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Sample records for hozakinofusamo ga hoshutsushita

  1. Concurrently inhibitory and allelopathic effects of allelochemicals secreted by Myriophyllum spicatum on growth of blue-green algae; Hozakinofusamo ga hoshutsushita areropashi busshitsu no aisorui ni taisuru fukugo sayo oyobi areropashi koka no hyoka

    Energy Technology Data Exchange (ETDEWEB)

    Nakai, S.; Inoue, Y.; Hosomi, M.; Murakami, A. [Tokyo Univ. of Agriculture and Technology, Tokyo (Japan)

    1998-10-10

    This paper describes effects of allelochemicals secreted by Myriophyllum spicatum on growth of blue-green algae. In order to propose an effective growth inhibitory method of blue-green algae with less impact on the ecosystem, biological interaction (allelopathy) between large aquatic plants and algae was investigated. Pyrogallic acid, gallic acid, catechin and ellagic acid secreted by M. spicatum provided growth inhibitory effects of blue-green algae (Microcyctis aeruginosa), individually. Complex interaction and allelopathic contribution of these four polyphenols were evaluated. By comparing the actual effects with the expected values, synergetic growth inhibitory effects were recognized by adding four polyphenols at the same time. Furthermore, growth inhibitory effects were evaluated for actual culture solution of M. spicatum and simulated culture solution made by four polyphenols. As a result, it was found that these four polyphenols relate to allelopathy of M. spicatum. 25 refs., 6 figs., 4 tabs.

  2. Ligand "Brackets" for Ga-Ga Bond.

    Science.gov (United States)

    Fedushkin, Igor L; Skatova, Alexandra A; Dodonov, Vladimir A; Yang, Xiao-Juan; Chudakova, Valentina A; Piskunov, Alexander V; Demeshko, Serhiy; Baranov, Evgeny V

    2016-09-06

    The reactivity of digallane (dpp-Bian)Ga-Ga(dpp-Bian) (1) (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) toward acenaphthenequinone (AcQ), sulfur dioxide, and azobenzene was investigated. The reaction of 1 with AcQ in 1:1 molar ratio proceeds via two-electron reduction of AcQ to give (dpp-Bian)Ga(μ2-AcQ)Ga(dpp-Bian) (2), in which diolate [AcQ](2-) acts as "bracket" for the Ga-Ga bond. The interaction of 1 with AcQ in 1:2 molar ratio proceeds with an oxidation of the both dpp-Bian ligands as well as of the Ga-Ga bond to give (dpp-Bian)Ga(μ2-AcQ)2Ga(dpp-Bian) (3). At 330 K in toluene complex 2 decomposes to give compounds 3 and 1. The reaction of complex 2 with atmospheric oxygen results in oxidation of a Ga-Ga bond and affords (dpp-Bian)Ga(μ2-AcQ)(μ2-O)Ga(dpp-Bian) (4). The reaction of digallane 1 with SO2 produces, depending on the ratio (1:2 or 1:4), dithionites (dpp-Bian)Ga(μ2-O2S-SO2)Ga(dpp-Bian) (5) and (dpp-Bian)Ga(μ2-O2S-SO2)2Ga(dpp-Bian) (6). In compound 5 the Ga-Ga bond is preserved and supported by dithionite dianionic bracket. In compound 6 the gallium centers are bridged by two dithionite ligands. Both 5 and 6 consist of dpp-Bian radical anionic ligands. Four-electron reduction of azobenzene with 1 mol equiv of digallane 1 leads to complex (dpp-Bian)Ga(μ2-NPh)2Ga(dpp-Bian) (7). Paramagnetic compounds 2-7 were characterized by electron spin resonance spectroscopy, and their molecular structures were established by single-crystal X-ray analysis. Magnetic behavior of compounds 2, 5, and 6 was investigated by superconducting quantum interference device technique in the range of 2-295 K.

  3. GA-Gammon

    DEFF Research Database (Denmark)

    Irineo-Fuentes, Oscar; Cruz-Cortes, Nareli; Rodriguez-Henriquez, Francisco

    2006-01-01

    of the best board positions during a game. Best GA-Gammon individuals so obtained were tested in separated 5000-game tournaments against Pubeval itself, and Fuzzeval, a fuzzy controller-based player. Our experimental results indicate that the best individuals generated by GA-Gammon show similar performance...

  4. GaAs/GaSb nanowire heterostructures grown by MOVPE

    DEFF Research Database (Denmark)

    Jeppsson, Mattias; Dick, Kimberly A.; Wagner, Jakob Birkedal

    2008-01-01

    We report Au-assisted growth of GaAs/GaSb nanowire heterostructures on GaAs(1 1 1)B-substrates by metal-organic vapor phase epitaxy. The growth is studied at various precursor molar fractions and temperatures, in order to optimize the growth conditions for the GaSb nanowire segment. In contrast t...

  5. GaN HEMTs

    Science.gov (United States)

    Anderson, Jonathan W.; Lee, Kyoung-Keun; Piner, Edwin L.

    2012-03-01

    Gallium nitride (GaN) has enormous potential for applications in high electron mobility transistors (HEMTs) used in RF and power devices. Intrinsic device properties such as high electron mobility, high breakdown voltage, very high current density, electron confinement in a narrow channel, and high electron velocity in the 2-dimensional electron gas of the HEMT structure are due in large part to the wide band gap of this novel semiconductor material system. This presentation discusses the properties of GaN that make it superior to other semiconductor materials, and outlines the research that will be undertaken in a new program at Texas State University to advance GaN HEMT technology. This program's aim is to further innovate the exceptional performance of GaN through improved material growth processes and epitaxial structure design.

  6. GaSbBi/GaSb quantum well laser diodes

    Science.gov (United States)

    Delorme, O.; Cerutti, L.; Luna, E.; Narcy, G.; Trampert, A.; Tournié, E.; Rodriguez, J.-B.

    2017-05-01

    We report on the structural and optical properties of GaSbBi single layers and GaSbBi/GaSb quantum well heterostructures grown by molecular beam epitaxy on GaSb substrates. Excellent crystal quality and room-temperature photoluminescence are achieved in both cases. We demonstrate laser operation from laser diodes with an active zone composed of three GaSb0.885Bi0.115/GaSb quantum wells. These devices exhibit continuous-wave lasing at 2.5 μm at 80 K, and lasing under pulsed operation at room-temperature near 2.7 μm.

  7. Highly Polarized Electrons from GaAs-GaAsP and InGaAs-AlGaAs Strained Layer Superlattice Photocathodes

    CERN Document Server

    Nakanishi, T; Kuwahara, M; Naniwa, K; Nishitani, T; Okumi, S; Yamamoto, N; Yasui, K

    2004-01-01

    GaAs-GaAsP strained layer superlattice photocathode has been developed for highly polarized electron beams. This cathode achieved a maximum polarization of 92% with a quantum efficiency of 0.5%. Criteria for achieving the highest polarization together with high quantum efficiency using superlattice photocathodes are discussed based on experimental spin-resolved quantum efficiency spectra of GaAs-AlGaAs, InGaAs-AlGaAs and GaAs-GaAsP superlattice structures.

  8. 2015 Lowndes County (GA) Lidar

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: NOAA OCM Lidar for Lowndes County, GA with the option to Collect Lidar in Cook and Tift Counties, GA Lidar Data Acquisition and Processing Production Task...

  9. Coulomb excitation of Ga-73

    NARCIS (Netherlands)

    Diriken, J.; Stefanescu, I.; Balabanski, D.; Blasi, N.; Blazhev, A.; Bree, N.; Cederkaell, J.; Cocolios, T. E.; Davinson, T.; Eberth, J.; Ekstrom, A.; Fedorov, D. V.; Fedosseev, V. N.; Fraile, L. M.; Franchoo, S.; Georgiev, G.; Gladnishki, K.; Huyse, M.; Ivanov, O. V.; Ivanov, V. S.; Iwanicki, J.; Jolie, J.; Konstantinopoulos, T.; Kroell, Th.; Kruecken, R.; Koester, U.; Lagoyannis, A.; Lo Bianco, G.; Maierbeck, P.; Marsh, B. A.; Napiorkowski, P.; Patronis, N.; Pauwels, D.; Reiter, P.; Seliverstov, M.; Sletten, G.; Van de Walle, J.; Van Duppen, P.; Voulot, D.; Walters, W. B.; Warr, N.; Wenander, F.; Wrzosek, K.

    2010-01-01

    The B(E2; I-i -> I-f) values for transitions in Ga-71(31)40 and Ga-73(31)42 were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of Ga-71,Ga-73 at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were dete

  10. TMR study of GaMnAs/AlGaAs:Be/GaMnAs trilayers

    Science.gov (United States)

    Hagmann, Joseph; Liu, Xinyu; Dobrowolska, Malgorzata; Furdyna, Jacek; Yoo, Taehee; Khym, Sungwon; Lee, Sanghoon

    2011-03-01

    GaMnAs/GaAs:Be/GaMnAs trilayers have recently demonstrated antiferromagnetic (AFM) coupling between the two ferromagnetic (FM) layers, mediated by holes in the spacer layer. In this work, GaMnAs/ Al x Ga 1-x :Be/GaMnAs trilayer samples with varying Al concentrations were fabricated into magnetic tunnel junction (MTJ) devices with range of pillar diameters to measure tunneling magnetoresistance (TMR) under various conditions. SQUID measurements were use to measure the magnetization of the samples, including switching fields for parallel and antiparallel magnetization alignments of the FM layers. TMR was observed in the sample with Al 0.22 Ga 0.78 As:Be spacer, but was massively suppressed in the samples with lower Al content. The presence of holes in the spacer layer is shown to suppress TMR. This illustrates the difference in conditions for TMR and for AFM interlayer coupling. Supported by NSF Grant DMR-1005851 and OISE-1015458.

  11. Environments of Ga in MFI-type Ga-silicates and their catalytic performance; MFI gata Ga-silicate chu no Ga no sonzai jotai to shokubai seino

    Energy Technology Data Exchange (ETDEWEB)

    Nagata, H.; Takiyama, Y.; Higashida, K.; Otsuka, S.; Kishida, M.; Wakabayashi, K. [Kyushu University, Fukuoka (Japan); Shoji, H. [Maruzen Petrochemical Co. Ltd., Chiba (Japan)

    1998-07-01

    MFI-type Ga-silicates (GaS) of varying atomic Si/Ga ratio are synthesized from the gel stocks, to compare them one another for their properties and C4H10 conversion performance. GaS (M) synthesized by the Mobil method shows a broader Ga-MASNMR spectral peak relevant to the GaO4 tetrahedron and lower unit cell increase rate, when it contains a high proportion of Ga, than GaS (A) synthesized by the alkoxide method. It is therefore considered that GaS (M) has an increased content of the GaO4 tetrahedron of low symmetry, as Ga content increases. GaS (M) loses a larger quantity of Ga eluted out as a result of HCl treatment than GaS (A), indicating that the former contains the GaO4 tetrahedron of low symmetry under a less stable condition. GaS (M) gives a higher aromatic hydrocarbon yield in the C4H10 conversion than GaS (A), as its Ga content increases. This results from difference between their dehydrogenation performances, indicating that Ga in the GaO4 tetrahedron of lower symmetry has a higher dehydrogenation performance. 19 refs., 6 figs., 3 tabs.

  12. Contactless electroreflectance study of a GaAIAs/lnGaAs/ GaAs/GaAIAs step quantum well structure

    Science.gov (United States)

    Moneger, S.; Qiang, H.; Pollak, Fred H.; Noble, T. F.

    1995-10-01

    Using contactless electroreflectance at 300 and 77K, we have studied the inter-subband transitions from a GaAlAs/InGaAs/GaAs/GaALAs step quantum well structure (small well inside a large well) consisting of two layers A (InxGa1-xAs) and B (GaAs) with widths LA and LB, respectively, bounded by two thick barrier regions of Gax AlyAs. By comparison of the observed spectral features with an envelope function calculation, including the effects of strain, we have been able to characterize the potential profile of the structure, i.e., LA, LB, x, and y. There is very good agreement between experiment and the intended materials param-eters. Such configurations are of considerable importance since (a) they form the basis for pseudomorphic high electron mobility transistors, and (b) also have applications in optoelectronics due to their large Stark shifts.

  13. Si上GaN研究

    Institute of Scientific and Technical Information of China (English)

    陈裕权

    2004-01-01

    <正> 亚琛电磁研究所订购了一台Aixtron公司的AIX200/4 RF—S设备。这台设备将用来研究基于Si衬底的GaN淀积。预计低成本的Si衬底与GaN结构相结合会大大影响未来高功率RF器件的价格。亚琛电磁研究所将用AIX 200/4 RF—S设备淀积高品质的AlGaN/GaN层和器件

  14. High breakdown voltage in AlGaN/GaN HEMTs using AlGaN/GaN/AlGaN quantum-well electron-blocking layers.

    Science.gov (United States)

    Lee, Ya-Ju; Yao, Yung-Chi; Huang, Chun-Ying; Lin, Tai-Yuan; Cheng, Li-Lien; Liu, Ching-Yun; Wang, Mei-Tan; Hwang, Jung-Min

    2014-01-01

    In this paper, we numerically study an enhancement of breakdown voltage in AlGaN/GaN high-electron-mobility transistors (HEMTs) by using the AlGaN/GaN/AlGaN quantum-well (QW) electron-blocking layer (EBL) structure. This concept is based on the superior confinement of two-dimensional electron gases (2-DEGs) provided by the QW EBL, resulting in a significant improvement of breakdown voltage and a remarkable suppression of spilling electrons. The electron mobility of 2-DEG is hence enhanced as well. The dependence of thickness and composition of QW EBL on the device breakdown is also evaluated and discussed.

  15. Robust AlGaN/GaN MMIC Receiver Components

    NARCIS (Netherlands)

    Heijningen, M. van; Janssen, J.P.B.; Vliet, F.E. van

    2009-01-01

    Apart from delivering very high output powers, GaN can also be used to realize robust receiver components, such as Low Noise Amplifiersand Switches. This paper presents the designand measurement results of two GaN X-band switch and LNA MMICs, designed for integration in a radar front end. The switch

  16. Antisites and anisotropic diffusion in GaAs and GaSb

    KAUST Repository

    Tahini, H. A.

    2013-10-02

    The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport. To reconcile the existence of Ga vacancies under Ga-rich conditions, transformation reactions have been proposed. Here, density functional theory is employed to calculate the formation energies of vacancies on both sublattices and the migration energy barriers to overcome the formation of the vacancy-antisite defect. Transformation reactions enhance the vacancy concentration in both materials and migration energy barriers indicate that Ga vacancies will dominate.

  17. DLTS measurements on GaSb/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Hoegner, Annika; Nowozin, Tobias; Marent, Andreas; Bimberg, Dieter [Institut fuer Festkoerperphysik, TU Berlin (Germany); Tseng, Chi-Che [Institute of Photonics Technologies, NTHU (China); Lin, Shih-Yen [Institute of Optoelectronic Sciences, NTOU (China)

    2010-07-01

    Memory devices based on hole storage in self-organized quantum dots offer significant advantages with respect to storage time and scalability. Recently, we demonstrated a first prototype based on InAs/GaAs quantum dots at low temperatures. To enable feasible storage times at room temperature the localisation energy of the quantum dots has to be increased by using other material systems. A first step in this direction is the use of GaSb quantum dots within a GaAs matrix. We have characterized self-organized GaSb/GaAs quantum dots embedded into a n{sup +}p-diode structure. DLTS measurements on hole emission were conducted and yield a strong peak from which a mean emission energy of about 400 meV can be extracted. The reference sample without the quantum dots (containing only the wetting layer) shows no such peak.

  18. Growth and Optimization of 2 Micrometers InGaSb/AlGaSb Quantum-Well-Based VECSELs on GaAs/AlGaAs DBRs

    Science.gov (United States)

    2013-08-01

    optically pumped vertical-external-cavity surface-emitting lasers (VECSELs) based on InGaSb/AlGaSb quantum wells grown on GaAs/ AlGaAs distributed Bragg...cross-sectional transmission electron microscopy. The optical properties of the III-Sb active regions are characterized by time-resolved... optically pumped vertical- external-cavity surface-emitting lasers (VECSELs) based on InGaSb/AlGaSb quantum wells grown on GaAs/ AlGaAs distri- buted Bragg

  19. Effect of GaN buffer polarization on electron distribution of AlGaN/GaN heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    He, Xiaoguang; Zhao, Degang, E-mail: dgzhao@red.semi.ac.cn; Liu, Wei; Yang, Jing; Li, Xiaojing; Li, Xiang

    2016-06-15

    The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. A misunderstanding about the 2DEG sheet density expression is clarified. It is predicted by theoretical analysis and validated by self-consistent Schrodinger–Poisson numerical simulation that under the force of GaN polarization, large amounts of electrons will accumulate at the GaN/substrate interface in AlGaN/GaN/substrate HEMT structure. - Highlights: • The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. • Self-consistent Schrodinger–Poisson numerical simulation is used to modulate the AlGaN/GaN/substrate structure. • It is predicted by that large amounts of electrons will accumulate at the GaN/substrate interface.

  20. 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.

  1. Prostatic uptake of Ga-67

    Energy Technology Data Exchange (ETDEWEB)

    Sullivan, W.T.; Rosen, P.R.; Weiland, F.L.; Ritchey, M.L.

    1984-08-01

    Midline activity low in the pelvis seen on Ga-67 scans is frequently attributed to colonic excretion of radionuclide. Two cases of infectious prostatitis with focal uptake of Ga-67 within the prostate gland are described. A technique of using limited quantities of barium administered by enema and appropriate positional imaging, which localized pelvic activity to the prostate, is described.

  2. 31% European InGaP/GaAs/InGaAs Solar Cells for Space Application

    Directory of Open Access Journals (Sweden)

    Campesato Roberta

    2017-01-01

    Full Text Available We report a triple junction InGaP/GaAs/InGaNAs solar cell with efficiency of ~31% at AM0, 25 °C fabricated using a combined molecular beam epitaxy (MBE and metal-organic chemical vapour deposition (MOCVD processes. The prototype cells comprise of InGaNAs (Indium Gallium Nitride Arsenide bottom junction grown on a GaAs (Gallium Arsenide substrate by MBE and middle and top junctions deposited by MOCVD. Repeatable cell characteristics and uniform efficiency pattern over 4-inch wafers were obtained. Combining the advantages offered by MBE and MOCVD opens a new perspective for fabrication of high-efficiency space tandem solar cells with three or more junctions. Results of radiation resistance of the sub-cells are also presented and critically evaluated to achieve high efficiency in EOL conditions.

  3. Interface properties and deep levels in InGaAsN/GaAs and GaAsN/GaAs heterojunctions

    Science.gov (United States)

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Botchkarev, Andrei E.; Nelson, Nicole N.; Fahmi, M. M. E.; Griffin, James A.; Khan, Arif; Noor Mohammad, S.; Johnstone, D. K.; Bublik, V. T.; Chsherbatchev, K. D.; Voronova, M. I.

    2002-12-01

    Interface properties of dilute slightly lattice mismatched GaAsN/GaAs (0.35 at.% N) and closely lattice matched InGaAsN (1 at.% In, 0.35 at.% N) heterojunctions (HJs) were studied by means of capacitance-voltage profiling, deep levels transient spectroscopy (DLTS) and current-voltage measurements. It is found that the lattice matched HJs show no electrical breakdown when the space charge region crosses the interface. The carrier concentration profiles in such HJ show, as expected, the accumulation region on the low-bandgap side and the depletion region on the high-bandgap side of the HJ. This is not the case for the GaAsN/GaAs (GaAsN layer on top) and the GaAs/GaAsN (GaAs layer on top) HJ. The density of deep traps in GaAsN, InGaAsN films and in GaAs films grown on GaAsN underlayers was very much higher than in epitaxial GaAs films. The dominant deep centers were the EL6 and the EL3 electron traps. The interface regions of the GaAs/GaAsN and the InGaAsN/GaAs HJs were shown to be enriched by EL3 traps, while for the GaAsN/GaAs HJ those regions were enriched by EL6 traps which was associated with the former films being Ga-rich and thus facilitating incorporation of oxygen on As sites.

  4. Performance improvement of GaN-based LEDs with step stage InGaN/GaN strain relief layers in GaN-based blue LEDs.

    Science.gov (United States)

    Jia, Chuanyu; Yu, Tongjun; Lu, Huimin; Zhong, Cantao; Sun, Yongjian; Tong, Yuzhen; Zhang, Guoyi

    2013-04-08

    The performance of nitride-based LEDs was improved by inserting dual stage and step stage InGaN/GaN strain relief layer (SRL) between the active layer and n-GaN template. The influences of step stage InGaN/GaN SRL on the structure, electrical and optical characteristics of GaN-based LEDs were investigated. The analysis of strain effect on recombination rate based k·p method indicated 12.5% reduction of strain in InGaN/GaN MQWs by inserting SRL with step stage InGaN/GaN structures. The surface morphology was improved and a smaller blue shift in the electroluminescence (EL) spectral with increasing injection current was observed for LEDs with step stage SRL compared with conventional LEDs. The output power of LEDs operating at 20 mA was about 15.3 mW, increased by more than 108% by using step stage InGaN/GaN SRL, which shows great potential of such InGaN/GaN SRL in modulating InGaN/GaN MQWs optical properties based on its strain relief function.

  5. Influence of GaAsP Insertion Layers on Performance of InGaAsP/InGaP/AlGaAs Quantum-Well Laser

    Institute of Scientific and Technical Information of China (English)

    CAO Yu-Lian; CHEN Liang-Hui; LIAN Peng; MA Wen-Quan; WANG Qing; WU Xu-Ming; HE Guo-Rong; LI Hui; WANG Xiao-Dong; SONG Guo-Feng

    2006-01-01

    @@ We report on the use of very thin GaAsP insertion layers to improve the performance of an InGaAsP/InGaP/AlGaAs single quantum-well laser structure grown by metal organic chemical vapour deposition.

  6. GaInNAs laser gain

    Energy Technology Data Exchange (ETDEWEB)

    CHOW,WENG W.; JONES,ERIC D.; MODINE,NORMAND A.; KURTZ,STEVEN R.; ALLERMAN,ANDREW A.

    2000-05-23

    The optical gain spectra for GaInNAs/GaAs quantum wells are computed using a microscopic laser theory. From these spectra, the peak gain and carrier radiative decay rate as functions of carrier density are determined. These dependences allow the study of the lasing threshold current density of GaInNAs/GaAs quantum well structures.

  7. Hydrogenation of GaSb/GaAs quantum rings

    Energy Technology Data Exchange (ETDEWEB)

    Hodgson, P. D., E-mail: pdhodgson@hotmail.co.uk; Hayne, M.; Zhuang, Q. D. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Ahmad Kamarudin, M. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Department of Physics, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Darul Ehsan (Malaysia); Birindelli, S.; Capizzi, M. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale A. Moro 2, 00185 Roma (Italy)

    2014-08-25

    We present the results of photoluminescence measurements on hydrogenated type-II GaSb/GaAs quantum dot/ring (QD/QR) samples at temperatures ranging from 4.2 K to 400 K. Hydrogenation is found to suppress optically induced charge depletion (associated with the presence of carbon acceptors in this system). A redshift of the QD\\QR emission energy of a few tens of meV is observed at temperatures ≥300 K, consistent with a reduction in average occupancy by ∼1 hole. These effects are accompanied by a reduction in PL intensity post-hydrogenation. We conclude that although hydrogenation may have neutralized the carbon acceptors, multiple hole occupancy of type-II GaSb/GaAs QD/QRs is very likely a precondition for intense emission, which would make extending the wavelength significantly beyond 1300 nm at room temperature difficult.

  8. Gibberellin biosynthesis in maize. Metabolic studies with GA{sub 15}, GA{sub 24}, GA{sub 25}, GA{sub 7}, and 2,3-dehydro-GA{sub 9}

    Energy Technology Data Exchange (ETDEWEB)

    Davis, G.; Kobayashi, Masatomo; Phinney, B.O.; Lange, T.; Croker, S.J.; Gaskin, P.; MacMillan, J.

    1999-11-01

    [17-{sup 14}C]-Labeled GA{sub 15}, GA{sub 24}, GA{sub 25}, GA{sub 7}, and 2,3-dehydro-GA{sub 9} were separately injected into normal, dwarf-1 (d1), and dwarf-5 (d5) seedlings of maize (Zea mays L.). Purified radioactive metabolites from the plant tissues were identified by sull-scan gas chromatography-mass spectrometry and Kovats retention index data. The metabolites from GA{sub 15} were GA{sub 44}, GA{sub 19}, GA{sub 20}, GA{sub 113}, and GA{sub 15}-15,16-ene (artifact?). GA{sub 24} was metabolized to GA{sub 19}, GA{sub 20}, and GA{sub 17}. The metabolites from GA{sub 25} were GA{sub 17}, GA{sub 25} 16{alpha},17-H{sub 2}-17-OH, and HO-GA{sub 25} (hydroxyl position not determined). GA{sub 7} was metabolized to GA{sub 30}, GA{sub 3}, isoGA{sub 3} (artifact?), and trace amounts of GA{sub 7}-diene-diacid (artifact?). 2,3-Dehydro-GA{sub 9} was metabolized to GA{sub 5}, GA{sub 7} (trace amounts), 2,3-dehydro-GA{sub 10} (artifact?), GA{sub 31}, and GA{sub 62}. Their results provide additional in vivo evidence of a metabolic grid in maize (i.e., pathway convergence). The grid connects members of a putative, non-early 3,130hydroxylation branch pathway to the corresponding members of the previously documented early 13-hydroxylation branch pathway. The inability to detect the sequence GA{sub 12}{r{underscore}arrow} GA{sub 15} {r{underscore}arrow} GA{sub 24} {r{underscore}arrow} GA{sub 9} indicates that the non-early 3,13-hydroxylation pathway probably plays a minor role in the origin of bioactive gibberellins in maize.

  9. Evolution of morphology and microstructure of GaAs/GaSb nanowire heterostructures.

    Science.gov (United States)

    Shi, Suixing; Zhang, Zhi; Lu, Zhenyu; Shu, Haibo; Chen, Pingping; Li, Ning; Zou, Jin; Lu, Wei

    2015-01-01

    In this paper, we successfully grow GaAs/GaSb core-shell heterostructure nanowires (NWs) by molecular beam epitaxy (MBE). The as-grown GaSb shell layer forms a wurtzite structure instead of the zinc blende structure that has been commonly reported. Meanwhile, a bulgy GaSb nanoplate also appears on top of GaAs/GaSb core-shell NWs and possesses a pure zinc blende phase. The growth mode for core-shell morphology and underlying mechanism for crystal phase selection of GaAs/GaSb nanowire heterostructures are discussed in detail.

  10. GaAs-MnAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Sadowski, Janusz [MAX-Lab, Lund University, P.O. Box 118, 221 00 Lund (Sweden); Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warszawa (Poland); Siusys, Aloyzas; Wojciechowski, Tomasz; Reszka, Anna; Kowalski, Bogdan [Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warszawa (Poland); Kovacs, Andras; Kasama, Takeshi [Center for Electron Nanoscopy, Technical University of Denmark, Kgs. Lyngby 2800 (Denmark); Dunin-Borkowski, Rafal E. [Center for Electron Nanoscopy, Technical University of Denmark, Kgs. Lyngby 2800 (Denmark); Institute for Microstructure Research, Peter Gruenberg Institute, Forschungszentrum Juelich, 52425 Juelich (Germany)

    2011-07-15

    Different strategies for obtaining nanowires (NWs) with ferromagnetic properties using the molecular beam epitaxy (MBE) grown nanostructures combining GaAs and Mn were investigated. Four types of structures have been studied: (i) self-catalyzed GaAs:Mn NWs grown at low temperatures on GaAs(100) substrates; (ii) GaAs:Mn NWs grown at high temperatures on Si(100) substrates; (iii) GaAs-GaMnAs core-shell NW structures; (iv) GaAs-MnAs core-shell NW structures grown on Si(100). Structures of types (i), (iii), and (iv) exhibit ferromagnetic properties. Right: Scanning electron microscopy image of Mn doped GaAs NWs with Ga droplets at the tops, grown by MBE on oxidized Si(100) substrate in the autocatalytic growth mode. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. MOCVD growth of GaAs on Si using (Al,In) GaAs/GaAs buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, K.; Shiba, Y.; Asai, K. (Advanced Tech. Research Labs., Sumitomo Metal Industries, Ltd., Hyogo (Japan))

    1991-01-01

    GaAs was grown on Si using an (Al,In)GaAs/GaAs buffer layer. The etch pit density (EPD) revealed by molten KOH could be reduced by adding Al{sub x}Ga{sub 1-x}As or In{sub x}Ga{sub 1-x}As to the GaAs buffer layer, depending on the composition (x); the lowest EPD, 4x10{sup 6} cm{sup -2} was obtained when x was 0.3 in Al{sub x}Ga{sub 1-x}As. To understand the results, the initial growth stage of GaAs on Si was investigated by scanning electron microscopy. GaAs growth using an Al{sub 0.3}Ga{sub 0.7}As layer produced small islands at a sufficiently high density that the islands coalesced, unlike those without the layer. The dependence of EPD and island density on the composition (x) were almost the same. This result indicates that improvement of the quality of the GaAs layer is related to the coalescence of the GaAs island at an early stage of the growth of GaAs on Si. (orig.).

  12. Intense terahertz emission from molecular beam epitaxy-grown GaAs/GaSb(001)

    Energy Technology Data Exchange (ETDEWEB)

    Sadia, Cyril P.; Laganapan, Aleena Maria; Agatha Tumanguil, Mae; Estacio, Elmer; Somintac, Armando; Salvador, Arnel [National Institute of Physics, University of the Philippines Diliman, Quezon City 1101 (Philippines); Que, Christopher T. [Physics Department, De La Salle University, 2401 Taft Avenue, Manila 1004 (Philippines); Yamamoto, Kohji; Tani, Masahiko [Research Center for Development of Far-Infrared Region, University of Fukui, Fukui 910-8507 (Japan)

    2012-12-15

    Intense terahertz (THz) electromagnetic wave emission was observed in undoped GaAs thin films deposited on (100) n-GaSb substrates via molecular beam epitaxy. GaAs/n-GaSb heterostructures were found to be viable THz sources having signal amplitude 75% that of bulk p-InAs. The GaAs films were grown by interruption method during the growth initiation and using various metamorphic buffer layers. Reciprocal space maps revealed that the GaAs epilayers are tensile relaxed. Defects at the i-GaAs/n-GaSb interface were confirmed by scanning electron microscope images. Band calculations were performed to infer the depletion region and electric field at the i-GaAs/n-GaSb and the air-GaAs interfaces. However, the resulting band calculations were found to be insufficient to explain the THz emission. The enhanced THz emission is currently attributed to a piezoelectric field induced by incoherent strain and defects.

  13. Recombination dynamics of type-II excitons in (Ga,In)As/GaAs/Ga(As,Sb) heterostructures

    Science.gov (United States)

    Gies, S.; Holz, B.; Fuchs, C.; Stolz, W.; Heimbrodt, W.

    2017-01-01

    (Ga,In)As/GaAs/Ga(As,Sb) multi-quantum well heterostructures have been investigated using continuous wave and time-resolved photoluminescence spectroscopy at various temperatures. A complex interplay was observed between the excitonic type-II transitions with electrons in the (Ga,In)As well and holes in the Ga(As,Sb) well and the type-I excitons in the (Ga,In)As and Ga(As,Sb) wells. The type-II luminescence exhibits a strongly non-exponential temporal behavior below a critical temperature of T c = 70 K. The transients were analyzed in the framework of a rate-equation model. It was found that the exciton relaxation and hopping in the localized states of the disordered ternary Ga(As,Sb) are the decisive processes to describe the dynamics of the type-II excitons correctly.

  14. Fabrication of GaN-Based Heterostructures with an InAlGaN/AlGaN Composite Barrier

    Institute of Scientific and Technical Information of China (English)

    Ru-Dai Quan; Jin-Cheng Zhang; Jun-Shuai Xue; Yi Zhao; Jing Ning; Zhi-Yu Lin; Ya-Chao Zhang

    2016-01-01

    GaN-based heterostructures with an InAlGaN/AlGaN composite barrier on sapphire (0001) substrates are grown by a low-pressure metal organic chemical vapor deposition system.Compositions of the InAlGaN layer are determined by x-ray photoelectron spectroscopy,structure and crystal quality of the heterostructures are identified by high resolution x-ray diffraction,surface morphology of the samples are examined by an atomic force microscope,and Hall effect and capacitance-voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures.The Al/In ratio of the InAlGaN layer is 4.43,which indicates that the InAlGaN quaternary layer is nearly lattice-matched to the GaN channel.Capacitance-voltage results show that there is no parasitic channel formed between the InAlGaN layer and the AlGaN layer.Compared with the InAlGaN/GaN heterostructure,the electrical properties of the InAlGaN/AlGaN/GaN heterostructure are improved obviously.Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied.With the optimal thickness of the AlGaN layer to be 5 nm,the 2DEG mobility,sheet density and the sheet resistance of the sample is 1889.61 cm2/V.s,1.44 × 1013 cm-2 and as low as 201.1 Ω/sq,respectively.

  15. Micromechanical sensors based on GaAs/AlGaAs

    OpenAIRE

    Fricke, K; Dehe, A.; SchuBler, M; Lee, W.Y.; Hartnagel, H.L.

    1994-01-01

    The combination of high temperature stable electro­nics with micromachining is a powerful means to de­velop a variety of intelligent sensors. Especially in the GaAs/AlGaAs material system all advantages fit to­gether to realize micromachined sensors with integrated high temperature electronics. The technology includes new ohmic and Schottky contacts with high stability at increased ambient temperature. A thermal sensor is pre­sented that can detect total pressure, gas type as well as gas velo...

  16. Electrical Characteristics of InGaN/AlGaN and InGaN/GaN MQW Near UV-LEDs

    Institute of Scientific and Technical Information of China (English)

    MU Sen; YU Tong-Jun; HUANG Liu-Bing; JIA Chuan-Yu; PAN Yao-Bo; YANG Zhi-Jian; CHEN Zhi-Zhong; QIN Zhi-Xin; ZHANG Guo-Yi

    2007-01-01

    Electrical characteristics of Ino.05Gao.95N/AJo.07Gao.93N and Ino.05Gao.95N/GaN multiple quantum well (MQW) ultraviolet light-emitting diodes (UV-LEDs) at 400 nm wavelength are measured. It is found that for In-GaN/AlGaN MQW LEDs, both ideality factor and parallel resistance are similar to those of InGaN/GaN MQW LEDs, while series resistance is two times larger. It is suggested that the AJ0.07Ga0.93N barrier layer did not change crystal quality and electrical characteristic ofp-n junction either, but brought larger series resistance. As a result, InGaN/AlGaN MQW LEDs suffer more serious thermal dissipation problem although they show higher light output efficiency.

  17. Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As

    Energy Technology Data Exchange (ETDEWEB)

    Adell, J; Ulfat, I; Ilver, L; Kanski, J [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Sadowski, J [Institute of Physics, Polish Academy of Sciences, PL-02-668 Warsaw (Poland); Karlsson, K [Department of Life Sciences, University of Skoevde, SE-541 28 Skoevde (Sweden)

    2011-03-02

    Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.

  18. Multilayers of InGaAs Nanostructures Grown on GaAs(210 Substrates

    Directory of Open Access Journals (Sweden)

    Wang Zhiming

    2010-01-01

    Full Text Available Abstract Multilayers of InGaAs nanostructures are grown on GaAs(210 by molecular beam epitaxy. With reducing the thickness of GaAs interlayer spacer, a transition from InGaAs quantum dashes to arrow-like nanostructures is observed by atomic force microscopy. Photoluminescence measurements reveal all the samples of different spacers with good optical properties. By adjusting the InGaAs coverage, both one-dimensional and two-dimensional lateral ordering of InGaAs/GaAs(210 nanostructures are achieved.

  19. Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As.

    Science.gov (United States)

    Adell, J; Ulfat, I; Ilver, L; Sadowski, J; Karlsson, K; Kanski, J

    2011-03-02

    Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.

  20. InGaAs/GaAs异质薄膜的MBE生长研究%The MBE growth research on InGaAs/GaAs heterofilms

    Institute of Scientific and Technical Information of China (English)

    罗子江; 周勋; 杨再荣; 贺业全; 何浩; 邓朝勇; 丁召

    2011-01-01

    This paper reports an experiment research which utilized of the molecular beam epitaxy technology to grow the InGaAs/GaAs film. The growth conditions was monitored through the RHEED patterns in real-time,the growth rate was measured and the composition of InGaAs film was determined by RHEED intensity oscillations,and a method was put forward to control the composition of In/Ga in InGaAs/GaAs film. According to the R HEED patterns, the surface of InGaAs film was (2 × 3) reconstructed. After growth, the sample was quenched down to room temperature then transferred into STM for scanning. A smooth,atomically flat surface of InGaAs/GaAs film was confirmed by the STM images.%利用分子束外延技术,在GaAs(001)基片上外延InGaAs/GaAs异质薄膜,通过RHEED图像演变实时监控薄膜生长状况,采用RHEED强度振荡测量薄膜生长速率,确定薄膜中In/Ga的组分比,并提出控制InGaAs薄膜中In/Ga组分比的生长方法.根据RHEED图像,指出获得的InGaAs薄膜处于(2×3)表面重构相.样品经过淬火至室温后对样品做STM扫描分析,证实样品为表面原子级平整的InGaAs/GaAs异质薄膜.

  1. Thermal Stability of Strained AlGaN/GaN Heterostructures

    Institute of Scientific and Technical Information of China (English)

    ZHANG Min; XIAO Hong-Di; LIN Zhao-Jun

    2006-01-01

    @@ The thermal stability of strained AlGaN/GaN heterostructures is characterized by comparing unannealed and 700℃ 30-min annealed Ni Schottky contacts prepared on strained AlGaN/GaN heterostructures. Using photoemission, capacitance-voltage measurements, and the self-consistent solution of Schrodinger's and Poisson's equations, it is found that after 700℃ 30-min thermal annealing the Schottky barrier height of Ni Schottky contacts on strained AlGaN/GaN heterostructures is increased, and the sheet density of polarization charges and the sheet density of two-dimensional electron gas (2DEG) electrons for the strained AlGaN/GaN heterostructures are reduced. These results are closely related to the performance of AlGaN/GaN HFETs at high temperature.

  2. Development of GaN/AlGaN Terahertz Quantum Cascade Laser

    Science.gov (United States)

    2008-11-19

    AFOSR-Taiwan Nanoscience Initiative Project Final Report Project Title Development of GaN /AlGaN Terahertz Quantum Cascade Laser...DATES COVERED 14-06-2007 to 13-06-2008 4. TITLE AND SUBTITLE Development of GaN -Based Terahertz Quantum Cascade Laser 5a. CONTRACT NUMBER...the GaN /AlGaN active region for terahertz quantum cascade lasers using MOCVD system based on the quantum cascade structure proposed by Prof. Greg Sun

  3. Chemistry and electrical properties of surfaces of GaN and GaN/AlGaN heterostructures

    OpenAIRE

    Hashizume, Tamotsu; Ootomo, Shinya; Oyama, Susumu; Konishi, Masanobu; Hasegawa, Hideki

    2001-01-01

    Chemical and electrical properties of the surfaces of GaN and GaN/AlGaN heterostructures were systematically investigated by x-ray photoelectron spectroscopy (XPS), capacitance–voltage, and current–voltage measurements. From in situ XPS study, relatively smaller band bending of 0.6 eV was seen at the GaN (2×2) surface grown by radio frequency-assisted molecular beam epitaxy on the metalorganic vapor phase epitaxy GaN template. After exposing the sample surface to air, strong band bending took...

  4. InGaN/GaN Tunnel Junctions For Hole Injection in GaN Light Emitting Diodes

    OpenAIRE

    Krishnamoorthy, Sriram; Akyol, Fatih; Rajan, Siddharth

    2014-01-01

    InGaN/GaN tunnel junction contacts were grown on top of an InGaN/GaN blue (450 nm) light emitting diode wafer using plasma assisted molecular beam epitaxy. The tunnel junction contacts enable low spreading resistance n-GaN top contact layer thereby requiring less top metal contact coverage on the surface. A voltage drop of 5.3 V at 100 mA, forward resistance of 2 x 10-2 ohm cm2 and a higher light output power are measured in tunnel junction LED. A low resistance of 5 x 10-4 ohm cm2 was measur...

  5. AlGaN/GaN High Electron Mobility Transistors with Multi-MgxNy/GaN Buffer

    Directory of Open Access Journals (Sweden)

    P. C. Chang

    2014-01-01

    Full Text Available We report the fabrication of AlGaN/GaN high electron mobility transistors with multi-MgxNy/GaN buffer. Compared with conventional HEMT devices with a low-temperature GaN buffer, smaller gate and source-drain leakage current could be achieved with this new buffer design. Consequently, the electron mobility was larger for the proposed device due to the reduction of defect density and the corresponding improvement of crystalline quality as result of using the multi-MgxNy/GaN buffer.

  6. Utilisation of GaN and InGaN/GaN with nanoporous structures for water splitting

    Energy Technology Data Exchange (ETDEWEB)

    Benton, J.; Bai, J.; Wang, T., E-mail: t.wang@sheffield.ac.uk [Department of Electronic and Electrical Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)

    2014-12-01

    We report a cost-effective approach to the fabrication of GaN based nanoporous structure for applications in renewable hydrogen production. Photoelectrochemical etching in a KOH solution has been employed to fabricate both GaN and InGaN/GaN nanoporous structures with pore sizes ranging from 25 to 60 nm, obtained by controlling both etchant concentration and applied voltage. Compared to as-grown planar devices the nanoporous structures have exhibited a significant increase of photocurrent with a factor of up to four times. An incident photon conversion efficiency of up to 46% around the band edge of GaN has been achieved.

  7. Temperature coefficients for GaInP/GaAs/GaInNAsSb solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Aho, Arto; Isoaho, Riku; Tukiainen, Antti; Polojärvi, Ville; Aho, Timo; Raappana, Marianna; Guina, Mircea [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FIN-33101 Tampere (Finland)

    2015-09-28

    We report the temperature coefficients for MBE-grown GaInP/GaAs/GaInNAsSb multijunction solar cells and the corresponding single junction sub-cells. Temperature-dependent current-voltage measurements were carried out using a solar simulator equipped with a 1000 W Xenon lamp and a three-band AM1.5D simulator. The triple-junction cell exhibited an efficiency of 31% at AM1.5G illumination and an efficiency of 37–39% at 70x real sun concentration. The external quantum efficiency was also measured at different temperatures. The temperature coefficients up to 80°C, for the open circuit voltage, the short circuit current density, and the conversion efficiency were determined to be −7.5 mV/°C, 0.040 mA/cm{sup 2}/°C, and −0.09%/°C, respectively.

  8. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Xing, Huili; Jena, Debdeep, E-mail: djena@cornell.edu [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States)

    2015-10-19

    By the insertion of thin In{sub x}Ga{sub 1−x}N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors.

  9. GaAsP/InGaP heterojunction bipolar transistors grown by MOCVD

    Science.gov (United States)

    Heidelberger, Christopher; Fitzgerald, Eugene A.

    2017-01-01

    Heterojunction bipolar transistors with GaAsxP1-x bases and collectors and InyGa1-yP emitters were grown on GaAs substrates via metalorganic chemical vapor deposition, fabricated using conventional techniques, and electrically tested. Four different GaAsxP1-x compositions were used, ranging from x = 0.825 to x = 1 (GaAs), while the InyGa1-yP composition was adjusted to remain lattice-matched to the GaAsP. DC gain close to or exceeding 100 is measured for 60 μm diameter devices of all compositions. Physical mechanisms governing base current and therefore current gain are investigated. The collector current is determined not to be affected by the barrier caused by the conduction band offset between the InGaP emitter and GaAsP base. While the collector current for the GaAs/InGaP devices is well-predicted by diffusion of electrons across the quasi-neutral base, the collector current of the GaAsP/InGaP devices exceeds this estimate by an order of magnitude. This results in higher transconductance for GaAsP/InGaP than would be estimated from known material properties.

  10. MOVPE of n-doped GaAs and modulation doped GaAs/AlGaAs nanowires

    Science.gov (United States)

    Sladek, K.; Klinger, V.; Wensorra, J.; Akabori, M.; Hardtdegen, H.; Grützmacher, D.

    2010-02-01

    Two different fabrication approaches were compared to obtain conductive GaAs nanowires: on one hand by modulation doping of GaAs/AlGaAs core/shell nanowires, on the other hand by Si-doping of GaAs nanowires. Modulation doped GaAs/AlGaAs core-shell nanowires were grown by selective area metal organic vapor phase epitaxy (MOVPE) on GaAs (1 1 1) substrates. The influences of growth parameters and mask design on aspect ratio of the core structures were investigated. The specialty of this study was that the growth mode was switched from vertical GaAs wire growth to the AlGaAs conformal shell overgrowth by intentionally changing the growth chemistry from the use of a more stable group III source - trimethylgallium (TMGa) to more easily decomposed sources - the alternative sources triethylgallium (TEGa) and dimethylethylaminealane (DMEAAl). It was found that the diameter and length of the core structures strongly depend on the arsenic partial pressure and growth temperature as well as mask design. The uniformity of shell growth is also influenced by the mask design. Additionally an alternative approach for the production of conductive GaAs nanowires was under study. To this end, the influence of Si-doping on GaAs core growth was investigated. It was found that doping has a detrimental impact on growth morphology leading to an undesirable enhanced growth rate on the nanowire side facets.

  11. Status and Advances of Researches on GA 20-oxidases

    Institute of Scientific and Technical Information of China (English)

    Li Wei; Chen Xiaoyang; Li Hui; Guo Hai

    2003-01-01

    GA 20-oxidase, the most important limiting enzyme, can catalyze a series of oxidization of GA biosynthesis pathwayfrom GA12 to GA9 and from GA53 to GA20 in the higher plants. This paper reviews the studies on the characters of GA 20-oxidase,the gene and the protein of GA 20-oxidase and the regulation of GA 20-oxidase gene expression in recent years. At the same time,the prospects for the gene transformation of GA 20-oxidase in agriculture, forestry and horticulture are also discussed.

  12. Modeling and optimization of a double-well double-barrier GaN/AlGaN/GaN/AlGaN resonant tunneling diode

    Science.gov (United States)

    Liu, Yang; Gao, Bo; Gong, Min; Shi, Ruiying

    2017-06-01

    The influence of a GaN layer as a sub-quantum well for an AlGaN/GaN/AlGaN double barrier resonant tunneling diode (RTD) on device performance has been investigated by means of numerical simulation. The introduction of the GaN layer as the sub-quantum well turns the dominant transport mechanism of RTD from the 3D-2D model to the 2D-2D model and increases the energy difference between tunneling energy levels. It can also lower the effective height of the emitter barrier. Consequently, the peak current and peak-to-valley current difference of RTD have been increased. The optimal GaN sub-quantum well parameters are found through analyzing the electrical performance, energy band, and transmission coefficient of RTD with different widths and depths of the GaN sub-quantum well. The most pronounced electrical parameters, a peak current density of 5800 KA/cm2, a peak-to-valley current difference of 1.466 A, and a peak-to-valley current ratio of 6.35, could be achieved by designing RTD with the active region structure of GaN/Al0.2Ga0.8 N/GaN/Al0.2Ga0.8 N (3 nm/1.5 nm/1.5 nm/1.5 nm).

  13. Simulation of polarization effects in AlGaN/GaN heterojunction

    Institute of Scientific and Technical Information of China (English)

    LI; Na; ZHAO; Degang; YANG; Hui

    2004-01-01

    A method for introducing polarization effects in the simulation of GaN-based heterojunction devices is proposed. A δ doping layer is inserted at the interface of heterojunction and the ionized donors or acceptors act as polarization induced fixed charges. Thus polarization effects can be taken into account in a traditional device simulator. Ga-face and N-face single AlGaN/GaN heterostructures are simulated, and the simulation results show that carrier confinement takes place only in the former structure while not in the latter one. The sheet density of free electrons at the interface of Ga-face AlGaN/GaN increases with the Al composition and the thickness of AlGaN. The consistence of simulation results with the experiments and calculations reported elsewhere shows that this method can effectively introduce polarization effects in the simulation of GaN-based heterojunction devices.

  14. Gate Leakage Current Reduction With Advancement of Graded Barrier AlGaN/GaN HEMT

    Directory of Open Access Journals (Sweden)

    Palash Das

    2011-01-01

    Full Text Available The gate leakage current reduction solution of AlGaN/GaN HEMT device issue has been addressed in this paper with compositional grading of AlGaN barrier layer. This work is also conjugated with the critical thickness limitation of heterostructure material growth. Hence, critical thickness calculation of AlGaN over GaN has been kept in special view. 1D Schrodinger and Poisson solver was used to calculate the 2DEG concentration and effective location to use it in the ATLAS device simulator for the predictions. The proposed Al0.50Ga0.50N/Al0.35Ga0.65N/Al0.20Ga0.80N/GaN HEMT structure exhibits the leakage current of the order of around 15 nA/mm at gate voltage of 1 V.

  15. Titanium induced polarity inversion in ordered (In,Ga)N/GaN nanocolumns

    Science.gov (United States)

    Kong, X.; Li, H.; Albert, S.; Bengoechea-Encabo, A.; Sanchez-Garcia, M. A.; Calleja, E.; Draxl, C.; Trampert, A.

    2016-02-01

    We report on the formation of polarity inversion in ordered (In,Ga)N/GaN nanocolumns grown on a Ti-masked GaN-buffered sapphire substrate by plasma assisted molecular beam epitaxy. High-resolution transmission electron microscopy and electron energy-loss spectroscopy reveal a stacking fault-like planar defect at the homoepitaxial GaN interface due to Ti incorporation, triggering the generation of N-polar domains in Ga-polar nanocolumns. Density functional theory calculations are applied to clarify the atomic configurations of a Ti monolayer occupation on the GaN (0002) plane and to prove the inversion effect. The polarity inversion leads to an enhanced indium incorporation in the subsequent (In,Ga)N segment of the nanocolumn. This study provides a deeper understanding of the effects of Ti mask in the well-controlled selective area growth of (In,Ga)N/GaN nanocolumns.

  16. Effect of substrate offcut on AlGaN/GaN HFET structures on bulk GaN substrates

    Science.gov (United States)

    Leach, J. H.; Biswas, N.; Paskova, T.; Preble, E. A.; Evans, K. R.; Wu, M.; Ni, X.; Li, X.; Özgür, Ü.; Morkoç, H.

    2011-02-01

    Bulk GaN substrates promise to bring the full potential of nitride-based devices to bear since they offer a low thermal and lattice mismatched alternative to foreign substrates for epitaxial growth. However, due to the high cost and low availability of bulk GaN substrates, effects such as surface misorientation (offcut), surface polishing, and preparation of such substrates on subsequent epitaxy are still not well understood. As such, AlGaN/GaN heterostructures with nominal Al compositions of 25% were grown by MOCVD on semi-insulating bulk GaN substrates with offcuts ranging from 0.05 to 1.95° in the m-direction (10 10) to attempt to determine the optimal offcut for bulk GaN substrates for AlGaN-based HFET devices. X-ray diffraction (XRD) studies indicate that the Al composition does not vary with offcut, however reciprocal space mapping shows evidence of strain relaxation of the AlGaN in samples grown on substrates with offcut >1.1°. Additionally, we observed a minimum in sheet resistance of the 2DEGs for substrates with offcuts near 0.5°, arising from higher mobilities in these samples. Evidence of an optimal substrate misorientation is important for AlGaN-based devices grown on bulk GaN substrates.

  17. AlGaN/GaN high electron mobility transistors with selective area grown p-GaN gates

    Science.gov (United States)

    Yuliang, Huang; Lian, Zhang; Zhe, Cheng; Yun, Zhang; Yujie, Ai; Yongbing, Zhao; Hongxi, Lu; Junxi, Wang; Jinmin, Li

    2016-11-01

    We report a selective area growth (SAG) method to define the p-GaN gate of AlGaN/GaN high electron mobility transistors (HEMTs) by metal-organic chemical vapor deposition. Compared with Schottky gate HEMTs, the SAG p-GaN gate HEMTs show more positive threshold voltage (V th) and better gate control ability. The influence of Cp2Mg flux of SAG p-GaN gate on the AlGaN/GaN HEMTs has also been studied. With the increasing Cp2Mg from 0.16 μmol/min to 0.20 μmol/min, the V th raises from -0.67 V to -0.37 V. The maximum transconductance of the SAG HEMT at a drain voltage of 10 V is 113.9 mS/mm while that value of the Schottky HEMT is 51.6 mS/mm. The SAG method paves a promising way for achieving p-GaN gate normally-off AlGaN/GaN HEMTs without dry etching damage. Project supported by the National Natural Sciences Foundation of China (Nos. 61376090, 61306008) and the National High Technology Program of China (No. 2014AA032606).

  18. Ultraviolet Phototransistors on AlGaN/GaN Heterostructures

    Institute of Scientific and Technical Information of China (English)

    CHEN Chen; JIANG Wen-Hai; REN Chun-Jiang; LI Zhong-Hui; JIAO Gang; DONG Xun; CHEN Tang-Sheng

    2007-01-01

    We report on the fabrication and characterization of phototransistors based on AlGaN/GaN heterostructure grown over 6H-SiC substrates. The device has two functions: as a high electron mobility transistor (HEMT) and an ultraviolet photodetector at the same time. As an HEMT, its maximum transconductance is 170 mS/mm, while the minimum cutoff frequency fT and the maximum oscillation frequency fm axe 19 and 35 GHz, respectively.As a photodetector, the device is visible blind, with an ultraviolet/green contrast of three orders of magnitude,and a responsivity as high as 1700 A/W at the wavelength of 362nm.

  19. InGaN/GaN Nanowire LEDs and Lasers

    KAUST Repository

    Zhao, Chao

    2016-01-01

    The large specific surface, and the associated high density of surface states was found to limit the light output power and quantum efficiency of nanowire-array devices, despite their potential for addressing the “green-gap” and efficiency-droop issues. The phonon and carrier confinement in nanowires also led to junction heating, and reduced heat dissipation. In this paper, we will present our studies on effective surface states passivation in InGaN/GaN quantum-disks (Qdisks)-in-nanowire light-emitting diodes (LEDs) and lasers grown on silicon (Si), as well as our recent work on nanowires LEDs grown on bulk-metal, a non-conventional substrate.

  20. Medium energy proton radiation damage to (AlGa)As-GaAs solar cells

    Science.gov (United States)

    Loo, R. Y.; Kamath, G. S.; Knechtli, R. C.

    1982-01-01

    The performance of (AlGa)As-GaAs solar cells irradiated by medium energy 2, 5, and 10 MeV protons was evaluated. The Si cells without coverglass and a number of GaAs solar cells with 12 mil coverglass were irradiated simultaneously with bare GaAs cells. The cell degradation is directly related to the penetration of depth of protons with GaAs. The influence of periodic and continuous thermal annealing on the GaAs solar cells was investigated.

  1. SEMICONDUCTOR DEVICES: AlGaN/GaN double-channel HEMT

    Science.gov (United States)

    Si, Quan; Yue, Hao; Xiaohua, Ma; Pengtian, Zheng; Yuanbin, Xie

    2010-04-01

    The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied.

  2. Blue light emission from the heterostructured ZnO/InGaN/GaN

    OpenAIRE

    Wang, Ti; WU Hao; Wang, Zheng; Chen, Chao; Liu, Chang

    2013-01-01

    ZnO/InGaN/GaN heterostructured light-emitting diodes (LEDs) were fabricated by molecular beam epitaxy and atomic layer deposition. InGaN films consisted of an Mg-doped InGaN layer, an undoped InGaN layer, and a Si-doped InGaN layer. Current-voltage characteristic of the heterojunction indicated a diode-like rectification behavior. The electroluminescence spectra under forward biases presented a blue emission accompanied by a broad peak centered at 600 nm. With appropriate emission intensity r...

  3. Brittle-Ductile Relaxation Kinetics of Strained AlGaN/GaN

    Energy Technology Data Exchange (ETDEWEB)

    CHASON, E.; FLORO, JERROLD A.; FOLLSTAEDT, DAVID M.; HAN, JUNG; HEARNE, SEAN JOSEPH; LEE, STEPHEN R.; TSONG, I.S.T.

    1999-10-05

    The authors have directly measured the stress evolution during metal organic chemical vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stress measurements were correlated with ex situ microstructural analysis to directly determine a critical thickness for cracking and the subsequent relaxation kinetics of tensile-strained Al{sub x}Ga{sub 1{minus}x}N on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, which account for the majority of the strain relaxation.

  4. Contactless Mobility, Carrier Density, and Sheet Resistance Measurements on Si, GaN, and AlGaN/GaN High Electron Mobility Transistor (HEMT) Wafers

    Science.gov (United States)

    2015-02-01

    Si, GaN, and AlGaN/GaN High Electron Mobility Transistor (HEMT) Wafers by Randy P Tompkins and Danh Nguyen Approved for...High Electron Mobility Transistor (HEMT) Wafers by Randy P. Tompkins Sensors and Electron Devices Directorate Danh Nguyen Lehighton...Resistance Measurements on Si, GaN, and AlGaN/GaN High Electron Mobility Transistor (HEMT) Wafers 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

  5. Engineering of electric field distribution in GaN(cap)/AlGaN/GaN heterostructures: theoretical and experimental studies

    Science.gov (United States)

    Gladysiewicz, M.; Janicki, L.; Misiewicz, J.; Sobanska, M.; Klosek, K.; Zytkiewicz, Z. R.; Kudrawiec, R.

    2016-09-01

    Polarization engineering of GaN-based heterostructures opens a way to develop advanced transistor heterostructures, although measurement of the electric field in such heterostructures is not a simple task. In this work, contactless electroreflectance (CER) spectroscopy has been applied to measure the electric field in GaN-based heterostructures. For a set of GaN(d  =  0, 5, 15, and 30 nm)/AlGaN(20 nm)/GaN(buffer) heterostructures a decrease of electric field in the GaN(cap) layer from 0.66 MV cm-1 to 0.27 MV cm-1 and an increase of the electric field in the AlGaN layer from 0.57 MV cm-1 to 0.99 MV cm-1 have been observed with the increase in the GaN(cap) thickness from 5-30 nm. For a set of GaN(20 nm)/AlGaN(d  =  10, 20, 30, and 40 nm)/GaN(buffer) heterostructures a decrease of the electric field in the AlGaN layer from 1.77 MV cm-1 to 0.64 MV cm-1 and an increase of the electric field in the GaN layer from 0.57 MV cm-1 to 0.99 MV cm-1 were observed with the increase in the AlGaN thickness from 10-40 nm. To determine the distribution of the electric field in these heterostructures the Schrödinger and Poisson equations are solved in a self-consistent manner and matched with experimental data. It is shown that the built-in electric field in the GaN(cap) and AlGaN layers obtained from measurements does not reach values of electric field resulting only from polarization effects. The measured electric fields are smaller due to a screening of polarization effects by free carriers, which are inhomogeneously distributed across the heterostructure and accumulate at interfaces. The results clearly demonstrate that CER measurements supported by theoretical calculations are able to determine the electric field distribution in GaN-based heterostructures quantitatively, which is very important for polarization engineering in this material system.

  6. Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

    OpenAIRE

    Wang Yongjin; Hu Fangren; Hane Kazuhiro

    2011-01-01

    Abstract We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE). Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place wit...

  7. Internal quantum efficiency in yellow-amber light emitting AlGaN-InGaN-GaN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Thi Huong; Gil, Bernard; Valvin, Pierre [Laboratoire Charles Coulomb – UMR 5221, CNRS and University Montpellier, Case courier 074, 34095 Montpellier Cedex 5 (France); Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe [CRHEA-CNRS Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, rue Bernard Gregory, 06560 Valbonne (France)

    2015-09-21

    We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Iwata et al. [J. Appl. Phys. 117, 075701 (2015)]. Our results indicate that low temperature internal quantum efficiencies sit in the 50% range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57% with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5% up to 4.3% at room temperature.

  8. High-temperature characteristics of AixGa1-xN/GaN Schottky diodes

    Institute of Scientific and Technical Information of China (English)

    Zhang Xiaoling; Li Fei; Lv Changzhi; Xie Xuesong; Li Ying; Mohammad S N

    2009-01-01

    High-temperature characteristics of the metal/AlxGa1_xN/GaN M/S/S (M/S/S) diodes have been studied with current-voltage (I-V) and capacitance-voltage (C-V) measurements at high temperatures. Due to the presence of the piezoelectric polarization field and a quantum well at the AIxGa1_xN/GaN interface, the AIxGa1_xN/GaNdiodes show properties distinctly different from those of the AIxGa1_xN diodes. For the AIxGa1_xN/GaN diodes, an increase in temperature accompanies an increase in barrier height and a decrease in ideality factor, while the AIxGa1_xN diodes are opposite. Furthermore, at room temperature, both reverse leakage current and reverse break-down voltage are superior for the AIxGa1_xN/GaN diodes to those for the AIxGa1_xN diodes.

  9. Optical and magnetotransport properties of InGaAs/GaAsSb/GaAs structures doped with a magnetic impurity

    Energy Technology Data Exchange (ETDEWEB)

    Kalentyeva, I. L., E-mail: vikhrova@nifti.unn.ru; Zvonkov, B. N.; Vikhrova, O. V.; Danilov, Yu. A.; Demina, P. B.; Dorokhin, M. V.; Zdoroveyshchev, A. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation)

    2015-11-15

    InGaAs/GaAsSb/GaAs bilayer quantum-well structures containing a magnetic-impurity δ-layer (Mn) at the GaAs/InGaAs interface are experimentally studied for the first time. The structures are fabricated by metal organic chemical-vapor deposition (MOCVD) and laser deposition on substrates of conducting (n{sup +}) and semi-insulating GaAs in a single growth cycle. The InGaAs-layer thickness is varied from 1.5 to 5 nm. The significant effect of a decrease in the InGaAs quantum-well thickness on the optical and magnetotransport properties of the structures under study is detected. Nonlinear magnetic-field dependence of the Hall resistance and negative magnetoresistance at temperatures of ≤30–40 K, circular polarization of the electroluminescence in a magnetic field, opposite behaviors of the photoluminescence and electroluminescence emission intensities in the structures, and an increase in the contribution of indirect transitions with decreasing InGaAs thickness are observed. Simulation shows that these effects can be caused by the influence of the δ-layer of acceptor impurity (Mn) on the band structure and the hole concentration distribution in the bilayer quantum well.

  10. A novel oxidation-based wet etching method for AlGaN/GaN heterostructures

    Institute of Scientific and Technical Information of China (English)

    Cai Jinbao; Wang Jinyan; Liu Yang; Xu Zhe; Wang Maojun; Yu Min; Xie Bing

    2013-01-01

    A novel wet etching method for AlGaN/GaN heterojunction structures is proposed using thermal oxidation followed by wet etching in KOH solution.It is found that an AlGaN/GaN heterostructure after high temperature oxidation above 700 ℃ could be etched off in a homothermal (70 ℃) KOH solution while the KOH solution had no etching effects on the region of the A1GaN/GaN heterostructure protected by a SiO2 layer during the oxidation process.A groove structure with 150 nm step depth on an AlGaN/GaN heterostructure was formed after 8 h thermal oxidation at 900 ℃ followed by 30 min treatment in 70 ℃ KOH solution.As the oxidation time increases,the etching depth approaches saturation and the roughness of the etched surface becomes much better.The physical mechanism of this phenomenon is also discussed.

  11. GaAsP solar cells on GaP/Si with low threading dislocation density

    Science.gov (United States)

    Yaung, Kevin Nay; Vaisman, Michelle; Lang, Jordan; Lee, Minjoo Larry

    2016-07-01

    GaAsP on Si tandem cells represent a promising path towards achieving high efficiency while leveraging the Si solar knowledge base and low-cost infrastructure. However, dislocation densities exceeding 108 cm-2 in GaAsP cells on Si have historically hampered the efficiency of such approaches. Here, we report the achievement of low threading dislocation density values of 4.0-4.6 × 106 cm-2 in GaAsP solar cells on GaP/Si, comparable with more established metamorphic solar cells on GaAs. Our GaAsP solar cells on GaP/Si exhibit high open-circuit voltage and quantum efficiency, allowing them to significantly surpass the power conversion efficiency of previous devices. The results in this work show a realistic path towards dual-junction GaAsP on Si cells with efficiencies exceeding 30%.

  12. GaN Bulk Growth and Epitaxy from Ca-Ga-N Solutions Project

    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. InGaAs quantum well-dots based GaAs subcell with enhanced photocurrent for multijunction GaInP/GaAs/Ge solar cells

    Science.gov (United States)

    Mintairov, S. A.; Kalyuzhnyy, N. A.; Maximov, M. V.; Nadtochiy, A. M.; Zhukov, A. E.

    2017-01-01

    MOCVD-grown GaAs single-junction solar cells (SC) with quantum well-dots (QWD) were fabricated and tested. The QWD were formed by the deposition of In0.4Ga0.6As layers separated with GaAs spacers. A remarkable improvement of photocurrent was achieved and the reduction of open-circuit voltage was partly suppressed by decreasing the spacers’ growth rate as well as increasing their thickness up to 40 nm. Based on the experimentally obtained characteristics of these single-junction SCs we estimated that using QWD media in the middle (GaAs-based) subcell can provide 1 abs. %, increasing the efficiency of the triple-junction GaInP/GaAs/Ge SCs.

  14. AlGaN nanocolumns and AlGaN/GaN/AlGaN nanostructures grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ristic, J.; Sanchez-Garcia, M.A.; Ulloa, J.M.; Calleja, E. [Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Sanchez-Paramo, J.; Calleja, J.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Jahn, U.; Trampert, A.; Ploog, K.H. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2002-12-01

    This work reports on the characterization of hexagonal, single crystal AlGaN nanocolumns with diameters in the range of 30 to 100 nm grown by molecular beam epitaxy on Si(111) substrates. The change of the flux ratio between the Al and the total III-element controls the alloy composition. The Al composition trend versus the Al flux is consistent both with the E{sub 2} phonon energy values measured by inelastic light scattering and the luminescence emission peaks position. High quality low dimensional AlGaN/GaN/AlGaN heterostructures with five GaN quantum discs, 2 and 4 nm thick, embedded into the AlGaN columns, were designed in order to study the quantum confinement effects. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  15. Theoretical and experimental studies of electric field distribution in N-polar GaN/AlGaN/GaN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Gladysiewicz, M., E-mail: marta.gladysiewicz@pwr.edu.pl; Janicki, L.; Kudrawiec, R. [Faculty of Fundamental Problems of Technology, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław (Poland); Siekacz, M.; Cywinski, G. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland); Skierbiszewski, C. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw (Poland); TopGaN Sp. z o.o., Sokołowska 29/37, 01-142 Warsaw (Poland)

    2015-12-28

    Electric field distribution in N-polar GaN(channel)/AlGaN/GaN(buffer) heterostructures was studied theoretically by solving Schrodinger and Poisson equations in a self-consistent manner for various boundary conditions and comparing results of these calculations with experimental data, i.e., measurements of electric field in GaN(channel) and AlGaN layers by electromodulation spectroscopy. A very good agreement between theoretical calculations and experimental data has been found for the Fermi-level located at ∼0.3 eV below the conduction band at N-polar GaN surface. With this surface boundary condition, the electric field distribution and two dimensional electron gas concentration are determined for GaN(channel)/AlGaN/GaN(buffer) heterostructures of various thicknesses of GaN(channel) and AlGaN layers.

  16. GaSb on GaAs solar cells Grown using interfacial misfit arrays (Conference Presentation)

    Science.gov (United States)

    Nelson, George T.; Juang, Bor-Chau; Slocum, Michael A.; Bittner, Zachary S.; Laghumavarapu, Ramesh Babu B.; Huffaker, Diana L.; Hubbard, Seth M.

    2017-04-01

    State of the art InGaP2/GaAs/In0.28Ga0.72As inverted metamorphic (IMM) solar cells have achieved impressive results, however, the thick metamorphic buffer needed between the lattice matched GaAs and lattice mismatched InGaAs requires significant effort and time to grow and retains a fairly high defect density. One approach to this problem is to replace the bottom InGaAs junction with an Sb-based material such as 0.73 eV GaSb or 1.0 eV Al0.2Ga0.8Sb. By using interfacial misfit (IMF) arrays, the high degree of strain (7.8%) between GaAs and GaSb can be relaxed solely by laterally propagating 90° misfit dislocations that are confined to the GaAs-GaSb interface layer. We have used molecular beam epitaxy to grow GaSb single junction solar cells homoepitaxially on GaSb and heteroepitaxially on GaAs using IMF. Under 15-sun AM1.5 illumination, the control cell achieved 5% efficiency with a WOC of 366 mV, while the IMF cell was able to reach 2.1% with WOC of 546 mV. Shunting and high non-radiative dark current were main cause of FF and efficiency loss in the IMF devices. Threading dislocations or point defects were the expected source behind the losses, leading to minority carrier lifetimes less than 1ns. Deep level transient spectroscopy (DLTS) was used to search for defects electrically and two traps were found in IMF material that were not detected in the homoepitaxial GaSb device. One of these traps had a trap density of 7 × 1015 cm-3, about one order of magnitude higher than the control cell defect at 4 × 1016 cm-3.

  17. Fabrication of InGaN/GaN nanopillar light-emitting diode arrays

    DEFF Research Database (Denmark)

    Ou, Yiyu; Fadil, Ahmed; Ou, Haiyan

    Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction.......Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction....

  18. Multiple Applications of GaAs semiconductors

    Science.gov (United States)

    Martel, Jenrené; Wonka, Willy

    2003-03-01

    The object of this discussion will be to explore the many facets of Gallium Arsenide(GaAs) semiconductors. The session will begin with a brief overview of the basic properties of semiconductors in general(band gap, doping, charge mobility etc.). It will then follow with a closer look at the properties of GaAs and how these properties could potentially translate into some very exciting applications. Furthermore, current applications of GaAs semiconductors will be dicussed and analyzed. Finally, physical limits and advantages/disadvantages of GaAs will be considered.

  19. On SA, CA, and GA numbers

    CERN Document Server

    Caveney, Geoffrey; Sondow, Jonathan

    2011-01-01

    Gronwall's function $G$ is defined for $n>1$ by $G(n)=\\frac{\\sigma(n)}{n \\log\\log n}$ where $\\sigma(n)$ is the sum of the divisors of $n$. We call an integer $N>1$ a \\emph{GA1 number} if $N$ is composite and $G(N) \\ge G(N/p)$ for all prime factors $p$ of $N$. We say that $N$ is a \\emph{GA2 number} if $G(N) \\ge G(aN)$ for all multiples $aN$ of $N$. In arXiv 1110.5078, we used Robin's and Gronwall's theorems on $G$ to prove that the Riemann Hypothesis (RH) is true if and only if 4 is the only number that is both GA1 and GA2. Here, we study GA1 numbers and GA2 numbers separately. We compare them with superabundant (SA) and colossally abundant (CA) numbers (first studied by Ramanujan). We give algorithms for computing GA1 numbers; the smallest one with more than two prime factors is 183783600, while the smallest odd one is 1058462574572984015114271643676625. We find nineteen GA2 numbers $\\le 5040$, and prove that a GA2 number $N>5040$ exists if and only if RH is false, in which case $N$ is even and $>10^{8576}$.

  20. Tetrabromidobis(dicyclohexylphosphane-κPdigallium(Ga—Ga

    Directory of Open Access Journals (Sweden)

    Dennis H. Mayo

    2012-10-01

    Full Text Available The title compound, a GaII dimer, [Ga2Br4(C12H23P2], was synthesized by reaction of GaBr(THFn (THF is tetrahydrofuran with dicyclohexylphosphine in toluene. At 150 K the crystallographically centrosymmetric molecule exhibits disorder in which one of the two independent cyclohexyl groups is modelled over two sites in a 62 (1:38 (1 ratio. In d6-benzene solution, the compound exhibits virtual C2h symmetry as determined by 1H NMR. The coordination environment of the GaII atom is distorted tetrahedral.

  1. Effect of Ga on the Wettability of CuGa10 on 304L Steel

    Science.gov (United States)

    Silze, Frank; Wiehl, Gunther; Kaban, Ivan; Kühn, Uta; Eckert, Jürgen; Pauly, Simon

    2015-08-01

    In the present work, the effect of Ga on the wetting behavior of the Cu-rich braze filler CuGa10 (wt pct, Cu90.8Ga9.2 at. pct) on the steel 304L was investigated. For this, the macroscopic and microscopic effects governing the wetting of pure Ga, pure Cu, and CuGa10 alloy (wt pct) on the austenitic steel were analyzed and compared. Contact angle and surface tension measurements were carried out by means of the sessile drop technique, and, in addition, the phase formation at the interface was determined. Pure liquid Ga spreads on 304L, which supposedly is related to the formation of intermetallic Fe-Ga phases growing into the liquid Ga. Depending on the annealing time, FeGa3 and Fe14.5Ga12 were identified. In contrast, CuGa10 as well as pure Cu shows secondary wetting on the steel surface. Especially, liquid Cu prefers spreading laterally and vertically along the grain boundaries of the steel substrate. In spite of rather similar mechanisms, CuGa10 wets 304L steel at lower rate than pure Cu above the liquidus temperature.

  2. Element specific investigation of ultrathin Co2MnGa/GaAs heterostructures

    DEFF Research Database (Denmark)

    Claydon, Jill S.; Hassan, Sameh; Damsgaard, Christian Danvad;

    2007-01-01

    We have used x-ray magnetic circular dichroism to study the element specific magnetic properties of ultrathin films of the Heusler alloy Co2MnGa at room temperature. Nine films were grown by molecular beam epitaxy on GaAs substrates and engineered to vary in stoichiometry as Co1.86Mn0.99Ga1, Co1...

  3. Ga self-diffusion in isotopically enriched GaAs heterostructures doped with Si and Zn

    Energy Technology Data Exchange (ETDEWEB)

    Norseng, Marshall Stephen [Univ. of California, Berkeley, CA (United States)

    1999-12-01

    This study attempts to advance the modeling of AlGaAs/GaAs/AlAs diffusion by experimental investigation of Ga self-diffusion in undoped, as-grown doped and Zinc diffused structures. We utilize novel, isotopically enriched superlattice and heterostructure samples to provide direct observation and accurate measurement of diffusion with a precision not possible using conventional techniques.

  4. Effect of silicon doping in InGaN/GaN heterostructure grown by MOCVD

    Science.gov (United States)

    Surender, S.; Pradeep, S.; Prabakaran, K.; Singh, Shubra; Baskar, K.

    2017-05-01

    In this work the effect of Si doped InGaN/GaN heterostructure is systematically studied. The n-InGaN /GaN heterostructure are grown on c-plane sapphire substrate by horizontal flow Metal Organic Chemical Vapor Deposition (MOCVD). The heterostructure samples are investigated by structural, optical, morphological and electrical studies using High Resolution X-ray diffraction (HRXRD), room temperature Photoluminescence (PL), Atomic Force Microscopy (AFM) and Hall measurement respectively. The composition of indium in n-InGaN/GaN heterostructure was calculated as 15.9% using epitaxy smooth fit software. The energy band gap (Eg) of the InGaN epilayer has been calculated as 2.78 eV using vigard's law. PL emission obtained at 446 nm for n-InGaN epilayer. AFM results indicate that the Si doped InGaN/GaN heterostructure has the root mean square (rms) roughness of about 0.59 nm for a scan area of 5×5 µm2 which has island like growth. Moreover, Hall measurements results shows that Si doped InGaN/GaN heterostructure possess carrier concentration of 4.2 × 1018cm-3 and mobility of 257 cm2/V s at room temperature.

  5. Process dependency on threshold voltage of GaN MOSFET on AlGaN/GaN heterostructure

    Science.gov (United States)

    Wang, Qingpeng; Jiang, Ying; Miyashita, Takahiro; Motoyama, Shin-ichi; Li, Liuan; Wang, Dejun; Ohno, Yasuo; Ao, Jin-Ping

    2014-09-01

    GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) with recessed gate on AlGaN/GaN heterostructure are reported in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. Negative threshold voltages were commonly observed in all devices. To investigate the reasons of the negative threshold voltages, different oxide thickness, etching gas and bias power of inductively-coupled plasma (ICP) system were utilized in the fabrication process of the GaN MOSFETs. It is found that positive charges of around 1 × 1012 q/cm2 exist near the interface at the just threshold condition in both silane- and tetraethylorthosilicate (TEOS)-based devices. It is also found that the threshold voltages do not obviously change with the different etching gas (SiCl4, BCl3 and two-step etching of SiCl4/Cl2) at the same ICP bias power level (20-25 W) and will become deeper when higher bias power is used in the dry recess process which may be related to the much serious ion bombardment damage. Furthermore, X-ray photoelectron spectroscopy (XPS) experiments were done to investigate the surface conditions. It is found that N 1s peaks become lower with higher bias power of the dry etching process. Also, silicon contamination was found and could be removed by HNO3/HF solution. It indicates that the nitrogen vacancies are mainly responsible for the negative threshold voltages rather than the silicon contamination. It demonstrates that optimization of the ICP recess conditions and improvement of the surface condition are still necessary to realize enhancement-mode GaN MOSFETs on AlGaN/GaN heterostructure.

  6. Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

    Science.gov (United States)

    Yang, Lin'an; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue

    2016-04-01

    Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al0.15Ga0.85N emitter barrier and a 1.7-nm-thick Al0.25Ga0.75N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al0.2Ga0.8N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In0.03Ga0.97N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.

  7. Isotype InGaN/GaN heterobarrier diodes by ammonia molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Fireman, Micha N.; Browne, David A.; Speck, James S. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Mishra, Umesh K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, California 93106 (United States)

    2016-02-07

    The design of isotype InGaN/GaN heterobarrier diode structures grown by ammonia molecular beam epitaxy is presented. On the (0001) Ga-polar plane, a structure consisting of a surface n{sup +} GaN contact layer, followed by a thin InGaN layer, followed by a thick unintentionally doped (UID) GaN layer, and atop a buried n{sup +} GaN contact layer induces a large conduction band barrier via a depleted UID GaN layer. Suppression of reverse and subthreshold current in such isotype barrier devices under applied bias depends on the quality of this composite layer polarization. Sample series were grown under fixed InGaN growth conditions that varied either the UID GaN NH{sub 3} flow rate or the UID GaN thickness, and under fixed UID GaN growth conditions that varied InGaN growth conditions. Decreases in subthreshold current and reverse bias current were measured for thicker UID GaN layers and increasing InGaN growth rates. Temperature-dependent analysis indicated that although extracted barrier heights were lower than those predicted by 1D Schrödinger Poisson simulations (0.9 eV–1.4 eV for In compositions from 10% to 15%), optimized growth conditions increased the extracted barrier height from ∼11% to nearly 85% of the simulated values. Potential subthreshold mechanisms are discussed, along with those growth factors which might affect their prevalence.

  8. Growth and Annealing Study of Mg-Doped AlGaN and GaN/AlGaN Superlattices

    Institute of Scientific and Technical Information of China (English)

    WANG Bao-Zhu; LI Jin-Min; WANG Zhan-Guo; WANG Xiao-Liang; HU Guo-Xin; RAN Jun-Xue; WANG Xin-Hua; GUO Lun-Chun; XIAO Hong-Ling; LI Jian-Ping; ZENG Yi-Ping

    2006-01-01

    @@ Mg-doped AlGaN and GaN/AlGaN superlattices are grown by metalorganic chemical vapour deposition (MOCVD).Rapid thermal annealing (RTA) treatments are carried out on the samples. Hall and high resolution x-ray diffraction measurements are used to characterize the electrical and structural prosperities of the as-grown and annealed samples, respectively. The results of hall measurements show that after annealing, the Mg-doped AlGaN sample can not obtain the distinct hole concentration and can acquire a resistivity of 1.4×103 Ωcm. However, with the same annealing treatment, the GaN/AlGaN superlattice sample has a hole concentration of 1.7×1017 cm-3 and a resistivity of 5.6Ωcm. The piezoelectric field in the GaN/AlGaN superlattices improves the activation efficiency of Mg acceptors, which leads to higher hole concentration and lower p-type resistivity.

  9. Normally-off p-GaN/AlGaN/GaN high electron mobility transistors using hydrogen plasma treatment

    Science.gov (United States)

    Hao, Ronghui; Fu, Kai; Yu, Guohao; Li, Weiyi; Yuan, Jie; Song, Liang; Zhang, Zhili; Sun, Shichuang; Li, Xiajun; Cai, Yong; Zhang, Xinping; Zhang, Baoshun

    2016-10-01

    In this letter, we report a method by introducing hydrogen plasma treatment to realize normally-off p-GaN/AlGaN/GaN HEMT devices. Instead of using etching technology, hydrogen plasma was adopted to compensate holes in the p-GaN above the two dimensional electron gas (2DEG) channel to release electrons in the 2DEG channel and form high-resistivity area to reduce leakage current and increase gate control capability. The fabricated p-GaN/AlGaN/GaN HEMT exhibits normally-off operation with a threshold voltage of 1.75 V, a subthreshold swing of 90 mV/dec, a maximum transconductance of 73.1 mS/mm, an ON/OFF ratio of 1 × 107, a breakdown voltage of 393 V, and a maximum drain current density of 188 mA/mm at a gate bias of 6 V. The comparison of the two processes of hydrogen plasma treatment and p-GaN etching has also been made in this work.

  10. Cw and time-resolved spectroscopy in homoepitaxial GaN films and GaN-GaAlN quantum wells grown by molecular beam epitaxy.

    OpenAIRE

    Taliercio, Thierry; Gallart, Mathieu; Lefebvre, Pierre; Morel, Aurélien; Gil, Bernard; Allègre, Jacques; Grandjean, Nicolas; Massies, Jean; Grzegory, Izabella; Porowsky, Sylvester

    2001-01-01

    International audience; We have grown GaN films and GaN–AlGaN quantum wells (QWs) on homoepitaxial substrates, by molecular beam epitaxy using ammonia. Both the GaN film and the QW are found to have superior excitonic recombination properties which are extremely promising for the development of indium free ultra-violet lasers based on nitrides.

  11. Improvement of the efficiency droop of GaN-LEDs using an AlGaN/GaN superlattice insertion layer

    Institute of Scientific and Technical Information of China (English)

    Ji Panfeng; Liu Naixin; Wei Tongbo; Liu Zhe; Lu Hongxi; Wang Junxi; Li Jinmin

    2011-01-01

    With an n-AlGaN (4 nm)/GaN (4 nm) superlattice (SL) inserted between an n-GaN and an InGaN/GaN multiquantum well active layer,the efficiency droop of GaN-based LEDs has been improved.When the injection current is lower than 100 mA,the lumen efficiency of the LED with an n-AlGaN/GaN SL is relatively small compared to that without an n-A1GaN/GaN SL.However,as the injection current increases more than 100 mA,the lumen efficiency of the LED with an n-AlGaN/GaN SL surpasses that of an LED without an n-AlGaN/GaN SL.The wall plug efficiency of an LED has the same trend as lumen efficiency.The improvement of the efficiency droop of LEDs with n-A1GaN/GaN SLs can be attributed to a decrease in electron leakage due to the enhanced current spreading ability and electron blocking effect at high current densities.The reverse current of LEDs at -5 V reverse voltage decreases from 0.2568029 to 0.0070543 μA,and the electro-static discharge (ESD) pass yield of an LED at human body mode (HBM)-ESD impulses of 2000 V increases from 60% to 90%.

  12. InGaN light-emitting diodes with embedded nanoporous GaN distributed Bragg reflectors

    Science.gov (United States)

    Shieh, Bing-Cheng; Jhang, Yuan-Chang; Huang, Kun-Pin; Huang, Wan-Chun; Dai, Jing-Jie; Lai, Chun-Feng; Lin, Chia-Feng

    2015-08-01

    InGaN-based light-emitting diodes (LEDs) with embedded conductive nanoporous GaN/undoped GaN (NP-GaN/u-GaN) distributed Bragg reflectors (DBRs) were demonstrated. Nanoporous GaN DBR structures were fabricated by pulsed 355 nm laser scribing and electrochemical etching processes. Heavily Si-doped n-type GaN:Si layers (n+-GaN) in an eight-period n+-GaN/u-GaN stack structure were transformed into a low-refractive-index, conductive nanoporous GaN structure. The measured center wavelength, peak reflectivity, and bandwidth of the nanoporous GaN DBR structure were 417 nm, 96.7%, and 34 nm, respectively. Resonance cavity modes of the photoluminescence spectra were observed in the treated LED structure with the nanoporous DBR structure.

  13. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Science.gov (United States)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  14. Studies of Ga NMR and NQR in SrGa4

    Science.gov (United States)

    Niki, H.; Higa, N.; Nakamura, S.; Kuroshima, H.; Toji, T.; Yogi, M.; Nakamura, A.; Hedo, M.; Nakama, T.; Ōnuki, Y.; Harima, H.

    2015-04-01

    In order to microscopically investigate the properties in SrGa4, the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of 69&71Ga (a nuclear spin I = 3/2) in the powder sample of SrGa4 do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the 69Ga NQR in SrGa4. The Knight shifts of the 69Ga(I) and 69Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the 69Ga(I) and 69Ga(II) are 0.01 and -0.11 % at 4.2 K, and 0.09 and -0.08 % at 300 K, respectively. The values of the 1/ T 1 T of the NMR of both 69Ga(I) and 69Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s -1 K -1 at 69Ga(I) and 0.12 s -1 K -1 at 69Ga(II), while the 1/ T 1 T slightly increase above 100K with increasing temperature. The value of T 1 of 69Ga(I) is one order of magnitude less than that of 69Ga(II).

  15. Studies of Ga NMR and NQR in SrGa{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Niki, H., E-mail: niki@sci.u-ryukyu.ac.jp; Higa, N.; Nakamura, S.; Kuroshima, H.; Toji, T.; Yogi, M.; Nakamura, A.; Hedo, M.; Nakama, T.; Ōnuki, Y. [University of the Ryukyus, Faculty of Science (Japan); Harima, H. [Kobe University, Faculty of Science (Japan)

    2015-04-15

    In order to microscopically investigate the properties in SrGa{sub 4}, the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of {sup 69&71}Ga (a nuclear spin I = 3/2) in the powder sample of SrGa{sub 4} do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the {sup 69}Ga NQR in SrGa{sub 4}. The Knight shifts of the {sup 69}Ga(I) and {sup 69}Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the {sup 69}Ga(I) and {sup 69}Ga(II) are 0.01 and –0.11 % at 4.2 K, and 0.09 and –0.08 % at 300 K, respectively. The values of the 1/ T{sub 1}T of the NMR of both {sup 69}Ga(I) and {sup 69}Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s {sup −1}K{sup −1} at {sup 69}Ga(I) and 0.12 s {sup −1}K{sup −1} at {sup 69}Ga(II), while the 1/ T{sub 1}T slightly increase above 100K with increasing temperature. The value of T{sub 1} of {sup 69}Ga(I) is one order of magnitude less than that of {sup 69}Ga(II)

  16. Methods of Ga droplet consumption for improved GaAs nanowire solar cell efficiency

    Science.gov (United States)

    Dastjerdi, M. H. T.; Boulanger, J. P.; Kuyanov, P.; Aagesen, M.; LaPierre, R. R.

    2016-11-01

    We describe methods of Ga droplet consumption in Ga-assisted GaAs nanowires, and their impact on the crystal structure at the tip of nanowires. Droplets are consumed under different group V flux conditions and the resulting tip crystal structure is examined by transmission electron microscopy. The use of GaAsP marker layers provides insight into the behavior of the Ga droplet during different droplet consumption conditions. Lower group V droplet supersaturations lead to a pure zincblende stacking-fault-free tip crystal structure, which improved the performance of a nanowire-based photovoltaic device.

  17. Proximity Effects of Beryllium-Doped GaN Buffer Layers on the Electronic Properties of Epitaxial AlGaN/GaN Heterostructures

    Science.gov (United States)

    2010-05-17

    properties of AlGaN/ GaN HEMTs grown on SiC sub- strates [11,15], and that these effects may vary with the proximity of the doped layer to the two...properties of Al- GaN / GaN HEMTs grown by rf-MBE on native GaN substrates. 2. Experimental Seven AlGaN/ GaN heterostructures were grown by rf-plasma assisted...buffer needs to include Be-doped GaN isolation layers in MBE-grown AlGaN/ GaN HEMTs and must be separated from the 2DEG by 200 nm to 500 nm. Acknowledgments

  18. Effect of GaAs native oxide upon the surface morphology during GaAs MBE growth

    Science.gov (United States)

    Ageev, O. A.; Solodovnik, M. S.; Balakirev, S. V.; Mikhaylin, I. A.; Eremenko, M. M.

    2016-08-01

    The GaAs native oxide effect upon the surface morphology of the GaAs epitaxial layer was studied with taking into account the main growth parameters of MBE technology: substrate temperature, effective As4/Ga flux ratio and growth rate. The MBE modes of atomically smooth and rough surfaces and surfaces with Ga droplet array formation were determined. The possibility of the obtaining of GaAs nanowires via GaAs native oxide layer was shown.

  19. Bulk ammonothermal GaN

    Science.gov (United States)

    Dwiliński, R.; Doradziński, R.; Garczyński, J.; Sierzputowski, L. P.; Puchalski, A.; Kanbara, Y.; Yagi, K.; Minakuchi, H.; Hayashi, H.

    2009-05-01

    In this work, results of structural characterization of high-quality ammonothermal GaN are presented. Besides expected low dislocation density (being of the order of 10 3 cm -2) the most interesting feature seems perfect flatness of the crystal lattice of studied crystals. Regardless the size of crystals, lattice curvature radius exceeds 100 m, whereas better crystals reveal radius of several hundred meters and the best above 1000 m. Excellent crystallinity manifests in very narrow X-ray diffraction peaks of full-width at half-maximum (FWHM) values about 16 arcsec.

  20. Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Naresh-Kumar, G., E-mail: naresh.gunasekar@strath.ac.uk; Trager-Cowan, C. [Dept of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Vilalta-Clemente, A.; Morales, M.; Ruterana, P. [CIMAP UMR 6252 CNRS-ENSICAEN-CEA-UCBN 14050 Caen Cedex (France); Pandey, S.; Cavallini, A.; Cavalcoli, D. [Dipartimento di Fisica Astronomia, Università di Bologna, 40127 Bologna (Italy); Skuridina, D.; Vogt, P.; Kneissl, M. [Institute of Solid State Physics, Technical University Berlin, 10623 Berlin (Germany); Behmenburg, H.; Giesen, C.; Heuken, M. [AIXTRON SE, Kaiserstr. 98, 52134 Herzogenrath (Germany); Gamarra, P.; Di Forte-Poisson, M. A. [Thales Research and Technology, III-V Lab, 91460 Marcoussis (France); Patriarche, G. [LPN, Route de Nozay, 91460 Marcoussis (France); Vickridge, I. [Institut des NanoSciences, Université Pierre et Marie Curie, 75015 Paris (France)

    2014-12-15

    We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3μm)/ AlN(100nm)/Al{sub 2}O{sub 3} high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

  1. Multicharacterization approach for studying InAl(GaN/Al(GaN/GaN heterostructures for high electron mobility transistors

    Directory of Open Access Journals (Sweden)

    G. Naresh-Kumar

    2014-12-01

    Full Text Available We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(GaN(33nm barrier/Al(GaN(1nm interlayer/GaN(3μm/ AlN(100nm/Al2O3 high electron mobility transistor (HEMT heterostructure grown by metal organic vapor phase epitaxy (MOVPE. In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(GaN interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

  2. Fermi level and bands offsets determination in insulating (Ga,Mn)N/GaN structures.

    Science.gov (United States)

    Janicki, L; Kunert, G; Sawicki, M; Piskorska-Hommel, E; Gas, K; Jakiela, R; Hommel, D; Kudrawiec, R

    2017-02-02

    The Fermi level position in (Ga,Mn)N has been determined from the period-analysis of GaN-related Franz-Keldysh oscillation obtained by contactless electroreflectance in a series of carefully prepared by molecular beam epitaxy GaN/Ga1-xMnxN/GaN(template) bilayers of various Mn concentration x. It is shown that the Fermi level in (Ga,Mn)N is strongly pinned in the middle of the band gap and the thickness of the depletion layer is negligibly small. For x > 0.1% the Fermi level is located about 1.25-1.55 eV above the valence band, that is very close to, but visibly below the Mn-related Mn(2+)/Mn(3+) impurity band. The accumulated data allows us to estimate the Mn-related band offsets at the (Ga,Mn)N/GaN interface. It is found that most of the band gap change in (Ga,Mn)N takes place in the valence band on the absolute scale and amounts to -0.028 ± 0.008 eV/% Mn. The strong Fermi level pinning in the middle of the band gap, no carrier conductivity within the Mn-related impurity band, and a good homogeneity enable a novel functionality of (Ga,Mn)N as a semi-insulating buffer layers for applications in GaN-based heterostuctures.

  3. Anelasticity of GaN Epitaxial Layer in GaN LED

    Science.gov (United States)

    Chung, C. C.; Yang, C. T.; Liu, C. Y.

    2016-10-01

    In this work, the anelasticity of the GaN layer in the GaN light-emitting-diode device was studied. The present results show that the forward-voltage of GaN LED increases with time, as the GaN light-emitting-diode was maintained at a constant temperature of 100 °C. We found that the increase of the forward-voltage with time attributes to the delay-response of the piezoelectric fields (internal electrical fields in GaN LED device). And, the delay-response of the internal electrical fields with time is caused by the anelasticity (time-dependent strain) of the GaN layer. Therefore, using the correlation of strain-piezoelectric-forward voltage, a plot of thermal strain of the GaN layer against time can be obtained by measuring the forward-voltage of the studied GaN LED against time. With the curves of the thermal strain of GaN epi-layers versus time, the anelasticity of the GaN compound can be studied. The key anelasticity parameter, characteristic relaxation time, of the GaN is defined to be 2623.76 min in this work.

  4. Preparation and characterization of GaN films grown on Ga-diffused Si(111) substrates

    Institute of Scientific and Technical Information of China (English)

    SUN Zhencui; CAO Wentian; WEI Qinqin; WANG Shuyun; XUE Chengshan; SUN Haibo

    2005-01-01

    Hexagonal GaN films were prepared by nitriding Ga2O3 films with flowing ammonia. Ga2O3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.) magnetron sputtering. This paper have investigated the change of structural properties of GaN films nitrided in NH3 atmosphere at the temperatures of 850, 900, and 950℃ for 15min and nitrided at the temperature of 900℃ for 10, 15, and 20 min, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure, surface morphology and composition of synthesized samples. The results reveal that the as-grown films are polycrystalline GaN with hexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained when nitrided at 900℃ for 15 min.

  5. Orbital pseudotumor imaged with Ga-67 citrate

    Energy Technology Data Exchange (ETDEWEB)

    Jaikishen, P.; Bateman, J.L.; Shreeve, W.W. (Veterans Administration Medical Center, Northport, NY (USA))

    1989-11-01

    An orbital pseudotumor causing proptosis, diplopia, and gaze palsy was imaged with Ga-67 citrate and showed persistent intense activity for five days. This may be the first case of gallium uptake into an orbital pseudotumor to be reported in the literature. This case report demonstrates the use of Ga-67 citrate imaging in the early diagnostic workup of this disorder.

  6. Radiative and non-radiative recombination in GaInN/GaN quantum wells; Strahlende und nichtstrahlende Rekombination in GaInN/GaN-Quantenfilmen

    Energy Technology Data Exchange (ETDEWEB)

    Netzel, C.

    2007-02-08

    The studies presented in this thesis deal with the occurence of V defectsin GaInN/GaN quantum film structures grown by means of organometallic gas phase epitaxy, and the effects, which have the V defects respectively the GaInN quantum films on the V-defect facets on the emission and recombination properties of the whole GaInN/GaN quantum film structure. The V-defects themselves, inverse pyramidal vacancies with hexagonal base in the semiconductor layers, arise under suitable growth conditions around the percussion violations, which extend in lattice-mismatched growth of GaN on the heterosubstrates sapphire or silicon carbide starting in growth direction through the crystal. If GaInN layers are grown over V-defect dispersed layers on the (1-101) facets of the V defects and the (0001) facets, the growth front of the structure, different growth velocities are present, which lead to differently wide GaInN quantum films on each facets.

  7. Optical Properties of GaSb Nanofibers

    Directory of Open Access Journals (Sweden)

    Perez-Bergquist Alejandro

    2011-01-01

    Full Text Available Abstract Amorphous GaSb nanofibers were obtained by ion beam irradiation of bulk GaSb single-crystal wafers, resulting in fibers with diameters of ~20 nm. The Raman spectra and photoluminescence (PL of the ion irradiation-induced nanofibers before and after annealing were studied. Results show that the Raman intensity of the GaSb LO phonon mode decreased after ion beam irradiation as a result of the formation of the amorphous nanofibers. A new mode is observed at ~155 cm-1 both from the unannealed and annealed GaSb nanofiber samples related to the A1g mode of Sb–Sb bond vibration. Room temperature PL measurements of the annealed nanofibers present a wide feature band at ~1.4–1.6 eV. The room temperature PL properties of the irradiated samples presents a large blue shift compared to bulk GaSb. Annealed nanofibers and annealed nanofibers with Au nanodots present two different PL peaks (400 and 540 nm, both of which may originate from Ga or O vacancies in GaO. The enhanced PL and new band characteristics in nanostructured GaSb suggest that the nanostructured fibers may have unique applications in optoelectronic devices.

  8. Origin of magnetostriction in Fe-Ga

    DEFF Research Database (Denmark)

    Mudivarthi, Chaitanya; Laver, Mark; Cullen, James

    2010-01-01

    This paper investigates the origin of large magnetostriction in Fe-Ga alloys using small-angle neutron scattering (SANS) and Kerr microscopy. The SANS data for a single-crystal, electron irradiated, and quenched Fe81Ga19 sample under externally applied magnetic and elastic fields revealed...

  9. Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chao; Cai, Yuefei; Liu, Zhaojun; Ma, Jun; Lau, Kei May, E-mail: eekmlau@ust.hk [Photonics Technology Center, Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2015-05-04

    We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrown n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme.

  10. Effects of AlGaAs cladding layers on the luminescence of GaAs/GaAs1-xBix/GaAs heterostructures.

    Science.gov (United States)

    Mazur, Yu I; Dorogan, V G; de Souza, L D; Fan, D; Benamara, M; Schmidbauer, M; Ware, M E; Tarasov, G G; Yu, S-Q; Marques, G E; Salamo, G J

    2014-01-24

    The structural and optical properties of GaAs1-xBix quantum wells (QWs) symmetrically clad by GaAs barriers with and without additional confining AlGaAs layers are studied. It is shown that a GaAs/GaAs1-xBix/GaAs QW with x ~ 4% and well width of ~ 4 nm grown by molecular beam epitaxy demonstrates efficient photoluminescence (PL) that becomes significantly more thermally stable when a cladding AlGaAs layer is added to the QW structure. The PL behavior for temperatures between 10 and 300 K and for excitation intensities varying by seven orders of magnitude can be well described in terms of the dynamics of excitons including carrier capture in the QW layer, thermal emission and diffusion into the cladding barriers. Understanding the role of these processes in the luminescence of dilute GaAs1-xBix QW structures facilitates the creation of highly efficient devices with reduced thermal sensitivity and low threshold current.

  11. Improved interface quality and luminescence capability of InGaN/GaN quantum wells with Mg pretreatment

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Zhengyuan; Shen, Xiyang; Xiong, Huan; Li, Qingfei; Kang, Junyong; Fang, Zhilai [Xiamen University, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen (China); Lin, Feng; Yang, Bilan; Lin, Shilin [San' an Optoelectronics Co., Ltd, Xiamen (China); Shen, Wenzhong [Shanghai Jiao Tong University, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai (China); Zhang, Tong-Yi [Shanghai University, Shanghai University Materials Genome Institute and Shanghai Materials Genome Institute, Shanghai (China)

    2016-02-15

    Interface modification of high indium content InGaN/GaN quantum wells was carried out by Mg pretreatment of the GaN barrier surface. The indium in the Mg-pretreated InGaN layer was homogeneously distributed, making the interfaces abrupt. The improved interface quality greatly enhanced light emission capacity. The cathodoluminescence intensity of the Mg-pretreated InGaN/GaN quantum wells was correspondingly much stronger than those of the InGaN/GaN quantum wells without Mg pretreatment. (orig.)

  12. AlGaN/GaN HEMT技术与其专利申请分析研究

    Institute of Scientific and Technical Information of China (English)

    2016-01-01

    AlGaN/GaN HEMT器件在微波大功率和高温应用方面均具有明显的优势,已经成为当前研究的热点之一.本文介绍了AlGaN/GaN HEMT的工作原理,并结合全球与本国的关于AlGaN/GaN HEMT的相关专利申请情况,梳理出当AlGaN/GaN HEMT的专利申请趋势.

  13. Bandgap engineering of GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Ming, Bang-Ming; Yan, Hui [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Wang, Ru-Zhi, E-mail: wrz@bjut.edu.cn, E-mail: yamcy@csrc.ac.cn [College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124 (China); Beijing Computational Science Research Center, Beijing, 100094 (China); Yam, Chi-Yung, E-mail: wrz@bjut.edu.cn, E-mail: yamcy@csrc.ac.cn [Beijing Computational Science Research Center, Beijing, 100094 (China); Xu, Li-Chun [College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024 (China); Lau, Woon-Ming [Beijing Computational Science Research Center, Beijing, 100094 (China); Chengdu Green Energy and Green Manufacturing Technology R& D Center, Chengdu, Sichuan, 610207 (China)

    2016-05-15

    Bandgap engineering has been a powerful technique for manipulating the electronic and optical properties of semiconductors. In this work, a systematic investigation of the electronic properties of [0001] GaN nanowires was carried out using the density functional based tight-binding method (DFTB). We studied the effects of geometric structure and uniaxial strain on the electronic properties of GaN nanowires with diameters ranging from 0.8 to 10 nm. Our results show that the band gap of GaN nanowires depends linearly on both the surface to volume ratio (S/V) and tensile strain. The band gap of GaN nanowires increases linearly with S/V, while it decreases linearly with increasing tensile strain. These linear relationships provide an effect way in designing GaN nanowires for their applications in novel nano-devices.

  14. Gallium incorporation kinetics during GSMBE of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Jones, C.R.; Kaspi, R. [Wright State Univ. Research Center, Dayton, OH (United States); Lei, T.; Evans, K.R. [Wright Lab., Wright-Patterson AFB, OH (United States). Solid State Electronics Directorate

    1996-11-01

    The kinetics of Ga incorporation during gas-source molecular beam epitaxy of GaN are investigated for varying substrate temperature and incident ammonia flux. Incident Ga atoms eventually either: (1) react with NH{sub 3} to form GaN; (2) accumulate on the film surface, or (3) desorb. Low substrate temperatures lead to significant Ga surface accumulation due to the temperature-dependent reactivity of NH{sub 3} towards Ga. High substrate temperatures give rise to significant Ga desorption. Increasing NH{sub 3} flux retards both Ga surface accumulation and Ga desorption. The GaN formation rate variation with substrate temperature peaks near 750 C and increases with NH{sub 3} flux. The observation of two distinct and very low activation energies for Ga desorption suggests a relatively complex surface chemistry and a strong likelihood that hydrogen is playing an important role.

  15. Resonant Transport in Nb/GaAs/AlGaAs/GaAs Microstructures

    CERN Document Server

    Giazotto, F; Beltram, F; Lazzarino, M; Orani, D; Rubini, S; Franciosi, A

    2002-01-01

    Resonant transport in a hybrid semiconductor-superconductor microstructure grown by MBE on GaAs is presented. This structure experimentally realizes the prototype system originally proposed by de Gennes and Saint-James in 1963 in \\emph{all}-metal structures. A low temperature single peak superimposed to the characteristic Andreev-dominated subgap conductance represents the mark of such resonant behavior. Random matrix theory of quantum transport was employed in order to analyze the observed magnetotransport properties and ballistic effects were included by directly solving the Bogoliubov-de Gennes equations.

  16. Characteristics of AlGaN/GaN/AlGaN double heterojunction HEMTs with an improved breakdown voltage

    Institute of Scientific and Technical Information of China (English)

    Ma Juncai; Zhang Jincheng; Xue Junshuai; Lin Zhiyu; Liu Ziyang; Xue Xiaoyong; Ma Xiaohua; Hao Yue

    2012-01-01

    We studied the performance of AlGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with an AlGaN buffer layer,which leads to a higher potential barrier at the backside of the twodimensional electron gas channel and better carrier confinement.This,remarkably,reduces the drain leakage current and improves the device breakdown voltage.The breakdown voltage of AlGaN/GaN double heterojunction HEMTs (~ 100 V) was significantly improved compared to that of conventional AlGaN/GaN HEMTs (~50 V) for the device with gate dimensions of 0.5 × 100 μm and a gate-drain distance of 1μm.The DH-HEMTs also demonstrated a maximum output power of 7.78 W/mm,a maximum power-added efficiency of 62.3% and a linear gain of 23 dB at the drain supply voltage of 35 V at 4 GHz.

  17. High magnetic field studies of AlGaN/GaN heterostructures grown on bulk GaN

    Energy Technology Data Exchange (ETDEWEB)

    Siekacz, M.; Nowak, G.; Porowski, S. [High Pressure Research Center, Polish Academy of Sciences, 01-142 Warsaw (Poland); Dybko, K. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Skierbiszewski, C. [High Pressure Research Center, Polish Academy of Sciences, 01-142 Warsaw (Poland); TopGaN Ltd., Warsaw (Poland); Knap, W. [High Pressure Research Center, Polish Academy of Sciences, 01-142 Warsaw (Poland); GES -UMR, CNRS - Universite Montpellier 2, Place E. Bataillon, 34950 Montpellier (France); Wasilewski, Z. [Institute for Microstructural Sciences, National Research Council, Ottawa (Canada); Maude, D. [Grenoble High Magnetic Field Laboratory, MPI-CNRS, 38042 Grenoble (France); Lusakowski, J. [Institute of Experimental Physics, University of Warsaw, Hoza 69, 00-681 Warsaw (Poland); Krupczynski, W.; Bockowski, M. [TopGaN Ltd., Warsaw (Poland)

    2005-03-01

    We present transport properties of AlGaN/GaN heterostructures grown over high-pressure bulk GaN substrates. The experimental results include the conductivity tensor measurements in a magnetic field up to 23 T in a wide temperature range 2 K-300 K for Hall bar samples. The room temperature high field data allow us to clearly separate contributions of a parasitic parallel conduction from 2DEG conduction in all investigated heterostructures. The room temperature mobility limit for 2D electrons in GaN/AlGaN heterojunctions grown on defect free GaN bulk substrates is around 2400 cm{sup 2}/Vs. The Quantum Hall Effect studies are performed in the magnetic fields up to 23 T and temperatures between 1.6 K and 15 K This high magnetic field in combination with very high mobility (over 60000 cm{sup 2}/Vs) in the sample grown on the bulk GaN substrate allow us to determine the activation energy in cyclotron gap from longitudinal magnetoresistance. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Emission properties of heterostructures with a (GaAsSb-InGaAs)/GaAs bilayer quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Zvonkov, B. N.; Nekorkin, S. M.; Vikhrova, O. V.; Dikareva, N. V., E-mail: dikareva@nifti.unn.ru [Nizhni Novgorod State University, Physical-Technical Research Institute (Russian Federation)

    2013-09-15

    The specific features of the emission characteristics of GaAs-based heterostructures with a GaAs{sub 1-x}Sb{sub x}-In{sub y}Ga{sub 1-y}As bilayer quantum well are studied. The heterostructures are grown by metal-organic chemical vapor deposition (MOCVD). With an analysis of previously reported data on the MOCVD growth process taken into account, the temperature range (560-580 Degree-Sign C), the relation between the fluxes emitted by the sources of Group-V and -III elements ( Less-Than-Or-Equivalent-To 1), and the order of layer growth for the production of the active region of a GaAs/InGaP laser heterostructure are determined experimentally. The active region is a GaAs{sub 0.75}Sb{sub 0.25}-In{sub 0.2}Ga{sub 0.8}As bilayer quantum well. For the structure, a 1075-nm electroluminescence signal attributed to indirect transitions between the valence band of the GaAs{sub 0.75}Sb{sub 0.25} layer and the conduction band of the In{sub 0.2}Ga{sub 0.8}As layer is observed. An increase in the continuous-wave pump current yields a decrease in the 1075-nm emission intensity and initiates stable lasing at a wavelength of 1022 nm at a threshold current density of 1.4 kA cm{sup -2} at room temperature. Lasing occurs at transitions direct in coordinate space.

  19. Dilute GaAsN and GaInAsN grown by liquid phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Milanova, M; Koleva, G; Kakanakov, R [Central Laboratory of Applied Physics, Bulgarian Academy of Sciences, 59 St. Petersburg Blvd, 4000 Plovdiv (Bulgaria); Vitanov, P K; Alexieva, Z; Goranova, E A [Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, 1784 Sofia (Bulgaria); Arnaudov, B; Evtimova, S [Faculty of Physics, St. Kl. Ohridski University of Sofia, 5 J. Bourchier Blvd, 1164 Sofia (Bulgaria); Barthou, C; Clerjaud, B, E-mail: vitanov@phys.bas.b [Universite Pierre et Marie Curie, Institut des NanoSciences de Paris, rue de Lourmel 140, 75015 Paris (France)

    2010-04-01

    Dilute III-nitrides, such as GaAsN and GaInAsN, are of considerable current interest both from a fundamental point of view and for applications in solar cells, GaAs-based long-wavelength photodetectors and diode lasers. The addition of nitrogen leads to material properties that deviate strongly from those expected for conventional III-V solid solutions. The possibility was investigated to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures. The structures were grown from Ga- and Ga-In- melts containing powder GaN as a nitrogen source. The initial growth temperature was varied in the range 560{sup 0}C - 660{sup 0}C. The low temperature growth favors nitrogen incorporation in the epilayers. The optical transmission and photoluminescence spectra of a set of structures grown at different temperatures were studied showing ternary and quaternary dilute nitride solid solutions with nitrogen content about 0.2 at.%. The photoluminescence spectra show emission from localized nitrogen states as well.

  20. Dilute GaAsN and GaInAsN grown by liquid phase epitaxy

    Science.gov (United States)

    Milanova, M.; Koleva, G.; Kakanakov, R.; Vitanov, P. K.; Alexieva, Z.; Goranova, E. A.; Arnaudov, B.; Evtimova, S.; Barthou, C.; Clerjaud, B.

    2010-04-01

    Dilute III-nitrides, such as GaAsN and GaInAsN, are of considerable current interest both from a fundamental point of view and for applications in solar cells, GaAs-based long-wavelength photodetectors and diode lasers. The addition of nitrogen leads to material properties that deviate strongly from those expected for conventional III-V solid solutions. The possibility was investigated to use liquid phase epitaxy to incorporate nitrogen in epitaxial GaAsN/GaAs and GaInAsN/GaAs heterostructures. The structures were grown from Ga- and Ga-In- melts containing powder GaN as a nitrogen source. The initial growth temperature was varied in the range 560°C - 660°C. The low temperature growth favors nitrogen incorporation in the epilayers. The optical transmission and photoluminescence spectra of a set of structures grown at different temperatures were studied showing ternary and quaternary dilute nitride solid solutions with nitrogen content about 0.2 at.%. The photoluminescence spectra show emission from localized nitrogen states as well.

  1. Time-Resolved Photoluminescence Studies of InGaN/AlGaN Multiple Quantum Wells

    Science.gov (United States)

    Zeng, K. C.; Smith, M.; Lin, J. Y.; Jiang, H. X.; Robert, J. C.; Piner, E. L.; McIntosh, F. G.; Bahbahani, M.; Bedair, S. M.; Zavada, J.

    1997-03-01

    Picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the dynamic processes of optical transitions in InGaN/AlGaN multiple quantum wells (MQW) grown by metal-organic chemical vapor deposition (MOCVD). The dynamical behavior of the PL emission reveals that the main emission line in these MQW is the combination of the localized exciton and a band-to-impurity emission lines. The spectral lineshape and the recombination dynamics of the localized exciton and of the band-to-impurity transitions have been systematically investigated at different temperatures and excitation intensities and for MQW with different structures and growth conditions. From these studies, important parameters, including the localization energy and the recombination lifetimes of the localized excitons in InGaN/AlGaN quantum wells, the well width fluctuation, alloy compositions in the well and the barrier materials, and the band offset between InGaN and AlGaN can be deduced. Comparing with time-resolved PL results of InGaN/GaN and GaN/AlGaN MQW, important effects of interface on the optical properties of the III-nitride MQW have been evaluated. Implications of our results to device applications will be discussed.

  2. Strain gauges of GaSbFeGa{sub 1.3} eutectic composites

    Energy Technology Data Exchange (ETDEWEB)

    Aliyev, M.I.; Khalilova, A.A.; Arasly, D.H.; Rahimov, R.N. [National Academy of Sciences, Institute of Physics of Azerbaijan, Baku (Azerbaijan); Tanoglu, M. [Izmir Institute of Technology, Department of Mechanical Engineering, Izmir (Turkey); Ozyuzer, L. [Izmir Institute of Technology, Department of Physics, Izmir (Turkey)

    2004-12-01

    A needle-shaped metallic FeGa{sub 1.3} phase oriented in a specific direction and uniformly distributed within a GaSb matrix was grown by a vertical Bridgman method. Strain-gauge characteristics, such as strain-sensitivity coefficient (S), temperature coefficient of strain sensitivity (TCS) and temperature coefficient of resistance, of GaSb and GaSbFeGa{sub 1.3} eutectic alloy have been investigated in the range of 200 to 400 K under deformation up to strains of 1.3 x 10{sup -3}. The value of S of the GaSbFeGa{sub 1.3} composition is measured to be 40{+-}5 and its TCS is about 0.2% deg{sup -1} when the current is perpendicular to the needles and the needles are parallel to the plane of the gauge substrate. The strain-sensitivity characteristics are linear and hysteresis free in the investigated temperature range in the aforementioned direction. It was found that GaSbFeGa{sub 1.3}-based strain gauges possess better deformation characteristics than GaSb-based gauges. (orig.)

  3. Monte Carlo simulation of the kinetic effects on GaAs/GaAs(001) MBE growth

    Science.gov (United States)

    Ageev, Oleg A.; Solodovnik, Maxim S.; Balakirev, Sergey V.; Mikhaylin, Ilya A.; Eremenko, Mikhail M.

    2017-01-01

    The molecular beam epitaxial growth of GaAs on the GaAs(001)-(2×4) surface is investigated using a kinetic Monte Carlo-based method. The developed algorithm permits to focus on the kinetic effects in a wide range of growth conditions and enables considerable computational speedup. The simulation results show that the growth rate has a dramatic influence upon both the island morphology and Ga surface diffusion length. The average island size reduces with increasing growth rate while the island density increases with increasing growth rate as well as As4/Ga beam equivalent pressure ratio. As the growth rate increases, the island density becomes weaker dependent upon the As4/Ga pressure ratio and approaches to a saturation value. We also discuss three characteristics of Ga surface diffusion, namely a diffusion length of a Ga adatom deposited first, an average diffusion length, and an island spacing as an average distance between islands. The calculations show that the As4/Ga pressure ratio dependences of these characteristics obey the same law, but with different coefficients. An increase of the As4/Ga pressure ratio leads to a decrease in both the diffusion length and island spacing. However, its influence becomes stronger with increasing growth rate for the first Ga adatom diffusion length and weaker for the average diffusion length and for the island spacing.

  4. Low Turn-on Voltage of InGaP/GaAsSb/GaAs Double Heterojunction Bipolar Transistor%低开启电压的InGaP/GaAsSb/GaAs双异质结晶体管

    Institute of Scientific and Technical Information of China (English)

    郑丽萍; 严北平; 孙海锋; 刘新宇; 和致经; 吴德馨

    2003-01-01

    采用窄禁带宽度材料GaAsSb作为异质结晶体管的基区材料,成功研制出了能有效降低电路工作电压和功率损耗的低开启电压的NPN InGaP/GaAsSb/GaAs双异质结晶体管(double heterojunction bipolar transistor,DHBT).器件性能如下:BE结的正向开启电压(turn-on voltage)仅为0.73V;当IB=1μA/step时,直流增益达到了100,BVCEO=5~6V.通过对基区不同Sb含量器件的比较得到,器件的直流特性与基区Sb的含量有关.

  5. Meningiomas: a comparative study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for molecular imaging in mice.

    Directory of Open Access Journals (Sweden)

    María Luisa Soto-Montenegro

    Full Text Available PURPOSE: The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three (68Ga-DOTA-labeled somatostatin analogues ((68Ga-DOTATOC, (68Ga-DOTANOC, and (68Ga-DOTATATE using PET/CT in a murine model with subcutaneous meningioma xenografts. METHODS: The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN. (68Ga-DOTATOC, (68Ga-DOTANOC, and (68Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L and tumor-to-muscle (T/M SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt was determined. RESULTS: Hepatic SUVmax and Vt were significantly higher with (68Ga-DOTANOC than with (68Ga-DOTATOC and (68Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between (68Ga-DOTATATE and (68Ga-DOTATOC, both of which had a higher fraction than (68Ga-DOTANOC. The T/M SUV ratio was significantly higher with (68Ga-DOTATATE than with (68Ga-DOTATOC and (68Ga-DOTANOC. The Vt for tumor was higher with (68Ga-DOTATATE than with (68Ga-DOTANOC and relatively similar to that of (68Ga-DOTATOC. CONCLUSIONS: This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with (68Ga-DOTATATE and (68Ga-DOTATOC, uptake was higher with (68Ga-DOTATATE in the tumor than with (68Ga-DOTANOC and (68Ga-DOTATOC, suggesting a higher diagnostic value of (68Ga-DOTATATE for detecting meningiomas.

  6. GaN/AlGaN nanocavities with AlN/GaN Bragg reflectors grown in AlGaN nanocolumns by plasma assisted MBE

    Energy Technology Data Exchange (ETDEWEB)

    Ristic, J.; Calleja, E.; Fernandez-Garrido, S. [ISOM and Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s n, 28040 Madrid (Spain); Trampert, A.; Jahn, U.; Ploog, K.H. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Povoloskyi, M.; Carlo, A. Di [Dept. di Ingegneria Elettronica, Universita di Roma ' ' Tor Vegata' ' , 00133 Roma (Italy)

    2005-02-01

    The successful growth of AlGaN nanocolumns by plasma assisted MBE, with different Al compositions, opened the way for achieving nano-heterostructures including GaN Quantum Discs (QDss). The luminescence emission from the QDss embedded in the AlGaN nanocolumns was tuned by changing their thickness and/or the Al composition of the barriers. Such a nano-heterostructure was then enclosed between two AlN/GaN Distributed Bragg Reflectors (DBR), with nominal reflectivities of 90 and 50%. The choice of the AlN/GaN bilayers for the DBRs allowed to reach these reflectivity values with a significantly lower number of periods, as compared to the AlGaN/GaN stacks. The resulting nanocavity has been characterized by cathodoluminescence (CL), and Scanning and Transmission Electron Microscopy (SEM, TEM). CL measurements show that the emission from the nanocavity is quite close to the targeted value. TEM data points to the need of optimized conditions to grow AlN columnar layers in order to avoid the lateral overgrowth in the columnar nanostructure. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Accelerated aging of GaAs concentrator solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Gregory, P.E.

    1982-04-01

    An accelerated aging study of AlGaAs/GaAs solar cells has been completed. The purpose of the study was to identify the possible degradation mechanisms of AlGaAs/GaAs solar cells in terrestrial applications. Thermal storage tests and accelerated AlGaAs corrosion studies were performed to provide an experimental basis for a statistical analysis of the estimated lifetime. Results of this study suggest that a properly designed and fabricated AlGaAs/GaAs solar cell can be mechanically rugged and environmentally stable with projected lifetimes exceeding 100 years.

  8. Role of electronic correlations in Ga

    KAUST Repository

    Zhu, Zhiyong

    2011-06-13

    An extended around mean field (AMF) functional for less localized pelectrons is developed to quantify the influence of electronic correlations in α-Ga. Both the local density approximation (LDA) and generalized gradient approximation are known to mispredict the Ga positional parameters. The extended AMF functional together with an onsite Coulomb interaction of Ueff=1.1 eV, as obtained from constraint LDA calculations, reduces the deviations by about 20%. The symmetry lowering coming along with the electronic correlations turns out to be in line with the Ga phase diagram.

  9. Channel Temperature Measurement of AlGaN/GaN HEMTs by Forward Schottky Characteristics

    Institute of Scientific and Technical Information of China (English)

    ZHANG Guang-Chen; FENG Shi-Wei; HU Pei-Feng; ZHAO Yan; GUO Chun-Sheng; XU Yang; CHEN Tang-Sheng; JIANG Yi-Jian

    2011-01-01

    Channel temperature measurements of multi-finger AlGaN/GaN HEMTs by forward Schottky characteristics are presented. The temperature dependence of the forward gate-source Schottky junction voltage is investigated and it is used as the temperature sensitive parameter (TSP) by pulsed switching technique. The channel-to-mounting thermal resistance of the tested AlGaN/GaN HEMT sample is 19.6℃/W. Compared with both the measured results by micro-Raman method and simulated results of a three-dimensional heat conduction model, the physical meaning of the channel temperature for AlGaN/GaN HEMT tested by pulsed switching electrical TSP method is investigated quantitatively for the first time.

  10. 60Co gamma radiation effect on AlGaN/AlN/GaN HEMT devices

    Institute of Scientific and Technical Information of China (English)

    WANG Yan-Ping; LUO Yin-Hong; WANG Wei; ZHANG Ke-Ying; GUO Hong-Xia; GUO Xiao-Qiang; WANG Yuan-Ming

    2013-01-01

    The testing techniques and experimental methods of the 60Co gamma irradiation effect on AlGaN/AlN/GaN high electron mobility transistors (HEMTs) are established.The degradation of the electrical properties of the device under the actual radiation environment are analyzed theoretically,and studies of the total dose effects of gamma radiation on AlGaN/AlN/GaN HEMTs at three different radiation bias conditions are carried out.The degradation patterns of the main parameters of the AlGaN/AlN/GaN HEMTs at different doses are then investigated,and the device parameters that were sensitive to the gamma radiation induced damage and the total dose level induced device damage are obtained.

  11. Characterization of Inx Ga1-x As-GaAs heterostructures via electron beam techniques

    Science.gov (United States)

    Gomez-Barojas, Estela; Silva-Gonzalez, Rutilo; Serrano-Rojas, Rosa Maria; Vidal-Borbolla, Miguel Angel

    2005-03-01

    In the case of strained superlattices abrupt heterointerfaces are required because compositional fluctuations at heterointerfaces results in uncertainty in both composition and lattice constant. The aim of this work is to study exsitu the surface morphology, the periodicity and elemental composition of a set of 3 InGaAs-GaAs heterostructures grown on GaAs (100) substrates by a molecular beam epitaxy system. The heterostructures are formed by 10 periods of InGaAs-GaAs epitaxially grown on GaAs substrates with nominal thickness of 500 and 1000 å, respectively. The techniques used for this purpose are the scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). The In content in the heterostructures is determined from corresponding Auger depth profiles. This work has been supported by VIEP-BUAP, Project No. II53G02.

  12. Tunability of InGaN/GaN quantum well light emitting diodes through current

    Science.gov (United States)

    Biswas, Dipankar; Panda, Siddhartha

    2013-07-01

    In the recent years, InGaN/GaN quantum well (QW) light emitting diodes (LEDs) have gathered much importance through the introduction of white LEDs and dual wavelength LEDs. However, the continuous tunability of InGaN/GaN QW LEDs has not been well addressed or discussed. In this paper, we introduce the tunability of an InGaN/GaN QW LED having a well width of 4 nm and In mole fraction of 0.3. The results, obtained from self-consistent solutions of the Schrödinger and Poisson equations, show that the transition energy of the LED may be continuously tuned by the device current. A prominent nonlinearity of the transition energy with the device current is generated, which should be of interest to the research workers in the field of optoelectronics.

  13. Growth and structural characterizations of GaSe and GaSe:Cd single crystals

    Science.gov (United States)

    Ashkhasi, Afsoun; Gürbulak, Bekir; Şata, Mehmet; Turgut, Güven; Duman, Songül

    2017-02-01

    GaSe and GaSe:Cd single crystals used in this research were grown by using the Bridgman/Stockbarger method. All of the samples were freshly and gently cleaved with a razor blade from the grown ingots and no further polishing and cleaning treatments were required because of the natural mirror-like cleavage faces. The Samples were cleaved along the cleavage planes (001). The structure and lattice parameters of the undoped GaSe and GaSe:Cd semiconductors have been analyzed using a X-ray diffractometer (XRD), Scanning electron microscopy (SEM) and energy dispersive X-rays (EDX) techniques. It is found that GaSe and GaSe:Cd crystals have hexagonal structure, quite close 2θ peak values. XRD measurements indicate that there is an increase in peak intensities at specific annealing temperatures (500°C). Cd doping causes a significant decrease in the XRD peak intensity.

  14. Investigation of the confinement potential within GaNAs/GaAs multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Goshima, Keishiro; Kittaka, Akinobu; Fujii, Kensuke; Shiraga, Masahiro; Tsurumachi, Noriaki; Nakanishi, Shunsuke; Koshiba, Shyun; Itoh, Hiroshi [Engineering, Kagawa University, 2217-20, Takamatsu, Kagawa 761-0396 (Japan); Akiyama, Hidefumi [Institute of Solid State Physics, University of Tokyo, Chiba 277-8581 (Japan)

    2011-02-15

    We conducted a detailed investigation of the potential structure within GaNAs/GaAs multiple quantum wells (MQWs) using three independent experimental techniques: the temperature dependence of Photo-luminescence (PL) spectroscopy, time-resolved PL spectroscopy, and degenerate four-wave mixing (DFWM) measurements. We observed a very long lifetime (T{sub 1} = 12 ns) and dephasing time (T{sub 2} = 130 ps) of excitons in the GaNAs/GaAs MQWs. We suggested that the GaNAs/GaAs MQWs have a strong and deep confinement structure that is comparable to that of quantum dots (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. An optically pumped GaN/AlGaN quantum well intersubband terahertz laser

    Science.gov (United States)

    Fu, Ai-Bing; Hao, Ming-Rui; Yang, Yao; Shen, Wen-Zhong; Liu, Hui-Chun

    2013-02-01

    We propose an optically pumped nonpolar GaN/AlGaN quantum well (QW) active region design for terahertz (THz) lasing in the wavelength range of 30 μm ~ 40 μm and operating at room temperature. The fast longitudinal optical (LO) phonon scattering in GaN/AlGaN QWs is used to depopulate the lower laser state, and more importantly, the large LO phonon energy is utilized to reduce the thermal population of the lasing states at high temperatures. The influences of temperature and pump intensity on gain and electron densities are investigated. Based on our simulations, we predict that with a sufficiently high pump intensity, a room temperature operated THz laser using a nonpolar GaN/AlGaN structure is realizable.

  16. N incorporation in GaInNSb alloys and lattice matching to GaSb

    Energy Technology Data Exchange (ETDEWEB)

    Ashwin, M. J.; Jones, T. S. [Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom); Walker, D.; Thomas, P. A. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Veal, T. D. [Stephenson Institute for Renewable Energy, School of Physical Sciences, University of Liverpool, Liverpool L69 4ZF (United Kingdom)

    2013-01-21

    The incorporation of N into MBE grown GaNSb and GaInNSb is investigated. Measurements of the N fraction in GaNSb show the familiar linear dependence on inverse growth rate, followed by a departure from this at low growth rates; a similar behaviour is observed for GaInNSb. Unexpectedly, the point at which there is a departure from this linear behaviour is found to be extended to lower growth rates by the addition of small amounts of In. These results are compared to a kinetic theory-based model from which it is postulated that the change in behaviour can be attributed to an In-induced change in the characteristic surface residence lifetime of the N atoms. In addition, a method is demonstrated for growing GaInNSb lattice-matched to GaSb(001) for compositions with band gaps covering the 2-5 {mu}m region.

  17. Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

    Science.gov (United States)

    Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

    2008-12-01

    Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

  18. Intraband Spectroscopy of GaSe Nanoparticles and InSe/GaSe Nanoparticle Heterojunctions

    Science.gov (United States)

    Kelley, David F.; Tu, Haohua; Chen, Xiang-Bai

    The spectroscopic and dynamical characteristics of electron and hole intraband transitions in several sizes of GaSe nanoparticles have been studied using polarized femtosecond transient absorption spectroscopy. Assignments of the observed absorptions are made in terms of the known GaSe band structure and a model in which the electron and hole states are described by particle-in-a-cylinder states. The results indicate that the transient absorption spectrum is due to a size-independent, z-polarized hole intraband transition, and in the smaller particles, an x,y-polarized electron transition. In InSe/GaSe mixed aggregates, direct electron transfer from InSe to GaSe nanoparticles occurs upon photoexcitation of a charge transfer band. An exciton on GaSe nanoparticles can undergo diffusion and charge separation the an InSe/GaSe heterojunction.

  19. Modeling and simulation of InGaN/GaN quantum dots solar cell

    Science.gov (United States)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-07-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In0.25Ga0.75N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In0.25Ga0.75N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  20. Short-wavelength infrared photodetector with InGaAs/GaAsSb superlattice

    Science.gov (United States)

    Jin, Chuan; Xu, Qingqing; Yu, Chengzhang; Chen, Jianxin

    2016-05-01

    In this paper, our recent study on InGaAs/GaAsSb Type II photodetector for extended short wavelength infrared detection is reported. The high quality InGaAs/GaAsSb superlattices (SLs) was grown successfully by molecular beam epitaxy. The full width of half maximum of the SLs peak is 39". Its optical properties were characterized by photoluminescence (PL) at different temperature. The dependences of peak energy on temperature were measured and analyzed. The photodetector with InGaAs/GaAsSb absorption regions has a Quantum Efficiency (QE) product of 12.51% at 2.1um and the 100% cutoff wavelength is at 2.5um, at 300K under zero bias. The dominant mechanism of the dark current is discussed.

  1. Surface photovoltage spectroscopy of an InGaAs/GaAs/AlGaAs single quantum well laser structure

    Science.gov (United States)

    Ashkenasy, N.; Leibovitch, M.; Shapira, Yoram; Pollak, Fred H.; Burnham, G. T.; Wang, X.

    1998-01-01

    An InGaAs/GaAs/AlGaAs single quantum well graded-index-of-refraction separate-confinement hetero-structure laser has been analyzed using surface photovoltage spectroscopy (SPS) in a contactless, nondestructive way at room temperature. Numerical simulation of the resulting spectrum made it possible to extract growth parameters, such as the InGaAs well width, the well and cladding compositions, as well as important electro-optic structure data of this device, including the lasing wavelength and built-in electric field. The results highlight the power of SPS in obtaining performance parameters of actual laser devices, containing two-dimensional structures, in a contactless, nondestructive way.

  2. 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.

  3. Improving Performance of InGaN/GaN Light-Emitting Diodes and GaAs Solar Cells Using Luminescent Gold Nanoclusters

    Directory of Open Access Journals (Sweden)

    M. D. Yang

    2009-01-01

    Full Text Available We studied the optoelectronic properties of the InGaN/GaN multiple-quantum-well light emitting diodes (LEDs and single-junction GaAs solar cells by introducing the luminescent Au nanoclusters. The electroluminescence intensity for InGaN/GaN LEDs increases after incorporation of the luminescent Au nanoclusters. An increase of 15.4% in energy conversion efficiency is obtained for the GaAs solar cells in which the luminescent Au nanoclusters have been incorporated. We suggest that the increased light coupling due to radiative scattering from nanoclusters is responsible for improving the performance of the LEDs and solar cells.

  4. Current transport in graphene/AlGaN/GaN vertical heterostructures probed at nanoscale

    Science.gov (United States)

    Fisichella, Gabriele; Greco, Giuseppe; Roccaforte, Fabrizio; Giannazzo, Filippo

    2014-07-01

    Vertical heterostructures combining two or more graphene (Gr) layers separated by ultra-thin insulating or semiconductor barriers represent very promising systems for next generation electronics devices, due to the combination of high speed operation with wide-range current modulation by a gate bias. They are based on the specific mechanisms of current transport between two-dimensional-electron-gases (2DEGs) in close proximity. In this context, vertical devices formed by Gr and semiconductor heterostructures hosting an ``ordinary'' 2DEG can be also very interesting. In this work, we investigated the vertical current transport in Gr/Al0.25Ga0.75N/GaN heterostructures, where Gr is separated from a high density 2DEG by a ~24 nm thick AlGaN barrier layer. The current transport from Gr to the buried 2DEG was characterized at nanoscale using conductive atomic force microscopy (CAFM) and scanning capacitance microscopy (SCM). From these analyses, performed both on Gr/AlGaN/GaN and on AlGaN/GaN reference samples using AFM tips with different metal coatings, the Gr/AlGaN Schottky barrier height ΦB and its lateral uniformity were evaluated, as well as the variation of the carrier densities of graphene (ngr) and AlGaN/GaN 2DEG (ns) as a function of the applied bias. A low Schottky barrier (~0.40 eV) with excellent spatial uniformity was found at the Gr/AlGaN interface, i.e., lower compared to the measured values for metal/AlGaN contacts, which range from ~0.6 to ~1.1 eV depending on the metal workfunction. The electrical behavior of the Gr/AlGaN contact has been explained by Gr interaction with AlGaN donor-like surface states located in close proximity, which are also responsible of high n-type Gr doping (~1.3 × 1013 cm-2). An effective modulation of ns by the Gr Schottky contact was demonstrated by capacitance analysis under reverse bias. From this basic understanding of transport properties in Gr/AlGaN/GaN heterostructures, novel vertical field effect transistor concepts

  5. 68Ga-triacetylfusarinine C and 68Ga-ferrioxamine E for Aspergillus infection imaging: uptake specificity in various microorganisms

    NARCIS (Netherlands)

    Petrik, M.; Haas, H. de; Laverman, P.; Schrettl, M.; Franssen, G.M.; Blatzer, M.; Decristoforo, C.

    2014-01-01

    (68)Ga-triacetylfusarinine C ((68)Ga-TAFC) and (68)Ga-ferrioxamine E ((68)Ga-FOXE) showed excellent targeting properties in Aspergillus fumigatus rat infection model. Here, we report on the comparison of specificity towards different microorganisms and human lung cancer cells (H1299).The in vitro up

  6. Growth of InGaN and double heterojunction structure with InGaN back barrier

    Energy Technology Data Exchange (ETDEWEB)

    Shi Linyu; Zhang Jincheng; Wang Hao; Xue Junshuai; Ou Xinxiu; Fu Xiaofan; Chen Ke; Hao Yue, E-mail: sly_yolanda@163.com [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, Institutes of Microelectronics, Xidian University, Xi' an 710071 (China)

    2010-12-15

    We study the growth of an InGaN and AlGaN/GaN/InGaN/GaN double heterojunction structure by metal organic chemical vapor deposition (MOCVD). It is found that the crystal quality of the InGaN back barrier layer significantly affects the electronic property of the AlGaN/GaN/InGaN/GaN double heterojunction. A high crystal quality InGaN layer is obtained by optimizing the growth pressure and temperature. Due to the InGaN layer polarization field opposite to that in the AlGaN layer, an additional potential barrier is formed between the GaN and the InGaN layer, which enhances carrier confinement of the 2DEG and reduces the buffer leakage current of devices. The double heterojunction high-electron-mobility transistors with an InGaN back barrier yield a drain induced barrier lowering of 1.5 mV/V and the off-sate source-drain leakage current is as low as 2.6 {mu}A/mm at V{sub DS} = 10 V. (semiconductor materials)

  7. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.;

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...

  8. Red to near-infrared emission from InGaN/GaN quantum-disks-in-nanowires LED

    KAUST Repository

    Ng, Tien Khee

    2014-01-01

    The InGaN/GaN quantum-disks-in-nanowire light-emitting diode (LED) with emission centered at ~830nm, the longest emission wavelength ever reported in the InGaN/GaN system, and spectral linewidth of 290nm, has been fabricated with p-side-down on a Cu substrate.

  9. SEMICONDUCTOR MATERIALS Growth of InGaN and double heterojunction structure with InGaN back barrier

    Science.gov (United States)

    Linyu, Shi; Jincheng, Zhang; Hao, Wang; Junshuai, Xue; Xinxiu, Ou; Xiaofan, Fu; Ke, Chen; Yue, Hao

    2010-12-01

    We study the growth of an InGaN and AlGaN/GaN/InGaN/GaN double heterojunction structure by metal organic chemical vapor deposition (MOCVD). It is found that the crystal quality of the InGaN back barrier layer significantly affects the electronic property of the AlGaN/GaN/InGaN/GaN double heterojunction. A high crystal quality InGaN layer is obtained by optimizing the growth pressure and temperature. Due to the InGaN layer polarization field opposite to that in the AlGaN layer, an additional potential barrier is formed between the GaN and the InGaN layer, which enhances carrier confinement of the 2DEG and reduces the buffer leakage current of devices. The double heterojunction high-electron-mobility transistors with an InGaN back barrier yield a drain induced barrier lowering of 1.5 mV/V and the off-sate source-drain leakage current is as low as 2.6 μA/mm at VDS = 10 V.

  10. Simplified 2DEG carrier concentration model for composite barrier AlGaN/GaN HEMT

    Energy Technology Data Exchange (ETDEWEB)

    Das, Palash, E-mail: d.palash@gmail.com; Biswas, Dhrubes, E-mail: d.palash@gmail.com [Indian Institute of Technology Kharagpur, Kharagpur - 721302, West Bengal (India)

    2014-04-24

    The self consistent solution of Schrodinger and Poisson equations is used along with the total charge depletion model and applied with a novel approach of composite AlGaN barrier based HEMT heterostructure. The solution leaded to a completely new analytical model for Fermi energy level vs. 2DEG carrier concentration. This was eventually used to demonstrate a new analytical model for the temperature dependent 2DEG carrier concentration in AlGaN/GaN HEMT.

  11. Theoretical study of gallium nitride molecules, GaN2 and GaN4.

    Science.gov (United States)

    Tzeli, Demeter; Theodorakopoulos, Giannoula; Petsalakis, Ioannis D

    2008-09-18

    The electronic and geometric structures of gallium dinitride GaN 2, and gallium tetranitride molecules, GaN 4, were systematically studied by employing density functional theory and perturbation theory (MP2, MP4) in conjunction with the aug-cc-pVTZ basis set. In addition, for the ground-state of GaN 4( (2)B 1) a density functional theory study was carried out combining different functionals with different basis sets. A total of 7 minima have been identified for GaN 2, while 37 structures were identified for GaN 4 corresponding to minima, transition states, and saddle points. We report geometries and dissociation energies for all the above structures as well as potential energy profiles, potential energy surfaces and bonding mechanisms for some low-lying electronic states of GaN 4. The dissociation energy of the ground-state GaN 2 ( X (2)Pi) is 1.1 kcal/mol with respect to Ga( (2)P) + N 2( X (1)Sigma g (+)). The ground-state and the first two excited minima of GaN 4 are of (2)B 1( C 2 v ), (2)A 1( C 2 v , five member ring), and (4)Sigma g (-)( D infinityh ) symmetry, respectively. The dissociation energy ( D e) of the ground-state of GaN 4, X (2)B 1, with respect to Ga( (2)P) + 2 N 2( X (1)Sigma g (+)), is 2.4 kcal/mol, whereas the D e of (4)Sigma g (-) with respect to Ga( (4)P) + 2 N 2( X (1)Sigma g (+)) is 17.6 kcal/mol.

  12. Epitaxial growth of aligned GaN nanowires and nanobridges

    OpenAIRE

    2007-01-01

    Homo-epitaxialy grown aligned GaN nanowires were prepared on crystalline GaN mesas. The GaN nanowires showed preferential growth along the 〈100〉 direction (m-axis direction). By using selectively positioned and crystallographically well defined GaN epitaxial lateral overgrowth (ELO) mesas as substrate, we obtained horizontally aligned GaN nanowires, in comb-like arrays and hexagonal network interconnecting the ELO mesas. Preliminary testing of the nanomechanical behavior of horizontal nanowir...

  13. Performance of AlGaN/GaN High Electron Mobility Transistors with AlSiN Passivation

    Science.gov (United States)

    2010-03-04

    NOTES 20100402017 14. ABSTRACT This program was focused on the development of alternative and superior dielectric passivations to AlGaN/ GaN HEMT ...efficiency were demonstrated. Index Terms GaN , MODFETs, Microwave power FETs, passivation. I. INTRODUCTION THE AlGaN/ GaN HEMT has been studied for its...deposition (LPCVD) system onto etched mesa-isolated AlGaN/ GaN HEMT structures with 25 nm Alo.25Gao.75N barriers grown on S.I. SiC. Dielectric

  14. Fast and ultrafast processes in AlGaN/GaN channels

    Energy Technology Data Exchange (ETDEWEB)

    Matulionis, A.; Liberis, J.; Ardaravicius, L.; Ramonas, M.; Zubkute, T.; Matulioniene, I. [Semiconductor Physics Institute, A. Goitauto 11, Vilnius 2600 (Lithuania); Eastman, L.F.; Shealy, J.R. [Cornell University, 425 Phillips Hall, Ithaca, NY 14853 (United States); Smart, J. [RF Micro Devices, 10420 Harris Oaks Blvd., Charlotte, NC 28269 (United States); Pavlidis, D.; Hubbard, S. [University of Michigan, 1301 Beal Avenue, Ann Arbor, MI 48109-2122 (United States)

    2002-12-01

    Extrapolated experimental dependence of electron energy relaxation time is used to treat hot-electron sharing by the adjacent Al{sub 0.15}Ga{sub 0.85}N and GaN layers in Al{sub 0.15}Ga{sub 0.85}N/GaN. The results fit the available experimental data on microwave noise when hot-phonon effect on the energy relaxation time is taken into account. The relaxation time of the occupancy fluctuations of the shared states is estimated to be 6 ps at 80 K lattice temperature. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  15. Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Wang, M.; Wadley, P.; Campion, R. P.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom); Charlton, T. R.; Kinane, C. J.; Langridge, S. [ISIS, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Science and Technology Facilities Council, Oxon OX11 0QX (United Kingdom)

    2015-08-07

    We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields.

  16. Energy characteristics of excitons in InGaN/GaN heterostructures

    Science.gov (United States)

    Usov, S. O.; Tsatsul'nikov, A. F.; Lundin, W. V.; Sakharov, A. V.; Zavarin, E. E.; Sinitsyn, M. A.; Ledentsov, N. N.

    2008-04-01

    The structure and optical properties of the heterostructures, which contain an ultra-thin InGaN layers with GaN or AlGaN barriers, grown by MOCVD method were investigated by photoluminescence and high resolution X-ray diffraction (HRXRD) tehnigue. The exciton localization energy, Urbah energy and charge carries activation energies were obtained from analysis of the temperature dependences of the photoluminescence spectra for the In-rich areas (QDs). In these structures the In-rich areas are shown to appear in ultrathin InGaN layers due to phase decomposition. That leads to exciton and carrier localization in fluctuation minima, which prevents them from tranport to nonradiative recombination centres. The indium composition in the InGaN QDs were obtained using theoretical model, which describes the electron transition energy as a function of In-rich areas parameters. The parameters such as deformation of InGaN/GaN region and layer thickness were determined from HRXRD. The suggested approach is supposed to be effective method for analysis of the optical properties of InGaN/GaN heterostructures.

  17. Thermodynamic properties of gadolinium in Ga-Sn and Ga-Zn eutectic based alloys

    Science.gov (United States)

    Maltsev, Dmitry S.; Volkovich, Vladimir A.; Yamshchikov, Leonid F.; Chukin, Andrey V.

    2016-09-01

    Thermodynamic properties of gadolinium in Ga-Sn and Ga-Zn eutectic based alloys were studied. Temperature dependences of gadolinium activity in the studied alloys were determined at 573-1073 K employing the EMF method. Solubility of gadolinium in the Ga-Sn and Ga-Zn alloys was measured at 462-1073 K using IMCs sedimentation method. Activity coefficients as well as partial and excess thermodynamic functions of gadolinium in the studied alloys were calculated on the basis of the obtained experimental data.

  18. Compositional analysis of GaAs/AlGaAs heterostructures using quantitative scanning transmission electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kauko, H.; Helvoort, A. T. J. van [Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim (Norway); Zheng, C. L.; Glanvill, S. [Monash Centre for Electron Microscopy, Monash University, VIC 3800 (Australia); Zhu, Y.; Etheridge, J., E-mail: joanne.etheridge@monash.edu [Monash Centre for Electron Microscopy, Monash University, VIC 3800 (Australia); Department of Materials Engineering, Monash University, VIC 3800 (Australia); Dwyer, C. [Monash Centre for Electron Microscopy, Monash University, VIC 3800 (Australia); Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, and Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich (Germany); Munshi, A. M.; Fimland, B. O. [Department of Electronics and Telecommunications, Norwegian University of Science and Technology (NTNU), Trondheim (Norway)

    2013-12-02

    We demonstrate a method for compositional mapping of Al{sub x}Ga{sub 1–x}As heterostructures with high accuracy and unit cell spatial resolution using quantitative high angle annular dark field scanning transmission electron microscopy. The method is low dose relative to spectroscopic methods and insensitive to the effective source size and higher order lens aberrations. We apply the method to study the spatial variation in Al concentration in cross-sectioned GaAs/AlGaAs core-shell nanowires and quantify the concentration in the Al-rich radial band and the AlGaAs shell segments.

  19. GaN/AlGaN microcavities for enhancement of non linear optical effects

    CERN Document Server

    Tasco, V; Campa, A; Massaro, A; Stomeo, T; Epifani, G; Passaseo, A; Braccini, M; Larciprete, M C; Sibilia, C; Bovino, F A

    2011-01-01

    We present a study on the design, growth and optical characterization of a GaN/AlGaN microcavity for the enhancement of second order non linear effects. The proposed system exploits the high second order nonlinear optical response of GaN due to the non centrosymmetric crystalline structure of this material. It consists of a GaN cavity embedded between two GaN/AlGaN Distributed Bragg Reflectors designed for a reference mode coincident with a second harmonic field generated in the near UV region (~ 400 nm). Critical issues for this target are the crystalline quality of the material, together with sharp and abrupt interfaces among the multi-stacked layers. A detailed investigation on the growth evolution of GaN and AlGaN epilayers in such a configuration is reported, with the aim to obtain high quality factor in the desiderated spectral range. Non linear second harmonic generation experiments have been performed and the results were compared with bulk GaN sample, highlighting the effect of the microcavity on the...

  20. Characterization of a Ga-assisted GaAs nanowire array solar cell on si substrate

    DEFF Research Database (Denmark)

    Boulanger, J. P.; Chia, A. C. E.; Wood, B.

    2016-01-01

    A single-junction core-shell GaAs nanowire (NW) solar cell on Si (1 1 1) substrates is presented. A Ga-assisted vapor–liquid–solid growth mechanism was used for the formation of a patterned array of radial p-i-n GaAs NWs encapsulated in AlInP passivation. Novel device fabrication utilizing facet......-dependent properties to minimize passivation layer removal for electrical contacting is demonstrated. Thorough electrical characterization and analysis of the cell is reported. The electrostatic potential distribution across the radial p-i-n junction GaAs NW is investigated by off-axis electron holography....

  1. Fabrication of InGaN/GaN double heterojunction solar cells with p-GaN nanorod arrays%含有p-GaN纳米阵列的InGaN/GaN双异质结太阳能电池的制作

    Institute of Scientific and Technical Information of China (English)

    唐龙娟; 郑新和; 张东炎; 董建荣; 王辉; 杨辉

    2011-01-01

    A method with p-GaN nanorod arrays is proposed to enhance the external quantum efficiency (EQE) of p-GaN/i-InGaN/n-GaN double heterojunctional solar cells. Inductively coupled plasma ethcing is utilized to form the p-GaN nanorod arrays with self-assembled Ni cluster as the etching mask. To form a smooth n-GaN surface for subsequent metal deposition, we demonstrate two-step etching of n-GaN mesa. The peak EQE of solar cells with p-GaN nanorod arrays reaches 55%, which shows an enhancement of 10% as compared with the conventional device with p-GaN film.%提出了一种提高p-GaN/i-InGaN/n-GaN双异质结太阳能电池外量子效率的方法,即将p-GaN刻蚀成纳米阵列结构.我们使用Ni退火形成微结构掩模,通过感应耦合等离子体(ICP)将p-GaN刻蚀纳米阵列结构.同时,提出了两步刻蚀n-GaN台面的制作工艺,以此在形成p-GaN纳米阵列结构时获得光滑的n-GaN层表面,以此改善后续金属电极的沉积.经测试,含有p-GaN纳米阵列结构的电池峰值外量子效率可达55%,比常规p-GaN膜层基InGaN/GaN太阳能电池的外量子效率提高了10%.

  2. Laser-Combined Scanning Tunneling Microscopy on the Carrier Dynamics in Low-Temperature-Grown GaAs/AlGaAs/GaAs

    Directory of Open Access Journals (Sweden)

    Yasuhiko Terada

    2011-01-01

    Full Text Available We investigated carrier recombination dynamics in a low-temperature-grown GaAs (LT-GaAs/AlGaAs/GaAs heterostructure by laser-combined scanning tunneling microscopy, shaken-pulse-pair-excited STM (SPPX-STM. With the AlGaAs interlayer as a barrier against the flow of photocarriers, recombination lifetimes in LT-GaAs of 4.0 ps and GaAs of 4.8 ns were successfully observed separately. We directly demonstrated the high temporal resolution of SPPX-STM by showing the recombination lifetime of carriers in LT-GaAs (4.0 ps in the range of subpicosecond temporal resolution. In the carrier-lifetime-mapping measurement, a blurring of recombination lifetime up to 50 nm was observed at the LT-GaAs/AlGaAs boundary, which was discussed in consideration of the screening length of the electric field from the STM probe. The effect of the built-in potential on the signal, caused by the existence of LT-GaAs/AlGaAs/GaAs boundaries, was discussed in detail.

  3. AlGaN/GaN high electron mobility transistors with a low sub-threshold swing on free-standing GaN wafer

    Directory of Open Access Journals (Sweden)

    Xinke Liu

    2017-09-01

    Full Text Available This paper reported AlGaN/GaN high electron mobility transistors (HEMTs with low sub-threshold swing SS on free-standing GaN wafer. High quality AlGaN/GaN epi-layer has been grown by metal-organic chemical vapor deposition (MOCVD on free-standing GaN, small full-width hall maximum (FWHM of 42.9 arcsec for (0002 GaN XRD peaks and ultralow dislocation density (∼104-105 cm-2 were obtained. Due to these extremely high quality material properties, the fabricated AlGaN/GaN HEMTs achieve a low SS (∼60 mV/decade, low hysteresis of 54 mV, and high peak electron mobility μeff of ∼1456 cm2V-1s-1. Systematic study of materials properties and device characteristics exhibits that GaN-on-GaN AlGaN/GaN HEMTs are promising candidate for next generation high power device applications.

  4. AlGaN/GaN high electron mobility transistors with a low sub-threshold swing on free-standing GaN wafer

    Science.gov (United States)

    Liu, Xinke; Gu, Hong; Li, Kuilong; Guo, Lunchun; Zhu, Deliang; Lu, Youming; Wang, Jianfeng; Kuo, Hao-Chung; Liu, Zhihong; Liu, Wenjun; Chen, Lin; Fang, Jianping; Ang, Kah-Wee; Xu, Ke; Ao, Jin-Ping

    2017-09-01

    This paper reported AlGaN/GaN high electron mobility transistors (HEMTs) with low sub-threshold swing SS on free-standing GaN wafer. High quality AlGaN/GaN epi-layer has been grown by metal-organic chemical vapor deposition (MOCVD) on free-standing GaN, small full-width hall maximum (FWHM) of 42.9 arcsec for (0002) GaN XRD peaks and ultralow dislocation density (˜104-105 cm-2) were obtained. Due to these extremely high quality material properties, the fabricated AlGaN/GaN HEMTs achieve a low SS (˜60 mV/decade), low hysteresis of 54 mV, and high peak electron mobility μeff of ˜1456 cm2V-1s-1. Systematic study of materials properties and device characteristics exhibits that GaN-on-GaN AlGaN/GaN HEMTs are promising candidate for next generation high power device applications.

  5. Graphene-GaN Schottky Photodiodes Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Integration of graphene as the top metal on GaN Schottky. This will replace platinum, which is 50% transparent at the desired wavelength, with graphene, which has...

  6. EXAFS characterization of amorphous GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ridgway, M.C.; Glover, C.J. [Australia National Univ., Canberra (Australia); Foran, G.J. [Australian Nuclear Science and Technology Organization, Menai (Australia); Yu, K.M. [Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.

    1998-12-31

    The structural parameters of stoichiometric, amorphous GaAs have been determined with extended x-ray absorption fine structure (EXAFS) measurements performed in transmission mode at 10 K. Amorphous GaAs samples were fabricated with a combination of epitaxial growth, ion implantation and selective chemical etching. Relative to a crystalline sample, the nearest-neighbor bond length and Debye-Waller factor both increased for amorphous material. In contrast, the coordination numbers about both Ga and As atoms in the amorphous phase decreased to {approximately} 3.85 atoms from the crystalline value of four. All structural parameters were independent of implantation conditions and as a consequence, were considered representative of intrinsic, amorphous GaAs as opposed to an implantation-induced extrinsic structure.

  7. Optical anisotropy in GaSe

    Energy Technology Data Exchange (ETDEWEB)

    Seyhan, A.; Karabulut, O.; Akinoglu, B.G.; Aslan, B.; Turan, R. [Department of Physics, Middle East Technical University, 06531, Ankara (Turkey)

    2005-09-01

    Optical anisotropy of the layer semiconductor GaSe has been studied by photoluminescence (PL) and Fourier Transform Infrared Spectroscopy (FTIR). The PL spectra are dominated by two closely positioned emission bands resulting from the free exciton and the bound exciton connected direct band edge of GaSe. Photoluminescence and transmission spectra of GaSe crystals have been measured for two cases in which the propagation vector k is perpendicular (k perpendicular to c) and parallel to the c-axis (k//c). Peak position of the PL emission band and the onset of the transmission have been found to be significantly different for these two cases. This observed anisotropy is related to anisotropic band structure and the selection rules for the optical absorption in layered GaSe. FTIR transmission spectrum is in good agreement with PL results. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Hydrogen molecules in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Lavrov, E.V.; Weber, J

    2003-12-31

    GaAs samples treated in a hydrogen plasma have been studied by Raman spectroscopy. In addition to the known Raman line at 3912 cm{sup -1} of H{sub 2} trapped at the interstitial T{sub Ga} site surrounded by Ga neighbors, two new Raman signals at 4043 and 4112 cm{sup -1} have been observed at room temperature. The 4043 cm{sup -1} line is assigned to H{sub 2} trapped at the interstitial T{sub As} site with As closest neighbors and the 4112 cm{sup -1} line is associated with H{sub 2} trapped in voids formed by the hydrogen plasma. Para-H{sub 2} trapped at the interstitial T{sub Ga} site is shown to be unstable against irradiation with the band-gap light at room temperature and can be observed only at temperatures below 120 K.

  9. Triangle and GA Methods for UAVs Jamming

    Directory of Open Access Journals (Sweden)

    Yu Zhang

    2014-01-01

    Full Text Available We focus on how to jam UAVs network efficiently. The system model is described and the problem is formulated. Based on two properties and a theorem which helps to decide good location for a jammer, we present the Triangle method to find good locations for jammers. The Triangle method is easy to understand and has overall computational complexity of ON2. We also present a genetic algorithm- (GA- based jamming method, which has computational complex of OLMN2. New chromosome, mutation, and crossover operations are redefined for the GA method. The simulation shows that Triangle and GA methods perform better than Random method. If the ratio of jammers’ number to UAVs’ number is low (lower than 1/5 in this paper, GA method does better than Triangle method. Otherwise, Triangle method performs better.

  10. GaN three dimensional nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Dmitriev, V.; Irvin, K. [Cree Research, Inc., Durham, NC (United States); Zubrilov, A.; Tsvetkov, D.; Nikolaev, V. [Cree Research EED, St. Petersburg (Russian Federation); Jakobson, M.; Nelson, D.; Sitnikova, A. [A.F. Ioffe Inst., St. Petersburg (Russian Federation)

    1996-11-01

    The authors report on the growth and characterization of three dimensional nanoscale structures of GaN. GaN dots were grown by metal organic chemical vapor deposition (MOCVD) on 6H-SiC substrates. The actual size of the dots measured by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) ranged from {approximately}20 nm to more than 2 {micro}m. The average dot density ranged from 10{sup 7} to 10{sup 9} cm{sup {minus}2}. The single crystal structure of the dots was verified by reflectance high energy electron diffraction (HEED) and TEM. Cathodoluminescence (CL) and photoluminescence (PL) of the dots were studied at various temperatures and excitation levels. The PL and CL edge peak for the GaN dots exhibited a blue shift as compared with edge peak position for continuous GaN layers grown on SiC.

  11. 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.

  12. Data processing system of GA and PPPL

    Energy Technology Data Exchange (ETDEWEB)

    Oshima, Takayuki [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment

    2001-11-01

    Results of research in 1997 to General Atomics (GA) and Princeton Plasma Physics Laboratory (PPPL) are reported. The author visited the computer system of fusion group in GA. He joined the tokamak experiment in DIII-D, especially on the demonstration of the remote experiment inside U.S., and investigated the data processing system of DIII-D and the computer network, etc. After the visit to GA, He visited PPPL and exchanged the information about the equipment of remote experiment between JAERI and PPPL based on the US-Japan fusion energy research cooperation. He also investigated the data processing system of TFTR tokamak, the computer network and so on. Results of research of the second visit to GA in 2000 are also reported, which describes a rapid progress of each data processing equipment by the advance on the computer technology in just three years. (author)

  13. 2015 Cook & Tift County (GA) Lidar

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: NOAA OCM Tift and Cook Counties GA Lidar Data Acquisition and Processing Production Task NOAA Contract No. EA133C-11-CQ-0010 Woolpert Order No. 75271...

  14. Influence of doping on the microstructure and kinetic parameters of GaSb-FeGa1.3 eutectics

    Science.gov (United States)

    Mamedov, I. Kh.; Ragimov, R. N.; Khalilova, A. A.; Arasly, D. G.; Aliev, M. I.

    2012-12-01

    Electron microscopy and X-ray spectroscopy analysis of GaSb-FeGa1.3 eutectic composite doped with tellurium atoms is performed. It is established that doping changes the GaSb-FeGa1.3 eutectics microstructure; sizes, shape, and density of FeGa1.3 metallic inclusions; and the interface regions between the matrix and inclusions. Influence of doping on the anisotropy of kinetic parameters is shown.

  15. Scaling behavior of GaAs and GaMnAs quantum rings grown by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Placidi, E. [Istituto di Struttura della Materia, CNR, Via del Fosso del Cavaliere 100, 00133 Roma (Italy); Dipartimento di Fisica, Universita di Roma ' Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy (Italy); Arciprete, F.; Balzarotti, A.; Patella, F. [Dipartimento di Fisica, Universita di Roma ' Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy (Italy)

    2012-10-01

    The transition from the liquid phase of Ga droplets to the formation of GaAs and GaMnAs quantum rings has been studied as a function of temperature. We show that different aggregation processes involve the GaAs (GaMnAs) island and the droplet formation. Furthermore, the aspect ratio of the islands exhibits an anomalous scaling law related to a tendency to aggregate in the vertical direction.

  16. Strongly polarized quantum-dot-like light emitters embedded in GaAs/GaNAs core/shell nanowires

    OpenAIRE

    Filippov, Stanislav; Jansson, Mattias; Stehr, Jan Eric; Palisaitis, Justinas; Persson, Per O.Å.; Ishikawa, Fumitaro; Chen, Weimin M.; Buyanova, Irina A.

    2016-01-01

    Recent developments in fabrication techniques and extensive investigations of the physical properties of III-V semiconductor nanowires (NWs), such as GaAs NWs, have demonstrated their potential for a multitude of advanced electronic and photonics applications. Alloying of GaAs with nitrogen can further enhance the performance and extend the device functionality via intentional defects and heterostructure engineering in GaNAs and GaAs/GaNAs coaxial NWs. In this work, it is shown that incorpora...

  17. Photoluminescence of Ga(AsBi)

    Energy Technology Data Exchange (ETDEWEB)

    Rosemann, Nils; Chernikov, Alexej; Bornwasser, Verena; Koester, N.S.; Koch, Martin; Kolata, Kolja; Chetterjee, Sangam; Koch, Stephan W. [Fachbereich Physik, Philipps-Universitaet Marburg (Germany); Imhof, Sebastian; Wagner, Christian; Traenhardt, Angela [Institut fuer Physik, Technische Universitaet Chemnitz (Germany); Lu, Xianfeng; Johnson, Shane R. [Department of Electrical Engineering, Arizona State University, Tempe, AZ (United States); Beaton, Dan A. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC (Canada); Tiedje, Thomas [Department of Electrical and Computer Engineering, University of Victoria, BC (Canada); Rubel, Oleg [Thunder Bay Regional Research Institute, Thunder Bay, ON (Canada); Department of Physics, Lakehead University, Thunder Bay, ON (Canada)

    2011-07-01

    Ga(AsBi) is a promising candidate for GaAs-based near-infrared emitters at telecommunication wavelength. To evaluate the potential of this material system we study the photoluminescence from such a bulk sample as function of pump power and lattice temperature. Strong disorder-related features are observed. To better quantify the experiments we analyze the data using a Monte Carlo approach. A two-scale model is introduced to account for both cluster localization and alloy disorder.

  18. Groove-type channel enhancement-mode AlGaN/GaN MIS HEMT with combined polar and nonpolar AlGaN/GaN heterostructures

    Science.gov (United States)

    Duan, Xiao-Ling; Zhang, Jin-Cheng; Xiao, Ming; Zhao, Yi; Ning, Jing; Hao, Yue

    2016-08-01

    A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor (GTCE-HEMT) with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 mS/mm, and subthreshold slope of 85 mV/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage (V B) is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode (D-mode) polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits. Project supported by the National Science and Technology Major Project, China (Grant No. 2013ZX02308-002) and the National Natural Science Foundation of China (Grant Nos. 11435010, 61474086, and 61404099).

  19. The Y-Ag-Ga system

    Energy Technology Data Exchange (ETDEWEB)

    Krachan, T.; Stel' makhovych, B.; Kuz' ma, Yu

    2005-01-11

    The isothermal section at 670 K of the Y-Ag-Ga system in the region of 0-33 at.% Y has been constructed using X-ray diffraction data. The existence of earlier known ternary gallides has been confirmed. Their homogeneity regions, atomic coordinates and distribution of atoms in the structures have been determined: Y{sub 3}Ag{sub 2.55}Ga{sub 8.45} (La{sub 3}Al{sub 11}-type structure, a 0.4310(1) nm, b = 1.2865(3) nm, c = 0.9552(3) nm, R{sub F} = 0.043), YAg{sub 0.22}Ga{sub 1.78} (CaIn{sub 2}-type structure, a = 0.44565(1) nm, c 0.72032(2) nm, R{sub I} = 0.081), YAg{sub 0.74}Ga{sub 1.26} (KHg{sub 2}-type structure, a 0.45302(2) nm, b = 0.70805(3) nm, c = 0.78056(3) nm, R{sub I} = 0.059). The crystal structure of the new ternary compound YAg{sub 1.1}Ga{sub 1.9} ({beta}-YbAgGa{sub 2}-type structure, Pnma, a = 0.69654(3) nm, b = 0.43391(2) nm, c = 1.02126(5) nm, R{sub I} = 0.087) has been studied for the first time.

  20. Investigation of gate-diode degradation in normally-off p-GaN/AlGaN/GaN high-electron-mobility transistors

    Science.gov (United States)

    Tapajna, M.; Hilt, O.; Bahat-Treidel, E.; Würfl, J.; Kuzmík, J.

    2015-11-01

    Gate diode conduction mechanisms were analyzed in normally-off p-GaN/AlGaN/GaN high-electron mobility transistors grown on Si wafers before and after forward bias stresses. Electrical characterization of the gate diodes indicates forward current to be limited by channel electrons injected through the AlGaN/p-GaN triangular barrier promoted by traps. On the other hand, reverse current was found to be consistent with carrier generation-recombination processes in the AlGaN layer. Soft breakdown observed after ˜105 s during forward bias stress at gate voltage of 7 V was attributed to formation of conductive channel in p-GaN/AlGaN gate stack via trap generation and percolation mechanism, likely due to coexistence of high electric field and high forward current density. Possible enhancement of localized conductive channels originating from spatial inhomogeneities is proposed to be responsible for the degradation.

  1. Lattice pulling effect and strain relaxation in axial (In,Ga)N/GaN nanowire heterostructures grown on GaN-buffered Si(111) substrate

    Energy Technology Data Exchange (ETDEWEB)

    Kong, X.; Trampert, A. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117, Berlin (Germany); Albert, S.; Bengoechea-Encabo, A.; Sanchez-Garcia, M.A.; Calleja, E. [Dpto. Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica, Ciudad Universitaria, 28040, Madrid (Spain)

    2015-04-01

    Transmission electron microscopy and spatially resolved electron energy-loss spectroscopy have been applied to investigate the indium distribution and the interface morphology in axial (In,Ga)N/GaN nanowire heterostructures. The ordered axial (In,Ga)N/GaN nanowire heterostructures with an indium concentration up to 80% are grown by molecular beam epitaxy on GaN-buffered Si(111) substrates. We observed a pronounced lattice pulling effect in all the nanowire samples given in a broad transition region at the interface. The lattice pulling effect becomes smaller and the (In,Ga)N/GaN interface width is reduced as the indium concentration is increased in the (In,Ga)N section. The result can be interpreted in terms of the increased plastic strain relaxation via the generation of the misfit dislocations at the interface. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers.

    Science.gov (United States)

    Lv, Wenbin; Wang, Lai; Wang, Jiaxing; Hao, Zhibiao; Luo, Yi

    2012-11-07

    InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm.

  3. GaP ring-like nanostructures on GaAs (100) with In{sub 0.15}Ga{sub 0.85}As compensation layers

    Energy Technology Data Exchange (ETDEWEB)

    Prongjit, Patchareewan, E-mail: rsomchai@chula.ac.th; Pankaow, Naraporn, E-mail: rsomchai@chula.ac.th; Boonpeng, Poonyasiri, E-mail: rsomchai@chula.ac.th; Thainoi, Supachok, E-mail: rsomchai@chula.ac.th; Panyakeow, Somsak, E-mail: rsomchai@chula.ac.th; Ratanathammaphan, Somchai, E-mail: rsomchai@chula.ac.th [Semiconductor Device Research Laboratory (Nanotec Center of Excellence) Department of Electrical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330 (Thailand)

    2013-12-04

    We present the fabrication of GaP ring-like nanostructures on GaAs (100) substrates with inserted In{sub 0.15}Ga{sub 0.85}As compensation layers. The samples are grown by droplet epitaxy using solid-source molecular beam epitaxy. The dependency of nanostructural and optical properties of GaP nanostructures on In{sub 0.15}Ga{sub 0.85}As layer thickness is investigated by ex-situ atomic force microscope (AFM) and photoluminescence (PL). It is found that the characteristics of GaP ring-like structures on GaAs strongly depend on the In{sub 0.15}Ga{sub 0.85}As layer thickness.

  4. Optical Properties and Carrier Dynamics of GaAs/GaInAs Multiple-Quantum-Well Shell Grown on GaAs Nanowire by Molecular Beam Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kwangwook; Ravindran, Sooraj; Ju, Gun Wu; Min, Jung-Wook; Kang, Seokjin; Myoung, NoSoung; Yim, Sang-Youp; Jo, Yong-Ryun; Kim, Bong-Joong; Lee, Yong Tak

    2016-12-01

    GaAs/GaInAs multiple-quantum-well (MQW) shells having different GaInAs shell width formed on the surface of self-catalyzed GaAs core nanowires (NWs) are grown on (100) Si substrate using molecular beam epitaxy. The photoluminescence emission from GaAs/GaInAs MQW shells and the carrier lifetime could be varied by changing the width of GaInAs shell. Time-resolved photoluminescence measurements showed that the carrier lifetime had a fast and slow decay owing to the mixing of wurtzite and zinc-blende structures of the NWs. Furthermore, strain relaxation caused the carrier lifetime to decrease beyond a certain thickness of GaInAs quantum well shells.

  5. Cubic AlGaN/GaN structures for device application

    Energy Technology Data Exchange (ETDEWEB)

    Schoermann, Joerg

    2007-05-15

    The aim of this work was the growth and the characterization of cubic GaN, cubic AlGaN/GaN heterostructures and cubic AlN/GaN superlattice structures. Reduction of the surface and interface roughness was the key issue to show the potential for the use of cubic nitrides in futur devices. All structures were grown by plasma assisted molecular beam epitaxy on free standing 3C-SiC (001) substrates. In situ reflection high energy electron diffraction was first investigated to determine the Ga coverage of c-GaN during growth. Using the intensity of the electron beam as a probe, optimum growth conditions were found when a 1 monolayer coverage is formed at the surface. GaN samples grown under these conditions reveal excellent structural properties. On top of the c-GaN buffer c-AlGaN/GaN single and multiple quantum wells were deposited. The well widths ranged from 2.5 to 7.5 nm. During growth of Al{sub 0.15}Ga{sub 0.85}N/GaN quantum wells clear reflection high energy electron diffraction oscillations were observed indicating a two dimensional growth mode. We observed strong room-temperature, ultraviolet photoluminescence at about 3.3 eV with a minimum linewidth of 90 meV. The peak energy of the emission versus well width is reproduced by a square-well Poisson- Schroedinger model calculation. We found that piezoelectric effects are absent in c-III nitrides with a (001) growth direction. Intersubband transition in the wavelength range from 1.6 {mu}m to 2.1 {mu}m was systematically investigated in AlN/GaN superlattices (SL), grown on 100 nm thick c-GaN buffer layers. The SLs consisted of 20 periods of GaN wells with a thickness between 1.5 nm and 2.1 nm and AlN barriers with a thickness of 1.35 nm. The first intersubband transitions were observed in metastable cubic III nitride structures in the range between 1.6 {mu}m and 2.1 {mu}m. (orig.)

  6. Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

    Energy Technology Data Exchange (ETDEWEB)

    Kalygina, V. M., E-mail: Kalygina@ngs.ru; Vishnikina, V. V.; Petrova, Yu. S.; Prudaev, I. A.; Yaskevich, T. M. [National Research Tomsk State University (Russian Federation)

    2015-03-15

    We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga{sub 2}O{sub 3}-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga{sub 2}O{sub 3} crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga{sub 2}O{sub 3} crystallites and become transparent. Under illumination of the Ga{sub 2}O{sub 3}-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga{sub 2}O{sub 3} film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga{sub 2}O{sub 3}-GaAs interface and in the Ga{sub 2}O{sub 3} film.

  7. Interaction of terahertz radiation with surface and interface plasmon-phonons in AlGaAs/GaAs and GaN/Al2O3 heterostructures

    Science.gov (United States)

    Požela, J.; Požela, K.; Šilėnas, A.; Širmulis, E.; Jucienė, V.

    2013-01-01

    Surface phonon and plasmon-phonon polariton characteristics of GaAs, Al x Ga1- x As/GaAs, and GaN/Al2O3 layered structures are investigated by means of terahertz radiation reflection spectroscopy. The strong resonant absorption peaks and selective emission of the THz radiation dependent upon the lattice composition and free electron density in these layered structures are experimentally observed and analyzed.

  8. A dual-blue light-emitting diode based on strain-compensated InGaN-AlGaN/GaN quantum wells

    Institute of Scientific and Technical Information of China (English)

    Yan Qi-Rong; Yan Qi-Ang; Shi Pei-Pei; Niu Qiao-Li; Li Shu-Ti; Zhang Yong

    2013-01-01

    A strain-compensated InGaN quantum well (QW) active region employing a tensile A1GaN barrier is analyzed.Its spectral stability and efficiency droop for a dual-blue light-emitting diode (LED) are improved compared with those of the conventional InGaN/GaN QW dual-blue LEDs based on a stacking structure of two In0.18Ga0.82N/GaN QWs and two In0.12Ga0.88N/GaN QWs on the same sapphire substrate.It is found that the optimal performance is achieved when the AI composition of the strain-compensated A1GaN layer is 0.12 in blue QW and 0.21 in blue-violet QW.The improvement performance can be attributed to the strain-compensated InGaN-AlGaN/GaN QW,which can provide a better carrier confinement and effectively reduce leakage current.

  9. Effect of extra nonmagnetic Ga atoms on lattice ordering and magnetic properties of Fe2CoGa and Co2FeGa Heusler compounds

    Directory of Open Access Journals (Sweden)

    Hakimi

    2014-04-01

    Full Text Available Arc-melting with ball milling was used for preparing Fe2CoGa1+x and Co2FeGa1+x (x=0,0.2 Heusler samples. Effect of extra nonmagnetic Ga atoms on lattice ordering and magnetic properties of Fe2CoGa and Co2FeGa Heusler compounds was studied. Rietveld refinement showed that lattice parameter of the samples increases in the presence of extra Ga atoms. Results showed that Co2FeGa1.2 has a partial lattice disordering. Saturation magnetization of Co2FeGa sample was lower than Slater – Paulig prediction due to the crystallite size on a scale of nanometer. Reduction of saturation magnetization by increasing Ga atoms was explained through the change of lattice parameter, lattice ordering, and crystallite size. Saturation magnetization of Fe2CoGa sample was greater than Slater – Paulig value. Change of lattice parameter by increasing Ga atoms resulted a decrease of saturation magnetization in Fe2CoGa1.2

  10. 71Ga Chemical Shielding and Quadrupole Coupling Tensors of the Garnet Y(3)Ga(5)O(12) from Single-Crystal (71)Ga NMR

    DEFF Research Database (Denmark)

    Vosegaard, Thomas; Massiot, Dominique; Gautier, Nathalie

    1997-01-01

    A single-crystal (71)Ga NMR study of the garnet Y(3)Ga(5)O(12) (YGG) has resulted in the determination of the first chemical shielding tensors reported for the (71)Ga quadrupole. The single-crystal spectra are analyzed in terms of the combined effect of quadrupole coupling and chemical shielding ...

  11. Patterned growth of InGaN/GaN quantum wells on freestanding GaN grating by molecular beam epitaxy

    Directory of Open Access Journals (Sweden)

    Wang Yongjin

    2011-01-01

    Full Text Available Abstract We report here the epitaxial growth of InGaN/GaN quantum wells on freestanding GaN gratings by molecular beam epitaxy (MBE. Various GaN gratings are defined by electron beam lithography and realized on GaN-on-silicon substrate by fast atom beam etching. Silicon substrate beneath GaN grating region is removed from the backside to form freestanding GaN gratings, and the patterned growth is subsequently performed on the prepared GaN template by MBE. The selective growth takes place with the assistance of nanoscale GaN gratings and depends on the grating period P and the grating width W. Importantly, coalescences between two side facets are realized to generate epitaxial gratings with triangular section. Thin epitaxial gratings produce the promising photoluminescence performance. This work provides a feasible way for further GaN-based integrated optics devices by a combination of GaN micromachining and epitaxial growth on a GaN-on-silicon substrate. PACS 81.05.Ea; 81.65.Cf; 81.15.Hi.

  12. Capture and release of carriers in InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Turchinovich, Dmitry; Porte, Henrik; Daghestani, N.;

    2009-01-01

    We observe the ultrafast capture and release of charge carriers in InGaAs/GaAs quantum dots (QDs) at room-temperature with time-resolved terahertz spectroscopy. For excitation into the barrier states, a decay of the photoinduced conductivity, due to capture of carriers into the nonconducting QD s...

  13. InAlGaAs/AlGaAs quantum wells: line widths, transition energies and segregation

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, Wolfgang

    2000-01-01

    We investigate the optical properties of InAlCaAs/AlGaAs quantum wells pseudomorphically grown on GaAs using molecular beam epitaxy (MBE). The transition energies, measured with photoluminescence (PL), are modelled solving the Schrodinger equation, and taking into account segregation in the group...

  14. Collective Behavior of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher;

    2000-01-01

    Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell excition in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circular polarized light, the...

  15. FIR Induced Intrinsic Exciton Transitions in GaAs/AlGaAs Superlattices

    DEFF Research Database (Denmark)

    Dremin, A. A.; Timofeev, V. B.; Birkedal, Dan;

    1997-01-01

    Intrinsic transitions of confined excitons in GaAs/AlGaAs superlattices with different barrier widths have been studied with the use of resonant far-infrared absorption under variation of magnetic field perpendicular and tilted with respect to the growth directions. Few resonances have been...

  16. MBE Growth and Characterization of Zincblende GaN and GaN/AlN Structures

    Science.gov (United States)

    1997-07-15

    This Program includes fundamental studies of Molecular beam epitaxial ( MBE ) growth of GaN and its related alloys and heterostructures. In additions...physics of MBE growth , and the optical and electrical properties for GaN-based device application. 1

  17. Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

    Institute of Scientific and Technical Information of China (English)

    Lü Ling; Zhang Jin-Cheng; Xue Jun-Shuai; Ma Xiao-Hua; Zhang Wei; Bi Zhi-Wei; Zhang Yue; Hao Yue

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 1015 cm-2.The dc characteristics of the devices,such as the drain saturation current and the maximum transconductance,decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation.However,the rf characteristics,such as the cut-off frequency and the maximum frequency,were hardly affected by neutron irradiation.The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism.It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation.There was no evidence of the full-width at half-maximum of X-ray diffraction (XRD) rocking curve changing after irradiation,so the dislocation was not influenced by neutron irradiation.It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.

  18. Carrier dynamics in submonolayer InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Zhang, Yating; Hvam, Jørn Märcher

    2006-01-01

    Carrier dynamics of submonolayer InGaAs/GaAs quantum dots (QDs) were studied by microphotoluminecence (MPL), selectively excited photoluminescence (SEPL), and time-resolved photoluminescence (TRPL). MPL and SEPL show the coexistence of localized and delocalized states, and different local phonon...

  19. Exciton dynamics in GaAs/AlxGa1-xAs quantum wells

    DEFF Research Database (Denmark)

    Litvinenko, K.; Birkedal, Dan; Lyssenko, V. G.

    1999-01-01

    The changes induced in the optical absorption spectrum of a GaAs/AlxGa1-xAs multiple quantum well due to a photoexcited carrier distribution are reexamined. We use a femtosecond pump-probe technique to excite excitons and free electron-hole pairs. We find that for densities up to 10(11) cm(-2...

  20. Excitonic complexes in GaN/(Al,Ga)N quantum dots

    Science.gov (United States)

    Elmaghraoui, D.; Triki, M.; Jaziri, S.; Muñoz-Matutano, G.; Leroux, M.; Martinez-Pastor, J.

    2017-03-01

    Here we report a theoretical investigation of excitonic complexes in polar GaN/(Al,Ga)N quantum dots (QDs). A sum rule between the binding energies of charged excitons is used to calculate the biexciton binding energy. The binding energies of excitonic complexes in GaN/AlN are shown to be strongly correlated to the QD size. Due to the large hole localization, the positively charged exciton energy is found to be always blueshifted compared to the exciton one. The negatively charged exciton and the biexciton energy can be blueshifted or redshifted according to the QD size. Increasing the size of GaN/AlN QDs makes the identification of charged excitons difficult, and the use of an Al0.5Ga0.5N barrier can be advantageous for clear identification. Our theoretical results for the binding energy of exciton complexes are also confronted with values deduced experimentally for InAs/GaAs QDs, confirming our theoretical prediction for charged excitonic complexes in GaN/(Al,Ga)N QDs. Finally, we realize that the trends of excitonic complexes in QDs are significantly related to competition between the local charge separation (whatever its origin) and the correlation effect. Following our findings, entangled photons pairs can be produced in QDs with careful control of their size in order to obtain zero exciton–biexciton energy separation.

  1. Spin injection from Co2MnGa into an InGaAs quantum well

    DEFF Research Database (Denmark)

    Hickey, M. C.; Damsgaard, Christian Danvad; Holmes, S. N.;

    2008-01-01

    We have demonstrated spin injection from a full Heusler alloy Co2MnGa thin film into a (100) InGaAs quantum well in a semiconductor light-emitting diode structure at a temperature of 5 K. The detection is performed in the oblique Hanle geometry, allowing quantification of the effective spin...

  2. Characterization of different-Al-content AlGaN/GaN heterostructures on sapphire

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Al x Ga 1-x N/GaN high-electron-mobility transistor (HEMT) structures with Al composition ranging from x = 0.13 to 0.36 are grown on sapphire substrates by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The effects of Al content on crystal quality, surface morphology, optical and electrical characteristics of the AlGaN/GaN heterostructures have been analyzed. Although high Al-content (36%) heterostructure exhibits a distinguished photoluminescence peak related to recombination between the two-dimensional electron gas and photoexcited holes (2DEG-h), its crystal quality and rough surface morphology are poor. 2DEG mobility increases with the Al content up to 26% and then it apparently decreases for high Al-content (36%) AlGaN/GaN heterostructure. The increase of sheet carrier density with the increase of Al content has been observed. A high mobility at room temperature of 2105 cm 2 /V s with a sheet carrier density of n s = 1.10 × 10 13 cm -2 , for a 26% Al-content AlGaN/GaN heterostructure has been obtained, which is approaching state-of-the-art for HEMT grown on SiC. Sheet resistance as low as 274 Ω/□ has also been achieved.

  3. Submicron-AlGaN/GaN MMICs for Space Applications

    NARCIS (Netherlands)

    Quay, R.; Waltereit, P.; Kühn, J.; Brückner, P.; Heijningen, M. van; Jukkala, P.; Hirche, K.; Ambacher, O.

    2013-01-01

    This paper reports on two AlGaN/GaN MMICtechnologies, performances of MMICs and modules, and reliability for space applications at X-band to W-band frequencies. Quarter-micron gate length HEMTs deliver 5 W/mm output power density at 30 V drain bias with >58% PAE at 10 GHz operating frequency. Dual-s

  4. Photocorrosion metrology of photoluminescence emitting GaAs/AlGaAs heterostructures

    Science.gov (United States)

    Aithal, Srivatsa; Liu, Neng; Dubowski, Jan J.

    2017-01-01

    High sensitivity of the photoluminescence (PL) effect to surface states and chemical reactions on surfaces of PL emitting semiconductors has been attractive in monitoring photo-induced microstructuring of such materials. To address the etching at nano-scale removal rates, we have investigated mechanisms of photocorrosion of GaAs/Al0.35Ga0.65As heterostructures immersed either in deionized water or aqueous solution of NH4OH and excited with above-bandgap radiation. The difference in photocorrosion rates of GaAs and Al0.35Ga0.65As appeared weakly dependent on the bandgap energy of these materials, and the intensity of an integrated PL signal from GaAs quantum wells or a buried GaAs epitaxial layer was found dominated by the surface states and chemical reactivity of heterostructure surfaces revealed during the photocorrosion process. Under optimized photocorrosion conditions, the method allowed resolving a 1 nm thick GaAs sandwiched between Al0.35Ga0.65As layers. We demonstrate that this approach can be used as an inexpensive, and simple room temperature tool for post-growth diagnostics of interface locations in PL emitting quantum wells and other nano-heterostructures.

  5. Ka-Band AlGaN/GaN HEMT high power and driver amplifier MMICs

    NARCIS (Netherlands)

    Heijningen, M. van; Vliet, F.E. van; Quay, R.; Raay, F. van; Kiefer, R.; Mueller, S.; Krausse, D.; Seelmann-Eggebert, M.; Mikulla, M.; Schlechtweg, M.

    2005-01-01

    In this paper the MMIC technology, design and characterization of a high power amplifier and driver amplifier MMIC at 30 GHz in AlGaN/GaN HEMT technology are presented. The MMICs are designed using CPW technology on a 390 μm thick SiC substrate. The measured small-signal gain of the driver is 14 dB

  6. Submicron-AlGaN/GaN MMICs for Space Applications

    NARCIS (Netherlands)

    Quay, R.; Waltereit, P.; Kühn, J.; Brückner, P.; Heijningen, M. van; Jukkala, P.; Hirche, K.; Ambacher, O.

    2013-01-01

    This paper reports on two AlGaN/GaN MMICtechnologies, performances of MMICs and modules, and reliability for space applications at X-band to W-band frequencies. Quarter-micron gate length HEMTs deliver 5 W/mm output power density at 30 V drain bias with >58% PAE at 10 GHz operating frequency. Dual-s

  7. Analysis of Time Dependent Electric Field Degradation in AlGaN/GaN HEMTs (POSTPRINT)

    Science.gov (United States)

    2014-10-01

    identifying and understanding the failure mechanisms that limit the safe operating area of GaN HEMTs. 15. SUBJECT TERMS aluminum gallium nitride ... gallium nitride , HEMTs, semiconductor device reliability, transistors 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER...area of GaN HEMTs. Index Terms— Aluminum gallium nitride , gallium nitride , HEMTs, semiconductor device reliability, transistors. I. INTRODUCTION A

  8. Robust X-band LNAs in AlGaN/GaN technology

    NARCIS (Netherlands)

    Janssen, J.P.B.; Heijningen, M. van; Visser, G.C.; Rodenburg, M.; Johnson, H.K.; Uren, M.J.; Morvan, E.; Vliet, F.E. van

    2009-01-01

    Gallium-Nitride technology is known for its high power density and power amplifier designs, but is also very well suited to realise robust receiver components. This paper presents the design, realisation and measurement of two robust AlGaN/GaN low noise amplifiers. The two versions have been designe

  9. Coherent dynamics of interwell excitons in GaAs/AlxGa1-xAs superlattices

    DEFF Research Database (Denmark)

    Mizeikis, V.; Birkedal, Dan; Langbein, Wolfgang Werner;

    1997-01-01

    Coherent exciton dynamics in a GaAs/AlxGa1-xAs narrow-miniband superlattice is studied by spectrally resolved transient four-wave mixing. Coherent optical properties of the investigated structure are found to be strongly affected by the existence of two different heavy-hole excitonic states. One ...

  10. Epitaxial lift-off GaAs solar cell from a reusable GaAs substrate

    Energy Technology Data Exchange (ETDEWEB)

    Geelen, A. van [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Hageman, P.R. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Bauhuis, G.J. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Rijsingen, P.C. van [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Schmidt, P. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Giling, L.J. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.

    1997-03-01

    Modifications to the existing epitaxial lift-off (ELO) method are described, which enable lift-off of large area devices (like solar cells). With the modified ELO method crack-free III-V films were obtained, up to 2 inch, in diameter and 1-6 {mu}m thick. For the first time epitaxial lift-off GaAs solar cells were made which contained an etch sensitive Al{sub 0.85}Ga{sub 0.15}As window layer. An energy conversion efficiency of 9.9% (AM1.5Gx1) was measured for the ELO GaAs cells. Compared to the thick GaAs reference cell, ELO cells still suffer from a low fill factor due to series and shunt resistances. Current GaAs ELO cells represent a power to weight ratio of 200 W kg{sup -1}. Because of the high selectivity of the ELO method, GaAs substrates remain unaffected after ELO. Reuse of a GaAs substrate after ELO was investigated in order to reduce the cost of III-V solar cell modules. With a simple cleaning procedure, GaAs substrates could be used at least four times without degradation of the minority carrier lifetime or carrier mobility of the grown epilayers. (orig.)

  11. Micro-photoluminescence of GaAs/AlGaAs triple concentric quantum rings.

    Science.gov (United States)

    Abbarchi, Marco; Cavigli, Lucia; Somaschini, Claudio; Bietti, Sergio; Gurioli, Massimo; Vinattieri, Anna; Sanguinetti, Stefano

    2011-10-31

    A systematic optical study, including micro, ensemble and time resolved photoluminescence of GaAs/AlGaAs triple concentric quantum rings, self-assembled via droplet epitaxy, is presented. Clear emission from localized states belonging to the ring structures is reported. The triple rings show a fast decay dynamics, around 40 ps, which is expected to be useful for ultrafast optical switching applications.

  12. Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    We studied the THz conductivity of InGaN/GaN multiple quantum wells (MQWs)by time-resolved terahertz spectroscopy. A nonexponential carrier density decay is observed due to the restoration of a built-in piezoelectric field. Terahertz conductivity spectra show a nonmetallic behavior of the carriers....

  13. Terahertz study of ultrafast carrier dynamics in InGa/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    2009-01-01

    Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells is measured by time-resolved terahertz spectroscopy. The built-in piezoelectric field is initially screened by photoexcited, polarized carriers, and is gradullay restored as the carriers recombine. We observe a nonexponential decay...

  14. Terahertz microbolometers based on disordered GaAs and GaN heterostructures

    Science.gov (United States)

    Wang, Kai; Ramaswamy, R.; Muraviev, A.; Sergeev, A.; Mitin, V.; Gaska, R.

    2011-03-01

    We present our results on design, fabrication, and characterization of hot-electron bolometers based on low-mobility two-dimensional electron gas (2DEG) heterostructures for THz heterodyne detection. Microbolometers based on GaAs/AlGaAs and GaN/AlGaN heterostructures have been fabricated and tested. Low contact resistances (0.2 ohm-mm for GaN and 0.7 ohm-mm for GaAs) were achieved. We determined the carrier concentration from the Hall measurements and the electron relaxation time from the mobility measurements. We also investigated kinetic parameters: temperature derivate of the resistivity and the electron cooling time. Optical characterization includes the transitivity measurements. The results show that the coupling to the THz radiation is mainly due to the Drude absorption, which increases in disordered structures. Temperature-dependent resistivity and electron cooling are determined by inelastic electron scattering on optical phonons. Finally, we compare GaAs and GaN microbolometers and analyze their parameters for various applications in THz sensing.

  15. Isothermal currents in InSe, GaSe, and GaS single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Micocci, G.; Rizzo, A.; Tepore, A.; Zuanni, F. (Lecce Univ. (Italy). Ist. di Fisica)

    1983-11-16

    Isothermal current-time measurements are performed on InSe, GaSe, and GaS single crystals. The results reveal the presence of trapping centres and their activation energies and capture cross-sections are determined. The limitations of this method for the determination of trapping parameters in crystals are also discussed.

  16. Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

    NARCIS (Netherlands)

    Hajlasz, M.; Donkers, J.J.T.M.; Sque, S.J.; Heil, S.B.S.; Gravesteijn, Dirk J; Rietveld, F.J.R.; Schmitz, Jurriaan

    2014-01-01

    For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact i

  17. Achieving Room Temperature Orange Lasing Using InGaP/InAlGaP Diode Laser

    KAUST Repository

    Al-Jabr, A. A.

    2015-09-28

    We demonstrated the first orange laser diode at room temperature with a decent total output power of ∼46mW and lasing wavelength of 608nm, using a novel strain-induced quantum well intermixing in InGaP/InAlGaP red laser structure.

  18. Submicron-AlGaN/GaN MMICs for Space Applications

    NARCIS (Netherlands)

    Quay, R.; Waltereit, P.; Kühn, J.; Brückner, P.; Heijningen, M. van; Jukkala, P.; Hirche, K.; Ambacher, O.

    2013-01-01

    This paper reports on two AlGaN/GaN MMICtechnologies, performances of MMICs and modules, and reliability for space applications at X-band to W-band frequencies. Quarter-micron gate length HEMTs deliver 5 W/mm output power density at 30 V drain bias with >58% PAE at 10 GHz operating frequency.

  19. Radio-frequency reflectometry on an undoped AlGaAs/GaAs single electron transistor

    DEFF Research Database (Denmark)

    MacLeod, S. J.; See, A. M.; Keane, Z. K.

    2014-01-01

    Radio frequency reflectometry is demonstrated in a sub-micron undoped AlGaAs/GaAs device. Undoped single electron transistors (SETs) are attractive candidates to study single electron phenomena, due to their charge stability and robust electronic properties after thermal cycling. However...

  20. Anomalous Hall effect in epitaxially grown ferromagnetic FeGa/Fe3Ga hybrid structure: Evidence of spin carrier polarized by clusters

    Science.gov (United States)

    Duc Dung, Dang; Cho, Sunglae

    2013-05-01

    The anomalous Hall resistance relative with magnetic anisotropy of clusters Fe3Ga in Fe3Ga/Fe-Ga hybrid structural epitaxial was reported. The out-of-plane magnetic anisotropy was obtained for Fe3Ga/Fe-Ga hybrid structure, while in-plane magnetic anisotropy is shown in the single Fe-Ga phase epitaxial on GaAs(001). The observation of trend of saturation Hall resistance in Fe3Ga/Fe-Ga hybrid structural is compared with the Fe-Ga single crystal, which is solid evidence for spin polarization by local magnetic clusters.

  1. Surface morphology and composition studies in InGaN/GaN film grown by MOCVD

    Institute of Scientific and Technical Information of China (English)

    Tao Tao; Han Ping; Shi Yi; Zheng Youdou; Zhang Zhao; Liu Lian; Su Hui; Xie Zili; Zhang Rong; Liu Bin; Xiu Xiangqian; Li Yi

    2011-01-01

    InGaN filmsweredepositedon(0001)sapphiresubstrates with GaN buffer layers under different growth temperatures by metalorganic chemical vapor deposition.The In-composition of InGaN film was approximately controlled by changing the growth temperature.The connection between the growth temperature,In content,surface morphology and defect formation was obtained by X-ray diffraction,scanning electron microscopy (SEM) and atomic force microscopy (AFM).Meanwhile,by comparing the SEM and AFM surface morphology images,we proposed several models of three different defects and discussed the mechanism of formation.The prominent effect of higher growth temperature on the quality of the InGaN films and defect control were found by studying InGaN films at various growth temperatures.

  2. Raman scattering from confined phonons in GaAs/AlGaAs quantum wires

    Science.gov (United States)

    Bairamov, B. H.; Aydinli, A.; Tanatar, B.; Güven, K.; Gurevich, S.; Mel'tser, B. Ya.; Ivanov, S. V.; Kop'ev, P. S.; Smirnitskii, V. B.; Timofeev, F. N.

    1998-10-01

    We report on photoluminescence and Raman scattering performed at low temperature (T = 10 K) on GaAs/Al0.3Ga0.7As quantum-well wires with effective wire widths ofL = 100.0 and 10.9 nm prepared by molecular beam epitaxial growth followed by holographic patterning, reactive ion etching, and anodic thinning. We find evidence for the existence of longitudinal optical phonon modes confined to the GaAs quantum wire. The observed frequency at οL10 = 285.6 cm-1forL = 11.0 nm is in good agreement with that calculated on the basis of the dispersive dielectric continuum theory of Enderleinas applied to the GaAs/Al0.3Ga0.7As system. Our results indicate the high crystalline quality of the quantum-well wires fabricated using these techniques.

  3. Substrate-Free InGaN/GaN Nanowire Light-Emitting Diodes.

    Science.gov (United States)

    Neplokh, Vladimir; Messanvi, Agnes; Zhang, Hezhi; Julien, Francois H; Babichev, Andrey; Eymery, Joel; Durand, Christophe; Tchernycheva, Maria

    2015-12-01

    We report on the demonstration of substrate-free nanowire/polydimethylsiloxane (PDMS) membrane light-emitting diodes (LEDs). Metal-organic vapour-phase epitaxy (MOVPE)-grown InGaN/GaN core-shell nanowires were encapsulated into PDMS layer. After metal deposition to p-GaN, a thick PDMS cap layer was spin-coated and the membrane was manually peeled from the sapphire substrate, flipped upside down onto a steel holder, and transparent indium tin oxide (ITO) contact to n-GaN was deposited. The fabricated LEDs demonstrate rectifying diode characteristics. For the electroluminescence (EL) measurements, the samples were manually bonded using silver paint. The EL spectra measured at different applied voltages demonstrate a blue shift with the current increase. This shift is explained by the current injection into the InGaN areas of the active region with different average indium content.

  4. Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors.

    Science.gov (United States)

    Fontserè, A; Pérez-Tomás, A; Placidi, M; Llobet, J; Baron, N; Chenot, S; Cordier, Y; Moreno, J C; Jennings, M R; Gammon, P M; Fisher, C A; Iglesias, V; Porti, M; Bayerl, A; Lanza, M; Nafría, M

    2012-10-05

    AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50 nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.

  5. High quality UV AlGaN/AlGaN distributed Bragg reflectors and microcavities

    Science.gov (United States)

    Mitrofanov, Oleg; Schmult, S.; Manfra, M. J.; Siegrist, T.; Weimann, N. G.; Sergent, A. M.; Molnar, R. J.

    2007-02-01

    We demonstrate high-reflectivity crack-free Al 0.18Ga 0.82N/Al 0.8Ga 0.2N distributed Bragg reflectors (DBR) and monolithic microcavities grown by molecular beam epitaxy on thick c-axis GaN templates. The elastic strain energy in the epilayer is minimized by compensating the compressive and tensile stress in every period of the DBR structure. A 25 period DBR mirror provides a 26nm-wide stop band centered at 347 nm with the maximum reflectivity higher than 99%. The high-reflectivity DBRs can be used to form high Q-factor monolithic AlGaN/AlGaN microcavities.

  6. InGaAs/GaAs multiquantum-well electroabsorption modulator with integrated waveguide

    Science.gov (United States)

    Das, Utpal; Berger, Paul R.; Bhattacharya, Pallab K.

    1987-10-01

    A monolithically integrated guided-wave modulator has been realized by using molecular-beam epitaxial regrowth and ion-milling techniques. The guiding and modulating regions consist, respectively, of In-doped GaAs and GaAs/In(0.34)Ga(0.66)As strained-layer multiquantum wells. Modulation is achieved by field-enhanced electroabsorption in the multiquantum wells. The insertion loss of the modulator is 0.9 dB, and the transmission loss in the guides is less than or equal to 1 dB/cm. The temporal response of similar GaAs/InGaAs as-grown photodiodes to pulsed laser excitation is characterized by a rise time of 115 psec.

  7. Ga crystallization dynamics during annealing of self-assisted GaAs nanowires.

    Science.gov (United States)

    Scarpellini, David; Fedorov, Alexey; Somaschini, Claudio; Frigeri, Cesare; Bollani, Monica; Bietti, Sergio; Nöetzel, Richard; Sanguinetti, Stefano

    2017-01-27

    In As atmosphere, we analyzed the crystallization dynamics during post-growth annealing of Ga droplets residing at the top of self-assisted GaAs nanowires grown by molecular beam epitaxy. The final crystallization steps, fundamental to determining the top facet nanowire morphology, proceeded via a balance of Ga crystallization via vapor-liquid-solid and layer-by-layer growth around the droplet, promoted by Ga diffusion out of the droplet perimeter, As desorption, and diffusion dynamics. By controlling As flux and substrate temperature the transformation of Ga droplets into nanowire segments with a top surface flat and parallel to the substrate was achieved, thus opening the possibility to realize atomically sharp vertical heterostructures in III-As self-assisted nanowires through group III exchange.

  8. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    Energy Technology Data Exchange (ETDEWEB)

    Bietti, Sergio, E-mail: sergio.bietti@mater.unimib.it; Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano [L–NESS and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Via Cozzi 55, I–20125 Milano (Italy); Fedorov, Alexey [L–NESS and CNR–IFN, via Anzani 42, I-22100 Como (Italy)

    2014-09-21

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E{sub A}=1.31±0.15 eV, a diffusivity prefactor of D₀=0.53(×2.1±1) cm² s⁻¹ that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

  9. Monte Carlo study of GaN versus GaAs terahertz quantum cascade structures

    Science.gov (United States)

    Bellotti, Enrico; Driscoll, Kristina; Moustakas, Theodore D.; Paiella, Roberto

    2008-03-01

    Due to their large optical phonon energies, nitride semiconductors are promising for the development of terahertz quantum cascade lasers with dramatically improved high-temperature performance relative to existing GaAs devices. Here, we present a rigorous Monte Carlo study of carrier dynamics in two structures based on the same design scheme for emission at 2THz, consisting of GaN /AlGaN or GaAs /AlGaAs quantum wells. The population inversion and hence the gain coefficient of the nitride device are found to exhibit a much weaker (by a factor of over 3) temperature dependence and to remain large enough for laser action even without cryogenic cooling.

  10. Generation of acoustic terahertz waves in hybrid InGaN/GaN quantum wells

    Science.gov (United States)

    Mahat, Meg; Llopis, Antonia; Choi, Tae Youl; Periera, Sergio; Watson, Ian; Neogi, Arup

    2015-03-01

    We have carried out differential transmission measurements on InGaN/ GaN quantum wells with Au nanoparticles inserted inside V-pits with high filling fraction. We have observed acoustic wave packets generated with multiple THz frequencies as 0.12 THz from GaN buffer layer, 0.22 THz from Au-InGaN multiple quantum wells region, 0.07 THz from sapphire substrate, and 0.17 THz mixed signals from the sample. These THz wave packets are observed as a result of generation of coherent acoustic phonons propagating in hybrid Au-InGaN quantum wells. The study of these acoustic THz wave generation is crucial for the imaging of nanostructures.

  11. Near-field microscopy of waveguide architectures of InGaN/GaN diode lasers

    Science.gov (United States)

    Friede, Sebastian; Tomm, Jens W.; Kühn, Sergei; Hoffmann, Veit; Wenzel, Hans; Weyers, Markus

    2016-11-01

    Waveguide (WG) architectures of 420 nm emitting InGaN/GaN diode lasers are analyzed by photoluminescence and photocurrent spectroscopy using a nearfield scanning optical microscope that scans along their front facets. The components of the ‘optical active cavity’, quantum wells, WGs, and cladding layers are individually inspected with a spatial resolution of ∼100 nm. Separate analysis of the p- and n-sections of the WG was achieved, and reveals defect levels in the p-part. Moreover, it is demonstrated that the homogeneity of the n-WG section directly affects the quantum wells that are grown on top of this layer. Substantially increased carrier capture efficiencies into InGaN/GaN-WGs compared to GaN-WGs are demonstrated.

  12. A hole accelerator for InGaN/GaN light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Wang, Liancheng; Zhu, Binbin; Zhang, Yiping; Lu, Shunpeng; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei, E-mail: EXWSUN@ntu.edu.sg, E-mail: VOLKAN@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Demir, Hilmi Volkan, E-mail: EXWSUN@ntu.edu.sg, E-mail: VOLKAN@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800 Ankara (Turkey)

    2014-10-13

    The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED.

  13. Structural and optical properties of InGaN/GaN nanowire heterostructures grown by PA-MBE.

    Science.gov (United States)

    Tourbot, G; Bougerol, C; Grenier, A; Den Hertog, M; Sam-Giao, D; Cooper, D; Gilet, P; Gayral, B; Daudin, B

    2011-02-18

    The structural and optical properties of InGaN/GaN nanowire heterostructures grown by plasma-assisted molecular beam epitaxy have been studied using a combination of transmission electron microscopy, electron tomography and photoluminescence spectroscopy. It is found that, depending on In content, the strain relaxation of InGaN may be elastic or plastic. Elastic relaxation results in a pronounced radial In content gradient. Plastic relaxation is associated with the formation of misfit dislocations at the InGaN/GaN interface or with cracks in the InGaN nanowire section. In all cases, a GaN shell was formed around the InGaN core, which is assigned to differences in In and Ga diffusion mean free paths.

  14. High-power AlInGaN-based violet laser diodes with InGaN optical confinement layers

    Science.gov (United States)

    Lee, Sung-Nam; Son, J. K.; Paek, H. S.; Sung, Y. J.; Kim, K. S.; Kim, H. K.; Kim, H.; Sakong, T.; Park, Y.; Ha, K. H.; Nam, O. H.

    2008-09-01

    InGaN optical confinement layers (OCLs) were introduced into blue-violet AlInGaN-based laser diodes (LDs), resulting in the drastic improvements of lasing performance. Comparing with conventional LD structure, the lowest threshold current density of 2.3kA/cm2 has been achieved by adding 100-nm-thick InGaN OCLs which represented maximum optical confinement factor. Additionally, we observed the high quantum efficiency and the uniform emission intensity distribution of InGaN quantum wells grown on lower InGaN OCL than on typical GaN layer. Upper InGaN OCL can reduce Mg diffusion from p-type layers to InGaN active region by separating the distance between InGaN quantum wells and p-type layers.

  15. 蓝宝石衬底上AlGaN/GaN HEMT自热效应研究%Study of Self-heating on AlGaN/GaN HEMTs Grown on Sapphire Substrate

    Institute of Scientific and Technical Information of China (English)

    杨燕; 郝跃

    2005-01-01

    建立了包含"自热效应"的AlGaN/GaN HEMT(高电子迁移率晶体管)直流I-V特性解析模型.从理论的角度分析了自热效应对AlGaN/GaN HEMT器件的影响,并同已有的实验结果进行了对比,符合较好.证明基于这种模型的理论分析适于AlGaN/GaN HEMT器件测试及应用的实际情况.

  16. Free-exciton states in crystalline GaTe

    Science.gov (United States)

    Wan, J. Z.; Brebner, J. L.; Leonelli, R.

    1995-12-01

    Polarized properties of both the singlet and triplet ground exciton states in the photoluminescence and transmission spectra of crystalline GaTe are explained based on the possible symmetry properties of the energy band edge of GaTe. Some experimental results about excited exciton states in GaTe are presented and discussed. The energy positions of exciton series in GaTe follow the three-dimensional direct allowed Wannier exciton formula just as in the the other III-VI layered compounds of GaSe and InSe. The nonthermalized, ``hot'' nature of excitons inside GaTe under higher optical excitation intensities is also discussed.

  17. Growth optimisation of the GaN layers and GaN/AlGaN heterojunctions on bulk GaN substrates using plasma-assisted molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Skierbiszewski, C.; Siekacz, M.; Feduniewicz, A.; Pastuszka, B.; Grzegory, I.; Leszczynski, M.; Porowski, S. [High Pressure Research Center, Polish Academy of Sciences, 01-142 Warsaw (Poland); Wasilewski, Z. [Institute for Microstructural Sciences, National Research Council, Ottawa (Canada)

    2004-01-01

    Influence of growth conditions in plasma assisted molecular beam epitaxy on quality of GaN layers and GaN/AlGaN heterojunctions is studied. The growth diagram for step-flow growth mode and different nitrogen flux is presented. The low defect density of bulk GaN substrates together with very low impurity background concentrations resulted in high electron mobility for GaN/AlGaN heterojunctions: 109,000 cm{sup 2}/Vs at 1.5 K, and 2500 cm{sup 2}/Vs at 295 K. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Heterojunction DDR THz IMPATT diodes based on AlxGa1-xN/GaN material system

    Science.gov (United States)

    Banerjee, Suranjana; Mitra, Monojit

    2015-06-01

    Simulation studies are made on the large-signal RF performance and avalanche noise properties of heterojunction double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on AlxGa1-xN/GaN material system designed to operate at 1.0 THz frequency. Two different heterojunction DDR structures such as n-Al0.4Ga0.6N/p-GaN and n-GaN/p-Al0.4Ga0.6N are proposed in this study. The large-signal output power, conversion efficiency and noise properties of the heterojunction DDR IMPATTs are compared with homojunction DDR IMPATT devices based on GaN and Al0.4Ga0.6N. The results show that the n-Al0.4Ga0.6N/p-GaN heterojunction DDR device not only surpasses the n-GaN/p-Al0.4Ga0.6N DDR device but also homojunction DDR IMPATTs based on GaN and Al0.4Ga0.6N as regards large-signal conversion efficiency, power output and avalanche noise performance at 1.0 THz.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-11-30

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

  20. Effect of structural properties on optical characteristics of InGaN/GaN nanocolumns fabricated by selective-area growth

    Science.gov (United States)

    Oto, Takao; Mizuno, Yutaro; Yanagihara, Ai; Ema, Kazuhiro; Kishino, Katsumi

    2017-04-01

    The effect of the structural properties on the optical characteristics was investigated for In0.3Ga0.7N nanocolumns (NCs) grown on GaN NCs as a function of GaN column diameter, D GaN. With increasing D GaN, the photoluminescence spectra changed from single-peak to double-peak emissions at the diameter D 0 where InGaN axial NCs change to InGaN–InGaN core–shell NCs. For the core–shell NCs, the volume recombination probabilities of the InGaN cores did not change with D GaN. Whereas the surface recombination probability of the InGaN cores exponentially decreased because of the spontaneous formation of InGaN shells for D GaN > D 0, it drastically increased for D GaN ≤ D 0.

  1. High temperature electron transport properties of AlGaN/GaN heterostructures with different Al-contents

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Electron transport properties in AlGaN/GaN heterostructures with different Al-contents have been in-vestigated from room temperature up to 680 K. The temperature dependencies of electron mobility have been systematically measured for the samples. The electron mobility at 680 K were measured as 154 and 182 cm2/V.s for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures,respectively. It was found that the electron mobility of low Al-content Al0.15Ga0.85N/GaN heterostructure was less than that of high Al-content Al0.40Ga0.60N/GaN heterostructure at high temperature of 680 K,which is different from that at room temperature. Detailed analysis showed that electron occupations in the first subband were 75% and 82% at 700 K for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures,respectively,and the two dimensional gas (2DEG) ratios in the whole electron system were 30% and near 60%,respectively. That indicated the 2DEG was better confined in the well,and was still dominant in the whole electron system for higher Al-content AlGaN/GaN heterostructure at 700 K,while lower one was not. Thus it had a higher electron mobility. So a higher Al-content AlGaN/GaN heterostructure is more suitable for high-temperature applications.

  2. Deep Green And Monolithic White LEDs Based On Combination Of Short-Period InGaN/GaN Superlattice And InGaN QWs

    Science.gov (United States)

    Tsatsulnikov, A. F.; Lundin, W. V.; Sakharov, A. V.; Zavarin, E. E.; Usov, S. O.; Nikolaev, A. E.; Kryzhanovskaya, N. V.; Chernyakov, A. E.; Zakgeim, A. L.; Cherkashin, N. A.; Hytch, M.

    2011-12-01

    This work presents the results of the investigation of approaches to the synthesis of the active region of LED with extended optical range. Combination of short-period InGaN/GaN superlattice and InGaN quantum well was applied to extend optical range of emission up to 560 nm. Monolithic white LED structures containing two blue and one green QWs separated by the short-period InGaN/GaN superlattice were grown with external quantum efficiency up to 5-6%.

  3. Carbon doping of GaAs NWs

    Science.gov (United States)

    Salehzadeh Einabad, Omid

    Nanowires (NWs) have been proposed and demonstrated as the building blocks for nanoscale electronic and photonic devices such as NW field effect transistors and NW solar cells which rely on doping and trap-free carrier transport. Controlled doping of NWs and a high degree of structure and morphology control are required for device applications. However, doping of III-V nanowires such as GaAs nanowires has not been reported extensively in the literature. Carbon is a well known p-type dopant in planar GaAs due to its low diffusivity and high solubility in bulk GaAs; however its use as an intentional dopant in NW growth has not yet been investigated. In this work we studied the carbon doping of GaAs nanowires using CBr4 as the dopant source. Gold nanoparticles (NP) at the tip ofthe NWs have been used to drive the NW growth. We show that carbon doping suppresses the migration ofthe gold NPs from the tip of the NWs. In addition, we show that the carbon doping of GaAs NWs is accompanied by an increase of the axial growth rate and decrease of the lateral growth rate ofthe NWs. Carbon-doped GaAs NWs, unlike the undoped ones which are highly tapered, are rod-like. The origin of the observed morphological changes is attributed to the carbon adsorbates on the sidewalls ofthe nanowires which suppress the lateral growth of the nanowires and increase the diffusion length of the gallium adatoms on the sidewalls. Stacking fault formation consisting of alternating regIOns of zincblende and wurtzite structures has been commonly observed in NWs grown along the (111) direction. In this work, based on transmission electron microscopy (TEM) analysis, we show that carbon doping ofGaAs NWs eliminates the stacking fault formation. Raman spectroscopy was used to investigate the effects of carbon doping on the vibrational properties of the carbon-doped GaAs nanowires. Carbon doping shows a strong impact on the intrinsic longitudinal and transverse optical (La and TO) modes of the Ga

  4. Magnetic field-dependent of binding energy in GaN/InGaN/GaN spherical QDQW nanoparticles

    Science.gov (United States)

    El Ghazi, Haddou; Jorio, Anouar; Zorkani, Izeddine

    2013-10-01

    Simultaneous study of magnetic field and impurity's position effects on the ground-state shallow-donor binding energy in GaN│InGaN│GaN (core│well│shell) spherical quantum dot-quantum well (SQDQW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated within the framework of the effective-mass approximation and an infinite deep potential describing the quantum confinement effect. A Ritz variational approach is used taking into account of the electron-impurity correlation and the magnetic field effect in the trial wave-function. It appears that the binding energy depends strongly on the external magnetic field, the impurity's position and the structure radius. It has been found that: (i) the magnetic field effect is more marked in large layer than in thin layer and (ii) it is more pronounced in the spherical layer center than in its extremities.

  5. MBE growth of high electron mobility 2DEGs in AlGaN/GaN heterostructures controlled by RHEED

    Directory of Open Access Journals (Sweden)

    D. Broxtermann

    2012-03-01

    Full Text Available We have grown 2DEG AlGaN/GaN heterostructures by molecular beam epitaxy (MBE with electron mobilities up to 21500 cm2V−1s−1 at 2 K. In-situ RHEED was applied to optimize different aspects of Ga-rich growth. This paper gives a compact overview of the experimental key aspects that significantly affect the low temperature electron mobility in AlGaN/GaN heterostructures. Growth at the transition towards Ga droplet formation produced the best results. A quantitative analysis of the magnetoresistance confirmes scattering at dislocations as the dominant scattering process at low temperature.

  6. Field-Induced Defect Morphology in Ni-gate AlGaN/GaN High Electron Mobility Transistors

    Science.gov (United States)

    2013-07-10

    mobility transistors. VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4813535] AlGaN/ GaN high electron mobility transistors ( HEMTs ) remain...interactions could enhance the reliability of AlGaN/ GaN HEMTs by circumventing the defect formation conditions and preventing device degradation...AlGaN/ GaN HEMTs used for this work were all grown on the same semi-insulating 6H-SiC substrate and received the same processing. An AlN nucleation layer

  7. Reverse Gate Bias-Induced Degradation of AlGaN/GaN High Electron Mobility Transistors

    Science.gov (United States)

    2010-09-23

    contributions from hot electrons and self-heating.13,19,20 In this article, we report on the degradation of AlGaN/ GaN HEMTs under step-stressing of...characteristic of the AlGaN/ GaN HEMTs before and after stress. FIG. 6. !Color online" PL spectra of stressed and unstressed devices. FIG. 7. EL images of stressed...high electric fields present under reverse bias stressing of AlGaN/ GaN HEMTs , the devices exhibit a five order of magnitude increase in gate current

  8. HgNO3 sensitivity of AlGaN/GaN field effect transistors functionalized with phytochelating peptides

    Science.gov (United States)

    Rohrbaugh, Nathaniel; Hernandez-Balderrama, Luis; Kaess, Felix; Kirste, Ronny; Collazo, Ramon; Ivanisevic, Albena

    2016-06-01

    This study examined the conductance sensitivity of AlGaN/GaN field effect transistors in response to varying Hg/HNO3 solutions. FET surfaces were covalently functionalized with phytochelatin-5 peptides in order to detect Hg in solution. Results showed a resilience of peptide-AlGaN/GaN bonds in the presence of strong HNO3 aliquots, with significant degradation in FET ID signal. However, devices showed strong and varied response to Hg concentrations of 1, 10, 100, and 1000 ppm. The gathered statistically significant results indicate that peptide terminated AlGaN/GaN devices are capable of differentiating between Hg solutions and demonstrate device sensitivity.

  9. Electrical and structural properties of GaN films and GaN/InGaN light-emitting diodes grown on porous GaN templates fabricated by combined electrochemical and photoelectrochemical etching

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Lee-Woon; Jeon, Dae-Woo [School of Advanced Materials Engineering and Research Center for Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Polyakov, A.Y.; Govorkov, A.V. [Institute of Rare Metals, B. Tolmachevsky, 5, Moscow 119017 (Russian Federation); Sokolov, V.N. [Department of Engineering and Ecological Geology, Moscow State University, Vorobyovygory, Moscow 119991 (Russian Federation); Smirnov, N.B. [Institute of Rare Metals, B. Tolmachevsky, 5, Moscow 119017 (Russian Federation); Cho, Han-Su; Yun, Jin-Hyeon [School of Advanced Materials Engineering and Research Center for Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Shcherbatchev, K.D. [National University of Science and Technology MISiS, Leninsky Ave. 4, Moscow 119049 (Russian Federation); Baek, Jong-Hyeob [LED R and D Division, Korea Photonics Technology Institute, Gwangju 500-779 (Korea, Republic of); Lee, In-Hwan, E-mail: ihlee@jbnu.ac.kr [School of Advanced Materials Engineering and Research Center for Advanced Materials Development, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

    2014-03-15

    Highlights: • Porous GaN template was prepared by electrochemical and photoelectrochemical etching scheme. • InGaN/GaN light-emitting diode (LED) structure was overgrown on the etched GaN template. • Overgrown GaN films and LEDs showed lower strain and lower density of surface defects. • The overgrown LED structures showed enhanced electroluminescence efficiency. -- Abstract: Porous GaN templates were prepared by combined electrochemical etching (ECE) and back-side photoelectrochemical etching (PECE), followed by the overgrowth of GaN films and InGaN/GaN multiple quantum well (MQW) light-emitting diode (LED) structures. Structural, luminescent, and electrical properties of the GaN and LED structures were studied and compared with the properties of structures grown under the same conditions on templates not subjected to ECE–PECE treatment. Overgrowth of LED structures on the ECE–PECE templates reduced strain, cracking, and micropits, leading to increased internal quantum efficiency and light extraction efficiency. This luminescence enhancement was observed in overgrown GaN films, but was more pronounced for InGaN/GaN LED structures due to suppression of piezoelectric polarization field in QWs.

  10. Defect studies in low-temperature-grown GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Bliss, D.E.

    1992-11-01

    High content of excess As is incorporated in GaAs grown by low-temperature molecular-beam-epitaxy (LTMBE). The excess As exists primarily as As antisite defects AsGa and a lesser extent of gallium vacancies V[sub Ga]. The neutral AsGa-related defects were measured by infrared absorption at 1[mu]m. Gallium vacancies, V[sub Ga], was investigated by slow positron annihilation. Dependence of defect contents on doping was studied by Si and Be dopants. No free carriers are generated by n-type or p-type doping up to 10[sup 19] cm[sup [minus]3] Si or Be. Raman data indicate Be occupies Ga substitutional sites but Si atom is not substitutional. Si induces more As[sub Ga] in the layer. As As[sub Ga] increases, photoquenchable As[sub Ga] decreases. Fraction of photoquenchable defects correlates to defects within 3 nearest neighbor separations disrupting the metastability. Annealing reduces neutral As[sub Ga] content around 500C, similar to irradiation damaged and plastically deformed Ga[sub As], as opposed to bulk grown GaAs in which As[sub Ga]-related defects are stable up to 1100C. The lower temperature defect removal is due to V[sub Ga] enhanced diffusion of As[sub Ga] to As precipitates. The supersaturated V[sub GA] and also decreases during annealing. Annealing kinetics for As[sub Ga]-related defects gives 2.0 [plus minus] 0.3 eV and 1.5 [plus minus] 0.3 eV migration enthalpies for the As[sub Ga] and V[sub Ga]. This represents the difference between Ga and As atoms hopping into the vacancy. The non-photoquenchable As[sub Ga]-related defects anneal with an activation energy of 1.1 [plus minus] 0.3eV. Be acceptors can be activated by 800C annealing. Temperature difference between defect annealing and Be activation formation of As[sub Ga]-Be[sub Ga] pairs. Si donors can only be partially activated.

  11. Defect studies in low-temperature-grown GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Bliss, David Emory [Univ. of California, Berkeley, CA (United States)

    1992-11-01

    High content of excess As is incorporated in GaAs grown by low-temperature molecular-beam-epitaxy (LTMBE). The excess As exists primarily as As antisite defects AsGa and a lesser extent of gallium vacancies VGa. The neutral AsGa-related defects were measured by infrared absorption at 1μm. Gallium vacancies, VGa, was investigated by slow positron annihilation. Dependence of defect contents on doping was studied by Si and Be dopants. No free carriers are generated by n-type or p-type doping up to 1019 cm-3 Si or Be. Raman data indicate Be occupies Ga substitutional sites but Si atom is not substitutional. Si induces more AsGa in the layer. As AsGa increases, photoquenchable AsGa decreases. Fraction of photoquenchable defects correlates to defects within 3 nearest neighbor separations disrupting the metastability. Annealing reduces neutral AsGa content around 500C, similar to irradiation damaged and plastically deformed GaAs, as opposed to bulk grown GaAs in which AsGa-related defects are stable up to 1100C. The lower temperature defect removal is due to VGa enhanced diffusion of AsGa to As precipitates. The supersaturated VGa and also decreases during annealing. Annealing kinetics for AsGa-related defects gives 2.0 ± 0.3 eV and 1.5 ± 0.3 eV migration enthalpies for the AsGa and VGa. This represents the difference between Ga and As atoms hopping into the vacancy. The non-photoquenchable AsGa-related defects anneal with an activation energy of 1.1 ± 0.3eV. Be acceptors can be activated by 800C annealing. Temperature difference between defect annealing and Be activation formation of AsGa-BeGa pairs. Si donors can only be partially activated.

  12. Two-dimensional electron and hole gases in GaN/AlGaN heterostructures; Zweidimensionale Elektronen- und Loechergase in GaN/AlGaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Link, A.

    2004-12-01

    The aim of this PhD thesis is to investigate the electronic properties of electron and hole gases in GaN/AlGaN heterostructures. Particularly, a deeper and broadened understanding of scattering mechanisms and transport properties is in the focus of this work. The main experimental techniques used for this purpose are the study of Shubnikov-de Haas (SdH) effect and Hall measurements at low temperatures. By means of these magnetotransport measurements, a series of GaN/AlGaN heterostructures with different Al content of the AlGaN barrier were investigated. Since the sheet carrier density of the 2DEG in these semiconductor structures is strongly dependent on the Al content (n{sub s}=2 x 10{sup 12}-10{sup 13} cm{sup -2}), the variation of transport parameters was determined as a function of sheet carrier concentration. First, from the temperature dependence of the SdH oscillations the effective transport mass was calculated. A Hall bar structure with an additional gate contact was used as an alternative to tune the carrier density of a 2DEG system independent of varying structural parametes such as Al content. Thus, the scattering mechanisms were investigated in the carrier density region between 3 x 10{sup 12} and 9.5 x 10{sup 12} cm{sup -2}. The transport properties of subband electrons were studied for a 2DEG system with two occupied subbands. (orig.)

  13. 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.)

  14. Quantum confinement in GaP nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Laurich, B.K.; Smith, D.C.; Healy, M.D.

    1994-06-01

    We have prepared GaP and GaAs nanoclusters from organometallic condensation reactions of E[Si(ChH{sub 3})3]3 (E = P, As) and GaCl{sub 3}. The size of the as synthesized clusters is 10 {Angstrom} to 15 {Angstrom}. Larger clusters of 20 {Angstrom} to 30 {Angstrom} size were obtained by thermal annealing of the as grown material. X-ray diffraction and transmission electron microscopy confirm the high crystalline quality. A lattice contraction of 6.7% could be seen for 10 {Angstrom} sized GaAs clusters. The clusters are nearly spherical in shape. Optical absorption spectra show a distinct line which can be assigned to the fundamental transition of the quantum confined electronic state. The measured blue shift, with respect to the GaP bulk absorption edge is 0.53 eV. As the cluster is smaller than the exciton radius, we can calculate the cluster size from this blue shift and obtain 20.2 {Angstrom}, consistent with the results from X-ray diffraction of 19.5 {Angstrom} for the same sample.

  15. Growth and characterisation of GaN

    CERN Document Server

    Li, T

    2002-01-01

    This thesis describes mainly the studies on growth mechanism of GaN in UHV-MOVPE process, and structural and optical properties of As-doped GaN films grown by PA-MBE. In a novel Thomas Swan growth chamber, we have grown GaN films on Si substrates using TEGa, plasma nitrogen and ammonia. Using a combination of in-situ optical reflectivity and mass spectrometry, we have investigated the parameters controlling the growth process of UHV-MOVPE. In particular we have used sup 1 sup 5 N in order to distinguish gas phase species containing N from those associated purely with metal-organics. We found the surface pyrolysis of TEGa is the rate limiting step, which is similar to GaAs grown by CBE. We also identify the parasitic reactions costing the active nitrogen from plasma, which in turn limits the growth rate. Using Philips X' pert MRD, we have investigated the structural properties of As-doped GaN epitaxial films on sapphire grown by PA-MBE including phase, lattice parameters and mosacity. We have also studied the ...

  16. Investigation of surface-plasmon coupled red light emitting InGaN/GaN multi-quantum well with Ag nanostructures coated on GaN surface

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yi; Liu, Bin, E-mail: bliu@nju.edu.cn, E-mail: rzhang@nju.edu.cn; Zhang, Rong, E-mail: bliu@nju.edu.cn, E-mail: rzhang@nju.edu.cn; Xie, Zili; Zhuang, Zhe; Dai, JiangPing; Tao, Tao; Zhi, Ting; Zhang, Guogang; Chen, Peng; Ren, Fangfang; Zhao, Hong; Zheng, Youdou [Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People' s Republic of China and Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093 (China)

    2015-04-21

    Surface-plasmon (SP) coupled red light emitting InGaN/GaN multiple quantum well (MQW) structure is fabricated and investigated. The centre wavelength of 5-period InGaN/GaN MQW structure is about 620 nm. The intensity of photoluminescence (PL) for InGaN QW with naked Ag nano-structures (NS) is only slightly increased due to the oxidation of Ag NS as compared to that for the InGaN QW. However, InGaN QW with Ag NS/SiO{sub 2} structure can evidently enhance the emission efficiency due to the elimination of surface oxide layer of Ag NS. With increasing the laser excitation power, the PL intensity is enhanced by 25%–53% as compared to that for the SiO{sub 2} coating InGaN QW. The steady-state electric field distribution obtained by the three-dimensional finite-difference time-domain method is different for both structures. The proportion of the field distributed in the Ag NS for the GaN/Ag NS/SiO{sub 2} structure is smaller as compared to that for the GaN/naked Ag NS structure. As a result, the energy loss of localized SP modes for the GaN/naked Ag NS structure will be larger due to the absorption of Ag layer.

  17. High-efficiency of AlInGaN/Al(In)GaN-delta AlGaN quantum wells for deep-ultraviolet emission

    Science.gov (United States)

    Saidi, Hosni; Ridene, Said

    2016-10-01

    Band structure and optical gain properties of AlInGaN/AlInGaN-delta-AlGaN quantum wells for deep-ultraviolet light emitting and lasers diodes with wavelength λ ∼229 nm and TE-polarized optical gain peak intensity ∼1.7 times larger than the conventional AlInN-delta-GaN was proposed and investigated in this work. The active region is made up of 20 Å staggered Al0.89In0.03Ga0.08N/Al0.8In 0.01Ga0.19N layers with a 3 Å Al0.46Ga0.54N delta layer. The use of the quaternary AlInGaN well layer permits the independent control of the band gap and the lattice parameter, so that the internal electric field induced by polarizations can be reduced and interband transition energy increases. Therefore, we can predict that the optical performance of the AlInGaN-delta-AlGaN is more convenient for an emission in the deep-ultraviolet than that of the conventional AlInN-delta-GaN-based quantum wells.

  18. Comparative study of defect levels in GaInNAs, GaNAsSb, and GaInNAsSb for high-efficiency solar cells

    Science.gov (United States)

    Polojärvi, Ville; Aho, Arto; Tukiainen, Antti; Schramm, Andreas; Guina, Mircea

    2016-03-01

    Background doping and defect levels in GaInNAs, GaNAsSb, and GaInNAsSb solar cells with 1 eV band-gap are reported. Localized point defect induced traps were observed showing broadest defect distribution in GaInNAsSb. Incorporation of Sb reduced the unintentional p-type background doping by an order of magnitude, but increased the capture cross sections of deep levels by three orders of magnitude. The thermal activation energy of the dominating hole trap was increased from 350 meV for GaInNAs to 560 meV for GaNAsSb. Annealing of GaNAsSb solar cells improved the open circuit voltage from 280 mV to 415 mV, owing to the reduction in trap density.

  19. Investigation of room-temperature wafer bonded GaInP/GaAs/InGaAsP triple-junction solar cells

    Science.gov (United States)

    Yang, Wen-xian; Dai, Pan; Ji, Lian; Tan, Ming; Wu, Yuan-yuan; Uchida, Shiro; Lu, Shu-long; Yang, Hui

    2016-12-01

    We report on the fabrication of III-V compound semiconductor multi-junction solar cells using the room-temperature wafer bonding technique. GaInP/GaAs dual-junction solar cells on GaAs substrate and InGaAsP single junction solar cell on InP substrate were separately grown by all-solid state molecular beam epitaxy (MBE). The two cells were then bonded to a triple-junction solar cell at room-temperature. A conversion efficiency of 30.3% of GaInP/GaAs/InGaAsP wafer-bonded solar cell was obtained at 1-sun condition under the AM1.5G solar simulator. The result suggests that the room-temperature wafer bonding technique and MBE technique have a great potential to improve the performance of multi-junction solar cell.

  20. Strain-compensated (Ga,In)N/(Al,Ga)N/GaN multiple quantum wells for improved yellow/amber light emission

    Energy Technology Data Exchange (ETDEWEB)

    Lekhal, K.; Damilano, B., E-mail: bd@crhea.cnrs.fr; De Mierry, P.; Vennéguès, P. [CRHEA-CNRS, Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Valbonne 06560 (France); Ngo, H. T.; Rosales, D.; Gil, B. [Laboratoire Charles Coulomb, CNRS-INP-UMR 5221, Université Montpellier 2, F-34095 Montpellier (France); Hussain, S. [CRHEA-CNRS, Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Valbonne 06560 (France); Université de Nice Sophia Antipolis, Parc Valrose, 28 av. Valrose, 06108 Nice cedex 2 (France)

    2015-04-06

    Yellow/amber (570–600 nm) emitting In{sub x}Ga{sub 1−x}N/Al{sub y}Ga{sub 1−y}N/GaN multiple quantum wells (QWs) have been grown by metal organic chemical vapor deposition on GaN-on- sapphire templates. When the (Al,Ga)N thickness of the barrier increases, the room temperature photoluminescence is red-shifted while its yield increases. This is attributed to an increase of the QW internal electric field and an improvement of the material quality due to the compensation of the compressive strain of the In{sub x}Ga{sub 1−x}N QWs by the Al{sub y}Ga{sub 1−y}N layers, respectively.

  1. Thermal etching rate of GaN during MOCVD growth interruption in hydrogen and ammonia ambient determined by AlGaN/GaN superlattice structures

    Science.gov (United States)

    Zhang, Feng; Ikeda, Masao; Zhang, Shuming; Liu, Jianping; Tian, Aiqin; Wen, Pengyan; Cheng, Yang; Yang, Hui

    2017-10-01

    Thermal etching effect of GaN during growth interruption in the metalorganic chemical vapor deposition reactor was investigated in this paper. The thermal etching rate was determined by growing a series of AlGaN/GaN superlattice structures with fixed GaN growth temperature at 735 °C and various AlGaN growth temperature changing from 900 °C to 1007 °C. It was observed that the GaN layer was etched off during the growth interruption when the growth temperature ramped up to AlGaN growth temperature. The etching thickness was determined by high resolution X-ray diffractometer and the etching rate was deduced accordingly. An activation energy of 2.53 eV was obtained for the thermal etching process.

  2. Characteristics of Ga-Rich Cu(In, Ga)Se2 Solar Cells Grown on Ga-Doped ZnO Back Contact.

    Science.gov (United States)

    Sun, Qian; Kim, Kyoung-Bo; Jeon, Chan-Wook

    2016-05-01

    Wide bandgap Cu(In,Ga)Se2 (CIGS) thin films were deposited on Ga-rich Ga:ZnO (GZO) or MoN/GZO by single-stage co-evaporation. CIGS/TCO interface phases, such as resistive n-type Ga2O3, which are likely to have formed during the high temperature growth of Ga-rich CIGS, can deteriorate the solar cell performance. Although some Ga accumulation was observed in both of the CIGS/GZO and CIGS/MoN/GZO interfaces formed at 520 degrees C, the Ga oxide layer was absent. On the other hand, their current-voltage characteristics showed strong roll-over behavior regardless of the MoN diffusion barrier. The strong Schottky barrier formation at the CLGS/GZO junction due to the low work function of GZO, was attributed to current blocking at a high forward bias.

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

    Science.gov (United States)

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

    2016-11-01

    A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

  4. InGaN/GaN quantum well improved by in situ SiN{sub x} pretreatment of GaN template

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Demeng; Wu, Zhengyuan; Fang, Zhilai [Department of Physics, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Xiamen University (China)

    2016-12-15

    In situ SiN{sub x} pretreatment was employed to modify the growth behavior and optical properties of InGaN/GaN quantum wells (QWs). With moderate SiN{sub x} pretreatment surface smoothness of InGaN/GaN QWs was improved and attributed to enhanced layer growth by Ga surfactant effect. Significant increase of photoluminescence peak intensity and relatively uniform and bright cathodoluminescence images were observed, which were attributed to the improvement in crystalline quality and strain reduction for the InGaN/GaN QWs with moderate SiN{sub x} pretreatment. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  5. Gate length scaling effect on high-electron mobility transistors devices using AlGaN/GaN and AlInN/AlN/GaN heterostructures.

    Science.gov (United States)

    Liao, S Y; Lu, C C; Chang, T; Huang, C F; Cheng, C H; Chang, L B

    2014-08-01

    Compared to AlGaN/GaN HEMT with 0.15 μm T-gate length, the AlInN/AlN/GaN one exhibits much higher current density and transconductance of 1558 mA/mm at Vd = 2 V and 330 mS/mm, respectively. The high extrinsic ft and fmax of 82 GHz and 70 GHz are extracted from AlInN/AlN/GaN HEMT. Besides, we find that the transconductance roll-off is significant in AlGaN/GaN, but largely improved in AlInN/AlN/GaN HEMT, suggesting that the high carrier density and lattice-matched epitaxial heterostructure is important to reach both large RF output power and high operation frequency, especially for an aggressively gate length scaling.

  6. Dependence of ohmic contact properties on AlGaN layer thickness for AlGaN/GaN high-electron-mobility transistors

    Science.gov (United States)

    Takei, Yusuke; Tsutsui, Kazuo; Saito, Wataru; Kakushima, Kuniyuki; Wakabayashi, Hitoshi; Iwai, Hiroshi

    2016-04-01

    The dependence of ohmic contact resistance on the AlGaN layer thickness was evaluated for AlGaN/GaN high-electron-mobility transistor (HEMT) structures. Mo/Al/Ti contacts were formed on AlGaN layers with various thicknesses. The observed resistance characteristics are discussed on the basis of a model in which the overall contact resistance is composed of a series of three resistance components. Different dependences on the AlGaN layer thickness was observed after annealing at low temperatures (800-850 °C) and at high temperatures (900-950 °C). It was determined that lowering the resistance at the metal/AlGaN interface and that of the AlGaN layer is important for obtaining low-resistance ohmic contacts.

  7. Electron field emission from nanostructured surfaces of GaN and AlGaN

    Energy Technology Data Exchange (ETDEWEB)

    Evtukh, A.; Litovchenko, V.; Semenenko, M.; Gorbanyuk, T.; Grygoriev, A. [Institute of Semiconductor Physics, 41 prospekt Nauki, 03028 Kiev (Ukraine); Yilmazoglu, O.; Hartnagel, H.; Pavlidis, D. [Technische Universitaet Darmstadt, Institut fuer Hochfrequenztechnik, Merckstr. 25, 64283 Darmstadt (Germany)

    2008-07-01

    The possibility of high frequency electromagnetic wave generation by field emission based devices has great interest. The wide bandgap materials GaN and AlGaN are very promising for these applications due to low electron affinity and the existence of satellite valleys in conduction band. The results of investigations of the peculiarities of electron field emission from nanostructured surfaces of GaN and AlGaN are presented. Multilayer GaN and AlGaN structures with various levels of layer doping on sapphire and bulk GaN substrates were used as initial wafers. The surface of the upper layers was nanostructured by photoelectrochemical etching in water solution of KOH. Intensive electron field emission into vacuum was observed and explained by low electron affinity and electric field enhancement on surface nanowires. A decrease of the slope in the Fowler-Nordheim characteristics was revealed. The changing slope suggests a lowering of effective work function. It is caused by electron heating and transfer into an upper satellite valley with lower electron affinity. A theory was developed for the observed phenomena and interpretation of results. It is based on electron intervalley transition upon heating and on energy band reconstruction of the surface of the nanowires due to quantum size-confinement effect. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Photoluminescence Probing of Complex H2O Adsorption on InGaN/GaN Nanowires.

    Science.gov (United States)

    Maier, Konrad; Helwig, Andreas; Müller, Gerhard; Hille, Pascal; Teubert, Jörg; Eickhoff, Martin

    2017-02-08

    We demonstrate that the complex adsorption behavior of H2O on InGaN/GaN nanowire arrays is directly revealed by their ambient-dependent photoluminescence properties. Under low-humidity, ambient-temperature, and low-excitation-light conditions, H2O adsorbates cause a quenching of the photoluminescence. In contrast, for high humidity levels, elevated temperature, and high excitation intensity, H2O adsorbates act as efficient photoluminescence enhancers. We show that this behavior, which can only be detected due to the low operation temperature of the InGaN/GaN nanowires, can be explained on the basis of single H2O adsorbates forming surface recombination centers and multiple H2O adsorbates forming surface passivation layers. Reversible creation of such passivation layers is induced by the photoelectrochemical splitting of adsorbed water molecules and by the interaction of reactive H3O(+) and OH(-) ions with photoactivated InGaN surfaces. Due to electronic coupling of adsorbing molecules with photoactivated surfaces, InGaN/GaN nanowires act as sensitive nanooptical probes for the analysis of photoelectrochemical surface processes.

  9. Investigation of InGaN/GaN quantum wells for polariton laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Glauser, M.; Rossbach, G.; Cosendey, G.; Levrat, J.; Cobet, M.; Carlin, J.F.; Butte, R.; Grandjean, N. [Institute of Condensed Matter Physics, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne (Switzerland); Besbas, J.; Gallart, M.; Gilliot, P. [IPCMS-DON Unite mixte CNRS-ULP (UMR 7504), 67034 Strasbourg Cedex 2 (France)

    2012-05-15

    III-nitride based microcavities (MCs) appear as one of the most promising candidates for the realization of room temperature (RT) polariton laser diodes. The present work focuses on the properties of low In content InGaN/GaN multiple quantum wells (MQWs) in terms of inhomogeneous broadening, exciton localization energy, and plastic strain relaxation. For a small number of such QWs, an inhomogeneous line broadening of 41 meV is reported, which is compatible with strong coupling regime requirements. By contrast when considering an InGaN/GaN MQW set, a high density of defects is reported, which is ascribed to plastic strain relaxation. From the evolution of the inhomogeneous line broadening as a function of the number of QWs probed by microphotoluminescence measurements, it is concluded that for the realization of polariton light-emitting devices the QW number should not go beyond 30 for MC structures grown on FS-GaN substrate relying on InGaN/GaN QWs with an indium content {proportional_to}12-15% and thicknesses of 1.5-2 nm/3 nm for the wells and the barriers, respectively. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. A gate current 1/f noise model for GaN/AlGaN HEMTs

    Science.gov (United States)

    Yu'an, Liu; Yiqi, Zhuang

    2014-12-01

    This work presents a theoretical and experimental study on the gate current 1/f noise in AlGaN/GaN HEMTs. Based on the carrier number fluctuation in the two-dimensional electron gas channel of AlGaN/GaN HEMTs, a gate current 1/f noise model containing a trap-assisted tunneling current and a space charge limited current is built. The simulation results are in good agreement with the experiment. Experiments show that, if Vg Vx (critical gate voltage of dielectric relaxation), gate current 1/f noise comes from the superimposition of trap-assisted tunneling RTS (random telegraph noise), while Vg > Vx, gate current 1/f noise comes from not only the trap-assisted tunneling RTS, but also the space charge limited current RTS. This indicates that the gate current 1/f noise of the GaN-based HEMTs device is sensitive to the interaction of defects and the piezoelectric relaxation. It provides a useful characterization tool for deeper information about the defects and their evolution in AlGaN/GaN HEMTs.

  11. Fabrication and characterization of graphene/AlGaN/GaN ultraviolet Schottky photodetector

    Science.gov (United States)

    Kumar, M.; Jeong, H.; Polat, K.; Okyay, A. K.; Lee, D.

    2016-07-01

    We report on the fabrication and characterization of a Schottky ultraviolet graphene/AlGaN/GaN photodetector (PD). The fabricated device clearly exhibits rectification behaviour, indicating that the Schottky barrier is formed between the AlGaN and the mechanically transferred graphene. The Schottky parameters are evaluated using an equivalent circuit with two diodes connected back-to-back in series. The PD shows a low dark current of 4.77  ×  10-12 A at a bias voltage of  -2.5 V. The room temperature current-voltage (I-V) measurements of the graphene/AlGaN/GaN Schottky PD exhibit a large photo-to-dark contrast ratio of more than four orders of magnitude. Furthermore, the device shows peak responsivity at a wavelength of 350 nm, corresponding to GaN band edge and a small hump at 300 nm associated to the AlGaN band edge. In addition, we examine the behaviour of Schottky PDs with responsivities of 0.56 and 0.079 A W-1 at 300 and 350 nm, respectively, at room temperature.

  12. Simulation of Nonpolar p-GaN/i-N/n-GaN Solar Cells

    Directory of Open Access Journals (Sweden)

    Ming-Jer Jeng

    2012-01-01

    Full Text Available It is well known that nitride-based devices suffer the polarization effects. A promising way to overcome the polarization effects is growth in a direction perpendicular to the c-axis (nonpolar direction. Nonpolar devices do not suffer polarization charge, and then they have a chance to achieve the high solar efficiency. The understanding of the solar performance of non-polar InGaN-based solar cells will be interesting. For a pin non-polar solar cell with GaN p- and n-cladding layers, the conduction band offset (or barrier height, between an intrinsic layer and n-GaN layer is an important issue correlating to the efficiency and fill factor. The efficiency and fill factor will be seriously degraded due to sufficiently high barrier height. To reduce a high barrier height, some graded layers with an energy bandgap between the energy bandgap of n-GaN and InxGa1−xN intrinsic layer can be inserted to the interface of n-GaN and InxGa1-xN layers. From simulation, it indicates that the insertion of graded layer is an effective method to lower energy barrier when there exists a high energy band offset in non-polar nitride devices.

  13. Microstructure of GaAs/AlAs/GaAs with and without oxidation

    CERN Document Server

    Wang Yong; Wang Wen Chong; Liu Cui Xiu; Chen Xiang Ming; Mai Zhen Hong; Zheng Wen Li; Jia Quan Jie; Jiang Xiao Ming

    2002-01-01

    The Changes of compositions and microstructures of GaAs/AlAS/GaAs trilayer before and after oxidation were investigated. GaAs/Al sub 2 O sub 3 /GaAs thin film was obtained from GaAs/AlAs/GaAs by lateral oxidation and its microstructures were investigated by use of X-ray small angle reflectivity and high angle diffraction. The results show that before oxidation there exists an even transition layer with the thickness of 110 Angstrom between the AlAs layer and the upper GaAs layer. The AlAs layer was separated into two layers, one is of 40 Angstrom thickness and the other 1050 Angstrom. The average atomic density of the thin AlAs layer is less than that of the thick AlAs layer. After lateral oxidation, AlAs was oxidized into Al sub 2 O sub 3 , and the thickness and roughness of the transition layer mentioned above decrease

  14. Functionalization of AlGaN/GaN heterostructures with TFAAD

    Energy Technology Data Exchange (ETDEWEB)

    Schwarz, Stefan Udo [Institute of Microsystem Technology (IMTEK), University of Freiburg, Georges-Koehler-Allee 106, 79110 Freiburg (Germany); Cimalla, Volker; Nebel, Christoph; Ambacher, Oliver [Fraunhofer Institute for Applied Solid State Physics, Tullastrasse 72, 79108 Freiburg (Germany)

    2010-07-01

    AlGaN/GaN high electron mobility transistors (HEMTs) show great promise for the realization of sensors for biomolecular, pharmaceutical and medical purposes. The high sensitivity and the stability in biological solutions are great advantages of this principle. The transduction is based on the AlGaN/GaN heterostructure. Charges on its surface influence the electron density in the 2-dimensional electron gas (2DEG) near the interface of the heterostructure. For a specific sensor, biological recognition methods shall be used. Therefore biomolecules need to be covalently linked to the semiconductor. The surface must be functionalized with a single layer of molecules that form covalent bonds to the surface and present functional groups for the connection with the biomolecule. In this work we investigate the functionalization of AlGaN/GaN heterostructures with 10-Trifluoroacetamiddec-1-ene (TFAAD), a molecule that can bond to GaN in a photochemical reaction and has a protected Amino group for the further procedure. The focus is on the influence of the illumination spectrum and surface pretreatments on the reaction kinetics and the resulting layer morphology with respect to the designated application.

  15. Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

    Science.gov (United States)

    Pérez-Tomás, A; Catalàn, G; Fontserè, A; Iglesias, V; Chen, H; Gammon, P M; Jennings, M R; Thomas, M; Fisher, C A; Sharma, Y K; Placidi, M; Chmielowska, M; Chenot, S; Porti, M; Nafría, M; Cordier, Y

    2015-03-20

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

  16. AlGaN/GaN based field effect transistors for terahertz detection and imaging

    Science.gov (United States)

    Sakowicz, M.; Lifshits, M. B.; Klimenko, O. A.; Coquillat, D.; Dyakonova, N.; Teppe, F.; Gaquière, C.; Poisson, M. A.; Delage, S.; Knap, W.

    2012-03-01

    AlGaN/GaN based FETs have great potential as sensitive and fast operating detectors because of their material advantages such as high breakdown voltage, high electron mobility, and high saturation velocity. These advantages could be exploited for resonant and non-resonant terahertz detection. We have designed, fabricated, and characterized AlGaN/GaN based FETs as single pixel terahertz detectors. This work focuses on non-resonant detection and imaging using GaN field plate FETs. To evaluate their performances as terahertz detectors, we have measured the responsivity as a function of gate voltage, the azimuthal angle between the terahertz electric field, the source-to-drain direction, and the temperature. A simple analytical model of the response is developed. It is based on plasma density perturbation in the transistor channel by the incoming terahertz radiation. The model shows how the non-resonant detection signal is related to static (dc) transistor characteristics and it fully describes the experimental results on the non-resonant sub-terahertz detection by the AlGaN/GaN based FETs. The imaging performances are evaluated by scanning objects in transmission mode and an example of application of terahertz imaging as new non-destructive technique for the quality control of materials is given. Results indicate that these FETs can be considered as promising devices for terahertz detection and imaging applications.

  17. High-resistivity GaN buffer templates and their optimization for GaN-based HFETs

    Science.gov (United States)

    Hubbard, S. M.; Zhao, G.; Pavlidis, D.; Sutton, W.; Cho, E.

    2005-11-01

    High-resistance (HR) GaN templates for AlGaN/GaN heterojunction field effect transistor (HFET) applications were grown using organometallic vapor phase epitaxy. The GaN sheet resistance was tuned using final nucleation layer (NL) annealing temperature and NL thickness. Using an annealing temperature of 1033 °C and NL thickness of 26 nm, GaN with sheet resistance of 10 10 Ω/sq was achieved, comparable to that of Fe-doped GaN. Material characterization results show that the high-resistance GaN is achieved due to compensating acceptor levels that may be introduced through edge-type threading dislocations. Optimization of annealing temperature and NL thickness provided a means to maximize GaN sheet resistance without significantly degrading material quality. In situ laser reflectance was used to correlate the NL properties to sheet resistance and material quality, providing a figure of merit for expected sheet resistance. AlGaN/GaN HFET layers grown using HR GaN templates with R of 10 10 Ω/sq gave surface and interface roughness of 14 and 7 Å, respectively. The 2DEG Hall mobility and sheet charge of HFETs grown using HR GaN templates was comparable to similar layers grown using unintentionally doped (UID) GaN templates.

  18. Effect of ammonification temperature on the formation of coaxial GaN/Ga2O3 nanowires

    Science.gov (United States)

    Kumar, Mukesh; Sarau, George; Heilmann, Martin; Christiansen, Silke; Kumar, Vikram; Singh, R.

    2017-01-01

    The effect of ammonification temperature on the formation of coaxial GaN/Ga2O3 nanowires from β-Ga2O3 nanowires is reported in this work. High quality wurtzite GaN material showing a single c-plane phase is achieved from β-Ga2O3 nanowires having monoclinic crystal structure at a high ammonification temperature of 1050 °C. Lower ammonification temperatures such as 900 °C are also adequate for achieving coaxial GaN/Ga2O3 nanowire heterostructures, and the degree of GaN phase can be adjusted by varying the ammonification temperature. The crystalline quality of GaN/Ga2O3 nanowires improves with increasing the ammonification temperature. Resonant Raman spectra of GaN/Ga2O3 nanowires show Raman progression through multiple longitudinal-optical-phonon modes with overtones of up to second order. The development and improvement of the emission peak toward the near band edge of GaN at different ammonification temperatures were investigated using cathodoluminescence and photoluminescence characterization.

  19. The structures, stability, and photoelectron spectroscopy of GaPX - (X = C, Si, Ge; O, S; P and Ga) clusters

    Science.gov (United States)

    Zhang, Congjie; Jia, Wenhong

    2006-08-01

    The equilibrium geometries and vibrational frequencies of GaPX - and GaPX (X = C, Si, Ge; O, S; P and Ga) have been studied by hybrid B3LYP functional at cc-PVTZ and aug-cc-PVTZ levels. The results predict that the most stable structure of GaPC - is linear while the others are trigonal. As for GaPX (X = C, Si, Ge; O, S; P and Ga), the ground structures of GaPC and GaPO are linear while the others are trigonal. The adiabatic electron affinities (AEAs) and vertical detachment energies (VDEs) of GaPX - are calculated at B3LYP/aug-cc-PVTZ level. And the order of the AEAs and VDEs of GaPX - are C < O < Ge ≈ Si < P < S < Ga and C < Ge ≈ Si < P < O < S < Ga, respectively. GaPC exhibits the lowest adiabatic electron affinities of all the clusters studied, indicating a particularly stable neutral species.

  20. 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.

  1. Synthetic Strategies and Applications of GaN Nanowires

    Directory of Open Access Journals (Sweden)

    Guoquan Suo

    2014-01-01

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

  2. Disorder effects in Ga(AsBi)

    Energy Technology Data Exchange (ETDEWEB)

    Imhof, Sebastian; Thraenhardt, Angela [Technische Universitaet Chemnitz (Germany); Chernikov, Alexej; Chatterjee, Sangam; Koch, Stephan W. [Philipps-Universitaet Marburg (Germany); Lu, Xianfeng; Johnson, Shane [Arizona State University (United States); Beaton, Dan [University of British Columbia (Canada); Tiedje, Thomas [University of Victoria (Canada); Rubel, Oleg [Lakehead University and Thunder-Bay Regional Research Institute (Canada)

    2010-07-01

    The incorporation of Bi into GaAs reduces the band gap by as much as 60-80 meV per percent Bi. Thus a wide wavelength range in the near and middle infrared region can be reached and Ga(AsBi) is a serious candidate for many applications e.g. diode lasers. The photoluminesence of the present Ga(AsBi) samples show an S-shape and the PL linewidth has a maximum at intermediate temperatures. These are typical indications of disorder effects on a very large energy scale. We describe the disorder effects using a kinetic Monte-Carlo simulation. In order to characterize the disorder effects we use experimental time-integrated and time-resolved data and compare these to our theoretical results.

  3. Endogenous gibberellins in Arabidopsis thaliana and possible steps blocked in the biosynthetic pathways of the semidwarf ga4 and ga5 mutants

    Energy Technology Data Exchange (ETDEWEB)

    Talon, M. Zeevaart, J.A.D. (Michigan State Univ., East Lansing (USA)); Koornneef, M. (Agricultural Univ., (Netherlands))

    1990-10-01

    Twenty gibberellins (GAs) have been identified in extracts from shoots of the Landsberg erecta line of Arabidopsis thaliana by full-scan gas chromatography-mass spectrometry and Kovats retention indices. Eight of them are members of the early-13-hydroxylation pathway (GA{sub 53}, GA{sub 44}, GA{sub 19}, GA{sub 17}, GA{sub 20}, GA{sub 1}, GA{sub 29}, and GA{sub 8}), six are members of the early-3-hydroxylation pathway (GA{sub 37}, GA{sub 27}, GA{sub 36}, GA{sub 13}, GA{sub 4}, and GA{sub 34}), and the remaining six are members of the non-3,13-hydroxylation pathway (GA{sub 12}, GA{sub 15}, GA{sub 24}, GA{sub 25}, GA{sub 9}, and GFA{sub 51}). Seven of these GAs were quantified in the Landsberg erecta line of Arabidopsis and in the semidwarf ga4 and ga5 mutants by gas chromatography-selected ion monitoring (SIM) using internal standards. The relative levels of the remaining 13 GAs were compared by the use of ion intensities only. The growth-response data, as well as the accumulation of GA{sub 9} in the ga4 mutant, indicate that GA{sub 9} is not active in Arabidopsis, but it must be 3{beta}-hydroxytlated to GA{sub 4} to become bioactive. It is concluded that the reduced levels of the 3{beta}-hydroxy-GAs, GA{sub 1} and GA{sub 4}, are the cause of the semidwarf growth habit of both mutants.

  4. Gallium Nitride (GaN) High Power Electronics (FY11)

    Science.gov (United States)

    2012-01-01

    for HPE GaN high electron mobility transistors ( HEMTs ) compared to SiC metal-oxide-semiconductor field effect transistors (MOSFETs). Although a few...Figure 16. Asymmetric rocking curve for an HVPE film grown on an HVPE substrate. ............19 Figure 17. Schematic of a GaN /AlGaN HEMT structure grown...frequency (RF) HEMTs . These considerable investments can be leveraged for GaN HPE. Some people are concerned about the relative scarcity of gallium

  5. 微波功率AlGaN/GaN HEMT的研究进展%Progress in the Development of Microwave Power AlGaN/GaN's HEMT

    Institute of Scientific and Technical Information of China (English)

    马香柏; 郝跃; 张进城

    2006-01-01

    文章论述了AlGaN/GaN高电子迁移率晶体管(HEMT)在微波功率领域应用的优势,详细介绍了微波功率AlGaN/GaN HEMT的工艺进展以及器件的直流和频率特性,评述了其最新进展及今后发展方向.

  6. 68Ga-Based Radiopharmaceuticals: Production and Application Relationship

    OpenAIRE

    Irina Velikyan

    2015-01-01

    The contribution of 68Ga to the promotion and expansion of clinical research and routine positron emission tomography (PET) for earlier better diagnostics and individualized medicine is considerable. The potential applications of 68Ga-comprising imaging agents include targeted, pre-targeted and non-targeted imaging. This review discusses the key aspects of the production of 68Ga and 68Ga-based radiopharmaceuticals in the light of the impact of regulatory requirements and endpoint pre-clinical...

  7. Synthesis, Characterisation and Application of 68Ga-labelled Macromolecules

    OpenAIRE

    Velikyan, Irina

    2005-01-01

    The positron emitting radionuclide 68Ga (T1/2 = 68 min) might become of practical interest for clinical positron emission tomography (PET). The metallic cation, 68Ga(III), is suitable for complexation with chelators, either naked or conjugated with biological macromolecules. Such labelling procedures require pure and concentrated preparations of 68Ga(III), which cannot be sufficiently fulfilled by the presently available 68Ge/68Ga generator eluate. This thesis presents methods to increase the...

  8. Unconventional superconductivity in PuRhGa{sub 5}: Ga NMR/NQR study

    Energy Technology Data Exchange (ETDEWEB)

    Sakai, H. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)]. E-mail: sakai.hironori@jaea.go.jp; Tokunaga, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Fujimoto, T. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Kambe, S. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Walstedt, R.E. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Yasuoka, H. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Aoki, D. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Homma, Y. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamamoto, E. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Nakamura, A. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Nakajima, K. [Department of Nuclear Energy System, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Arai, Y. [Department of Nuclear Energy System, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Matsuda, T.D. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Haga, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Onuki, Y. [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

    2006-05-01

    {sup 69,71}Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa{sub 5} with T{sub c}{approx}9K. The spin-lattice relaxation rate 1/T{sub 1} reveals that PuRhGa{sub 5} is an unconventional superconductor having an anisotropic superconducting gap. Moreover, Korringa behavior (1/T{sub 1}T=const.) is observed in the normal state below {approx}30K. This result suggests that the superconductivity sets in after the formation of a Fermi liquid state in this compound.

  9. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.; Jancu, J.-M.; Even, J.; Durand, O. [Université Européenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes, 35708 Rennes (France); Nestoklon, M. O. [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Pereira da Silva, K. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Departamento de Física, Universidade Federal do Ceará, P.O. Box 6030, Fortaleza–CE, 60455-970 (Brazil); Alonso, M. I. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Goñi, A. R. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); ICREA, Passeig Lluís Companys 23, 08010 Barcelona (Spain); Turban, P. [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Université de Rennes 1, F-35042 Rennes Cedex (France)

    2014-01-06

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

  10. InGaAs/GaAs quantum dot interdiffiusion induced by cap layer overgrowth

    Energy Technology Data Exchange (ETDEWEB)

    Jasinski, J.; Babinski, A.; Czeczott, M.; Bozek, R.

    2000-06-28

    The effect of thermal treatment during and after growth of InGaAs/GaAs quantum dot (QD) structures was studied. Transmission electron microscopy and atomic force microscopy confirmed the presence of interacting QDs, as was expected from analysis of temperature dependence of QD photoluminescence (PL) peak. The results indicate that the effect of post-growth annealing can be similar to the effect of elevated temperature of capping layer growth. Both, these thermal treatments can lead to a similar In and Ga interdiffiusion resulting in a similar blue-shift of QD PL peak.

  11. Ripening of single-layer InGaAs islands on GaAs (001)

    Institute of Scientific and Technical Information of China (English)

    Liu Ke; Zhou Qing; Zhou Xun; Guo Xiang; Luo Zi-Jiang; Wang Ji-Hong; Hu Ming-Zhe

    2013-01-01

    The present paper discusses our investigation of InGaAs surface morphology annealed for different lengths of time.After annealing for 15 rmin,the ripening of InGaAs islands is completed.The real space scanning tunneling microscopy (STM) images show the evolution of InGaAs surface morphology.A half-terrace diffusion theoretical model based on thermodynamic theory is proposed to estimate the annealing time for obtaining flat morphology.The annealing time calculated by the proposed theory is in agreement with the experimental results.

  12. Impact of UV/ozone surface treatment on AlGaN/GaN HEMTs

    Institute of Scientific and Technical Information of China (English)

    Yuan Tingting; Liu Xinyu; Zheng Yingkui; Li Chengzhan; Wei Ke; Liu Guoguo

    2009-01-01

    Surface treatment plays an important role in the process of making high performance AIGaN/GaN HEMTs. A clean surface is critical for enhancing device performance and long-term reliability. By experiment-ing with different surface treatment methods, we find that using UV/ozone treatment significantly influences the electrical properties of Ohmic contacts and Schottky contacts. According to these experimental phenomena and X-ray photoelectron spectroscopy surface analysis results, the effect of the UV/ozone treatment and the reason that it influences the Ohmic/Schottky contact characteristics of A1GaN/GaN HEMTs is investigated.

  13. 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.

  14. Simulation and design of AlGaAs/InGaAs CCDs based on PHEMT technology

    OpenAIRE

    Tan, HT; Hunter, IC; Snowden, CM

    2007-01-01

    This paper describes the modeling, design and fabrication of quarter-micron double delta doped AlGaAs/InGaAs charge coupled devices whose epitaxial layers and geometry were based around the device structure of commercial pHEMTs. A quasi-two-dimensional physical model has been developed to investigate the properties of this novel 2 dimensional electron gas charge coupled device (2DEG-CCD). This physical model allows the characteristics of the InGaAs transport channel as well as the DC characte...

  15. Refractive index of TlGaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ohnishi, K.; Shiba, M.; Yamakage, M.; Kajikawa, Y. [Department of Electric and Control Systems Engineering, Interdisciplinary Faculty of Science and Engineering, Shimane University (Japan)

    2008-07-01

    Refractive index has been determined from reflectance measurements at 77-300 K for Tl{sub x}Ga{sub 1-x}As samples with x{<=}0.077 prepared by low-temperature molecular-beam epitaxy. A very high refractive index of around 4.5 at room temperature in the transparent wavelength region has been revealed for Tl{sub x}Ga{sub 1-x}As with x=0.077. The temperature coefficient of the refractive index was found to increase with Tl content. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Dielectric function and electro-optical properties of (Al,Ga)N/GaN-heterostructures; Dielektrische Funktion und elektrooptische Eigenschaften von (Al,Ga)N/GaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Buchheim, Carsten

    2010-04-23

    In this work extensive investigations on nitride semiconductors by optical spectroscopy are presented. The ordinary and the extraordinary component of the dielectric function of GaN in the spectral range from 1.2 to 9.8 eV is shown for the first time. It is demonstrated, that the transparent spectral range is clearly influenced by higher energetic critical points of the band structure. The optical selection rules for GaN and AlN are verified considering the actual strain state. The change of the valence band ordering of AlN in comparison to GaN is proven and the crystal field splitting is estimated for AlN. The ordinary dielectric function of AlGaN is determined for different Al contents. The data are used for developing an analytical model, which includes excitonic effects and bowings. It allows the calculation of the dielectric function for arbitrary alloy compositions. (GaN/)AlGaN/GaN heterostructures are investigated by spectroscopic ellipsometry as well as by photoreflectance and electroreflectance. The optical data yields the electric field strengths of the individual layers to determine the density of the two-dimensional carrier gases at the heterointerfaces with high accuracy. The surface potential is calculated from the combination of experiments and Schroedinger-Poisson calculations. Its dependency on the Al content is quantified. For the special case of thick cap layers the coexistence of electron and hole gases in one sample is experimentally proven for the first time. Several interband transitions between quantized states in AlN/GaN superlattices are observed by electroreflectance. The comparison to quantum mechanical calculations demonstrates the influence of strain and electrical fields (quantum confined Stark effect). For both the ratio of the thicknesses of quantum wells and barriers is crucial. From the dielectric function of the superlattices it becomes obvious, that quantum size effects are not only important for the vicinity of the bandgap, but

  17. 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.

  18. Metamagnetism in Ce(Ga,Al)2

    Indian Academy of Sciences (India)

    K G Suresh; S Radha; A K Nigam

    2002-05-01

    Effect of Al substitution on the magnetic properties of Ce(Ga1-Al)2 ( = 0, 0.1 and 0.5) system has been studied. The magnetic state of CeGa2 is found to be FM with a C of 8 K, whereas the compounds with =0.1 and 0.5 are AFM and possess N of about 9 K. These two compounds undergo metamagnetic transition and the critical fields are about 1.2 T and 0.5 T, respectively at 2 K. These variations are explained on the basis of helical spin structure in these compounds.

  19. Circularly polarized electroluminescence of light-emitting InGaAs/GaAs (III, Mn)V diodes on the basis of structures with a tunneling barrier

    Energy Technology Data Exchange (ETDEWEB)

    Malysheva, E. I., E-mail: malysheva@phys.unn.ru; Dorokhin, M. V.; Ved’, M. V.; Kudrin, A. V.; Zdoroveishchev, A. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation)

    2015-11-15

    The comparative investigation of circularly polarized electroluminescence in Zener diodes based on InGaAs/n-GaAs/n{sup +}-GaAs/GaMnAs and InGaAs/n-GaAs/n{sup +}-GaAs/GaMnSb is carried out. It is established that the circularly polarized electroluminescence is associated with the spin injection of electrons from a ferromagnetic semiconductor layer. The luminescence parameters are determined by the properties of these layers. It is shown that the ferromagnetic properties of the GaMnSb layer allow us to obtain circularly polarized emission at room temperature from InGaAs/n-GaAs/n{sup +}-GaAs/GaMnSb heterostructures.

  20. A Ga2O·11Al2O3 nanonet prepared by interfacial reaction growth approach and its application in fabricating GaN nanowires

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    A Ga2O·11Al2O3 nanonet was synthesized by using Ga2O3 powder as the precursor to generate Ga2O vapor in H2 atmosphere which further reacted with Al2O3 at 730 °C to form Ga2O·11Al2O3 at the interfaces of a porous anodic aluminum oxide (AAO) template. The prepared Ga2O·11Al2O3 nanonet then served as a Ga2O-stablizing reservoir to fabricate single crystal GaN nanowires. The residual Ga2O3 powder at the surface of the produced Ga2O·11Al2O3 nanonet and the metallic Ga or Ga2O from the Ga2O·11Al2O3 decomposition reacted with ammonia to yield GaN nanowires at 780 °C. The reaction mechanisms were investigated.

  1. Stress distribution of GaN layer grown on micro-pillar patterned GaN templates

    Science.gov (United States)

    Nagarajan, S.; Svensk, O.; Ali, M.; Naresh-Kumar, G.; Trager-Cowan, C.; Suihkonen, S.; Sopanen, M.; Lipsanen, H.

    2013-07-01

    High-resolution Raman mapping of the stress distribution in an etched GaN micro-pillar template and a 5 μm thick GaN layer grown on a micro-pillar patterned GaN template is investigated. Raman mapping of the E2 (high) phonon shows differences in stress between the coalescing boundary, the top surface of the pillar region and around the GaN micro-pillar. Increased compressive stress is observed at the coalescing boundary of two adjacent GaN micro-pillars, when compared to the laterally grown GaN regions. The electron channeling contrast image reveals the reduction of threading dislocation density in the GaN layer grown on the micro-pillar patterned GaN template.

  2. Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

    Institute of Scientific and Technical Information of China (English)

    Cheng Zhi-Qun; Hu Sha; Liu Jun; Zhang Qi-Jun

    2011-01-01

    In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor (HEMT) with an artificial neural network (ANN). The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping (neuro-SM) technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model.

  3. InGaN/GaN multiple quantum well solar cells with an enhanced open-circuit voltage

    Institute of Scientific and Technical Information of China (English)

    Zhang Xiao-Bin; Wang Xiao-Liang; Xiao Hong-Ling; Yang Cui-Bai; Hou Qi-Feng; Yin Hai-Bo; Chen Hong; Wang Zhan-Guo

    2011-01-01

    In this paper, InGaN/GaN multiple quantum well solar cells (MQWSCs) with an In content of 0.15 are fabricated and studied. The short-circuit density, fill factor and open-circuit voltage (Voc) of the device are 0.7 mA/cm2, 0.40 and 2.22 V, respectively. The results exhibit a significant enhancement of Voc compared with those of InGaN-based hetero and homojunction cells. This enhancement indicates that the InGaN/GaN MQWSC offers an effective way for increasing Voc of an In-rich InxGa1-xN solar cell. The device exhibits an external quantum efficiency (EQE) of 36% (7%) at 388 nm (430 nm). The photovoltaic performance of the device can be improved by optimizing the structure of the InGaN/GaN multiple quantum well.

  4. Observation of spin-polarized photoconductivity in (Ga,Mn)As/GaAs heterojunction without magnetic field

    Science.gov (United States)

    Wu, Qing; Liu, Yu; Wang, Hailong; Li, Yuan; Huang, Wei; Zhao, Jianhua; Chen, Yonghai

    2017-01-01

    In the absent of magnetic field, we have observed the anisotropic spin polarization degree of photoconduction (SPD-PC) in (Ga,Mn)As/GaAs heterojunction. We think three kinds of mechanisms contribute to the magnetic related signal, (i) (Ga,Mn)As self-producing due to the valence band polarization, (ii) unequal intensity of left and right circularly polarized light reaching to GaAs layer to excite unequal spin polarized carriers in GaAs layer, and (iii) (Ga,Mn)As as the spin filter layer for spin transport from GaAs to (Ga,Mn)As. Different from the previous experiments, the influence coming from the Zeeman splitting induced by an external magnetic field can be avoided here. While temperature dependence experiment indicates that the SPD-PC is mixed with the magnetic uncorrelated signals, which may come from current induced spin polarization. PMID:28084437

  5. Growth and Characterization of Modulation-Doped AlxGa1-xN/GaN Heterostructures

    Institute of Scientific and Technical Information of China (English)

    沈波; 张荣; 施毅; 郑有炓; T. Someya; Y. Arakawa

    2001-01-01

    The modulation-doped Al0.22Ga0.78N/GaN heterostructures with different Al0.22Ga0.78N barrier thicknesses were grown by means of metal-organic chemical vapour deposition. The Al0.22Ga0. 78N layer still has pseudomorphic growth when its thickness is 53nm. The mobility of the two-dimensional electron gas (2DEG) at the heterointerfaces is much higher than that of the electrons in GaN films at both 300 and 77K. The dramatic decrease of the 2DEG mobility in an Al0.22Ga0.78N/GaN heterostructure corresponds to the partial relaxation of the Al0.22 Ga0.78N barrier.

  6. Current transport mechanism in graphene/AlGaN/GaN heterostructures with various Al mole fractions

    Science.gov (United States)

    Pandit, Bhishma; Seo, Tae Hoon; Ryu, Beo Deul; Cho, Jaehee

    2016-06-01

    The current transport mechanism of graphene formed on AlxGa1-xN/GaN heterostructures with various Al mole fractions (x = 0.15, 0.20, 0.30, and 0.40) is investigated. The current-voltage measurement from graphene to AlGaN/GaN shows an excellent rectifying property. The extracted Schottky barrier height of the graphene/AlGaN/GaN contacts increases with the Al mole fraction in AlGaN. However, the current transport mechanism deviates from the Schottky-Mott theory owing to the deterioration of AlGaN crystal quality at high Al mole fractions confirmed by reverse leakage current measurement.

  7. Differences between GaAs/GaInP and GaAs/AlInP interfaces grown by movpe revealed by depth profiling and angle-resolved X-ray photoelectron spectroscopies

    Energy Technology Data Exchange (ETDEWEB)

    López-Escalante, M.C., E-mail: mclopez@uma.es [Nanotech Unit, Laboratorio de Materiales y Superficies, Departamento de Ingeniería Química, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga (Spain); Gabás, M. [The Nanotech Unit, Depto. de Física Aplicada I, Andalucía Tech, Universidad de Málaga, Campus de Teatinos s/n, 29071 Málaga Spain (Spain); García, I.; Barrigón, E.; Rey-Stolle, I.; Algora, C. [Instituto de Energía Solar, Universidad Politécnica de Madrid, Avda. Complutense 30, 28040 Madrid Spain (Spain); Palanco, S.; Ramos-Barrado, J.R. [The Nanotech Unit, Depto. de Física Aplicada I, Andalucía Tech, Universidad de Málaga, Campus de Teatinos s/n, 29071 Málaga Spain (Spain)

    2016-01-01

    Graphical abstract: - Highlights: • GaAs, AlInP and GaInP epi-layers grown in a MOVPE facility. • GaAs/GaInP and GaAs/AlInP interfaces studied through the combination of angle resolved and depth profile X-ray photoelectros spectroscopies. • GaAs/GaInP interface shows no features appart from GaAs, GaInP and mixed GaInAs or GaInAsP phases. • GaAs/AlInP interface shows traces of an anomalous P environment, probably due to P-P clusters. - Abstract: GaAs/GaInP and GaAs/AlInP interfaces have been studied using photoelectron spectroscopy tools. The combination of depth profile through Ar{sup +} sputtering and angle resolved X-ray photoelectron spectroscopy provides reliable information on the evolution of the interface chemistry. Measurement artifacts related to each particular technique can be ruled out on the basis of the results obtained with the other technique. GaAs/GaInP interface spreads out over a shorter length than GaAs/AlInP interface. The former could include the presence of the quaternary GaInAsP in addition to the nominal GaAs and GaInP layers. On the contrary, the GaAs/AlInP interface exhibits a higher degree of compound mixture. Namely, traces of P atoms in a chemical environment different to the usual AlInP coordination were found at the top of the GaAs/AlInP interface, as well as mixed phases like AlInP, GaInAsP or AlGaInAsP, located at the interface.

  8. MOCVD growth and characterization of near-surface InGaN/GaN single quantum wells for non-radiative coupling of optical excitations

    DEFF Research Database (Denmark)

    Svensk, O.; Suihkonen, S.; Sintonen, S.

    2012-01-01

    with InGaN/GaN superlattice structures instead of a single InGaN underneath layer. Time‐resolved photoluminescence measurements of samples with different GaN capping thicknesses show that room temperature photoluminescence decay time increases with decreasing GaN capping thickness until surface states...

  9. Photoluminescence in Er-implanted AlGaN/GaN superlattices and GaN epilayers

    Energy Technology Data Exchange (ETDEWEB)

    Sobolev, N.A.; Emel' yanov, A.M.; Sakharov, V.I.; Serenkov, I.T.; Shek, E.I.; Besyul' kin, A.I.; Lundin, W.V.; Shmidt, N.M.; Usikov, A.S.; Zavarin, E.E

    2003-12-31

    Photoluminescence (PL), structural and electrophysical properties of Al{sub 0.26}Ga{sub 0.74}N/GaN superlattices grown by metal-organic chemical vapor deposition, implanted by erbium (Er) ions with 1 MeV energy and 1x10{sup 15} cm{sup -2} dose as well as annealed at 700-1100 deg. C for 4 min in argon have been investigated. A comparison of the properties of the superlattices with that of the GaN epilayers grown, implanted and annealed at the same conditions is also given. The Er-related peak with a maximum at {lambda}{approx}1.54 {mu}m dominated and the defect-related emission band at {lambda}{approx}1-1.4 {mu}m was observed in the PL spectra of both types of samples. When the measurement temperature was increased from 80 to 300 K, practically the same temperature quenching of the Er-related intensity was observed in the superlattices and GaN epilayers implanted and annealed at the same conditions. The Er-related intensity at 300 K increased monotonically as the annealing temperature was raised from 700 to 1000 deg. C, but the intensity in the superlattices was higher by several times than that in the epilayers. A decrease of the Er-related PL intensity in the superlattice after annealing at 1100 deg. C is associated with the formation of non-radiative recombination centers.

  10. Field and thermionic-field transport in GaAs/AlGaAs/GaAs heterojunction barriers

    Energy Technology Data Exchange (ETDEWEB)

    Morgan, D.V.; Porch, A.; Krishna, R. [School of Engineering, Cardiff University, Cardiff, CF24 3AA (United Kingdom)

    2007-02-15

    This paper considers the transport of conduction band electrons as a result of tunneling through a triangular potential barrier fabricated within a GaAs/Al{sub x}Ga{sub 1-x}As/GaAs heterojunction. The triangular barrier was formed by the composition grading of the Al{sub x}Ga{sub 1-x}As region from x=0 to x=0.3, which forms part of a cathode emitter in a commercial Gunn diode. The experimental data for the current-voltage characteristics obtained for a range of temperatures from 77 to 273 K were used to test a simplified thermionic-field model. Good agreement has been obtained between theory and experiment, thus confirming the usefulness of this simple model for device evaluation. The comparison of the data over the experimental temperature range shows that the thermionic-field emission observed at 273 K gives way to field emission at 77 K. This is a result of the removal of the more energetic electrons in the conduction band at lower temperatures. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Dynamics of Pre-3 Ga Crust-Mantle Evolution

    Science.gov (United States)

    Patchett, P. J.; Chase, C. G.; Vervoort, J. D.

    2004-05-01

    During 3.0 to 2.7 Ga, the Earth's crust underwent a non-uniformitarian change from a pre-3.0 Ga environment where long-term preservation of cratons was rare and difficult, to post-2.7 Ga conditions where cratons were established and new continental crust generation took place largely at craton margins. Many models view the Earth's surface during pre-3 Ga time as broadly equivalent to the post 2.7 Ga regime. Any such uniformitarian or gradual evolution cannot explain the conundrum that only a tiny amount of pre-3 Ga crust is preserved today coupled with the fact that very little pre-3 Ga crust was incorporated into the large amount of new craton that came into existence during 3.0-2.7 Ga. If large volumes of pre-3 Ga continental crust existed, it disappeared either just prior to 3 Ga, or during 3.0-2.7 Ga. To explain sudden appearance of surviving but dominantly juvenile continental crust in a model where continents were large prior to 3 Ga, it would be necessary either that pre-3 Ga continent was recycled into the mantle at sites systematically different from those where new 3.0-2.7 Ga crust was made, or that widespread continent destruction preceded the 3.0-2.7 Ga crustal genesis. From expected mantle overturn in response to the heat budget, it is likely that most pre-3 Ga crust was both more mafic and shorter-lived than after 3 Ga. Although Nd and Hf ratios for pre-3 Ga rocks are uncertain due to polymetamorphism, it appears that depleted upper mantle was widespread by 2.7 Ga, even pre-3 Ga. Depletion may have been largely achieved by formation, subduction and storage of mafic crust for periods of 200-500 m.y. The rapid change to large surviving continents during 3.0-2.7 Ga was due to declining mantle overturn, and particularly to development of the ability to maintain subduction in one zone of the earth's surface for the time needed to allow evolution to felsic igneous rock compositions. In as much as storage of subducted slabs is probably occurring today, and

  12. Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High Electron Mobility Transistors

    Science.gov (United States)

    2016-06-07

    heterostructures. In summary, we have synthesized dislocation-free single- crystal GaN/AlN/Al0 25Ga0 75N nanowire heterostructures with well-controlled...were synthesized on a c-plane Al2O3 substrate in a MOCVD reactor (Thomas Swan Scientific Equipment Ltd.) using trimethylgallium, trimethylaluminium...and ammonia as Ga, Al, and N sources, respectively. We deposited 0.01 M nickel nitrate solution as the nickel nanocluster precursor. GaN cores were

  13. Investigation on quality of cubic GaN/GaAs (100) by double-crystal X-ray diffraction

    Institute of Scientific and Technical Information of China (English)

    徐大鹏; 王玉田; 杨辉; 郑联喜; 李建斌; 段俐宏; 吴荣汉

    1999-01-01

    Cubic GaN was grown on GaAs (100) by low pressure metal organic chemical vapor deposition (MOCVD). X-ray diffraction, scanning electron microscope (SEM) and photoluminescence (PL) spectra were performed to characterize the quality of the GaN film. The PL spectra of cubic GaN thin films being thicker than 1.5 μm were reported. Triple-crystal diffraction to analyze orientation distributions and strain of the thin films was also demonstrated.

  14. Correlated terahertz acoustic and electromagnetic emission in dynamically screened InGaN/GaN quantum wells

    OpenAIRE

    Van Capel, P.J.S.; Turchinovich, D.; Porte, H.P.; Lahmann, S.; Rossow, U.; Dijkhuis, J.I.

    2011-01-01

    We investigate acoustic and electromagnetic emission from optically excited strained piezoelectric In0.2Ga0.8N/GaN multiple quantum wells (MQWs), using optical pump-probe spectroscopy, time-resolved Brillouin scattering, and THz emission spectroscopy. A direct comparison of detected acoustic signals and THz electromagnetic radiation signals demonstrates that transient strain generation in InGaN/GaN MQWs is correlated with electromagnetic THz generation, and both types of emission find their o...

  15. Correlated terahertz acoustic and electromagnetic emission in dynamically screened InGaN/GaN quantum wells

    OpenAIRE

    Van Capel, P.J.S.; Turchinovich, Dmitry; Porte, Henrik; Lahmann, S.; Rossow, U.; Hangleiter, A.; Dijkhuis, J.I.

    2011-01-01

    We investigate acoustic and electromagnetic emission from optically excited strained piezoelectric In0.2Ga0.8N/GaN multiple quantum wells (MQWs), using optical pump-probe spectroscopy, time-resolved Brillouin scattering, and THz emission spectroscopy. A direct comparison of detected acoustic signals and THz electromagnetic radiation signals demonstrates that transient strain generation in InGaN/GaN MQWs is correlatedwith electromagnetic THz generation, and both types of emission find their or...

  16. First demonstration of InGaP/InAlGaP based orange laser emitting at 608 nm

    KAUST Repository

    Mohammed, Abdul Majid

    2015-06-26

    The fabrication of orange-emitting semiconductor laser on interdiffused InGaP/InAlGaP structure is reported. The lasers lased at 22°C at a wavelength as short as 608 nm with threshold current density of 3.4 KAcm −2 and a maximum output power of ∼46 mW. This is the shortest wavelength electrically pumped semiconductor laser emission from the InGaP/InAlGaP structure.

  17. Effect of annealing on the structure and optical properties of InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Leosson, Kristjan; Birkedal, Dan

    2002-01-01

    We report the effect of annealing on self-assembled InGaAs/GaAs quantum dots, as investigated by means of resonant photoluminescence (PL), resonant Raman scattering, polarization dependent PL, and high resolution X-ray diffraction.......We report the effect of annealing on self-assembled InGaAs/GaAs quantum dots, as investigated by means of resonant photoluminescence (PL), resonant Raman scattering, polarization dependent PL, and high resolution X-ray diffraction....

  18. Selective area growth of In(Ga)N/GaN nanocolumns by molecular beam epitaxy on GaN-buffered Si(111): from ultraviolet to infrared emission.

    Science.gov (United States)

    Albert, S; Bengoechea-Encabo, A; Sánchez-García, M A; Kong, X; Trampert, A; Calleja, E

    2013-05-03

    Selective area growth of In(Ga)N/GaN nanocolumns was performed on GaN-buffered Si(111) substrates by plasma-assisted molecular beam epitaxy. Undoped and Si-doped GaN buffer layers were first grown on Si(111) substrates, showing photoluminescence excitonic emission without traces of other low energy contributions, in particular, the yellow band. The GaN buffer surface roughness (between 10 and 14 nm, the rms value in a 10 × 10 μm(2) area) was low enough to allow the fabrication of a thin (7 nm thick) well defined Ti nanohole mask, for the selective area growth. Ordered In(Ga)N/GaN nanocolumns emitting from the ultraviolet (3.2 eV) to the infrared (0.78 eV) were obtained. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting at a given wavelength could be substantially improved by tuning the In/Ga and total III/N ratios. An estimated internal quantum efficiency of 36% was derived from photoluminescence data for green emitting nanocolumns.

  19. Impact of strain relaxation of AlGaN barrier layer on the performance of high Al-content AlGaN/GaN HEMT

    Institute of Scientific and Technical Information of China (English)

    YANG Yan; HAO Yue; ZHANG Jincheng; WANG Chong; FENG Qian

    2006-01-01

    The effects of strain relaxation of AlGaN barrier layer on the conduction band profile, electron concentration and two-dimensional gas (2DEG) sheet charge density in a high Al-content AlGaN/GaN high electron mobility transistor (HEMT) are calculated by self-consistently solving Poisson's and Schr(o)dinger's equations. The effect of strain relaxation on dc I-V characteristics of AlxGa1-xN/GaN HEMT is obtained by developing a nonlinear charge-control model that describes the accurate relation of 2DEG sheet charge density and gate voltage. The model predicts a highest 2DEG sheet charge density of 2.42×1013 cm-2 and maximum saturation current of 2482.8 mA/mm at a gate bias of 2 V for 0.7 μm Al0.50Ga0.50N/GaN HEMT with strain relaxation r =0 and 1.49×1013 cm-2 and 1149.7 mA/mm with strain relaxation r =1. The comparison between simulations and physical measurements shows a good agreement. Results show that the effect of strain relaxation must be considered when analyzing the characteristics of high Al-content AlGaN/GaN HEMT theoretically, and the performance of the devices is improved by decreasing the strain relaxation of AlGaN barrier layer.

  20. A comparative QSPR study on aqueous solubility of polycyclic aromatic hydrocarbons by GA-SVM, GA-RBFNN and GA-PLS

    Institute of Scientific and Technical Information of China (English)

    Jun QI; Jia WEI; Changhong SUN; Tao PAN

    2011-01-01

    A novel method to develop quantitative structure-property relationship(QSPR)models of organic contaminants was proposed based on genetic algorithm (GA)and support vector machine(SVM).GA was used to perform the variable selection and SVM was used to construct QSPR models.In this study,GA-SVM was applied to develop the QSPR model for aqueous solubility (Sw,mol·L-1)of polycyclic aromatic hydrocarbons (PAHs).The R2(0.98)of the model developed by GASVM indicated a good predictive precision for 1g Sw values of PAHs.According to leave-one-out(LOO)cross validation,the results of GA-SVM were compared with those of genetic algorithm-radial based function neural network(GA-RBFNN)and genetic algorithm-partial leastsquares(GA-PLS)regression.The comparisons showed that the cross validation correlation coefficient(Q2LOO =0.92)and root mean square error of LOO cross validation (RMSELoo =0.49)of GA-SVM were the highest and lowest,respectively,which illustrated that GA-SVM was more suitable to develop QSPR model for the lg Sw values of PAHs than GA-RBFNN and GA-PLS.

  1. MOVPE growth of Ga(PBi) on GaP and GaP on Si with Bi fractions up to 8%

    Science.gov (United States)

    Nattermann, L.; Beyer, A.; Ludewig, P.; Hepp, T.; Sterzer, E.; Volz, K.

    2017-04-01

    Dilute bismide containing materials can play an important role in addressing the issue of finding new highly efficient lasers for telecommunications as well as sensing applications. In the last several years a growing body of literature has emerged, particularly on the growth of Ga(AsBi). However, the metal organic vapor phase epitaxy growth of Ga(AsBi) with high amounts of Bi, which are necessary to overcome Auger recombination and reach telecommunications wavelengths, still remains a challenge. Ga(PBi) could be a promising alternative, but has not been deposited with significant amounts of Bi so far. A second argument for Ga(PBi) is that it could be grown on GaP, which was already deposited on Si. A number of researchers have reported theoretical calculations on the band structure of Ga(PBi), but experimental results are still lacking. In this work we present the first Ga(PBi) structures, grown by metal organic vapor phase epitaxy on GaP and on GaP on Si. By careful characterization with high resolution X-ray diffraction, atomic force microscopy, secondary ion mass spectrometry and scanning transmission electron microscopy, we will show that we have realized high quality Ga(PBi) with Bi fractions over 8%.

  2. New Al0.25Ga0.75N/GaN high electron mobility transistor with partial etched AlGaN layer

    Science.gov (United States)

    Yuan, Song; Duan, Baoxing; Yuan, Xiaoning; Cao, Zhen; Guo, Haijun; Yang, Yintang

    2016-05-01

    In this letter, a new Al0.25Ga0.75N/GaN high electron mobility transistor (HEMT) with the AlGaN layer is partial etched is reported for the first time. The two-dimensional electron gas (2DEG) density in the HEMTs is changed by partially etching the AlGaN layer. A new electric field peak is introduced along the interface between the AlGaN layer and the GaN buffer by the electric field modulation effect. The high electric field near the gate in the proposed Al0.25Ga0.75N/GaN HEMT is effectively decreased, which makes the surface electric field more uniform. Compared with the conventional structure, the breakdown voltage can be improved by 58% for the proposed Al0.25Ga0.75N/GaN HEMT and the current collapse can be reduced resulting from the more uniform surface electric field.

  3. Analysis of the AlGaN/GaN vertical bulk current on Si, sapphire, and free-standing GaN substrates

    Energy Technology Data Exchange (ETDEWEB)

    Perez-Tomas, A.; Fontsere, A.; Llobet, J. [IMB-CNM-CSIC, Campus UAB, 08193 Bellaterra, Barcelona, CAT (Spain); Placidi, M. [IREC, Jardins Dones de Negre 1, 08930 Sant Adria de Besos, Barcelona (Spain); Rennesson, S.; Chenot, S.; Moreno, J. C.; Cordier, Y. [CRHEA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); Baron, N. [CRHEA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); PICOGIGA International, Pl M. Rebuffat, Courtaboeuf 7, 91140 Villejust (France)

    2013-05-07

    The vertical bulk (drain-bulk) current (I{sub db}) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental I{sub db} (25-300 Degree-Sign C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (E{sub a}), the (soft or destructive) vertical breakdown voltage (V{sub B}), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (E{sub a} = 0.35 eV at T = 25-300 Degree-Sign C; V{sub B} = 840 V), GaN-on-sapphire follows the trap assisted mechanism (E{sub a} = 2.5 eV at T > 265 Degree-Sign C; V{sub B} > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (E{sub a} = 0.35 eV at T > 150 Degree-Sign C; V{sub B} = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored.

  4. Selective area growth of In(Ga)N/GaN nanocolumns by molecular beam epitaxy on GaN-buffered Si(111): from ultraviolet to infrared emission

    Science.gov (United States)

    Albert, S.; Bengoechea-Encabo, A.; Sánchez-García, M. A.; Kong, X.; Trampert, A.; Calleja, E.

    2013-05-01

    Selective area growth of In(Ga)N/GaN nanocolumns was performed on GaN-buffered Si(111) substrates by plasma-assisted molecular beam epitaxy. Undoped and Si-doped GaN buffer layers were first grown on Si(111) substrates, showing photoluminescence excitonic emission without traces of other low energy contributions, in particular, the yellow band. The GaN buffer surface roughness (between 10 and 14 nm, the rms value in a 10 × 10 μm2 area) was low enough to allow the fabrication of a thin (7 nm thick) well defined Ti nanohole mask, for the selective area growth. Ordered In(Ga)N/GaN nanocolumns emitting from the ultraviolet (3.2 eV) to the infrared (0.78 eV) were obtained. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting at a given wavelength could be substantially improved by tuning the In/Ga and total III/N ratios. An estimated internal quantum efficiency of 36% was derived from photoluminescence data for green emitting nanocolumns.

  5. Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

    Science.gov (United States)

    Hu, Hongpo; Zhou, Shengjun; Liu, Xingtong; Gao, Yilin; Gui, Chengqun; Liu, Sheng

    2017-03-01

    We report on the demonstration of GaN-based ultraviolet light-emitting diodes (UV LEDs) emitting at 375 nm grown on patterned sapphire substrate (PSS) with in-situ low temperature GaN/AlGaN nucleation layers (NLs) and ex-situ sputtered AlN NL. The threading dislocation (TD) densities in GaN-based UV LEDs with GaN/AlGaN/sputtered AlN NLs were determined by high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM), which revealed that the TD density in UV LED with AlGaN NL was the highest, whereas that in UV LED with sputtered AlN NL was the lowest. The light output power (LOP) of UV LED with AlGaN NL was 18.2% higher than that of UV LED with GaN NL owing to a decrease in the absorption of 375 nm UV light in the AlGaN NL with a larger bandgap. Using a sputtered AlN NL instead of the AlGaN NL, the LOP of UV LED was further enhanced by 11.3%, which is attributed to reduced TD density in InGaN/AlInGaN active region. In the sputtered AlN thickness range of 10-25 nm, the LOP of UV LED with 15-nm-thick sputtered AlN NL was the highest, revealing that optimum thickness of the sputtered AlN NL is around 15 nm.

  6. 阶梯AlGaN外延新型Al0.25Ga0.75N/GaN HEMTs击穿特性分析%Breakdown voltage analysis for the new Al0.25 Ga0.75N/GaN HEMTs with the step AlGaN layers

    Institute of Scientific and Technical Information of China (English)

    段宝兴; 杨银堂

    2014-01-01

    In order to optimize the surface electric field of AlGaN/GaN high electron mobility transistors (HEMTs), a novel AlGaN/GaN HEMT has been grown with a step AlGaN layer, made for the first time as far as we know, to improve the breakdown voltage. The discipline of the 2DEG concentration varying with the thickness of the AlGaN epitaxy layer has been applied to the new AlGaN/GaN HEMTs with AlGaN/GaN heterostructure. By thinning the AlGaN layer near the gate edge, the 2DEG concentration in the channel is made to form the low concentration region near the gate edge. New electric field peak has appeared at the corner of the step AlGaN layer. The high electric field has been decreased effectively due to the emergence of new electric field peak; this optimizes the surface electric field of the new AlGaN/GaN HEMTs. Then the breakdown voltage is improved to 640 V in the new AlGaN/GaN HEMTs with the step AlGaN layer as compared with 446 V for the conventional structure. In order to let the breakdown curve consistent with the test results, a certain concentration of the acceptor-like traps is added to the GaN buffer to capture the leaking current coming from the source electrode. Simulation results verify the causes for doping acceptor type ions to the GaN buffer, given by foreign researchers. The breakdown curves have been obtained which are consistent with the test results in this paper.%为了优化AlGaN/GaN HEMTs器件表面电场,提高击穿电压,本文首次提出了一种新型阶梯Al-GaN/GaN HEMTs结构.新结构利用AlGaN/GaN异质结形成的2DEG浓度随外延AlGaN层厚度降低而减小的规律,通过减薄靠近栅边缘外延的AlGaN层,使沟道2DEG浓度分区,形成栅边缘低浓度2DEG区,低的2DEG使阶梯AlGaN交界出现新的电场峰,新电场峰的出现有效降低了栅边缘的高峰电场,优化了AlGaN/GaN HEMTs器件的表面电场分布,使器件击穿电压从传统结构的446 V,提高到新结构的640 V.为了获得与实际测试结

  7. The influence of MOVPE process parameters on the buffer resistivity used in AlGaN/GaN heterostructures

    Science.gov (United States)

    Szymański, T.; Wośko, M.; Paszkiewicz, B.; Paszkiewicz, R.

    2013-07-01

    The influence of growth conditions on properties of high temperature GaN (HT-GaN) buffer used in AlGaN/GaN HEMT heterostructures was studied. Many various factors are presumed to have significant impact on the concluding properties of HT-GaN buffer. In this paper the nucleation layer growth time as well as temperature during high temperature GaN layer growth was selected as a factors alleged to cause variation in final GaN layer properties. The study was designed to show step by step improvement of HT-GaN buffer with consecutive changes of particular parameters. Electrical properties of the AlGaN/GaN heterostructures were determined using impedance spectroscopy method performed with HP 4192A impedance meter equipped in two contact mercury probe. Laser reflectance traces acquired in-situ during MOVPE (Metalorganic Vapor Phase Epitaxy) growth were compered and analyzed in order to correlate growth mechanism with electrical properties of HT-GaN buffer. The improvement of HT-GaN resistivity was shown through decrement of capacitance in the depleted space-charge region.

  8. 11.9 W output power at 4 GHz from 1 mm AlGaN/GaN HEMT

    NARCIS (Netherlands)

    Krämer, M.C.J.C.M.; Karouta, F.; Kwaspen, J.J.M.; Rudzinski, M.; Larsen, P.K.; Suijker, E.M.; Hek, P.A. de; Rödle, T.; Volokhine, I.; Kaufmann, L.M.F.

    2008-01-01

    A high electrical breakdown field combined with a high electron saturation velocity make GaN very attractive for high power high frequency electronics. The maximum drain current densities of AlGaN/GaN HFETs range from 1.0 A/mm to 1.5 A/mm [1-3]. Hence, it is obvious that breakdown voltages over 160

  9. Electronic structures of GaAs/AlxGa1-xAs quantum double rings

    Directory of Open Access Journals (Sweden)

    Li Shu-Shen

    2006-01-01

    Full Text Available AbstractIn the framework of effective mass envelope function theory, the electronic structures of GaAs/AlxGa1-xAs quantum double rings (QDRs are studied. Our model can be used to calculate the electronic structures of quantum wells, wires, dots, and the single ring. In calculations, the effects due to the different effective masses of electrons and holes in GaAs and AlxGa1-xAs and the valence band mixing are considered. The energy levels of electrons and holes are calculated for different shapes of QDRs. The calculated results are useful in designing and fabricating the interrelated photoelectric devices. The single electron states presented here are useful for the study of the electron correlations and the effects of magnetic fields in QDRs.

  10. Height stabilization of GaSb/GaAs quantum dots by Al-rich capping

    Energy Technology Data Exchange (ETDEWEB)

    Smakman, E. P., E-mail: e.p.smakman@tue.nl; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven (Netherlands); DeJarld, M.; Martin, A. J.; Millunchick, J. [Department of Material Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Luengo-Kovac, M.; Sih, V. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2014-09-01

    GaSb quantum dots (QDs) in a GaAs matrix are investigated with cross-sectional scanning tunneling microscopy (X-STM) and photoluminescence (PL). We observe that Al-rich capping materials prevent destabilization of the nanostructures during the capping stage of the molecular beam epitaxy (MBE) growth process and thus preserves the QD height. However, the strain induced by the absence of destabilization causes many structural defects to appear around the preserved QDs. These defects originate from misfit dislocations near the GaSb/GaAs interface and extend into the capping layer as stacking faults. The lack of a red shift in the QD PL suggests that the preserved dots do not contribute to the emission spectra. We suggest that a better control over the emission wavelength and an increase of the PL intensity is attainable by growing smaller QDs with an Al-rich overgrowth.

  11. Magnetic and mechanical properties of Ni-Mn-Ga/Fe-Ga ferromagnetic shape memory composite

    Science.gov (United States)

    Tan, Chang-Long; Zhang, Kun; Tian, Xiao-Hua; Cai, Wei

    2015-05-01

    A ferromagnetic shape memory composite of Ni-Mn-Ga and Fe-Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni-Mn-Ga alloy, the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe-Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved. Projects supported by the National Natural Science Foundation of China (Grant Nos. 51271065 and 51301054), the Program for New Century Excellent Talents in Heilongjiang Provincial Education Department, China (Grant No. 1253-NCET-009), the Youth Academic Backbone in Heilongjiang Provincial Education Department, China (Grant No. 1251G022), the Projects of Heilongjiang, China, and China Postdoctoral Science Foundation.

  12. GaAs/AlGaAs heterostructure point-contact concentrator cells

    Science.gov (United States)

    Gale, R. P.; Zavracky, P. M.; Mcclelland, R. W.; Fan, John C. C.

    1987-01-01

    Point-contact cells fabricated in silicon have recently achieved very high efficiencies. Applying this structure to GaAs is difficult as it requires both surface passivation of the GaAs and a film of GaAs with thickness less than 10 microns. The authors propose to overcome these difficulties by (1) using AlGaAs layers grown by OMCVD to act as front- and back-surface fields in order to confine the photogenerated minority carriers away from the surfaces, and (2) using the CLEFT technology to produce thin, separated films of this structure. It has been found that much of the necessary technologies have been developed and that the primary problem remaining to be solved is localized junction formation.

  13. Height stabilization of GaSb/GaAs quantum dots by Al-rich capping

    Directory of Open Access Journals (Sweden)

    E. P. Smakman

    2014-09-01

    Full Text Available GaSb quantum dots (QDs in a GaAs matrix are investigated with cross-sectional scanning tunneling microscopy (X-STM and photoluminescence (PL. We observe that Al-rich capping materials prevent destabilization of the nanostructures during the capping stage of the molecular beam epitaxy (MBE growth process and thus preserves the QD height. However, the strain induced by the absence of destabilization causes many structural defects to appear around the preserved QDs. These defects originate from misfit dislocations near the GaSb/GaAs interface and extend into the capping layer as stacking faults. The lack of a red shift in the QD PL suggests that the preserved dots do not contribute to the emission spectra. We suggest that a better control over the emission wavelength and an increase of the PL intensity is attainable by growing smaller QDs with an Al-rich overgrowth.

  14. Electron Transport in Ga-Rich InxGa1-xN Alloys

    Institute of Scientific and Technical Information of China (English)

    A. Yildiz; S. B. Lisesivdin; S. Acar; M. Kasap; M. Bosi

    2007-01-01

    Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN (0.06≤x≤0.135) alloys grown by metal-organic vapour phase epitaxy (MOVPE) technique are carried out as a function of temperature (15-350 K). Within the experimental error, the electron concentration in Inx Ga1- x N alloys is independent of temperature while the resistivity decreases as the temperature increases. Therefore, Inx Ga1-xN(0.06≤x≤0.135) alloys are considered in the metallic phase near the Mott transition. It has been shown that the temperaturedependent metallic conductivity can be well explained by the Mott model that takes into account electron-electron interactions and weak localization effects.

  15. The activation energy for Mg acceptor in the Ga-rich InGaN alloys

    Science.gov (United States)

    Zhao, Chuan-Zhen; Wei, Tong; Chen, Li-Ying; Wang, Sha-Sha; Wang, Jun

    2017-02-01

    The activation energy for Mg acceptor in InxGa1-xN alloys is investigated. It is found that there are three factors to influence the activation energy for Mg acceptor. One is the stronger dependence of the VBM of InxGa1-xN depending on In content than that of the Mg acceptor energy level. The other is the concentration of Mg acceptors. Another is the extending of the valence band-tail states into the band gap. In addition, a model based on modifying the effective mass model is developed. It is found that the model can describe the activation energy for Mg acceptor in the Ga-rich InxGa1-xN alloys well after considering the influence of the valence band-tail states.

  16. Implantation and diffusion of $^{73}$As in GaAs and GaP

    CERN Document Server

    Bösker, G; Stolwijk, N A; Mehrer, H; Burchard, A

    2000-01-01

    Self-diffusion on the As sublattice in intrinsic GaAs and foreign- atom diffusion on the P sublattice in intrinsic GaP were investigated in a direct way by As tracer diffusion measurements using the radioisotope /sup 73/As. For this purpose /sup 73/As was implanted in both materials at the ISOLDE facility of CERN. Then diffusion annealings were performed followed by serial sectioning and counting of the radioactivity in each section. The resulting profiles were simulated within a computer model which accounts for the observed loss of tracer to the diffusion ambient. The so-obtained diffusion coefficients for As in GaAs and GaP are compared with existing diffusivities in these compounds. (25 refs).

  17. Fabrication and characterization of an undoped GaAs/AlGaAs quantum dot device

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hai-Ou; Cao, Gang; Xiao, Ming, E-mail: maaxiao@ustc.edu.cn; You, Jie; Wei, Da; Tu, Tao; Guo, Guang-Can; Guo, Guo-Ping, E-mail: gpguo@ustc.edu.cn [Key Laboratory of Quantum Information, CAS, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Jiang, Hong-Wen [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States)

    2014-11-07

    We demonstrate the development of a double quantum dot with an integrated charge sensor fabricated in undoped GaAs/AlGaAs heterostructures using a double top-gated design. Based on the evaluation of the integrated charge sensor, the double quantum dot can be tuned to a few-electron region. Additionally, the inter-dot coupling of the double quantum dot can be tuned to a large extent according to the voltage on the middle gate. The quantum dot is shown to be tunable from a single dot to a well-isolated double dot. To assess the stability of such design, the potential fluctuation induced by 1/f noise was measured. Based on the findings herein, the quantum dot design developed in the undoped GaAs/AlGaAs semiconductor shows potential for the future exploitation of nano-devices.

  18. Single chip super broadband InGaN/GaN LED enabled by nanostructured substrate.

    Science.gov (United States)

    Yin, Stuart Shizhuo; Wang, Chao; Zhu, Wenbin; Yao, Jimmy; Zou, Jun; Lin, Xiaoyan; Luo, Claire

    2014-08-25

    A new type of LED, single chip super broadband InGaN/GaN LED is presented in this paper. The LED is composed of an InGaN/GaN quantum well layer deposited on the nanostructured sapphire substrate, inscribed by femtosecond laser ablation. The super broadband emission is enabled due to the large variation of indium composition in a small local area so that different wavelengths can be emitted over a small area and the summation of these different emission wavelengths forms super broadband emission, which covers the entire visible spectral range. The result of this paper represents a major technological advance in white light LED lighting because it enables single chip white LED lighting without the need of phosphor down converter that can significantly improve the efficiency without the Stokes loss and reduce the cost.

  19. Use of AlGaN in the notch region of GaN Gunn diodes

    Science.gov (United States)

    Yang, Linan; Hao, Yue; Zhang, Jincheng

    2009-10-01

    The wurtzite gallium nitride (GaN) Gunn diodes with aluminum gallium nitride (AlGaN) as launcher in the notch region are investigated by negative-differential-mobility model based simulation. Under the operation of self-excitation oscillation with dipole domain mode, the simulations show that the diode with two-step-graded AlGaN launcher structure can yield the maximal rf power of 1.95 W and dc/rf conversion efficiency of 1.72% at the fundamental oscillation frequency of around 215 GHz. This kind of Gunn diode structure without the low doping process is convenient for accurately controlling the dopant concentration of GaN epitaxial growth.

  20. Composition profiling of GaAs/AlGaAs quantum dots grown by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Bocquel, J.; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Giddings, A. D.; Prosa, T. J.; Larson, D. J. [CAMECA Instruments, Inc., 5500 Nobel Drive, Madison, Wisconsin 53711 (United States); Mano, T. [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)

    2014-10-13

    Droplet epitaxy (DE) is a growth method which can create III-V quantum dots (QDs) whose optoelectronic properties can be accurately controlled through the crystallisation conditions. In this work, GaAs/AlGaAs DE-QDs have been analyzed with the complimentary techniques of cross-sectional scanning tunneling microscopy and atom probe tomography. Structural details and a quantitative chemical analysis of QDs of different sizes are obtained. Most QDs were found to be pure GaAs, while a small proportion exhibited high intermixing caused by a local etching process. Large QDs with a high aspect ratio were observed to have an Al-rich crown above the GaAs QD. This structure is attributed to differences in mobility of the cations during the capping phase of the DE growth.

  1. Solid Phase Equilibria in the Pi-Ga-As and Pt-Ga-Sb Systems

    Science.gov (United States)

    1988-07-22

    OFFICE OF NAVAL RESEARCH Research Contract N00014-87-K-0014 R&T Code 413E026---01 AD-A 198 654 TECHNICAL REPORT No. 9 SOLID PHASE EQUILIBRIA IN THE...Classtcation) UNCLASSLFIED: Tech.Rept.#9 SOLID PHASE EQUILIBRIA IN T11: Pt-Ga-As AND Pt-Ga-Sb SYST’IS 12 PERSONAL AuTiOR(S) C.T. Tsai and R.S. Williats 13a TYPE

  2. Single-mode GaAs/AlGaAs quantum cascade microlasers

    Institute of Scientific and Technical Information of China (English)

    Gao Yu; Liu Junqi; Liu Fengqi; Zhang Wei; Zhang Quande; Liu Wanfeng; Li Lu; Wang Lijun; Wang Zhanguo

    2009-01-01

    Single-mode edge emitting GaAs/A1GaAs quantum cascade microlasers at a wavelength of about 11.4 μm were realized by shortening the Fabry-P6rot cavity length. The spacing of the longitudinal resonator modes is inversely proportional to the cavity length. Stable single-mode emission with a side mode suppression ratio of about 19 dB at 85 K for a 150-μm-long device was demonstrated.

  3. High-Gain AlxGa1-xAs/GaAs Transistors For Neural Networks

    Science.gov (United States)

    Kim, Jae-Hoon; Lin, Steven H.

    1991-01-01

    High-gain AlxGa1-xAs/GaAs npn double heterojunction bipolar transistors developed for use as phototransistors in optoelectronic integrated circuits, especially in artificial neural networks. Transistors perform both photodetection and saturating-amplification functions of neurons. Good candidates for such application because structurally compatible with laser diodes and light-emitting diodes, detect light, and provide high current gain needed to compensate for losses in holographic optical elements.

  4. Recent progress in InGaAsSb/GaSb TPV devices

    Energy Technology Data Exchange (ETDEWEB)

    Shellenbarger, Z.A.; Mauk, M.G.; DiNetta, L.C. [AstroPower, Inc., Newark, DE (United States); Charache, G.W. [Lockheed Martin Corp., Schenectady, NY (United States)

    1996-05-01

    AstroPower is developing InGaAsSb thermophotovoltaic (TPV) devices. This photovoltaic cell is a two-layer epitaxial InGaAsSb structure formed by liquid-phase epitaxy on a GaSb substrate. The (direct) bandgap of the In{sub 1{minus}x}Ga{sub x}As{sub 1{minus}y}Sb{sub y} alloy is 0.50 to 0.55 eV, depending on its exact alloy composition (x,y); and is closely lattice-matched to the GaSb substrate. The use of the quaternary alloy, as opposed to a ternary alloy--such as, for example InGaAs/InP--permits low bandgap devices optimized for 1,000 to 1,500 C thermal sources with, at the same time, near-exact lattice matching to the GaSb substrate. Lattice matching is important since even a small degree of lattice mismatch degrades device performance and reliability and increases processing complexity. Internal quantum efficiencies as high as 95% have been measured at a wavelength of 2 microns. At 1 micron wavelengths, internal quantum efficiencies of 55% have been observed. The open-circuit voltage at currents of 0.3 A/cm{sup 2} is 0.220 volts and 0.280 V for current densities of 2 A/cm{sup 2}. Fill factors of 56% have been measured at 60 mA/cm{sup 2}. However, as current density increases there is some decrease in fill factor. The results to date show that the GaSb-based quaternary compounds provide a viable and high performance energy conversion solution for thermophotovoltaic systems operating with 1,000 to 1,500 C source temperatures.

  5. Optically detected cyclotron resonance in a single GaAs/AlGaAs heterojunction

    Energy Technology Data Exchange (ETDEWEB)

    Bartsch, Gregor

    2011-09-23

    Optically detected far-infrared cyclotron resonance (FIR-ODCR) in GaAs/AlGaAs HJs is interpreted in the frame of an exciton-dissociation mechanism. It is possible to explain the ODR mechanism by an exciton drag, mediated by ballistically propagating phonons. Furthermore, very narrow resonances are presented and realistic electron mobility values can be calculated. The exceptionally narrow ODCRs allow to measure conduction-band nonparabolicity effects and resolve satellite resonances, close to the main cyclotron resonance line.

  6. InGaAs/GaAs (110) quantum dot formation via step meandering

    Energy Technology Data Exchange (ETDEWEB)

    Diez-Merino, Laura; Tejedor, Paloma [Department of Nanostructures and Surfaces, Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Ines de la Cruz 3, 28049-Madrid (Spain)

    2011-07-01

    InGaAs (110) semiconductor quantum dots (QDs) offer very promising prospects as a material base for a new generation of high-speed spintronic devices, such as single electron transistors for quantum computing. However, the spontaneous formation of InGaAs QDs is prevented by two-dimensional (2D) layer-by-layer growth on singular GaAs (110) substrates. In this work we have studied, by using atomic force microscopy and photoluminescence spectroscopy (PL), the growth of InGaAs/GaAs QDs on GaAs (110) stepped substrates by molecular beam epitaxy (MBE), and the modification of the adatom incorporation kinetics to surface steps in the presence of chemisorbed atomic hydrogen. The as-grown QDs exhibit lateral dimensions below 100 nm and emission peaks in the 1.35-1.37 eV range. It has been found that a step meandering instability derived from the preferential attachment of In adatoms to [110]-step edges relative to [11n]-type steps plays a key role in the destabilization of 2D growth that leads to 3D mound formation on both conventional and H-terminated vicinal substrates. In the latter case, the driving force for 3D growth via step meandering is enhanced by H-induced upward mass transport in addition to the lower energy cost associated with island formation on H-terminated substrates, which results in a high density array of InGaAs/GaAs dots selectively nucleated on the terrace apices with reduced lateral dimensions and improved PL efficiency relative to those of conventional MBE-grown samples.

  7. Device Performance and Reliability Improvements of AlGaBN/GaN/Si MOSFET

    Science.gov (United States)

    2016-02-04

    on a p-type Si(111) substrate by metal organic chemical vapor deposition (see the wafer structure in Fig. 1.1 (a) in the supplemental material30... Metal insulator semiconductor AlGaN /GaN high electron mobility transistors (MISHEMTs) are promising for power device applications due to a lower leakage...introduced into an ultra-high vacuum (UHV) system, described in detail elsewhere,30 which consists of a number of vacuum chambers interconnected by a UHV

  8. On-sun concentrator performance of GaInP/GaAs tandem cells

    Energy Technology Data Exchange (ETDEWEB)

    Friedman, D.J.; Kurtz, S.R.; Sinha, K.; McMahon, W.E.; Olson, J.M. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    The GaInP/GaAs concentrator device has been adapted for and tested in a prototype {open_quotes}real-world{close_quotes} concentrator power system. The device achieved an on-sun efficiency of 28% {+-} 1% in the range of approximately 200-260 suns with device operating temperatures of 38{degrees}C to 42{degrees}C. The authors discuss ways of further improving this performance for future devices.

  9. Carrier localization mechanisms in InGaN/GaN quantum wells

    OpenAIRE

    Watson-Parris, D.; Godfrey, M. J.; Dawson, P.; Oliver, R. A.; Galtrey, M. J.; Kappers, M. J.; Humphreys, C J

    2010-01-01

    Localization lengths of the electrons and holes in InGaN/GaN quantum wells have been calculated using numerical solutions of the effective mass Schr\\"odinger equation. We have treated the distribution of indium atoms as random and found that the resultant fluctuations in alloy concentration can localize the carriers. By using a locally varying indium concentration function we have calculated the contribution to the potential energy of the carriers from band gap fluctuations, the deformation p...

  10. Preparation and properties of thick not intentionally doped GaInP(As)/GaAs layers

    CERN Document Server

    Nohavica, D; Zdansky, K

    1999-01-01

    We report on liquid-phase epitaxial growth of thick layers of GaInP(As), lattice matched to GaAs. Layers with thicknesses up to 10 mu m were prepared in a multi-melt bin, step-cooling, one-phase configuration. Unintentionally doped layers, grown from moderate purity starting materials, show a significant decrease in the residual impurity level when erbium is added to the melt. Fundamental electrical and optical properties of the layers were investigated. (author)

  11. Investigation the absorption efficiency of GaAs/InGaAs nanowire solar cells

    Science.gov (United States)

    Ali, Latef M.; Abed, Farah A.

    2017-10-01

    This study investigated the absorption efficiency of GaAs/In0.2Ga0.8As cylindrical core-shell nanowire (NW) solar cells with a circular cross-section for normal incident light. Numerical results obtained through finite-difference time-domain simulation showed that NW dimensions influenced the absorption efficiency of the solar cells. The band structure of the wires was also investigated.

  12. Numerical analysis of AlGaAs/GaAs multi-quantum well superluminescent diodes

    Science.gov (United States)

    Navaeipour, Parvin; Asgari, Asghar

    2014-09-01

    In this paper, we have investigated numerically AlGaAs/GaAs multi-quantum well superluminescent diodes. In these devices the dependence of optical gain, output power on the cavity length and the density states have been analyzed. It is observed that the optical gain and its FWHM bandwidth increase with the increasing density state. Furthermore, the output power increases with the increasing cavity length, whereas the FWHM bandwidth decreases.

  13. Luminescence studies on green emitting InGaN/GaN MQWs implanted with nitrogen

    OpenAIRE

    2015-01-01

    We studied the optical properties of metalorganic chemical vapour deposited (MOCVD) InGaN/GaN multiple quantum wells (MQW) subjected to nitrogen (N) implantation and post-growth annealing treatments. The optical characterization was carried out by means of temperature and excitation density-dependent steady state photoluminescence (PL) spectroscopy, supplemented by room temperature PL excitation (PLE) and PL lifetime (PLL) measurements. The as-grown and as-implanted samples were found to exhi...

  14. Optical characteristics of InAlAs/GaAlAs/GaAs quantum dots (Conference Presentation)

    Science.gov (United States)

    Liang, Baolai; Huffaker, Diana L.; Mazur, Yuriy I.; Ware, Morgan; Salamo, Gregory J.; Su, Linlin; Wang, Ying; Guo, Qinglin

    2017-02-01

    The type-I to type-II band alignment transition in InAlAsAs/AlGaAs/GaAs self-assembled quantum dots (QDs) is investigated when the Al-composition in QDs and barrier are changed. In particular, the In0.46Al0.54As/Ga0.46Al0.54As/GaAs QDs show unique optical properties. The PL peak energy has a blue-shift of >40 meV when the laser intensity increases by four orders of magnitude, indicating a type-II band alignment of the QDs. The formation of the type-II band alignment is explained by that the quantum-confinement effect pulls up the minimum electron energy level in the QDs and the Γ→X transition in the Ga0.46Al0.54As barrier. The time-resolved PL (TRPL) spectrum of QDs at peak wavelength exhibits a double-component decay behavior, suggesting the possibility of type-I and type-II band alignment coexistence in this QD sample. The continuum state of the QDs is also investigated. Emission associated with the continuum states of the QDs is directly observed in PL spectra. The PL excitation (PLE) and TRPL spectra reveal an efficient carrier relaxation from the AlGaAs barrier into the InAlAs QD ground state via the continuum states. The carrier recombination in the continuum states can compete with that in the QDs due to the long recombination lifetime in the type-II QDs. This feature of continuum state emission can not be observed for normal InGaAs/GaAs QDs with the type-I band structure.

  15. 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.

  16. Evaluation of resonant tunneling transmission coefficient from multilayer structures GaAlAs/GaAs

    Directory of Open Access Journals (Sweden)

    L. Moghaddasi

    2003-12-01

    Full Text Available   A theoretical study of resonant tunneling in multilayered GaAlAs/GaAs structures are presented. The spectrum of resonant energies and its dependence on the barrier structure are analyzed from calculated profiles of barrier transparency versus energy, and from current voltage characteristics computed at selected temperatures and Fermi levels. The present formalism is based on the effective mass approximation and results are via direct numerical evaluations.

  17. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    Energy Technology Data Exchange (ETDEWEB)

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Andreev, Viacheslav [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021 (Russian Federation); Luque, Antonio [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021, Russia and Instituto de Energia Solar, Universidad Politecnica de Madrid, Madrid (Spain)

    2014-09-26

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (λ = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

  18. Electron spin dynamics in GaAsN and InGaAsN structures

    Energy Technology Data Exchange (ETDEWEB)

    Lagarde, D.; Lombez, L.; Marie, X.; Balocchi, A.; Amand, T. [Laboratoire de Nanophysique, Magnetisme et Optoelectronique, INSA 135 avenue de Rangueil 31077 Toulouse Cedex 4 (France); Kalevich, V.K.; Shiryaev, A.; Ivchenko, E.; Egorov, A. [A.F. Ioffe Physico-Technical Institute, 194021 St-Petersburg (Russian Federation)

    2007-01-15

    We report on optical orientation experiments in undoped GaAsN epilayers and InGaAsN quantum wells (QW), showing that a strong electron spin polarisation can persist at room temperature. We demonstrate that the spin dynamics in these dilute nitride structures is governed by a spin-dependent recombination process of free conduction electrons on deep paramagnetic centres. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. GaAs/AlGaAs nanoheterostructures: simulation and application on high mobility transistors

    OpenAIRE

    Eduardo Martín Rodríguez; Estrella González R.

    2011-01-01

     This work analyses the features of GaAs/AlGaAs heterostructure, highlighting semiconductor junction properties. Charge confinement was produced when two materials having different band-gap were fixed; such high electron concentration is called two-dimensional electron gas (2DEG). Device simulation for smart integrated systems (DESSIS) is simulation software which uses physical models and robust numerical methods for simulating semiconductor devices and 3-5 element heterostructures. Results f...

  20. Thermal Expansion in YbGaGe

    OpenAIRE

    Bobev, Svilen; Williams, Darrick J.; Thompson, J.D.; Sarrao, J L

    2004-01-01

    Thermal expansion and magnetic susceptibility measurements as a function of temperature are reported for YbGaGe. Despite the fact that this material has been claimed to show zero thermal expansion over a wide temperature range, we observe thermal expansion typical of metals and Pauli paramagnetic behavior, which perhaps indicates strong sample dependence in this system.

  1. 76 FR 59177 - Georgia Disaster #GA-00036

    Science.gov (United States)

    2011-09-23

    ... ADMINISTRATION Georgia Disaster GA-00036 AGENCY: U.S. Small Business Administration. ACTION: Notice. SUMMARY: This is a notice of an Administrative declaration of a disaster for the State of GEORGIA dated 09/13..., Office of Disaster Assistance, U.S. Small Business Administration, 409 3rd Street, SW., Suite...

  2. 77 FR 51099 - Georgia Disaster #GA-00046

    Science.gov (United States)

    2012-08-23

    ... ADMINISTRATION Georgia Disaster GA-00046 AGENCY: U.S. Small Business Administration. ACTION: Notice. SUMMARY...: 05/14/2013. ADDRESSES: Submit completed loan applications to: U.S. Small Business Administration... CONTACT: A. Escobar, Office of Disaster Assistance, U.S. Small Business Administration, 409 3rd Street...

  3. Ga-67 uptake post cesarean section

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, O.L.; Maisano, E.R.

    1984-02-01

    Gallium-67 distribution in normal patients is well known; it is also known that the concentration in some tissues may vary according to an individual physiologic stimulus. In this report, the case of a young woman is presented who was studied 15 days after a cesarean section and showed physiologic and pathologic Ga-67 accumulation.

  4. Si diffusion in GaAs

    Indian Academy of Sciences (India)

    P Murugan; R Pothiraj; S D D Roy; K Ramachandran

    2002-08-01

    Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutional–interstitial pair or neutral defect pair.

  5. GaAs optoelectronic neuron arrays

    Science.gov (United States)

    Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

    1993-01-01

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

  6. Assessment of Ga2O3 technology

    Science.gov (United States)

    2016-09-15

    architecture [60]. ....................................................................... 10 Figure 5: Photograph of 4-inch diameter Ga2O3 wafer...breakdown voltages can provide orders of magnitude reduction in system size, cost and weight. Figure 4: A More-Electric Aircraft (MEA) architecture [60...Technology base is narrowly located in Japan . Mainstream technology. Czochralski • Mature technology base. • Crucible-free crystal growth

  7. Temperature Dependence of GaN HEMT Small Signal Parameters

    Science.gov (United States)

    2011-11-01

    original work is properly cited. This study presents the temperature dependence of small signal parameters of GaN /SiC HEMTs across the 0–150◦C range...the performance of GaN /SiC device, two state-of-the-art AlGaN/ GaN HEMT devices were characterized at −25, 25, 75, and 125◦C base plate (on-wafer...number. 1. REPORT DATE NOV 2011 2. REPORT TYPE 3. DATES COVERED 00-00-2011 to 00-00-2011 4. TITLE AND SUBTITLE Temperature Dependence of GaN HEMT

  8. Nanometer scale fabrication and optical response of InGaN/GaN quantum disks

    Science.gov (United States)

    Lai, Yi-Chun; Higo, Akio; Kiba, Takayuki; Thomas, Cedric; Chen, Shula; Lee, Chang Yong; Tanikawa, Tomoyuki; Kuboya, Shigeyuki; Katayama, Ryuji; Shojiki, Kanako; Takayama, Junichi; Yamashita, Ichiro; Murayama, Akihiro; Chi, Gou-Chung; Yu, Peichen; Samukawa, Seiji

    2016-10-01

    In this work, we demonstrate homogeneously distributed In0.3Ga0.7N/GaN quantum disks (QDs), with an average diameter below 10 nm and a high density of 2.1 × 1011 cm-2, embedded in 20 nm tall nanopillars. The scalable top-down fabrication process involves the use of self-assembled ferritin bio-templates as the etch mask, spin coated on top of a strained In0.3Ga0.7N/GaN single quantum well (SQW) structure, followed by a neutral beam etch (NBE) method. The small dimensions of the iron cores inside ferritin and nearly damage-free process enabled by the NBE jointly contribute to the observation of photoluminescence (PL) from strain-relaxed In0.3Ga0.7N/GaN QDs at 6 K. The large blueshift of the peak wavelength by over 70 nm manifests a strong reduction of the quantum-confined Stark effect (QCSE) within the QD structure, which also agrees well with the theoretical prediction using a 3D Schrödinger equation solver. The current results hence pave the way towards the realization of large-scale III-N quantum structures using the combination of bio-templates and NBE, which is vital for the development of next-generation lighting and communication devices.

  9. InGaN/GaN laser diode characterization and quantum well number effect

    Institute of Scientific and Technical Information of China (English)

    S. M. Thahab; H. Abu Hassan; Z. Hassan

    2009-01-01

    The effect of quantum well number on the quantum efficiency and temperature characteristics of In-GaN/GaN laser diodes (LDs) is determined and investigated. The 3-nm-thick In0.13Ga0.87TN wells and two 6-nm-thick GaN barriers are selected as an active region for Fabry-Perot (FP) cavity waveguide edge emitting LD. The internal quantum efficiency and internal optical loss coefficient are extracted through the simulation software for single, double, and triple InGaN/GaN quantum wells. The effects of device temperature on the laser threshold current, external differential quantum efficiency (DQE), and output wavelength are also investigated. The external quantum efficiency and characteristic temperature are improved significantly when the quantum well number is two. It is indicated that the laser structures with many quantum wells will suffer from the inhomogeneity of the carrier density within the quantum well itself which affects the LD performance.

  10. Formation of Ga droplets on patterned GaAs (100) by molecular beam epitaxy.

    Science.gov (United States)

    Li, Ming-Yu; Hirono, Yusuke; Koukourinkova, Sabina D; Sui, Mao; Song, Sangmin; Kim, Eun-Soo; Lee, Jihoon; Salamo, Gregory J

    2012-10-03

    In this paper, the formation of Ga droplets on photo-lithographically patterned GaAs (100) and the control of the size and density of Ga droplets by droplet epitaxy using molecular beam epitaxy are demonstrated. In extension of our previous result from the journal Physical Status Solidi A, volume 209 in 2012, the sharp contrast of the size and density of Ga droplets is clearly observed by high-resolution scanning electron microscope, atomic force microscope, and energy dispersive X-ray spectrometry. Also, additional monolayer (ML) coverage is added to strength the result. The density of droplets is an order of magnitude higher on the trench area (etched area), while the size of droplets is much larger on the strip top area (un-etched area). A systematic variation of ML coverage results in an establishment of the control of size and density of Ga droplets. The cross-sectional line profile analysis and root mean square roughness analysis show that the trench area (etched area) is approximately six times rougher. The atomic surface roughness is suggested to be the main cause of the sharp contrast of the size and density of Ga droplets and is discussed in terms of surface diffusion.

  11. Quantum transport in high mobility AlGaN/GaN 2DEGs and nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Schmult, S.; Manfra, M.J.; Sergent, A.M.; Punnoose, A. [Bell Laboratories, Lucent Technologies, 600 Mountain Ave, Murray Hill, NJ 07974 (United States); Chou, H.T. [Department of Applied Physics, Stanford University, Stanford, CA 94305 (United States); Goldhaber-Gordon, D. [Department of Physics, Stanford University, Stanford, CA 94305 (United States); Molnar, R.J. [MIT Lincoln Laboratory, 244 Wood Street, Lexington, MA 02420 (United States)

    2006-06-15

    High mobility two-dimensional electron systems in GaN/AlGaN heterostructures have been realized by plasma assisted molecular beam epitaxy on GaN templates. In the density range of 10{sup 11} cm{sup -2} to 10{sup 12} cm{sup -2}, mobility values exceeding 160000 cm{sup 2}/Vs have been achieved. Scattering mechanisms that presently limit the production of higher mobility samples are discussed. We present results of a systematic study of the weak localization and antilocalization corrections to the classical conductivity at very low magnetic fields. The unambiguous observation of a conductivity maximum at B=0 suggests that spin-orbit scattering is not negligible in GaN heterostructures as one might expect for a wide-bandgap system. We have recently realized electron transport through GaN nanostructures. We report on the transport properties of the first quantum point contacts (QPCs) in GaN. These devices are used to study one-dimensional transport in the Nitride system. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Assembly of phosphonic acids on GaN and AlGaN

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-01-13

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

  13. 15.3%-Efficient GaAsP Solar Cells on GaP/Si Templates

    Energy Technology Data Exchange (ETDEWEB)

    Vaisman, Michelle [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Perl, Emmett [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Fan, Shizhao [University of Illinois Urbana-Champaign; Yaung, Kevin Nay [Yale University; Martin-Martin, Diego [Universidad Rey Juan Carlos; Yu, Zhengshan J. [Arizona State University; Leilaeioun, Mehdi [Arizona State University; Holman, Zachary C. [Arizona State University; Lee, Minjoo L. [University of Illinois Urbana-Champaign

    2017-07-26

    As single-junction Si solar cells approach their practical efficiency limits, a new pathway is necessary to increase efficiency in order to realize more cost-effective photovoltaics. Integrating III-V cells onto Si in a multijunction architecture is a promising approach that can achieve high efficiency while leveraging the infrastructure already in place for Si and III-V technology. In this Letter, we demonstrate a record 15.3%-efficient 1.7 eV GaAsP top cell on GaP/Si, enabled by recent advances in material quality in conjunction with an improved device design and a high-performance antireflection coating. We further present a separate Si bottom cell with a 1.7 eV GaAsP optical filter to absorb most of the visible light with an efficiency of 6.3%, showing the feasibility of monolithic III-V/Si tandems with >20% efficiency. Through spectral efficiency analysis, we compare our results to previously published GaAsP and Si devices, projecting tandem GaAsP/Si efficiencies of up to 25.6% based on current state-of-the-art individual subcells. With the aid of modeling, we further illustrate a realistic path toward 30% GaAsP/Si tandems for high-efficiency, monolithically integrated photovoltaics.

  14. Optical gain in GaAsBi/GaAs quantum well diode lasers

    Science.gov (United States)

    Marko, Igor P.; Broderick, Christopher A.; Jin, Shirong; Ludewig, Peter; Stolz, Wolfgang; Volz, Kerstin; Rorison, Judy M.; O'Reilly, Eoin P.; Sweeney, Stephen J.

    2016-07-01

    Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10-15 cm-1 and a peak modal gain of 24 cm-1, corresponding to a material gain of approximately 1500 cm-1 at a current density of 2 kA cm-2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared.

  15. Degradation Mechanisms for GaN and GaAs High Speed Transistors

    Directory of Open Access Journals (Sweden)

    Fan Ren

    2012-11-01

    Full Text Available We present a review of reliability issues in AlGaN/GaN and AlGaAs/GaAs high electron mobility transistors (HEMTs as well as Heterojunction Bipolar Transistors (HBTs in the AlGaAs/GaAs materials systems. Because of the complex nature and multi-faceted operation modes of these devices, reliability studies must go beyond the typical Arrhenius accelerated life tests. We review the electric field driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plate, and the effect of device fabrication processes for both DC and RF stress conditions. We summarize the degradation mechanisms that limit the lifetime of these devices. A variety of contact and surface degradation mechanisms have been reported, but differ in the two device technologies: For HEMTs, the layers are thin and relatively lightly doped compared to HBT structures and there is a metal Schottky gate that is directly on the semiconductor. By contrast, the HBT relies on pn junctions for current modulation and has only Ohmic contacts. This leads to different degradation mechanisms for the two types of devices.

  16. DC Characteristics of AlGaN/GaN HEMTs Using a Dual-Gate Structure.

    Science.gov (United States)

    Hong, Sejun; Rana, Abu ul Hassan Sarwar; Heo, Jun-Woo; Kim, Hyun-Seok

    2015-10-01

    Multiple techniques such as fluoride-based plasma treatment, a p-GaN or p-AlGaN gate contact, and a recessed gate structure have been employed to modulate the threshold voltage of AlGaN/GaN-based high-electron-mobility transistors (HEMTs). In this study, we present dual-gate AlGaN/GaN HEMTs grown on a Si substrate, which effectively shift the threshold voltage in the positive direction. Experimental data show that the threshold voltage is shifted from -4.2 V in a conventional single-gate HEMT to -2.8 V in dual-gate HEMTs. It is evident that a second gate helps improve the threshold voltage by reducing the two-dimensional electron gas density in the channel. Furthermore, the maximum drain current, maximum transconductance, and breakdown voltage values of a single-gate device are not significantly different from those of a dual-gate device. For the fabricated single- and dual-gate devices, the values of the maximum drain current are 430 mA/mm and 428 mA/mm, respectively, whereas the values of the maximum transconductance are 83 mS/mm and 75 mS/mm, respectively.

  17. Lateral and Vertical Transistors Using the AlGaN/GaN Heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Chowdhury, S; Mishra, UK

    2013-10-01

    Power conversion losses are endemic in all areas of electricity consumption, including motion control, lighting, air conditioning, and information technology. Si, the workhorse of the industry, has reached its material limits. Increasingly, the lateral AlGaN/GaN HEMT based on gallium nitride (GaN-on-Si) is becoming the device of choice for medium power electronics as it enables high-power conversion efficiency and reduced form factor at attractive pricing for wide market penetration. The reduced form factor enabled by high-efficiency operation at high frequency further enables significant system price reduction because of savings in bulky extensive passive elements and heat sink costs. The high-power market, however, still remains unaddressed by lateral GaN devices. The current and voltage demand for high power conversion application makes the chip area in a lateral topology so large that it becomes more difficult to manufacture. Vertical GaN devices would play a big role alongside of silicon carbide (SiC) to address the high power conversion needs. In this paper, the development, performance, and status of lateral and vertical GaN devices are discussed.

  18. Modeling and simulation of InGaN/GaN quantum dots solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Aissat, A., E-mail: sakre23@yahoo.fr [LATSI Laboratory, Faculty of Technology, University of Blida 1 (Algeria); LASICOMLaboratory, Faculty of Sciences, University of Blida 1 (Algeria); Benyettou, F. [LASICOMLaboratory, Faculty of Sciences, University of Blida 1 (Algeria); Vilcot, J. P. [Institute of Electronics, Micro-Electronics and Nanotechnologies,UMR CNRS 8520, Université des Sciences et Technologies de Lille1, Avenue Poincaré, CS 60069, 59652 Villeneuve d’Ascq (France)

    2016-07-25

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In{sub 0.25}Ga{sub 0.75}N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In{sub 0.25}Ga{sub 0.75}N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  19. Ultrahigh gain AlGaN/GaN high energy radiation detectors

    Energy Technology Data Exchange (ETDEWEB)

    Howgate, J.D.; Schoell, S.J.; Schaefer, S.; Stutzmann, M.; Sharp, I.D. [Walter Schottky Institut and Physik Department, Technische Universitaet Muenchen, Am Coulombwall 4, 85748 Garching (Germany); Hofstetter, M.; Schmid, M.; Thalhammer, S. [Helmholtz Zentrum Muenchen, Ingolstaedter Landstrasse 1, 85764 Neuherberg (Germany); Zizak, I. [Helmholtz Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Hable, V.; Greubel, C.; Dollinger, G. [Institut fuer Angewandte Physik und Messtechnik LRT2, Werner-Heisenberg-Weg 39, 85577 Neubiberg (Germany)

    2012-08-15

    Due to its remarkable tolerance to high energy ionizing radiation, GaN has recently attracted attention as a promising material for dosimetry applications. However, materials issues that lead to persistent photoconductivity, poor sensitivity, and requirements for large operational voltages have been hurdles to realization of the full potential of this material. Here we demonstrate that the introduction of a two-dimensional electron gas channel, through the addition of AlGaN/GaN heterointerfaces, can be used to create intrinsic amplification of the number of electrons that can be collected from single ionization events, yielding exceptionally large sensitivities in ultralow dose rate regimes. Furthermore, anomalous photo-responses, which severely limit response times of GaN-based devices, can be eliminated using these heterostructures. Measurements using focused monochromatic synchrotron radiation at 1-20 keV, as well as focused 20 MeV protons, reveal that these devices provide the capability for high sensitivity and resolution real time monitoring, which is competitive with and complementary to state-of-the-art detectors. Therefore, AlGaN/GaN heterostructure devices are extremely promising for future applications in fields ranging from high energy physics to medical imaging. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Spacer-thickness dependence of interlayer exchange coupling in GaMnAs/InGaAs/GaMnAs trilayers grown on ZnCdSe buffers

    Science.gov (United States)

    Tivakornsasithorn, Kritsanu; Yoo, Taehee; Lee, Hakjoon; Choi, Seonghoon; Lee, Sanghoon; Liu, Xinyu; Dobrowolska, M.; Furdyna, Jacek K.

    2017-03-01

    Interlayer exchange coupling (IEC) between GaMnAs layers in GaMnAs/InGaAs/GaMnAs tri-layers was studied by magnetization measurements. Minor hysteresis loops are observed to shift in a direction indicating the presence of ferromagnetic (FM) IEC in the structures. The strength of the FM IEC clearly exhibits an exponential decrease with respect to nonmagnetic InGaAs spacer thickness. The fitting of the spacer thickness dependence of the FM IEC to an exponential decay function provides a decay length of 3.3±0.3 nm, which is relatively large compared to metallic multilayers, indicating a long ranged IEC in systems based on GaMnAs.

  1. Improved light extraction of InGaN/GaN blue LEDs by GaOOH NRAs using a thin ATO seed layer.

    Science.gov (United States)

    Lee, Hee Kwan; Joo, Dong Hyuk; Kim, Myung Sub; Yu, Jae Su

    2012-08-16

    We investigated the effect of gallium oxide hydroxide (GaOOH) nanorod arrays (NRAs) on the light extraction of InGaN/GaN multiple quantum well blue light-emitting diodes (LEDs). GaOOH NRAs were prepared on an indium tin oxide electrode (ITO) layer of LEDs by electrochemical deposition method. The GaOOH NRAs with preferred orientations were grown on the ITO surface by sputtering a thin antimony-doped tin oxide seed layer, which enhances heterogeneous reactions. Surface density and coverage were also efficiently controlled by the different growth voltages. For LEDs with GaOOH NRAs grown at -2 V, the light output power was increased by 22% without suffering from any serious electrical degradation and wavelength shift as compared with conventional LEDs.

  2. GaAs and AlGaAs APDs with GaSb absorption regions in a separate absorption and multiplication structure using a hetero-lattice interface

    Science.gov (United States)

    Marshall, A. R. J.; Craig, A. P.; Reyner, C. J.; Huffaker, D. L.

    2015-05-01

    Interfacial misfit (IMF) arrays were used to create two APD structures, allowing GaSb absorption layers to be combined with wide-gap multiplication regions, grown using GaAs and Al0.8Ga0.2As, respectively. The GaAs APD represents a proof-of-principle, which is developed in the Al0.8Ga0.2As APD to achieve reduced dark currents, of 5.07 μA cm-2 at 90% of the breakdown voltage, and values for effective k = β/α below 0.2. A random-path-length (RPL) simulation was used to model the excess noise in both structures, taking into account the effects of dead space. It is envisaged that the GaSb absorption regions could be replaced with other materials from the 6.1 Å family, allowing for long-wavelength APDs with reduced dark currents and excess noise.

  3. Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs

    Directory of Open Access Journals (Sweden)

    Nigamananda Samal

    2010-02-01

    Full Text Available An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW on GaAs by molecular beam epitaxy (MBE are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM of ~60 meV in room temperature (RT photoluminescence (PL indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation.

  4. Electroluminescence from a forward-biased Schottky barrier diode on modulation Si {delta}-doped GaAs/InGaAs/AlGaAs heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, Adam; Witczak, P.; Twardowski, A.; Baranowski, J. M.

    2001-06-18

    Electroluminescence (EL) from a forward-biased Schottky barrier diode on modulation Si {delta}-doped pseudomorphic GaAs/InGaAs/AlGaAs heterostructure with high mobility electron gas is investigated in this work. It has been found that the EL from the InGaAs quantum well can be observed at temperatures up to 90 K. The EL line shape depends on the current density, which reflects the filling of the InGaAs channel with electrons. The total integrated EL intensity depends linearly on the current density. We propose that hole diffusion from an inversion layer at the Schottky barrier is responsible for the observed optical recombination with electrons in the InGaAs quantum well. {copyright} 2001 American Institute of Physics.

  5. Carbon-nanotube-assisted nanoepitaxy of Si-doped GaN for improved performance of InGaN/GaN light-emitting diodes

    Science.gov (United States)

    Park, Ah Hyun; Chandramohan, S.; Seo, Tae Hoon; Lee, Gun Hee; Min, Kyung Hyun; Hong, Chang-Hee; Jong Kim, Myung; Suh, Eun-Kyung

    2016-07-01

    Using single-walled carbon nanotubes (SWCNTs) as nanomasks on an undoped GaN template, a significant biaxial stress relaxation was achieved in the subsequently-grown Si-doped n-GaN layer. Enhanced near band edge (NBE) emission intensity, similar free carrier concentrations, and the reduced peak width of the asymmetric (102) crystallographic plane all confirmed the suppression of threading dislocations due to the nanoepitaxial growth process. Temperature-dependent photoluminescence (PL) revealed improved internal quantum efficiency (IQE) of InGaN/GaN multi-quantum wells (MQWs) grown on this n-GaN layer. Furthermore, enhanced light output power and a remarkable reduction in efficiency droop were observed for the blue light-emitting diodes (LEDs), especially at higher injection currents. Our results emphasize the strong potential for SWCNTs as nanomasks in the heteroepitaxy of GaN-based devices without the exploitation of complicated lithography or etching processes.

  6. The effects of InGaN layer thickness on the performance of InGaN/GaN p-i-n solar cells

    Institute of Scientific and Technical Information of China (English)

    Li Liang; Zhao De-Gang; Jiang De-Sheng; Liu Zong-Shun; Chen Ping; Wu Liang-Liang; Le Ling-Cong

    2013-01-01

    InGaN/GaN p-i-n solar cells,each with an undoped Ino.12Gao.88N absorption layer,are grown on c-plane sapphire substrates by metal-organic chemical vapor deposition.The effects of the thickness and dislocation density of the absorption layer on the collection efficiency of InGaN-based solar cells are analyzed,and the experimental results demonstrate that the thickness of the InGaN layer and the dislocation density significantly affect the performance.An optimized InGaN-based solar cell with a peak external quantum efficiency of 57% at a wavelength of 371 nm is reported.The full width at half maximum of the rocking curve of the (0002) InGaN layer is 180 arcsec.

  7. Effects of NH3 Flow Rate During AlGaN Barrier Layer Growth on the Material Properties of AlGaN/GaN HEMT Heterostructure

    Science.gov (United States)

    Lumbantoruan, Franky J.; Wong, Yuen-Yee; Huang, Wei-Ching; Yu, Hung-Wei; Chang, Edward-Yi

    2017-10-01

    NH3 flow rate during AlGaN barrier layer growth not only affects the growth efficiency and surface morphology as a result of parasitic reactions but also influences the concentration of carbon impurity in the AlGaN barrier. Carbon, which decomposes from metal precursors, plays a role in electron compensation for AlGaN/GaN HEMT. No 2-dimensional electron gas (2-DEG) was detected in the AlGaN/GaN structure if grown with 0.5 slm of NH3 due to the presence of higher carbon impurity (2.6 × 1019 cm-2). When the NH3 flow rate increased to 6.0 slm, the carbon impurity reduced to 2.10 × 1018 atom cm-3 and the 2 DEG electron density recovered to 9.57 × 1012 cm-2.

  8. [Bi3GaS5]2[Ga3Cl10]2[GaCl4]2·S8 containing heterocubane-type [Bi3GaS5]2+, star-shaped [Ga3Cl10]-, monomeric [GaCl4]- and crown-like S8.

    Science.gov (United States)

    Freudenmann, Dominic; Feldmann, Claus

    2011-01-14

    By reaction of elemental bismuth, sulfur, bismuth(III) chloride and gallium(III) chloride in the ionic liquid (BMIm)Cl (BMIm: 1-butyl-3-methylimidazolium), [Bi(3)GaS(5)](2)[Ga(3)Cl(10)](2)[GaCl(4)](2)·S(8) is obtained as red transparent crystals. According to X-ray structure analysis based on single crystals, the title compound crystallizes with triclinic lattice symmetry and is composed of heterocubane-type [Bi(3)GaS(5)](2+) cations, trimeric star-shaped [Ga(3)Cl(10)](-) anions with three (GaCl(4)) tetrahedra sharing a single central chlorine atom, monomeric [GaCl(4)](-) tetrahedra and neutral, crown-shaped S(8)-rings. Here, the heterocubane [Bi(3)GaS(5)](2+) as well as the star-shaped [Ga(3)Cl(10)](-) are observed as building units for the first time. [Bi(3)GaS(5)](2)[Ga(3)Cl(10)](2)[GaCl(4)](2)·S(8) is further characterized by X-ray powder diffraction as well as by thermogravimetry/differential thermal analysis.

  9. Enhanced output power of GaN-based LEDs with embedded AlGaN pyramidal shells.

    Science.gov (United States)

    Tu, Shang-Ju; Sheu, Jinn-Kong; Lee, Ming-Lun; Yang, Chih-Ciao; Chang, Kuo-Hua; Yeh, Yu-Hsiang; Huang, Feng-Wen; Lai, Wei-Chih

    2011-06-20

    In this article, the characteristics of GaN-based LEDs grown on Ar-implanted GaN templates to form inverted Al0.27Ga0.83N pyramidal shells beneath an active layer were investigated. GaN-based epitaxial layers grown on the selective Ar-implanted regions had lower growth rates compared with those grown on the implantation-free regions. This resulted in selective growth, and formation of V-shaped concaves in the epitaxial layers. Accordingly, the inverted Al0.27Ga0.83N pyramidal shells were formed after the Al0.27Ga0.83N and GaN layers were subsequently grown on the V-shaped concaves. The experimental results indicate that the light-output power of LEDs with inverted AlGaN pyramidal shells was higher than those of conventional LEDs. With a 20 mA current injection, the output power was enhanced by 10% when the LEDs were embedded with inverted Al0.27Ga0.83N pyramidal shells. The enhancement in output power was primarily due to the light scattering at the Al0.27Ga0.83N/GaN interface, which leads to a higher escape probability for the photons, that is, light-extraction efficiency. Based on the ray tracing simulation, the output power of LEDs grown on Ar-implanted GaN templates can be enhanced by over 20% compared with the LEDs without the embedded AlGaN pyramidal shells, if the AlGaN layers were replaced by Al0.5Ga0.5N layers.

  10. Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

    Science.gov (United States)

    Yang, Liu; Changchun, Chai; Chunlei, Shi; Qingyang, Fan; Yuqian, Liu

    2016-12-01

    Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2 × 1016 to 5 × 1019 cm-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices. Project supported by the National Basic Research Program of China (No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (No. 2015-0214.XY.K).

  11. GaN membrane MSM ultraviolet photodetectors

    Science.gov (United States)

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

    2006-12-01

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

  12. Growth and characterization of cubic AlGaN/GaN based devices

    Energy Technology Data Exchange (ETDEWEB)

    Potthast, S.

    2006-11-15

    Cubic GaN and AlGaN layers are grown by radio frequency plasma assisted molecular beam epitaxy on freestanding 3C-SiC (001) substrates. Detailed analysis of the substrate quality reveal a direct dependence of the roughness of the 3C-SiC on the dislocation density. Additionally a strong influence of the substrate quality on the quality of cubic GaN layers is found. GaN, AlGaN and AlN buffer layers grown at different temperatures are used to improve the structural properties of the c-GaN buffer. Best values are obtained for AlN buffers deposited at T{sub Subs}=720 C. Furthermore, the growth temperature of the buffer itself is varied. Optimized results are found for T{sub Subs}=720 C grown under a Ga coverage of one monolayer. On top of the GaN buffer, AlGaN films (0Ga coverages of one monolayer and much greater than one monolayer. A linear dependence between the Al metal flux and the Al mole fraction is measured. Investigation of the growth front using reflection high energy electron diffraction as a probe, show a predominant two-dimensional growth mode. With increasing Al mole fraction, a change in the resistivity of the AlGaN layer is observed due to the gettering of oxygen by aluminum and the variation of the oxygen ionization energy as a function of the Al content. Schottky diodes are fabricated on GaN and AlGaN using nickel as contact material. A strong deviation of the current voltage characteristics from thermionic emission theory is found, measuring anormal high leakage current, caused by the presence of oxygen donors near the surface. It is investigated, that thermal annealing in air reduces the reverse current by three orders of magnitude. AlGaN/GaN are used to fabricate heterojunction field effect transistor structures. Analysis of the capacitance-voltage characteristics at T=150 K revealed clear evidence for the existence of a two-dimensional electron gas, and a sheet carrier concentration of about 1.6 x 10{sup 12}cm{sup -2} is

  13. Formation, atomic structure, and electronic properties of GaSb quantum dots in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Timm, R.

    2007-12-14

    In this work, cross-sectional scanning tunneling microscopy and spectroscopy are used for the first time to study the shape, size, strain, chemical composition, and electronic properties of capped GaSb/GaAs QDs at the atomic scale. By evaluating such structural results on a variety of nanostructures built using different epitaxy methods and growth conditions, details on the underlying QD formation processes can be revealed. A cross-over from flat quantum wells (QWs) to optically active QDs can be observed in samples grown by metalorganic chemical vapor deposition (MOCVD) with increasing amount of GaSb, including self-assembled Sb accumulations within a still two-dimensional layer and tiny three-dimensional GaSb islands probably acting as precursor structures. The QWs consist of significantly intermixed material with stoichiometries of maximally 50% GaSb, additionally exhibiting small gaps filled with GaAs. A higher GaSb content up to nearly pure material is found in the QDs, being characterized by small sizes of up to 8 nm baselength and about 2 nm height. In spite of the intermixing, all nanostructures have rather abrupt interfaces, and no significant Sb segregation in growth direction is observed. This changes completely when molecular beam epitaxy (MBE) is used as growth method, in which case individual Sb atoms are found to be distributed over several nm above the nanostructures. Massive group-V atomic exchange processes are causing this strong inter-mixing and Sb segregation during GaAs overgrowth. In combination with the large strain inherent to GaSb/GaAs QDs, this segregation upon overgrowth is assumed to be the reason for a unique structural phenomenon: All MBE-grown QDs, independent of the amount of deposited GaSb, exhibit a ring structure, consisting of a ring body of high GaSb content and a more or less extended central gap filled with GaAs. These rings have formed in a self-assembled way even when the initial GaSb layer was overgrown considerably fast

  14. 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.

  15. InGaN multiple-quantum-well epifilms on GaN-sillicon substrates for microcavities and surface-emitting lasers

    Energy Technology Data Exchange (ETDEWEB)

    Lee, June Key [Chonnam National University, Gwangju (Korea, Republic of); Cho, Hoon; Kim, Bok Hee; Park, Si Hyun [Chosun University, Gwangju (Korea, Republic of); Gu, Erdan; Watson, Ian; Dawson, Martin [University of Strathclyde, Wolfson Centre, Glasgow (United Kingdom)

    2006-07-15

    We report the processing of InGaN/GaN epifilms on GaN-silicon substrates. High-quality InGaN/GaN multi-quantum wells (MQWs) were grown on GaN-silicon substrates, and their membranes were successfully fabricated using a selective wet etching of silicon followed by a dry etching of the AlGaN buffer layer. With atomic force microscope (AFM) measurements and photoluminescence (PL) measurements, we investigated the physical and the optical properties of the InGaN/GaN MQWs membranes. On the InGaN/GaN MQW membranes, dielectric distributed Bragg reflector (DBRs) were successfully deposited, which give, new possibilities for use in GaN microcavity and surface-emitting laser fabrication.

  16. On the optimization of asymmetric barrier layers in InAlGaAs/AlGaAs laser heterostructures on GaAs substrates

    DEFF Research Database (Denmark)

    Zhukov, A. E.; Asryan, L. V.; Semenova, Elizaveta;

    2015-01-01

    Band offsets at the heterointerface are calculated for various combinations of InAlGaAs/AlGaAs heteropairs that can be synthesized on GaAs substrates in the layer-by-layer pseudomorphic growth mode. Patterns which make it possible to obtain an asymmetric barrier layer providing the almost obstruc...... for the critical thickness of the indium-containing quaternary solid solution....

  17. Effect on Ordering of the Growth of GaInP Layers on (111)-GaAs Faces

    Science.gov (United States)

    Martínez, O.; Hortelano, V.; Jiménez, J.; Parra, V.; Pelosi, C.; Attolini, G.; Prutskij, T.

    2010-06-01

    GaInP, an essential material for multijunction structures of III-V compounds for solar cells, can achieve better photovoltaic responses when grown on (111)GaAs faces, due to the large internal electric fields generated by the off-diagonal strain. In this work, we explored metalorganic chemical vapor deposition growth of GaInP layers on (001)-, (111)Ga-, and (111)As-GaAs substrates, using different phosphine flow rates. The structural and optical properties of the layers have been studied by micro-Raman spectroscopy, microphotoluminescence, and cathodoluminescence. Problems such as composition control, growth rate, and the presence of ordered phases are addressed.

  18. Mn-induced modifications of Ga 3d photoemission from (Ga, Mn)As: evidence for long range effects.

    Science.gov (United States)

    Kanski, J; Ulfat, I; Ilver, L; Leandersson, M; Sadowski, J; Karlsson, K; Pal, P

    2012-10-31

    Using synchrotron based photoemission, we have investigated the Mn-induced changes in Ga 3d core level spectra from as-grown Ga(1-x)Mn(x)As. Although Mn is located in Ga substitutional sites, and therefore does not have any Ga nearest neighbors, the impact of Mn on the Ga core level spectra is pronounced even at Mn concentrations in the region of 0.5%. The analysis shows that each Mn atom affects a volume corresponding to a sphere with around 1.4 nm diameter.

  19. Chemical beam epitaxy growth of AlGaAs/GaAs tunnel junctions using trimethyl aluminium for multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Paquette, B.; DeVita, M.; Turala, A.; Kolhatkar, G.; Boucherif, A.; Jaouad, A.; Aimez, V.; Arès, R. [Institut Interdisciplinaire d' Innovation Technologique (3IT), Université de Sherbrooke, Sherbrooke, Québec (Canada); Wilkins, M.; Wheeldon, J. F.; Walker, A. W.; Hinzer, K. [Centre for Research in Photonics, University of Ottawa, Ottawa, ON (Canada); Fafard, S. [Cyrium Technologies Inc., Ottawa, ON (Canada)

    2013-09-27

    AlGaAs/GaAs tunnel junctions for use in high concentration multijunction solar cells were designed and grown by chemical beam epitaxy (CBE) using trimethyl aluminium (TMA) as the p-dopant source for the AlGaAs active layer. Controlled hole concentration up to 4⋅10{sup 20} cm{sup −3} was achieved through variation in growth parameters. Fabricated tunnel junctions have a peak tunneling current up to 6140 A/cm{sup 2}. These are suitable for high concentration use and outperform GaAs/GaAs tunnel junctions.

  20. Surface plasmon coupling dynamics in InGaN/GaN quantum-well structures and radiative efficiency improvement

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Iida, Daisuke; Chen, Yuntian

    2014-01-01

    for InGaN/GaN quantum-well structures. By using a thin SiN dielectric layer between Ag and GaN we manage to modify and improve surface plasmon coupling effects, and we attribute this to the improved scattering of the nanoparticles at the quantum-well emission wavelength. The results are interpreted using...... numerical simulations, where absorption and scattering cross-sections are studied for different sized particles on GaN and GaN/SiN substrates....

  1. Pulsed electron-beam-pumped laser based on AlGaN/InGaN/GaN quantum-well heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Gamov, N A; Zhdanova, E V; Zverev, M M; Peregudov, D V; Studenov, V B [Moscow State Institute of Radio-Engineering, Electronics and Automation (Technical University), Moscow (Russian Federation); Mazalov, A V; Kureshov, V A; Sabitov, D R; Padalitsa, A A; Marmalyuk, A A [Open Joint-Stock Company M.F. Stel' makh Polyus Research Institute, Moscow (Russian Federation)

    2015-07-31

    The parameters of pulsed blue-violet (λ ≈ 430 nm at T = 300 K) lasers based on an AlGaN/InGaN/GaN structure with five InGaN quantum wells and transverse electron-beam pumping are studied. At room temperature of the active element, the minimum electron energy was 9 keV and the minimum threshold electron beam current density was 8 A cm{sup -2} at an electron energy of 18 keV. (lasers)

  2. InGaP/GaAs heterojunction photosensor powered by an on-chip GaAs solar cell for energy harvesting

    Science.gov (United States)

    Than, Phuc Hong; Uchida, Kazuo; Makino, Takahiro; Ohshima, Takeshi; Nozaki, Shinji

    2016-04-01

    In this study, an InGaP/GaAs heterojunction phototransistor (HPT) and a GaAs solar cell were monolithically integrated into an HPT epitaxial wafer, and the battery-free operation of the HPT was demonstrated for energy harvesting. Although the thickness and doping condition of the layers were optimized for the HPT performance, but not for the solar cell performance, the obtained short-circuit current was high enough to operate the InGaP/GaAs HPT in a two-terminal (2T) configuration. A collector photocurrent of 0.63 mA was obtained when the energy-harvesting InGaP/GaAs 2T-HPT was exposed to white light with a power density of 35 mW/cm2, and it linearly increased with the power density. For a potential application of the energy-harvesting InGaP/GaAs HPT as a photosensor in space, the device was irradiated with electrons of 1 MeV energy and 1015 cm-2 fluence. No significant degradation of the fabricated energy-harvesting 2T-HPT after the high-energy electron irradiation guarantees its battery-free operation in space.

  3. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    Science.gov (United States)

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

  4. Hydrogen Generation using non-polar coaxial InGaN/GaN Multiple Quantum Well Structure Formed on Hollow n-GaN Nanowires

    Science.gov (United States)

    Park, Ji-Hyeon; Mandal, Arjun; Kang, San; Chatterjee, Uddipta; Kim, Jin Soo; Park, Byung-Guon; Kim, Moon-Deock; Jeong, Kwang-Un; Lee, Cheul-Ro

    2016-08-01

    This article demonstrates for the first time to the best of our knowledge, the merits of InGaN/GaN multiple quantum wells (MQWs) grown on hollow n-GaN nanowires (NWs) as a plausible alternative for stable photoelectrochemical water splitting and efficient hydrogen generation. These hollow nanowires are achieved by a growth method rather not by conventional etching process. Therefore this approach becomes simplistic yet most effective. We believe relatively low Ga flux during the selective area growth (SAG) aids the hollow nanowire to grow. To compare the optoelectronic properties, simultaneously solid nanowires are also studied. In this present communication, we exhibit that lower thermal conductivity of hollow n-GaN NWs affects the material quality of InGaN/GaN MQWs by limiting In diffusion. As a result of this improvement in material quality and structural properties, photocurrent and photosensitivity are enhanced compared to the structures grown on solid n-GaN NWs. An incident photon-to-current efficiency (IPCE) of around ~33.3% is recorded at 365 nm wavelength for hollow NWs. We believe that multiple reflections of incident light inside the hollow n-GaN NWs assists in producing a larger amount of electron hole pairs in the active region. As a result the rate of hydrogen generation is also increased.

  5. Electronic properties of GaSe, InSe, GaS and GaTe layered semiconductors: charge neutrality level and interface barrier heights

    Science.gov (United States)

    Brudnyi, V. N.; Sarkisov, S. Yu; Kosobutsky, A. V.

    2015-11-01

    Density functional theory calculations have been applied to study the structural and electronic properties of layered ɛ-GaSe, γ-InSe, β-GaS and GaTe compounds. The optimized lattice parameters have been obtained using vdW-DF2-C09 exchange-correlation functional, which is able to describe dispersion forces and produces interlayer distances in close agreement with experiments. Based on the calculated electronic band structures, the energy position of the charge neutrality level (CNL) in the III-VI semiconductors has been estimated for the first time. The room-temperature values of CNL are found to be 0.80 eV, 1.02 eV, 0.72 eV and 0.77 eV for ɛ-GaSe, β-GaS, GaTe and γ-InSe, respectively. The persistent p-type conductivity of the intentionally undoped ɛ-GaSe, β-GaS and GaTe and n-type conductivity of γ-InSe crystals are discussed and explained using the concept of CNL. We also estimated the barrier heights for a number of metal/semiconductor and semiconductor/semiconductor interfaces assuming partial Fermi level pinning at the CNL. A reasonable agreement between our calculations and the available experimental data has been obtained.

  6. Spin Polarization of Carriers in InGaAs Self-Assembled Quantum Rings Inserted in GaAs-AlGaAs Resonant Tunneling Devices

    Science.gov (United States)

    Orsi Gordo, V.; Gobato, Y. Galvão; Galeti, H. V. A.; Brasil, M. J. S. P.; Taylor, D.; Henini, M.

    2017-03-01

    In this work, we have investigated transport and polarization resolved photoluminescence (PL) of n-type GaAs-AlGaAs resonant tunneling diodes (RTDs) containing a layer of InGaAs self-assembled quantum rings (QRs) in the quantum well (QW). All measurements were performed under applied voltage, magnetic fields up to 15 T and using linearly polarized laser excitation. It was observed that the QRs' PL intensity and the circular polarization degree (CPD) oscillate periodically with applied voltage under high magnetic fields at 2 K. Our results demonstrate an effective voltage control of the optical and spin properties of InGaAs QRs inserted into RTDs.

  7. Recombination-current suppression in GaAs p-n junctions grown on AlGaAs buffer layers by molecular-beam epitaxy

    Science.gov (United States)

    Rancour, D. P.; Melloch, M. R.; Pierret, R. F.; Lundstrom, M. S.; Klausmeier-Brown, M. E.; Kyono, C. S.

    1987-08-01

    n+pp+GaAs and n+pP+ GaAs/GaAs/Al0.3Ga0.7As mesa diodes have been fabricated from films grown by molecular-beam epitaxy. The diodes made from films employing an AlGaAs buffer layer show marked improvements (a factor of 5 reduction) in recombination current densities. Deep level transient spectroscopy measurements moreover indicate that deep level concentrations are reduced by the AlGaAs buffer.

  8. InGaN Light-Emitting Diodes with an Embedded Nanoporous GaN Distributed Bragg Reflectors

    Science.gov (United States)

    Shiu, Guo-Yi; Chen, Kuei-Ting; Fan, Feng-Hsu; Huang, Kun-Pin; Hsu, Wei-Ju; Dai, Jing-Jie; Lai, Chun-Feng; Lin, Chia-Feng

    2016-07-01

    InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n+-GaN) in the 12-period n+-GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.3 nm with a 57 nm linewidth and a 97.1% peak reflectivity. The effective cavity length (6.0λ), the effective penetration depth (278 nm) in the nanoporous DBR structure, and InGaN active layer matching to Fabry-Pérot mode order 12 were observed in the far-field photoluminescence radiative spectra. High electroluminescence emission intensity and line-width narrowing effect were measured in the DBR-LED compared with the non-treated LED structure. Non-linear emission intensity and line-width reducing effect, from 11.8 nm to 0.73 nm, were observed by increasing the laser excited power. Resonant cavity effect was observed in the InGaN LED with bottom nanoporous-DBR and top GaN/air interface.

  9. Temperature dependency of the Ga/In distribution in Cu(In,Ga)Se2 absorbers in high temperature processes

    Science.gov (United States)

    Mueller, B. J.; Demes, T.; Lill, P. C.; Haug, V.; Hergert, F.; Zweigart, S.; Herr, U.

    2016-05-01

    The current article reports about the influence of temperature and glass substrate on Ga/In interdiffusion and chalcopyrite phase formation in the stacked elemental layer process. According to the Shockley-Queisser limit the optimum for single junction devices is near 1.4 eV, which is strongly coupled on the Ga/(Ga+In) ratio of Cu(In,Ga)Se2 thin film solar cells. To increase the Ga content in the active region of the Cu(In,Ga)Se2 a 70:30 CuGa alloy target is used. An increase of the selenization temperature leads to a more homogeneous Ga/In distribution and a less pronounced Ga agglomeration at the back contact. The Ga/In interdiffusion rates for different selenization temperatures and substrates were estimated with the model of a two layer system. At the highest selenization temperature used an absorber band gap of 1.12 eV was realized, which is similar to typical values of absorbers produced during the co-evaporation process. The Na diffusion into the Cu(In,Ga)Se2 is weakly temperature dependent but strongly influenced by the choice of the glass substrate composition.

  10. All-wurtzite (In,Ga)As-(Ga,Mn)As core-shell nanowires grown by molecular beam epitaxy.

    Science.gov (United States)

    Siušys, Aloyzas; Sadowski, Janusz; Sawicki, Maciej; Kret, Sławomir; Wojciechowski, Tomasz; Gas, Katarzyna; Szuszkiewicz, Wojciech; Kaminska, Agnieszka; Story, Tomasz

    2014-08-13

    Structural and magnetic properties of (In,Ga)As-(Ga,Mn)As core-shell nanowires grown by molecular beam epitaxy on GaAs(111)B substrate with gold catalyst have been investigated. (In,Ga)As core nanowires were grown at high temperature (500 °C) whereas (Ga,Mn)As shells were deposited on the {11̅00} side facets of the cores at much lower temperature (220 °C). High-resolution transmission electron microscopy images and high spectral resolution Raman scattering data show that both the cores and the shells of the nanowires have wurtzite crystalline structure. Scanning and transmission electron microscopy observations show smooth (Ga,Mn)As shells containing 5% of Mn epitaxially deposited on (In,Ga)As cores containing about 10% of In without any misfit dislocations at the core-shell interface. With the In content in the (In,Ga)As cores larger than 5% the (In,Ga)As lattice parameter is higher than that of (Ga,Mn)As and the shell is in the tensile strain state. Elaborated magnetic studies indicate the presence of ferromagnetic coupling in (Ga,Mn)As shells at the temperatures in excess of 33 K. This coupling is maintained only in separated mesoscopic volumes resulting in an overall superparamagnetic behavior which gets blocked below ∼ 17 K.

  11. Raman measurements of dilute nitride alloys GaP(As)N grown on GaP substrates

    Science.gov (United States)

    Lazarenko, A.; Pirogov, E.; Sobolev, M.; Bukatin, A.; Nikitina, E.

    2016-08-01

    The structural properties of GaP(As)N dilute nitrides alloys grown on GaP substrates by molecular-beam epitaxy are investigated. The samples were studied by Raman scattering and high-resolution X-ray diffraction. In this work the impact of lattice mismatch of GaP(As)N layer and GaP substrate on the form of the spectrum of Raman scattering of samples was detected. It was shown that the addition of arsenic in solid solution GaPAsN can compensate the elastic stresses in the crystal lattice, and we can estimate the lattice mismatch between epitaxial layer GaP(As)N and GaP substrate by the intensity ratio of LOX/TOr phonon peaks.

  12. Rapid fabrication and packaging of AlGaN/GaN high-temperature ultraviolet photodetectors using direct wire bonding

    Science.gov (United States)

    So, Hongyun; Senesky, Debbie G.

    2016-07-01

    Cost-effective fabrication and rapid packaging of AlGaN/GaN ultraviolet (UV) photodetectors was demonstrated using direct wire bonding between aluminum wires and a GaN surface. The fabricated photodetectors showed stable dark current levels through the highly conductive 2D electron gas (2DEG), which was electrically connected to aluminum bonding wires. At room temperature, the current passing through the 2DEG rapidly increased upon exposure to UV light because of the generated electrons excited in the AlGaN/GaN layers. In addition, the devices showed consistent and reliable operation at high temperatures up to 100 °C with mechanically stable bonding wires (pull strength of 3-5.2 gram-force), supporting the use of direct wire bonding techniques to fabricate simple AlGaN/GaN sensors for UV detection within harsh environments, such as downhole and space exploration applications.

  13. Magnetic domain pattern asymmetry in (Ga, Mn)As/(Ga,In)As with in-plane anisotropy

    Science.gov (United States)

    Herrera Diez, L.; Rapp, C.; Schoch, W.; Limmer, W.; Gourdon, C.; Jeudy, V.; Honolka, J.; Kern, K.

    2012-04-01

    Appropriate adjustment of the tensile strain in (Ga, Mn)As/(Ga,In)As films allows for the coexistence of in-plane magnetic anisotropy, typical of compressively strained (Ga, Mn)As/GaAs films, and the so-called cross-hatch dislocation pattern seeded at the (Ga,In)As/GaAs interface. Kerr microscopy reveals a close correlation between the in-plane magnetic domain and dislocation patterns, absent in compressively strained materials. Moreover, the magnetic domain pattern presents a strong asymmetry in the size and number of domains for applied fields along the easy [11¯0] and hard [110] directions which is attributed to different domain wall nucleation/propagation energies. This strong influence of the dislocation lines in the domain wall propagation/nucleation provides a lithography-free route to the effective trapping of domain walls in magneto-transport devices based on (Ga, Mn)As with in-plane anisotropy.

  14. Monolithic semiconductor saturable absorber mirror with strain-compensated GaInAs/GaAsP quantum wells

    Science.gov (United States)

    Xiang, N.; Liu, H. F.; Kong, J.; Tang, D. Y.; Pessa, M.

    2007-04-01

    We report a monolithic broadband semiconductor saturable absorber mirror (SESAM) operating for 1025-1100 nm wavelength range with strain-compensated GaInAs/GaAsP quantum wells (QWs). By introducing tensile-strained GaAsP barriers, the compressive strain caused by the GaInAs QWs can be compensated and good quality QWs are obtained. Strain-compensated GaInAs/GaAsP QWs are grown on top of a GaAs/AlAs distributed Bragg reflector (DBR) to form the SESAM structure. The SESAM has a broad high-reflective stopband of about 120 nm and has been successfully used in passively modelocking a Nd:Gd 0.64Y 0.36VO 4 solid-state laser operating at 1064 nm wavelength. Optical pulses as short as 4.5 ps are generated with a peak power of 3.7 kW.

  15. Spin dynamics in GaAs and (110)-GaAs heterostructures; Spindynamik in GaAs und (110)-GaAs-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Oertel, Stefan

    2012-07-01

    This thesis investigates the spin dynamics in both bulk GaAs and (llO)GaAs heterostructures using time- and polarization-resolved photoluminescence spectroscopy. In bulk GaAs the spin relaxation t ime is measured for the first time in the high temperature regime from 280 K to 400 K and is compared to numerical calculations. The numerical calculations are based on the spin relaxation theory of the Dyakonov-Perel mechanism effected by momentum scattering with polar optical phonons and electron-electron scattering and are in good agreement with the experimental results. Measurements of the dependence on the electron density serve to determine the energy dependent proportional factor between the electron density and the effective electron-electron scattering time. Also in bulk GaAs the interaction between the electron spin system and the nuclear spin system is investigated. The measured electron Lande g-factor under the influence of the nuclear magnetic field is used as an indicator to monitor the temporal evolution of the nuclear magnetic field under sustained dynamic nuclear polarization. Measurements with polarization modulated excitation enable the determination of the relevant time scale at which dynamic nuclear polarization takes place. Furthermore, the temporal evolution of the measured electron Lande g-factor shows the complex interplay of the dynamic nuclear polarization, the nuclear spin diffusion and the nuclear spin relaxation. In symmetric (110)-GaAs quantum wells the dependence of the inplane anisotropy of the electron Lande g-factor on the quantum well thickness is determined experimentally. The measurements are in very good agreement with calculations based upon k . p-theory and reveal a maximum of the anisotropy at maximum carrier localization in the quantum well. The origin of the anisotropy that is not present in symmetric (001) quantum wells is qualitatively described by means of a simplified model based on fourth-order perturbation theory. A

  16. XPS investigation of ion beam induced conversion of GaAs(0 0 1) surface into GaN overlayer

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Praveen [Surface Physics and Nanostructure Group, National Physical Laboratory, New Delhi 110012 (India); Department of Physics, Indian Institute of Technology, New Delhi 110016 (India); Kumar, Mahesh; Govind [Surface Physics and Nanostructure Group, National Physical Laboratory, New Delhi 110012 (India); Mehta, B.R. [Department of Physics, Indian Institute of Technology, New Delhi 110016 (India); Shivaprasad, S.M., E-mail: smsprasad@jncasr.ac.in [Jawaharlal Nehru Centre for Advanced Scientific Research, International Center for Material Science and Chemistry and Physics Materials Unit, Jakkur, 560064 Bangalore, Karnataka (India)

    2009-10-30

    For the advance of GaN based optoelectronic devices, one of the major barriers has been the high defect density in GaN thin films, due to lattice parameter and thermal expansion incompatibility with conventional substrates. Of late, efforts are focused in fine tuning epitaxial growth and in search for a low temperature method of forming low defect GaN with zincblende structure, by a method compatible to the molecular beam epitaxy process. In principle, to grow zincblende GaN the substrate should have four-fold symmetry and thus zincblende GaN has been prepared on several substrates including Si, 3C-SiC, GaP, MgO, and on GaAs(0 0 1). The iso-structure and a common shared element make the epitaxial growth of GaN on GaAs(0 0 1) feasible and useful. In this study ion-induced conversion of GaAs(0 0 1) surface into GaN at room temperature is optimized. At the outset a Ga-rich surface is formed by Ar{sup +} ion bombardment. Nitrogen ion bombardment of the Ga-rich GaAs surface is performed by using 2-4 keV energy and fluence ranging from 3 x 10{sup 13} ions/cm{sup 2} to 1 x 10{sup 18} ions/cm{sup 2}. Formation of surface GaN is manifested as chemical shift. In situ core level and true secondary electron emission spectra by X-ray photoelectron spectroscopy are monitored to observe the chemical and electronic property changes. Using XPS line shape analysis by deconvolution into chemical state, we report that 3 keV N{sub 2}{sup +} ions and 7.2 x 10{sup 17} ions/cm{sup 2} are the optimal energy and fluence, respectively, for the nitridation of GaAs(0 0 1) surface at room temperature. The measurement of electron emission of the interface shows the dependence of work function to the chemical composition of the interface. Depth profile study by using Ar{sup +} ion sputtering, shows that a stoichiometric GaN of 1 nm thickness forms on the surface. This, room temperature and molecular beam epitaxy compatible, method of forming GaN temperature can serve as an excellent template for

  17. Pressure Study of Photoluminescence in GaN/InGaN/ AlGaN Quantum Wells

    Science.gov (United States)

    Perlin, Piotr; Iota, V.; Weinstein, B. A.; Wisniewski, P.; Osinski, M.; Eliseev, P. G.

    1997-03-01

    We have studied the photoluminescence (PL) from two commercial high brightness single quantum well light emitting diodes (Nichia Chem. Industs.) with In_xGa_1-x N (x=0.45 and 0.2) as the active layers under hydrostatic pressures up to 7 GPa. These diodes are the best existing light emitters at short wavelengths, having the emission wavelengths of 430 nm and 530 nm depending on the content of indium in the 30 Åthick quantum wells. Although these devices show a remarkable quality and efficiency (luminosity as high as 12 cd), the mechanism of recombination remains obscure. We discovered that the pressure coefficient for each of the observed PL peaks is dramatically (2-3 times) lower than that of the energy gap of its InGaN active layer. These observations, in conjunction with the fact that the observed emission occurs below the energy gap of the quantum well material, and also considering the anomalous temperature behavior of the emission (peak energy increasing with temperature) suggest the involvement of localized states and exclude a simple band-to-band recombination picture. These localized states may be tentatively attributed to the presence of band tails in the gap which stem from composition fluctuations in the InGaN alloy. vih>(figures)

  18. Magnetic field-dependent of binding energy in GaN/InGaN/GaN spherical QDQW nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    El Ghazi, Haddou, E-mail: hadghazi@gmail.com [Solid State Laboratory, Faculty of science, Dhar EL Mehrez, BP 1796 Fes-Atlas (Morocco); Special mathematics, CPGE Kénitra, Chakib Arsalane Street (Morocco); Jorio, Anouar; Zorkani, Izeddine [Solid State Laboratory, Faculty of science, Dhar EL Mehrez, BP 1796 Fes-Atlas (Morocco)

    2013-10-15

    Simultaneous study of magnetic field and impurity's position effects on the ground-state shallow-donor binding energy in GaN|InGaN|GaN (core|well|shell) spherical quantum dot–quantum well (SQDQW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated within the framework of the effective-mass approximation and an infinite deep potential describing the quantum confinement effect. A Ritz variational approach is used taking into account of the electron-impurity correlation and the magnetic field effect in the trial wave-function. It appears that the binding energy depends strongly on the external magnetic field, the impurity's position and the structure radius. It has been found that: (i) the magnetic field effect is more marked in large layer than in thin layer and (ii) it is more pronounced in the spherical layer center than in its extremities.

  19. High-performance 980-nm emission wavelength InGaAs/AlGaAs/GaAs laser diodes

    Science.gov (United States)

    Suruceanu, Grigore I.; Caliman, Andrei N.; Vieru, Stanislav T.; Iakovlev, V. P.; Sarbu, A. V.; Mereuta, Alexandru Z.

    2000-02-01

    This paper present the fabrication and mirrors passivation process of InGaAs/AlGaAs/GaAs narrow stripe 980 nm emission wavelength laser diodes. After mesa-stripe definition and Au-contact deposition procedures, a procedure of in-vacuum cleaving and in-situ passivation with (lambda) /2-thick ZnSe layers was performed. 960 micrometers and 500 micrometers length laser diodes bars was fabricated as a result. Antireflection-high reflectivity coating were formed on the bars facets. Laser diodes were soldered p-junction-side down on copper submounts. The room temperature CW threshold current value of 20 mA and CW maximum output power of 440 mW at 760 mA pumping current were obtained. The far-field emission pattern of laser diodes is lateral single mode in large range of output powers. These laser diodes were used for laser diode module fabrication. In this module the laser diodes was coupled with tapered single mode 9 micrometers /125 micrometers optical fiber with a fused microlens at the end. CW output optical power of 40 mW from the fiber was obtained at 240 mA operating current of the laser diode module.

  20. Addressing the chemical sorcery of "GaI": benefits of solid-state analysis aiding in the synthesis of P→Ga coordination compounds.

    Science.gov (United States)

    Malbrecht, Brian J; Dube, Jonathan W; Willans, Mathew J; Ragogna, Paul J

    2014-09-15

    The differing structures and reactivities of "GaI" samples prepared with different reaction times have been investigated in detail. Analysis by FT-Raman spectroscopy, powder X-ray diffraction, (71)Ga solid-state NMR spectroscopy, and (127)I nuclear quadrupole resonance (NQR) provides concrete evidence for the structure of each "GaI" sample prepared. These techniques are widely accessible and can be implemented quickly and easily to identify the nature of the "GaI" in hand. The "GaI" prepared from exhaustive reaction times (100 min) is shown to possess Ga2I3 and an overall formula of [Ga(0)]2[Ga(+)]2[Ga2I6(2-)], while the "GaI" prepared with the shortest reaction time (40 min) contains GaI2 and has the overall formula [Ga(0)]2[Ga(+)][GaI4(-)]. Intermediate "GaI" samples were consistently shown to be fractionally composed of each of these two preceding formulations and no other distinguishable phases. These "GaI" phases were then shown to give unique products upon reactions with the anionic bis(phosphino)borate ligand class. The reaction of the early-phase "GaI" gives rise to a unique phosphine Ga(II) dimeric coordination compound (3), which was isolated reproducibly in 48% yield and convincingly characterized. A base-stabilized GaI→GaI3 fragment (4) was also isolated using the late-phase "GaI" and characterized by multinuclear NMR spectroscopy and X-ray crystallography. These compounds can be considered unique examples of low-oxidation-state P→Ga coordination compounds and possess relatively long Ga-P bond lengths in the solid-state structures. The anionic borate backbone therefore results in interesting architectures about gallium that have not been observed with neutral phosphines.

  1. GaN Micromechanical Resonators with Meshed Metal Bottom Electrode

    Directory of Open Access Journals (Sweden)

    Azadeh Ansari

    2015-03-01

    Full Text Available 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.

  2. Detectability of metastatic bone tumor by Ga-67 scintigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Koizumi, Kiyoshi; Uchiyama, Guio; Araki, Tsutomu; Hihara, Toshihiko; Ogata, Hitoshi; Monzawa, Shuichi; Kachi, Kenji; Matsusako, Masaki

    1989-03-01

    Ga-67 scintigrams in patients with malignant diseases sometimes reveal uptake of the tracer in the bone metastases. Detectability of Ga-67 scintigraphy for metastatic bone tumors and benign bone lesions was compared with that of Tc-99m bone scintigraphy. Countable bone metastases detected by bone scintigraphy were evaluated whether the lesion showed apparent, faint, or negative Ga-67 uptake. Of 47 lesions 23 (49%) showed apparent uptake and 17 (36%) showed negative uptake, only 7 (10%) mostly fracture/osteotomy, showed apparent uptake of the tracer. Uptake in the other benign lesions such as trauma of the ribs, spondylosis deformans, and arthrosis deformans was rather faint. In patients with multiple bone metastases, 9 patients (82%) out of 11 showed more prominent abnormal findings in Tc-99m MDP bone scintigraphy than in Ga-67 scintigraphy; that is, Ga-67 scintigraphy was not able to reveal all metastatic bone lesions. In patients with untreated or recurrent tumors, relation between Ga-67 uptake in the tumors and that in the bone metastases was evaluated. Of 7 patients with negative Ga-67 uptake in the bone metastases; that is, there seemed to be little relation between Ga-67 affinity to the primary tumors and that to the bone metastases. Mechanisms of the Ga-67 uptake in the bone metastases were discussed. Not only the tumor cells or tissues in the bone metastases but also bone mineral or osteoclasts might be the deposition sites of Ga-67.

  3. Fabry-Perot Microcavity Modes in Single GaP/GaNP Core/Shell Nanowires.

    Science.gov (United States)

    Dobrovolsky, Alexander; Stehr, Jan E; Sukrittanon, Supanee; Kuang, Yanjin; Tu, Charles W; Chen, Weimin M; Buyanova, Irina A

    2015-12-16

    Semiconductor nanowires (NWs) are attracting increasing interest as nanobuilding blocks for optoelectronics and photonics. A novel material system that is highly suitable for these applications are GaNP NWs. In this article, we show that individual GaP/GaNP core/shell nanowires (NWs) grown by molecular beam epitaxy on Si substrates can act as Fabry-Perot (FP) microcavities. This conclusion is based on results of microphotoluminescence (μ-PL) measurements performed on individual NWs, which reveal periodic undulations of the PL intensity that follow an expected pattern of FP cavity modes. The cavity is concluded to be formed along the NW axis with the end facets acting as reflecting mirrors. The formation of the FP modes is shown to be facilitated by an increasing index contrast with the surrounding media. Spectral dependence of the group refractive index is also determined for the studied NWs. The observation of the FP microcavity modes in the GaP/GaNP core/shell NWs can be considered as a first step toward achieving lasing in this quasidirect bandgap semiconductor in the NW geometry.

  4. Suppression of alloy fluctuations in GaAs-AlGaAs core-shell nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Loitsch, Bernhard; Winnerl, Julia; Parzinger, Eric; Matich, Sonja; Wurstbauer, Ursula; Riedl, Hubert; Abstreiter, Gerhard; Finley, Jonathan J.; Koblmüller, Gregor [Walter Schottky Institut and Physik Department, Technische Universität München, 85748 Garching (Germany); Jeon, Nari; Lauhon, Lincoln J. [Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Döblinger, Markus [Department of Chemistry, Ludwig-Maximilians-Universität Munich, 81377 München (Germany)

    2016-08-29

    Probing localized alloy fluctuations and controlling them by growth kinetics have been relatively limited so far in nanoscale structures such as semiconductor nanowires (NWs). Here, we demonstrate the tuning of alloy fluctuations in molecular beam epitaxially grown GaAs-AlGaAs core-shell NWs by modifications of shell growth temperature, as investigated by correlated micro-photoluminescence, scanning transmission electron microscopy, and atom probe tomography. By reducing the shell growth temperature from T > 600 °C to below 400 °C, we find a strong reduction in alloy fluctuation mediated sharp-line luminescence, concurrent with a decrease in the non-randomness of the alloy distribution in the AlGaAs shell. This trend is further characterized by a change in the alloy compositional structure from unintentional quasi-superlattices of Ga- and Al-rich AlGaAs layers at high T to a nearly homogeneous random alloy distribution at low T.

  5. Heterointegration of InGaAs/GaAs quantum wells on micro-patterned Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Jung, A., E-mail: junga@phys.ethz.ch; Taboada, A. G.; Stumpf, W.; Kreiliger, T.; Känel, H. von [Laboratory for Solid State Physics, ETH Zürich, Otto-Stern-Weg 1, CH-8093 Zürich (Switzerland); Isa, F. [Laboratory for Solid State Physics, ETH Zürich, Otto-Stern-Weg 1, CH-8093 Zürich (Switzerland); L-NESS, Department of Physics, Politecnico di Milano, via Anzani 42, I-22100 Como (Italy); Isella, G. [L-NESS, Department of Physics, Politecnico di Milano, via Anzani 42, I-22100 Como (Italy); Barthazy Meier, E. [Scientific Center for Optical and Electron Microscopy (ScopeM), ETH Zürich, Auguste-Piccard-Hof 1, CH-8093 Zürich (Switzerland)

    2015-08-21

    InGaAs/GaAs quantum wells (QWs) grown on μ-patterned Ge/Si substrates by metal organic vapor phase epitaxy are investigated by electron microscopy and spatially resolved photoluminescence (PL) spectroscopy. The lattice parameter mismatch of GaAs and Si is overcome by a Ge buffer layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals form truncated pyramids whose shape is strongly affected by the geometry of the underlying pattern consisting of 8 μm deep and 3–50 μm wide square Si pillars. Comparing the measured PL energies with calculations performed in the effective mass approximation reveals that the QW emission energies are significantly influenced by the GaAs morphology. It is shown that the geometry favors indium diffusion during growth from the inclined facets towards the top (001) facet. The Si pillar-size dependent release of thermally induced strain observed in the PL measurements is confirmed by X-ray diffraction.

  6. AlGaAs/GaAs tunnel junctions in a 4-J tandem solar cell

    Institute of Scientific and Technical Information of China (English)

    Lü Siyu; Qu Xiaosheng

    2011-01-01

    The Ⅲ-Ⅴ compound tandem solar cell is a third-generation new style solar cell with ultra-high efficiency.The energy band gaps of the sub-cells in a GaInP/GaAs/InGaAs/Ge 4-J tandem solar cell are 1.8,1.4,1.0and 0.7 eV,respectively.In order to match the currents between sub-cells,tunnel junctions are used to connect the sub-cells.The characteristics of the tunnel junction,the material used in the tunnel junction,the compensation of the tunnel junction to the overall cell's characteristics,the tunnel junction's influence on the current density of sub-cells and the efficiency increase are discussed in the paper.An A1GaAs/GaAs tunnel junction is selected to simulate the cell's overall characteristics by PC 1 D,current densities of 16.02,17.12,17.75 and 17.45 mA/cm2 are observed,with a Voc of 3.246 V,the energy conversion efficiency under AM0 is 33.9%.

  7. DLTS characterization of silicon nitride passivated AlGaN/GaN heterostructures

    Science.gov (United States)

    Mosca, R.; Gombia, E.; Passaseo, A.; Tasco, V.; Peroni, M.; Romanini, P.

    2004-10-01

    Passivating the ungated surface of AlGaN/GaN HEMTs with silicon nitride (SiN) is effective in improving the microwave output power performances of these devices. However, very little information is available about surface states in GaN-based HEMTs after SiN passivation. In this work we investigate AlGaN/GaN HEMTs structures having either metal-semiconductor or metal-SiN-semiconductor gate contacts. In short gate devices conductance DLTS measurements point out a hole-like peak that shows an anomalous behaviour and can be ascribed to surface states in the access regions of the device. In insulated gate HEMTs a band of levels is detected and ascribed to surface states, whose energy ranges from 0.14 to 0.43 eV. Capacitance-voltage measurements allow us to point out the existence of a second band of interface states deeper in energy than the former one. This band is responsible for slow transients observed in the characteristics of the insulated gate FAT-HEMT.

  8. Positron emitting [68Ga]Ga-based imaging agents: chemistry and diversity.

    Science.gov (United States)

    Velikyan, Irina

    2011-09-01

    Positron Emission Tomography (PET) field and, in particular utilization of (68)Ga radiometal is getting momentum. The development of new imaging agents for targeted, pre-targeted, non-targeted imaging and their clinical applications is accelerating worldwide. The pharmacopoeia monographs regarding generator produced (68)Ga radionuclide and (68)Ga-labeled somatostatin (SST) analogues are in progress. The number of commercial generators and automated synthesizers for (68)Ga-labeling chemistry is increasing constantly. Development of a molecular imaging agent is a complex process including identification of the biological target, respective lead compound, synthesis of the imaging agent, its chemical characterization, pre-clinical, and clinical evaluation. The introduction of new radiopharmaceuticals and their accessibility are important factors determining the expansion of clinical nuclear medicine for early disease detection and personalized medicine with higher therapeutic efficiency. Further, the availability of the technology for GMP compliant automated tracer production can facilitate the introduction of new radiopharmaceuticals due to the ability to conduct standardized and harmonized multi-center studies for regulatory approval. This review reflects on the current status of (68)Ga in PET field with the focus on the achievements in the chemistry as well as diversity and potential of the resulting tracers.

  9. Growth initiation processes for GaAs and AlGaAs in CBE

    CERN Document Server

    Hill, D

    2002-01-01

    'in-growth' reconstruction to stabilise. However unlike for TMGa, GaAs growth with TEGa proceeds by a non-self limiting growth mode and TEGa rapidly dissociates. The result of this is that TEGa decomposes on top of other TEGa molecules, or their fragments and due to the high flux rate this leads to a 'stacking-up' of Ga on the surface. The presence of excess Ga provides a rapid increase of surface reflectance and then its subsequent decay as the excess Ga is incorporated by the increasing As content of the surface. The average growth rate during the transient period is equal to that of subsequent 'post-transient' period. However it is not certain as to whether the growth rate is constant throughout the transient period. The aim of this work was to investigate the nature of the transient period found in reflectance anisotropy (RA) measurements of high III:V BEP ratio growth of gallium arsenide (GaAs) and aluminium gallium arsenide (AIGaAs) by chemical beam epitaxy (CBE). Growth at substrate temperatures betwee...

  10. Strain relief InGaN/GaN MQW micro-pillars for high brightness LEDs

    KAUST Repository

    Shen, Chao

    2013-01-01

    Micro-structured group-III-nitrides are considered as promising strain relief structures for high efficiency solid state lighting. In this work, the strain field in InGaN/GaN multi-quantum wells (MQWs) micro-pillars is investigated using micro-Raman spectroscopy and the design of micro-pillars were studied experimentally. We distinguished the strained and strain-relieved signatures of the GaN layer from the E2 phonon peak split from the Raman scattering signatures at 572 cm-1 and 568 cm-1, respectively. The extent of strain relief is examined considering the height and size of micro-pillars fabricated using focused ion beam (FIB) micro-machining technique. A significant strain relief can be achieved when one micro-machined through the entire epi-layers, 3 μm in our study. The dependence of strain relief on micro-pillar diameter (D) suggested that micro-pillar with D < 3 μm showed high degree of strain relief. Our results shed new insights into designing strain-relieved InGaN/GaN microstructures for high brightness light emitting diode arrays. © 2013 IEEE.

  11. Beta decay of {sup 61}Ga

    Energy Technology Data Exchange (ETDEWEB)

    Oinonen, M.; Dendooven, P.; Jokinen, A.; Penttilae, H.; Aeystoe, J. [Jyvaeskylae Univ. (Finland). Dept. of Physics; Baumann, P.; Knipper, A.; Ramdhane, M.; Walter, G. [Institut de Recherches Subatomiques, F-67037 Strasbourg (France); Fujita, Y. [Department of Physics, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Gorska, M.; Grawe, H.; Hu, Z.; Kirchner, R.; Klepper, O.; Liu, W.; Roeckl, E. [Gesellschaft fuer Schwerionenforschung, Postfach 110552, D-64220 Darmstadt (Germany); Janas, Z.; Plochocki, A. [Institute of Experimental Physics, Warsaw University, PL-00681 Warsaw (Poland)

    1999-06-01

    The {beta} decay of {sup 61}Ga to its mirror nucleus {sup 61}Zn has been measured for the first time by using on-line mass separation and {beta}-delayed gamma-ray spectroscopy. The observed decay strength to the ground state implies superallowed character in accordance with the systematics of the mirror decays in the sd and fp shell. The {beta} feedings observed to four excited states in {sup 61}Zn are consistent with earlier spin-parity assignments based on in-beam experiments. The ground-state spin and parity for {sup 61}Ga were determined to be 3/2{sup -}. (orig.) With 3 figs., 2 tabs., 37 refs.

  12. GaN-based green laser diodes

    Science.gov (United States)

    Lingrong, Jiang; Jianping, Liu; Aiqin, Tian; Yang, Cheng; Zengcheng, Li; Liqun, Zhang; Shuming, Zhang; Deyao, Li; Ikeda, M.; Hui, Yang

    2016-11-01

    Recently, many groups have focused on the development of GaN-based green LDs to meet the demand for laser display. Great progresses have been achieved in the past few years even that many challenges exist. In this article, we analysis the challenges to develop GaN-based green LDs, and then the approaches to improve the green LD structure in the aspect of crystalline quality, electrical properties, and epitaxial layer structure are reviewed, especially the work we have done. Project supported by the National Key Research and Development Progress of China (Nos. 2016YFB0401803, 2016YFB0402002), the National Natural Science Foundation of China (Nos. 61574160, 61334005), the Strategic Priority Research Program of the Chinese Academy of Science (No. XDA09020401), and the Science and Technology Support Project of Jiangsu Province (No. BE2013007).

  13. Preparation of AlGaN/GaN Heterostructures on Sapphire Using Light Radiation Heating Metal-Organic Chemical Vapor Deposition at Low Pressure

    Institute of Scientific and Technical Information of China (English)

    ZHOU Yu-Gang; ZHENG You-Dou; SHEN Bo; ZHANG Rong; LI Wei-Ping; CHEN Peng; CHEN Zhi-Zhong; GU Shu-Lin; SHI Yi; Z. C. Huang

    2000-01-01

    AlGaN/GaN heterostructures on sapphire substrate were fabricated by using light radiation heating metalor ganic chemical vapor deposition. Photoluminescence excitation spectra show that there are two abrupt slopes corresponding to the absorption edges of AlGaN and GaN, respectively. X-ray diffraction spectra clearly exhibit the GaN (0002), (0004), and A1GaN (0002), (0004) diffraction peaks, and no diffraction peak other than those from the GaN {0001} and A1GaN {0001} planes is found. Reciprocal space mapping indicates that there is no tilt between the AlGaN layer and the GaN layer. All results also indicate that the sample is of sound quality and the Al composition in the AlGaN layer is of high uniformity.

  14. Ga-Polar (In ,Ga )N /GaN Quantum Wells Versus N-Polar (In,Ga)N Quantum Disks in GaN Nanowires: A Comparative Analysis of Carrier Recombination, Diffusion, and Radiative Efficiency

    Science.gov (United States)

    Feix, F.; Flissikowski, T.; Sabelfeld, K. K.; Kaganer, V. M.; Wölz, M.; Geelhaar, L.; Grahn, H. T.; Brandt, O.

    2017-07-01

    We investigate the radiative and nonradiative recombination processes in planar (In ,Ga )N /GaN (0001 ) quantum wells and (In,Ga)N quantum disks embedded in GaN (000 1 ¯ ) nanowires using photoluminescence (PL) spectroscopy under both continuous-wave and pulsed excitation. The PL intensities of these two samples quench only slightly between 10 and 300 K, which is commonly taken as evidence for high internal quantum efficiencies. However, a side-by-side comparison shows that the absolute intensity of the Ga-polar quantum wells is two orders of magnitude higher than that of the N-polar quantum disks. A similar difference is observed for the initial decay time of PL transients obtained by time-resolved measurements, indicating the presence of a highly efficient nonradiative decay channel for the quantum disks. In apparent contradiction to this conjecture, the decay of both samples is observed to slow down dramatically after the initial rapid decay. Independent of temperature, the transients approach a power law for longer decay times, reflecting the fact that recombination occurs between individual electrons and holes with varying spatial separation. Employing a coupled system of stochastic integro-differential equations taking into account both radiative and nonradiative Shockley-Read-Hall recombination of spatially separate electrons and holes as well as their diffusion, we obtain simulated transients matching the experimentally obtained ones. The results reveal that even dominant nonradiative recombination conserves the power-law decay for (In ,Ga )N /GaN {0001 } quantum wells and disks.

  15. Optical properties of InAlGaAs quantum wells: Influence of segregation and band bowing

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, Wolfgang

    1999-01-01

    Knowledge of the quaternary InAlGaAs material system is very limited for the composition range relevant for growth on GaAs substrates. We report on the characterization and modeling of InAlGaAs quantum wells with AlGaAs barriers, grown pseudomorphically on a GaAs substrate with molecular beam...

  16. Parameter Optimization Based on GA and HFSS

    Institute of Scientific and Technical Information of China (English)

    SUN Shu-hui; WANG Bing-zhong

    2005-01-01

    A new project based on genetic algorithm (GA) and high frequency simulation software (HFSS) is proposed to optimize microwave passive devices effectively. This project is realized with a general program named as optimization program. The program is compiled by Matlab and the macro language of HFSS which is a fast and effective way to accomplish tasks. In the paper, two examples are used to show the project's feasibility.

  17. Piezoelectric field in strained GaAs.

    Energy Technology Data Exchange (ETDEWEB)

    Chow, Weng Wah; Wieczorek, Sebastian Maciej

    2005-11-01

    This report describes an investigation of the piezoelectric field in strained bulk GaAs. The bound charge distribution is calculated and suitable electrode configurations are proposed for (1) uniaxial and (2) biaxial strain. The screening of the piezoelectric field is studied for different impurity concentrations and sample lengths. Electric current due to the piezoelectric field is calculated for the cases of (1) fixed strain and (2) strain varying in time at a constant rate.

  18. Piezoelectric effects of single-crystal GaAs and multi-layered AlxGa1-xAs/GaAs material measured by the Michelson interferometer

    Directory of Open Access Journals (Sweden)

    Patara Aiyarak

    2003-09-01

    Full Text Available The inverse piezoelectric effect, in which the strains were electrically induced, in a single crystal of GaAs and in a multilayer structure of AlxGa1-xAs/GaAs was measured using a simple optical system, i.e., Michelson interferometer. An ac driving voltage was applied to the sample to produce a change in the order of 10-13 m in sample thickness. These changes were detected by the optical system to give the sample displacement as a function of applied driving voltage. The slope of the plot of this relationship led to the piezoelectric coefficients of (2.8±0.1×10-12 and (3.9±0.1×10-12 m/V for GaAs and AlxGa1-xAs/GaAs, respectively. The first agreed well with reported values and the latter was the first report for AlxGa1-xAs/GaAs. Owing to the equality for the inverse effect and the direct effect, in which an electric field can be mechanically induced, it is anticipated that in the absence of external electric field, the internal piezoelectric field can be induced in the multi-layered semiconductor.

  19. Formation process and superparamagnetic properties of (Mn,Ga)As nanocrystals in GaAs fabricated by annealing of (Ga,Mn)As layers with low Mn content

    DEFF Research Database (Denmark)

    Sadowski, Janusz; Domagala, Jaroslaw Z.; Mathieu, Roland;

    2011-01-01

    °C) annealing of (Ga,Mn)As layers with Mn concentrations between 0.1% and 2%, grown by molecular beam epitaxy at 270°C. Decomposition of (Ga,Mn)As is already observed at the lowest annealing temperature of 400°C for layers with initial Mn content of 1% and 2%. Both cubic and hexagonal (Mn...

  20. Improved breakdown voltage of AlGaN/GaN HEMTs grown on Si substrates using partially Mg-doped GaN buffer layer by MOCVD

    Institute of Scientific and Technical Information of China (English)

    LAU; KeiMay

    2010-01-01

    AlGaN/GaN high electron mobility transistors(HEMTs) were grown on Si substrates by MOCVD.In the HEMT structure,a 1 μm GaN buffer layer was partially doped with Mg in an attempt to increase the resistivity and minimize the buffer leakage.The AlGaN/GaN HEMTs grown on undoped and partially Mg-doped GaN buffer layers were processed and the DC characteristics of the devices were characterized for comparing the effect of Mg doping.For the device with the partially Mg-doped GaN buffer layer,a lower drain leakage current density of 55.8 nA/mm,a lower gate leakage current density of 2.73 μA/mm,and a higher off-state breakdown voltage of 104 V were achieved with device dimensions Lg/Wg/Lgs/Lgd=1/10/1/1 μm,better than the device with the undoped GaN buffer layer,which has a higher drain leakage current density of 9.2 μA/mm,a higher gate leakage current density of 91.8 μA/mm,and a lower off-state breakdown voltage of 87 V with the same device dimensions.

  1. Investigation of gate-diode degradation in normally-off p-GaN/AlGaN/GaN high-electron-mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Ťapajna, M., E-mail: milan.tapajna@savba.sk; Kuzmík, J. [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Hilt, O.; Bahat-Treidel, E.; Würfl, J. [Ferdinand-Braun-Institut, Leibniz Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany)

    2015-11-09

    Gate diode conduction mechanisms were analyzed in normally-off p-GaN/AlGaN/GaN high-electron mobility transistors grown on Si wafers before and after forward bias stresses. Electrical characterization of the gate diodes indicates forward current to be limited by channel electrons injected through the AlGaN/p-GaN triangular barrier promoted by traps. On the other hand, reverse current was found to be consistent with carrier generation-recombination processes in the AlGaN layer. Soft breakdown observed after ∼10{sup 5 }s during forward bias stress at gate voltage of 7 V was attributed to formation of conductive channel in p-GaN/AlGaN gate stack via trap generation and percolation mechanism, likely due to coexistence of high electric field and high forward current density. Possible enhancement of localized conductive channels originating from spatial inhomogeneities is proposed to be responsible for the degradation.

  2. Efficiency enhancement of InGaN/GaN light-emitting diodes with pin-doped GaN quantum barrier

    Science.gov (United States)

    Sirkeli, Vadim P.; Yilmazoglu, Oktay; Al-Daffaie, Shihab; Oprea, Ion; Ong, Duu Sheng; Küppers, Franko; Hartnagel, Hans L.

    2017-01-01

    Blue InGaN/GaN light-emitting diodes with undoped, heavily Si-doped, Si delta-doped, heavily Mg-doped, Mg delta-doped, and Mg–Si pin-doped GaN barrier are investigated numerically. The simulation results demonstrate that the Mg–Si pin-doping in the GaN barrier effectively reduces the polarization-induced electric field between the InGaN well and the GaN barrier in the multiple quantum well, suppresses the quantum-confined Stark effect, and enhances the hole injection and electron confinement in the active region. For this light-emitting diode (LED) device structure, we found that the turn-on voltage is 2.8 V, peak light emission is at 415.3 nm, and internal quantum efficiency is 85.9% at 100 A cm‑2. It is established that the LED device with Mg–Si pin-doping in the GaN barrier has significantly improved efficiency and optical output power performance, and lower efficiency droop up to 400 A cm‑2 compared with LED device structures with undoped or Si(Mg)-doped GaN barrier.

  3. Suppressing efficiency droop using graded AlGaN/InGaN superlattice electron blocking layer for InGaN-based light-emitting diodes

    Science.gov (United States)

    Wang, C. K.; Hung, K. C.; Chiou, Y. Z.; Jheng, J. S.; Chang, S. P.; Chang, S. J.

    2017-06-01

    In this study, the numerical simulations with graded p-AlxGa1-xN/InyGa1-yN shortperiod superlattice (SPS) electron blocking layer (EBL) of blue InGaN/GaN light-emitting diodes (LEDs) have been investigated by the Advance Physical Model of Semiconductor Devices (APSYS) program. The simulation results show that the LEDs with graded p-AlxGa1-xN/InyGa1-yN SPS EBL exhibit better performances of internal quantum efficiency (IQE) and efficiency droop than those of conventional p-AlGaN/GaN SPS EBL. This is attributed to higher and lower effective potential barrier heights created in the conduction and valence band for electron and hole, respectively. The electron overflow effect can be effectively suppressed and the hole injection ability can also be remarkably enhanced. Therefore, the simulation results exhibit a significant increment in the IQE and the ratio of efficiency droop of the LEDs can be obviously reduced from 17.2% to 4.7%.

  4. The low-temperature mobility of two-dimensional electron gas in AlGaN/GaN heterostructures

    Institute of Scientific and Technical Information of China (English)

    Zhang Jin-Feng; Mao Wei; Zhang Jin-Cheng; Hao Yue

    2008-01-01

    To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scattering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGan/GaN interface roughness increases due to the stress accumulation in AlGaN layer.

  5. Radiation damage effects on double-junction GaInP{sub 2}/GaAs solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yueyuan [Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Hu, Jianmin, E-mail: hujianmin@foxmail.com [Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Wu, Yiyong [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Xu, Jianwen; Lu, Jianfeng [Shanghai Institute of Space Power Sources, Shanghai 200233 (China); Zhao, Huijie [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Qian, Bin [Shanghai Institute of Space Power Sources, Shanghai 200233 (China)

    2014-07-01

    The radiation effects on a double-junction GaInP{sub 2}/GaAs solar cell were studied under exposures of 100 keV protons, 10 MeV protons and 1 MeV electrons, in terms of changes on electrical properties and spectral response. The results indicate that the electrical property degradation of the double-junction GaInP{sub 2}/GaAs solar cell under irradiation occurs mainly due to the damage in the GaAs sub-cell. The GaAs sub-cell damage is primarily attributed to the decrease in collection efficiency of the minority carriers coming from its base bottom. It is revealed from the cell behavior under exposure to 100 keV protons irradiation that under the AM0 illumination, there is no obvious damage defected in the tunnel junction between the GaInP{sub 2} and the GaAs sub cells. In addition, the tunnel junction between the GaInP{sub 2} and the GaAs sub-cells is stable and no boundary traps are formed.

  6. Effect of Al substitution for Ga on the mechanical properties of directional solidified Fe-Ga alloys

    Science.gov (United States)

    Liu, Yangyang; Li, Jiheng; Gao, Xuexu

    2017-02-01

    Alloys of Fe82Ga18-xAlx (x=0, 4.5, 6, 9, 12, 13.5) were prepared by directional solidification technique and exhibited a preferred orientation along the axis of alloy rods. The saturation magnetostriction value of the Fe82Ga13.5Al4.5 alloy was 247 ppm under no pre-stress. The tensile properties of alloys of Fe82Ga18-xAlx at room temperature were investigated. The results showed that tensile ductility of binary Fe-Ga alloy was significantly improved with Al addition. The fracture elongation of the Fe82Ga18 alloy was only 1.3%, while that of the Fe82Ga9Al9 alloy increased up to 16.5%. Addition of Al increased the strength of grain boundary and cleavage, resulting in the enhancement of tensile ductility of the Fe-Ga-Al alloys. Analysis of deformation microstructure showed that a great number of deformation twins formed in the Fe-Ga-Al alloys, which were thought to be the source of serrated yielding in the stress-strain curves. The effect of Al content in the Fe-Ga-Al alloys on tensile ductility was also studied by the analysis of deformation twins. It indicated that the joint effect of slip and twinning was beneficial to obtain the best ductility in the Fe82Ga9Al9 alloy.

  7. Indium-Induced Effect on Polarized Electroluminescence from InGaN/GaN MQWs Light Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    RUAN Jun; YU Tong-Jun; JIA Chuan-Yu; TAO Ren-Chun; WANG Zhan-Guo; ZHANG Guo-Yi

    2009-01-01

    Polarization-resolved edge-emitting electroluminescence (EL) studies of InGaN/GaN MQWs of wavelengths from near-UV (390nm) to blue (468nm) light-emitting diodes (LEDs) are performed.Although the TE mode is dominant in all the samples of InGaN/GaN MQW LEDs,an obvious difference of light polarization properties is found in the InGaN/GaN MQW LEDs with different wavelengths.The polarization degree decreases from 52.4% to 26.9% when light wavelength increases.Analyses of band structures of InGaN/GaN quantum wells and luminescence properties of quantum dots imply that quantum-dot-like behavior is the dominant reason for the low luminescence polarization degree of blue LEDs,and the high luminescence polarization degree of UV LEDs mainly comes from QW confinement and the strain effect.Therefore,indium induced carrier confinement (quantum-dot-like behavior) might play a major role in the polarization degree change of InGaN/GaN MQW LEDs from near violet to blue.

  8. Effect of Growth Temperature on Size Distribution of GaSb/GaAs Quantum Dots%温度对GaSb/GaAs量子点尺寸分布的影响

    Institute of Scientific and Technical Information of China (English)

    刘仁俊; 李天天; 杨皓宇; 王连锴; 吕游; 张宝林

    2013-01-01

    The GaSb/GaAs quantum dots (QDs) were prepared by the technique of low pressure metalorganic chemical vapor deposition (LP-MOCVD).Based on analysis of samples for different growth temperatures,it turns out that the growth temperatures have little contribution to the morphology of GaSb/GaAs QDs and the shape of GaSb/GaAs QDs turns to be lens.The stress distributions between GaSb/GaAs interface lead to the "self-limiting" formation of GaSb QDs.Besides,due to discontinuous chemical potential of QDs,coupled with the effect of curing mechanism of Ostwald,the size distribution of QDs in certain range is discrete and two modes of QDs size appear.The surface mobility of antimony (Sb) adatoms has an important influence on the growth of GaSb/GaAs QDs.The discreteness of QDs can be efficiently improved by raising the growth temperature.With the process of heating up,the curing process of QDs can be presented.%采用低压金属有机物化学气相沉积(LP-MOCVD)法制备GaSb/GaAs量子点.通过对不同生长温度的样品进行分析发现温度的变化对GaSb/GaAs量子点的相位角无明显影响,量子点的形状是透镜型.由于量子点特殊的应力分布,可实现量子点的“自限制”生长.量子点的化学势不连续性以及Ostwald熟化机制的影响使得量子点尺寸分布在一定范围内不连续,会出现两种尺寸模式的量子点生长.Sb原子的表面迁移率对GaSb/GaAs量子点生长有较大的影响.升高温度可有效改善量子点的分立性,在升温过程中量子点体现出其熟化过程,高温时表面原子的解析附作用对量子点尺寸和密度的影响较大.

  9. Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar (11(2)over-bar2) GaN templates

    OpenAIRE

    M. Niehle; Trampert, A; Albert, S; Bengoechea-Encabo, A.; Calleja, E.

    2015-01-01

    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( 11 2 ̄ 2 ) substrate surface by molecular beam epitaxy. For the pract...

  10. New Decay Studies of 66Ga

    Science.gov (United States)

    Kumar, Suresh; Ahmad, I.; Carpenter, M. P.; Chen, J.; Greene, J. P.; Kondev, F. G.; Zhu, S.

    2014-03-01

    High-energy γ rays with energies up to 5.0 MeV are emitted in the radioactive decay of 66Ga (T1/2 = 9.49 h). Thus, this radionuclide appears to be a suitable candidate for energy and efficiency calibrations of high-resolution, γ-ray spectrometers that are employed in studies of very neutron-rich nuclei which have large Qβ values. In addition, accurate emission probabilities of this isotope are of interest to medical imaging applications, owing to the existence of large β+ decay branches, which need to be characterized with better accuracy. Decay studies of 66Ga were initiated using the γ-ray spectroscopy technique. The source was produced by means of the 66Zn(p,n) reaction at a beam energy of 12 MeV. Singles and γ - γ coincidences measurements were carried out using a single Ge detector and Gammasphere, respectively. The previously known 66Ga decay scheme was extended and many new γ rays were placed in the daughter nuclide 66Zn. The work at ANL was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. S. Kumar acknowledges support from the Indo-US Science and Technology Forum for the award of a Research Fellowship.

  11. Europium gallium garnet (Eu3Ga5O12) and Eu3GaO6: Synthesis and material properties

    Science.gov (United States)

    Sawada, Kenji; Nakamura, Toshihiro; Adachi, Sadao

    2016-10-01

    Eu-Ga-O ternary compounds were synthesized from a mixture of cubic (c-) Eu2O3 and monoclinic Ga2O3 (β-Ga2O3) raw powders using the solid-state reaction method by calcination at Tc = 1200 °C. The structural and optical properties of the Eu-Ga-O ternary compounds were investigated using X-ray diffraction analysis, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and Raman scattering measurements. Stoichiometric compounds such as cubic Eu3Ga5O12 (EGG) and orthorhombic Eu3GaO6 were synthesized using molar ratios of x = 0.375 and 0.75 [x≡Eu2O3/(Eu2O3 + Ga2O3)], respectively, together with the end-point binary compounds β-Ga2O3 (x = 0) and monoclinic (m-) Eu2O3 (x = 1.0). The structural change from "cubic" to "monoclinic" in Eu2O3 is due to the structural phase transition occurring at Tc ≥ 1050 °C. In principle, the perovskite-type EuGaO3 and monoclinic Eu4Ga2O9 can also be synthesized at x = 0.5 and 0.667, respectively; however, such stoichiometric compounds could not be synthesized in this study. The PL and PLE properties of EGG and Eu3GaO6 were studied in detail. The temperature dependence of the PL spectra was observed through measurements carried out between T = 20 and 300 K and explained using a newly developed model. Raman scattering measurements were also performed on the Eu-Ga-O ternary systems over the entire composition range from x = 0 (β-Ga2O3) to 1.0 (m-Eu2O3).

  12. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

    S Pal; C Jacob

    2004-12-01

    Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not available in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development 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 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.

  13. Synthesis of GaN films on porous silicon substrates

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A novel and simple method was employed to synthesize GaN films on porous silicon (PS) substrates. GaN films were obtained through the reaction between NH3 and Ga2O3 films deposited on the substrates with magnetron sputtering.Since GaN and PS are all good materials for luminescence, it is expected to obtain some new properties from GaN on PS.The samples were analyzed with X-ray diffraction (XRD) to identify crystalline structure. Fourier transmit infrared (FTIR)spectrum was used to analyze the chemical state of the samples. The films were observed with scanning electron microscopy (SEM) and were found to consist of many big crystal grains. Photoluminescence (PL) spectrum was used to illuminate the optical property of the GaN films.

  14. AlGaN/GaN HEMT材料外延技术研究%Research on the Materials Epitaxial Technology of AlGaN/GaN HEMT

    Institute of Scientific and Technical Information of China (English)

    杨红伟; 刘英斌

    2007-01-01

    采用低压MOCVD技术在蓝宝石和SiC衬底上生长了本征GaN和AlGaN/GaN HEMT结构材料.生长过程中采用了EpiTUNE Ⅱ在位监测技术,对材料生长工艺进行了模型分析以及优化控制.在获得具有良好表面形貌、晶体质量以及光荧光谱的GaN本征材料基础上,生长了AlGaN/GaN HEMT结构材料,获得了良好的2DEG性能.

  15. Growth orientation dependent photoluminescence of GaAsN alloys

    Energy Technology Data Exchange (ETDEWEB)

    Han, Xiuxun; Tanaka, Tomohiro; Kojima, Nobuaki; Ohshita, Yoshio; Yamaguchi, Masafumi [Toyota Technological Institute, 2-12-1 Hisakata, Tempaku, Nagoya 468-8511 (Japan); Sato, Shinichiro [Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292 (Japan)

    2012-01-16

    We report photoluminescence (PL) studies of both as-grown and electron-irradiated GaAsN epilayers on (311)A/B and (100) GaAs substrates. A long room-temperature (RT) PL lifetime, as well as an enhanced N incorporation, is observed in (311)B GaAsN epilayers as compared with (311)A and (100) samples. There is no direct correlation between the RT PL lifetime and the emission intensity from Ga vacancy complex detected at low temperature. The lifetime damage coefficient is relatively low for (311)B GaAsN. The irradiation-induced nonradiative recombination defects are suggested to be N- and/or As-related according to a geometrical analysis based on the tetrahedral coordination of GaAsN crystal.

  16. Alternating InGaN barriers with GaN barriers for enhancing optical performance in InGaN light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Yujue; Zeng, Yiping, E-mail: ypzeng@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China)

    2015-01-21

    InGaN-based light-emitting diodes (LEDs) with some specific designs on the quantum barrier layers by alternating InGaN barriers with GaN barriers are proposed and studied numerically. In the proposed structure, simulation results show that the carriers are widely dispersed in the multi-quantum well active region, and the radiative recombination rate is efficiently improved and the electron leakage is suppressed accordingly, due to the appropriate band engineering. The internal quantum efficiency and light-output power are thus markedly enhanced and the efficiency droop is smaller, compared to the original structures with GaN barriers or InGaN barriers. Moreover, the gradually decrease of indium composition in the alternating quantum barriers can further promote the LED performance because of the more uniform carrier distribution, which provides us a simple but highly effective approach for high-performance LED applications.

  17. Epitaxial Al/GaN and Au/GaN junctions on as-grown GaN(0001) 1 x 1 surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Orani, D.; Rubini, S.; Pelucchi, E.; Bonanni, B. [Laboratorio Nazionale TASC-INFM, Area di Ricerca, S.S. 14, Km. 163.5, 34012 Trieste (Italy); Piccin, M. [Laboratorio Nazionale TASC-INFM, Area di Ricerca, S.S. 14, Km. 163.5, 34012 Trieste (Italy); Also with Dipartimento di Fisica, Universita' di Trieste, 34127 Trieste (Italy); Franciosi, A. [Laboratorio Nazionale TASC-INFM, Area di Ricerca, S.S. 14, Km. 163.5, 34012 Trieste (Italy); Passaseo, A.; Cingolani, R. [INFM e Dipartimento di Scienza dei Materiali, Universita' di Lecce, Via per Arnesano, 73100 Lecce (Italy); Khan, A. [Department of Electrical and Computer Engineering, University of South Carolina, Columbia, SC 29208 (United States)

    2005-04-01

    GaN(0001) epilayers were fabricated by rf-plasma enhanced molecular beam epitaxy on GaN templates. The templates were grown by metalorganic chemical vapor deposition on sapphire. The layers exhibited the 2 x 2 reconstruction of the Ga-face during growth and the 1 x 1 reconstruction upon cooling. On such surfaces, Al/n-GaN and Au/n-GaN junctions were fabricated in-situ by molecular beam epitaxy. X-ray photoemission spectroscopy studies allowed us to determine n-type Schottky barrier heights of 0.61{+-}0.06 and 0.98{+-}0.06 eV, respectively, for the two types of epitaxial junctions. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Surface States in the AlxGa1-xN Barrier in AlxGa1-xN/GaN Heterosturctures

    Institute of Scientific and Technical Information of China (English)

    刘杰; 沈波; 王茂俊; 周玉刚; 陈敦军; 张荣; 施毅; 郑有炓

    2004-01-01

    Frequency-dependent capacitance-voltage (C-V) measurements have been performed on modulation-doped Al0.22Ga0.78N/GaN heterostructures to investigate the characteristics of the surface states in the Alx Ga1-xN barrier.Numerical fittings based on the experimental data indicate that there are surface states with high density locating on the AlxGa1-xN barrier. The density of the surface states is about 1012 cm-2 eV-1, and the time constant is about 1 μs. It is found that an insulating layer (Si3N4) between the metal contact and the surface of AlxGa1-xN can passivate the surface states effectively.

  19. Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values

    Institute of Scientific and Technical Information of China (English)

    马晓华; 张亚嫚; 王鑫华; 袁婷婷; 庞磊; 陈伟伟; 刘新宇

    2015-01-01

    In this paper, the off-state breakdown characteristics of two different AlGaN/GaN high electron mobility transistors (HEMTs), featuring a 50-nm and a 150-nm GaN thick channel layer, respectively, are compared. HEMT with thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage (BVoff). Device simu-lation indicates that thickening channel increases the drain-induced barrier lowering (DIBL) but reduces the lateral electric field in the channel and buffer underneath the gate. The increase of BVoff in thick channel device is due to the reduction of the electric field. These results demonstrate that it is necessary to select an appropriate channel thickness to balance DIBL and BVoff in AlGaN/GaN HEMT.

  20. 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.

  1. Electron tomography of (In,Ga)N insertions in GaN nanocolumns grown on semi-polar ( 11 2 ¯ 2 ) GaN templates

    Science.gov (United States)

    Niehle, M.; Trampert, A.; Albert, S.; Bengoechea-Encabo, A.; Calleja, E.

    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( 11 2 ¯ 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.

  2. Electron tomography of (In,GaN insertions in GaN nanocolumns grown on semi-polar ( 11 2 ̄ 2 GaN templates

    Directory of Open Access Journals (Sweden)

    M. Niehle

    2015-03-01

    Full Text Available We present results of scanning transmission electron tomography on GaN/(In,GaN/GaN nanocolumns (NCs that grew uniformly inclined towards the patterned, semi-polar GaN( 11 2 ̄ 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,GaN 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.

  3. Modeling of characteristics of ionizing radiation detector based on AlGaAs-GaAs heterostructure

    CERN Document Server

    Ayzenshtat, G I; Tolbanov, O P; Khan, V A

    2002-01-01

    Calculations of parameters of an ionizing radiation detector on the basis of the transistor heterostructure n(AlGaAs)-p sup + (GaAs)-n sup - (GaAs) have been carried out. The parameters of the structure have been optimized to achieve a maximum amplification factor at a minimum density of a collector current. It has been shown that in dynamics, when the detector is connected as a phototransistor with the broken base, the implementation of intrinsic amplification of the signal from one X-ray photon is impossible. However, the irradiation with continuous X-ray flux allows to achieve high amplification in the structure with small sizes of the emitter.

  4. Modeling the intermixing effects in highly strained asymmetric InGaAs/GaAs quantum well

    Directory of Open Access Journals (Sweden)

    M. Souaf

    2015-09-01

    Full Text Available In this work, we have theoretically investigated the intermixing effect in highly strained In0.3Ga0.7As/GaAs QW taking into consideration the composition profile change resulting from in-situ indium surface segregation. To study the impact of the segregation effects on the postgrowth intermixing, one dimensional steady state Schrodinger equation and Fick's second law of diffusion have been numerically solved by using the finite difference methods. The impact of the In/Ga interdiffusion on the QW emission energy is considered for different In segregation coefficient. Our results show that the intermixed QW emission energy is strongly dependent on the segregation effects. The interdiffusion enhanced energy shift is found to be considerably reduced for higher segregation coefficients. This work adds considerable insight into the understanding and modeling of the effects of interdiffusion in semiconductor nanostructures.

  5. Analysis of defect-related inhomogeneous electroluminescence in InGaN/GaN QW LEDs

    Science.gov (United States)

    Ren, C. X.; Rouet-Leduc, B.; Griffiths, J. T.; Bohacek, E.; Wallace, M. J.; Edwards, P. R.; Hopkins, M. A.; Allsopp, D. W. E.; Kappers, M. J.; Martin, R. W.; Oliver, R. A.

    2016-11-01

    The inhomogeneous electroluminescence (EL) of InGaN/GaN quantum well light emitting diode structures was investigated in this study. Electroluminescence hyperspectral images showed that inhomogeneities in the form of bright spots exhibited spectrally blue-shifted and broadened emission. Scanning electron microscopy combined with cathodoluminescence (SEM-CL) was used to identify hexagonal pits at the centre of approximately 20% of these features. Scanning transmission electron microscopy imaging with energy dispersive X-ray spectroscopy (STEM-EDX) indicated there may be p-doped AlGaN within the active region caused by the presence of the pit. Weak beam dark-field TEM (WBDF-TEM) revealed the presence of bundles of dislocations associated with the pit, suggesting the surface features which cause the inhomogeneous EL may occur at coalescence boundaries, supported by trends in the number of features observed across the wafer.

  6. Influence of Rapid Thermal Annealing on the Characteristics of InGaN/GaN MQWs

    Directory of Open Access Journals (Sweden)

    Tian Yuan

    2016-01-01

    Full Text Available N-type InGaN/GaN multiple-quantum-wells (MQWs were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD. The crystal quality and optical properties of samples after rapid thermal annealing (RTA at different temperatures in a range from 400 to 800°C are investigated by X-ray diffraction (XRD and photoluminescence (PL spectrum. The experimental results show that the peaks of InGaN, InN and In can be observed in all samples. And the results are induced by the phase separation and In-clusters. The luminescence peak of the samples annealed showed a red shift. It is caused by strain stress relaxation during the RTA process. Furthermore, some defects can be eliminated and the best annealing temperature is from 500°C to 700°C.

  7. Effect of Temperature on GaGdO/GaN Metal Oxide Semiconductor Field Effect Transistors

    Energy Technology Data Exchange (ETDEWEB)

    Abernathy, C.R.; Baca, A.; Chu, S.N.G.; Hong, M.; Lothian, J.R.; Marcus, M.A.; Pearton, S.J.; Ren, F.; Schurman, M.J.

    1998-10-14

    GaGdO was deposited on GaN for use as a gate dielectric in order to fabricate a depletion metal oxide semiconductor field effect transistor (MOSFET). This is the fmt demonstration of such a device in the III-Nitride system. Analysis of the effect of temperature on the device shows that gate leakage is significantly reduced at elevated temperature relative to a conventional metal semiconductor field effeet transistor (MESFET) fabricated on the same GaN layer. MOSFET device operation in fact improved upon heating to 400 C. Modeling of the effeet of temperature on contact resistance suggests that the improvement is due to a reduction in the parasitic resistances present in the device.

  8. Scaling animal to human biodistribution of the radiopharmaceutical [68Ga]Ga-PSMA-HBED-CC

    Energy Technology Data Exchange (ETDEWEB)

    Parra, Pamela Ochoa, E-mail: lapochoap@unal.edu.co; Veloza, Stella [Grupo de Física Nuclear, Departamento de Física, Universidad Nacional de Colombia, Bogota, D.C. (Colombia)

    2016-07-07

    The radiotracer called {sup 68}Ga-labelled Glu-urea-Lys(Ahx)-HBED-CC ([68Ga]Ga-PSMA-HBED-CC) is a novel radiophar-maceutical for the detection of prostate cancer lesions by positron emission tomography (PET) imaging. Setting up a cost-effective manual synthesis of this radiotracer and making its clinical translation in Colombia will require two important elements: the evaluation of the procedure to yield a consistent product, meeting standards of radio-chemical purity and low toxicity and then, the evaluation of the radiation dosimetry. In this paper a protocol to extrapolate the biokinetic model made in normal mice to humans by using the computer software for internal dose assessment OLINDA/EXM® is presented as an accurate and standardized method for the calculation of radiation dosimetry estimates.

  9. A InGaN/GaN quantum dot green (λ=524 nm) laser

    KAUST Repository

    Zhang, Meng

    2011-01-01

    The characteristics of self-organized InGaN/GaN quantum dot lasers are reported. The laser heterostructures were grown on c-plane GaN substrates by plasma-assisted molecular beam epitaxy and the laser facets were formed by focused ion beam etching with gallium. Emission above threshold is characterized by a peak at 524 nm (green) and linewidth of 0.7 nm. The lowest measured threshold current density is 1.2 kA/ cm2 at 278 K. The slope and wall plug efficiencies are 0.74 W/A and ∼1.1%, respectively, at 1.3 kA/ cm 2. The value of T0 =233 K in the temperature range of 260-300 K. © 2011 American Institute of Physics.

  10. GaInSb and GaInAsSb thermophotovoltaic device fabrication and characterization

    Energy Technology Data Exchange (ETDEWEB)

    Hitchcock, C.; Gutmann, R.; Borrego, J.; Ehsani, H.; Bhat, I. [Rensselaer Polytechnic Inst., Troy, NY (United States); Freeman, M.; Charache, G. [Lockheed Martin, Inc., Schenectady, NY (United States)

    1997-05-01

    Thermophotovoltaic (TPV) devices have been fabricated using epitaxial ternary and quaternary layers grown on GaSb substrates. The GaInSb layers were grown by organometallic vapor phase epitaxy (OMVPE) and the InGaAsSb lattice-matched layers were grown by liquid phase epitaxy (LPE). Device fabrication steps include unannealed p-type ohmic contacts, annealed Sn/Au n-type ohmic contacts, and a thick Ag top-surface contact using a lift-off process. Devices are characterized primarily by dark I-V, photo I-V, and quantum efficiency measurements, which are correlated to microscopic and macroscopic material properties. Particular emphasis has been on material enhancements to increase quantum efficiency and decrease dark saturation current density. TPV device performance is presently limited by the base diffusion length, typically 1 to 2 microns.

  11. Zigzag GaN/Ga2O3 heterogeneous nanowires: Synthesis, optical and gas sensing properties

    Directory of Open Access Journals (Sweden)

    Li-Wei Chang

    2011-09-01

    Full Text Available Zigzag GaN/Ga2O3 heterogeneous nanowires (NWs were fabricated, and the optical properties and NO gas sensing ability of the NWs were investigated. We find that NWs are most effective at 850 °C at a switching process once every 10 min (on/off = 10 min per each with a mixture flow of NH3 and Ar. The red shift of the optical bandgap (0.66 eV is observed from the UV-vis spectrum as the GaN phase forms. The gas sensing characteristics of the developed sensor are significantly replaced to those of other types of NO sensors reported in literature.

  12. Terahertz intersubband photodetectors based on semi-polar GaN/AlGaN heterostructures

    Science.gov (United States)

    Durmaz, Habibe; Nothern, Denis; Brummer, Gordie; Moustakas, Theodore D.; Paiella, Roberto

    2016-05-01

    Terahertz intersubband photodetectors are developed based on GaN/AlGaN quantum wells grown on a free-standing semi-polar ( 20 2 ¯ 1 ¯ ) GaN substrate. These quantum wells are nearly free of the polarization-induced internal electric fields that severely complicate the design of nitride intersubband devices on traditional c-plane substrates. As a result, a promising bound-to-quasi-bound THz photodetector design can be implemented. Pronounced photocurrent peaks at the design frequency near 10 THz are measured, covering frequencies that are fundamentally inaccessible to existing arsenide intersubband devices due to reststrahlen absorption. This materials system provides a favorable platform to utilize the intrinsic advantages of nitride semiconductors for THz optoelectronics.

  13. Terahertz intersubband absorption in GaN/AlGaN step quantum wells

    Science.gov (United States)

    Machhadani, H.; Kotsar, Y.; Sakr, S.; Tchernycheva, M.; Colombelli, R.; Mangeney, J.; Bellet-Amalric, E.; Sarigiannidou, E.; Monroy, E.; Julien, F. H.

    2010-11-01

    We demonstrate terahertz intersubband absorptions at frequencies of 2.1 THz (λ ≈143 μm) and 4.2 THz (λ ≈70 μm) in nitride-based semiconductor quantum wells. The structures consist of a 3 nm thick GaN well, an Al0.05Ga0.95N step barrier, and a 3 nm thick Al0.1Ga0.9N barrier. The absorption is detected at 4.7 K. The structure design has been optimized to approach a flat-band potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moments.

  14. Optical characterization of AlGaN/GaN quantum disc structures in single nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Rigutti, L.; Tchernycheva, M.; De Luna Bugallo, A.; Jacopin, G.; Julien, F.H. [Institut d' Electronique Fondamentale, UMR 8622 CNRS, University of Paris Sud XI, Bat. 220, 91405 Orsay (France); Fortuna, F. [Centre de Spectrometrie Nucleaire et de Spectroscopie de Masse, UMR 8609 CNRS, University of Paris Sud XI, Bat. 108, 91405 Orsay (France); Furtmayr, F.; Stutzmann, M. [Walter-Schottky-Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany); Eickhoff, M. [I. Physikalisches Institut, Justus-Liebig-Universitaet, Giessen (Germany)

    2010-07-15

    We report a systematic study of the luminescence properties of Al{sub x}Ga{sub 1-x}N/GaN single and multi quantum disc structures in single nanowires with Al fraction x{sub Al} varying from 0.05 to 1. These quantum structures are situated on the top of GaN nanowires grown in the polar[0001] direction. Nanowires are synthesized by Plasma Assisted Molecular Beam Epitaxy under nitrogen rich growth conditions at a substrate temperature of T=80 C on Si (111) substrates. The PL energy of single and multi-quantum disc systems is explained in terms of Al content in the barriers, band bending at the upper polar surface, and strain relaxation in the heterostructure region (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Drain current DLTS of AlGaN/GaN HEMTs

    Energy Technology Data Exchange (ETDEWEB)

    Mizutani, T.; Okino, T.; Kawada, K.; Ohno, Y.; Kishimoto, S.; Maezawa, K. [Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)

    2003-11-01

    The transient behaviour of AlGaN/GaN HEMTs was studied by current DLTS. One electron trap and two hole-trap-like signals were observed. The electron trap had an activation energy of 0.61 eV, which was similar to the defect level in n-GaN obtained by capacitance DLTS. It has been pointed out that the hole-trap-like signals dit not originate from changes in hole trap population in the channel, but probably reflected the changes in the electron population in the surface states of the HEMT access regions. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Raman study of N bonding in AlGaAs/InGaAsN multiquantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lazic, S.; Calleja, J.M. [Dept. Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Hey, R.; Ploog, K. [Paul-Drude Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2006-06-15

    We report resonant Raman scattering measurements on InGaAsN/AlGaAs multiquantum wells grown by plasma-assisted molecular beam epitaxy. Sharp vibration modes have been observed at 323, 402, 454 and 501 cm{sup -1}. They are resonant in the energy range 1.81-1.87 eV at decreasing energies for increasing N concentration. The resonance energies reveal the influence of the N concentration on the barrier gap at the multiquantum well interfaces. The peaks are interpreted in terms of local vibrations involving GaN and AlN units and pairs. They seem to form mostly at the quantum well interfaces due to preferential N bonding to Al. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Optical and structural properties of MOVPE-grown GaInSb/GaSb quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Wagener, Viera, E-mail: viera.wagener@nmmu.ac.z [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa); Olivier, E.J.; Botha, J.R. [Physics Department, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031 (South Africa)

    2009-12-15

    This paper reports on the optical and structural properties of strained type-I Ga{sub 1-x}In{sub x}Sb quantum wells embedded in GaSb from a metal-organic vapour phase epitaxial growth perspective. Photoluminescence measurements and transmission electron microscopy were used to evaluate the effect of the growth temperature on the quality of Ga{sub 1-x}In{sub x}Sb strained layers with varied alloy compositions and thicknesses. Although the various factors contributing to the overall quality of the strained layers are difficult to separate, the quantum well characteristics are significantly altered by the growth temperature. Despite the high growth rates (approx2 nm/s), quantum wells grown at 607 deg. C display photoluminescence emissions with full-width at half-maximum of 3.5-5.0 meV for an indium solid content (x) up to 0.15.

  18. Optical and electronic properties of AlGaN/GaN heterostructures; Optische und elektronische Eigenschaften von AlGaN/GaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Winzer, Andreas T.

    2008-10-28

    The electronic material properties of AlGaN/GaN heterostructures were investigated. The analysis of optical spectra by complex models allowed for the first time to confirm the theoretically predicted dependence of the polarisation discontinuity (also called polarisation charge) on the Al content by reliable experiments. Furthermore, it is shown that the polarisation discontinuity is constant over the temperature range from 5 K up to room temperature. The method employed here is based on the analysis of electroreflectance (ER) spectra and exploits the specific dependence of the electric field strength within a layer on the applied electric voltage. In this work this method is consequently refined to surpass all alternative methods in accuracy. ER spectra of group-III-nitrides posses some general peculiarities: (i) In di- rect proximity to the band gap they can not be described by constant Seraphin coefficients in contrast to small gap semiconductors (e.g. GaAs). (ii) Though, the analysis of the Franz-Keldysh oscillations by Aspnes' method yields the correct values of the electric field strength as it is the case for small gap semiconductors. Optical and especially ER spectra of group-III-nitrides can only be described completely by taking into account for excitons in electric fields. For this a mo- del proposed by Blossey was applied to nitride semiconductors and implemented into a software program. By extensive numerical simulations it was found that the energetic position of the exciton main resonance as well as its spectral width depend linearly on the electric field strength. The approach presented is unique since it allows for a quantitative description of excitons in inhomogeneous electric fields. The good agreement between experiment and simulation supports the reliability of the material properties presented in this work. The operation of AlGaN/GaN heterostructures as chemical sensors was investigated by means of optical spectra too. If Pt contacted

  19. Hot-electron real-space transfer and longitudinal transport in dual AlGaN/AlN/{AlGaN/GaN} channels

    Science.gov (United States)

    Šermukšnis, E.; Liberis, J.; Matulionis, A.; Avrutin, V.; Ferreyra, R.; Özgür, Ü.; Morkoç, H.

    2015-03-01

    Real-space transfer of hot electrons is studied in dual-channel GaN-based heterostructure operated at or near plasmon-optical phonon resonance in order to attain a high electron drift velocity at high current densities. For this study, pulsed electric field is applied in the channel plane of a nominally undoped Al0.3Ga0.7N/AlN/{Al0.15Ga0.85N/GaN} structure with a composite channel of Al0.15Ga0.85N/GaN, where the electrons with a sheet density of 1.4 × 1013 cm-2, estimated from the Hall effect measurements, are confined. The equilibrium electrons are situated predominantly in the Al0.15Ga0.85N layer as confirmed by capacitance-voltage experiment and Schrödinger-Poisson modelling. The main peak of the electron density per unit volume decreases as more electrons occupy the GaN layer at high electric fields. The associated decrease in the plasma frequency induces the plasmon-assisted decay of non-equilibrium optical phonons (hot phonons) confirmed by the decrease in the measured hot-phonon lifetime from 0.95 ps at low electric fields down below 200 fs at fields of E \\gt 4 kV cm-1 as the plasmon-optical phonon resonance is approached. The onset of real-space transfer is resolved from microwave noise measurements: this source of noise dominates for E \\gt 8 kV cm-1. In this range of fields, the longitudinal current exceeds the values measured for a mono channel reference Al0.3Ga0.7N/AlN/GaN structure. The results are explained in terms of the ultrafast decay of hot phonons and reduced alloy scattering caused by the real-space transfer in the composite channel.

  20. GaInP/GaAs tandem solar cells with highly Te-and Mg-doped GaAs tunnel junctions grown by MBE

    Institute of Scientific and Technical Information of China (English)

    郑新和; 刘三姐; 夏宇; 甘兴源; 王海啸; 王乃明; 杨辉

    2015-01-01

    We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction (TJ) with using tellurium (Te) and magnesium (Mg) as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy (MBE) at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm2. The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 mA/cm2, but a low open-circuit voltage range of 1.4 V∼1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy (SIMS) analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended GaAs n++/p++junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of∼2.5 × 1020 in GaAs could cause a lattice strain of 10−3 in magnitude and thus a surface roughening, which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell.

  1. Thermal instability of GaSb surface oxide

    Science.gov (United States)

    Tsunoda, K.; Matsukura, Y.; Suzuki, R.; Aoki, M.

    2016-05-01

    In the development of InAs/GaSb Type-II superlattice (T2SL) infrared photodetectors, the surface leakage current at the mesa sidewall must be suppressed. To achieve this requirement, both the surface treatment and the passivation layer are key technologies. As a starting point to design these processes, we investigated the GaSb oxide in terms of its growth and thermal stability. We found that the formation of GaSb oxide was very different from those of GaAs. Both Ga and Sb are oxidized at the surface of GaSb. In contrast, only Ga is oxidized and As is barely oxidized in the case of GaAs. Interestingly, the GaSb oxide can be formed even in DI water, which results in a very thick oxide film over 40 nm after 120 minutes. To examine the thermal stability, the GaSb native oxide was annealed in a vacuum and analyzed by XPS and Raman spectroscopy. These analyses suggest that SbOx in the GaSb native oxide will be reduced to metallic Sb above 300°C. To directly evaluate the effect of oxide instability on the device performance, a T2SL p-i-n photodetector was fabricated that has a cutoff wavelength of about 4 μm at 80 K. As a result, the surface leakage component was increased by the post annealing at 325°C. On the basis of these results, it is possible to speculate that a part of GaSb oxide on the sidewall surface will be reduced to metallic Sb, which acts as an origin of additional leakage current path.

  2. Development of GaN-based micro chemical sensor nodes

    Science.gov (United States)

    Son, Kyung-ah; Prokopuk, Nicholas; George, Thomas; Moon, Jeong S.

    2005-01-01

    Sensors based on III-N technology are gaining significant interest due to their potential for monolithic integration of RF transceivers and light sources and the capability of high temperature operations. We are developing a GaN-based micro chemical sensor node for remote detection of chemical toxins, and present electrical responses of AlGaN/GaN HEMT (High Electron Mobility Transistor) sensors to chemical toxins as well as other common gases.

  3. Pulsed terahertz emission from GaN/InN heterostructure

    Science.gov (United States)

    Reklaitis, Antanas

    2011-11-01

    Dynamics of the electron-hole plasma excited by the femtosecond optical pulse in wurtzite GaN/InN heterostructure is investigated by Monte Carlo simulations. The GaN/InN heterostructure for pulsed terahertz emission is suggested. The results of Monte Carlo simulations show that the power of terahertz emission from the GaN/InN heterostructure exceeds the power of terahertz emission from the surface of InN by one order of magnitude.

  4. High Performance InGaN-Based Solar Cells

    Science.gov (United States)

    2012-05-12

    electric field for an AlGaAs /GaAs MQW with 9.5 nm GaAs QWs (right). Regardless of the physical origin of the above observations, there was a clear...morphology, contact resistance, and carrier extraction; investigating the properties of solar cells grown by NH3-based molecular beam epitaxy (MBE); measuring...device performance are also discussed. Building on these advances, the unique thermal properties of high indium content multiple quantum well (MQW

  5. Capture and release of carriers in InGaAs/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Turchinovich, D; Porte, H P; Jepsen, P Uhd [DTU Fotonik - Department of Photonics Engineering Technical University of Denmark Oersteds Plads 343, DK 2800 Kongens Lyngby (Denmark); Daghestani, N; Wilcox, K G; Rafailov, E U, E-mail: dmtu@fotonik.dtu.d [School of Engineering, Physics and Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom)

    2009-11-15

    We observe the ultrafast capture and release of charge carriers in InGaAs/GaAs quantum dots (QDs) at room-temperature with time-resolved terahertz spectroscopy. For excitation into the barrier states, a decay of the photoinduced conductivity, due to capture of carriers into the nonconducting QD states is observed. The increase of the decay time constant with increasing pump fluence is attributed to filling of the QD states. In the case of resonantly excitation into the QD ground state a maximum conductivity is reached 35 ps after photoexcitation, which is assigned to the release of carriers from the QDs into the wetting layer and barrier states.

  6. Effect of CO on Characteristics of AlGaN/GaN Schottky Diode

    Institute of Scientific and Technical Information of China (English)

    FENG Chun; WANG Zhan-Guo; WANG Xiao-Liang; YANG Cui-Bai; XIAO Hong-Ling; ZHANG Ming-Lan; JIANG Li-Juan; TANG Jian; HU Guo-Xin; WANG Jun-Xi

    2008-01-01

    @@ Pt Schottky diode gas sensors for CO are fabricated using AlGaN/GaN high electron mobility transistor (HEMTs) structure. The diodes show a remarkable sensor signal (3 mA, in N2; 2mA in air ambient) biased 2 V after 1% CO is introduced at 50℃. The Schottky barrier heights decrease for 36 meV and 27 meV in the two cases respectively. The devices exhibit a slow recovery characteristic in air ambient but almost none in the background of pure N2, which reveals that oxygen molecules could accelerate the desorption of CO and offer restrictions to CO detection.

  7. Collective Behavior of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher

    2000-01-01

    Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell excition in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circular polarized light......, the luminescence line of interwell excitions exhibits a significant narrowing and a drastic increase in the degree of circular polarization of photoluminescence with increasing exciton concentration. It is found that the radiative recombination rate significantly increases under these conditions. This phenomenon...

  8. Resonant Plasmonic Enhancement of InGaN/GaN LED using Periodically Structured Ag Nanodisks

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Iida, Daisuke; Zhu, Xiaolong

    2013-01-01

    Ag nanodisks are fabricated on GaN-based LED to enhance emission efficiency. Nanosphere lithography is used to obtain a periodic nano-structure, and a photoluminescence enhancement of 2.7 is reported with Ag nanodisk diameter of 330 nm.......Ag nanodisks are fabricated on GaN-based LED to enhance emission efficiency. Nanosphere lithography is used to obtain a periodic nano-structure, and a photoluminescence enhancement of 2.7 is reported with Ag nanodisk diameter of 330 nm....

  9. Temperature dependence of photoluminescence from submonolayer deposited InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Leosson, K.; Birkedal, Dan

    2002-01-01

    The temperature dependence of photoluminescence (PL) from self-assembled InGaAs quantum dots (QD's) grown by submonolayer deposition mode (non-SK mode), is investigated. It is found that the PL spectra are dominated by the ground-state transitions at low temperatures, but increasingly by the exci......The temperature dependence of photoluminescence (PL) from self-assembled InGaAs quantum dots (QD's) grown by submonolayer deposition mode (non-SK mode), is investigated. It is found that the PL spectra are dominated by the ground-state transitions at low temperatures, but increasingly...

  10. Picosecond luminescence approach to vertical transport in GaAs/GaAlAs superlattices

    Science.gov (United States)

    Deveaud, B.; Chomette, A.; Lambert, B.; Regreny, A.; Romestain, R.; Edel, P.

    1986-03-01

    Picosecond luminescence of GaAs/GaAlAs superlattices has been measured at 5 K. Asymetrical structures where one larger well is introduced at 9000 Å from the surface are studied. It is then possible to estimate the mean transfer time of photoexcited carriers through 9000 Å of superlattice. This time is found to be about 4 nsec in a 40/40 Å superlattice and 800 psec in a 30/30 Å one. This evidences the rather high mobility of small period superlattices in the growth direction.

  11. Photoluminescence studies of individual and few GaSb/GaAs quantum rings

    Directory of Open Access Journals (Sweden)

    M. P. Young

    2014-11-01

    Full Text Available We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at half maximum of 200 μeV. The detail provided by these measurements allows the characteristic type-II blueshift, observed with increasing excitation power, to be studied at the level of individual nanostructures. These findings are in agreement with hole-charging being the origin of the observed blueshift.

  12. Photoluminescence studies of individual and few GaSb/GaAs quantum rings

    Energy Technology Data Exchange (ETDEWEB)

    Young, M. P.; Woodhead, C. S.; Roberts, J.; Noori, Y. J.; Noble, M. T.; Krier, A.; Hayne, M.; Young, R. J., E-mail: aip@r-j-y.com [Department of Physics, Lancaster University, LA1 4YB (United Kingdom); Smakman, E. P.; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology (Netherlands)

    2014-11-15

    We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at half maximum of 200 μeV. The detail provided by these measurements allows the characteristic type-II blueshift, observed with increasing excitation power, to be studied at the level of individual nanostructures. These findings are in agreement with hole-charging being the origin of the observed blueshift.

  13. [Raman spectra studies of MBE-grown n-GaAs/SI-GaAs films].

    Science.gov (United States)

    Wang, Bin; Xu, Xiao-xuan; Qin, Zhe; Song, Ning; Zhang, Cun-zhou

    2008-09-01

    n-GaAs films doped with Si were grown by MBE on semi-insulated GaAs (100) substrates. The films with different doping concents were characterized by Raman spectra at room temperature. It is obviously that the Raman peaks shifted. Some peaks were enhanced and some were weakened. This is attributed to the fact that the higher the doping contents, the highertge lattice mismatch. And the lattice misfit induced the imperfection in epitaxy layers. This experimental result coincides with the theory.

  14. Intermixing effects on emission properties of InGaN/GaN coupled Quantum wells

    KAUST Repository

    Susilo, Tri B.

    2015-02-01

    Intermixing processes in quantum wells have been extensively studied in order to modify characteristic of semiconductor devices such as LEDs. Controlling the band gap of material by introducing intermixing process can be used to enable broadband and controllable emission of LEDs. Quantum well intermixing (QWI) in InGaN/GaN double quantum well (DQW) is discussed in this paper. By varying the interdiffusion and separation lengths, the effects of intermixing process on the quantum eigen energies of the wells are studied. The investigation is carried out using a homegrown Quantum-FDTD simulator. © 2015 IEEE.

  15. Polar-optical-phonon-limited electron mobility in GaN/AlGaN heterojunctions

    Science.gov (United States)

    Rizwana, K. Begum; Sankeshwar, N. S.

    2012-06-01

    The phonon-scattering-limited mobility of a two dimensional electron gas (2DEG) at GaN/AlGaN heterojunctions (HJs) is investigated for temperatures T<300K. Scattering by acoustic phonons is assumed to be quasielastic and that by polar LO phonons to be inelastic. Solving the linearized Boltzmann equation (LBE) using an iteration method, the carrier energy dependence of first order perturbation distribution (φ) is studied. Numerical results of φ are compared with commonly used closed-form low-temperature (τLT) and high-energy (τHE) relaxation time approximations. Good agreement with experimental data is obtained.

  16. A new small-signal model for asymmetrical AlGaN/GaN HEMTs

    Energy Technology Data Exchange (ETDEWEB)

    Ma Teng; Hao Yue; Chen Chi; Ma Xiaohua, E-mail: mateng03@gmail.co [National Key Laboratory of Wide Band-Gap Semiconductor Technology, Department of Microelectronics, Xidian University, Xi' an 710071 (China)

    2010-06-15

    A new small-signal model for anisomerous AlGaN/GaN high electron mobility transistors (HEMTs) is proposed for accurate prediction of HEMT behavior up to 20 GHz. The parasitic elements are extracted from both cold-FET and pinch-off bias to obtain more precise results and the intrinsic part is directly extracted. All the parameters needed in this process are determined by the device structure rather than optimization methods. This guarantees consistency between the parameter values and the component's physical meaning. (semiconductor devices)

  17. State-of-the-art performance of GaAlAs/GaAs avalanche photodiodes

    Science.gov (United States)

    Law, H. D.; Nakano, K.; Tomasetta, L. R.

    1979-01-01

    Ga(0.15)Al(0.85)As/GaAs avalanche photodiodes have been successfully fabricated. The performance of these detectors is characterized by a rise time of less than 35 ps, an external quantum efficiency with an antireflection coating of 95% at 0.53 microns, and a microwave optical gain of 42 dB. The dark current density is in the low range (10 to the minus A/sq cm) at one-half the breakdown voltages, and rises to 0.0001 A/sq cm at 42 dB optical gain.

  18. Resonant behaviour of GaAs LO phonons in a GaAs-AlAs superlattice

    Science.gov (United States)

    Zhang, Shulin; T, A. Gant; M, Delaney; M, V. Klein; J, Klem; H, Morkoc

    1988-03-01

    Resonant Raman scattering from GaAs LO phonons in a 59Å GaAs/20Å AlAs superlattice was studied. The relevant intersubband energies were determined. The results suggest that all of the exciton transitions from the hole subbands HH1, LH1, HH2, HH3, LH2 and HH4 to the electron subbands CB1 and CB2 in the energy region covered by our incident dye laser were observed and a justificative analysis may involve effects due to valence band mixing and to 3D electronic miniband structure.

  19. The disintegration of GaSb/GaAs nanostructures upon capping

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Andrew J; Jinyoung, Hwang; Marquis, Emmanuelle A; Smakman, Erwin; Saucer, Timothy W; Rodriguez, Garrett; Hunter, Allen H; Sih, Vanessa; Koenraad, Paul M; Phillips, Jamie D.; Millunchick, Joanna M

    2013-01-01

    Atom probe tomography and cross-sectional scanning tunneling microscopy show that GaSb/GaAs quantum dots disintegrate into ring-like clusters of islands upon capping. Band transition energies calculated using an 8-band k.p model of the capped dots with the observed dimensions are consistent with emission energies observed in photoluminescence data. These results emphasize the need for full three-dimensional characterization to develop an accurate understanding of the structure, and thus the optical properties, of buried quantum dots.

  20. Temperature characteristics of InGaAs/GaAs vertical cavity surface emitting laser

    Institute of Scientific and Technical Information of China (English)

    QU Hong-wei; GUO Xia; DONG Li-min; WANG Hong-hang; DENG Jun; LIAN Peng; ZHOU De-shu; SHEN Guang-di

    2005-01-01

    The temperature characteristics for the different lasing modes at 300 K of intracavity contacted InGaAs/GaAs Vertical Cavity Surface Emitting Lasers(VCSELs) have been investigated experimentally by using the SV-32 cryostat and LD2002C5 test system.In combination with the simulation results of the reflective spectrum and the gain peak at different temperatures,the measurement results have been analyzed.In addition,the dependence of device size on temperature characteristics is discussed.The experimental data can be used to optimally design of VCSEL at high or cryogenic temperature.