong, Yam Fong; Zainuriah, Hassan; Tiginyanu, Ion; Siang, Chuah Lee

    2013-01-01

    In this paper, we report the formation of porous GaN films under a novel alternating current (sine-wave a.c. (50 Hz)) photo-assisted electrochemical (ACPEC) etching conditions. The ACPEC formed porous GaN with excellent structural and surface morphology. Field emission scanning electron microscope (FESEM), atomic force microscopy (AFM) and high resolution X-ray diffraction (HR-XRD) phi-scan and rocking curves measurements evidenced important features of the pore morphology and nanostructures. According to the FESEM micrographs, the spatial nano architecture of the porous structures exhibits pores with perfect hexagonal shape. The AFM measurements revealed an increase in the surface roughness induced by porosification. X-ray diffraction phi-scan showed that porous GaN sample maintained the epitaxial. (authors)

  7. Physical Properties of GaN Nanotubes as Revealed by Computer Simulation

    International Nuclear Information System (INIS)

    Wang, Zhiguo; Gao, Fei; Zu, Xiaotao; Weber, William J.

    2008-01-01

    Single-crystalline wurtzite GaN nanotubes have been synthesized recently with proposed applications in nanoscale electronics, optoelectronics and the biochemical-sensing field. Molecular dynamics methods with a Stillinger-Weber potential are used to investigate the melting behavior, thermal conductivity and mechanical properties of these wurtzite-type single crystalline GaN nanotubes. Four major topical areas are summarized in this chapter. (1) The melting temperature of the GaN nanotubes increases with the thickness of the nanotubes to a saturation value, which is close to the melting temperature of bulk GaN. The simulations result reveal that the nanotubes begin to melt at the surface, and then the melting rapidly extends to the interior of the nanotubes as the temperature increases. (2) The thermal conductivity of nanotubes is smaller than that of the bulk GaN single crystal. The thermal conductivity is also found to decrease with temperature and increase with increasing wall thickness of the nanotubes. The change of phonon spectrum and surface inelastic scattering may account for the reduction of thermal conductivity in the nanotubes, while thermal softening and high frequency phonon interactions at high temperatures may provide an explanation for its decrease with increasing temperature. (3) At low temperatures, the simulation results show that the nanotubes exhibit brittle properties; whereas at high temperatures, they behave as ductile materials. The brittle to ductile transition temperature generally increases with increasing wall thickness of the nanotubes and increasing strain rate. (4) The simulation temperature, tube length and strain rate affect the buckling behavior of GaN nanotubes. The critical stress decreases with the increase of simulation temperature and tube length. The dependence of buckling on tube length is consistent with the analysis of equivalent continuum structures using Euler buckling theory

  8. 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.

  9. Optical quenching of X-ray photoconductor based on GaN

    International Nuclear Information System (INIS)

    Yan Changsheng; Fu Kai; Wang Guo; Lu Min

    2011-01-01

    X-ray photoconductor based on GaN have been made by using advanced semiconductor microfabrication technology. Optical quenching phenomenon of GaN X-ray detector was presented. The photocurrent had a mutation when the fluorescent light was turned on and off. Experiments have been carried out to analyze the optical quenching and current mutation phenomenons. The results have indicated that optical quenching effect associates with a hole trap and recombination centers, while the current mutation results from a UV light which excited the electron from valence band to conduction band. (authors)

  10. Lergodset från Höganäsbolaget 1832-1926

    OpenAIRE

    Weimarck, Ann-Charlotte; Weimarck, Torsten

    2005-01-01

    Two hundred year's ago, Höganä's, a town situated in the north-west part of the county of Skåne, about 20 km north of the city of Helsingborg, had no local pottery tradition's. Höganä's wa's then a tiny fishing village that even lacked a harbour. Coal had now and then been quarried from an opencast mine and the local inhabitant's had collected it from the beach at low tide for their personal need's. When the mining industry started in 1797 and, with time, even the ...

  11. Nucleation and Growth of GaN on GaAs (001) Substrates

    Energy Technology Data Exchange (ETDEWEB)

    Drummond, Timothy J.; Hafich, Michael J.; Heller, Edwin J.; Lee, Stephen R.; Liliental-Weber, Zuzanna; Ruvimov, Sergei; Sullivan, John P.

    1999-05-03

    The nucleation of GaN thin films on GaAs is investigated for growth at 620 "C. An rf plasma cell is used to generate chemically active nitrogen from N2. An arsenic flux is used in the first eight monolayer of nitride growth to enhance nucleation of the cubic phase. Subsequent growth does not require an As flux to preserve the cubic phase. The nucleation of smooth interfaces and GaN films with low stacking fault densities is dependent upon relative concentrations of active nitrogen species in the plasma and on the nitrogen to gallium flux ratio.

  12. 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.

  13. Electrical characterization of acceptor levels in Be-implanted GaN

    OpenAIRE

    Yoshitaka, Nakano; Takashi, Jimbo

    2002-01-01

    We have investigated electrically the acceptor levels that are present in Be-implanted GaN. Slight p-type conductivity was attained in undoped GaN films by Be implantation and subsequent annealing at 1050°C with a SiO2 encapsulation layer. Capacitance-frequency measurements showed a typical dispersion effect characteristic of deep acceptors in fabricated Schottky diodes. Thermal admittance spectroscopy measurements revealed a discrete deep level located at ? 231meV above the valence band. Thi...

  14. Reliability improvement in GaN HEMT power device using a field plate approach

    Science.gov (United States)

    Wu, Wen-Hao; Lin, Yueh-Chin; Chin, Ping-Chieh; Hsu, Chia-Chieh; Lee, Jin-Hwa; Liu, Shih-Chien; Maa, Jer-shen; Iwai, Hiroshi; Chang, Edward Yi; Hsu, Heng-Tung

    2017-07-01

    This study investigates the effect of implementing a field plate on a GaN high-electron-mobility transistor (HEMT) to improve power device reliability. The results indicate that the field plate structure reduces the peak electrical field and interface traps in the device, resulting in higher breakdown voltage, lower leakage current, smaller current collapse, and better threshold voltage control. Furthermore, after high voltage stress, steady dynamic on-resistance and gate capacitance degradation improvement were observed for the device with the field plate. This demonstrates that GaN device reliability can be improved by using the field plate approach.

  15. 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 - Electronic s ; Optoelectronics, Electrical Engineering (URE-Y) OBOR OECD: Nuclear physics; Electrical and electronic engineering (URE-Y) Impact factor: 1.109, year: 2016

  16. 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

  17. Structural and optical properties of Gd implanted GaN with various crystallographic orientations

    Czech Academy of Sciences Publication Activity Database

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

    2017-01-01

    Roč. 638, SEP (2017), s. 63-72 ISSN 0040-6090 R&D Projects: GA ČR GA13-20507S; GA ČR GA15-01602S; GA MŠk LM2015056 Institutional support: RVO:67985882 ; RVO:61389005 Keywords : GaN implantation * RBS channelling * optical properties of Gd implanted GaN Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders; BH - Optics, Masers, Lasers (URE-Y) OBOR OECD: 1.3 Physical sciences; Optics (including laser optics and quantum optics) (URE-Y) Impact factor: 1.879, year: 2016

  18. Optimization of GaN Nanorod Growth Conditions for Coalescence Overgrowth

    Science.gov (United States)

    2016-02-04

    from your AOARD supported project: SCI Journal papers: 1. Charng-Gan Tu, Yu-Feng Yao, Che-Hao Liao, Chia -Ying Su, Chieh Hsieh, Chi-Ming Weng, Chun...Optics Express, Vol. 23, No. 17, pp. 21919-21930, 24 August 2015. 2. Charng-Gan Tu, Chia -Ying Su, Che-Hao Liao, Chieh Hsieh, Yu-Feng Yao, Hao-Tsung Chen...Vapor-phase Epitaxy,” Superlattices and Microstructures, Vol. 83, pp. 329-341, July 2015. (Invited) 3. Chun-Han Lin, Chia -Ying Su, Erwin Zhu, Chieh

  19. Study on high-speed deep etching of GaN film by UV laser ablation

    Science.gov (United States)

    Zhang, J.; Sugioka, K.; Wada, S.; Tashiro, H.; Midorikawa, K.

    1998-06-01

    High-speed deep etching of GaN thin films by UV (266 nm) laser ablation followed by a treatment in HCl solution, was achieved. The etch rate was as high as 50 nm/pulse. Scanning electron microscopy and scanning probe microscopy measurement results indicate that the surface of the etched films was structurally well-defined and cleanly patterned. Micro-photoluminescence measurements of ablated samples revealed no severe damage to the optical properties or the crystal structure. In addition, coupling with VUV (133-184 nm) laser beams, the etch quality of GaN was markedly improved. The etch rate was 55 nm/pulse

  20. 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...

  1. Doping Induced Structural Stability and Electronic Properties of GaN Nanotubes

    Directory of Open Access Journals (Sweden)

    Anurag Srivastava

    2014-01-01

    Full Text Available The present paper discusses the effect of manganese doping on the structural stability and electronic band gap of chiral (2, 1, armchair (3, 3, and zigzag ((6, 0 and (10, 0 single walled GaN nanotube by using density functional theory based Atomistix Toolkit (ATK Virtual NanoLab (VNL. The structural stability has been analyzed in terms of minimum ground state total energy, binding, and formation energy. As an effect of Mn doping (1–4 atoms, all the GaN nanotubes taken into consideration show semiconducting to metallic transition first and after certain level of Mn doping changes its trend.

  2. Room temperature ferromagnetism in thermally diffused Cr in GaN

    Science.gov (United States)

    Suggisetti, P.; Banerjee, D.; Adari, R.; Pande, N.; Patil, T.; Ganguly, S.; Saha, D.

    2013-03-01

    We report room temperature ferromagnetism in crystalline GaCrN prepared by Cr deposition and drive-in diffusion with Curie temperature much above 300 K. The Curie temperature increases with increasing active Cr concentration. Cr doped GaN acts as an n-type material with significant increase in electron carrier concentration due to the presence of Cr. Optical property of GaCrN is found to be very similar to GaN with an additional peak at 3.29 eV due to Cr. The hysteresis measurements show that the ferromagnetic ordering is maintained up to 300 K with no significant change in saturation magnetization.

  3. 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.

  4. Structural analysis of GaN using high-resolution X-ray diffraction at variable temperatures; Analyse struktureller Eigenschaften von GaN mittels hochaufloesender Roentgenbeugung bei variabler Messtemperatur

    Energy Technology Data Exchange (ETDEWEB)

    Roder, C.

    2007-02-26

    The main topic of this thesis was the study of stress phenomena in GaN layers by application of high-resolution X-ray diffractometry at variable measurement temperature. For this a broad spectrum of different GaN samples was studied, which extended from bulk GaN crystals as well as thick c-plane oriented HVPE-GaN layers on c-plane sapphire over laterlaly overgrown c-plane GaN Layers on Si(111) substrates toon-polar a-plnae GaN layers on r-plane sapphire. The main topic of the measurements was the determination of the lattice parameters. Supplementarily the curvature of the waver as well as the excitonic resosance energies were studied by means of photoluminescence respectively photoreflection spectroscopy. By the measurement of the temperature-dependent lattice parameters of different GaN bulk crystals for the first time a closed set of thermal-expansion coefficients of GaN was determined from 12 to 1205 K with large accuracy. Analoguously the thermal-expansion coefficents of the substrate material sapphire were determinde over a temperature range from 10 to 1166 K.

  5. Computational study of adsorption, diffusion, and dissociation of precursor species on the GaN (0 0 0 1) surface during GaN MOCVD

    Science.gov (United States)

    Won, Yong Sun; Lee, Jinuk; Kim, Changsung Sean; Park, Sung-Soo

    2009-02-01

    The adsorption, diffusion, and dissociation of precursor species, MMGa (monomethylgallium) and NH 3, on the GaN (0 0 0 1) surface have been investigated using the DFT (density functional theory) calculation combined with a GaN (0 0 0 1) surface cluster model. The energetics of NH 3(ad) dissociation on the surface proposed of NH 3(ad) via NH 2(ad) to NH(ad) was facile with small activation barriers. A combined analysis with surface diffusion of adatoms demonstrated Ga(ad) and NH(ad) become primary reactant species for 2D film growth, and N(ad) develops into a nucleation center. Our studies suggest the control of NH 3(ad) dissociation are essential to improve epitaxial film quality as well as Ga-rich condition. In addition, the adsorbability of H(ad)s resulted from NH 3(ad) dissociation were found to influence on the surface chemistry during film growth.

  6. Potential study of the enhanced breakdown voltage GaN MISFET based on partial AlN buried layer

    Science.gov (United States)

    Fei, Xin-Xing; Wang, Ying; Luo, Xin; Cao, Fei; Yu, Cheng-Hao

    2018-02-01

    In this paper, a new structure for GaN MISFET is proposed to enhance its breakdown voltage. The proposed structure uses an Aluminum nitride (AlN) buried layer embedded inside the GaN buffer layer. The AlN buried layer is employed to reduce the peak electric field strength near the gate, introducing a high electric field peak in the GaN buffer layer. The GaN/AlN heterojunction formed by the GaN buffer layer and the AlN buried layer introduces two electric field peaks, and enhances the uniformity of the electric field distribution in the GaN buffer layer. Simulation results of the proposed structure show that the breakdown voltage is enhanced by 78% when compared to the conventional GaN MISFET. Moreover, the specific on-resistance (Ron,sp) is improved since the AlN buried layer provides two-dimensional electron gases in the GaN buffer which can cause the charge to increase.

  7. 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.

  8. 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.)

  9. Synthesis and characterization of silicon-doped polycrystalline GaN ...

    Indian Academy of Sciences (India)

    Administrator

    and high frequency devices as well. The main technologi- cal interest in the polycrystalline-based devices stems from its very low-cost production. Among different group. III nitrides, GaN ..... Li Z Q, Chen H, Liu H F, Wan L, Huang Q and Zhou J M. 2001 J. Cryst. Growth 227–228 420. 4. Hasegawa S, Nishida S, Yamashita T ...

  10. Discussion of enthalpy, entropy and free energy of formation of GaN

    Science.gov (United States)

    Jacob, K. T.; Rajitha, G.

    2009-07-01

    Presented in this letter is a critical discussion of a recent paper on experimental investigation of the enthalpy, entropy and free energy of formation of gallium nitride (GaN) published in this journal [T.J. Peshek, J.C. Angus, K. Kash, J. Cryst. Growth 311 (2008) 185-189]. It is shown that the experimental technique employed detects neither the equilibrium partial pressure of N 2 corresponding to the equilibrium between Ga and GaN at fixed temperatures nor the equilibrium temperature at constant pressure of N 2. The results of Peshek et al. are discussed in the light of other information on the Gibbs energy of formation available in the literature. Entropy of GaN is derived from heat-capacity measurements. Based on a critical analysis of all thermodynamic information now available, a set of optimized parameters is identified and a table of thermodynamic data for GaN developed from 298.15 to 1400 K.

  11. Global Action Network Impacts Community of Practice (GAN-Net ICOP)

    International Development Research Centre (IDRC) Digital Library (Canada)

    Global action networks - networks of organizations and institutions from the public, private and nonprofit sectors operating around a common issue - are an emerging innovation that is fast becoming a mechanism for change in the 21st Century. Global Action Network-Net (GAN-Net) is the global network of and for global ...

  12. Structural and luminescence properties of GaN nanowires grown using cobalt phthalocyanine as catalyst

    Science.gov (United States)

    Yadav, Shivesh; Rodríguez-Fernández, Carlos; de Lima, Mauricio M.; Cantarero, Andres; Dhar, Subhabrata

    2015-12-01

    Catalyst free methods have usually been employed to avoid any catalyst induced contamination for the synthesis of GaN nanowires with better transport and optical properties. Here, we have used a catalytic route to grow GaN nanowires, which show good optical quality. Structural and luminescence properties of GaN nanowires grown by vapor-liquid-solid technique using cobalt phthalocyanine as catalyst are systematically investigated as a function of various growth parameters such as the growth temperature and III/V ratio. The study reveals that most of the nanowires, which are several tens of microns long, grow along [ 10 1 ¯ 0 ] direction. Interestingly, the average wire diameter has been found to decrease with the increase in III/V ratio. It has also been observed that in these samples, defect related broad luminescence features, which are often present in GaN, are completely suppressed. At all temperatures, photoluminescence spectrum is found to be dominated only by a band edge feature, which comprises of free and bound excitonic transitions. Our study furthermore reveals that the bound excitonic feature is associated with excitons trapped in certain deep level defects, which result from the deficiency of nitrogen during growth. This transition has a strong coupling with the localized vibrational modes of the defects.

  13. 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.

  14. Low loss GaN waveguides at the visible spectral wavelengths for integrated photonics applications.

    Science.gov (United States)

    Chen, Hong; Fu, Houqiang; Huang, Xuanqi; Zhang, Xiaodong; Yang, Tsung-Han; Montes, Jossue A; Baranowski, Izak; Zhao, Yuji

    2017-12-11

    We perform comprehensive studies on the fundamental loss mechanisms in III-nitride waveguides in the visible spectral region. Theoretical analysis shows that free carrier loss dominates for GaN under low photon power injection. When optical power increases, the two photon absorption loss becomes important and eventually dominates when photon energy above half-bandgap of GaN. When the dimensions of the waveguides reduce, the sidewall scattering loss will start to dominate. To verify the theoretical results, a high performance GaN-on-sapphire waveguide was fabricated and characterized. Experimental results are consistent with the theoretical findings, showing that under high power injection the optical loss changed significantly for GaN waveguides. A low optical loss ~2 dB/cm was achieved on the GaN waveguide, which is the lowest value ever reported for the visible spectral range. The results and fabrication processes developed in this work pave the way for the development of III-nitride integrated photonics in the visible and potentially ultraviolet spectral range for nonlinear optics and quantum photonics applications.

  15. Effect of TMBi supply on low-temperature MOVPE growth behavior of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Saidi, C.; Chaaben, N.; Laifi, J.; Sekrafi, T. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir (Tunisia); Tottereau, O. [Centre de Recherche sur l’Hétéro-Epitaxie et Ses Applications, Centre National de la Recherche Scientifique, CRHEA-CNRS, Rue Bernard Grégory, F-06560 Valbonne, Sophia Antipolis (France); Bchetnia, A.; El Jani, B. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir (Tunisia)

    2015-03-15

    Highlights: • We examined the Bi doping effect on GaN layers properties, grown by LT-MOVPE. • No obvious dependence of growth rate with TMBi flow rate. • TMBi flow rate addition resulted in a reduction of reflectivity oscillation mean value. • We note the appearance of islands and columns containing Bi on layers surface. • While there is a decrease in surface roughness suggesting Bi surfactant effect. - Abstract: Undoped GaN and diluted GaNBi alloys were grown on (0 0 0 1) sapphire substrate by metal–organic vapor phase epitaxy (MOVPE) at 480 °C. By using in-situ laser reflectometry, it is found that the increase of TMBi flow rate leads to a reduction of the average value of reflectivity oscillations. Scanning electron microscopy (SEM) images gave a clear observation of the TMBi increasing amount effect on the surface morphology. The appearance of different structure (islands and columns) on GaN surface could be responsible to the reduction of the reflectivity oscillations average value. The energy dispersive X-ray (EDX) analysis showed that the observed structures were only composed of Bi compared to the flat GaN surface. Moreover, the surface morphology between islands and columns is improved when we increase the TMBi flow rate. This improvement is consistent with the decrease of root mean square (RMS) roughness, as measured by atomic force microscopy (AFM)

  16. Efficient Incorporation of Mg in Solution Grown GaN Crystals

    Science.gov (United States)

    2013-10-11

    large area GaN wafers. Presently, only hydride vapor phase epitaxy (HVPE) and ammonothermal growth methods have produced commercial quality substrates.1–3...Cd laser line. The sample was sandwiched between cupper mashes and aluminum foils to allow sequential measurement of both faces. The scale bar is

  17. GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium

    International Nuclear Information System (INIS)

    Bartram, Michael E.; Creighton, J. Randall

    1999-01-01

    Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N 15 H 3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N 2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia

  18. GaN C-band HPA for phased-array applications

    NARCIS (Netherlands)

    Wanum, M. van; Hek, A.P. de; Vliet, F.E. van

    2013-01-01

    In the UMS GH25-10 GaN MMIC technology a Cband high power amplifier (HPA) has been realized. The current design is primarily intended for use in a space-based SAR system with a center frequency of 5.4 GHz and a sweep bandwidth of 100 MHz. To enable reuse of the amplifier in other radar systems such

  19. 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.

  20. Structural properties of CrN buffers for GaN growth

    International Nuclear Information System (INIS)

    Lee, W. H.; Im, I. H.; Minegishi, T.

    2006-01-01

    We have investigated the structural properties of CrN layers grown on (0001) Al 2 O 3 substrates by molecular-beam epitaxy. The CrN layers of high-crystal quality are obtained at a low growth temperature of 500 .deg. C. X-ray diffraction studies indicate that the CrN layers grow along the direction with a cubic structure. In-situ reflection high-energy electron diffraction investigations clarify that the CrN layers have the following epitaxy relationship with the Al 2 O 3 substrates: of (111) cubic CrN // of (0001) corundum Al 2 O 3 and of (111) cubic CrN // of (0001) corundum Al 2 O 3 . Based on the above results, the mismatch of the in-plane lattice spacing between the CrN layers and the Al 2 O 3 substrates is evaluated to be around 6.6 %. When the CrN layers are used as the buffer layers for GaN growth, the GaN layers grown on the CrN layers show well-resolved excitonic emission lines in the photoluminescence spectra, whereas the GaN layers grown without the CrN layers exhibit a broad near-band-edge emission. It is suggested that CrN buffers are effective in relieving the lattice mismatch between Al 2 O 3 substrates and GaN layers.

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

    Directory of Open Access Journals (Sweden)

    R. Velazquez

    2016-08-01

    Full Text Available 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.

  2. 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.

  3. Barrier characteristics of Pt/Ru Schottky contacts on n-type GaN ...

    Indian Academy of Sciences (India)

    Keywords. Pt/Ru Schottky rectifiers; -type GaN; temperature–dependent electrical properties; inhomogeneous barrier heights; double Gaussian distribution. Abstract. We have investigated the current–voltage (–) and capacitance–voltage (–) characteristics of Ru/Pt/-GaN Schottky diodes in the temperature range ...

  4. GaN growth on silane exposed AlN seed layers

    Energy Technology Data Exchange (ETDEWEB)

    Ruiz-Zepeda, F. [Posgrado en Fisica de Materiales, Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Km. 107 Carret, Tijuana-Ensenada, C.P. 22860, Ensenada, B.C. (Mexico); Contreras, O. [Centro de Ciencias de la Materia Condesada, Universidad Nacional Autonoma de Mexico, Apdo. Postal 356, C.P. 22800, Ensenada, B.C. (Mexico); Dadgar, A.; Krost, A. [Otto-von-Guericke-Universitaet Magdeburg, FNW-IEP, Universitaetsplatz 2, 39106 Magdeburg (Germany)

    2008-07-01

    The microstructure and surface morphology of GaN films grown on AlN seed layers exposed to silane flow has been studied by TEM and AFM. The epilayers were grown on silicon(111) substrates by MOCVD. The AlN seed layer surface was treated at different SiH{sub 4} exposure times prior to the growth of the GaN film. A reduction in the density of threading dislocations is observed in the GaN films and their surface roughness is minimized for an optimal SiH{sub 4} exposure time between 75-90 sec. At this optimal condition a step-flow growth mode of GaN film is predominant. The improvement of the surface and structure quality of the epilayers is observed to be related to an annihilation process of threading dislocations done by SiN{sub x} masking. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. 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.

  6. Evaluation of freestanding GaN as an alpha and neutron detector

    Energy Technology Data Exchange (ETDEWEB)

    Mulligan, Padhraic; Wang, Jinghui; Cao, Lei, E-mail: cao.152@osu.edu

    2013-08-11

    The wide bandgap (3.39) eV and large dislocation energy of the III–V semiconductor gallium nitride (GaN) make this a desirable material for charged particle spectroscopy in high temperature, high radiation environments. While other research groups have established that charged particle detectors can be fabricated from high quality, thin films of molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) grown GaN, this work demonstrates the feasibility of ionizing radiation detectors created from significantly thicker freestanding n-type GaN, grown via hydride vapor phase epitaxy (HVPE). Detectors were fabricated by depositing Ni/Au pads on n-type GaN, forming a Schottky barrier diode. Capacitance–voltage measurements on the detectors showed an intrinsic carrier concentration in the range of 10{sup −16} cm{sup −3}–10{sup –15} cm{sup −3}, and indicated an inhomogeneous distribution between diodes on the same wafer. The radiation sensitivity of the fabricated detectors was analyzed using alpha particles from an {sup 241}Am source. Charge collection efficiency (CCE) calculations from these experiments indicate an efficiency of 100 percent. The detectors were also successfully used to detect neutron induced charged particles using a Li{sub 2}O foil in a neutron beam.

  7. Studies on Anti-Hepatoma Effect of Gan-Ai-Xiao Decoction | Yuan ...

    African Journals Online (AJOL)

    Purpose: To explore the anti-hepatoma effect of Gan-Ai-Xiao Decoction (GAXD), a folk remedy. Methods: High performance liquid chromatography (HPLC) was used to identify the major chemical components of GAXD ethanol extract (EE). The cytotoxic effect of GAXD EE against HepG2 cells was measured by methyl ...

  8. 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

  9. GaN nanostructure-based light emitting diodes and semiconductor lasers.

    Science.gov (United States)

    Viswanath, Annamraju Kasi

    2014-02-01

    GaN and related materials have received a lot of attention because of their applications in a number of semiconductor devices such as LEDs, laser diodes, field effect transistors, photodetectors etc. An introduction to optical phenomena in semiconductors, light emission in p-n junctions, evolution of LED technology, bandgaps of various semiconductors that are suitable for the development of LEDs are discussed first. The detailed discussion on photoluminescence of GaN nanostructures is made, since this is crucial to develop optical devices. Fabrication technology of many nanostructures of GaN such as nanowires, nanorods, nanodots, nanoparticles, nanofilms and their luminescence properties are given. Then the optical processes including ultrafast phenomena, radiative, non-radiative recombination, quantum efficiency, lifetimes of excitons in InGaN quantum well are described. The LED structures based on InGaN that give various important colors of red, blue, green, and their design considerations to optimize the output were highlighted. The recent efforts in GaN technology are updated. Finally the present challenges and future directions in this field are also pointed out.

  10. Leakage current reduction of vertical GaN junction barrier Schottky diodes using dual-anode process

    Science.gov (United States)

    Hayashida, Tetsuro; Nanjo, Takuma; Furukawa, Akihiko; Watahiki, Tatsuro; Yamamuka, Mikio

    2018-04-01

    The origin of the leakage current of a trench-type vertical GaN diode was discussed. We found that the edge of p-GaN is the main leakage spot. To reduce the reverse leakage current at the edge of p-GaN, a dual-anode process was proposed. As a result, the reverse blocking voltage defined at the leakage current density of 1 mA/cm2 of a vertical GaN junction barrier Schottky (JBS) diode was improved from 780 to 1,190 V, which is the highest value ever reported for vertical GaN Schottky barrier diodes (SBDs).

  11. A 99%-efficiency GaN converter for 6.78 MHz magnetic resonant wireless power transfer system

    OpenAIRE

    Yoshiyuki Akuzawa; Yuki Ito; Toshihiro Ezoe; Kiyohide Sakai

    2014-01-01

    The authors developed a high-efficiency gallium-nitride (GaN) Class-E converter for a 6.78 MHz magnetic resonant wireless power transfer system. A negative-bias gate driver circuit made it possible to use a depletion mode GaN high-electron-mobility transistor (HEMT), and simplified the converter circuit. As the depletion mode GaN HEMT with very small gate–source capacitance provided almost ideal zero-voltage switching, the authors attained a drain efficiency of 98.8% and a total efficiency of...

  12. Improvement of GaN epilayer by gradient layer method with molecular-beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yen-Liang [Department of Physics, Institute of Material Science and Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, ROC (China); Lo, Ikai, E-mail: ikailo@mail.phys.nsysu.edu.tw [Department of Physics, Institute of Material Science and Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, ROC (China); Gau, Ming-Hong; Hsieh, Chia-Ho; Sham, Meng-Wei; Pang, Wen-Yuan; Hsu, Yu-Chi [Department of Physics, Institute of Material Science and Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan, ROC (China); Tsai, Jenn-Kai [Department of Electronics Engineering, National Formosa University, Hu-Wei, Yun-Lin County 63208, Taiwan, ROC (China); Schuber, Ralf; Schaadt, Daniel [Institute of Applied Physics/DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology (KIT), Karlsruhe (Germany)

    2012-07-31

    We demonstrated a molecular beam epitaxy method to resolve the dilemma between structural and morphological quality in growth of the GaN epilayer. A gradient buffer layer was grown in such a way that the N/Ga ratio was gradually changed from nitrogen-rich to gallium-rich. The GaN epitaxial layer was then grown on the gradient buffer layer. In the X-ray diffraction analysis of GaN(002) rocking curves, we found that the full width at half-maximum was improved from 531.69 Double-Prime to 59.43 Double-Prime for the sample with a gradient buffer layer as compared to a purely gallium-rich grown sample. Atomic force microscopy analysis showed that the root-mean-square roughness of the surface was improved from 18.28 nm to 1.62 nm over an area of 5 Multiplication-Sign 5 {mu}m{sup 2} with respect to a purely nitrogen-rich grown sample. Raman scattering showed the presence of a slightly tilted plane in the gradient layer. Furthermore we showed that the gradient layer can also slash the strain force caused by either Ga-rich GaN epitaxial layer or AlN buffer layer. - Highlights: Black-Right-Pointing-Pointer The samples were grown by plasma-assisted molecular beam epitaxy. Black-Right-Pointing-Pointer The GaN epilayer was grown on sapphire substrate. Black-Right-Pointing-Pointer The samples were characterized by X-ray diffraction and atomic force microscopy. Black-Right-Pointing-Pointer The sample quality was improved by gradient buffer layer.

  13. Ab initio density functional theory study of non-polar (101¯0), (112¯0) and semipolar (202¯1) GaN surfaces

    International Nuclear Information System (INIS)

    Mutombo, P.; Romanyuk, O.

    2014-01-01

    The atomic structures of non-polar GaN(101 ¯ 0), (112 ¯ 0) and semipolar GaN(202 ¯ 1), (202 ¯ 1 ¯ ) surfaces were studied using ab initio calculations within density functional theory. The bulk-like truncated (1 × 1) structure with buckled Ga-N or Ga-Ga dimers was found stable on the non-polar GaN(101 ¯ 0) surface in agreement with previous works. Ga-N heterodimers were found energetically stable on the GaN(112 ¯ 0)-(1 × 1) surface. The formation of vacancies and substitution site defects was found unfavorable for non-polar GaN surfaces. Semipolar GaN(202 ¯ 1)-(1 × 1) surface unit cells consist of non-polar (101 ¯ 0) and semipolar (101 ¯ 1) nano-facets. The (101 ¯ 1) nano-facets consist of two-fold coordinated atoms, which form N-N dimers within a (2 × 1) surface unit cell on a GaN(202 ¯ 1) surface. Dimers are not formed on the GaN(202 ¯ 1 ¯ ) surface. The stability of the surfaces with single (101 ¯ 0) or (101 ¯ 1) nano-facets was analyzed. A single non-polar (101 ¯ 0)-(1 × 1) nano-facet was found stable on the GaN(202 ¯ 1) surface, but unstable on the GaN(202 ¯ 1 ¯ ) surface. A single (101 ¯ 1) nano-facet was found unstable. Semipolar GaN surfaces with (202 ¯ 1) and (202 ¯ 1 ¯ ) polarity can be stabilized with a Ga overlayer at Ga-rich experimental conditions.

  14. Comparison of the photoemission behaviour between negative electron affinity GaAs and GaN photocathodes

    International Nuclear Information System (INIS)

    Zhang Yi-Jun; Zou Ji-Jun; Wang Xiao-Hui; Chang Ben-Kang; Qian Yun-Sheng; Zhang Jun-Ju; Gao Pin

    2011-01-01

    In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoemission behaviour, namely the activation process and quantum yield decay, between the two typical types of III—V compound photocathodes have been investigated using a multi-information measurement system. The activation experiment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs—O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes. (interdisciplinary physics and related areas of science and technology)

  15. Optical Properties of GaN and Other III-Nitride Semiconductor Materials Studied by Variable Angle Spectroscopic Ellipsometry

    National Research Council Canada - National Science Library

    Yao, Huade

    2000-01-01

    .... It is for the first time, the ordinary and extraordinary optical constants of the important III-Nitride materials, GaN, AlN and sapphire, have been determined by variable angle spectroscopic ellipsometry (VASE...

  16. Structural characterization of thick (11 anti 22) GaN layers grown by HVPE on m-plane sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Usikov, Alexander; Soukhoveev, Vitali; Shapovalov, Lisa; Syrkin, Alexander; Ivantsov, Vladimir; Scanlan, Bernard [Technologies and Devices International, Oxford Instruments Company, 12214 Plum Orchard Dr., Silver Spring, MD 20852 (United States); Nikiforov, Alexey [Department of Electrical and Computer Engineering, Boston University, 8 Saint Mary' s Street, Boston, MA 02215 (United States); Strittmatter, Andre; Johnson, Noble [Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304 (United States); Zheng, Jian-Guo [Materials Characterization Center, LEXI/Calit2, University of California, Irvine, CA 92697 (United States); Spiberg, Philippe; El-Ghoroury, Hussein [Ostendo Technologies, Inc., 6185 Paseo del Norte, Ste. 200, Carlsbad, CA 92011 (United States)

    2010-06-15

    This paper reports structural characterization of thick (11 anti 22)-oriented GaN layers by means of XRD, TEM, and micro- CL. The semi-polar (11 anti 22) GaN layers were grown on m-plane sapphire substrates by HVPE. Their structural quality improved with thickness. Threading dislocation density of 3 x 10{sup 8} cm{sup -2} and stacking faults density of 4 x 10{sup 4} cm{sup -1} were measured at the surface of 20 {mu}m thick (11 anti 22) GaN layers. The semi-polar GaN layers were used as template substrates to grow InGaN/GaN MQW heterostructures by MOCVD that demonstrated optically pumped lasing at 500 nm wavelength. The results demonstrate the longest wavelength yet reported for a photo-pumped laser on template substrates. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  17. Integrated Production of Ultra-Low Defect GaN Films and Devices for High-Power Amplifiers, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — High quality GaN epitaxial films are key to current efforts for development of both high-power/high-speed electronic devices and optoelectronic devices. In fact,...

  18. 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

    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...... 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...

  19. The structure, morphology and Raman scattering study on Mn-implanted nonpolar a-plane GaN films

    International Nuclear Information System (INIS)

    Sun Lili; Yan Fawang; Zhang Huixiao; Wang Junxi; Zeng Yiping; Wang Guohong; Li Jinmin

    2009-01-01

    Dilute magnetic nonpolar GaN films with a Curie temperature above room temperature have been fabricated by implanting Mn ions into unintentionally doped nonpolar a-plane (112-bar0) GaN films and a subsequent rapid thermal annealing (RTA) process. The impact of the implantation and RTA on the structure and morphology of the nonpolar GaN films is studied in this paper. The scanning electron microscopy analysis shows that the RTA process can effectively recover the implantation-induced damage to the surface morphology of the sample. The X-ray diffraction and micro-Raman scattering spectroscopy analyses show that the RTA process can just partially recover the implantation-induced crystal deterioration. Therefore, the quality of the Mn-implanted nonpolar GaN films should be improved further for the application in spintronic devices.

  20. Integrated Production of Ultra-Low Defect GaN Films and Devices for High-Power Amplifiers, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — High quality GaN epitaxial films are one of the keys to current efforts for development of both high-power/high-speed electronic devices and optoelectronic devices....

  1. 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.

  2. Broadband 1.2- and 2.4-mm Gallium Nitride (GaN) Power Amplifier Designs

    Science.gov (United States)

    2017-10-01

    ARL-TR-8180 ● OCT 2017 US Army Research Laboratory Broadband 1.2- and 2.4-mm Gallium Nitride (GaN) Power Amplifier Designs by...Nitride (GaN) Power Amplifier Designs by John E Penn Sensors and Electron Devices Directorate, ARL Approved for...should be aware that notwithstanding any other provision of law , no person shall be subject to any penalty for failing to comply with a collection of

  3. 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.

  4. Planar Homojunction Gallium Nitride (GaN) P-i-N Device Evaluated for Betavoltaic Energy Conversion: Measurement and Analysis

    Science.gov (United States)

    2016-09-01

    7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) US Army Research Laboratory ATTN: RDRL-SED-E 2800 Powder Mill Road Adelphi, MD 20783-1138...3). 10. Wang G-q, Yang , Liu. Electrical performance of GaN diode as betavoltaic isotope battery energy converter. Atomic Energy Sci and Tech...Conference, Orlando, FL, 2005 Jan 3. 16. Li F , Gao X, Yuan Y, Yuan J, Lu M. GaN PIN betavoltaic nuclear batteries. Science China Technological

  5. Effects of material growth technique and Mg doping on Er3+ photoluminescence in Er-implanted GaN

    International Nuclear Information System (INIS)

    Kim, S.; Henry, R. L.; Wickenden, A. E.; Koleske, D. D.; Rhee, S. J.; White, J. O.; Myoung, J. M.; Kim, K.; Li, X.; Coleman, J. J.

    2001-01-01

    Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies have been carried out at 6 K on the ∼1540 nm 4 I 13/2 - 4 I 15/2 emissions of Er 3+ in Er-implanted and annealed GaN. These studies revealed the existence of multiple Er 3+ centers and associated PL spectra in Er-implanted GaN films grown by metalorganic chemical vapor deposition, hydride vapor phase epitaxy, and molecular beam epitaxy. The results demonstrate that the multiple Er 3+ PL centers and below-gap defect-related absorption bands by which they are selectively excited are universal features of Er-implanted GaN grown by different techniques. It is suggested that implantation-induced defects common to all the GaN samples are responsible for the Er site distortions that give rise to the distinctive, selectively excited Er 3+ PL spectra. The investigations of selectively excited Er 3+ PL and PLE spectra have also been extended to Er-implanted samples of Mg-doped GaN grown by various techniques. In each of these samples, the so-called violet-pumped Er 3+ PL band and its associated broad violet PLE band are significantly enhanced relative to the PL and PLE of the other selectively excited Er 3+ PL centers. More importantly, the violet-pumped Er 3+ PL spectrum dominates the above-gap excited Er 3+ PL spectrum of Er-implanted Mg-doped GaN, whereas it was unobservable under above-gap excitation in Er-implanted undoped GaN. These results confirm the hypothesis that appropriate codopants can increase the efficiency of trap-mediated above-gap excitation of Er 3+ emission in Er-implanted GaN. [copyright] 2001 American Institute of Physics

  6. Effect of strain on space charge layer in GaN nanowires investigated by in-situ off-axis electron holography

    Directory of Open Access Journals (Sweden)

    Xiao Chen

    2017-04-01

    Full Text Available Effect of strain on space charge (SC layer in nanowires (NWs has been examined by in situ off-axis electron holography, where GaN NWs attach to an Au electrode inside a transmission electron microscope (TEM. Based on the phase image reconstructed from the complex hologram, the width of SC layer in a strained GaN NW is significantly reduced to about 60 nm, comparing to the 85 nm of the unstrained NW. About 29% reduction of the SC layer in the strained GaN NW resulted from significant decrease of electrons flowed from the GaN into Au. First principle calculations show that the strain reduced bandgap of GaN, narrowing the difference between GaN NW and Au electrode in Fermi level.

  7. Formation of distinctive structures of GaN by inductively-coupled-plasma and reactive ion etching under optimized chemical etching conditions

    Directory of Open Access Journals (Sweden)

    N. Okada

    2017-06-01

    Full Text Available We focused on inductively coupled plasma and reactive ion etching (ICP–RIE for etching GaN and tried to fabricate distinctive GaN structures under optimized chemical etching conditions. To determine the optimum chemical etching conditions, the flow rates of Ar and Cl2, ICP power, and chamber pressure were varied in the etching of c-plane GaN layers with stripe patterns. It was determined that the combination of Ar and Cl2 flow rates of 100 sccm, chamber pressure of 7 Pa, and ICP power of 800 W resulted in the most enhanced reaction, yielding distinctive GaN structures such as pillars with inverted mesa structures for c-plane GaN and a semipolar GaN layer with asymmetric inclined sidewalls. The selectivity and etching rate were also investigated.

  8. The possibly important role played by Ga2O3 during the activation of GaN photocathode

    International Nuclear Information System (INIS)

    Fu, Xiaoqian; Wang, Honggang; Zhang, Junju; Li, Zhiming; Cui, Shiyao; Zhang, Lejuan

    2015-01-01

    Three different chemical solutions are used to remove the possible contamination on GaN surface, while Ga 2 O 3 is still found at the surface. After thermal annealing at 710 °C in the ultrahigh vacuum (UHV) chamber and activated with Cs/O, all the GaN samples are successfully activated to the effective negative electron affinity (NEA) photocathodes. Among all samples, the GaN sample with the highest content of Ga 2 O 3 after chemical cleaning obtains the highest quantum efficiency. By analyzing the property of Ga 2 O 3 , the surface processing results, and electron affinity variations during Cs and Cs/O 2 deposition on GaN of other groups, it is suggested that before the adsorption of Cs, Ga 2 O 3 is not completely removed from GaN surface in our samples, which will combine with Cs and lead to a large decrease in electron affinity. Furthermore, the effective NEA is formed for GaN photocathode, along with the surface downward band bending. Based on this assumption, a new dipole model Ga 2 O 3 -Cs is suggested, and the experimental effects are explained and discussed

  9. The possibly important role played by Ga2O3 during the activation of GaN photocathode

    Science.gov (United States)

    Fu, Xiaoqian; Wang, Honggang; Zhang, Junju; Li, Zhiming; Cui, Shiyao; Zhang, Lejuan

    2015-08-01

    Three different chemical solutions are used to remove the possible contamination on GaN surface, while Ga2O3 is still found at the surface. After thermal annealing at 710 °C in the ultrahigh vacuum (UHV) chamber and activated with Cs/O, all the GaN samples are successfully activated to the effective negative electron affinity (NEA) photocathodes. Among all samples, the GaN sample with the highest content of Ga2O3 after chemical cleaning obtains the highest quantum efficiency. By analyzing the property of Ga2O3, the surface processing results, and electron affinity variations during Cs and Cs/O2 deposition on GaN of other groups, it is suggested that before the adsorption of Cs, Ga2O3 is not completely removed from GaN surface in our samples, which will combine with Cs and lead to a large decrease in electron affinity. Furthermore, the effective NEA is formed for GaN photocathode, along with the surface downward band bending. Based on this assumption, a new dipole model Ga2O3-Cs is suggested, and the experimental effects are explained and discussed.

  10. 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.

  11. Structure Shift of GaN Among Nanowall Network, Nanocolumn, and Compact Film Grown on Si (111) by MBE.

    Science.gov (United States)

    Zhong, Aihua; Fan, Ping; Zhong, Yuanting; Zhang, Dongping; Li, Fu; Luo, Jingting; Xie, Yizhu; Hane, Kazuhiro

    2018-02-13

    Structure shift of GaN nanowall network, nanocolumn, and compact film were successfully obtained on Si (111) by plasma-assisted molecular beam epitaxy (MBE). As is expected, growth of the GaN nanocolumns was observed in N-rich condition on bare Si, and the growth shifted to compact film when the Ga flux was improved. Interestingly, if an aluminum (Al) pre-deposition for 40 s was carried out prior to the GaN growth, GaN grows in the form of the nanowall network. Results show that the pre-deposited Al exits in the form of droplets with typical diameter and height of ~ 80 and ~ 6.7 nm, respectively. A growth model for the nanowall network is proposed and the growth mechanism is discussed. GaN grows in the area without Al droplets while the growth above Al droplets is hindered, resulting in the formation of continuous GaN nanowall network that removes the obstacles of nano-device fabrication.

  12. Leakage currents and Fermi-level shifts in GaN layers upon iron and carbon-doping

    Science.gov (United States)

    Fariza, A.; Lesnik, A.; Neugebauer, S.; Wieneke, M.; Hennig, J.; Bläsing, J.; Witte, H.; Dadgar, A.; Strittmatter, A.

    2017-07-01

    Semi-insulating GaN is a prerequisite for lateral high frequency and high power electronic devices to isolate the device region from parasitic conductive channels. The commonly used dopants for achieving semi-insulating GaN, Fe, and C cause distinct properties of GaN layers since the Fermi-level is located either above (Fe) or below (C) the midgap position. In this study, precursor-based doping of GaN in metalorganic vapor phase epitaxy is used at otherwise identical growth conditions to control the dopant concentrations in the layer. Using electric force microscopy, we have investigated the contact potentials of Fe- and C-doped samples with respect to a cobalt metal probe tip in dependence of on the dopant concentration. While in Fe-doped samples the sign of the contact potential is constant, a change from positive to negative contact potential values is observed at high carbon concentrations, indicating the shift of the Fermi-level below the midgap position. In vertical transport measurements, C-doped GaN layers with a dopant concentration of 4.6 × 1018 cm-3 exhibit up to 5 orders of magnitude lower dark current at room temperature and significantly lower temperature dependence than Fe-doped samples with a similar dopant concentration. Therefore, precursor-based carbon doping is the superior doping technique to achieve semi-insulating GaN.

  13. 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.

  14. Effect of growth temperature on defects in epitaxial GaN film grown by plasma assisted molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    S. S. Kushvaha

    2014-02-01

    Full Text Available We report the effect of growth temperature on defect states of GaN epitaxial layers grown on 3.5 μm thick GaN epi-layer on sapphire (0001 substrates using plasma assisted molecular beam epitaxy. The GaN samples grown at three different substrate temperatures at 730, 740 and 750 °C were characterized using atomic force microscopy and photoluminescence spectroscopy. The atomic force microscopy images of these samples show the presence of small surface and large hexagonal pits on the GaN film surfaces. The surface defect density of high temperature grown sample is smaller (4.0 × 108 cm−2 at 750 °C than that of the low temperature grown sample (1.1 × 109 cm−2 at 730 °C. A correlation between growth temperature and concentration of deep centre defect states from photoluminescence spectra is also presented. The GaN film grown at 750 °C exhibits the lowest defect concentration which confirms that the growth temperature strongly influences the surface morphology and affects the optical properties of the GaN epitaxial films.

  15. 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

  16. Thermodynamical properties of III-V nitrides and crystal growth of GaN at high N 2 pressure

    Science.gov (United States)

    Porowski, S.; Grzegory, I.

    1997-06-01

    In this paper, thermodynamical properties of AIN, GaN and InN are considered. It is shown that significant differences in melting conditions, thermal stability and solubilities in liquid group III metals lead to different possibilities of growing crystals from high temperature solutions, at N 2 pressure up to 20 kbar. It is shown that the best conditions for crystal growth at available pressure and temperature conditions can be achieved for GaN. High quality 6-10 mm single crystals of GaN have been grown at high N 2 pressure in 60-150 h processes. The mechanisms of nucleation and growth of GaN crystals are discussed on the basis of the experimental results. The crystallization of AlN is less efficient due to relatively low solubility of AlN in liquid Al. Possibility for the growth of InN crystals is strongly limited since this compound loses its stability at T > 600°C, even at 2 GPa N 2 pressure. The crystals of GaN grown at high pressure are the first crystals of this material used for homoepitaxial layer deposition. Both MOCVD and MBE methods have been successfully applied. Structural, electrical and optical properties of both GaN single crystals and homoepitaxial layers are reviewed.

  17. Materials physics and device development for improved efficiency of GaN HEMT high power amplifiers.

    Energy Technology Data Exchange (ETDEWEB)

    Kurtz, Steven Ross; Follstaedt, David Martin; Wright, Alan Francis; Baca, Albert G.; Briggs, Ronald D.; Provencio, Paula Polyak; Missert, Nancy A.; Allerman, Andrew Alan; Marsh, Phil F.; Koleske, Daniel David; Lee, Stephen Roger; Shul, Randy John; Seager, Carleton Hoover; Tigges, Christopher P.

    2005-12-01

    GaN-based microwave power amplifiers have been identified as critical components in Sandia's next generation micro-Synthetic-Aperture-Radar (SAR) operating at X-band and Ku-band (10-18 GHz). To miniaturize SAR, GaN-based amplifiers are necessary to replace bulky traveling wave tubes. Specifically, for micro-SAR development, highly reliable GaN high electron mobility transistors (HEMTs), which have delivered a factor of 10 times improvement in power performance compared to GaAs, need to be developed. Despite the great promise of GaN HEMTs, problems associated with nitride materials growth currently limit gain, linearity, power-added-efficiency, reproducibility, and reliability. These material quality issues are primarily due to heteroepitaxial growth of GaN on lattice mismatched substrates. Because SiC provides the best lattice match and thermal conductivity, SiC is currently the substrate of choice for GaN-based microwave amplifiers. Obviously for GaN-based HEMTs to fully realize their tremendous promise, several challenges related to GaN heteroepitaxy on SiC must be solved. For this LDRD, we conducted a concerted effort to resolve materials issues through in-depth research on GaN/AlGaN growth on SiC. Repeatable growth processes were developed which enabled basic studies of these device layers as well as full fabrication of microwave amplifiers. Detailed studies of the GaN and AlGaN growth of SiC were conducted and techniques to measure the structural and electrical properties of the layers were developed. Problems that limit device performance were investigated, including electron traps, dislocations, the quality of semi-insulating GaN, the GaN/AlGaN interface roughness, and surface pinning of the AlGaN gate. Surface charge was reduced by developing silicon nitride passivation. Constant feedback between material properties, physical understanding, and device performance enabled rapid progress which eventually led to the successful fabrication of state of the

  18. Influence of vicinal sapphire substrate on the properties of N-polar GaN films grown by metal-organic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Zhiyu; Zhang, Jincheng, E-mail: jchzhang@xidian.edu.cn; Xu, Shengrui; Chen, Zhibin; Yang, Shuangyong; Tian, Kun; Hao, Yue [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an, Shaanxi 710071 (China); Su, Xujun [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou, Jiangsu 215123 (China); Shi, Xuefang [School of Advanced Materials and Nanotechnology, Xidian University, Xi' an, Shaanxi 710071 (China)

    2014-08-25

    The influence of vicinal sapphire substrates on the growth of N-polar GaN films by metal-organic chemical vapor deposition is investigated. Smooth GaN films without hexagonal surface feature are obtained on vicinal substrate. Transmission electron microscope results reveal that basal-plane stacking faults are formed in GaN on vicinal substrate, leading to a reduction in threading dislocation density. Furthermore, it has been found that there is a weaker yellow luminescence in GaN on vicinal substrate than that on (0001) substrate, which might be explained by the different trends of the carbon impurity incorporation.

  19. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    International Nuclear Information System (INIS)

    Hodges, C.; Pomeroy, J.; Kuball, M.

    2014-01-01

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate

  20. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    Energy Technology Data Exchange (ETDEWEB)

    Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Pomeroy, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)

    2014-02-14

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  1. Dependence of local electronic structure in p-type GaN on crystal polarity and presence of inversion domain boundaries

    OpenAIRE

    Zhou, X; Yu, E T; Green, D S; Speck, J S

    2006-01-01

    Scanning probe techniques including scanning capacitance microscopy, scanning capacitance spectroscopy, scanning Kelvin probe force microscopy, and atomic force microscopy have been used to assess structure and local electronic properties of Ga-face and N-face p-type GaN and of inversion domain boundaries in p-type GaN. Epitaxial layers of p-type GaN were grown by molecular-beam epitaxy, and by adjustment of the Ga:N flux ratio samples containing both Ga-face and N-face material were obtained...

  2. Ambient-temperature diffusion and gettering of Pt atoms in GaN with surface defect region under 60Co gamma or MeV electron irradiation

    Science.gov (United States)

    Hou, Ruixiang; Li, Lei; Fang, Xin; Xie, Ziang; Li, Shuti; Song, Weidong; Huang, Rong; Zhang, Jicai; Huang, Zengli; Li, Qiangjie; Xu, Wanjing; Fu, Engang; Qin, G. G.

    2018-01-01

    Generally, the diffusion and gettering of impurities in GaN needs high temperature. Calculated with the ambient-temperature extrapolation value of the high temperature diffusivity of Pt atoms in GaN reported in literature, the time required for Pt atoms diffusing 1 nm in GaN at ambient temperature is about 19 years. Therefore, the ambient-temperature diffusion and gettering of Pt atoms in GaN can hardly be observed. In this work, the ambient-temperature diffusion and gettering of Pt atoms in GaN is reported for the first time. It is demonstrated by use of secondary ion mass spectroscopy that in the condition of introducing a defect region on the GaN film surface by plasma, and subsequently, irradiated by 60Co gamma-ray or 3 MeV electrons, the ambient-temperature diffusion and gettering of Pt atoms in GaN can be detected. It is more obvious with larger irradiation dose and higher plasma power. With a similar surface defect region, the ambient-temperature diffusion and gettering of Pt atoms in GaN stimulated by 3 MeV electron irradiation is more marked than that stimulated by gamma irradiation. The physical mechanism of ambient-temperature diffusion and gettering of Pt atoms in a GaN film with a surface defect region stimulated by gamma or MeV electron irradiation is discussed.

  3. Ku and K band GaN High Power Amplifier MMICs

    Science.gov (United States)

    2017-03-20

    15.5 GHz 50W GaN Power Amplifier, Qorvo Datasheet , http://www.triquint.com/products/p/TGA2239-CP. 6. Y.S.Noh et al, “Ku-band GaN HPA MMIC with high...Power Amplifier, Wolfspeed Datasheet , http://www.wolfspeed.com/media/downloads/478/ CMPA1D1E025F.pdf. 8. K.Yamauchi et al, “A 45% Power Added...Qorvo Datasheet , http://www.triquint.com/products/p/TGA2219. 10. C.Friesicke et al, “A 40 dBm AlGaN/GaN HEMT Power Amplifier MMIC for SatCom Applications

  4. Vacancy complexes induce long-range ferromagnetism in GaN

    KAUST Repository

    Zhang, Zhenkui

    2014-11-14

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μB, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  5. Resolution characteristics for reflection-mode exponential-doping GaN photocathode.

    Science.gov (United States)

    Wang, Honggang; Qian, Yunsheng; Du, Yujie; Xu, Yuan; Lu, Liubing; Chang, Benkang

    2014-01-20

    According to the expression for modulation transfer function obtained by solving the established 2D continuity equation, the resolution characteristics for reflection-mode exponential-doping and uniform-doping GaN photocathodes have been calculated and comparatively analyzed. These calculated results show that the exponential-doping structure can upgrade not only the resolution capability but also the quantum efficiency for a GaN photocathode. The improvement mechanism is different from the approach for high resolution applied by reducing Te and L(D) or increasing S(V), which leads to low quantum efficiency. The main contribution factor of this improvement is that the mechanism that transports electrons toward the NEA surface is facilitated by the built-in electric field formed by this exponential-doping structure, and the corresponding lateral diffusion is reduced.

  6. High quantum efficiency of depth grade doping negative-electron-affinity GaN photocathode

    Science.gov (United States)

    Guo, Xiangyang; Wang, Xiaohui; Chang, Benkang; Zhang, Yijun; Gao, Pin

    2010-08-01

    A depth grade doping sample gallium nitride (GaN) photocathode was designed to obtain an extremely high quantum efficiency (QE). Two other uniform doping samples were prepared in the same procedure as contrast. The calibrated QE curves were achieved; by comparing theoretical calculated values with the experimental QE plots, the escape probability and diffusion length were fitted. The QE value of gradient doping sample is as high as 68.7% at 5.17 eV; the diffusion length of gradient doping sample is fitted to be 250 nm which is much higher than uniform doping samples. That explains why depth-grade-doping can improve the QE of GaN photocathode significantly.

  7. Germanium doping of GaN by metalorganic chemical vapor deposition for polarization screening applications

    KAUST Repository

    Young, N.G.

    2016-10-01

    We demonstrate n-type doping of GaN with Ge by MOCVD at high concentrations that are necessary to fully screen the polarization fields in c-plane InGaN/GaN quantum wells. Hall measurements show linear Ge incorporation with dopant flow rate and carrier concentrations exceeding 1×10 cm. GaN:Ge layers exhibit excellent electron mobility, high conductivity, and contact resistivity comparable to the best unannealed contacts to Si-doped GaN. However, the surface morphology begins to degrade with Ge concentrations above 1×10 cm, resulting in severe step bunching and a network of plateaus and trenches, even in layers as thin as 10 nm.

  8. Origin of orange color in nominally undoped HVPE GaN crystals

    Science.gov (United States)

    Zimmermann, F.; Beyer, F. C.; Gärtner, G.; Röder, C.; Son, N. T.; Janzén, E.; Veselá, D.; Lorinčík, J.; Hofmann, P.; Krupinski, M.; Mikolajick, T.; Habel, F.; Leibiger, G.; Heitmann, J.

    2017-08-01

    In this article we investigated unintentionally doped (UID) GaN grown by hydride vapor phase epitaxy (HVPE) with respect to point defects and impurity concentration. The samples were orange tinted to different extent. Optical analysis was performed by micro-photoluminescence and absorption spectroscopy. Absorption measurements revealed an absorption peak at 1.5 eV related to an internal transition in Mn3+ impurities and a second band with low energy onset at 1.9 eV, both increasing with the extent of orange color. Electron paramagnetic resonance investigations showed the presence of Mn2+ and Fe3+ in the colored crystals. The overall impurity concentration was verified by secondary ion mass spectrometry. Orange tint is associated with an increase of transition metal contamination, especially Mn. Based on these observations we suggest that the orange coloring in the investigated UID HVPE GaN samples is caused by the presence of Mn impurities.

  9. 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.

  10. Study of residual gas adsorption on GaN nanowire arrays photocathode

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Sihao; Liu, Lei, E-mail: liu1133_cn@sina.com.cn; Diao, Yu; Kong, Yike

    2017-05-01

    Highlights: • H{sub 2}O is more easily to absorb on the nanowire surface. • The work function increase after residual gas adsorption. • Bandgaps of the nanowire increase slightly. • Absorption coefficient is reduced and moves to higher energy side. - Abstract: In order to find out the influences of residual gas on GaN nanowire arrays photocathode, the optoelectronic properties of adsorption system are calculated on the basis of first principles. Results suggest that the residual gas adsorption will increase the work function and introduce a dipole moment with a direction from the nanowire to the adsorbates. The surface structures are changed and electrons transfer from nanowire to gas molecule. The bandgaps are enhanced after adsorption. Besides, the peak of absorption coefficients is reduced and moves to higher energy side. It is discovered that residual gas will drastically degrade the characteristics and lifetime of GaN nanowire arrays photocathode.

  11. Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates

    KAUST Repository

    Hwang, David

    2016-09-23

    We demonstrate a thin-film flip-chip (TFFC) process for LEDs grown on freestanding c-plane GaN substrates. LEDs are transferred from a bulk GaN substrate to a sapphire submount via a photoelectrochemical (PEC) undercut etch. This PEC liftoff method allows for substrate reuse and exposes the N-face of the LEDs for additional roughening. The LEDs emitted at a wavelength of 432 nm with a turn on voltage of ~3 V. Etching the LEDs in heated KOH after transferring them to a sapphire submount increased the peak external quantum efficiency (EQE) by 42.5% from 9.9% (unintentionally roughened) to 14.1% (intentionally roughened).

  12. 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.

  13. Modeling and simulation of GaN step-up power switched capacitor converter

    Science.gov (United States)

    Alateeq, Ayoob S.; Almalaq, Yasser A.; Matin, Mohammad A.

    2017-08-01

    This paper discusses a proposed DC-DC switched capacitor converter for low voltage electronic products. The proposed converter is a two-level power switched capacitor (PSC) which is a boost converter. The suitability to convert a voltage into four times higher than its input is one of the converter's objectives. Because of the proposed two-level PSC consist of eight switches and five capacitors, it occupies a small area of the electronic products. The eight switches were selected to be GaN transistors to maintain the efficiency at high rated power or high temperatures. The LTSpice simulator was used to test the proposed model. Since the design contains semiconductor elements such (GaN transistor), then 10% error is a reasonable variance between the mathematical and simulation results.

  14. (-201) β-Gallium oxide substrate for high quality GaN materials

    KAUST Repository

    Roqan, Iman S.

    2015-03-13

    (-201) oriented β-Ga2O3 has the potential to be used as a transparent and conductive substrate for GaN-growth. The key advantages of Ga2O3 are its small lattice mismatches (4.7%), appropriate structural, thermal and electrical properties and a competitive price compared to other substrates. Optical characterization show that GaN layers grown on (-201) oriented β-Ga2O3 are dominated by intense bandedge emission with a high luminescence efficiency. Atomic force microscopy studies show a modest threading dislocation density of ~108 cm-2, while complementary Raman spectroscopy indicates that the GaN epilayer is of high quality with slight compressive strain. Room temperature time-findings suggest that the limitation of the photoluminescence lifetime (~500 ps) is due to nonradiative recombination arising from threading dislocation. Therefore, by optimizing the growth conditions, high quality material with significant optical efficiency can be obtained.

  15. 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.

  16. Electron transport in bulk GaN under ultrashort high-electric field transient

    Science.gov (United States)

    Korotyeyev, V. V.; Kochelap, V. A.; Kim, K. W.

    2011-10-01

    We have investigated nonlinear electron transport in GaN induced by high-electric field transients by analyzing the temporal dependence of the electron drift velocity and temperature. For picosecond transients, our calculations have established that the electron dynamics retain almost all the features of the steady-state velocity-field characteristics including the portion with negative differential conductivity. It was also found that transient currents in GaN samples give rise to the THz re-emission effect—radiation of electromagnetic field, temporal and spectral properties of which directly relate to the velocity-field characteristics of the sample. The results clearly indicate that existing methods for the generation of high-electric field transients and subpicosecond signal measurements can be applied to the characterization of hot electron transport at ultrahigh fields while avoiding Joule self-heating, hot phonon accumulation and other undesirable effects.

  17. Hydrogen interaction with GaN metal-insulator-semiconductor diodes

    International Nuclear Information System (INIS)

    Irokawa, Y.

    2012-01-01

    Interaction mechanism of hydrogen with GaN metal-insulator-semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO 2 dielectric, the current-voltage (I-V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler-Nordheim tunneling to Poole-Frenkel emission. In sharp contrast, Pt-Si x N y -GaN diodes exhibit Poole-Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance-voltage (C-V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.

  18. Improved large-signal GaN HEMT model suitable for intermodulation distortion analysis

    Science.gov (United States)

    Liu, Lin-Sheng; Luo, Ji

    2011-12-01

    In this article, a complete empirical large-signal model of GaN high electron-mobility transistors (HEMTs) is presented. The developed nonlinear model employs differentiable trigonometric function continuously to describe the drain-source current characteristic and its higher order derivatives, making itself suitable for the simulation of intermodulation distortion (IMD) in microwave circuits. Besides, an improved charge-conservative gate charge model is proposed to accurately trace the nonlinear gate-source and gate-drain capacitances. The model validity is demonstrated for different 0.25-µm gate-length GaN HEMTs. The simulation results of small-signal S-parameters, radio frequency (RF) large-signal power performances and two-tone IMD products show an excellent agreement with the measured data.

  19. 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.

  20. Molecular Beam Epitaxy of GaN Nanowires on Epitaxial Graphene.

    Science.gov (United States)

    Fernández-Garrido, Sergio; Ramsteiner, Manfred; Gao, Guanhui; Galves, Lauren A; Sharma, Bharat; Corfdir, Pierre; Calabrese, Gabriele; de Souza Schiaber, Ziani; Pfüller, Carsten; Trampert, Achim; Lopes, João Marcelo J; Brandt, Oliver; Geelhaar, Lutz

    2017-09-13

    We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial graphene layer structures synthesized on SiC. The different structures differ mainly in their total number of graphene layers. Because graphene is found to be etched under active N exposure, the direct growth of GaN nanowires on graphene is only achieved on multilayer graphene structures. The analysis of the nanowire ensembles prepared on multilayer graphene by Raman spectroscopy and transmission electron microscopy reveals the presence of graphene underneath as well as in between nanowires, as desired for the use of this material as contact layer in nanowire-based devices. The nanowires nucleate preferentially at step edges, are vertical, well aligned, epitaxial, and of comparable structural quality as similar structures fabricated on conventional substrates.

  1. High-performance N-polar GaN enhancement-mode device technology

    International Nuclear Information System (INIS)

    Singisetti, Uttam; Wong, Man Hoi; Mishra, Umesh K

    2013-01-01

    In this paper, we report the recent progress in the high-frequency performance of enhancement-mode devices in the novel N-polar GaN technology and provide a pathway for further scaling. The intrinsic advantages of electron confinement, polarization doping of the back-barrier and the absence of a source barrier in N-polar GaN technology were leveraged with polarization engineering with a top barrier for enhancement mode operation and advanced self-aligned source/drain technology for low parasitic access resistances. The scalability of the device structures are explored in terms of short-channel effects and high-frequency performance. Low-field electron mobility in vertically scaled channel was also investigated providing insights on the scattering mechanism. (invited review)

  2. Inductively Coupled Plasma-Induced Etch Damage of GaN p-n Junctions

    International Nuclear Information System (INIS)

    SHUL, RANDY J.; ZHANG, LEI; BACA, ALBERT G.; WILLISON, CHRISTI LEE; HAN, JUNG; PEARTON, S.J.; REN, F.

    1999-01-01

    Plasma-induced etch damage can degrade the electrical and optical performance of III-V nitride electronic and photonic devices. We have investigated the etch-induced damage of an Inductively Coupled Plasma (ICP) etch system on the electrical performance of mesa-isolated GaN pn-junction diodes. GaN p-i-n mesa diodes were formed by Cl 2 /BCl 3 /Ar ICP etching under different plasma conditions. The reverse leakage current in the mesa diodes showed a strong relationship to chamber pressure, ion energy, and plasma flux. Plasma induced damage was minimized at moderate flux conditions (≤ 500 W), pressures ≥2 mTorr, and at ion energies below approximately -275 V

  3. Fabrication of high reflectivity nanoporous distributed Bragg reflectors by controlled electrochemical etching of GaN

    Science.gov (United States)

    Lee, Seung-Min; Kang, Jin-Ho; Lee, June Key; Ryu, Sang-Wan

    2016-09-01

    The nanoporous medium is a valuable feature of optical devices because of its variable optical refractive index with porosity. One important application is in a GaN-based vertical cavity surface emitting laser having a distributed Bragg reflector (DBR) composed of alternating nanoporous and bulk GaNs. However, optimization of the fabrication process for high reflectivity DBRs having wellcontrolled high reflection bands has not been studied yet. We used electrochemical etching to study the fabrication process of a nanoporous GaN DBR and analyzed the relationship between the morphology and optical reflectivity. Several electrolytes were examined for the formation of the optimized nanoporous structure. A highly reflective DBRs having reflectivity of ~100% were obtained over a wide wavelength range of 450-750 nm. Porosification of semiconductors into nanoporous layers could provide a high reflectivity DBR due to controlled index-contrast, which would be advantages for the construction of a high-Q optical cavity.

  4. Plasmon enhanced green GaN light-emitting diodes - Invited paper

    DEFF Research Database (Denmark)

    Ou, Haiyan; Fadil, Ahmed; Iida, Daisuke

    High-efficiency garnium nitride (GaN) based blue light-emitting diode (LED) paves the way for solid statelighting to take the place of the conventional incandescent bulbs and fluorescent light tubes.Compared to the traditional light sources, solid state lighting is more efficient, more flexible...... in spectral design, more compact etc. TheIII-nitride (GaN, InNetc.) semiconductors are attracting a lot of research effort because the combination of both could emit light with wavelength range from UV to infrared. Basically one material platform could provide all the solutions to light sources.However huge...... point of view, the efficiency of green LED is being improved by growing the GaInN material on non-polar or semi-polar surface of sapphire substrate. In parallel with the material growth effort, surface plasmons are implemented by taking use of the interactionbetween metals and active areas to increase...

  5. Surfactant assisted growth of MgO films on GaN

    Energy Technology Data Exchange (ETDEWEB)

    Paisley, E. A.; Shelton, T. C.; Collazo, R.; Sitar, Z.; Maria, J.-P. [Department of Materials Science and Engineering, North Carolina State University, Box 7919-1001 Capability Drive, RB1, Rm 322 Raleigh, North Carolina 27606 (United States); Christen, H. M.; Biegalski, M. D. [Oak Ridge National Laboratory, Center for Nanophase Materials Science, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831 (United States); Mita, S.

    2012-08-27

    Thin epitaxial films of <111> oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy and pulsed laser deposition using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface by stabilizing the {l_brace}111{r_brace} rocksalt facet. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100 Multiplication-Sign reduction in leakage current density for the surfactant-assisted samples. These data verify numerous predictions regarding the role of H-termination in regulating the habit of rocksalt crystals.

  6. Electrical transport phenomena in magnesium-doped p-type GaN

    Energy Technology Data Exchange (ETDEWEB)

    Konczewicz, Leszek; Contreras, Sylvie [Universite Montpellier 2 (France). Groupe d' Etude des Semiconducteurs; CNRS, UMR5650, Montpellier (France); Litwin-Staszewska, Elzbieta; Piotrzkowski, Ryszard; Dmowski, Leslaw [Institute of High Pressure Physics Unipress, Polish Academy of Sciences, Warsaw (Poland)

    2009-03-15

    In this paper we present the resistivity and Hall-effect measurements on p-type GaN doped with Mg. The experiments were carried out as a function of hydrostatic pressure up to 1200 MPa in the temperature range 260-400 K. Both bulk GaN crystals as well as GaN:Mg epilayers were studied. In the investigated samples the decrease of resistivity and increase of hole concentration under pressure was observed. Such a behavior, which is contrary to the n-type material, strongly suggests a decrease of the ionization energy of Mg acceptor (E{sub a}=183 meV) with pressure. This shift is very weak, less than -2 meV/GPa. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Defect-impurity complex induced long-range ferromagnetism in GaN nanowires

    KAUST Repository

    Assa Aravindh, S

    2015-12-14

    Present work investigates the structural, electronic and magnetic properties of Gd doped wurtzite GaN nanowires (NWs) oriented along the [0001] direction in presence of intrinsic defects by employing the GGA + U approximation. We find that Ga vacancy (VGa) exhibits lower formation energy compared to N vacancy. Further stabilization of point defects occurs due to the presence of Gd. The strength of ferromagnetism (FM) increases by additional positive charge induced by the VGa. Electronic structure analysis shows that VGa introduces defect levels in the band gap leading to ferromagnetic coupling due to the hybridization of the p states of the Ga and N atoms with the Gd d and f states. Ferromagnetic exchange coupling energy of 76.4 meV is obtained in presence of Gd-VGa complex; hence, the FM is largely determined by the cation vacancy-rare earth complex defects in GaN NWs.

  8. Arsenic in ZnO and GaN: substitutional cation or anion sites?

    CERN Document Server

    Wahl, Ulrich; Rita, Elisabete; Marques, Ana Claudia; Alves, Eduardo; Carvalho Soares, José

    2007-01-01

    We have determined the lattice location of ion implanted As in ZnO and GaN by means of conversion electron emission channeling from radioactive $^{73}$As. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites in ZnO but in its large majority substitutional Zn sites. Arsenic in ZnO is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system. In contrast, in GaN the preference of As for substitutional cation sites is less pronounced and about half of the implanted As atoms occupy Ga and the other half N sites. Apparently, the smaller size-mismatch between As and N and the chemical similarity of both elements make it feasible that As partly substitutes for N atoms.

  9. Spin diffusion in bulk GaN measured with MnAs spin injector

    KAUST Repository

    Jahangir, Shafat

    2012-07-16

    Spin injection and precession in bulk wurtzite n-GaN with different doping densities are demonstrated with a ferromagnetic MnAs contact using the three-terminal Hanle measurement technique. Theoretical analysis using minimum fitting parameters indicates that the spin accumulation is primarily in the n-GaN channel rather than at the ferromagnet (FM)/semiconductor (SC) interface states. Spin relaxation in GaN is interpreted in terms of the D’yakonov-Perel mechanism, yielding a maximum spin lifetime of 44 ps and a spin diffusion length of 175 nm at room temperature. Our results indicate that epitaxial ferromagnetic MnAs is a suitable high-temperature spin injector for GaN.

  10. 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.

  11. Inductively Coupled Plasma-Induced Etch Damage of GaN p-n Junctions

    Energy Technology Data Exchange (ETDEWEB)

    SHUL,RANDY J.; ZHANG,LEI; BACA,ALBERT G.; WILLISON,CHRISTI LEE; HAN,JUNG; PEARTON,S.J.; REN,F.

    1999-11-03

    Plasma-induced etch damage can degrade the electrical and optical performance of III-V nitride electronic and photonic devices. We have investigated the etch-induced damage of an Inductively Coupled Plasma (ICP) etch system on the electrical performance of mesa-isolated GaN pn-junction diodes. GaN p-i-n mesa diodes were formed by Cl{sub 2}/BCl{sub 3}/Ar ICP etching under different plasma conditions. The reverse leakage current in the mesa diodes showed a strong relationship to chamber pressure, ion energy, and plasma flux. Plasma induced damage was minimized at moderate flux conditions ({le} 500 W), pressures {ge}2 mTorr, and at ion energies below approximately -275 V.

  12. Analysis on the semantic evolution of Chinese Gan dialect from the perspective of cognition

    Directory of Open Access Journals (Sweden)

    Xiao Jiugen

    2016-01-01

    Full Text Available The meaning of a word is the reflection of social life, and it is the result of the cognition of the object, phenomenon and relationship through the mental activity. The development and changes of lexical mean-ings essentially reflect the development and change of people’s cognitive activities, so people’s cognitive aware-ness is reflected in words, which is also reflected in the word meaning evolution of Chinese Gan dialect. Whether in the extended way or pattern, the linkage, radiation, complex comprehensive changes of the lexical meaning of Gan dialect in Chinese, all follow a rule: The expression of the meaning in cognitive process will corresponding-ly change with the continuous deepening of human cognition.

  13. Rare earths in GaN and ZnO studied with the PAC method; Seltene Erden in GaN und ZnO untersucht mit der PAC-Methode

    Energy Technology Data Exchange (ETDEWEB)

    Nedelec, R.

    2007-07-01

    The present thesis deals with the implantation and annealing behaviour of two examples of large-band-gap semiconductors GaN and ZnO. The studies begin with the annealing behaviour of GaN after the implantation of {sup 172}Lu. For GaN the annealing process begins at low temperatures with the decreasing of the damping of the lattice frequency. At essentially higher temperatures finally the substitunial contribution increases. This behaviour is also observed for other probe nuclei in GaN. For ZnO the behaviour at low temperature is different. Both for {sup 172}Lu and for {sup 181}Hf the damping is already after the implantation very low. The increasement of the substitutional contribution occurs like in GaN at higher temperatures. Thereafter for GaN and ZnO PAC spectra were token up at different measurement temperatures between 25 and 873 K. For {sup 172}Lu in GaN and in ZnO a strong temperature dependence of the lattice field gradient was observed. Also for {sup 181}Hf in ZnO a strong temperature dependence is observed. For {sup 172}Lu by means of a model for the interaction of quadrupole moments of electronic shells with the nucleus a lattice field gradient of {+-}5.9.10{sup 15} Vcm{sup -2} could be determined. For {sup 172}Lu in ZnO the model yields at 293 K a lattice field gradient of +14.10{sup 15} Vcm{sup -2} respectively -13.10{sup 15} Vcm{sup -2}. The corrsponding measurement with {sup 181}Hf yields a lattice field gradient of {+-}5.7.10{sup 15} Vcm{sup -2}.

  14. Das Erbrecht in weltgeschichtlicher Entwickelung (1824–1835 von Eduard Gans

    Directory of Open Access Journals (Sweden)

    Corrado Bertani

    2007-01-01

    Full Text Available Das Erbrecht in weltgeschichtlicher Entwickelung, although unquestionably the most ambitious work of Eduard Gans, has hitherto been generally neglected by scholars. While some parts of it are quite well known because of their polemical arguments against Savigny’s »Historical School of Law«, the way Gans tried to develop his own project of a »philosophical« history of succession law has received far less attention. This voluminous work, which encompasses the history of human civilisation from Ancient China and India up to the Middle Ages, relies on Hegel’s conceptualisation of world history as a key for interpreting the documents containing the law of succession of the most relevant nations. However, this is not applied consistently throughout, suggesting that, despite seeming to be a homogeneous study, his Erbrecht was a work-in-progress with three main stages of composition. In the most Hegelian part of his work – vol. 2: Das Römische Erbrecht – Gans manages to reconcile his philosophical approach with his juridical background. In the introduction and in the first chapter he follows the historical course of the Roman legislation on inheritance and succession from ancient times prior to the XII Tabulae up to Justinian’s codification, whereas in the remaining five chapters he attempts to reconstruct the whole system of the Roman law of succession from a dogmatic point of view. While in the former case the systematic principle was drawn from Hegel’s lectures on the Philosophy of History, in the latter case Gans followed current academic practice in reconstructing the Roman law of succession in a systematic way, nevertheless stressing that such a systemcould not satisfy the ethical needs of reason.

  15. Modeling and Simulation of a Gallium Nitride (GaN) Betavoltaic Energy Converter

    Science.gov (United States)

    2016-06-01

    are from reference [23]. The remaining values are from reference [24]. Parameters Silicon (Si) Gallium Arsenide (GaAs) Silicon Carbide (4H-SiC... Aluminum x.min=102 x.max=104 conductor #Electrodes – The connection to the device. The widths are set to match the active area of the device...resistive, to simulate a equivalent shunt resistance material material= Aluminum resistivity=1.763e13 #GaN material deep level traps trap mat

  16. Diodes GaN a haute efficacite : Extraction de la lumiere par cristaux photoniques et microcavites.

    OpenAIRE

    David , Aurélien

    2006-01-01

    Recent years have seen the advent of blue light-emitting diodes and efficient white-based gallium nitride (GaN). This technology is poised to replace conventional light bulbs in the near future, allowing considerable energy savings. However, this scenario requires that these diodes are fully optimized, since the quality of the material up how to extract the light. This thesis explores this latter aspect: the emitted light in a semiconductor is naturally trapped, and a strategy is needed for b...

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

    Science.gov (United States)

    2016-06-01

    towards our goal of a gamma discriminating device. Future studies should include determining the reason for double peaks appearing in the spectra of...Gadolinium-Based GaN for Neutron Detection with Gamma Discrimination Distribution Statement A. Approved for public release; distribution is...C kg –1 ) rad [absorbed dose] 1 × 10 –2 joule per kilogram (J kg –1 ) [gray (Gy)] rem [equivalent and effective dose] 1 × 10–2 joule per kilogram

  18. First-principle investigations on the structural dynamics of Ti2GaN

    International Nuclear Information System (INIS)

    Yang, Z.J.; Li, J.; Linghu, R.F.; Cheng, X.L.; Yang, X.D.

    2013-01-01

    Highlights: •Our calculated lattice parameter of Ti 2 GaN shows that c axis is always stiffer than a axis. •The elastic constants investigations demonstrated that the Ti 2 GaN is meta-stable between 350 and 600 GPa. •We observed an abnormal c-axis expansion behavior within 350–600 GPa resulting from the expansion of the Ti–Ti bond length and the increase of the Ti–Ti bond populations. •Study on the density of states we found that the Ti s and p electrons shift towards higher energies with pressure. -- Abstract: We report a first-principle study on the elastic and electronic properties of the nanolaminate Ti 2 GaN. Our calculated lattice parameter shows that c axis is always stiffer than a axis. The elastic constants investigations demonstrated that Ti 2 GaN is stable over a wide pressure range of 0–1000 GPa with the only exception of 350–600 GPa owing to the elastic softening. The softening behaviors of the Young’s and shear moduli are also found in the same pressure range of 350–600 GPa, indicating a structural metastability. Investigation on the axial compressibility we observed an abnormal c-axis expansion behavior within a pressure range of 350–600 GPa, resulting from the expansion of the Ti–Ti bond length and the increase of the Ti–Ti bond population. Study on the density of states (DOSs) we found that the Ti s and Ti p electrons shift towards higher energies with pressure

  19. Hafnium nitride buffer layers for growth of GaN on silicon

    Science.gov (United States)

    Armitage, Robert D.; Weber, Eicke R.

    2005-08-16

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  20. A 600 VOLT MULTI-STAGE, HIGH REPETITION RATE GAN FET SWITCH

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, D. [Fermilab; Pfeffer, H. [Fermilab; Saewert, G. [Fermilab

    2016-10-05

    Using recently available GaN FETs, a 600 Volt three- stage, multi-FET switch has been developed having 2 nanosecond rise time driving a 200 Ohm load with the potential of approaching 30 MHz average switching rates. Possible applications include driving particle beam choppers kicking bunch-by-bunch and beam deflectors where the rise time needs to be custom tailored. This paper reports on the engineering issues addressed, the design approach taken and some performance results of this switch.

  1. Physical model for GaN HEMT design optimization in high frequency switching applications

    OpenAIRE

    Cucak, Dejana; Vasic, Miroslav; García, Oscar; Bouvier, Yann; Oliver Ramírez, Jesús Angel; Alou Cervera, Pedro; Cobos Márquez, José Antonio; Wang, Ashu; Martin Horcajo, Sara; Romero Rojo, Fátima; Calle Gómez, Fernando

    2014-01-01

    In this paper, physical modeling of a GaN HEMT is proposed, with the objective of device design optimization for application in a high frequency DC/DC converter. From the point of view of a switching application, physical model for input, output and reverse capacitance as well as for channel resistance is very important, since the aforementioned parameters determine power losses in the circuit. The obtained physical model of the switching device can be used for simulation models such as PSpic...

  2. Characterisation and analytical modeling of GaN HEMT-based varactor diodes

    OpenAIRE

    Hamdoun , Abdelaziz; Roy , L.; Himdi , Mohamed; Lafond , Olivier

    2015-01-01

    International audience; Varactor diodes fabricated in 0.5 and 0.15 μm GaN HEMT (high-electron-mobility transistor) processes are modelled. The devices were characterised via DC and RF small-signal measurements up to 20 GHz, and fitted to a simple physical equivalent circuit. Approximate analytical expressions containing empirical coefficients are introduced for the voltage dependency of capacitance and series resistance. The analytical solutions agree remarkably well with the experimentally e...

  3. Structure and stability of threading edge and screw dislocations in bulk GaN

    Czech Academy of Sciences Publication Activity Database

    Gröger, Roman; Leconte, L.; Ostapovets, Andriy

    2015-01-01

    Roč. 99, MAR (2015), s. 195-202 ISSN 0927-0256 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA MŠk(CZ) EE2.3.30.0063 Institutional support: RVO:68081723 Keywords : Threading dislocation * Edge * Screw * GaN Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.086, year: 2015

  4. Improvement of luminescence properties of GaN buffer layer for fast nitride scintillator structures

    Czech Academy of Sciences Publication Activity Database

    Hubáček, T.; Hospodková, Alice; Oswald, Jiří; Kuldová, Karla; Pangrác, Jiří

    2017-01-01

    Roč. 464, Apr (2017), s. 221-225 ISSN 0022-0248 R&D Projects: GA ČR GA16-11769S; GA MŠk LO1603 Institutional support: RVO:68378271 Keywords : MOVPE * GaN * scintillators * yellow band Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

  5. eCommerceGAN : A Generative Adversarial Network for E-commerce

    OpenAIRE

    Kumar, Ashutosh; Biswas, Arijit; Sanyal, Subhajit

    2018-01-01

    E-commerce companies such as Amazon, Alibaba and Flipkart process billions of orders every year. However, these orders represent only a small fraction of all plausible orders. Exploring the space of all plausible orders could help us better understand the relationships between the various entities in an e-commerce ecosystem, namely the customers and the products they purchase. In this paper, we propose a Generative Adversarial Network (GAN) for orders made in e-commerce websites. Once trained...

  6. Electronic Characteristics of Rare Earth Doped GaN Schottky Diodes

    Science.gov (United States)

    2013-03-21

    types of diode. This revised value of A** is in exact agreement with the experimentally determined results of Hacke et al. [20] who also used gold...http://www1.eere.energy.gov/buildings/ssl/ . Accessed 6 Jan 2013. [15] Tung, Raymond T. Brooklyn College Schottky Barrier Height Tutorial ... Hacke , P., Detchprohm, T., Kiramatsu, K., Sawaki, N. (1993). Schottky barrier on n-type GaN grown by hydride vapor phase epitaxy. Applied Physics

  7. Catalyst and its diameter dependent growth kinetics of CVD grown GaN nanowires

    International Nuclear Information System (INIS)

    Samanta, Chandan; Chander, D. Sathish; Ramkumar, J.; Dhamodaran, S.

    2012-01-01

    Graphical abstract: GaN nanowires with controlled diameter and aspect ratio has been grown using a simple CVD technique. The growth kinetics of CVD grown nanowires investigated in detail for different catalysts and their diameters. A critical diameter important to distinguish the growth regimes has been discussed in detail. The results are important which demonstrates the growth of diameter and aspect ratio controlled GaN nanowires and also understand their growth kinetics. Highlights: ► Controlled diameter and aspect ratio of GaN nanowires achieved in simple CVD reactor. ► Nanowire growth kinetics for different catalyst and its diameters were understood. ► Adatoms vapor pressure inside reactor plays a crucial role in growth kinetics. ► Diffusion along nanowire sidewalls dominate for gold and nickel catalysts. ► Gibbs–Thomson effect dominates for palladium catalyst. -- Abstract: GaN nanowires were grown using chemical vapor deposition with controlled aspect ratio. The catalyst and catalyst-diameter dependent growth kinetics is investigated in detail. We first discuss gold catalyst diameter dependent growth kinetics and subsequently compare with nickel and palladium catalyst. For different diameters of gold catalyst there was hardly any variation in the length of the nanowires but for other catalysts with different diameter a strong length variation of the nanowires was observed. We calculated the critical diameter dependence on adatoms pressure inside the reactor and inside the catalytic particle. This gives an increasing trend in critical diameter as per the order gold, nickel and palladium for the current set of experimental conditions. Based on the critical diameter, with gold and nickel catalyst the nanowire growth was understood to be governed by limited surface diffusion of adatoms and by Gibbs–Thomson effect for the palladium catalyst.

  8. 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

  9. Electron band bending of polar, semipolar and non-polar GaN surfaces

    Czech Academy of Sciences Publication Activity Database

    Bartoš, Igor; Romanyuk, Olexandr; Houdková, Jana; Paskov, P.P.; Paskova, T.; Jiříček, Petr

    2016-01-01

    Roč. 119, č. 10 (2016), 1-7, č. článku 105303. ISSN 0021-8979 R&D Projects: GA ČR GA15-01687S Grant - others:AVČR(CZ) M100101201 Institutional support: RVO:68378271 Keywords : GaN * XPS * band bending Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.068, year: 2016

  10. 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.

  11. Results From Cs Activated GaN Photocathode Development for MCP Detector Systems at GSFC

    Science.gov (United States)

    Norton, Tim; Woodgate, Bruce; Stock, Joe; Hilton, George; Ulmer, Mel; Aslam, Shahid; Vispute, R. D.

    2003-01-01

    We describe the development of high quantum efficiency W photocathodes for use in large area two dimensional microchannel plate based detector arrays to enable new W space astronomy missions. Future W missions will require improvements in detector sensitivity, which has the most leverage for cost-effective improvements in overall telescope/instrument sensitivity. We use new materials such as p-doped GaN, AIGaN, ZnMgO, Sic and diamond. We have currently obtained QE values > 40 % at 185 nm with Cesiated GaN, and hope to demonstrate higher values in the future. By using controlled internal fields and nano-structuring of the surfaces, we plan to provide field emission assistance for photoelectrons while maintaining their energy distinction from dark noise electrons. We will transfer these methods from GaN to ZnMgO, a new family of wide band-gap materials more compatible with microchannel plates. We also are exploring technical parameters such as doping profiles, internal and external field strengths, angle of incidence, field emission assistance, surface preparation, etc.

  12. Study on photoemission mechanism for negative electron affinity GaN vacuum electron source

    International Nuclear Information System (INIS)

    Qiao, Jianliang; Chang, Benkang; Qian, Yunsheng; Wang, Xiaohui; Li, Biao; Fu, Xiaoqian

    2012-01-01

    The whole process including photoelectron excitation, transportation from bulk to surface and escape to vacuum by traversing surface barrier was analyzed in detail. Photoelectron excitation relates to the band structure of photocathode material and the absorption coefficient of the material. In the bulk of GaN photocathode, the photoelectrons mainly are transited into Γ valley first, when the energy is great enough, the photoelectrons can scatter into higher M-L valley or A valley from Γ valley. The electrons excitated in conduction band will move from bulk to surface by diffusing or drifting. The diffuse length for GaN photocathode is about 3μm by calculating. After the thermal electrons of Γ valley move into surface band bend area, they will drift to the surface because of the electric field of band bend area. The transmission coefficient relates to the incident electron energy, the height and width of the surface potential. The quantum yield formulas of NEA GaN photocathode were gotten by solving the diffuse equation of non-equilibrium carriers. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Study on photoemission mechanism for negative electron affinity GaN vacuum electron source

    Energy Technology Data Exchange (ETDEWEB)

    Qiao, Jianliang [School of Electronic Engineering and Optoelectronic Techniques, Nanjing University of Science and Technology, Nanjing (China); Department of Electronic and Electrical Engineering, Nanyang Institute of Technology, NanYang (China); Chang, Benkang; Qian, Yunsheng; Wang, Xiaohui; Li, Biao; Fu, Xiaoqian [School of Electronic Engineering and Optoelectronic Techniques, Nanjing University of Science and Technology, Nanjing (China)

    2012-01-15

    The whole process including photoelectron excitation, transportation from bulk to surface and escape to vacuum by traversing surface barrier was analyzed in detail. Photoelectron excitation relates to the band structure of photocathode material and the absorption coefficient of the material. In the bulk of GaN photocathode, the photoelectrons mainly are transited into {gamma} valley first, when the energy is great enough, the photoelectrons can scatter into higher M-L valley or A valley from {gamma} valley. The electrons excitated in conduction band will move from bulk to surface by diffusing or drifting. The diffuse length for GaN photocathode is about 3{mu}m by calculating. After the thermal electrons of {gamma} valley move into surface band bend area, they will drift to the surface because of the electric field of band bend area. The transmission coefficient relates to the incident electron energy, the height and width of the surface potential. The quantum yield formulas of NEA GaN photocathode were gotten by solving the diffuse equation of non-equilibrium carriers. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Results from Cs activated GaN photocathode development for MCP detector systems at NASA GSFC

    Science.gov (United States)

    Norton, Timothy J.; Woodgate, Bruce E.; Stock, Joseph; Hilton, George; Ulmer, Melville P.; Aslam, Shahid; Vispute, R. D.

    2003-12-01

    We describe the development of high quantum efficiency UV photocathodes for use in large area two dimensional microchannel plated based, detector arrays to enable new UV space astronomy missions. Future UV missions will require improvements in detector sensitivity, which has the most leverage for cost-effective improvements in overall telescope/instrument sensitivity. We use new materials such as p-doped GaN, AlGaN, ZnMgO, SiC and diamond. We have currently obtained QE values > 40% at 185 nm with Cesiated GaN, and hope to demonstrate higher values in the future. By using controlled internal fields and nano-structuring of the surfaces, we plan to provide field emission assistance for photoelectrons while maintaining their energy distinction from dark noise electrons. We will transfer these methods from GaN to ZnMgO a new family of wide band-gap materials more compatible with microchannel plates. We also are exploring technical parameters such as doping profiles, internal and external field strengths, angle of incidence, field emission assistance, surface preparation, etc.

  15. Development of UV-photocathodes using GaN film on Si substrate

    Science.gov (United States)

    Fuke, S.; Sumiya, M.; Nihashi, T.; Hagino, M.; Matsumoto, M.; Kamo, Y.; Sato, M.; Ohtsuka, K.

    2008-02-01

    We developed GaN photocathodes for detecting ultraviolet radiation by using Mg-doped GaN. Crack-free, 200 nm thick GaN:Mg layers were grown by metal organic chemical vapor phase epitaxy (MOVPE) on a GaN template having a structure of undoped GaN/(AlN/GaN) multilayers on Si (111) substrate. The Mg concentration was varied in the range from 7×10 18 to 7×10 19 cm -3. The grown film was mounted in a phototube to operate in reflection mode; i.e. the light was incident from the photoemission side. The photoemission surface was activated by sequential adsorption of cesium and oxygen to reduce electron affinity, ensuring efficient electron emission. Photoemission spectrum was measured in the range of 200-600 nm. We found that the quantum efficiency of photoemission was affected by the crystallinity of GaN:Mg, depending on the concentration of Mg dopant and the growth pressure of GaN:Mg top photoemissive layer. The lower Mg concentration and higher growth pressure resulted in higher quantum efficiency. The obtained maximum quantum efficiency was 45% at 200 nm (6.2 eV) and 25% at 350 nm (3.54 eV). The elimination ratio between visible and UV light was 4 decades and the slope of cutoff was 10 nm per decade.

  16. 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

  17. Energetics and electronic structures of thin films and heterostructures of a hexagonal GaN sheet

    Science.gov (United States)

    Gao, Yanlin; Okada, Susumu

    2017-06-01

    Using the density functional theory (DFT) combined with van der Waals correction and effective screening medium methods, we study the geometric and electronic structures of GaN thin films, each atomic layer of which exhibits a hexagonally bonded two-dimensional (2D) network. Our DFT calculations containing the van der Walls correction showed that the hexagonal GaN (h-GaN) sheets in the thin films are tightly bound to each other owing to the small interlayer spacing, such that their electronic structures are sensitive to the number of layers. We also investigate the energetics and electronic structures of hybrid structures of h-GaN with other layered materials, graphene and h-BN: For both hybrids, the optimum interlayer spacing is 3.4 Å, indicating that the h-GaN sheet is bound to graphene or h-BN via a weak van der Waal interaction. Owing to the weak interlayer interaction, graphene and h-BN retain their characteristic electronic structures. We further found that GaN thin films with a wurtzite structure undergo a structural phase transition into the layered structure of h-GaN when a biaxial tensile strain is applied.

  18. Growth mechanism of InGaN nanodots on three-dimensional GaN structures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Donghwy; Min, Daehong; Nam, Okhyun [Department of Nano-Optical Engineering, Convergence Center for Advanced Nano-Semiconductor (CANS), Korea Polytechnic University (KPU), Siheung-si, Gyeonggi-do (Korea, Republic of)

    2017-07-15

    In this study, we investigated the growth mechanism of indium gallium nitride (InGaN) nanodots (NDs) and an InGaN layer, which were simultaneously formed on a three-dimensional (3D) gallium nitride (GaN) structure, having (0001) polar, (11-22) semi-polar, and (11-20) nonpolar facets. We observed the difference in the morphological and compositional properties of the InGaN structures. From the high resolution transmission electron microscopy (HR-TEM) images, it can be seen that the InGaN NDs were formed only on the polar and nonpolar facets, whereas an InGaN layer was formed on the semi-polar facet. The indium composition variation in all the InGaN structures was observed using scanning transmission electron microscopy (STEM) and the energy dispersive X-ray spectroscopy (EDS). The different growth mechanism can be explained by two reasons: (i) The difference in the diffusivities of indium and gallium adatoms at each facet of 3D GaN structure; and (ii) the difference in the kinetic Wulff plots of polar, semi-polar, and nonpolar GaN planes. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Olefin metathesis reaction on GaN (0 0 0 1) surfaces

    International Nuclear Information System (INIS)

    Makowski, Matthew S.; Zemlyanov, Dmitry Y.; Ivanisevic, Albena

    2011-01-01

    Proof-of-concept reactions were performed on GaN (0 0 0 1) surfaces to demonstrate surface termination with desired chemical groups using an olefin cross-metathesis reaction. To prepare the GaN surfaces for olefin metathesis, the surfaces were hydrogen terminated with hydrogen plasma, chlorine terminated with phosphorous pentachloride, and then terminated with an alkene group via a Grignard reaction. The olefin metathesis reaction then bound 7-bromo-1-heptene. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and water contact angle measurements following each step in the reaction scheme. The XPS data was used to qualitatively identify surface chemical species and to quantitatively determine molecular surface coverage. The bromine atom in 7-bromo-1-heptene served as a heteroatom for identification with XPS. The reaction scheme resulted in GaN substrates with a surface coverage of 0.10 monolayers and excellent stability towards oxidation when exposed to oxygen plasma.

  20. Olefin metathesis reaction on GaN (0 0 0 1) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Makowski, Matthew S. [Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907 (United States); Zemlyanov, Dmitry Y. [Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907 (United States); Ivanisevic, Albena, E-mail: albena@purdue.edu [Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907 (United States); Department of Chemistry, Purdue University, West Lafayette, IN 47907 (United States)

    2011-03-01

    Proof-of-concept reactions were performed on GaN (0 0 0 1) surfaces to demonstrate surface termination with desired chemical groups using an olefin cross-metathesis reaction. To prepare the GaN surfaces for olefin metathesis, the surfaces were hydrogen terminated with hydrogen plasma, chlorine terminated with phosphorous pentachloride, and then terminated with an alkene group via a Grignard reaction. The olefin metathesis reaction then bound 7-bromo-1-heptene. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and water contact angle measurements following each step in the reaction scheme. The XPS data was used to qualitatively identify surface chemical species and to quantitatively determine molecular surface coverage. The bromine atom in 7-bromo-1-heptene served as a heteroatom for identification with XPS. The reaction scheme resulted in GaN substrates with a surface coverage of 0.10 monolayers and excellent stability towards oxidation when exposed to oxygen plasma.

  1. Electrical and luminescent properties and deep traps spectra of N-polar GaN films

    International Nuclear Information System (INIS)

    Polyakov, A.Y.; Smirnov, N.B.; Govorkov, A.V.; Sun, Q.; Zhang, Y.; Cho, Y.S.; Lee, I.-H.; Han, J.

    2010-01-01

    Electrical and luminescent properties of N-polar undoped GaN films grown using low temperature GaN buffers on on-axis and miscut sapphire and on-axis AlN buffers are compared to the properties of Ga-polar films grown on low temperature GaN buffers. It is shown that the concentration of residual donors increases by about an order of magnitude for on-axis N-polar growth and by two orders of magnitude for off-axis growth compared to Ga-polar films. On-axis films for both Ga-polar and N-polar polarities show the presence of n + interfacial layers greatly influencing the apparent electron concentration and mobility deduced from capacitance-voltage C-V measurements. These interfacial layers are much less prominent in the miscut N-polar films. Growth on N-polar greatly increases the concentration of electron traps with activation energy of 0.9 eV possibly related to Ga-interstitials.

  2. 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

  3. Thin-film GaN Schottky diodes formed by epitaxial lift-off

    Science.gov (United States)

    Wang, Jingshan; Youtsey, Chris; McCarthy, Robert; Reddy, Rekha; Allen, Noah; Guido, Louis; Xie, Jinqiao; Beam, Edward; Fay, Patrick

    2017-04-01

    The performance of thin-film GaN Schottky diodes fabricated using a large-area epitaxial lift-off (ELO) process is reported in this work. Comparison of the device characteristics before and after lift-off processing reveals that the Schottky barrier height remains unchanged by the liftoff processing and is consistent with expectations based on metal-semiconductor work function differences, with a barrier height of approximately 1 eV obtained for Ni/Au contacts on n- GaN. However, the leakage current in both reverse and low-forward-bias regimes is found to improve significantly after ELO processing. Likewise, the ideality factor of the Schottky diodes also improves after ELO processing, decreasing from n = 1.12-1.18 before ELO to n = 1.04-1.10 after ELO. A possible explanation for the performance improvement obtained for Schottky diodes after substrate removal by ELO processing is the elimination of leakage paths consisting of vertical leakage along threading dislocations coupled with lateral conduction through the underlying n+ buffer layer that is removed in the ELO process. Epitaxial liftoff with GaN may enable significant improvement in device performance and economics for GaN-based electronics and optoelectronics.

  4. GaN nanowire arrays with nonpolar sidewalls for vertically integrated field-effect transistors

    Science.gov (United States)

    Yu, Feng; Yao, Shengbo; Römer, Friedhard; Witzigmann, Bernd; Schimpke, Tilman; Strassburg, Martin; Bakin, Andrey; Schumacher, Hans Werner; Peiner, Erwin; Suryo Wasisto, Hutomo; Waag, Andreas

    2017-03-01

    Vertically aligned gallium nitride (GaN) nanowire (NW) arrays have attracted a lot of attention because of their potential for novel devices in the fields of optoelectronics and nanoelectronics. In this work, GaN NW arrays have been designed and fabricated by combining suitable nanomachining processes including dry and wet etching. After inductively coupled plasma dry reactive ion etching, the GaN NWs are subsequently treated in wet chemical etching using AZ400K developer (i.e., with an activation energy of 0.69 ± 0.02 eV and a Cr mask) to form hexagonal and smooth a-plane sidewalls. Etching experiments using potassium hydroxide (KOH) water solution reveal that the sidewall orientation preference depends on etchant concentration. A model concerning surface bonding configuration on crystallography facets has been proposed to understand the anisotropic wet etching mechanism. Finally, NW array-based vertical field-effect transistors with wrap-gated structure have been fabricated. A device composed of 99 NWs exhibits enhancement mode operation with a threshold voltage of 1.5 V, a superior electrostatic control, and a high current output of >10 mA, which prevail potential applications in next-generation power switches and high-temperature digital circuits.

  5. Trench formation and corner rounding in vertical GaN power devices

    Science.gov (United States)

    Zhang, Yuhao; Sun, Min; Liu, Zhihong; Piedra, Daniel; Hu, Jie; Gao, Xiang; Palacios, Tomás

    2017-05-01

    Trench formation and corner rounding are the key processes to demonstrate high-voltage trench-based vertical GaN devices. In this work, we developed a damage-free corner rounding technology combining Tetramethylammonium hydroxide wet etching and piranha clean. By optimizing the inductively coupled plasma dry etching conditions and applying the rounding technology, two main trench shapes were demonstrated: flat-bottom rounded trench and tapered-bottom rounded trench. TCAD simulations were then performed to investigate the impact of trench shapes and round corners on device blocking capability. GaN trench metal-insulator-semiconductor barrier Schottky rectifiers with different trench shapes were fabricated and characterized. A breakdown voltage over 500 V was obtained in the device with flat-bottom rounded trenches, compared to 350 V in the device with tapered-bottom rounded trenches and 150 V in the device with non-rounded trenches. Both experimental and simulation results support the use of rounded flat-bottom trenches to fabricate high-voltage GaN trench-based power devices.

  6. Maskless regrowth of GaN for trenched devices by MOCVD

    Science.gov (United States)

    Agarwal, Anchal; Koksaldi, Onur; Gupta, Chirag; Keller, Stacia; Mishra, Umesh K.

    2017-12-01

    Blanket regrowth studies were performed on GaN trenches with varying widths and optimized for two types of devices—those that required the profile of the trench to be maintained and those that required the complete filling of trenches, i.e., a planar surface after regrowth. Low temperature Al0.22Ga0.78N growth was optimized and used as the marker layer for SEM. GaN deposition at a medium temperature of 950 °C and using N2 as carrier gas resulted primarily in growth on the (0001) plane, while the growth on the sidewalls was governed by the formation of slow growing semi-polar planes. This gave a conformal profile to the regrown GaN—useful for regrown GaN interlayer based vertical trench MOSFETs. In contrast, high temperature (1150 °C) growth in H2 resulted in high lateral growth rates. The planar surface was achieved under these conditions—a very promising result for CAVET-type devices.

  7. Decay of stimulated and spontaneous emission in highly excited homoepitaxial GaN

    International Nuclear Information System (INIS)

    Jursenas, S.; Kurilcik, N.; Kurilcik, G.; Zukauskas, A.; Prystawko, P.; Leszcynski, M.; Suski, T.; Perlin, P.; Grzegory, I.; Porowski, S.

    2001-01-01

    The high-density effects in the recombination of electron - hole plasma in photoexcited homoepitaxial GaN epilayers were studied by means of transient photoluminescence at room temperature. Owing to the 'backward' and 'lateral' photoluminescence measurement geometries employed, the influence of stimulated transitions on the decay of degenerate nonthermalized plasma was revealed. The lateral stimulated emission was demonstrated to cause a remarkable increase in the recombination rate on the early stage of the luminescence transient. A delayed enhancement of the stimulated emission due to the cooling of plasma from the initial temperature of 1100 K was observed. After completion of the thermalization process and exhaustion of the stimulated emission, the spontaneous-luminescence decay exhibited an exponential slope that relates to the nonradiative recombination of the carriers. The homoepitaxially grown GaN layer featured a luminescence decay time of 445 ps that implies a room-temperature free-carrier lifetime of 890 ps (considered to be extremely high for undoped hexagonal GaN). [copyright] 2001 American Institute of Physics

  8. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces

    International Nuclear Information System (INIS)

    Krueger, David

    2009-01-01

    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.)

  9. 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.

  10. 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.

  11. Electromechanical Characterization of Single GaN Nanobelt Probed with Conductive Atomic Force Microscope

    Science.gov (United States)

    Yan, X. Y.; Peng, J. F.; Yan, S. A.; Zheng, X. J.

    2018-04-01

    The electromechanical characterization of the field effect transistor based on a single GaN nanobelt was performed under different loading forces by using a conductive atomic force microscope (C-AFM), and the effective Schottky barrier height (SBH) and ideality factor are simulated by the thermionic emission model. From 2-D current image, the high value of the current always appears on the nanobelt edge with the increase of the loading force less than 15 nN. The localized (I-V) characteristic reveals a typical rectifying property, and the current significantly increases with the loading force at the range of 10-190 nN. The ideality factor is simulated as 9.8 within the scope of GaN nano-Schottky diode unity (6.5-18), therefore the thermionic emission current is dominant in the electrical transport of the GaN-tip Schottky junction. The SBH is changed through the piezoelectric effect induced by the loading force, and it is attributed to the enhanced current. Furthermore, a single GaN nanobelt has a high mechanical-induced current ratio that could be made use of in a nanoelectromechanical switch.

  12. Basic Equations for the Modeling of Gallium Nitride (gan) High Electron Mobility Transistors (hemts)

    Science.gov (United States)

    Freeman, Jon C.

    2003-01-01

    Gallium nitride (GaN) is a most promising wide band-gap semiconductor for use in high-power microwave devices. It has functioned at 320 C, and higher values are well within theoretical limits. By combining four devices, 20 W has been developed at X-band. GaN High Electron Mobility Transistors (HEMTs) are unique in that the two-dimensional electron gas (2DEG) is supported not by intentional doping, but instead by polarization charge developed at the interface between the bulk GaN region and the AlGaN epitaxial layer. The polarization charge is composed of two parts: spontaneous and piezoelectric. This behavior is unlike other semiconductors, and for that reason, no commercially available modeling software exists. The theme of this document is to develop a self-consistent approach to developing the pertinent equations to be solved. A Space Act Agreement, "Effects in AlGaN/GaN HEMT Semiconductors" with Silvaco Data Systems to implement this approach into their existing software for III-V semiconductors, is in place (summer of 2002).

  13. Evaluation of the localized residual strain states of GaN layers by using a TEM-CBED method

    International Nuclear Information System (INIS)

    Shin, H. Y.; Chang, Y. I.; Jung, Y. W.; Cho, M. J.; Park, K. H.

    2006-01-01

    The convergent beam electron diffraction (CBED) method of transmission electron microscopy (TEM) is well known to be a useful technique for evaluating the localized residual strain by measuring the quantitative variations of the lattice parameters. The multi quantum wells (MQWs) affect on the localized residual strain in a GaN layer, where the AlGaN layer is deposited in order to reduce the strain. We used TEM in order to determine the variations of the lattice parameters of the GaN layer both with and without the AlGaN layer. The lattice parameters of the GaN layer were measured every 100 nm along to the transverse direction below the MQWs. The lattice parameters of the lower part of the GaN layer were shown to have lower values than those of the higher part (below MQWs), which is caused by the compressive stress formed by the sapphire substrate. Also, due to the tensile stress formed by an InGaN in the MQWs, the lattice parameters of the higher part were shown to have higher values. The AlGaN layer deposited on the MQWs produced a compressive stress on the GaN layer so that the average lattice parameters of the GaN layer with the AlGaN layer were lower than those without the AlGaN layer. Therefore, we conclude that the AlGaN layer plays a role in reducing the localized residual strain on the GaN layer below the MQWs.

  14. 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.

  15. The origins and properties of intrinsic nonradiative recombination centers in wide bandgap GaN and AlGaN

    Science.gov (United States)

    Chichibu, S. F.; Uedono, A.; Kojima, K.; Ikeda, H.; Fujito, K.; Takashima, S.; Edo, M.; Ueno, K.; Ishibashi, S.

    2018-04-01

    The nonradiative lifetime (τNR) of the near-band-edge emission in various quality GaN samples is compared with the results of positron annihilation measurement, in order to identify the origin and to determine the capture-cross-section of the major intrinsic nonradiative recombination centers (NRCs). The room-temperature τNR of various n-type GaN samples increased with decreasing the concentration of divacancies composed of a Ga vacancy (VGa) and a N vacancy (VN), namely, VGaVN. The τNR value also increased with increasing the diffusion length of positrons, which is almost proportional to the inverse third root of the gross concentration of all point defects. The results indicate that major intrinsic NRC in n-type GaN is VGaVN. From the relationship between its concentration and τNR, its hole capture-cross-section is estimated to be about 7 × 10-14 cm2. Different from the case of 4H-SiC, the major NRCs in p-type and n-type GaN are different: the major NRCs in Mg-doped p-type GaN epilayers are assigned to multiple vacancies containing a VGa and two (or three) VNs, namely, VGa(VN)n (n = 2 or 3). The ion-implanted Mg-doped GaN films are found to contain larger size vacancy complexes such as (VGa)3(VN)3. In analogy with GaN, major NRCs in Al0.6Ga0.4N alloys are assigned to vacancy complexes containing an Al vacancy or a VGa.

  16. A novel GaN HEMT with double recessed barrier layer for high efficiency-energy applications

    Science.gov (United States)

    Jia, Hujun; Luo, Yehui; Wu, Qiuyuan; Yang, Yintang

    2017-11-01

    In this paper, a novel GaN HEMT with high efficiency-energy characteristic is proposed. Different from the conventional structure, the proposed structure contains double recessed barriers layer (DRBL) beside the gate. The key idea in this work is to improve the microwave output characteristics. The simulated results show that the drain saturation current and peak transconductance of DRBL GaN HEMT is slightly decreased, the transconductance saturation flatness is increased by 0.5 V and the breakdown voltage is also enhanced too. Due to the both recessed barrier layer, the gate-drain/gate-source capacitance is decreased by 6.3% and 11.3%, respectively. The RF simulated results show that the maximum oscillation frequency for DRBL GaN HEMT is increased from 57 GHz to 64 GHz and the saturation power density is 8.7 W/mm at 600 MHz, 6.9 W/mm at 1200 MHz with the higher power added efficiency (PAE). Further investigation show that DRBL GaN HEMT can achieve to 6.4 W/mm and the maximum PAE 83.8% at 2400 MHz. Both are higher than the 5.0 W/mm and 80.3% for the conventional structure. When the operating frequency increases to X band, the DRBL GaN HEMT still exhibits the superior output performances. All the results show that the advantages and the potential capacities of DRBL GaN HEMT at high efficiency-energy are greater than the conventional GaN HEMT.

  17. Epitaxial MoS2/GaN structures to enable vertical 2D/3D semiconductor heterostructure devices

    Science.gov (United States)

    Ruzmetov, D.; Zhang, K.; Stan, G.; Kalanyan, B.; Eichfeld, S.; Burke, R.; Shah, P.; O'Regan, T.; Crowne, F.; Birdwell, A. G.; Robinson, J.; Davydov, A.; Ivanov, T.

    MoS2/GaN structures are investigated as a building block for vertical 2D/3D semiconductor heterostructure devices that utilize a 3D substrate (GaN) as an active component of the semiconductor device without the need of mechanical transfer of the 2D layer. Our CVD-grown monolayer MoS2 has been shown to be epitaxially aligned to the GaN lattice which is a pre-requisite for high quality 2D/3D interfaces desired for efficient vertical transport and large area growth. The MoS2 coverage is nearly 50 % including isolated triangles and monolayer islands. The GaN template is a double-layer grown by MOCVD on sapphire and allows for measurement of transport perpendicular to the 2D layer. Photoluminescence, Raman, XPS, Kelvin force probe microscopy, and SEM analysis identified high quality monolayer MoS2. The MoS2/GaN structures electrically conduct in the out-of-plane direction and across the van der Waals gap, as measured with conducting AFM (CAFM). The CAFM current maps and I-V characteristics are analyzed to estimate the MoS2/GaN contact resistivity to be less than 4 Ω-cm2 and current spreading in the MoS2 monolayer to be approx. 1 μm in diameter. Epitaxial MoS2/GaN heterostructures present a promising platform for the design of energy-efficient, high-speed vertical devices incorporating 2D layered materials with 3D semiconductors.

  18. Heteroepitaxial VO{sub 2} thin films on GaN: Structure and metal-insulator transition characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Zhou You; Ramanathan, Shriram [Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

    2012-10-01

    Monolithic integration of correlated oxide and nitride semiconductors may open up new opportunities in solid-state electronics and opto-electronics that combine desirable functional properties of both classes of materials. Here, we report on epitaxial growth and phase transition-related electrical properties of vanadium dioxide (VO{sub 2}) thin films on GaN epitaxial layers on c-sapphire. The epitaxial relation is determined to be (010){sub vo{sub 2}} parallel (0001){sub GaN} parallel (0001){sub A1{sub 2O{sub 3}}} and [100]{sub vo{sub 2}} parallel [1210]{sub GaN} parallel [0110]{sub A1{sub 2O{sub 3}}} from x-ray diffraction. VO{sub 2} heteroepitaxial growth and lattice mismatch are analyzed by comparing the GaN basal plane (0001) with the almost close packed corrugated oxygen plane in vanadium dioxide and an experimental stereographic projection describing the orientation relationship is established. X-ray photoelectron spectroscopy suggests a slightly oxygen rich composition at the surface, while Raman scattering measurements suggests that the quality of GaN layer is not significantly degraded by the high-temperature deposition of VO{sub 2}. Electrical characterization of VO{sub 2} films on GaN indicates that the resistance changes by about four orders of magnitude upon heating, similar to epitaxial VO{sub 2} films grown directly on c-sapphire. It is shown that the metal-insulator transition could also be voltage-triggered at room temperature and the transition threshold voltage scaling variation with temperature is analyzed in the framework of a current-driven Joule heating model. The ability to synthesize high quality correlated oxide films on GaN with sharp phase transition could enable new directions in semiconductor-photonic integrated devices.

  19. Ferromagnetism in with Fe implanted GaN and TiO{sub 2}; Ferromagnetismus in mit Fe implantierten GaN und TiO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Talut, Georg

    2009-12-15

    In the present study it was tried to create a diluted magnetic semiconductor on the basis of GaN and TiO{sub 2} by means of ion beam implantation. In most cases, by characterization of structural and magnetic properties, it was possible to prove that the ferromagnetic state is related to either spinodal decomposition or secondary phase formation. In case of Fe implanted GaN spinodal decomposition, epitaxially oriented {alpha}-Fe or {epsilon}-Fe{sub 3}N nanocrystals were found to be responsible for the ferromagnetic behavior. In addition, the formation of {gamma}-Fe clusters was observed. Similarly, in TiO{sub 2} the ferromagnetism is related to the formation of epitaxially oriented {alpha}-Fe clusters. Dependent on the process parameters during annealing experiments several various secondary phases were formed. A critical examination of the references in literature points out the significance of usage of sensitive and complementary probe techniques (like CEMS, SQUID, XRD, EXAFS), in order to be able to discuss the origin of ferromagnetism in the field of diluted magnetic semiconductors in a proper way. (orig.)

  20. Electric field dependence of optical phonon frequencies in wurtzite GaN observed in GaN high electron mobility transistors

    Science.gov (United States)

    Bagnall, Kevin R.; Dreyer, Cyrus E.; Vanderbilt, David; Wang, Evelyn N.

    2016-10-01

    Due to the high dissipated power densities in gallium nitride (GaN) high electron mobility transistors (HEMTs), temperature measurement techniques with high spatial resolution, such as micro-Raman thermography, are critical for ensuring device reliability. However, accurately determining the temperature rise in the ON state of a transistor from shifts in the Raman peak positions requires careful decoupling of the simultaneous effects of temperature, stress, strain, and electric field on the optical phonon frequencies. Although it is well-known that the vertical electric field in the GaN epilayers can shift the Raman peak positions through the strain and/or stress induced by the inverse piezoelectric (IPE) effect, previous studies have not shown quantitative agreement between the strain and/or stress components derived from micro-Raman measurements and those predicted by electro-mechanical models. We attribute this discrepancy to the fact that previous studies have not considered the impact of the electric field on the optical phonon frequencies of wurtzite GaN apart from the IPE effect, which results from changes in the atomic coordinates within the crystal basis and in the electronic configuration. Using density functional theory, we calculated the zone center E2 (high), A1 (LO), and E2 (low) modes to shift by -1.39 cm-1/(MV/cm), 2.16 cm-1/(MV/cm), and -0.36 cm-1/(MV/cm), respectively, due to an electric field component along the c -axis, which are an order of magnitude larger than the shifts associated with the IPE effect. Then, we measured changes in the E2 (high) and A1 (LO) Raman peak positions with ≈1 μm spatial resolution in GaN HEMTs biased in the pinched OFF state and showed good agreement between the strain, stress, and electric field components derived from the measurements and our 3D electro-mechanical model. This study helps to explain the reason the pinched OFF state is a suitable reference for removing the contributions of the electric field and

  1. 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

  2. Comparison of resolution characteristics between exponential-doping and uniform-doping GaN photocathodes

    Science.gov (United States)

    Wang, Hong-gang; Qian, Yun-sheng; Lu, Liu-bing; Cheng, Hong-chang; Chang, Ben-kang

    2013-08-01

    The studies of quantum efficiency, electronic energy distribution and stability are highly concerned in the application of Negative electron affinity (NEA) gallium nitride (GaN) photocathodes while the resolution of photocathodes are concerned rarely. The resolutions of some image intensifiers are smaller than computational value partly because of ignoring the resolution of photocathodes. To a certain extent, the resolutions of image intensifiers are influenced by photocathodes. Electronic transverse diffusion is the main cause of decreasing the resolution of photocathodes whereas the exponential-doping structure can reduce its influence. In this paper, the resolution characteristics of photocathodes have been studied by using the modulation transfer function (MTF) method. The MTF expressions of transmission-mode exponential-doping photocathodes have been obtained by solving the two-dimensional continuity equations. According to the MTF expressions, the resolution characteristics between exponential-doping and uniform-doping GaN photocathodes are calculated theoretically and analyzed comparatively. At the same time, the relationships between resolution and thickness of the emission layer Te, electron diffusion length LD are researched in detail. The calculated results show that, compared with the uniform-doping photocathode, the exponential-doping structure can increase the resolution of photocathode evidently. The resolution of exponential-doping GaN photocathode is improved distinctly when the spatial frequency varies from 400 to 800 lp/mm. The MTF characteristics approach gradually when f increases or decreases. Let f =600 lp/mm, the resolution increases by 20%-48% approximately. The constant built-in electric field for exponential-doping GaN photocathode can increase the resolution of photocathode. The improvement of resolution is different from decreasing Te, LD or increasing the recombination velocity of back-interface which are at the cost of reducing the

  3. Vertical current-flow enhancement via fabrication of GaN nanorod p–n junction diode on graphene

    International Nuclear Information System (INIS)

    Ryu, Sung Ryong; Ram, S.D. Gopal; Lee, Seung Joo; Cho, Hak-dong; Lee, Sejoon; Kang, Tae Won; Kwon, Sangwoo; Yang, Woochul; Shin, Sunhye; Woo, Yongdeuk

    2015-01-01

    Highlights: • Uniaxial p–n junction diode in GaN nanorod is made by Hydride vapor phase epitaxy method. • The p–n junction diode property is clearly observed from the fabricated uniaxial p–n junction nanorod GaN nanorod. • Graphene is used as a current spreading layer to reduce the lateral resistance up to 700 times when compared with the commercial sapphire substrate, which is clearly explained with the aid of an equivalent circuit. • Kelvin Force Probe microscopy method is employed to visualize the p- and n- regions in a single GaN nanorod. - Abstract: Mg doped GaN nanorods were grown on undoped n-type GaN nanorods uniaxial on monolayer graphene by hydride vapor phase epitaxy (HVPE) method. The monolayer graphene used as the bottom electrode and a substrate as well provides good electrical contact, acts as a current spreading layer, well suitable for the growth of hexagonal GaN nanorod. In addition it has a work function suitable to that of n-GaN. The formed p–n nanorods show a Schottky behavior with a turn on voltage of 3 V. Using graphene as the substrate, the resistance of the nanorod is reduced by 700 times when compared with the case without using graphene as the current spreading layer. The low resistance of graphene acts in parallel with the resistance of the GaN buffer layer, and reduces the resistance drastically. The formed p–n junction in a single GaN nanorod is visualized by Kelvin Force Probe Microscopy (KPFM) to have distinctively contrast p and n regions. The measured contact potential difference of p-and n-region has a difference of 103 mV which well confirms the formed regions are electronically different. Low temperature photoluminescence (PL) spectra give evidence of dopant related acceptor bound emission at 3.2 eV different from 3.4 eV of undoped GaN. The crystalline structure, compositional purity is confirmed by X-ray diffraction (XRD), Transmission and Scanning electron microcopies (SEM), (TEM), Energy dispersive analysis

  4. Buffer optimization for crack-free GaN epitaxial layers grown on Si(1 1 1) substrate by MOCVD

    International Nuclear Information System (INIS)

    Arslan, Engin; Ozbay, Ekmel; Ozturk, Mustafa K; Ozcelik, Suleyman; Teke, Ali

    2008-01-01

    We report the growth of GaN films on the Si(1 1 1) substrate by metalorganic chemical vapour phase deposition (MOCVD). Different buffer layers were used to investigate their effects on the structural and optical properties of GaN layers. A series of GaN layers were grown on Si(1 1 1) with different buffer layers and buffer thicknesses and were characterized by Nomarski microscopy, atomic force microscopy, high-resolution x-ray diffraction (XRD) and photoluminescence (PL) measurements. We first discuss the optimization of the LT-AlN/HT-AlN/Si(1 1 1) templates and then the optimization of the graded AlGaN intermediate layers. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.6 μm. The XRD and PL measurements results confirmed that a wurtzite GaN was successfully grown. The resulting GaN film surfaces were flat, mirror-like and crack-free. The mosaic structure in the GaN layers was investigated. With a combination of Williamson-Hall measurements and the fitting of twist angles, it was found that the buffer thickness determines the lateral coherence length, vertical coherence length, as well as the tilt and twist of the mosaic blocks in GaN films. The PL spectra at 8 K show that a strong band edge photoluminescence of GaN on Si (1 1 1) emits light at an energy of 3.449 eV with a full width at half maximum (FWHM) of approximately 16 meV. At room temperature, the peak position and FWHM of this emission become 3.390 eV and 58 meV, respectively. The origin of this peak was attributed to the neutral donor bound exciton. It was found that the optimized total thickness of the AlN and graded AlGaN layers played a very important role in the improvement of quality and in turn reduced the cracks during the growth of GaN/Si(1 1 1) epitaxial layers

  5. Photoluminescence and photoluminescence excitation studies in 80 MeV Ni ion irradiated MOCVD grown GaN

    Energy Technology Data Exchange (ETDEWEB)

    Devaraju, G. [School of Physics, University of Hyderabad, Central University P.O., Hyderabad 500 046 (India); Pathak, A.P., E-mail: appsp@uohyd.ernet.in [School of Physics, University of Hyderabad, Central University P.O., Hyderabad 500 046 (India); Srinivasa Rao, N.; Saikiran, V. [School of Physics, University of Hyderabad, Central University P.O., Hyderabad 500 046 (India); Enrichi, Francesco [Coordinamento Interuniversitario Veneto per le Nanotecnologie (CIVEN), via delle Industrie 5, Marghera, I-30175Venice (Italy); Trave, Enrico [Dipartimento di Chimica Fisica, Universita Ca' Foscari Venezia, Dorsoduro 2137, I-30123 Venice (Italy)

    2011-09-01

    Highlights: {yields} MOCVD grown GaN samples are irradiated with 80 MeV Ni ions at room temperature. {yields} PL and PLE studies have been carried out for band to band, BL and YL emissions. {yields} Ni ions irradiated GaN shows BL band at 450 nm besides YL band. {yields} Radiation annealed Ga vacancies have quenching effect on YL intensity. {yields} We speculated that BL and YL are associated with N and Ga vacancies, respectively. - Abstract: We report damage creation and annihilation under energetic ion bombardment at a fixed fluence. MOCVD grown GaN thin films were irradiated with 80 MeV Ni ions at a fluence of 1 x 10{sup 13} ions/cm{sup 2}. Irradiated GaN thin films were subjected to rapid thermal annealing for 60 s in nitrogen atmosphere to anneal out the defects. The effects of defects on luminescence were explored with photoluminescence measurements. Room temperature photoluminescence spectra from pristine sample revealed presence of band to band transition besides unwanted yellow luminescence. Irradiated GaN does not show any band to band transition but there is a strong peak at 450 nm which is attributed to ion induced defect blue luminescence. However, irradiated and subsequently annealed samples show improved band to band transitions and a significant decrease in yellow luminescence intensity due to annihilation of defects which were created during irradiation. Irradiation induced effects on yellow and blue emissions are discussed.

  6. [Comparative study of uniform-doping and gradient-doping negative electron affinity GaN photocathodes].

    Science.gov (United States)

    Li, Biao; Chang, Ben-Kang; Xu, Yuan; Du, Xiao-Qing; Du, Yu-Jie; Fu, Xiao-Qian; Wang, Xiao-Hui; Zhang, Jun-Ju

    2011-08-01

    High temperature annealing and Cs/O activation are external incentives, while the property of GaN material is internal factor in the preparation of negative electron affinity GaN photocathode. The similarities and differences of the performance of the two structure photocathodes are analysed based on the difference of the structure between uniform-doping and gradient-doping negative electron affinity GaN photocathodes and the changes in photocurrents in activation and the quantum yield after successfully activated of GaN photocathodes. Experiments show that: the photocurrent growth rate is slower in activation, activation time is longer and quantum efficiency is higher after successfully activated of gradient-doping GaN photocathode than those of uniform-doping photocathode respectively. The field-assisted photocathode emission model can explain the differences between the two, built-in electric field of gradient-doping structure creates additional electronic drift to the photocathode surface, and the probability of electrons to reach the photocathode surface is improved correspondingly.

  7. Fabrication and optical characterization of GaN waveguides on (−201)-oriented β-Ga_2O_3

    KAUST Repository

    Awan, Kashif M.

    2017-12-19

    Gallium nitride (GaN), a wide-bandgap III-V semiconductor material with a bandgap wavelength λ = 366 nm (for Wurtzite GaN) and transparency window covering the visible spectrum, has a large number of applications for photonics and optoelectronics. However, the optical quality of this material suffers from growth imperfections due to the lack of a suitable substrate. Recent studies have shown that GaN grown on (-201) β - GaO (gallium oxide) has better lattice matching and hence superior optical quality as compared to GaN grown traditionally on AlO (sapphire). In this work, we report on the fabrication of GaN waveguides on GaO substrate, followed by a wet-etch process aimed at the reduction of waveguide surface roughness and improvement of side-wall verticality in these waveguides. The propagation loss in the resulting waveguides has been experimentally determined to be 7.5 dB/cm.

  8. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Aseev, P., E-mail: pavel.aseev@isom.upm.es, E-mail: gacevic@isom.upm.es; Gačević, Ž., E-mail: pavel.aseev@isom.upm.es, E-mail: gacevic@isom.upm.es; Calleja, E. [ISOM-ETSIT, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Torres-Pardo, A.; González-Calbet, J. M. [Departamento de Química Inorgánica, Facultad de Químicas, Universidad Complutense (UCM), CEI Moncloa, 28040 Madrid (Spain)

    2016-06-20

    Series of GaN nanowires (NW) with controlled diameters (160–500 nm) and heights (420–1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established.

  9. High thermal stability of abrupt SiO2/GaN interface with low interface state density

    Science.gov (United States)

    Truyen, Nguyen Xuan; Taoka, Noriyuki; Ohta, Akio; Makihara, Katsunori; Yamada, Hisashi; Takahashi, Tokio; Ikeda, Mitsuhisa; Shimizu, Mitsuaki; Miyazaki, Seiichi

    2018-04-01

    The effects of postdeposition annealing (PDA) on the interface properties of a SiO2/GaN structure formed by remote oxygen plasma-enhanced chemical vapor deposition (RP-CVD) were systematically investigated. X-ray photoelectron spectroscopy clarified that PDA in the temperature range from 600 to 800 °C has almost no effects on the chemical bonding features at the SiO2/GaN interface, and that positive charges exist at the interface, the density of which can be reduced by PDA at 800 °C. The capacitance-voltage (C-V) and current density-SiO2 electric field characteristics of the GaN MOS capacitors also confirmed the reduction in interface state density (D it) and the improvement in the breakdown property of the SiO2 film after PDA at 800 °C. Consequently, a high thermal stability of the SiO2/GaN structure with a low fixed charge density and a low D it formed by RP-CVD was demonstrated. This is quite informative for realizing highly robust GaN power devices.

  10. The impact of SiC substrate treatment on the heteroepitaxial growth of GaN by plasma assisted MBE

    Energy Technology Data Exchange (ETDEWEB)

    Brown, A.S.; Kim, T.H.; Choi, S.; Morse, M.; Wu, P. [Department of Electrical and Computer Engineering, Duke University, Durham, NC 27709 (United States); Losurdo, M.; Giangregorio, M.M.; Capezzuto, P.; Bruno, G. [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, and INSTM via Orabona 4 -70126, Bari (Italy)

    2005-11-01

    We report on the impact of the preparation of the Si-face 4H-SiC(0001){sub Si} substrate using a Ga flash-off process on the epitaxial growth of GaN by plasma-assisted molecular beam epitaxy. The nucleation, as well as the resultant structural and morphological properties of GaN grown directly on 4H-SiC(0001){sub Si} are strongly influenced by the chemical and morphological modifications of the SiC surface induced by the Ga flash-off process. Herein we describe the impact of the specific concentration of Ga incident on the surface (quantified in terms of monolayer (ML) coverage): of 0.5 ML, 1ML and 2ML. The residual oxygen at the SiC surface, unintentional SiC nitridation and the formation of cubic GaN grains during the initial nucleation stage, are all reduced when a 2 ML Ga flash is used. All of the above factors result in structural improvement of the GaN epitaxial layers. The correlation between the SiC surface modification, the initial nucleation stage, and the GaN epitaxial layer structural quality has been articulated using x-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry data. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. 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.)

  12. 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.

  13. Size effect on compression properties of GaN nanocones examined using in situ transmission electron microscopy

    International Nuclear Information System (INIS)

    Kang, Shao-Hui; Fang, Te-Hua

    2014-01-01

    Highlights: • Strain-induced structural variations of GaN nanocones are estimated using in situ TEM. • Young’s modulus of GaN nanocones with a diameter of 100–350 nm are 190–290 GPa. • The E 2 peak was red-shifted, indicated increased compressive stress. - Abstract: Mechanical property measurements of single nanocones are challenging because the small scale of the nanostructures. In this study, critical-stress- and strain-induced structural variations of GaN nanocones are estimated using in situ transmission electron microscopy (TEM) compression experiments. For single GaN nanocones with a diameter of 100–350 nm, the Young’s modulus, plastic deformation energy (W p ), and elastic deformation energy (W e ) values were 190–290 GPa, 0.02–1.65 × 10 −11 J, and 0.04–3.85 × 10 −11 J, respectively. Raman spectra were used to measure GaN indentation. The E 2 peak was red-shifted, indicated increased compressive stress in the indented area

  14. Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Xingsheng, E-mail: xsxu@semi.ac.cn [State Key Laboratory of Integration Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China)

    2015-03-02

    For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreased with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.

  15. Carrier and photon dynamics in a topological insulator Bi2Te3/GaN type II staggered heterostructure

    Science.gov (United States)

    Chaturvedi, P.; Chouksey, S.; Banerjee, D.; Ganguly, S.; Saha, D.

    2015-11-01

    We have demonstrated a type-II band-aligned heterostructure between pulsed laser deposited topological insulator bismuth telluride and metal organic-chemical-vapour deposited GaN on a sapphire substrate. The heterostructure shows a large valence band-offset of 3.27 eV as determined from x-ray photoelectron spectroscopy, which is close to the bandgap of GaN (3.4 eV). Further investigation using x-ray diffraction, Raman spectroscopy, and energy-dispersive x-ray spectrum reveals the stoichiometric and material properties of bismuth telluride on GaN. Steady state photon emission from GaN is found to be modulated by the charge transfer process due to diffusion across the junction. The time constant involved with the charge transfer process is found to be 0.6 ns by transient absorption spectroscopy. The heterostructure can be used for designing devices with different functionalities and improving the performance of the existing devices on GaN.

  16. 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.

  17. Non-destructive assessment of the polarity of GaN nanowire ensembles using low-energy electron diffraction and x-ray photoelectron diffraction

    Czech Academy of Sciences Publication Activity Database

    Romanyuk, Olexandr; Fernández-Garrido, S.; Jiříček, Petr; Bartoš, Igor; Geelhaar, L.; Brandt, O.; Paskova, T.

    2015-01-01

    Roč. 106, č. 2 (2015), "021602-1"-"021602-4" ISSN 0003-6951 Grant - others:AVČR(CZ) M100101201 Institutional support: RVO:68378271 Keywords : GaN nanowires * X-ray photoelectron diffraction * LEED I-V * GaN polarity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.142, year: 2015

  18. Ab initio density functional theory study of non-polar (10-10), (11-20) and semipolar {20-21} GaN surfaces

    Czech Academy of Sciences Publication Activity Database

    Mutombo, Pingo; Romanyuk, Olexandr

    2014-01-01

    Roč. 115, č. 20 (2014), "203508-1"-"203508-5" ISSN 0021-8979 Grant - others:AVČR(CZ) M100101201 Institutional support: RVO:68378271 Keywords : non-polar GaN * semipolar GaN * surface reconstructions * DFT Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.183, year: 2014

  19. Selective area growth and characterization of GaN nanocolumns, with and without an InGaN insertion, on semi-polar (11–22) GaN templates

    Energy Technology Data Exchange (ETDEWEB)

    Bengoechea-Encabo, A.; Albert, S.; Barbagini, F.; Sanchez-Garcia, M. A.; Calleja, E. [ISOM and Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s/n 28040 Madrid (Spain); Zuñiga-Perez, J.; Mierry, P. de [CRHEA-CNRS, 06560 Valbonne (France); Trampert, A. [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2013-12-09

    The aim of this work is the selective area growth (SAG) of GaN nanocolumns, with and without an InGaN insertion, by molecular beam epitaxyon semi-polar (11–22) GaN templates. The high density of stacking faults present in the template is strongly reduced after SAG. A dominant sharp photoluminescence emission at 3.473 eV points to high quality strain-free material. When embedding an InGaN insertion into the ordered GaN nanostructures, very homogeneous optical properties are observed, with two emissions originating from different regions of each nanostructure, most likely related to different In contents on different crystallographic planes.

  20. Atomic-scale and pit-free flattening of GaN by combination of plasma pretreatment and time-controlled chemical mechanical polishing

    Science.gov (United States)

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2015-08-01

    Chemical mechanical polishing (CMP) combined with atmospheric-pressure plasma pretreatment was applied to a GaN (0001) substrate. The irradiation of a CF4-containing plasma was proven to be very useful for modifying the surface of GaN. When CMP was conducted on a plasma-irradiated surface, a modified layer of GaF3 acted as a protective layer on GaN by preventing the formation of etch pits. Within a short duration (8 min) of CMP using a commercially available CeO2 slurry, an atomically flat surface with a root mean square (rms) roughness of 0.11 nm was obtained. Moreover, etch pits, which are inevitably introduced in conventional CMP, could not be observed at the dislocation sites on the polished GaN surface. It was revealed that CMP combined with the plasma pretreatment was very effective for obtaining a pit-free and atomically flat GaN surface.

  1. Ohmic contact formation mechanism of nonalloyed Pd contacts to p-type GaN observed by positron annihilation spectroscopy

    Science.gov (United States)

    Lee, Jong-Lam; Weber, Marc; Kim, Jong Kyu; Lee, Jae Won; Park, Yong Jo; Kim, Taeil; Lynn, Kelvin

    1999-04-01

    The change of the Fermi energy level at the interface of Pd/p-type GaN by surface treatment was investigated using positron annihilation spectroscopy, and the results were used to provide interpretation of the electrical properties of the contact. Changes in the positron parameters at the interface in the aqua regia-treated GaN are more pronounced than that in the HCl-treated one. This provides evidence that the surface treatment with aqua regia prior to Pd metal deposition removes surface oxides, resulting in the shift of the Fermi level position from a middle of the bandgap to near the valence band. Thus, the barrier for hole injection from metal to p-type GaN is lowered, subsequent to the decrease of contact resistivity by two orders of magnitude.

  2. Characteristics of stimulated emission from optically pumped freestanding GaN grown by hydride vapor-phase epitaxy

    CERN Document Server

    Lee, M H; Kim, S T; Chung, S H; Moon, D C

    1999-01-01

    In this study, we observed optically pumped stimulated emission at room temperature in quasi-bulk GaN prepared from thick-film GaN grown on a sapphire substrate by using hydride vapor-phase epitaxy and subsequent mechanical removal of the sapphire substrate. The stimulated emission from the surface and 1-mm-wide-cleaved cavity of the GaN was red-shifted compared to the spontaneous emission by increasing the optical pumping-power density, and the full width at half maximum (FWHM) of the peak decreased. The stimulated emission was demonstrated to have a highly TE-mode polarized nature, and the super-linear dependence of the integrated emission intensity on the excitation power indicated a threshold pump-power density of I sub t sub h = 2 MW/cm sup 2 for one set of stimulated emissions.

  3. Morphological and optical comparison of the Si doped GaN thin film deposited onto the transparent substrates

    Science.gov (United States)

    Özen, Soner; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan

    2016-04-01

    The aim of this paper is to expand the body of knowledge about the silicon doped gallium nitride thin films deposited on different substrates. The physical properties of the Si doped GaN thin films deposited on the glass and polyethylene terephthalate substrates by thermionic vacuum arc which is plasma production technique were investigated. Thermionic vacuum arc method is a method of producing pure material plasma. The Si doped GaN thin films were analyzed using the following methods and the devices: atomic force microscopy, x-ray diffraction device, spectroscopic ellipsometer and energy dispersive x-ray spectroscopy detector. The produced Si doped GaN thin films are in the (113) orientation. The thicknesses and refractive index were determined by using Cauchy dispersion model. Surface morphologies of produced thin films are homogenous and low roughness. Our analysis showed that the thermionic vacuum arc method present important advantages for optical and industrial applications.

  4. Spatial characterization of a 2 in GaN wafer by Raman spectroscopy and capacitance-voltage measurements

    International Nuclear Information System (INIS)

    Huang, Y; Chen, X D; Fung, S; Beling, C D; Ling, C C

    2004-01-01

    Micro-Raman spectroscopy and capacitance-voltage (C-V) measurements have been used to investigate 2 in GaN epitaxial wafers grown by hydride vapour phase epitaxy on sapphire substrates. The position and line shape of the A 1 longitudinal optical (LO) phonon mode were used to determine the carrier concentration at different locations across the wafer. The line-shape fitting of the Raman A 1 (LO) coupled modes taken from horizontal lateral-different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data compare well with a carrier density map of the wafer obtained by C-V measurements, confirming the non-uniform distribution of carrier concentration in the GaN epitaxial film and that Raman spectroscopy of the LO phonon-plasmon mode can be used as a reliable and production friendly wafer quality test for GaN wafer manufacturing processes

  5. Characterising thermal resistances and capacitances of GaN high-electron-mobility transistors through dynamic electrothermal measurements

    DEFF Research Database (Denmark)

    Wei, Wei; Mikkelsen, Jan H.; Jensen, Ole Kiel

    2014-01-01

    This study presents a method to characterise thermal resistances and capacitances of GaN high-electron-mobility transistors (HEMTs) through dynamic electrothermal measurements. A measured relation between RF gain and the channel temperature (Tc) is formed and used for indirect measurements...... method ensures that trapping effects have insignificant impact on the measurements of Tc responses, which makes this method suitable for GaN HEMT characterisation. The applicability of this method is demonstrated by characterising thermal resistances and capacitances of a CREE CGH40006P GaN HEMT....... of dynamic Tc responses. Thermal resistances and capacitances are characterised on the basis of measured Tc responses and power dissipation (Pd) in HEMTs. The proposed method makes it possible to measure fast Tc responses and avoids the use of imaging and spectroscopy techniques. Additionally, the proposed...

  6. 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.

  7. 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

  8. Bulk GaN and its application as substrates in building quantum nanostructures for some electronic and optoelectronic devices

    Science.gov (United States)

    Bockowski, M.

    2014-09-01

    The use of GaN crystals grown by three methods (and their combinations): Hydride Vapor Phase Epitaxy (HVPE), high nitrogen pressure solution (HNPS) and ammonothermal method for optoelectronic (laser diodes) and electronic (transistors) devices is presented. After a brief review on the development of the three crystallization methods, the GaN crystals' uniform and unique properties, which allow to use them as substrates for building devices, are shown. The Metal Organic Vapor Phase Epitaxy (MOCVD) and Molecular Beam Epitaxy (MBE) technologies for growing the nitride quantum nanostructures as well as the structures' properties and processing of devices are demonstrated. Future challenges and perspectives for application of bulk GaN as substrates in building quantum nanostructures for some electronic and optoelectronic devices are discussed.

  9. Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (112{sup -}2) GaN templates

    Energy Technology Data Exchange (ETDEWEB)

    Niehle, M., E-mail: niehle@pdi-berlin.de; Trampert, A., E-mail: trampert@pdi-berlin.de [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Albert, S.; Bengoechea-Encabo, A.; Calleja, E. [ISOM and Departamento de Ingeniería Electrónica, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain)

    2015-03-01

    We present results of scanning transmission electron tomography on GaN/(In,Ga)N/GaN nanocolumns (NCs) that grew uniformly inclined towards the patterned, semi-polar GaN(112{sup -}2) substrate surface by molecular beam epitaxy. For the practical realization of the tomographic experiment, the nanocolumn axis has been aligned parallel to the rotation axis of the electron microscope goniometer. The tomographic reconstruction allows for the determination of the three-dimensional indium distribution inside the nanocolumns. This distribution is strongly interrelated with the nanocolumn morphology and faceting. The (In,Ga)N layer thickness and the indium concentration differ between crystallographically equivalent and non-equivalent facets. The largest thickness and the highest indium concentration are found at the nanocolumn apex parallel to the basal planes.

  10. 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.

  11. The asymmetric band structure and electrical behavior of the GdScO3/GaN system

    Science.gov (United States)

    Iacopetti, S.; Shekhter, P.; Winter, R.; Tromm, T. C. U.; Schubert, J.; Eizenberg, M.

    2017-05-01

    III-V nitrides are interesting materials for a very wide variety of electronic and optoelectronic devices. In this study, their interaction with GdScO3 (GSO), a ternary rare earth oxide, is investigated for MOS applications. We compare pulsed laser deposited amorphous and crystalline epitaxial GdScO3 in terms of their band alignment with the underlying GaN substrate and the resulting electrical characteristics of the MOS stack. The crystal structure of GdScO3 and GaN is investigated by means of x-ray diffraction, showing that crystalline oxide is growing epitaxially on GaN. X-ray photoelectron spectroscopy analysis shows a staggered band alignment with a GdScO3-GaN valence band offset of 3.6-3.7 eV, which is reflected in a very asymmetric current-voltage behaviour of the MOS capacitors: breakdown at positive bias, significantly earlier for the crystalline oxide (around 5 MV/cm) compared to the amorphous oxide (around 8 MV/cm), and no breakdown up to a field of -14 MV/cm at negative bias. Transmission electron microscopy images show a crystalline, two-atom thick interface layer between GaN and both crystalline and amorphous GdScO3, which is thought to be an electron barrier between GSO and GaN and a possible source of the staggered band alignment. The electrical behaviour can be exploited for asymmetric nano-electronic devices.

  12. The interplay of blocking properties with charge and potential redistribution in thin carbon-doped GaN on n-doped GaN layers

    Science.gov (United States)

    Koller, Christian; Pobegen, Gregor; Ostermaier, Clemens; Huber, Martin; Pogany, Dionyz

    2017-07-01

    In carbon-doped GaN (GaN:C) buffers used in a GaN-on-Si technology, the buffer is embedded in between transition and channel layers. This makes the analysis of buffer properties difficult due to e.g., carrier injection from or potential drop at these adjacent layers. Here, we analyze capacitance- and current-voltage characteristics of 200-300 nm thick GaN:C ([C] = 1019 cm-3) layers which are embedded between a top metal electrode and bottom n-doped GaN (n-GaN). Such structures allow a better potential control in GaN:C and thus determination of the band diagram quantitatively. The accumulation of negative charge (concentration up to 6 × 1017 cm-3) with bias is observed in GaN:C at both polarities. For biases Vappl GaN:C near to its interface with n-GaN so that GaN:C exhibits no potential drop and blocks leakage current. For Vappl > +1.7 V, accumulated negative charges in GaN:C raise an energy barrier of ˜1.1 eV for electron injection from n-GaN to GaN:C. This causes a potential drop in GaN:C leading to a significant leakage current increase. The Fermi level pinning in GaN:C at a commonly referred acceptor at EV + 0.7(±0.2) eV is extracted only from electrostatic considerations. The occupancy change of carbon acceptors is attributed to trapping processes where the dislocation-related conductive paths are supposed to be involved in carrier transport from the top metal electrode to the carbon defect.

  13. Analysis of Arbovirus Isolates from Australia Identifies Novel Bunyaviruses Including a Mapputta Group Virus from Western Australia That Links Gan Gan and Maprik Viruses.

    Directory of Open Access Journals (Sweden)

    Thomas Briese

    Full Text Available The Mapputta group comprises antigenically related viruses indigenous to Australia and Papua New Guinea that are included in the family Bunyaviridae but not currently assigned to a specific genus. We determined and analyzed the genome sequences of five Australian viruses isolated from mosquitoes collected during routine arbovirus surveillance in Western Australia (K10441, SW27571, K13190, and K42904 and New South Wales (12005. Based on matching sequences of all three genome segments to prototype MRM3630 of Trubanaman virus (TRUV, NB6057 of Gan Gan virus (GGV, and MK7532 of Maprik virus (MPKV, isolates K13190 and SW27571 were identified as TRUV, 12005 as GGV, and K42904 as a Mapputta group virus from Western Australia linking GGV and MPKV. The results confirmed serum neutralization data that had linked SW27571 to TRUV. The fifth virus, K10441 from Willare, was most closely related to Batai orthobunyavirus, presumably representing an Australian variant of the virus. Phylogenetic analysis also confirmed the close relationship of our TRUV and GGV isolates to two other recently described Australian viruses, Murrumbidgee virus and Salt Ash virus, respectively. Our findings indicate that TRUV has a wide circulation throughout the Australian continent, demonstrating for the first time its presence in Western Australia. Similarly, the presence of a virus related to GGV, which had been linked to human disease and previously known only from the Australian southeast, was demonstrated in Western Australia. Finally, a Batai virus isolate was identified in Western Australia. The expanding availability of genomic sequence for novel Australian bunyavirus variants supports the identification of suitably conserved or diverse primer-binding target regions to establish group-wide as well as virus-specific nucleic acid tests in support of specific diagnostic and surveillance efforts throughout Australasia.

  14. Analysis of Arbovirus Isolates from Australia Identifies Novel Bunyaviruses Including a Mapputta Group Virus from Western Australia That Links Gan Gan and Maprik Viruses.

    Science.gov (United States)

    Briese, Thomas; Williams, David T; Kapoor, Vishal; Diviney, Sinead M; Certoma, Andrea; Wang, Jianning; Johansen, Cheryl A; Chowdhary, Rashmi; Mackenzie, John S; Lipkin, W Ian

    2016-01-01

    The Mapputta group comprises antigenically related viruses indigenous to Australia and Papua New Guinea that are included in the family Bunyaviridae but not currently assigned to a specific genus. We determined and analyzed the genome sequences of five Australian viruses isolated from mosquitoes collected during routine arbovirus surveillance in Western Australia (K10441, SW27571, K13190, and K42904) and New South Wales (12005). Based on matching sequences of all three genome segments to prototype MRM3630 of Trubanaman virus (TRUV), NB6057 of Gan Gan virus (GGV), and MK7532 of Maprik virus (MPKV), isolates K13190 and SW27571 were identified as TRUV, 12005 as GGV, and K42904 as a Mapputta group virus from Western Australia linking GGV and MPKV. The results confirmed serum neutralization data that had linked SW27571 to TRUV. The fifth virus, K10441 from Willare, was most closely related to Batai orthobunyavirus, presumably representing an Australian variant of the virus. Phylogenetic analysis also confirmed the close relationship of our TRUV and GGV isolates to two other recently described Australian viruses, Murrumbidgee virus and Salt Ash virus, respectively. Our findings indicate that TRUV has a wide circulation throughout the Australian continent, demonstrating for the first time its presence in Western Australia. Similarly, the presence of a virus related to GGV, which had been linked to human disease and previously known only from the Australian southeast, was demonstrated in Western Australia. Finally, a Batai virus isolate was identified in Western Australia. The expanding availability of genomic sequence for novel Australian bunyavirus variants supports the identification of suitably conserved or diverse primer-binding target regions to establish group-wide as well as virus-specific nucleic acid tests in support of specific diagnostic and surveillance efforts throughout Australasia.

  15. Atomic Layer Epitaxy Dielectric Based GaN MOS Devices and Beyond

    Science.gov (United States)

    Zhou, Hong

    GaN HEMT usually suffers from high Ig and ID current collapse due to its limited Schottky barrier height and high density of surface states. Although GaN MOSHEMT with amorphous gate dielectric is an effective way to suppress the Ig and passivate the surface states, high-quality gate dielectric on GaN MOS devices are still lacking. In this work, single crystalline gate dielectric Mg0.25Ca0.75O, grown by ALE, has been successfully integrated into three kinds of GaN MOSHEMTs, namely InAlN/GaN/SiC, AlGaN/GaN/SiC and AlGaN/GaN/Si MOSHEMTs. With a nearly lattice-matched oxide, the interface quality between the oxide and barrier is significantly improved. Ig is reduced by several orders of magnitudes compared to HEMTs. All three kinds of MOSHEMTs exhibit high ID on/off ratio exceeding 1011, near ideal SS, negligible ID-V GS hysteresis and negligible current collapse. RF small-signal characteristics of AlGaN/GaN/SiC MOSHEMTs show ft/fmax of 101/150 GHz for a Lg of 120 nm device and large-signal characteristics with Pout of 4.18 W/mm for a Lg=150 nm device at f=35 GHz. Enhancement-mode non-recessed AlGaN/GaN/Si fin-MOSHEMTs are also realized through the side-wall depletion of the fin structures. Combining with the high ID, high peak gm, and low Ron, MgCaO turns out to be a new and very promising gate dielectric for GaN MOS technology. Beyond the wide bandgap semiconductor GaN, promising next generation ultra-wide bandgap semiconductor beta-Ga2O3 is also investigated. Piranha solution and PDA were first used to optimize the ALD Al2O3/beta-Ga2O3 interface. Low C-V hysteresis of 0.1 V and Dit=2.3x1011 cm-2˙eV-1 are achieved due to the passivated dangling bonds at the interface. Meanwhile, we have demonstrated a record high ID of 600/450 mA/mm for D/E-mode back-gate GOOI FETs at a beta-Ga2O3 doping concentration of 2.8x1018 cm-3. Following the motivation of chasing higher I D and lower Ron, we have increased the doping concentration to 7.8x1018 cm-3 and the record ID has been

  16. Microscopic evidence for the dissociation of water molecules on cleaved GaN(11[combining macron]00).

    Science.gov (United States)

    Wu, Shih-Yu; Lang, Liang-Wei; Cai, Pei-Yang; Chen, Yun-Wen; Lai, Yu-Ling; Lin, Ming-Wei; Hsu, Yao-Jane; Lee, Wei-I; Kuo, Jer-Lai; Luo, Meng-Fan; Kuo, Chien-Cheng

    2018-01-03

    The dissociation of water molecules absorbed on a cleaved non-polar GaN(11[combining macron]00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (macron]00) respectively. These results highlight the promising applications of the non-polar GaN(11[combining macron]00) surface in water dissociation and hydrogen generation.

  17. Characteristics of threading dislocations in ZnO grown on facet-controlled epitaxial overgrown GaN templates

    International Nuclear Information System (INIS)

    Zhou, H L; Chua, S J; Chow, S Y; Pan, H; Zhu, Y W; Feng, Y P; Wang, L S; Zang, K Y; Liu, W; Tripathy, S

    2007-01-01

    Using transmission electron microscopy (TEM), the authors have investigated the behavior of threading dislocations in ZnO selectively grown on a facet-controlled epitaxial overgrown GaN template. In this case, the ZnO is grown by a vapor transport method. The TEM study in the overgrown regions shows that all the pure-edge type dislocations in ZnO are parallel toward the mask area and vertical propagation of dislocation to the ZnO surface is minimized. Using such a selective growth technique on a faceted semi-polar GaN surface, a reduction of threading dislocation density in ZnO could be achieved

  18. Driving of a GaN enhancement mode HEMT transistor with zener diode protection for high efficiency and low EMI

    OpenAIRE

    Spro, Ole Christian; Basu, Supratim; Abuishmais, Ibrahim Abed; Midtgård, Ole-Morten; Undeland, Tore Marvin

    2017-01-01

    The ultra-low gate charge characteristics and low gate voltage limitation of a GaN enhancement mode HEMT in combination with stray circuit elements poses many challenges of driving them in power electronic applications. This paper investigates the effect of changing gate resistances and including a Zener diode for overvoltage protection in the gate circuit. The goal is to achieve low switching losses and low EMC signature. Due to the very low gate capacitance of the GaN HEMT compared to the j...

  19. Measuring the thermal conductivity of the GaN buffer layer in AlGaN/GaN HEMTs

    OpenAIRE

    Power, Maire; Pomeroy, James W; Otoki, Yohei; Tanaka, Takeshi; Wada, Jiro; Kuzuhara, Masaaki; Jantz, Wolfgang; Souzis, Andrew; Kuball, Martin H H

    2015-01-01

    The thermal conductivity of the GaN buffer layer in AlGaN/GaN devices can be determined by measuring the vertical temperature gradient through this layer. In this work, diamond micro-thermometers and standard micro-Raman thermography were used to determine the surface and volumetric depth average temperature, respectively, of the carbon-doped GaN buffer layer in AlGaN/GaN transistors. By comparing measured temperatures with finite element thermal simulation, a thermal conductivity of 200 ± 20...

  20. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    International Nuclear Information System (INIS)

    Mamand, S.M.; Omar, M.S.; Muhammad, A.J.

    2012-01-01

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: ► A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. ► A direct method is used to calculate phonon group velocity for these nanowires. ► 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. ► Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2–300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10 14 m −2 the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10 14 m −2 , lattice thermal conductivity would be independent of that.

  1. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Mamand, S.M., E-mail: soran.mamand@univsul.net [Department of Physics, College of Science, University of Sulaimani, Sulaimanyah, Iraqi Kurdistan (Iraq); Omar, M.S. [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq); Muhammad, A.J. [Department of Physics, College of Science, University of Kirkuk, Kirkuk (Iraq)

    2012-05-15

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.

  2. Interface characterization of atomic layer deposited high-k on non-polar GaN

    Science.gov (United States)

    Jia, Ye; Zeng, Ke; Singisetti, Uttam

    2017-10-01

    The interface properties between dielectrics and semiconductors are crucial for electronic devices. In this work, we report the electrical characterization of the interface properties between atomic layer deposited Al2O3 and HfO2 on non-polar a-plane ( 11 2 ¯ 0 ) and m-plane ( 1 1 ¯ 00 ) GaN grown by hybrid vapor phase epitaxy. A metal oxide semiconductor capacitor (MOSCAP) structure was used to evaluate the interface properties. The impact of annealing on the interface properties was also investigated. The border trap in the oxide, characterized by the capacitance-voltage (C-V) hysteresis loop, was low. The interface state density (Dit), extracted using the ac conductance method, is in the range of 0.5 × 1012/cm2 eV to 7.5 × 1011/cm2 eV within an energy range from 0.2 eV to 0.5 eV below the conduction band minimum. The m-plane GaN MOSCAPs exhibited better interface properties than the a-plane GaN MOSCAPs after annealing. Without annealing, Al2O3 dielectrics had higher border trap density and interface state density compared to HfO2 dielectrics. However, the annealing had different impacts on Al2O3 dielectrics as compared to HfO2. Our results showed that the annealing degraded the quality of the interface in HfO2, but it improved the quality of the interface in Al2O3 devices. The annealing also reduced the positive trapped oxide charge, resulting in a shift of C-V curves towards the positive bias region.

  3. Multibias and thermal behavior of microwave GaN and GaAs based HEMTs

    Science.gov (United States)

    Alim, Mohammad A.; Rezazadeh, Ali A.; Gaquiere, Christophe

    2016-12-01

    Multibias and thermal characterizations on 0.25 μm × (2 × 100) μm AlGaN/GaN/SiC HEMT and 0.5 μm × (2 × 100) μm AlGaAs/InGaAs pseudomorphic HEMT have carried out for the first time. Two competitive device technologies are investigated with the variations of bias and temperature in order to afford a detailed realization of their potentialities. The main finding includes the self heating effect in the GaN device, zero temperature coefficient points at the drain current and transconductance in the GaAs device. The thermal resistance RTH of 7.1, 8.2 and 9.4 °C mm/W for the GaN device was estimated at 25, 75 and 150 °C respectively which are consistent with those found in the open literature. The temperature trend of the threshold voltage VT, Schottky barrier height ϕb, sheet charge densities of two dimensional electron gas ns, and capacitance under the gate Cg are exactly opposite in the two devices; whereas the knee voltage Vk, on resistance Ron, and series resistance Rseries are shows similar trend. The multi-bias and thermal behavior of the output current Ids, output conductance gds, transconductance gm, cut-off frequency ft, maximum frequency fmax, effective velocity of electron, veff and field dependent mobility, μ demonstrates a great potential of GaN device. These results provide some valuable insights for technology of preference for future and current applications.

  4. Spectroscopic XPEEM of highly conductive SI-doped GaN wires

    Energy Technology Data Exchange (ETDEWEB)

    Renault, O., E-mail: olivier.renault@cea.fr [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Morin, J. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Tchoulfian, P. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Chevalier, N. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CEA, LETI, MINATEC Campus, F-38054 Grenoble (France); Feyer, V. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich (Germany); Pernot, J. [Univ. Grenoble Alpes, F-38000 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Institut Universitaire de France, F-75005 Paris (France); Schneider, C.M. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, D-52425 Jülich (Germany)

    2015-12-15

    Using soft X-ray photoelectron emission microscopy (XPEEM), complemented by scanning Auger microscopy (SAM) and scanning capacitance microscopy, we have quantitatively studied the incorporation of silicon and band bending at the surface (m-facet) of an individual, highly conductive Si-doped GaN micro-wires (Tchoulfian et al., Applied Physics Letters 102 (12), 2013). Electrically active n-dopants Si atoms in Ga interstitial sites are detected as nitride bonding states in the high-resolution Si2p core level spectra, and represent only a small fraction (<10%) of the overall Si surface concentration measured by SAM. The derived carrier concentration of 2×10{sup 21} at cm{sup −3} is in reasonable agreement with electrical measurements. A consistent surface band bending of ~1 eV is directly evidenced by surface photo-voltage measurements. Such an approach combining different surface-sensitive microscopies is of interest for studying other heavily doped semiconducting wires. - Highlights: • XPEEM analysis of state-of-the-art, heavily doped GaN wires with insights on the issue of the origin of the increased conductivity. • Combined microscopic approach with Scanning Auger microscopy and X-ray Photoeletron Emission Microscopy, to quantity the electrically active Si-dopants in GaN. • The determined concentration is found in reasonable agreement with the one derived from bulk electrical measurements. • The proposed method is of interest for studying the electronics and chemistry of doping in other heavily doped semiconducting wires.

  5. Efficiency and Linearity Enhancement of Microwave GaN Power Amplifiers using Harmonic Injection

    Science.gov (United States)

    Dani, Asmita Rajiv

    This thesis addresses an architecture for enhancing efficiency and linearity of GaN power amplifiers using external second harmonic injection at the output. This transmitter architecture has potential uses in communication and radar systems which have stringent requirements of low DC power dissipation and minimum out of band interference. An idealized theoretical analysis based on expansions of the nonlinear transfer function of a PA predicts the measured improvements in linearity and efficiency. The experimental demostration is performed with both hybrid and integrated harmonically-injected PA using discrete GaN 6W transistors in class-AB mode with 55% PAE at a fundamental frequency of 2.45 GHz. Harmonic injection at the output is shown to enhance the efficiency of the PA to 89%. For a slightly reduced efficiency of 78%, the linearity can be improved and > 15 dB reduction of third and fifth order intermodulation distortion tones is measured in compression. Integration of a dynamic supply of the harmonically-injected PA is also investigated in order to achieve high efficiency and linearity for signals with Peak-to-Average ratios (PARs) of 6 dB and higher. Experimental results demonstrate a 70-80% efficient HI-PA for an output power variation of 6 dB. Reduction in third order nonlinear products and AM-PM distortion shows improved linearity of the PA over the entire range of power levels. Finally, the concept is extended to an X-band GaN MMIC to demonstrate integration and efficiency enhancement at 10 GHz with a 4 W, 47% efficient class-AB PA, with an expected final efficiency of over 60% with harmonic injection.

  6. 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.

  7. Bulk GaN alpha-particle detector with large depletion region and improved energy resolution

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Qiang; Mulligan, Padhraic [Nuclear Engineering Program, Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210 (United States); Wang, Jinghui [Department of Radiology, Stanford University, 1201 Welch Rd, Stanford, CA 94305 (United States); Chuirazzi, William [Nuclear Engineering Program, Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210 (United States); Cao, Lei, E-mail: cao.152@osu.edu [Nuclear Engineering Program, Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210 (United States)

    2017-03-21

    An alpha-particle detector was fabricated using a freestanding n-type bulk GaN wafer with a Au/Ni/GaN sandwich Schottky structure. Current–voltage measurements at room temperature revealed a Schottky contact with a leakage current of 7.53±0.3 nA at a reverse bias of 200 V. The detector had a large depletion depth that can capture much of the energy from 5.486 MeV alpha particles emitted from a {sup 241}Am source. The resolution of its alpha-particle energy spectrum was improved to 2.2±0.2% at 5.486 MeV under a bias of 550 V. This superior resolution was attributed to the shortening of the carrier transit time and the large energy deposition within the large depletion depth, i.e., 27 µm at −550 V, which all resulted in a more complete charge collection. A model developed using the ATLAS simulation framework from Silvaco Inc. was employed to study the charge collection process. The simulation results were found to agree closely with the experimental results. This detector will be beneficial for research at neutron scattering facilities, the International Thermonuclear Experimental Reactor, and the Large Hadron Collider, among other institutions, where the Si-based charged particle detectors could be quickly degraded in an intense radiation field. - Highlights: • An alpha-particle detector based on a Schottky-structured GaN wafer was tested. • The detector's large depletion depth enables fuller energy spectra to be obtained. • The best resolution yet attained in GaN alpha-particle spectrometry was achieved. • The detector's short carrier transit time resulted in improved charge collection. • This detector is usable in extreme conditions, including intense radiation fields.

  8. 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.)

  9. Influence of the p-type doping concentration on reflection-mode GaN photocathode

    Science.gov (United States)

    Wang, Xiaohui; Chang, Benkang; Ren, Ling; Gao, Pin

    2011-02-01

    Four different p-type doping GaN photocathodes are activated by Cs/O, and the quantum efficiency (QE) curves are obtained. According to the QE equation, the curves are fitted. Both the QE curves and the fitting results show that the optimal p-type doping concentration is at 1017 cm-3. The electron diffusion length and surface-electron escape probability can be balanced well at 1017 cm-3. To a certain degree, thick emission layer is conducive to improving the QE, which is more obvious with the long wavelength.

  10. Atomic and electronic structure of N-terminated GaN(0001) (1 × 1) surface

    Czech Academy of Sciences Publication Activity Database

    Romanyuk, Olexandr; Jiříček, Petr; Paskova, T.

    2012-01-01

    Roč. 398, č. 1 (2012), s. 1-6 ISSN 1742-6588. [17th International School on Condensed Matter Pjysics (ISCMP): Open Problems in Condesed Matter Physics, BIiomedical Physics and their Applications. Varna, 02.09.2012-07..09.2012] R&D Projects: GA ČR GPP204/10/P028 Grant - others:AV ČR(CZ) M100101201 Institutional research plan: CEZ:AV0Z10100521 Keywords : clean surfaces * GaN * photoelectron diffraction * REELS * ab initio DFT * optical response Subject RIV: BM - Solid Matter Physics ; Magnetism http://iopscience.iop.org/1742-6596/398/1/012013

  11. MOCVD Growth of GAN, AlN and AlGaN for UV Photodetector Applications

    Science.gov (United States)

    1993-01-01

    00 1%%ý MOCVD Growth of GaN, AIN and AIGaN for OK UV Photodetector Applications ONR contract #N00014-93-1- 0235 ,a_ Principal Investigator: Prof...This work is supported by the .ONR contract through the contract No. N00014-93-1- 0235 . We would like to thank Dr. T. Okuda and the Ministry of...resolution X-ray diffractometer with a four crystal monochromecer (MPD 1880 / HP ) were used to identify the crystallinity of the films.5 Fourier

  12. N-Face GaN Electronics for Heteroepitaxial and Bonded Structures

    Science.gov (United States)

    2015-08-27

    material system, such as GaN, which supports higher breakdown limits, then the trade-off can be overcome. An III- Arsenide (III-As)/III-Nitride (III-N...Investigations may then start by forming a heterostructure comprising both III- Arsenide (III-As) and III-Nitride (III-N) material systems. But such formation is...in the choice of the type of ion and the ion-implantation dose, namely aluminum ions [Al+] and 1015 cm-2, respectively. The energy of ion

  13. Impact of the GaN nanowire polarity on energy harvesting

    International Nuclear Information System (INIS)

    Gogneau, Noelle; Galopin, Elisabeth; Guilet, Stephane; Travers, Laurent; Harmand, Jean-Christophe; Chrétien, Pascal; Houzé, Frédéric

    2014-01-01

    We investigate the piezoelectric generation properties of GaN nanowires (NWs) by atomic force microscopy equipped with a Resiscope module for electrical measurements. By correlating the topography profile of the NWs with the recorded voltage peaks generated by these nanostructures in response to their deformation, we demonstrate the influence of their polarity on the rectifying behavior of the Schottky diode formed between the NWs and the electrode of measurement. These results establish that the piezo-generation mechanism crucially depends on the structural characteristics of the NWs.

  14. High frequency dynamic bending response of piezoresistive GaN microcantilevers

    Science.gov (United States)

    Talukdar, Abdul; Qazi, Muhammad; Koley, Goutam

    2012-12-01

    Static and dynamic ac responses of piezoresistive GaN microcantilevers, with integrated AlGaN/GaN heterostructure field effect transistors as highly sensitive deflection transducers, have been investigated. Very high gauge factor exceeding 3500 was exhibited by the microcantilevers, with quality factor determined from electronically transduced ac response exceeding 200 in air and 4500 at low pressure. The gauge factor reduced at resonance frequency of the cantilevers, possibly due to reduced charge exchange with surface donor and trap states. Ultrasonic waves generated in air by a piezochip, and in the Si substrate through photoacoustic effect, could be detected by the cantilevers with high sensitivity.

  15. Analysis of noise spectra in GaAs and GaN Schottky barrier diodes

    International Nuclear Information System (INIS)

    Pardo, D; Grajal, J; Mencía, B; Pérez, S; Mateos, J; González, T

    2011-01-01

    The Monte Carlo method is applied in this paper to characterize the noise spectra of GaAs and GaN Schottky barrier diodes operating under static and time varying conditions. We show the influence of the structure of the diode and working regimes on the noise spectrum of the diodes. Besides, the paper evaluates the capabilities of published analytical models to describe the noise spectra in Schottky diodes under time varying conditions. This is a further step toward the development of a design tool that integrates both the electrical response and the intrinsic noise generated in the devices

  16. Metal contacts in nanocrystalline n-type GaN: Schottky diodes.

    Science.gov (United States)

    Das, S N; Sarangi, S; Sahu, S N; Pal, A K

    2009-04-01

    Contact properties in nanocrystalline n-GaN in thin film form were studied by depositing nanocrystalline films onto aluminium coated fused silica substrates by high pressure sputtering of Si (1 at%) doped GaN target. Schottky diodes were realized with Au, Ni and Pd as top contacts on the nanocrystalline n-GaN films to examine the contact properties of the diodes thus formed. Variation of current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Schottky diodes were recorded at different temperatures and analyzed in the light of the existing theories.

  17. Ion blocking and channeling studies of heteroepitaxial GaN layers

    International Nuclear Information System (INIS)

    Flagmeyer, R.; Ehrlich, C.; Geist, V.; Otto, G.

    1978-01-01

    Ion channeling and blocking in backscattering measurements were used for the characterization of thin epitaxial GaN layers, which have varied lattice imperfections involved by different growth conditions. In particular, the following characteristics were examined: (1) the thickness and the uniformity of the layers, (2) the depth dependence of the crystalline imperfection, (3) the dislocation density, (4) the spread in the orientation distribution of tilted crystallites, and (5) some other types of imperfections, such as stacking faults, double positioning, twins and bending of the layer

  18. Critical aspects of substrate nanopatterning for the ordered growth of GaN nanocolumns.

    Science.gov (United States)

    Barbagini, Francesca; Bengoechea-Encabo, Ana; Albert, Steven; Martinez, Javier; Sanchez García, Miguel Angel; Trampert, Achim; Calleja, Enrique

    2011-12-14

    Precise and reproducible surface nanopatterning is the key for a successful ordered growth of GaN nanocolumns. In this work, we point out the main technological issues related to the patterning process, mainly surface roughness and cleaning, and mask adhesion to the substrate. We found that each of these factors, process-related, has a dramatic impact on the subsequent selective growth of the columns inside the patterned holes. We compare the performance of e-beam lithography, colloidal lithography, and focused ion beam in the fabrication of hole-patterned masks for ordered columnar growth. These results are applicable to the ordered growth of nanocolumns of different materials.

  19. Formation mechanisms of GaN nanowires grown by selective area growth homoepitaxy.

    Science.gov (United States)

    Gačević, Žarko; Gómez Sánchez, Daniel; Calleja, Enrique

    2015-02-11

    This work provides experimental evidence and theoretical explanations regarding the formation mechanisms of GaN nanowires grown by selective area growth on GaN-on-sapphire templates. The first growth stage, driven by selective area growth kinetics, consists of initial nucleation (along the nanohole inner periphery), coalescence onset and full coalescence, producing a single nanocrystal within each nanohole. In the second growth stage, driven by free-surface-energy minimization, the formed nanocrystal undergoes morphological evolution, exhibiting initial cylindrical-like shape, intermediate dodecagonal shape and a final, thermodynamically stable hexagonal shape. From this point on, the nanowire vertical growth proceeds while keeping the stable hexagonal form.

  20. Investigation of a GaN Nucleation Layer on a Patterned Sapphire Substrate

    International Nuclear Information System (INIS)

    Wu Meng; Zeng Yi-Ping; Wang Jun-Xi; Hu Qiang

    2011-01-01

    A low-temperature GaN (LT-GaN) nucleation layer is grown on a patterned sapphire substrate (PSS) using metal-organic chemical vapor deposition (MOCVD). The surface morphology of the LT-GaN is investigated and the selective nucleation phenomenon in the growth process of the LT-GaN nucleation layer is discovered. Meanwhile, effects of thickness of the LT-GaN and the annealing process on the phenomenon are also discussed. A pattern model is also proposed to analyze the possible mechanisms in atomic scale. (cross-disciplinary physics and related areas of science and technology)

  1. Investigation of a GaN nucleation layer on a patterned sapphire substrate

    International Nuclear Information System (INIS)

    Wu Meng; Zeng Yiping; Wang Junxi; Hu Qiang

    2011-01-01

    A low-temperature GaN (LT-GaN) nucleation layer is grown on a patterned sapphire substrate (PSS) using metal-organic chemical vapor deposition (MOCVD). The surface morphology of the LT-GaN is investigated and the selective nucleation phenomenon in the growth process of the LT-GaN nucleation layer is discovered. Meanwhile, effects of thickness of the LT-GaN and the annealing process on the phenomenon are also discussed. A pattern model is also proposed to analyze the possible mechanisms in atomic scale. (authors)

  2. 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.

  3. -AGAn /-GAn AND -ICI SUFFIXES IN TURKISH AND THEIR USAGE IN SÛDÎ’S ANNOTATION TÜRKÇEDE -AGAn /-GAn VE -ICI EKLERİ VE SÛDÎ ŞERHİNDEKİ KULLANIMLARI

    Directory of Open Access Journals (Sweden)

    Mevlüt ERDEM

    2010-07-01

    Full Text Available The suffixes of -AGAn / -GAn used unfrequently in Modern Turkish exhibit some important features in the development of Turkish. In Karakhanid Turkic, the habitual meaning of the verb is formed with -GAn participle and in some cases with -AGAn. This usage increases gradually in Old Anatolian Turkish and Sudi’s annotation. Sudi utilizes the derivation of -AGAn/-GAn used in his time productively in word formation in order to translate the exact meaning of the Persian words into Turkish, which were called sıfat-ı müşebbehe (an adjective formed from a verb. In these derivations, although the habitual meaning of the verbs is stressed, some of them function as participles. On the other hand, Sudi uses Turkish -IcI suffix in order to substitute Persian agent nouns (ism-i fail. The suffix functions as non-finite verbs in some constructions like -AGAn /-GAn suffixes. Türkiye Türkçesinde işlek olmayan -AGAn/-GAn eki Türkçenin gelişiminde önemli özellikler sergiler. Karahanlı Türkçesinde fiildeki süreklilik anlamı -GAn sıfat-fiiliyle birlikte az da olsa -AGAn ekiyle de sağlanır. Bu kullanım EAT eserlerinde ve Sûdî şerhinde artarak devam eder. Sûdî, döneminde hâlâ işlek olarak kullanıldığını anladığımız -AGAn / -GAn’lı türetimleri Farsça sıfat-ı müşebbehe olan kelimelerin Türkçedeki anlamlarını tam olarak vermek için kullanır. Bu türetimlerde fiilin sürekli yapıldığı vurgulansa da bunların bir kısmı sıfat-fiil işleyişindedir. Sûdî, şerhinde ism-i failleri karşılamak için ise -IcI ekinden yararlanır. Bu ek de -AGAn/-GAn ekleri gibi bazı kullanımlarda bitimsiz fiil işleyişindedir.

  4. Influences of growth parameters on the reaction pathway during GaN synthesis

    Science.gov (United States)

    Zhang, Zhi; Liu, Zhongyi; Fang, Haisheng

    2018-01-01

    Gallium nitride (GaN) film growth is a complicated physical and chemical process including fluid flow, heat transfer, species transport and chemical reaction. Study of the reaction mechanism, i.e., the reaction pathway, is important for optimizing the growth process in the actual manufacture. In the paper, the growth pathway of GaN in a closed-coupled showerhead metal-organic chemical vapor deposition (CCS-MOCVD) reactor is investigated in detail using computational fluid dynamics (CFD). Influences of the process parameters, such as the chamber pressure, the inlet temperature, the susceptor temperature and the pre-exponential factor, on the reaction pathway are examined. The results show that increases of the chamber pressure or the inlet temperature, as well as reductions of the susceptor temperature or the pre-exponential factor lead to the adduct route dominating the growth. The deposition rate contributed by the decomposition route, however, can be enhanced dramatically by increasing the inlet temperature, the susceptor temperature and the pre-exponential factor.

  5. GaN directional couplers for on-chip optical interconnect

    Science.gov (United States)

    Yuan, Jialei; Gao, Xumin; Yang, Yongchao; Zhu, Guixia; Yuan, Wei; Choi, Hoi Wai; Zhang, Zhiyu; Wang, Yongjin

    2017-04-01

    Here, we propose, fabricate and characterize GaN directional couplers for on-chip optical interconnect on a GaN-on-silicon platform. Suspended InGaN/GaN multiple-quantum-well diodes are adopted for both the transmitter and the receiver, and GaN directional couplers are used to achieve the light coupling between suspended waveguides that are directly connected to the transmitter and the receiver. The proposed on-chip optical interconnects are experimentally demonstrated by light propagation and in-plane data transmission using visible light. The light propagation images directly show that the emitted light can be laterally coupled into the suspended waveguide, and the guided light from the input waveguide then couples to the coupled waveguide due to the overlapped slab. The receiver detects the transmitted light from the coupled waveguide to complete the in-plane visible light communication process, as confirmed by pseudo-random binary sequence data and eye diagrams at the transmission rate of 30 Mbps.

  6. Zn Electrodeposition on Single-Crystal GaN(0001 Surface: Nucleation and Growth Mechanism

    Directory of Open Access Journals (Sweden)

    Fei Peng

    2016-01-01

    Full Text Available The electrochemical deposition of zinc on single-crystal n-type GaN(0001 from a sulphate solution has been investigated on the basis of electrochemical techniques including cyclic voltammetry, chronoamperometry, and Tafel plot. The morphology and crystal structure of zinc deposits have been characterized by means of scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray analysis. The result has revealed that the deposition of Zn on GaN electrode commenced at a potential of −1.12 V versus Ag/AgCl. According to the Tafel plot, an exchange current density of ~0.132 mA cm−2 was calculated. In addition, the current transient measurements have shown that Zn deposition process followed the instantaneous nucleation in 10 mM ZnSO4 + 0.5 M Na2SO4 + 0.5 M H3BO3 (pH = 4.

  7. Self-Healing Thermal Annealing: Surface Morphological Restructuring Control of GaN Nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Conroy, Michele; Li, Haoning; Zubialevich, Vitaly Z.; Kusch, Gunnar; Schmidt, Michael; Collins, Timothy; Glynn, Colm; Martin, Robert W.; O’Dwyer, Colm; Morris, Michael D.; Holmes, Justin D.; Parbrook, Peter J.

    2016-12-07

    With advances in nanolithography and dry etching, top-down methods of nanostructuring have become a widely used tool for improving the efficiency of optoelectronics. These nano dimensions can offer various benefits to the device performance in terms of light extraction and efficiency, but often at the expense of emission color quality. Broadening of the target emission peak and unwanted yellow luminescence are characteristic defect-related effects due to the ion beam etching damage, particularly for III–N based materials. In this article we focus on GaN based nanorods, showing that through thermal annealing the surface roughness and deformities of the crystal structure can be “self-healed”. Correlative electron microscopy and atomic force microscopy show the change from spherical nanorods to faceted hexagonal structures, revealing the temperature-dependent surface morphology faceting evolution. The faceted nanorods were shown to be strain- and defect-free by cathodoluminescence hyperspectral imaging, micro-Raman, and transmission electron microscopy (TEM). In-situ TEM thermal annealing experiments allowed for real time observation of dislocation movements and surface restructuring observed in ex-situ annealing TEM sampling. This thermal annealing investigation gives new insight into the redistribution path of GaN material and dislocation movement post growth, allowing for improved understanding and in turn advances in optoelectronic device processing of compound semiconductors.

  8. 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

  9. Stopping Power and Energy Straggling of Channeled He-Ions in GaN

    International Nuclear Information System (INIS)

    Turos, A.; Ratajczak, R.; Pagowska, K.; Nowicki, L.; Stonert, A.; Caban, P.

    2011-01-01

    GaN epitaxial layers are usually grown on sapphire substrates. To avoid disastrous effect of the large lattice mismatch a thin polycrystalline nucleation layer is grown at 500 o C followed by the deposition of thick GaN template at much higher temperature. Remnants of the nucleation layer were visualized by transmission electron microscopy as defect agglomeration at the GaN/sapphire interface and provide a very useful depth marker for the measurement of channeled ions stopping power. Random and aligned spectra of He ions incident at energies ranging from 1.7 to 3.7 MeV have been measured and evaluated using the Monte Carlo simulation code McChasy. Impact parameter dependent stopping power has been calculated for channeling direction and its parameters have been adjusted according to experimental data. For virgin, i.e. as grown, samples, the ratio of channeled to random stopping power is constant and amounts to 0.7 in the energy range studied. Defects produced by ion implantation largely influence the stopping power. For channeled ions the variety of possible trajectories leads to different energy loss at a given depth, thus resulting in much larger energy straggling than that for the random path. Beam energy distributions at different depths have been calculated using the McChasy code. They are significantly broader than those predicted by the Bohr formula for random direction. (author)

  10. Transient current analysis of a GaN radiation detector by TCAD

    International Nuclear Information System (INIS)

    Wang, Jinghui; Mulligan, Padhraic L.; Cao, Lei R.

    2014-01-01

    A gallium nitride (GaN) Schottky diode radiation detector has been fabricated with a successfully demonstrated radiation response to alpha particles and neutrons when using Li as a convertor. In order to understand the charge collection process for further device modification, the Sentaurus TCAD software package is employed to quantitatively study the transient current produced by energetic charge particles. By comparing the simulation and experimental results, especially the capacitance–voltage relationship and charge collection efficiency, the device parameters and physics models used for the simulation are validated. The time behavior of the transient current is studied, and the carrier generation/loss by impact ionization, recombination, and trapping are discussed. The total collected charge contributed by various components, such as drift, funneling, and diffusion are also analyzed. - Highlights: • A TCAD model is established for a GaN Schottky diode radiation detector. • Schottky side mainly collects holes, while ohmic side solely collects electrons. • The funneling region evolution is visualized by carrier current densities. • Carrier generation/loss by impact ionization/trapping is insignificant. • The collected charges are primarily drift carriers in the depletion region

  11. Estimation of background carrier concentration in fully depleted GaN films

    International Nuclear Information System (INIS)

    Chandrasekar, Hareesh; Singh, Manikant; Raghavan, Srinivasan; Bhat, Navakanta

    2015-01-01

    Buffer leakage is an important parasitic loss mechanism in AlGaN/GaN high electron mobility transistors (HEMTs) and hence various methods are employed to grow semi-insulating buffer layers. Quantification of carrier concentration in such buffers using conventional capacitance based profiling techniques is challenging due to their fully depleted nature even at zero bias voltages. We provide a simple and effective model to extract carrier concentrations in fully depleted GaN films using capacitance–voltage (C–V) measurements. Extensive mercury probe C–V profiling has been performed on GaN films of differing thicknesses and doping levels in order to validate this model. Carrier concentrations as extracted from both the conventional C–V technique for partially depleted films having the same doping concentration, and Hall measurements show excellent agreement with those predicted by the proposed model thus establishing the utility of this technique. This model can be readily extended to estimate background carrier concentrations from the depletion region capacitances of HEMT structures and fully depleted films of any class of semiconductor materials. (paper)

  12. X-Band GaN Power Amplifier MMIC with a Third Harmonic-Tuned Circuit

    Directory of Open Access Journals (Sweden)

    Kyung-Tae Bae

    2017-11-01

    Full Text Available This paper presents an X-band GaN HEMT power amplifier with a third harmonic-tuned circuit for a higher power density per area and a higher power-added efficiency (PAE using a 0.25 μm GaN HEMT process of WIN semiconductors, Inc. The optimum load impedances at the fundamental and third harmonic frequencies are extracted from load-pull simulations at the transistor’s extrinsic plane, including the drain-source capacitance and the series drain inductance. The third harmonic-tuned circuit is effectively integrated with the output matching circuit at the fundamental frequency, without complicating the whole output matching circuit. The input matching circuit uses a lossy matching scheme, which allows a good return loss and a simple LC low-pass circuit configuration. The fabricated power amplifier monolithic microwave integrated circuit (MMIC occupies an area of 13.26 mm2, and shows a linear gain of 20 dB or more, a saturated output power of 43.2~44.7 dBm, and a PAE of 35~37% at 8.5 to 10.5 GHz.

  13. Estimation of background carrier concentration in fully depleted GaN films

    Science.gov (United States)

    Chandrasekar, Hareesh; Singh, Manikant; Raghavan, Srinivasan; Bhat, Navakanta

    2015-11-01

    Buffer leakage is an important parasitic loss mechanism in AlGaN/GaN high electron mobility transistors (HEMTs) and hence various methods are employed to grow semi-insulating buffer layers. Quantification of carrier concentration in such buffers using conventional capacitance based profiling techniques is challenging due to their fully depleted nature even at zero bias voltages. We provide a simple and effective model to extract carrier concentrations in fully depleted GaN films using capacitance-voltage (C-V) measurements. Extensive mercury probe C-V profiling has been performed on GaN films of differing thicknesses and doping levels in order to validate this model. Carrier concentrations as extracted from both the conventional C-V technique for partially depleted films having the same doping concentration, and Hall measurements show excellent agreement with those predicted by the proposed model thus establishing the utility of this technique. This model can be readily extended to estimate background carrier concentrations from the depletion region capacitances of HEMT structures and fully depleted films of any class of semiconductor materials.

  14. High-k Dielectric Passivation for GaN Diode with a Field Plate Termination

    Directory of Open Access Journals (Sweden)

    Michitaka Yoshino

    2016-03-01

    Full Text Available Vertical structured Gallium nitride (GaN p-n junction diodes with improved breakdown properties have been demonstrated using high-k dielectric passivation underneath the field plate. Simulation results at a reverse voltage of 1 kV showed that the maximum electric field near the mesa-etched p-n junction edges covered with film of dielectric constant k = 10 was reduced to 2.0 MV/cm from 3.0 MV/cm (SiO2 (k = 3.9. The diodes were fabricated using the high-k mixed oxide of SiO2 and CeO2 with k = 12.3. I–V characteristics of the diode with a field plate showed a breakdown voltage above 2 kV with an increased avalanche resistance. This means that the electric field reduces at the periphery of the mesa-etched p-n junction and is uniformly formed across the whole p-n junction. It is clear that high-k dielectric film passivation and filed plate termination are essential techniques for GaN power devices.

  15. Buffer transport mechanisms in intentionally carbon doped GaN heterojunction field effect transistors

    International Nuclear Information System (INIS)

    Uren, Michael J.; Cäsar, Markus; Kuball, Martin; Gajda, Mark A.

    2014-01-01

    Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer layers in a carbon doped GaN power heterojunction field effect transistor. Carbon doped GaN and multiple layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C doped layer is shown to occur by hole conduction in the valence band with activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.

  16. Ti/Al Ohmic Contacts to n-Type GaN Nanowires

    Directory of Open Access Journals (Sweden)

    Gangfeng Ye

    2011-01-01

    Full Text Available Titanium/aluminum ohmic contacts to tapered n-type GaN nanowires with triangular cross-sections were studied. To extract the specific contact resistance, the commonly used transmission line model was adapted to the particular nanowire geometry. The most Al-rich composition of the contact provided a low specific contact resistance (mid 10−8 Ωcm2 upon annealing at 600 °C for 15 s, but it exhibited poor thermal stability due to oxidation of excess elemental Al remaining after annealing, as revealed by transmission electron microscopy. On the other hand, less Al-rich contacts required higher annealing temperatures (850 or 900 °C to reach a minimum specific contact resistance but exhibited better thermal stability. A spread in the specific contact resistance from contact to contact was tentatively attributed to the different facets that were contacted on the GaN nanowires with a triangular cross-section.

  17. Implantation and annealing studies of Tm-implanted GaN

    International Nuclear Information System (INIS)

    Lorenz, K.; Alves, E.; Wahl, U.; Monteiro, T.; Dalmasso, S.; Martin, R.W.; O'Donnell, K.P.; Vianden, R.

    2003-01-01

    Thulium ions were implanted into metal organic chemical vapour deposition (MOCVD) grown GaN films with different fluences at implantation temperatures of 20, 400 and 500 deg. C. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. The lattice damage introduced by the implantation and the effect of post-implant annealing were investigated with the Rutherford backscattering (RBS)/channelling technique. We observe that implantation at 500 deg. C considerably reduces the induced lattice damage and increases the amorphisation threshold. The lattice-site location of the implanted ions was determined by performing detailed channelling measurements for the and crystal directions. The results show that Tm ions mainly occupy substitutional Ga-sites directly after implantation and after annealing. The optical properties of the ion-implanted GaN films have been studied by room temperature cathodoluminescence (CL) measurements. Well-defined emission due to intra-4f shell transitions of the Tm 3+ ions are observed in the blue spectral range at 477 nm and in the near infra-red (IR) at 804 nm

  18. Surfactant assisted growth of MgO films on GaN

    Energy Technology Data Exchange (ETDEWEB)

    Paisley, Elisibeth A. [North Carolina State University; Shelton, T C [North Carolina State University; Mita, S [North Carolina State University; Gaddy, Brian E. [North Carolina State University; Irving, D L [North Carolina State University; Christen, Hans M [ORNL; Sitar, Z [North Carolina State University; Biegalski, Michael D [ORNL; Maria, Jon Paul [North Carolina State University

    2012-01-01

    Thin epitaxial films of <111> oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface due to stabilizing the {111} rocksalt facet. MBE growth of MgO in water terminates after several monolayers, and is attributed to saturation of surface active sites needed to facilitate the Mg oxidation reaction. MgO films prepared by PLD grow continuously, this occurs due to the presence of excited oxidizing species in the laser plasma eliminate the need for catalytic surface sites. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly two order of magnitude reduction in leakage current density for the smoother surfactant-assisted samples. Collectively, these data verify numerous predictions and calculations regarding the role of H-termination in regulating the habit of MgO crystals.

  19. Mechanical responses of a-axis GaN nanowires under axial loads

    Science.gov (United States)

    Wang, R. J.; Wang, C. Y.; Feng, Y. T.; Tang, Chun

    2018-03-01

    Gallium nitride (GaN) nanowires (NWs) hold technological significance as functional components in emergent nano-piezotronics. However, the examination of their mechanical responses, especially the mechanistic understanding of behavior beyond elasticity (at failure) remains limited due to the constraints of in situ experimentation. We therefore performed simulations of the molecular dynamics (MD) of the mechanical behavior of [1\\bar{2}10]-oriented GaN NWs subjected to tension or compression loading until failure. The mechanical properties and critical deformation processes are characterized in relation to NW sizes and loading conditions. Detailed examinations revealed that the failure mechanisms are size-dependent and controlled by the dislocation mobility on shuffle-set pyramidal planes. The size dependence of the elastic behavior is also examined in terms of the surface structure determined modification of Young’s modulus. In addition, a comparison with c-axis NWs is made to show how size-effect trends vary with the growth orientation of NWs.

  20. Atomistic simulation of damage production by atomic and molecular ion irradiation in GaN

    International Nuclear Information System (INIS)

    Ullah, M. W.; Kuronen, A.; Nordlund, K.; Djurabekova, F.; Karaseov, P. A.; Titov, A. I.

    2012-01-01

    We have studied defect production during single atomic and molecular ion irradiation having an energy of 50 eV/amu in GaN by molecular dynamics simulations. Enhanced defect recombination is found in GaN, in accordance with experimental data. Instantaneous damage shows non-linearity with different molecular projectile and increasing molecular mass. Number of instantaneous defects produced by the PF 4 molecule close to target surface is four times higher than that for PF 2 molecule and three times higher than that calculated as a sum of the damage produced by one P and four F ion irradiation (P+4×F). We explain this non-linearity by energy spike due to molecular effects. On the contrary, final damage created by PF 4 and PF 2 shows a linear pattern when the sample cools down. Total numbers of defects produced by Ag and PF 4 having similar atomic masses are comparable. However, defect-depth distributions produced by these species are quite different, also indicating molecular effect.

  1. Photoluminescence studies of rare earth (Er, Eu, Tm) in situ doped GaN

    International Nuclear Information System (INIS)

    Hoemmerich, U.; Nyein, Ei Ei; Lee, D.S.; Heikenfeld, J.; Steckl, A.J.; Zavada, J.M.

    2003-01-01

    The emission properties of rare earth (RE)-doped GaN are of significant current interest for applications in full color displays, white lighting technology, and optical communications. We are currently investigating the photoluminescence (PL) properties of RE (Er, Eu, Tm)-doped GaN thin-films prepared by solid-source molecular beam epitaxy. The most intense visible PL under above-gap excitation is observed from GaN:Eu (red: 622 nm) followed by GaN:Er (green: 537 nm, 558 nm), and then GaN:Tm (blue: 479 nm). In this paper, we present spectroscopic results on the Ga-flux dependence of the Er 3+ PL properties from GaN:Er and we report on the identification of different Eu 3+ centers in GaN:Eu through high-resolution PL excitation (PLE) studies. In addition, we observed an enhancement of the blue Tm 3+ PL from AlGaN:Tm compared to GaN:Tm. Intense blue PL from Tm 3+ ions was also obtained from AlN:Tm under below-gap pumping

  2. Anisotropic thermal transport property of defect-free GaN

    International Nuclear Information System (INIS)

    Ju, Wenjing; Zhou, Zhongyuan; Wei, Zhiyong

    2016-01-01

    Non-equilibrium molecular dynamics (MD) simulation is performed to calculate the thermal conductivity of defect-free GaN along three high-symmetry directions. It is found that the thermal conductivity along [001] direction is about 25% higher than that along [100] or [120] direction. The calculated phonon dispersion relation and iso-energy surface from lattice dynamics show that the difference of the sound speeds among the three high-symmetry directions is quite small for the same mode. However, the variation of phonon irradiation with direction is qualitatively consistent with that of the calculated thermal conductivity. Our results indicate that the anisotropic thermal conductivity may partly result from the phonons in the low-symmetry region of the first Brillouin zone due to phonon focus effects, even though the elastic properties along the three high-symmetry directions are nearly isotropic. Thus, the phonon irradiation is able to better describe the property of thermal conductivity as compared to the commonly used phonon dispersion relation. The present investigations uncover the physical origin of the anisotropic thermal conductivity in defect-free GaN, which would provide an important guide for optimizing the thermal management of GaN-based device.

  3. Growth of N-polar GaN by ammonia molecular beam epitaxy

    Science.gov (United States)

    Fireman, M. N.; Li, Haoran; Keller, Stacia; Mishra, Umesh K.; Speck, James S.

    2018-01-01

    The homoepitaxial growth of N-polar GaN was investigated by ammonia molecular beam epitaxy. Systematic growth studies varying the V/III flux ratio and the growth temperature indicated that the strongest factor in realizing morphologically smooth films was the growth temperature; N-face films needed to be grown approximately 100 °C or greater than Ga-face films provided the same metal flux. Smooth N-face films could also be grown at temperatures only 50 °C greater than Ga-face films, albeit under reduced metal flux. Too high a growth temperature and too low a metal flux resulted in dislocation mediated pitting of the surface. The unintentional impurity incorporation of such films was also studied by secondary mass ion spectroscopy and most importantly revealed an oxygen content in the mid 1017 to the mid 1018 cm-3 range. Hall measurements confirmed that this oxygen impurity resulted in n-type films, with carrier concentrations and mobilities comparable to those of intentionally silicon doped GaN.

  4. Transient current analysis of a GaN radiation detector by TCAD

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jinghui; Mulligan, Padhraic L.; Cao, Lei R., E-mail: cao.152@osu.edu

    2014-10-11

    A gallium nitride (GaN) Schottky diode radiation detector has been fabricated with a successfully demonstrated radiation response to alpha particles and neutrons when using Li as a convertor. In order to understand the charge collection process for further device modification, the Sentaurus TCAD software package is employed to quantitatively study the transient current produced by energetic charge particles. By comparing the simulation and experimental results, especially the capacitance–voltage relationship and charge collection efficiency, the device parameters and physics models used for the simulation are validated. The time behavior of the transient current is studied, and the carrier generation/loss by impact ionization, recombination, and trapping are discussed. The total collected charge contributed by various components, such as drift, funneling, and diffusion are also analyzed. - Highlights: • A TCAD model is established for a GaN Schottky diode radiation detector. • Schottky side mainly collects holes, while ohmic side solely collects electrons. • The funneling region evolution is visualized by carrier current densities. • Carrier generation/loss by impact ionization/trapping is insignificant. • The collected charges are primarily drift carriers in the depletion region.

  5. Lattice location of Mg in GaN: a fresh look at doping limitations

    CERN Document Server

    AUTHOR|(CDS)2069243; Augustyns, Valerie; Granadeiro Costa, Angelo Rafael; David Bosne, Eric; De Lemos Lima, Tiago Abel; Lippertz, Gertjan; Martins Correia, Joao; Castro Ribeiro Da Silva, Manuel; Kappers, Menno; Temst, Kristiaan; Vantomme, André; Da Costa Pereira, Lino Miguel

    2017-01-01

    Radioactive 27Mg (t1/2=9.5 min) was implanted into GaN of different doping types at CERN’s ISOLDE facility and its lattice site determined via beta− emission channeling. Following implantations between room temperature and 800°C, the majority of 27Mg occupies the substitutional Ga sites, however, below 350°C significant fractions were also found on interstitial positions ~0.6 Å from ideal octahedral sites. The interstitial fraction of Mg was correlated with the GaN doping character, being highest (up to 31%) in samples doped p-type with 2E19 cm−3 stable Mg during epilayer growth, and lowest in Si-doped n-GaN, thus giving direct evidence for the amphoteric character of Mg. Implanting above 350°C converts interstitial 27Mg to substitutional Ga sites, which allows estimating the activation energy for migration of interstitial Mg as between 1.3 and 2.0 eV.

  6. Siamese-GAN: Learning Invariant Representations for Aerial Vehicle Image Categorization

    Directory of Open Access Journals (Sweden)

    Laila Bashmal

    2018-02-01

    Full Text Available In this paper, we present a new algorithm for cross-domain classification in aerial vehicle images based on generative adversarial networks (GANs. The proposed method, called Siamese-GAN, learns invariant feature representations for both labeled and unlabeled images coming from two different domains. To this end, we train in an adversarial manner a Siamese encoder–decoder architecture coupled with a discriminator network. The encoder–decoder network has the task of matching the distributions of both domains in a shared space regularized by the reconstruction ability, while the discriminator seeks to distinguish between them. After this phase, we feed the resulting encoded labeled and unlabeled features to another network composed of two fully-connected layers for training and classification, respectively. Experiments on several cross-domain datasets composed of extremely high resolution (EHR images acquired by manned/unmanned aerial vehicles (MAV/UAV over the cities of Vaihingen, Toronto, Potsdam, and Trento are reported and discussed.

  7. Irradiation-induced defects in InN and GaN studied with positron annihilation

    Energy Technology Data Exchange (ETDEWEB)

    Reurings, Floris; Tuomisto, Filip [Department of Applied Physics, Aalto University, Espoo (Finland); Egger, Werner; Loewe, Benjamin [Institut fuer Angewandte Physik und Messtechnik, Universitaet der Bundeswehr Muenchen, Neubiberg (Germany); Ravelli, Luca [Dipartimento di Fisica, Universita degli studi di Trento, Povo (Italy); Sojak, Stanislav [Department of Nuclear Physics and Technology, Slovak University of Technology in Bratislava (Slovakia); Liliental-Weber, Zuzanna; Jones, Rebecca E.; Yu, Kin M.; Walukiewicz, Wladek [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Schaff, William J. [Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY (United States)

    2010-05-15

    We use positron annihilation to study 2-MeV {sup 4}He{sup +} irradiated and subsequently rapid-thermal-annealed InN grown by molecular-beam epitaxy and GaN grown by metal-organic chemical-vapour deposition. The irradiation fluences were in the range 5 x 10{sup 14}-2 x 10{sup 16}cm{sup -2}. In vacancies are introduced in the irradiation at a low rate of 100 cm{sup -1}, with their concentration saturating in the mid-10{sup 17} cm{sup -3} range at an irradiation fluence of 2 x 10{sup 15} cm{sup -2}. The annealing, performed at temperatures between 425 and 475 C, is observed to result in an inhomogeneous redistribution of the In vacancies. The behaviour is opposite to GaN, where Ga vacancies are introduced at a much higher rate of 3600 cm{sup -1} showing no detectable saturation. About half of the Ga vacancies are found to recover in the annealing, in agreement with previous studies, while the remaining Ga vacancies undergo no spatial redistribution. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  8. Non-degenerate pump-probe spectroscopy of single GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Upadhya, Prashanth C [Los Alamos National Laboratory; Taylor, Antoinette J [Los Alamos National Laboratory; Prasankumar, Rohiy P [Los Alamos National Laboratory; Wang, George T [SNL; Martinez, Julio A [SNL; Li, Qiming [SNL; Swartzentruber, Brian S [SNL

    2010-01-01

    Spatially-resolved ultrafast transient absorption measurements on a single GaN nanowire give insight into carrier relaxation dynamics as a function of the probe polarization and position on the nanowire on a femtosecond timescale. The synthesis and optical characterization of semiconductor nanowires (NWs) has gained considerable attention in recent years owing to their unique electronic and optical properties that arise from their anisotropic geometry, large surface to volume ratio and two-dimensional quasiparticle confinement, Post-growth characterization of their properties is crucial in understanding the fundamental physical processes that can lead to enhanced functionality of NW-based devices, In particular, it is important to understand the carrier relaxation pathways in individual NWs, since the geometry of these nanostructures can significantly influence carrier recombination and/or trapping. In this respect, ultrafast optical techniques offer reliable and non-contact spectroscopic tools to study carrier dynamics in semiconductor nanostructures. In summary, time-resolved optical pump-probe spectroscopy was performed on single GaN NWs. These measurements give insight into the different processes that govern carrier capture, particularly at surface states, and relaxation in individual nanostructures. Our experiments thus demonstrate the value of single-particle ultrafast optical spectroscopy in understanding the physical processes that govern the properties of semiconductor NWs, while suggesting approaches to optimize NW-based devices for nanophotonic applications.

  9. First principles calculations of structural and electronic properties of GaN1−xBix alloys

    International Nuclear Information System (INIS)

    Mbarki, M.; Rebey, A.

    2012-01-01

    Highlights: ► The FPLAPW is used to calculate the structural and electronic properties of GaN 1−x Bi x . ► The lattice parameter of GaN 1−x Bi x shows an increase with Bi composition. ► We have studied the variation of the energy gap and the electron effective masses of the ternary compound with respect to the composition x of Bi. - Abstract: In this work we have calculated the structural and electronic properties of GaN 1−x Bi x alloy by using the density functional theory based on the full potential linearized augmented plane wave method (FPLAPW). The calculated lattice parameter of GaN 1−x Bi x alloys shows an increase by increasing the composition x of bismuth (Bi), while a significant deviation from Vegard's law is observed. We have studied the variation of the energy gap and the electron effective masses of the ternary compound with respect to the composition x of Bi.

  10. Counting Tm dopant atoms around GaN dots using high-angle annular dark field images

    International Nuclear Information System (INIS)

    Rouvière, J-L; Okuno, H; Jouneau, P H; Bayle-Guillemaud, P; Daudin, B

    2011-01-01

    High resolution Z-contrast STEM imaging is used to study the Tm doping of GaN quantum dots grown in AlN by molecular beam epitaxy (MBE). High-angle annular dark field (HAADF) imaging allows us to visualize directly individual Tm atoms in the AlN matrix and even to count the number of Tm atoms in a given AlN atomic column. A new visibility coefficient to determine quantitatively the number of Tm atoms in a given atomic column is introduced. It is based on locally integrated intensities rather than on peak intensities of HAADF images. STEM image simulations shows that this new visibility is less sensitive to the defocus-induced blurring or to the position of the Tm atom within the thin lamella. Most of the Tm atoms diffuse out of GaN dots. Tm atoms are found at different positions in the AlN matrix, (i) Above the wetting layer, Tm atoms are spread within a thickness of 14 AlN monolayers (MLs). (ii) Above the quantum dots all the Tm are located in the same plane situated at 2-3 MLs above the apex of the GaN dot, i.e. at a distance of 14 MLs from the wetting layer, (iii) In addition, Tm can diffuse very far from the GaN dot by following threading dislocations lines.

  11. Spectroscopic characterizations of individual single-crystalline GaN nanowires in visible/ultra-violet regime.

    Science.gov (United States)

    Wu, Chien-Ting; Chu, Ming-Wen; Chen, Li-Chyong; Chen, Kuei-Hsien; Chen, Chun-Wei; Chen, Cheng Hsuan

    2010-10-01

    Spectroscopic investigations of individual single-crystalline GaN nanowires with a lateral dimensions of approximately 30-90nm were performed using the spatially resolved technique of electron energy-loss spectroscopy in conjunction with scanning transmission electron microscope showing a 2-A electron probe. Positioning the electron probe upon transmission impact and at aloof setup with respect to the nanomaterials, we explored two types of surface modes intrinsic to GaN, surface exciton polaritons at approximately 8.3eV (approximately 150nm) and surface guided modes at 3.88eV (approximately 320nm), which are in visible/ultra-violet spectral regime above GaN bandgap of approximately 3.3eV (approximately 375nm) and difficult to access by conventional optical spectroscopies. The explorations of these electromagnetic resonances might expand the current technical interests in GaN nanomaterials from the visible/UV range below approximately 3.5eV to the spectral regime further beyond.

  12. Influence of highly-charged 209Bi33+ irradiation on structure and optoelectric characteristics of GaN epilayer

    Science.gov (United States)

    Zhang, L. Q.; Zhang, C. H.; Xu, C. L.; Li, J. J.; Yang, Y. T.; Ma, Y. Z.; Li, J. Y.; Liu, H. P.; Ding, Z. N.; Yan, T. X.; Song, Y.

    2017-09-01

    The microstructure and optoelectric properties of GaN epilayer irradiated by highly-charged 209Bi33+ to different fluences are investigated by means of atomic force microscopy, X-ray photoelectron spectroscopy, Raman scattering spectroscopy and photoluminescence spectroscopy. After Bi33+ irradiation, AFM observation shows the irradiated GaN surface is a swelling and swelling rate nonlinearly increases with increasing ions fluence. XPS analysis reveals the relative content of Ga-N bond reduces and Ga-O, Ga-Ga bonds have been produced as the fluence increases. Raman scattering spectra display the thickness of surface depletion layer increases, free carrier concentration and its mobility decrease generally with an increase in ions fluence. Furthermore, the length of Ga-N bond shortens and lattices experience compressive stress with increasing ions fluence are observed from Raman spectra. Room temperature PL spectra reflect the intensity of yellow luminescence (YL) emission increases and its peak has a blueshift after 1.061 × 1012 Bi33+/cm2 irradiation. Moreover, as the temperature rises, the thermal quenching of YL occurs and its peak position first exhibits a blueshift and then a redshift. Results may be served as a useful reference for HCI to be used in semiconductor fields.

  13. Effect of GaN cap thickness on carrier dynamics in InGaN quantum wells

    DEFF Research Database (Denmark)

    Kopylov, Oleksii; Shirazi, Roza; Svensk, O.

    2012-01-01

    We have studied optical properties of single In0.1Ga0.9N quantum wells with GaN barriers in close proximity to the wafer surface (<10 nm). We have found that at room temperature a balance of radiative, non-radiative recombination and complex surface states effects results in an optimum cap thickn...

  14. 4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication.

    Science.gov (United States)

    Lee, Changmin; Zhang, Chong; Cantore, Michael; Farrell, Robert M; Oh, Sang Ho; Margalith, Tal; Speck, James S; Nakamura, Shuji; Bowers, John E; DenBaars, Steven P

    2015-06-15

    We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.

  15. A Rapid Method for Deposition of Sn-Doped GaN Thin Films on Glass and Polyethylene Terephthalate Substrates

    Science.gov (United States)

    Pat, Suat; Özen, Soner; Korkmaz, Şadan

    2018-01-01

    We report the influence of Sn doping on microstructure, surface, and optical properties of GaN thin films deposited on glass and polyethylene terephthalate (PET) substrate. Sn-doped GaN thin films have been deposited by thermionic vacuum arc (TVA) at low temperature. TVA is a rapid deposition technology for thin film growth. Surface and optical properties of the thin films were presented. Grain size, height distribution, roughness values were determined. Grain sizes were calculated as 20 nm and 13 nm for glass and PET substrates, respectively. Nano crystalline forms were shown by field emission scanning electron microscopy. Optical band gap values were determined by optical methods and photoluminescence measurement. The optical band gap values of Sn doped GaN on glass and PET were determined to be approximately ˜3.40 eV and ˜3.47 eV, respectively. As a result, TVA is a rapid and low temperature deposition technology for the Sn doped GaN deposited on glass and PET substrate.

  16. Electrical Activation Studies of Silicon Implanted Al(x)Ga(1-x)N and Coimplanted GaN

    National Research Council Canada - National Science Library

    Chitwood, Elizabeth

    2003-01-01

    A comprehensive study of the electrical activation of silicon implanted Al(x)Ga(1-x)N was performed as a function ion dose, anneal temperature, and aluminum mole fraction, Also, GaN coimplanted with silicon and nitrogen was investigated...

  17. Transmission Electron Microscopy Study of Defect Reduction in Two-Step Lateral Epitaxial Overgrown Nonplanar GaN Substrate Templates

    National Research Council Canada - National Science Library

    Zhou, Wei; Ren, Dawei; Dapkus, P. D

    2005-01-01

    ...). The LEO nonplanar GaN substrate template has a trapezoidal cross section with smooth (0 0 0 1) and f11 22g facets. We demonstrate here the dislocation distribution and behavior in both ordinary LEO and two-step LEO...

  18. Growth Temperature Dependence of Morphology of GaN Single Crystals in the Na-Li-Ca Flux Method

    Science.gov (United States)

    Wu, Xi; Hao, Hangfei; Li, Zhenrong; Fan, Shiji; Xu, Zhuo

    2018-02-01

    In this paper, the effect of growth temperature on the morphology and transparency of the GaN crystals obtained by the Li-Ca-added Na Flux method was studied. Addition of Li-Ca was attempted to control the growth habit and further improve transparency of GaN crystals. The samples with wurtzite structure of GaN were confirmed by the x-ray powder diffraction analysis. GaN single crystal with maximum size of about 6 mm was grown at 750°C. As the growth temperature was increased from 700°C to 850°C, the morphology of the crystals changed from pyramid to prism, and their surfaces became smooth. It was found that high growth temperature was beneficial to obtain a transparent crystal, but the evaporation of sodium would suppress its further growth. The E 2 (high) mode in the Raman spectra was at 568 cm-1, and the full-width at half-maximum values of this peak for the crystals obtained at 700°C, 750°C, 800°C, and 850°C were 7.5 cm-1, 10.3 cm-1, 4.4 cm-1, and 4.0 cm-1, respectively. It indicates that all the crystals are stress free and the transparent crystal grown at high temperature has high structural quality or low impurity concentrations.

  19. Self-assembled flower-like nanostructures of InN and GaN grown by ...

    Indian Academy of Sciences (India)

    Administrator

    (SEM) were used to study the crystallinity and morphology of the nanostructures. Moreover, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to investigate the chemical compositions and optical properties of nano-flowers, respectively. Activation energy of free exciton transitions in GaN nano- ...

  20. Direct spontaneous growth and interfacial structural properties of inclined GaN nanopillars on r-plane sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Adikimenakis, A.; Aretouli, K. E.; Tsagaraki, K.; Androulidaki, M.; Georgakilas, A. [Microelectronics Research Group (MRG), IESL, FORTH, P.O. Box 1385, GR 711 10 Heraklion Crete, Greece and Physics Department, University of Crete, GR 710 03 Heraklion Crete (Greece); Lotsari, A.; Dimitrakopulos, G. P., E-mail: gdim@auth.gr; Kehagias, Th.; Komninou, Ph. [Physics Department, Aristotle University of Thessaloniki, GR 541 24, Thessaloniki (Greece)

    2015-06-28

    The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with increasing the duration of the nitridation process and the power applied on the radio-frequency plasma source, as well as the III/V flux ratio, while variation of the first two parameters enhanced the roughness of the substrate's surface. Transmission electron microscopy (TEM) techniques were employed to reveal the structural characteristics of the NPs and their nucleation mechanism from steps on the sapphire surface and/or interfacial semipolar GaN nanocrystals. Lattice strain measurements showed a possible Al enrichment of the first 5–6 monolayers of the NPs. By combining cross-sectional and plan-view TEM observations, the three-dimensional model of the NPs was constructed. The orientation relationship and interfacial accommodation between the NPs and the nonpolar a-plane GaN film were also elucidated. The NPs exhibited strong and narrow excitonic emission, suggesting an excellent structural quality.

  1. A new system for sodium flux growth of bulk GaN. Part II: in situ investigation of growth processes

    KAUST Repository

    Von Dollen, Paul

    2016-09-09

    We report recent results of bulk GaN crystal growth using the sodium flux method in a new crucible-free growth system. We observed a (0001) Ga face (+c-plane) growth rate >50 µm/h for growth at a N2 overpressure of ~5 MPa and 860 °C, which is the highest crystal growth rate reported for this technique to date. Omega X-ray rocking curve (ω-XRC) measurements indicated the presence of multiple grains, though full width at half maximum (FWHM) values for individual peaks were <100 arcseconds. Oxygen impurity concentrations as measured by secondary ion mass spectroscopy (SIMS) were >1020 atoms/cm3. By monitoring the nitrogen pressure decay over the course of the crystal growth, we developed an in situ method that correlates gas phase changes with precipitation of GaN from the sodium-gallium melt. Based on this analysis, the growth rate may have actually been as high as 90 µm/h, as it would suggest GaN growth ceased prior to the end of the run. We also observed gas phase behavior identified as likely characteristic of GaN polynucleation.

  2. 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.

  3. A 99%-efficiency GaN converter for 6.78 MHz magnetic resonant wireless power transfer system

    Directory of Open Access Journals (Sweden)

    Yoshiyuki Akuzawa

    2014-10-01

    Full Text Available The authors developed a high-efficiency gallium-nitride (GaN Class-E converter for a 6.78 MHz magnetic resonant wireless power transfer system. A negative-bias gate driver circuit made it possible to use a depletion mode GaN high-electron-mobility transistor (HEMT, and simplified the converter circuit. As the depletion mode GaN HEMT with very small gate–source capacitance provided almost ideal zero-voltage switching, the authors attained a drain efficiency of 98.8% and a total efficiency of 97.7%, including power consumption of a gate driver circuit, at a power output of 33 W. In addition, the authors demonstrated a 6.78 MHz magnetic resonant wireless power transfer system that consisted of the GaN Class-E converter, a pair of magnetic resonant coils 150 mm in diameter with an air-gap distance of 40 mm, and a full-bridge rectifier using Si Schottky barrier diodes. The system achieved a dc–dc efficiency of 82.8% at a power output of 25 W. The efficiencies of coil coupling and the rectifier were estimated to be ∼ 94 and 90%, respectively.

  4. Fabrication of extremely thermal-stable GaN template on Mo substrate using double bonding and step annealing process

    Science.gov (United States)

    Qing, Wang; Yang, Liu; Yongjian, Sun; Yuzhen, Tong; Guoyi, Zhang

    2016-08-01

    A new layer transfer technique which comprised double bonding and a step annealing process was utilized to transfer the GaN epilayer from a sapphire substrate to a Mo substrate. Combined with the application of the thermal-stable bonding medium, the resulting two-inch-diameter GaN template showed extremely good stability under high temperature and low stress state. Moreover, no cracks and winkles were observed. The transferred GaN template was suitable for homogeneous epitaxial, thus could be used for the direct fabrication of vertical LED chips as well as power electron devices. It has been confirmed that the double bonding and step annealing technique together with the thermal-stable bonding layer could significantly improve the bonding strength and stress relief, finally enhancing the thermal stability of the transferred GaN template. Project supported by the Guangdong Innovative Research Team Program (No. 2009010044), the China Postdoctoral Science Foundation (No. 2014M562233), the National Natural Science Foundation of Guangdong, China (No. 2015A030312011), and the Opened Fund of the State Key Laboratory on Integrated Optoelectronics (No. IOSKL2014KF17).

  5. 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.

  6. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    Science.gov (United States)

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-08

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.

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

    Directory of Open Access Journals (Sweden)

    Yasuaki Arakawa

    2016-08-01

    Full Text Available 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.

  8. Hydride vapor phase epitaxy growth of GaN, InGaN, ScN, and ScAIN

    NARCIS (Netherlands)

    Bohnen, T.

    2010-01-01

    Chemical vapor deposition (CVD); hydride vapor phase epitaxy (HVPE); gallium nitride (GaN); indium gallium nitride (InGaN); scandium nitride (ScN); scandium aluminum nitride (ScAlN); semiconductors; thin films; nanowires; III nitrides; crystal growth - We studied the HVPE growth of different III

  9. A new system for sodium flux growth of bulk GaN. Part II: in situ investigation of growth processes

    Science.gov (United States)

    Von Dollen, Paul; Pimputkar, Siddha; Alreesh, Mohammed Abo; Nakamura, Shuji; Speck, James S.

    2016-12-01

    We report recent results of bulk GaN crystal growth using the sodium flux method in a new crucible-free growth system. We observed a (0001) Ga face (+c-plane) growth rate >50 μm/h for growth at a N2 overpressure of 5 MPa and 860 °C, which is the highest crystal growth rate reported for this technique to date. Omega X-ray rocking curve (ω-XRC) measurements indicated the presence of multiple grains, though full width at half maximum (FWHM) values for individual peaks were 1020 atoms/cm3. By monitoring the nitrogen pressure decay over the course of the crystal growth, we developed an in situ method that correlates gas phase changes with precipitation of GaN from the sodium-gallium melt. Based on this analysis, the growth rate may have actually been as high as 90 μm/h, as it would suggest GaN growth ceased prior to the end of the run. We also observed gas phase behavior identified as likely characteristic of GaN polynucleation.

  10. A Compact Two-Stage 120 W GaN High Power Amplifier for SweepSAR Radar Systems

    Science.gov (United States)

    Thrivikraman, Tushar; Horst, Stephen; Price, Douglas; Hoffman, James; Veilleux, Louise

    2014-01-01

    This work presents the design and measured results of a fully integrated switched power two-stage GaN HEMT high-power amplifier (HPA) achieving 60% power-added efficiency at over 120Woutput power. This high-efficiency GaN HEMT HPA is an enabling technology for L-band SweepSAR interferometric instruments that enable frequent repeat intervals and high-resolution imagery. The L-band HPA was designed using space-qualified state-of-the-art GaN HEMT technology. The amplifier exhibits over 34 dB of power gain at 51 dBm of output power across an 80 MHz bandwidth. The HPA is divided into two stages, an 8 W driver stage and 120 W output stage. The amplifier is designed for pulsed operation, with a high-speed DC drain switch operating at the pulsed-repetition interval and settles within 200 ns. In addition to the electrical design, a thermally optimized package was designed, that allows for direct thermal radiation to maintain low-junction temperatures for the GaN parts maximizing long-term reliability. Lastly, real radar waveforms are characterized and analysis of amplitude and phase stability over temperature demonstrate ultra-stable operation over temperature using integrated bias compensation circuitry allowing less than 0.2 dB amplitude variation and 2 deg phase variation over a 70 C range.

  11. Built-in surface electric field, piezoelectricity and photoelastic effect in GaN nanorods for nanophotonic devices.

    Science.gov (United States)

    Su, W S; Chen, T T; Cheng, C L; Fu, S P; Chen, Y F; Hsiao, C L; Tu, L W

    2008-06-11

    Novel behaviors arising from the coupling between the built-in surface electric field, piezoelectricity, electron-hole pairs and external light beam were observed in GaN nanorods. An increase in the optical excitation density resulted in a blueshift in the photoluminescence spectra and a redshift in the frequency of the GaN A(1)(LO) phonon. The underlying mechanism was attributed to the screening of the built-in surface electric field by photoexcited carriers and, through the converse piezoelectric effect, a reduction in the internal strain. The existence of the built-in surface electric field in GaN nanorods was confirmed by scanning Kelvin probe microscopy. Our results firmly establish the existence of the photoelastic effect in GaN nanorods. In addition to underpinning the principle for applications in nanophotonic devices, this discovery also draws attention to the novel effects arising from the inherent large surface-to-volume ratio of nanostructures, which is possibly applicable to many other nanomaterials.

  12. 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...

  13. 4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication

    KAUST Repository

    Lee, Changmin

    2015-06-10

    We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.

  14. Transport phenomena and the effects of reactor geometry for epitaxial GaN growth in a vertical MOCVD reactor

    Science.gov (United States)

    Tseng, Chien-Fu; Tsai, Tsung-Yen; Huang, Yen-Hsiu; Lee, Ming-Tsang; Horng, Ray-Hua

    2015-12-01

    In this study a numerical simulation was carried out to analyze the transport phenomena in a vertical type metal organic chemical vapor deposition (MOCVD) reactor for Gallium Nitride (GaN) growth. The simulated results were compared and validated by experiment. The effects of showerhead design and chamber height are investigated and discussed. It was found that, by properly adjusting the height of the chamber, both the growth rate and film uniformity could be significantly improved. This is attributed to the suppression of the thermal and mass transfer boundary layers by the injection flow of reacting gas mixtures, as well as the confined vertical vortices caused by the geometry of the reduced space. However, inappropriate design of the distance between the showerhead and the susceptor can result in uneven distribution of the organic source in the vicinity of the substrate surface resulting in an uneven growth rate of the GaN film. Consequently, there exists an optimal chamber height that will give the best growth rate and uniformity to the GaN film as discussed in this study. This study provides comprehensive insight into the transport phenomena of GaN growth that includes coupled heat and mass transfer as well as chemical reactions. The results provide important information in a succinct format and enable decisions to be made about the showerhead and the geometrical design and size of a vertical MOCVD reactor.

  15. Compositional accuracy of atom probe tomography measurements in GaN: Impact of experimental parameters and multiple evaporation events.

    Science.gov (United States)

    Russo, E Di; Blum, I; Houard, J; Gilbert, M; Da Costa, G; Blavette, D; Rigutti, L

    2018-04-01

    A systematic study of the biases occurring in the measurement of the composition of GaN by Atom Probe Tomography was carried out, in which the role of surface electric field and laser pulse intensity has been investigated. Our data confirm that the electric field is the main factor influencing the measured composition, which exhibits a deficiency of N at low field and a deficiency of Ga at high field. The deficiency of Ga at high field is interpreted in terms of preferential evaporation of Ga. The detailed analysis of multiple evaporation events reveals that the measured composition is not affected by pile-up phenomena occurring in detection system. The analysis of correlation histograms yields the signature of the production of neutral N 2 due to the dissociation of GaN 3 2+ ions. However, the amount of N 2 neutral molecules that can be detected cannot account for the N deficiency found at low field. Therefore, we propose that further mechanisms of neutral N evaporation could be represented by dissociation reactions such as GaN + → Ga + + N and GaN 2+ → Ga 2 + + N. Copyright © 2018 Elsevier B.V. All rights reserved.

  16. The measurement of electrostatic potentials in core/shell GaN nanowires using off-axis electron holography

    DEFF Research Database (Denmark)

    Yazdi, Sadegh; Kasama, Takeshi; Ciechonski, R

    2013-01-01

    Core-shell GaN nanowires are expected to be building blocks of future light emitting devices. Here we apply off-axis electron holography to map the electrostatic potential distributions in such nanowires. To access the cross-section of selected individual nanowires, focused ion beam (FIB) milling...

  17. 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.

  18. Heteroepitaxial Growth of GaN Nanostructures via Metalorganic Vapor Phase Epitaxy on Sapphire and Silicon using Graphene as Buffer Layer

    OpenAIRE

    Heilmann, Martin

    2017-01-01

    Modern high efficient optoelectronic devices, such as blue light emitting diodes or laser diodes in Blu-ray player, are based on the compound semiconductor GaN. Through its additional field of application as high frequency and high power transistors GaN could in the future even outshine Si as the most important semiconducting material. The lack of large area and cost-effective GaN substrates makes a growth of the aforementioned device structures on non-native substrates (e.g. sapphire) necess...

  19. 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

  20. Impact of defects on the electrical transport, optical properties and failure mechanisms of GaN nanowires.

    Energy Technology Data Exchange (ETDEWEB)

    Armstrong, Andrew M.; Aubry, Sylvie; Shaner, Eric Arthur; Siegal, Michael P.; Li, Qiming; Jones, Reese E.; Westover, Tyler; Wang, George T.; Zhou, Xiao Wang; Talin, Albert Alec; Bogart, Katherine Huderle Andersen; Harris, C. Thomas; Huang, Jian Yu

    2010-09-01

    We present the results of a three year LDRD project that focused on understanding the impact of defects on the electrical, optical and thermal properties of GaN-based nanowires (NWs). We describe the development and application of a host of experimental techniques to quantify and understand the physics of defects and thermal transport in GaN NWs. We also present the development of analytical models and computational studies of thermal conductivity in GaN NWs. Finally, we present an atomistic model for GaN NW electrical breakdown supported with experimental evidence. GaN-based nanowires are attractive for applications requiring compact, high-current density devices such as ultraviolet laser arrays. Understanding GaN nanowire failure at high-current density is crucial to developing nanowire (NW) devices. Nanowire device failure is likely more complex than thin film due to the prominence of surface effects and enhanced interaction among point defects. Understanding the impact of surfaces and point defects on nanowire thermal and electrical transport is the first step toward rational control and mitigation of device failure mechanisms. However, investigating defects in GaN NWs is extremely challenging because conventional defect spectroscopy techniques are unsuitable for wide-bandgap nanostructures. To understand NW breakdown, the influence of pre-existing and emergent defects during high current stress on NW properties will be investigated. Acute sensitivity of NW thermal conductivity to point-defect density is expected due to the lack of threading dislocation (TD) gettering sites, and enhanced phonon-surface scattering further inhibits thermal transport. Excess defect creation during Joule heating could further degrade thermal conductivity, producing a viscous cycle culminating in catastrophic breakdown. To investigate these issues, a unique combination of electron microscopy, scanning luminescence and photoconductivity implemented at the nanoscale will be used in

  1. Strain and crystalline defects in epitaxial GaN layers studied by high-resolution X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Chierchia, Rosa

    2007-07-01

    This thesis treats strain and dislocations in MOVPE GaN layers. The mosaic structure of metalorganic vapour phase epitaxy (MOVPE)-grown GaN layers was studied in dependence on the grain diameter utilizing high-resolution XRD. Different models for the defect structure were analyzed, the edge type TD densities were calculated under the assumption that the dislocations are not randomly distributed but localized at the grain boundaries. Moreover, in situ measurements have shown that the layers are under tension in the c-plane when a nucleation layer is used. The second part of this thesis treats a particular approach to reduce dislocations in MOVPE GaN layers, i.e. maskless pendeo epitaxial growth of MOVPE GAN layers. FE simulations assuming the strain to be completely induced during cooling of the structures after growth agree only partly with experimental data. The strain state of single layers and stripes of GaN grown on SiC was studied to exploit the evolution of the strain in the different phases of the PE growth. The biaxial compressive stress, due to the lattice mismatch between the GaN layer and the AlN nucleation layer is plastically relieved before overgrowth. Temperature dependent measurements show a linear reduction of the wing tilt with increasing temperature varying from sample to sample. Bent TDs have been observed in TEM images of maskless PE samples. Stress induced from the mismatch between the AlN buffer layer and the GaN also contributes to the remaining part of the wing tilt not relieved thermally. It has to be noted that the rest tilt value varies from sample to sample at the growth temperature. In fact some of the data indicate that the wing tilt decreases with increasing V/III ratio. In the last Chapter the application of X-ray techniques for the analysis of strain and composition in layers of inhomogeneous composition is explored. In the first part of the Chapter the strain state and the Al content of AlGaN buffer layers grown directly on (0001

  2. Scattering Light by а Cylindrical Capsule with Arbitrary End Caps in the Rayleigh-Gans-Debye Approximation

    Directory of Open Access Journals (Sweden)

    K. A. Shapovalov

    2015-01-01

    Full Text Available The paper concerns the light scattering problem of biological objects of complicated structure.It considers optically “soft” (having a refractive index close to that of a surrounding medium homogeneous cylindrical capsules, composed of three parts: central one that is cylindrical and two symmetrical rounding end caps. Such capsules can model more broad class of biological objects than the ordinary shapes of a spheroid or sphere. But, unfortunately, if a particle has other than a regular geometrical shape, then it is very difficult or impossible to solve the scattering problem analytically in its most general form that oblige us to use numerical and approximate analytical methods. The one of such approximate analytical method is the Rayleigh-Gans-Debye approximation (or the first Born approximation.So, the Rayleigh-Gans-Debye approximation is valid for different objects having size from nanometer to millimeter and depending on wave length and refractive index of an object under small phase shift of central ray.The formulas for light scattering amplitude of cylindrical capsule with arbitrary end caps in the Rayleigh-Gans-Debye approximation in scalar form are obtained. Then the light scattering phase function [or element of scattering matrix f11] for natural incident light (unpolarized or arbitrary polarized light is calculated.Numerical results for light scattering phase functions of cylindrical capsule with conical, spheroidal, paraboloidal ends in the Rayleigh-Gans-Debye approximation are compared. Also numerical results for light scattering phase function of cylindrical capsule with conical ends in the Rayleigh-Gans-Debye approximation and in the method of Purcell-Pennypacker (or Discrete Dipole method are compared. The good agreement within an application range of the RayleighGans-Debye approximation is obtained.Further continuation of the work, perhaps, is a consideration of multilayer cylindrical capsule in the Rayleigh-Gans

  3. Study of Cs adsorption on (100) surface of [001]-oriented GaN nanowires: A first principle research

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Sihao [Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology Nanjing, 210094 (China); Liu, Lei, E-mail: liu1133_cn@sina.com.cn [Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology Nanjing, 210094 (China); Kong, Yike [Department of Optoelectronic Technology, School of Electronic and Optical Engineering, Nanjing University of Science and Technology Nanjing, 210094 (China); Wang, Honggang; Wang, Meishan [School of Information and Electrical Engineering, Ludong University, Yantai 264025 (China)

    2016-11-30

    Highlights: • B{sub N} is the most stable adsorption site. • Work function is reduced after Cs adsorption. • Surface atomic structures are reconstructed. • Surface states near fermi level is contributed to the hybridization of Cs 5s state with Ga 4p and N 2p state. • NEA surface is demonstrated after Cs adsorption on GaN nanowire surface. - Abstract: Based on first-principle study, the adsorption mechanism of Cs on (100) crystal plane of GaN nanowire surface with coverage of 1/12 monolayer is explored. It is discovered that the most stable adsorption site is B{sub N} because of its lowest adsorption energy. The work function of GaN nanowire surface is reduced by 1.69 eV and will be further reduced with increasing Cs adsorption, which promotes the development of negative electron affinity (NEA) state of the materials. Furthermore, Cs adatom will make a great influence on the surface atomic structure, oppositely, little influence on the center atomic structure. There appears a dipole moment valued −6.93 Debye on the nanowire surface contributed to the formation the heterojunction on the surface, which is beneficial to the photoelectrons liberation. After Cs adsorption, the valence band and conduction band both move to lower energy side. The surface states mainly result from the hybridization of Cs 5s state with Ga 4p state and N 2p state. This study can help us to further experiment on the Cs adsorption processing on GaN nanowire and improve the photoemission performance of GaN nanowire devices.

  4. Growth and characterization of GaN thin film on Si substrate by thermionic vacuum arc (TVA)

    Science.gov (United States)

    Kundakçı, Mutlu; Mantarcı, Asim; Erdoğan, Erman

    2017-01-01

    Gallium nitride (GaN) is an attractive material with a wide-direct band gap (3.4 eV) and is one of the significant III-nitride materials, with many advantageous device applications such as high electron mobility transistors, lasers, sensors, LEDs, detectors, and solar cells, and has found applications in optoelectronic devices. GaN could also be useful for industrial research in the future. Chemical vapor deposition (CVD), molecular beam epitaxy (MBE), sputter, and pulsed laser deposition (PLD) are some of the methods used to fabricate GaN thin film. In this research, a GaN thin film grown on a silicon substrate using the thermionic vacuum arc (TVA) technique has been extensively studied. Fast deposition, short production time, homogeneity, and uniform nanostructure with low roughness can be seen as some of the merits of this method. The growth of the GaN was conducted at an operating pressure of 1× {{10}-6} \\text{Torr} , a plasma current 0.6 \\text{A} and for a very short period of time of 40 s. For the characterization process, scanning electron microscopy (SEM) was conducted to determine the structure and surface morphology of the material. Energy dispersive x-ray spectroscopy (EDX) was used to comprehend the elemental analysis characterization of the film. X-ray diffraction (XRD) was used to analyze the structure of the film. Raman measurements were taken to investigate the phonon modes of the material. The morphological properties of the material were analyzed in detail by atomic force microscopy (AFM).

  5. Effect of initial growth on the quality of GaN on patterned sapphire substrate with ex situ physical vapor deposition AlN seed layer

    Science.gov (United States)

    Wang, Hongbo; Daigo, Yoshiaki; Seino, Takuya; Ishibashi, Sotaro; Sugiyama, Masakazu

    2016-10-01

    GaN epitaxy was explored on a cone-patterned sapphire substrate with an ex situ AlN seed layer prepared by physical vapor deposition (PVD). The effect of initial growth on the quality of the GaN epilayer was investigated using both ex situ PVD-AlN seed layers with various thicknesses and various deposition parameters such as temperature and reactor pressure in metal-organic vapor-phase epitaxy (MOVPE). It was found that the quality of GaN is insensitive to both the thickness of the ex situ PVD-AlN seed layer and the MOVPE growth conditions. A high-quality GaN film was realized, as indicated by room-temperature CL mapping (dark spot density of 1.6 × 108 cm-2), on a patterned sapphire substrate with a wide growth condition window by simply employing an ex situ PVD-AlN seed layer.

  6. Discovering a Defect that Imposes a Limit to Mg Doping in p-Type GaN

    International Nuclear Information System (INIS)

    Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; O'Keefe, M.A.

    2006-01-01

    Gallium nitride (GaN) is the III-V semiconductor used to produce blue light-emitting diodes (LEDs) and blue and ultraviolet solid-state lasers. To be useful in electronic devices, GaN must be doped with elements that function either as electron donors or as acceptors to turn it into either an n-type semiconductor or a p-type semiconductor. It has been found that GaN can easily be grown with n-conductivity, even up to large concentrations of donors--in the few 10 19 cm -3 range. However, p-doping, the doping of the structure with atoms that provide electron sinks or holes, is not well understood and remains extremely difficult. The only efficient p-type dopant is Mg, but it is found that the free hole concentration is limited to 2 x 10 18 cm -3 , even when Mg concentrations are pushed into the low 10 19 cm -3 range. This saturation effect could place a limit on further development of GaN based devices. Further increase of the Mg concentration, up to 1 x 10 20 cm -3 leads to a decrease of the free hole concentration and an increase in defects. While low- to medium-brightness GaN light-emitting diodes (LEDs) are remarkably tolerant of crystal defects, blue and UV GaN lasers are much less so. We used electron microscopy to investigate Mg doping in GaN. Our transmission electron microscopy (TEM) studies revealed the formation of different types of Mg-rich defects [1,2]. In particular, high-resolution TEM allowed us to characterize a completely new type of defect in Mg-rich GaN. We found that the type of defect depended strongly on crystal growth polarity. For crystals grown with N-polarity, planar defects are distributed at equal distances (20 unit cells of GaN); these defects can be described as inversion domains [1]. For growth with Ga-polarity, we found a different type of defect [2]. These defects turn out to be three-dimensional Mg-rich hexagonal pyramids (or trapezoids) with their base on the (0001) plane and their six walls formed on {1123} planes (Fig. 1a). In

  7. In situ variations of the scintillation characteristics in GaN and CdS layers under irradiation by 1.6 MeV protons

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-15

    Evolution of the non-radiative and radiative recombination in GaN and CdS 2.5–20 μm thick layers has been examined by the in situ measurements of the 1.6 MeV proton induced luminescence and laser excited photoconductivity characteristics. The introduction rate of radiation defects has been evaluated by the comparative analysis of the laser and proton beam induced luminescence for the examined GaN and CdS layers.

  8. Influence of wet chemical cleaning on quantum efficiency of GaN photocathode

    Science.gov (United States)

    Wang, Xiao-Hui; Gao, Pin; Wang, Hong-Gang; Li, Biao; Chang, Ben-Kang

    2013-02-01

    GaN samples 1-3 are cleaned by a 2:2:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%) to de-ionized water; hydrochloric acid (37%); or a 4:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%). The samples are activated by Cs/O after the same annealing process. X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows: sample 1 has the largest proportion of Ga, N, and O among the three samples, while its C content is the lowest. After activation the quantum efficiency curves show sample 1 has the best photocathode performance. We think the wet chemical cleaning method is a process which will mainly remove C contamination.

  9. Influence of wet chemical cleaning on quantum efficiency of GaN photocathode

    International Nuclear Information System (INIS)

    Wang Xiao-Hui; Gao Pin; Wang Hong-Gang; Li Biao; Chang Ben-Kang

    2013-01-01

    GaN samples 1–3 are cleaned by a 2:2:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%) to de-ionized water; hydrochloric acid (37%); or a 4:1 solution of sulfuric acid (98%) to hydrogen peroxide (30%). The samples are activated by Cs/O after the same annealing process. X-ray photoelectron spectroscopy after the different ways of wet chemical cleaning shows: sample 1 has the largest proportion of Ga, N, and O among the three samples, while its C content is the lowest. After activation the quantum efficiency curves show sample 1 has the best photocathode performance. We think the wet chemical cleaning method is a process which will mainly remove C contamination. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  10. Improvements in (112-bar2) semipolar GaN crystal quality by graded superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Xu, S.R., E-mail: shengruixidian@126.com [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China); Zhang, J.C. [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China); Cao, Y.R. [School of Electronical and Machanical Engineering, Xidian University, Xi' an, 710071 (China); Zhou, X.W.; Xue, J.S.; Lin, Z.Y.; Ma, J.C. [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China); Bao, F. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215125 (China); Hao, Y. [Key Lab of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China)

    2012-01-01

    We report on the use of graded superlattices (SLs) for defect reduction in semipolar (112-bar2) GaN films, grown by metal-organic chemical vapor deposition. High-resolution x-ray diffraction analysis revealed that there was a great reduction in the full width at half maximum, both on-axis and off-axis, with the SLs. Atomic force microscopy images revealed a significant decrease in slate features which was associated with the basal-plane stacking faults. The transmission electron microscopy images showed that the threading dislocation was greatly reduced after the graded superlattices. Room temperature photoluminescence measurement revealed that the band-edge emission intensity increased with the insertion of the SLs, which suggested reduction in the nonradiative recombination centers.

  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. 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

  13. Semi-polar GaN materials technology for high IQE green LEDs.

    Energy Technology Data Exchange (ETDEWEB)

    Koleske, Daniel; Lee, Stephen Roger; Crawford, Mary H; Coltrin, Michael Elliott; Fini, Paul

    2013-06-01

    The goal of this NETL funded program was to improve the IQE in green (and longer wavelength) nitride- based LEDs structures by using semi-polar GaN planar orientations for InGaN multiple quantum well (MQW) growth. These semi-polar orientations have the advantage of significantly reducing the piezoelectric fields that distort the QW band structure and decrease electron-hole overlap. In addition, semipolar surfaces potentially provide a more open surface bonding environment for indium incorporation, thus enabling higher indium concentrations in the InGaN MQW. The goal of the proposed work was to select the optimal semi-polar orientation and explore wafer miscuts around this orientation that produced the highest quantum efficiency LEDs. At the end of this program we had hoped to have MQWs active regions at 540 nm with an IQE of 50% and an EQE of 40%, which would be approximately twice the estimated current state-of-the-art.

  14. Plasmonic amplification of photoacoustic waves detected using piezotransistive GaN microcantilevers

    Science.gov (United States)

    Khan, Digangana; Bayram, Ferhat; Gajula, Durga; Talukdar, Abdul; Li, Hongmei; Koley, Goutam

    2017-08-01

    Strong enhancement in a photoacoustic signal due to plasmonic absorption in Au nanostructures was measured using piezotransistive GaN microcantilevers. A pulsed 790 nm laser focused on the Au metallization of the piezotransistor resulted in a much larger photoacoustic signal compared to the non-metallized areas. Upon deposition of a 5 nm Au layer, the photoacoustic signal increased significantly for both previously metallized and non-metallized areas, while 2 nm Ni deposition decreased the photoacoustic signal, confirming the role of Au nanostructures in facilitating plasmonic absorption. Infrared microscopy images covering the boundary of Au metallized and non-metallized surfaces indicated a much larger rise in temperature of the former region with laser exposure, explaining the generation of photoacoustic signals through plasmonic absorption.

  15. Design Considerations for Gan-Based Microinverter for Energy Storage Integration Into Ac Grid

    Science.gov (United States)

    Kroics, K.; Zakis, J.; Suzdalenko, A.; Husev, O.

    2017-10-01

    A full bridge converter with electrolytic capacitor on the dc bus is a widely used approach for a single phase interface for renewable energy source generation or energy storage integration in the utility grid. New wide bandgap devices enable higher switching frequency, higher efficiency and higher power density. In the paper, the authors introduce the challenges associated with an increase in switching frequency of a single phase inverter and implementation of wide bandgap GaN-based transistors instead of traditional Si-based transistors. The low gate threshold voltage of GaN transistor and unique reverse conduction behaviour require different driving circuit. The design of the driver circuit and other practical issues are analysed in the paper. The paper also presents some practical results. The research results can be useful to avoid mistakes by designing GaN-based power converters as these devices become increasingly interesting for commercial applications.

  16. Fabrication and characterization of 395 nm ultraviolet GaN light-emitting diodes

    Science.gov (United States)

    Lin, Min-Pang; Chen, Chien-Ju; Shan, Li-Wei; Wu, Meng-Chyi

    2017-09-01

    In this article, we demonstrated the fabrication and characterization of 395 nm GaN ultraviolet light-emitting diodes grown on patterned sapphire substrates. The current confining aperture is designed as 45, 55, 65, 75 and 85 μm. The indium tin oxide (ITO) was used as a current spreading layer. Use the metals of nickel and gold to form ohmic contact with P-AlGaN layer prior to dry etching. The 45-μm-diameter LED exhibits a 3-dB modulation bandwidth of 134 MHz at 50 mA and a light output power density of 1.2 mW (78 W/cm2) at 30 mA. In addition, the 3-dB frequency bandwidth is proportional to the square root of the injected current density.

  17. Green high-power tunable external-cavity GaN diode laser at 515 nm

    DEFF Research Database (Denmark)

    Chi, Mingjun; Jensen, Ole Bjarlin; Petersen, Paul Michael

    2016-01-01

    A 480 mW green tunable diode laser system is demonstrated for the first time to our knowledge. The laser system is based on a GaN broad-area diode laser and Littrow external-cavity feedback. The green laser system is operated in two modes by switching the polarization direction of the laser beam...... incident on the grating. When the laser beam is p-polarized, an output power of 50 mW with a tunable range of 9.2 nm is achieved. When the laser beam is s-polarized, an output power of 480 mW with a tunable range of 2.1 nm is obtained. This constitutes the highest output power from a tunable green diode...... laser system....

  18. On the design of GaN vertical MESFETs on commercial LED sapphire wafers

    Science.gov (United States)

    Atalla, Mahmoud R. M.; Noor Elahi, Asim M.; Mo, Chen; Jiang, Zhenyu; Liu, Jie; Ashok, S.; Xu, Jian

    2016-12-01

    Design of GaN-based vertical metal-semiconductor field-effect transistors (MESFETs) on commercial light-emitting-diode (LED) epi-wafers has been proposed and proof of principle devices have been fabricated. In order to better understand the IV curves, these devices have been simulated using the charge transport model. It was found that shrinking the drain pillar size would significantly help in reaching cut-off at much lower gate bias even at high carrier concentration of unintentionally doped GaN and considerable leakage current caused by the Schottky barrier lowering. The realization of these vertical MESFETs on LED wafers would allow their chip-level integration. This would open a way to many intelligent lighting applications like on-chip current regulator and signal regulation/communication in display technology.

  19. Optical and electrical characteristics of GaN vertical light emitting diode with current block layer

    International Nuclear Information System (INIS)

    Guo Enqing; Liu Zhiqiang; Wang Liancheng; Yi Xiaoyan; Wang Guohong

    2011-01-01

    A GaN vertical light emitting diode (LED) with a current block layer (CBL) was investigated. Vertical LEDs without a CBL, with a non-ohmic contact CBL and with a silicon dioxide CBL were fabricated. Optical and electrical tests were carried out. The results show that the light output power of vertical LEDs with a non-ohmic contact CBL and with a silicon dioxide CBL are 40.6% and 60.7% higher than that of vertical LEDs without a CBL at 350 mA, respectively. The efficiencies of vertical LEDs without a CBL, with a non-ohmic contact CBL and with a silicon dioxide CBL drop to 72%, 78% and 85.5% of their maximum efficiency at 350 mA, respectively. Moreover, vertical LEDs with a non-ohmic contact CBL have relatively superior anti-electrostatic ability. (semiconductor devices)

  20. Spin relaxation in InGaN quantum disks in GaN nanowires

    KAUST Repository

    Banerjee, Animesh

    2011-12-14

    The spin relaxation time of photoinduced conduction electrons has been measured in InGaN quantum disks in GaN nanowires as a function of temperature and In composition in the disks. The relaxation times are of the order of ∼100 ps at 300 K and are weakly dependent on temperature. Theoretical considerations show that the Elliott-Yafet scattering mechanism is essentially absent in these materials and the results are interpreted in terms of the D\\'yakonov-Perel\\' relaxation mechanism in the presence of Rashba spin-orbit coupling of the wurtzite structure. The calculated spin relaxation times are in good agreement with the measured values. © 2011 American Chemical Society.