WorldWideScience

Sample records for ga hoshutsushita areropashi

  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. Muchinako, GA

    African Journals Online (AJOL)

    Muchinako, GA. Vol 28, No 2 (2013) - Articles Children living and/or working on the streets in Harare: Issues and challenges. Abstract. ISSN: 1012-1080. AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians · for Authors · FAQ's · More about AJOL · AJOL's Partners · Terms and Conditions of ...

  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...... than Pubeval. Their winning rates are tied. Furthermore, GA-Gammon consistently outperforms Fuzzeval....

  4. Bagla JS (3) 216 (GA)

    Indian Academy of Sciences (India)

    Admin

    Ahmed Asma (5) 455, (6) 610 (GA). Ananthasuresh G K (6) 530, (9) 849 (GA). Arakeri Jaywant H (1) 32 (GA). Arunan E (12) 1210; (4) 346 (FA). Athreya K B (1) 66 (GA); (4) 384 (TIO). Bagla J S (3) 216 (GA). Balaji C (12) 1171 (GA). Balaram P (5) 416 (GA). Bhanu K S (11) 1119 (TIO). Bhat B V Rajarama (10) 970 (GA).

  5. 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...... to most other III–V nanowire systems, the GaSb nanowire growth is Group V-limited under most conditions. We found that depending on the TMSb molar fraction, the seed particle is either supersaturated AuGa or AuGa2 during GaSb growth. The high Ga content in the particle gives a characteristic diameter...... increase between the GaAs and GaSb segment. From TEM and XEDS measurements we conclude that the GaSb nanowire growth occurs along either the AuGa–GaSb or AuGa2–GaSb pseudo-binaries of the Au–Ga–Sb ternary phase diagram. Finally, the GaSb nanowires exhibit untapered radial growth on the {1 1¯ 0} side facets....

  6. 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...

  7. Unipolar Vertical Transport in GaN/AlGaN/GaN Heterostructures

    OpenAIRE

    Nath, D. N.; Park, P. S.; Yang, Z. C.; Rajan, S.

    2013-01-01

    In this letter, we report on unipolar vertical transport characteristics in c-plane GaN/AlGaN/GaN heterostructures. Vertical current in heterostructures with random alloy barriers was found to be independent of dislocation density and heterostructure barrier height, and significantly higher than theoretical estimates. Percolation-based transport due to random alloy fluctuations in the ternary AlGaN is suggested as the dominant transport mechanism, and confirmed through experiments showing tha...

  8. Reflectivity modulator based on GaSb/GaAs heterostructure

    International Nuclear Information System (INIS)

    Rabbaa, S

    2017-01-01

    A structure of gallium antimonide (GaSb) and gallium arsenide (GaAs) wafers is built to modulate light reflectivity at CO 2 laser wavelength. A quantum well composed of GaSb/GaAs heterojunction with highly doped GaAs up to 3×10 18 cm -3 is inserted inside a layer structure. A grating of periodic structure of GaAs and gold layer is added just below the substrate. Gsolver software is used to determine the reflectivity of incident light with the existence of free carriers. A voltage is applied to the doped layer to deplete the free electrons and the reflectivity is determined again. The significant difference in reflectivity between the two cases can be used to build a light reflectivity modulator device. (paper)

  9. Formation of GaAs/AlGaAs and InGaAs/GaAs nanorings by droplet molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Gong, Z.; Niu, Z.C.; Huang, S.S.; Fang, Z.D.; Sun, B.Q.; Xia, J.B.

    2005-01-01

    GaAs/AlGaAs lattice-matched nanorings are formed on GaAs (100) substrates by droplet epitaxy. The crucial step in the formation of nanorings is annealing Ga droplets under As flux for proper time. The observed morphologic evolution of Ga droplets during annealing does not support the hypothesis that As atoms preferentially react with Ga around the periphery of the droplets, but somehow relates to a dewetting process similar to that of unstable films. Photoluminescene (PL) test results confirm the quantum-confinement effect of these GaAs nanorings. Using similar methods, we have fabricated InGaAs/GaAs lattice-mismatched rings

  10. GaN High Power Devices

    Energy Technology Data Exchange (ETDEWEB)

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

    2000-07-17

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

  11. Spatially resolved In and As distributions in InGaAs/GaP and InGaAs/GaAs quantum dot systems

    International Nuclear Information System (INIS)

    Shen, J; Cha, J J; Song, Y; Lee, M L

    2014-01-01

    InGaAs quantum dots (QDs) on GaP are promising for monolithic integration of optoelectronics with Si technology. To understand and improve the optical properties of InGaAs/GaP QD systems, detailed measurements of the QD atomic structure as well as the spatial distributions of each element at high resolution are crucial. This is because the QD band structure, band alignment, and optical properties are determined by the atomic structure and elemental composition. Here, we directly measure the inhomogeneous distributions of In and As in InGaAs QDs grown on GaAs and GaP substrates at the nanoscale using energy dispersive x-ray spectral mapping in a scanning transmission electron microscope. We find that the In distribution is broader on GaP than on GaAs, and as a result, the QDs appear to be In-poor using a GaP matrix. Our findings challenge some of the assumptions made for the concentrations and distributions of In within InGaAs/GaAs or InGaAs/GaP QD systems and provide detailed structural and elemental information to modify the current band structure understanding. In particular, the findings of In deficiency and inhomogeneous distribution in InGaAs/GaP QD systems help to explain photoluminescence spectral differences between InGaAs/GaAs and InGaAs/GaP QD systems. (paper)

  12. Y ogananda CS (10) 8 (GA)

    Indian Academy of Sciences (India)

    Chinese remainder theorem (2) 78 (CR). Chlamydomonas (5) 22 (GA). Cholesterol (2) 74 (GA). Chromium compound (9) 72 (FA). Cananga odorata Hook! & Thoms. (11) (FT). Cicca disticha L. Syn. C.Acida Merr (2) (FT). Circadian rhythm (5) 10, 14, 32, (GA). Circadian rhythms (5) 22 (GA). Claim size distribution (10) 49 (GA).

  13. Investigation of the GaN-on-GaAs interface for vertical power device applications

    International Nuclear Information System (INIS)

    Möreke, Janina; Uren, Michael J.; Kuball, Martin; Novikov, Sergei V.; Foxon, C. Thomas; Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J.; Haigh, Sarah J.; Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain

    2014-01-01

    GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

  14. GaN/AlGaN nanostructures for intersubband optoelectronics

    Energy Technology Data Exchange (ETDEWEB)

    Tchernycheva, M.; Macchadani, H.; Nevou, L.; Mangeney, J.; Julien, F.H. [Institut d' Electronique Fondamentale, UMR 8622 CNRS, University Paris Sud XI, 91405 Orsay (France); Kandaswamy, P.K.; Wirthmueller, A.; Monroy, E. [CEA-Grenoble, INAC/SP2M/NPSC, 17 rue des Martyrs, 38054 Grenoble (France); Vardi, A.; Schacham, S.; Bahir, G. [Department of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 32000 (Israel)

    2010-06-15

    We have investigated intraband absorptions in GaN/AlN QDs for ultrafast all-optical switching applications at telecommunication wavelengths. Using time-resolved pump-probe experiments the electron lifetime in the excited state of the QDs is measured to be 165 fs. Intraband absorption saturation experiments reveal a record low switching energy. We then investigate quantum cascade ISB photodetectors based on GaN/AlGaN QWs and show that mesa devices with 17 x 17 {mu}m{sup 2} size provide a frequency response above 10 GHz at 1.5 {mu}m wavelength. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  15. GA microwave window development

    International Nuclear Information System (INIS)

    Moeller, C.P.; Kasugai, A.; Sakamoto, K.; Takahashi, K.

    1994-10-01

    The GA prototype distributed window was tested in a 32 mm diam. waveguide system at a power density suitable for a MW gyrotron, using the JAERI/Toshiba 110 GHz long pulse internal converter gyrotron in the JAERI test stand. The presence of the untilted distributed window had no adverse effect on the gyrotron operation. A pulse length of 10 times the calculated thermal equilibrium time (1/e time) of 30 msec was reached, and the window passed at least 750 pulses greater than 30 msec and 343 pulses greater than 60 msec. Beyond 100 msec, the window calorimetry reached steady state, allowing the window dissipation to be measured in a single pulse. The measured loss of 4.0% agrees both with the estimated loss, on which the stress calculations are based, and with the attenuation measured at low power in the HE 11 mode. After the end of the tests, the window was examined; no evidence of arcing air coating was found in the part of the window directly illuminated by the microwaves, although there was discoloration in a recess containing an optical diagnostic which outgassed, causing a local discharge to occur in that recess. Finally, there was no failure of the metal-sapphire joints during a total operating time of 50 seconds consisting of pulses longer than 30 msec

  16. 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.

  17. Metamorphic GaAs/GaAsBi Heterostructured Nanowires.

    Science.gov (United States)

    Ishikawa, Fumitaro; Akamatsu, Yoshihiko; Watanabe, Kentaro; Uesugi, Fumihiko; Asahina, Shunsuke; Jahn, Uwe; Shimomura, Satoshi

    2015-11-11

    GaAs/GaAsBi coaxial multishell nanowires were grown by molecular beam epitaxy. Introducing Bi results in a characteristic nanowire surface morphology with strong roughening. Elemental mappings clearly show the formation of the GaAsBi shell with inhomogeneous Bi distributions within the layer surrounded by the outermost GaAs, having a strong structural disorder at the wire surface. The nanowire exhibits a predominantly ZB structure from the bottom to the middle part. The polytipic WZ structure creates denser twin defects in the upper part than in the bottom and middle parts of the nanowire. We observe room temperature cathodoluminescence from the GaAsBi nanowires with a broad spectral line shape between 1.1 and 1.5 eV, accompanied by multiple peaks. A distinct energy peak at 1.24 eV agrees well with the energy of the reduced GaAsBi alloy band gap by the introduction of 2% Bi. The existence of localized states energetically and spatially dispersed throughout the NW are indicated from the low temperature cathodoluminescence spectra and images, resulting in the observed luminescence spectra characterized by large line widths at low temperatures as well as by the appearance of multiple peaks at high temperatures and for high excitation powers.

  18. 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.

  19. High speed, low noise ultraviolet photodetectors based on GaN p-i-n and AlGaN(p)-GaN(i)-GaN(n) structures

    Energy Technology Data Exchange (ETDEWEB)

    Xu, G.; Salvador, A.; Botchkarev, A.E.; Kim, W.; Lu, C.; Tang, H. [Illinois Univ., Urbana, IL (United States). Mater. Res. Lab. and Coordinated Sci.; Morkoc, H. [Illinois Univ., Urbana, IL (United States). Mater. Res. Lab. and Coordinated Sci.]|[Air Force Wright Lab., Wright Patterson, AFB, OH (United States)]|[Dept. of Electrical Eng., Virginia Commonwealth Univ., Richmond, VA (United States); Smith, G.; Estes, M.; Dang, T. [Air Force Wright Lab., Wright Patterson, AFB, OH (United States); Wolf, P. [Air Force Inst. of Tech., Wright-Patterson AFB, OH (United States). Dept. of Engineering Physics

    1998-08-01

    We have investigated the spectral response of front surface illuminated GaN, AlGaN/GaN and AlGaN p-i-n ultraviolet photodetectors grown by reactive molecular beam epitaxy on sapphire substrates. The GaN homojunction p-i-n photodiode exhibited a peaked response at 364 nm the origin of which is not yet clear. This response was absent in the AlGaN/GaN heterojunction p-i-n detectors. The maximum responsivity for the unbiased GaN and AlGaN/GaN is 0.07 and 0.12 A/W, respetively, and occurs at 364 nm. The responsivity drops by more than 3 orders of magnitude near 390 nm. The AlGaN homojunction p-i-n on the other hand has a peak responsivity of 0.08 A/W at 340 nm. The noise equivalent power of 4 pW and 8.3 pW were obtained for the GaN and AlGaN/GaN photodiodes respectively. We measured extremely fast decay times of 12 ns for the AlGaN/GaN and 29 ns for the GaN photodiodes. (orig.) 5 refs.

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

    OpenAIRE

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

    2015-01-01

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

  2. Influence of AlGaN/GaN superlattice inserted structure on the performance of InGaN/GaN multiple quantum well light emitting diodes

    International Nuclear Information System (INIS)

    Wang, C.-L.; Tsai, M.-C.; Gong, J.-R.; Liao, W.-T.; Lin, P.-Y.; Yen, K.-Y.; Chang, C.-C.; Lin, H.-Y.; Hwang, S.-K.

    2007-01-01

    Investigations were conducted to explore the effect of Al 0.3 Ga 0.7 N/GaN short-period superlattice (SPSL)-inserted structures in the GaN under layer on the performance of In 0.2 Ga 0.8 N/GaN multiple quantum well (MQW) light emitting diodes (LEDs). The Al 0.3 Ga 0.7 N/GaN SPSL-inserted LEDs were found to exhibit improved materials and device characteristics including decrements in ideality factor and reverse leakage current. The results of etch pit counts reveal that SPSL-induced threading dislocation density reduction in the SPSL-inserted In 0.2 Ga 0.8 N/GaN MQW LED structures enables the improved LED performance

  3. Rentgenovskaja diagnostika psevdomorfnoj AlGaAs/InGaAs/GaAs – kompozicii

    Czech Academy of Sciences Publication Activity Database

    Subbotin, I. A.; Čujev, M. A.; Pašajev, E. M.; Imamov, R. M.; Galiev, G. B.; Tichomirov, S. A.; Kacerovský, Pavel

    2007-01-01

    Roč. 52, č. 4 (2007), s. 638-644 ISSN 0023-4761 R&D Projects: GA ČR GA202/06/1315 Grant - others:RFFI(RU) 05-02-17585; NŠ(RU) 5133.2006.2 Institutional research plan: CEZ:AV0Z20670512 Source of funding: O - operačné programy ; O - operačné programy Keywords : diffraction * semiconductor thin films * X-ray spetrometers Subject RIV: BM - Solid Matter Physics ; Magnetism

  4. Coulomb excitation of 73Ga

    CERN Document Server

    Diriken, J; Balabanski, D; Blasi, N; Blazhev, A; Bree, N; Cederkäll, J; Cocolios, T E; Davinson, T; Eberth, J; Ekström, A; Fedorov, D V; Fedosseev, V N; Fraille, L M; Franchoo, S; Georgiev, G; Gladnishki, K; Huyse, M; Ivanov, O V; Ivanov, V S; Iwanicki, V; Jolie, J; Konstantinopoulos, T; Kröll, Th; Krücken, R; Köster, U; Lagoyannis, A; Bianco, G Lo; Maierbeck, P; March, B A; Napiarkowski, 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; Ii ! If ) values for transitions in 71Ga and 73Ga were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of 71,73Ga at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were detected by the MINIBALL-detector array and B(E2; Ii->If ) values were obtained from the yields normalized to the known strength of the 2+ -> 0+ transition in the 120Sn target. The comparison of these new results with the data of less neutron-rich gallium isotopes shows a shift of the E2 collectivity towards lower excitation energy when adding neutrons beyond N = 40. This supports conclusions from previous studies of the gallium isotopes which indicated a structural change in this isotopical chain between N = 40 and N = 42. Combined with recent measurements from collinear laser spectroscopy showing a 1/2- spin and parity for the ground state, the extracted results revealed evidence for a 1/2-; 3/2- doublet near the ground state in 73 31Ga...

  5. Anomalous disorder-related phenomena in InGaN/GaN multiple quantum well heterosystems

    International Nuclear Information System (INIS)

    Hu, Y.-J.; Huang, Y.-W.; Fang, C.-H.; Wang, J.-C.; Chen, Y.-F.; Nee, T.-E.

    2010-01-01

    The influences of InGaN/GaN multiple quantum well (MQW) heterostructures with InGaN/GaN and GaN barriers on carrier confinement were investigated. The degree of disordering over a broad range of temperatures from 20 to 300 K was considered. The optical and electrical properties were strongly influenced by structural and compositional disordering of the InGaN/GaN MQW heterostructures. To compare the degree of disordering we examined the temperature dependence of the luminescence spectra and electrical conductance contingent on the Berthelot-type mechanisms in the InGaN/GaN MQW heterostructures. We further considered carrier transport in the InGaN/GaN disordered systems, probability of carrier tunneling, and activation energy of the transport mechanism for devices with InGaN/GaN and GaN barriers. The optical properties of InGaN/GaN disordered heterosystems can be interpreted from the features of the absorption spectra. The anomalous temperature-dependent characteristics of the disordered InGaN/GaN MQW structures were attributable to the enhancement of the exciton confinement.

  6. Spectral-splitting concentrator photovoltaic modules based on AlGaAs/GaAs/GaSb and GaInP/InGaAs(P) solar cells

    Science.gov (United States)

    Vlasov, A. S.; Khvostikov, V. P.; Karlina, L. B.; Sorokina, S. V.; Potapovich, N. S.; Shvarts, M. Z.; Timoshina, N. Kh.; Lantratov, V. M.; Mintairov, S. A.; Kalyuzhnyi, N. A.; Marukhina, E. P.; Andreev, V. M.

    2013-07-01

    A concentrator photovoltaic module with sunlight spectral splitting by Fresnel lens and dichroic filters is developed. The photoelectric conversion efficiency of such a module is estimated at a level of 49.4% when three single-junction cells are used and may reach 48.5-50.6% when a tandem two-junction cell is combined with narrow-band cells. Single-junction AlGaAs, GaAs, GaSb, and InGa(P)As solar sells are fabricated by zinc diffusion from the vapor phase into an n-type epitaxial layer. GaInP/GaAs cascade solar cells are prepared by MOS hydride epitaxy. The overall efficiency of the three single-junction solar cells developed for the spectral-splitting module is 38.1% (AM1.5D) at concentration ratio K c = 200x. The combination of the solar cells with the cascade structure demonstrates an efficiency of 37.9% at concentrations of 400-800 suns. The parameters of the spectral-splitting photovoltaic module are measured. The photovoltaic efficiency of this module reaches 24.7% in the case of three single-junction cells and 27.9% when the two-junction and single-junction cells are combined.

  7. Phase equilibria in Sm-Ga-S ternary system according to SmGa2-GaS, SmGa2-SmS, Sm3S4-Ga2S3, SmS-GaS, Sm-GaS cross sections

    International Nuclear Information System (INIS)

    Alieva, O.A.; Aliev, O.M.; Ehjnullaev, A.V.

    1993-01-01

    Phase equilibria in ternary system Sm-Ga-S over cross sections SmGa 2 -GaS, SmGa 2 -SmS, SmS-GaS, Sm 3 S 4 -Ga 2 S 3 , Sm-GaS have been studied for the first time using the methods of physicochemical analysis, their T-x projections were plotted. The cross sections SmGa 2 -GaS, SmGa 2 -SmS, Sm 3 S 4 -Ga 2 S 3 and SmS-GaS are quasibinary, while Sm-GaS is nonquasibinary one. Formation of two ternary compounds of the composition Sm 4 GaS 5 and Sm 5 Ga 2 S 5 was ascertained by peritectic reactions

  8. GaAs, AlGaAs and InGaP Tunnel Junctions for Multi-Junction Solar Cells Under Concentration: Resistance Study

    International Nuclear Information System (INIS)

    Wheeldon, Jeffrey F.; Valdivia, Christopher E.; Walker, Alex; Kolhatkar, Gitanja; Hall, Trevor J.; Hinzer, Karin; Masson, Denis; Riel, Bruno; Fafard, Simon; Jaouad, Abdelatif; Turala, Artur; Ares, Richard; Aimez, Vincent

    2010-01-01

    The following four TJ designs, AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs are studied to determine minimum doping concentration to achieve a resistance of -4 ω·cm 2 and a peak tunneling current suitable for MJ solar cells up to 1500-suns concentration (operating current of 21 A/cm 2 ). Experimentally calibrated numerical models are used to determine how the resistance changes as a function of doping concentration. The AlGaAs/GaAs TJ design is determined to require the least doping concentration to achieve the specified resistance and peak tunneling current, followed by the GaAs/GaAs, and AlGaAs/AlGaAs TJ designs. The AlGaAs/InGaP TJ design can only achieve resistances >5x10 -4 ωcm 2 .

  9. Dose rate hardening of As Ga components by buffer layers with hetero structure Ga As/Ga Al As

    International Nuclear Information System (INIS)

    Dupont-Nivet, E.; Coic, Y.M.; Frijlink, P.; Nicolas, J.L.

    1989-01-01

    Radiation resistance of gallium arsenide components is improved by incorporation between the substrate and the active layer a potential barrier with GaAlAs which has a greater forbidden band than GaAs [fr

  10. 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.

  11. Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

    International Nuclear Information System (INIS)

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

    2006-01-01

    We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1 o . As the surface tilt angle increased to 0.35 o , the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4 o , surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers

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

    Science.gov (United States)

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

    2018-01-01

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

  13. High performance resonant tunnelling structures on GaAs substrates

    Science.gov (United States)

    Riechert, H.; Bernklau, D.; Reithmaier, J.-P.; Schnell, R. D.

    1990-03-01

    GaAs-based resonant tunneling structures of high quality were grown by molecular beam epitaxy. Room temperature peak-to-valley ratios of 4.8 for a GaAs/AlGaAs double barrier quantum well, 4.1 for GaAs/AlGaAs with InGaAs quantum well and 5.9 for GaAs/AlGaAs with adjacent InGaAs 'prewell' were obtained, in connection with reasonable peak current densities.

  14. Improvement of electrostatic discharge characteristics of InGaN/GaN MQWs light-emitting diodes by inserting an n+-InGaN electron injection layer and a p-InGaN/GaN hole injection layer

    International Nuclear Information System (INIS)

    Jia, Chuanyu; Zhong, Cantao; Yu, Tongjun; Wang, Zhe; Tong, Yuzhen; Zhang, Guoyi

    2012-01-01

    To improve the electrostatic discharge properties of InGaN/GaN LEDs, an n + -InGaN electron injection layer and a p-InGaN/GaN hole injection layer were inserted beneath and above the InGaN/GaN MQWs. The influences of activated donor concentration in n + -InGaN and acceptor concentration in p-InGaN/GaN and on the depletion width and the internal capacitance of GaN-based n + -P LED have been investigated. Our research results indicated that the capacitance of GaN-based n + -P LED is mainly determined by the depletion width which is dependent on the activated acceptor concentration N A in the p-InGaN/GaN hole injection layer. The relationship between the internal capacitance of InGaN–LEDs and the electrostatic discharge (ESD) properties was also investigated. It was found that the LEDs with large internal capacitance were more resistant to external ESD impulses. With optimized LED structures with n + -InGaN layer and a p-InGaN/GaN SLs, the HBM-ESD pass yield at −1500 V reached 95%, much higher than the value of 15% in reference samples without inserting layers above. (paper)

  15. Automated synthesis, characterization and biological evaluation of [{sup 68}Ga]Ga-AMBA, and the synthesis and characterization of {sup nat}Ga-AMBA and [{sup 67}Ga]Ga-AMBA

    Energy Technology Data Exchange (ETDEWEB)

    Cagnolini, Aldo; Chen Jianqing; Ramos, Kimberly; Marie Skedzielewski, Tina; Lantry, Laura E.; Nunn, Adrian D.; Swenson, Rolf E. [Ernst Felder Laboratories, Bracco Research USA Inc., 305 College Road East, Princeton, NJ 08540 (United States); Linder, Karen E., E-mail: karen.e.linder@gmail.co [Ernst Felder Laboratories, Bracco Research USA Inc., 305 College Road East, Princeton, NJ 08540 (United States)

    2010-12-15

    Ga-AMBA (Ga-DO3A-CH{sub 2}CO-G-[4-aminobenzoyl]-QWAVGHLM-NH{sub 2}) is a bombesin-like agonist with high affinity for gastrin releasing peptide receptors (GRP-R). Syntheses for {sup nat}Ga-AMBA, [{sup 67}Ga]Ga-AMBA and [{sup 68}Ga]Ga-AMBA were developed. The preparation of HPLC-purified and Sep-Pak purified [{sup 68}Ga]Ga-AMBA were fully automated, using the built-in radiodetector of the Tracerlab FX F-N synthesizer to monitor fractionated {sup 68}Ge/{sup 68}Ga generator elution and purification. The total synthesis time, including the fractional elution of the generator, was 20 min for Sep-Pak purified material and 40 min for HPLC-purified [{sup 68}Ga]Ga-AMBA. Both [{sup 67}Ga]Ga-AMBA and [{sup 177}Lu]Lu-AMBA showed comparable high affinity for GRP-R in the human prostate cancer cell line PC-3 in vitro (k{sub D}=0.46{+-}0.07; 0.44{+-}0.08 nM), high internalization (78; 77%) and low efflux from cells at 2 h (2.4{+-}0.7; 2.9{+-}1.8%). Biodistribution results in PC-3 tumor-bearing male nude mice showed comparable uptake for [{sup 177}Lu]Lu-, [{sup 111}In]In-, [{sup 67}Ga]Ga- and [{sup 68}Ga]Ga-AMBA.

  16. Capacitance properties and simulation of the AlGaN/GaN Schottky heterostructure

    International Nuclear Information System (INIS)

    Harmatha, Ladislav; Ľubica, Stuchlíková; Juraj, Racko; Juraj, Marek; Juraj, Pecháček; Peter, Benko; Michal, Nemec; Juraj, Breza

    2014-01-01

    Highlights: • Dependences of CV characteristics of the AlGaN/GaN structure on frequency and temperature variations. • Identification of electrical activity of defects by capacitance DLTS. • Simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure. - Abstract: The paper presents the results of capacitance measurements on GaN/AlGaN/GaN Schottky heterostructures grown on an Al 2 O 3 substrate by Low-Pressure Metal–Organic Vapour-Phase Epitaxy (LP-MOVPE). Dependences of the capacitance–voltage (CV) characteristics on the frequency of the measuring signal allow analysing the properties of the 2D electron gas (2DEG) at the AlGaN/GaN heterojunction. Exact location of the hetero-interface below the surface (20 nm) was determined from the concentration profile. Temperature variations of the CV curves reveal the influence of bulk defects in GaN and of the traps at the AlGaN/GaN interface. Electrical activity of these defects was characterized by capacitance Deep Level Transient Fourier Spectroscopy (DLTFS). Experimental results of CV measurements were supported by simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure in dependence on the influence of the concentration of donor-like traps in GaN and of the temperature upon the CV curves

  17. Graphene-GaN Schottky Photodiodes

    Data.gov (United States)

    National Aeronautics and Space Administration — Graphene-GaN Schottky Photodiodes is the development of the world's first graphene-based GaN Schottky device that has the potential to achieve a much greater total...

  18. GaN nanowire Schottky barrier diodes

    OpenAIRE

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

    2017-01-01

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

  19. Bipolar characteristics of AlGaN/AlN/GaN/AlGaN double heterojunction structure with AlGaN as buffer layer

    International Nuclear Information System (INIS)

    Peng, Enchao; Wang, Xiaoliang; Xiao, Hongling; Wang, Cuimei; Yin, Haibo; Chen, Hong; Feng, Chun; Jiang, Lijuan; Hou, Xun; Wang, Zhanguo

    2013-01-01

    Highlights: •2DEG and 2DHG coexist in the AlGaN/AlN/GaN/AlGaN DH-structure. •The sheet densities of 2DEG and 2DHG vary with buffer Al content and GaN thickness. •The conditions for the disappearance of 2DHG are discussed. •Increasing buffer Al content provides better electron confinement. •Dislocation scattering is reduced in the DH-structure. -- Abstract: This is a theoretical study of AlGaN/AlN/GaN/AlGaN double heterojunction (DH) structure with AlGaN as buffer layer. Our calculation shows that as the buffer Al content increases, though two-dimensional electron gas (2DEG) sheet density decreases, the channel back-barrier caused by polarization-induced electric field in GaN provides better electron confinement. And under certain conditions the DH-structure shows bipolar characteristics, with an additional two-dimensional hole gas (2DHG) formed at GaN/AlGaN interface. The influence of the buffer Al content and GaN channel thickness on the 2DEG and 2DHG sheet densities are investigated, and the conditions for the disappearance of 2DHG are discussed. Also, the mobility inhibited by dislocation scattering is enhanced in DH-structure due to the enhancement of screening effect of the 2DEG

  20. InGaAs and GaAsSb strain reducing layers covering InAs/GaAs quantum dots

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Hulicius, Eduard; Pangrác, Jiří; Oswald, Jiří; Vyskočil, Jan; Kuldová, Karla; Šimeček, Tomislav; Hazdra, P.; Caha, O.

    2010-01-01

    Roč. 312, č. 8 (2010), 1383-1387 ISSN 0022-0248 R&D Projects: GA AV ČR IAA100100719; GA ČR GA202/09/0676; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : low dimensional structures * photoluminescence * low-pressure MOVPE * InAs/GaAs quantum dots * semiconducting III/V materials Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.737, year: 2010

  1. Characteristics of GaN/InGaN Double-Heterostructure Photovoltaic Cells

    Directory of Open Access Journals (Sweden)

    Ming-Hsien Wu

    2012-01-01

    Full Text Available The p-GaN/i-InxGa1−xN/n-GaN double-heterostructure photovoltaic (PV cells have been fabricated and the theoretical photovoltaic properties were also calculated in this work. From theoretical simulation, higher efficiency can be obtained in GaN/InGaN double-heterostructure photovoltaic cells with higher In composition in i-InGaN intrinsic layer. GaN/InGaN double-heterostructure photovoltaic cells with In compositions of 10%, 12%, and 14% were fabricated and characterized for demonstrating with the simulated results. The corresponding photoelectrical conversion efficiency of fabricated GaN/InGaN photovoltaic cells with In compositions of 10%, 12%, and 14% is 0.51%, 0.53%, and 0.32% under standard AM 1.5G measurement condition, respectively. GaN/InGaN photovoltaic cells with In composition of 10% showed high open-circuit voltage (Voc of 2.07 V and fill factor (F.F. of 80.67%. The decrease of Voc and FF was observed as In composition increasing from 10% to 14%. For comparing with the fabricated GaN/InGaN photovoltaic cells, theoretical conversion efficiency of GaN/InGaN photovoltaic cells with In compositions of 10%, 12%, and 14%, is 1.80%, 2.04%, and 2.27%, respectively. The difference of GaN/InGaN photovoltaic properties between theoretical simulation and experimental measurement could be attributed to the inferior quality of InGaN epilayer and GaN/InGaN interface generated as the increase of In composition.

  2. Recessed insulator and barrier AlGaN/GaN HEMT

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 88; Issue 4. Recessed insulator and barrier AlGaN/GaN HEMT: A novel structure for improving DC and RF characteristics ... Keywords. AlGaN/GaN high electron mobility transistor; breakdown voltage; output power density; short channel effect; gate-drain capacitance ...

  3. Luminescence of the InGaN/GaN Blue Light-Emitting Diodes

    Science.gov (United States)

    2000-07-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADPO 11314 TITLE: Luminescence of the InGaN/GaN Blue Light -Emitting Diodes...ADP011332 UNCLASSIFIED Luminescence of the InGaN/GaN blue light -emitting diodes J. K. Sheu a), T. W. Yeh and G. C. Chi Optical Sciences Center, National

  4. Charge transport study and spectral response of GaSb/GaAs heterojunctions prepared by MOVPE

    Czech Academy of Sciences Publication Activity Database

    Toušková, J.; Kindl, Dobroslav; Samokhin, Jevgen; Toušek, J.; Hulicius, Eduard; Pangrác, Jiří; Šimeček, Tomislav; Výborný, Zdeněk

    2003-01-01

    Roč. 76, - (2003), s. 135-145 ISSN 0927-0248 R&D Projects: GA ČR GA102/99/0414 Institutional research plan: CEZ:AV0Z1010914 Keywords : thermophotovoltaics * GaSb/GaAs heterojunction * charge transport * band diagram Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.188, year: 2003

  5. Temperature Dependence of the Energy Band Diagram of AlGaN/GaN Heterostructure

    Directory of Open Access Journals (Sweden)

    Yanli Liu

    2018-01-01

    Full Text Available Temperature dependence of the energy band diagram of AlGaN/GaN heterostructure was investigated by theoretical calculation and experiment. Through solving Schrodinger and Poisson equations self-consistently by using the Silvaco Atlas software, the energy band diagram with varying temperature was calculated. The results indicate that the conduction band offset of AlGaN/GaN heterostructure decreases with increasing temperature in the range of 7 K to 200 K, which means that the depth of quantum well at AlGaN/GaN interface becomes shallower and the confinement of that on two-dimensional electron gas reduces. The theoretical calculation results are verified by the investigation of temperature dependent photoluminescence of AlGaN/GaN heterostructure. This work provides important theoretical and experimental basis for the performance degradation of AlGaN/GaN HEMT with increasing temperature.

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

    Science.gov (United States)

    2013-08-01

    active region consists of nine In0.2Ga0.8Sb QWs separated by pump absorbing Al0.25Ga0.75 Sb barriers. An AlSb confinement layer on each side of the...by pump absorbing Al0.25Ga0.75Sb barriers and AlSb top/bottom clad. The key feature of the antimonide VECSEL based on the GaAs/AlGaAs DBRs is the...also enhanced by the AlSb carrier con- finement layers. However, the “ABC” empirical model is not adequate to model the carrier losses at high carrier

  7. 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).

  8. Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Yablonsky, A. N., E-mail: yablonsk@ipm.sci-nnov.ru; Morozov, S. V.; Gaponova, D. M.; Aleshkin, V. Ya. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Shengurov, V. G.; Zvonkov, B. N.; Vikhrova, O. V.; Baidus’, N. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Krasil’nik, Z. F. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-11-15

    We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.

  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. Two new Np-Ga phases: α-NpGa2 and metastable m-NpGa2

    International Nuclear Information System (INIS)

    Giessen, B.C.; Elliott, R.O.

    1976-01-01

    Following an earlier study of metastable Np-rich Np-Ga alloys, rapidly quenched Np-Ga alloys with 63-80 at.% Ga were prepared and studied. Two new NpGa 2 phases, both with an AlB 2 type structure, were found: α-NpGa 2 , with a=4.246A, c=4.060A, c/a=0.956 and m-NpGa 2 , with a=4.412A, c=3.642A, c/a=0.825. While m-NpGa 2 was observed only in very fast quenched (splat cooled) samples and appears to be metastable, α-NpGa 2 is probably an equilibrium phase. In a splat cooled alloy with 75 at.% Ga, another, unidentified, metastable phase was observed. Crystal chemical discussions of atomic volumes, interatomic distances and axial ratios are given; the volume difference between the two forms of NpGa 2 is correlated with a valence change of Np. (Auth.)

  11. Green light emission by InGaN/GaN multiple-quantum-well microdisks

    International Nuclear Information System (INIS)

    Hsu, Yu-Chi; Lo, Ikai; Shih, Cheng-Hung; Pang, Wen-Yuan; Hu, Chia-Hsuan; Wang, Ying-Chieh; Tsai, Cheng-Da; Chou, Mitch M. C.; Hsu, Gary Z. L.

    2014-01-01

    The high-quality In x Ga 1−x N/GaN multiple quantum wells were grown on GaN microdisks with γ-LiAlO 2 substrate by using low-temperature two-step technique of plasma-assisted molecular beam epitaxy. We demonstrated that the hexagonal GaN microdisk can be used as a strain-free substrate to grow the advanced In x Ga 1−x N/GaN quantum wells for the optoelectronic applications. We showed that the green light of 566-nm wavelength (2.192 eV) emitted from the In x Ga 1−x N/GaN quantum wells was tremendously enhanced in an order of amplitude higher than the UV light of 367-nm wavelength (3.383 eV) from GaN

  12. 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.

  13. Comparative study of GaN and GaAs photocathodes

    Science.gov (United States)

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

    2008-02-01

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

  14. Wet etching of AlGaN/GaN photocathode grown by MOCVD

    Science.gov (United States)

    Hao, Guanghui; Chang, Benkang; Cheng, Hongchang

    2013-08-01

    The AlGaN/GaN with thin GaN surface was grown by metalorganic chemical vapor deposition (MOCVD). And one of two AlGaN/GaN photocathode samples was etched by molten KOH about 40s, and its reflectivity and transmittance are tested. The thickness of AlGaN and GaN layers are fitted by the matrix formula for thin film optics, and the GaN thickness of them are 7nm and 2.5nm respectively. And etch speed of GaN are got in molten KOH at about 400°C. Then the etched and original AlGaN/GaN photocathode samples are activated by Cs/O in the same way. The spectral response and the result of simulation show that the cut-off wavelength of the etched AlGaN/GaN deviate to the short-wave. And the quantum efficiency decline with the GaN thickness decrease.

  15. Density Functional Theory Study on Defect Feature of AsGaGaAs in Gallium Arsenide

    Directory of Open Access Journals (Sweden)

    Deming Ma

    2015-01-01

    Full Text Available We investigate the defect feature of AsGaGaAs defect in gallium arsenide clusters in detail by using first-principles calculations based on the density functional theory (DFT. Our calculations reveal that the lowest donor level of AsGaGaAs defect on the gallium arsenide crystal surface is 0.85 eV below the conduction band minimum, while the lowest donor level of the AsGaGaAs defect inside the gallium arsenide bulk is 0.83 eV below the bottom of the conduction band, consistent with gallium arsenide EL2 defect level of experimental value (Ec-0.82 eV. This suggests that AsGaGaAs defect is one of the possible gallium arsenide EL2 deep-level defects. Moreover, our results also indicate that the formation energies of internal AsGaGaAs and surface AsGaGaAs defects are predicted to be around 2.36 eV and 5.54 eV, respectively. This implies that formation of AsGaGaAs defect within the crystal is easier than that of surface. Our results offer assistance in discussing the structure of gallium arsenide deep-level defect and its effect on the material.

  16. AlGaN/GaN current aperture vertical electron transistors with regrown channels

    OpenAIRE

    Ben-Yaacov, I; Seck, Y K; Mishra, U K; DenBaars, S P

    2004-01-01

    AlGaN/GaN current aperture vertical electron transistors with regrown aperture and source regions have been fabricated and tested. A 2 mum thick GaN:Si drain region followed by a 0.4 mum GaN:Mg current-blocking layer were grown by metalorganic chemical vapor deposition on a c-plane sapphire substrate. Channel apertures were etched, and a maskless regrowth was performed to grow unintentionally doped GaN inside the aperture as well as above the insulating layer, and to add an AlGaN cap layer. C...

  17. Role of AlGaN/GaN interface traps on negative threshold voltage shift in AlGaN/GaN HEMT

    Science.gov (United States)

    Malik, Amit; Sharma, Chandan; Laishram, Robert; Bag, Rajesh Kumar; Rawal, Dipendra Singh; Vinayak, Seema; Sharma, Rajesh Kumar

    2018-04-01

    This article reports negative shift in the threshold-voltage in AlGaN/GaN high electron mobility transistor (HEMT) with application of reverse gate bias stress. The device is biased in strong pinch-off and low drain to source voltage condition for a fixed time duration (reverse gate bias stress), followed by measurement of transfer characteristics. Negative threshold voltage shift after application of reverse gate bias stress indicates the presence of more carriers in channel as compared to the unstressed condition. We propose the presence of AlGaN/GaN interface states to be the reason of negative threshold voltage shift, and developed a process to electrically characterize AlGaN/GaN interface states. We verified the results with Technology Computer Aided Design (TCAD) ATLAS simulation and got a good match with experimental measurements.

  18. Comparison of MOVPE grown GaAs, InGaAs and GaAsSb covering layers for different InAs/GaAs quantum dot applications

    Czech Academy of Sciences Publication Activity Database

    Zíková, Markéta; Hospodková, Alice; Pangrác, Jiří; Oswald, Jiří; Hulicius, Eduard

    2017-01-01

    Roč. 464, Apr (2017), s. 59-63 ISSN 0022-0248 R&D Projects: GA MŠk LO1603 Institutional support: RVO:68378271 Keywords : MOVPE * quantum dot * strain reducing layer * InAs * GaAsSb * InGaAs Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

  19. Capacitance properties and simulation of the AlGaN/GaN Schottky heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Harmatha, Ladislav, E-mail: ladislav.harmatha@stuba.sk; Ľubica, Stuchlíková; Juraj, Racko; Juraj, Marek; Juraj, Pecháček; Peter, Benko; Michal, Nemec; Juraj, Breza

    2014-09-01

    Highlights: • Dependences of CV characteristics of the AlGaN/GaN structure on frequency and temperature variations. • Identification of electrical activity of defects by capacitance DLTS. • Simulating the properties of the GaN/Al{sub 0.2}GaN{sub 0.8}/GaN Schottky heterostructure. - Abstract: The paper presents the results of capacitance measurements on GaN/AlGaN/GaN Schottky heterostructures grown on an Al{sub 2}O{sub 3} substrate by Low-Pressure Metal–Organic Vapour-Phase Epitaxy (LP-MOVPE). Dependences of the capacitance–voltage (CV) characteristics on the frequency of the measuring signal allow analysing the properties of the 2D electron gas (2DEG) at the AlGaN/GaN heterojunction. Exact location of the hetero-interface below the surface (20 nm) was determined from the concentration profile. Temperature variations of the CV curves reveal the influence of bulk defects in GaN and of the traps at the AlGaN/GaN interface. Electrical activity of these defects was characterized by capacitance Deep Level Transient Fourier Spectroscopy (DLTFS). Experimental results of CV measurements were supported by simulating the properties of the GaN/Al{sub 0.2}GaN{sub 0.8}/GaN Schottky heterostructure in dependence on the influence of the concentration of donor-like traps in GaN and of the temperature upon the CV curves.

  20. Multi-stacked GaSb/GaAs type-II quantum nanostructures for application to intermediate band solar cells

    Science.gov (United States)

    Shoji, Yasushi; Tamaki, Ryo; Okada, Yoshitaka

    2017-06-01

    We have investigated the performance of 10-layer stacked GaSb/GaAs quantum dot (QD) and quantum ring (QR) solar cells (SCs) having a type-II band alignment. For both SCs, the external quantum efficiency (EQE) increased in the longer wavelength region beyond GaAs bandedge wavelength of λ > 870 nm due to an additive contribution from GaSb/GaAs QD or QR layers inserted in the intrinsic region of p-i-n SC structure. The EQE of GaSb/GaAs QRSC was higher than that of QDSC at room temperature and the photoluminescence intensity from GaSb/GaAs QRs was stronger compared with GaSb/GaAs QDs. These results indicate that crystal quality of GaSb/GaAs QRs is superior to that of GaSb/GaAs QDs. Furthermore, a photocurrent production due to two-step photo-absorption via GaSb/GaAs QD states or QR states, ΔEQE was measured at low temperature and the ratio of two-step absorption to total carrier extraction defined as ΔEQE / (ΔEQE + EQE), was higher for GaSb/GaAs QRSC than that of QDSC. The ratio of GaSb/GaAs QRSC exceeds 80% over the wavelength region of λ = 950 - 1250 nm. This suggests that two-step absorption process is more dominant for carrier extraction from GaSb/GaAs QR structure.

  1. Liquidus surface of Sm-Ga-S system

    International Nuclear Information System (INIS)

    Alieva, O.A.; Aliev, O.M.

    1989-01-01

    Using methods of physicochemic alanalysis for the first time phase diagrams of SmS-Ga 2 S 3 , Sm 2 S 3 -Ga 2 S 3 , SmS-GaS, Sm-GaS, SmGa 2 -SmS, SmGa 2 -GaS, GaS-SmGa 2 S 4 , Sm 3 S 4 -Ga 2 S 3 , Sm 2 S 3 -GaS, Sm 3 S 4 -SmGa 2 S 4 cross sections are studied and the projection of the liquidus surface of the Sm-Ga-S ternary system is plotted. It is found that there exist 6 ternary compounds in the system (SmGa 2 S 4 , SmGaS 3 , SmGa 4 S 7 , Sm 4 GaS 5 , Sm 3 Ga 2 S 5 , Sm 6 Ga 10/3 S 14 ) and, besides, found solid solutions based on GaS, Ga 2 S 3 and SmGa 2 S 4

  2. Axial InGaAs/GaAs nanowire separate absorption-multiplication avalanche photodetectors (Conference Presentation)

    Science.gov (United States)

    Huffaker, Diana L.

    2017-05-01

    In0.53Ga0.47As/InP single photon avalanche detectors (SPADs) have a high photon detection efficiency in the near-IR, however the dark count rate is prohibitively high at room temperature. A nanowire-based In0.3Ga0.7As/GaAs SPAD can significantly reduce the DCR through a nearly three order of magnitude reduction in bulk InGaAs volume, as well as by reducing the indium composition for operation at 1064 nm. As a first step, we have successfully grown axial InGaAs/GaAs heterostructures using catalyst-free selective-area epitaxy. We will present the electrical characterization of a vertically oriented nanowire array InGaAs/GaAs SPADs operating at 1064 nm and use 3-dimensional modeling to aid in the analysis.

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

    Data.gov (United States)

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

  4. 67Ga and 66Ga yield in 66,67,68Zn(dxn) reactions

    International Nuclear Information System (INIS)

    Dmitriev, P.P.; Panarin, M.V.; Molin, G.A.; Dmitrieva, Z.P.

    1991-01-01

    Nowadays the 67 Ga (T 1/2 =78.255 h) is one of the most important radionuclides for medicine. The 67,66 Ga yields depending on deuteron energy were measured for thick targets of enriched by 66,67,68 Zn and natural zinc in the reactions: 66 Zn(dn) 67 Ga (thresholdless one), 66 Zn(d2n) 66 Ga (energy threshold of 8.43 MeV), 67 Zn(d2n) 67 Ga (4.13 MeV), 67 Zn(d3n) 66 Ga (15.7 MeV), 68 Zn(d3n) 67 Ga (14.6 MeV). The yields for thick targets were measured for each reaction up to E d ≅ 22 MeV. The yield of 67,66 Ga was also measured for the natural zinc

  5. InGaN nanoinclusions in an AlGaN matrix

    International Nuclear Information System (INIS)

    Sizov, V. S.; Tsatsul'nikov, A. F.; Lundin, V. V.

    2008-01-01

    GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80-300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective.

  6. Laser-induced transformation of GaS and GaSe nanosheets to ...

    Indian Academy of Sciences (India)

    Administrator

    Abstract. Experimental evidence for the transformation of nanosheets of GaS and GaSe into onion struc- tures on UV excimer pulsed laser irradiation is presented. Few-layer GaS and GaSe on Si substrates were exposed to KrF pulsed laser with wavelength of 248 nm and the effect was studied as a function of number of.

  7. Characterization of GaN/AlGaN epitaxial layers grown by ...

    Indian Academy of Sciences (India)

    s and carrier concentration is 4.5 × 1016/cm3. Dislocation density of GaN buffer layer, 2×108/cm2, was measured by AFM after wet etching. The refractive indices of GaN buffer layer at 633 nm is 2.3544 for TE mode and 2.1515 for TM mode. This data demonstrate the quality achieved for GaN and AlGaN epitaxial layers.

  8. 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....

  9. Molecular beam epitaxy of GaSb on GaAs substrates with AlSb/GaSb compound buffer layers

    International Nuclear Information System (INIS)

    Hao Ruiting; Deng Shukang; Shen Lanxian; Yang Peizhi; Tu Jielei; Liao Hua; Xu Yingqiang; Niu Zhichuan

    2010-01-01

    GaSb films with AlSb/GaSb compound buffer layers were grown by molecular beam epitaxy on GaAs (001) substrates. The crystal quality and optical properties were studied by high resolution transition electron microscopy and low temperature photoluminescence spectra (PL), respectively. It was found that the AlSb/GaSb compound buffer layers can restrict the dislocations into GaSb epilayers. The intensity of PL spectra of GaSb layer becomes large with the increasing the periods of AlSb/GaSb superlattices, indicating that the optical quality of GaSb films is improved.

  10. 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...

  11. 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.

  12. Temperature dependence of lattice parameter of (Ga,Mn)As on GaAs substrate

    Science.gov (United States)

    Matsukura, Fumihiro; Ohno, Hideo

    2015-09-01

    We measure the temperature dependence of the lattice parameter of (Ga,Mn)As by X-ray diffraction. The result shows that the lattice parameter of (Ga,Mn)As shows similar temperature dependence to that of GaAs, and no obvious change is observed in the vicinity of its Curie temperature.

  13. 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.

  14. Analysis of Interface Scattering in AlGaN/GaN/InGaN/GaN Double-Heterojunction High-Electron-Mobility Transistors

    Science.gov (United States)

    Wang, Lin; Hu, Weida; Chen, Xiaoshuang; Lu, Wei

    2012-08-01

    This paper presents detailed investigations on the direct-current (DC) characteristics of an AlGaN/GaN/InGaN/GaN double-heterojunction high-electron-mobility transistor (DH-HEMT) using two-dimensional numerical analysis. In this work, the hot-electron effect is taken into account and implemented in the hydrodynamic model. The results indicate that carrier transport in this kind of device exhibits properties significantly different from that in a conventional AlGaN/GaN HEMT. Due to imperfections at the GaN/InGaN interface, scattering caused by the interface roughness, phonons, etc. inhibit the negative differential conductance in high electric field. In addition, the velocity increment of electrons around the gate edge is dominated by the overshoot effect rather than the phonon effect. The energy exchange between phonons and electrons, as presented in this paper, illustrates that the dissipated power is just a small portion of the exchanged energy. For further performance improvement, more lattice-matched material with strong polarization for the barrier layer is proposed.

  15. AlGaAs and AlGaAs/GaAs/AlGaAs nanowires grown by molecular beam epitaxy on silicon substrates

    DEFF Research Database (Denmark)

    Cirlin, G E; Reznik, R R; Shtrom, I V

    2017-01-01

    The data on growth peculiarities and physical properties of GaAs insertions embedded in AlGaAs nanowires grown on different (1 1 1) substrates by Au-assisted molecular beam epitaxy are presented. The influence of nanowires growth conditions on structural and optical properties is studied in detail...

  16. GA BASED GLOBAL OPTIMAL DESIGN PARAMETERS FOR ...

    African Journals Online (AJOL)

    This article uses Genetic Algorithm (GA) for the global design optimization of consecutive reactions taking place in continuous stirred tank reactors (CSTRs) connected in series. GA based optimal design determines the optimum number of CSTRs in series to achieve the maximum conversion, fractional yield and selectivity ...

  17. Demonstration of GaN/InGaN Light Emitting Diodes on (100) β-Ga2O3 Substrates by Metalorganic Chemical Vapour Deposition

    International Nuclear Information System (INIS)

    Zi-Li, Xie; Rong, Zhang; Xiang-Qian, Xiu; Ping, Han; Bin, Liu; Hong, Zhao; Ruo-Lian, Jiang; Yi, Shi; You-Dou, Zheng; Chang-Tai, Xia

    2008-01-01

    The growth and fabrication of GaN/InGaN multiple quantum well (MQW) light emitting diodes (LEDs) on (100) β-Ga 2 O 3 single crystal substrates by metal-organic chemical vapour deposition (MOCVD) technique are reported. x-ray diffraction (XRD) θ – 2θ scan spectroscopy is carried out on the GaN buffer layer grown on a (100) β-Ga 2 O 3 substrate. The spectrum presents several sharp peaks corresponding to the (100) β-Ga 2 O 3 and (004) GaN. High-quality (0002) GaN material is obtained. The emission characteristics of the GaN/InGaN MQW LED are measurement. The first green LED on β-Ga 2 O 3 with vertical current injection is demonstrated. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  18. Electrochemical profiling of heterostructures with multiple quantum wells InGaN/GaN

    International Nuclear Information System (INIS)

    Zubkov, Vasily; Kucherova, Olga; Frolov, Dmitry; Zubkova, Anna

    2013-01-01

    A method of electrochemical capacitance-voltage profiling is used to characterize InGaN/GaN heterostructures with multiple quantum wells. Implementation of pulsed electrochemical etching allowed getting good planarity of etched surface despite of the high density of dislocations in GaN. The quality of etching, optimization of its parameters and independent check of etched depth were controlled by AFM measurements. Concentration profiles of InGaN/GaN QWs structures were evaluated then from capacitance-voltage measurements revealing several quantum wells with a period of 17 nm. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Interface and transport properties of GaN/graphene junction in GaN-based LEDs

    International Nuclear Information System (INIS)

    Wang Liancheng; Zhang Yiyun; Liu Zhiqiang; Guo Enqing; Yi Xiaoyan; Wang Junxi; Wang Guohong; Li Xiao; Zhu Hongwei

    2012-01-01

    A normalized circular transmission line method pattern with uniform interface area was developed to obtain contact resistances of p-, u-, n-GaN/graphene contacts (p, u and n represent p-type doped, unintentionally doped and n-type doped, respectively) and N-polar u-, n-GaN/graphene contacts in GaN-based LEDs. The resistances of the graphene/GaN contacts were mainly determined by the work function gap and the carrier concentration in GaN. Annealing caused diffusion of metal atoms and significantly influenced the interface transport properties.

  20. Reliability-Limiting Defects in GaN/AlGaN High Electron Mobility Transistors

    Science.gov (United States)

    2011-12-01

    100655. I am extremely thankful to our collaborators at University of California, Santa Barbara , for providing us with the GaN HEMTs, without which...California, Santa Barbara . These devices were grown by molecular beam epitaxy under Ga-rich, N-rich, and NH3-rich conditions. Devices grown using...Köhler, R. Kiefer , R. Quay, M. Baeumber, and L. Kirste, “Growth of AlGaN/GaN based electronic device structures with semi-insulating GaN buffer and AlN

  1. Above room temperature operation of InGaAs/AlGaAs/GaAs quantum cascade lasers

    Science.gov (United States)

    Pierścińska, D.; Gutowski, P.; Hałdaś, G.; Kolek, A.; Sankowska, I.; Grzonka, J.; Mizera, J.; Pierściński, K.; Bugajski, M.

    2018-03-01

    In this work we report on the performance of mid-infrared quantum cascade lasers (QCLs) based on strained InGaAs/AlGaAs grown by molecular beam epitaxy on GaAs substrate. Structures were grown with indium content from 1% to 6% in GaAs quantum wells (QW) and 45% of Al in AlGaAs barrier layers. The design results in strained heterostructure, however, no strain relaxation was observed as documented by x-ray diffraction measurements up to ∼3% of In content in QWs. The investigation of heterostructures and devices was performed, including structural measurements and electrooptical characterization of devices. Devices fabricated from epi wafers with 2.64% of In exhibited performance largely improved over GaAs/AlGaAs QCLs. Roughly two times reduction of the threshold current density was observed at lasing wavelength ∼9.45 μm. The lasers operated in pulsed mode up to T = 50 °C with characteristic temperature T 0 = 115 K. The decrease of the threshold current density has been mainly attributed to the reduction of interface roughness scattering and the increase of activation energy for the escape of carriers from the upper laser level to the 3D continuum. Further increase of In content in QWs resulted in the deterioration of device parameters.

  2. Optically-pumped lasing of semi-polar InGaN/GaN(1122) heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Strittmatter, A.; Teepe, M.; Yang, Z.; Chua, C.; Northrup, J.; Johnson, N.M. [Palo Alto Research Center, Palo Alto, CA (United States); Spiberg, P.; Brown, R.G.W. [Ostendo Technologies, Inc., Carlsbad, CA (United States); Ivantsov, V.; Syrkin, A.; Shapovalov, L.; Usikov, A. [TDI, Inc., an Oxford Instruments Company, Silver Spring, MD (United States)

    2010-07-15

    Results for long-wavelength emitters are presented for semi-polar InGaN/AlGaN/GaN heterostructures grown on GaN(11-22)/m-sapphire templates by metalorganic chemical vapor deposition. The semi-polar GaN layers were 10 to 25 {mu}m thick and grown by HVPE on sapphire substrates. X-ray diffraction measurements indicate high crystallographic quality that approaches that of GaN(0001) layers on sapphire. Growth studies on the semi-polar GaN templates established the high efficiency of indium incorporation into InGaN layers, with a wide growth-temperature window up to 800 C for green light emitting structures. Basic LEDs were fabricated with peak emission up to 527 nm wavelength. Further growth studies established conditions for growing reasonably smooth, undoped InGaN/GaN laser heterostructures suitable for optical pumping. Optically-pumped lasing was achieved at wavelengths from 400 nm up to 500 nm. The results demonstrate the viability of semi-polar GaN(11-22) on sapphire templates for long-wavelength nitride laser diodes (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Optical properties of InGaN/GaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Joo In; Lee, Chang Myung [Korea Research Institute of Standards and Science, Taejon (Korea, Republic of); Leem, Jae Young [Inje Univ., Kimhae (Korea, Republic of); Lim, Ki Soo [Chungbuk National Univ., Cheongju (Korea, Republic of); Han, Il Ki [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2002-03-01

    We have used steady-state and time-resolved photoluminescence to investigate optical properties of In{sub 0.13}Ga{sub 0.87}N/GaN multiple quantum wells (MQW) grown by using metalorganic chemical vapor deposition. The quantum well spectra were explained in terms of the radiative recombination of excitons in the localized states. Exciton formation of the InGaN MQW might be delayed for excitations above the GaN barrier excitation compared with exciton formation in excitations below the GaN barrier. The critical temperature at which nonradiative recombination dominantly occurred was increased under the excitation below the GaN barrier because screening caused by carriers in the GaN barrier vanished.

  4. GaAs quantum dots in a GaP nanowire photodetector

    Science.gov (United States)

    Kuyanov, P.; McNamee, S. A.; LaPierre, R. R.

    2018-03-01

    We report the structural, optical and electrical properties of GaAs quantum dots (QDs) embedded along GaP nanowires. The GaP nanowires contained p–i–n junctions with 15 consecutively grown GaAs QDs within the intrinsic region. The nanowires were grown by molecular beam epitaxy using the self-assisted vapor–liquid–solid process. The crystal structure of the NWs alternated between twinned ZB and WZ as the composition along the NW alternated between the GaP barriers and the GaAs QDs, respectively, leading to a polytypic structure with a periodic modulation of the NW sidewall facets. Photodetector devices containing QDs showed absorption beyond the bandgap of GaP in comparison to nanowires without QDs. Voltage-dependent measurements suggested a field emission process of carriers from the QDs.

  5. Uncorrelated electron-hole transition energy in GaN|InGaN|GaN spherical QDQW nanoparticles

    International Nuclear Information System (INIS)

    Haddou El Ghazi; Anouar Jorio and Izeddine Zorkani

    2013-01-01

    The electron (hole) energy and uncorrelated 1S e - 1S h electron-hole transition in Core(GaN)|well(In x Ga 1-x N)|shell(GaN) spherical QDQW nanoparticles is investigated as a function of the inner and the outer radii. The calculations are performed within the framework of the effective-mass approximation and the finite parabolic potential confinement barrier in which two confined parameters are taking account. The Indium composition effect is also investigated. A critical value of the outer and the inner ratio is obtained which constitutes the turning point of two indium composition behaviors. (author)

  6. The Arabidopsis NPF3 protein is a GA transporter

    DEFF Research Database (Denmark)

    Tal, Iris; Zhang, Yi; Jørgensen, Morten Egevang

    2016-01-01

    Gibberellins (GAs) are plant hormones that promote a wide range of developmental processes. While GA signalling is well understood, little is known about how GA is transported or how GA distribution is regulated. Here we utilize fluorescently labelled GAs (GA-Fl) to screen for Arabidopsis mutants...... deficient in GA transport. We show that the NPF3 transporter efficiently transports GA across cell membranes in vitro and GA-Fl in vivo. NPF3 is expressed in root endodermis and repressed by GA. NPF3 is targeted to the plasma membrane and subject to rapid BFA-dependent recycling. We show that abscisic acid...... (ABA), an antagonist of GA, is also transported by NPF3 in vitro. ABA promotes NPF3 expression and GA-Fl uptake in plants. On the basis of these results, we propose that GA distribution and activity in Arabidopsis is partly regulated by NPF3 acting as an influx carrier and that GA-ABA interaction may...

  7. Inductively Coupled Plasma Etching of III-V Semiconductors in BCl(3)-Based Chemistries: Part 1: GaAs, GaN, GaP, GaSb and AlGaAs

    Energy Technology Data Exchange (ETDEWEB)

    Abernathy, C.R,; Han, J.; Hobson, W.S.; Hong, J.; Lambers, E.S.; Lee, J.W.; Maeda, T.; Pearton, S.J.; Shul, R.J.

    1998-12-04

    BC13, with addition of Nz, Ar or Hz, is found to provide smooth anisotropic pattern transfer in GaAs, GaN, GaP, GaSb and AIGriAs under Inductively Coupled Plasma conditions, Maxima in the etch rates for these materials are observed at 33% N2 or 87$'40 Hz (by flow) addition to BC13, whereas Ar addition does not show this behavior. Maximum etch rates are typically much higher for GaAs, Gap, GaSb and AIGaAs (-1,2 @rein) than for GaN (-0.3 ymu'min) due to the higher bond energies of the iatter. The rates decrease at higher pressure, saturate with source power (ion flux) and tend to show maxima with chuck power (ion energy). The etched surfaces remain stoichiometric over abroad range of plasma conditions.

  8. Comparison of damage introduced into GaN/AlGaN/GaN heterostructures using selective dry etch recipes

    International Nuclear Information System (INIS)

    Green, R T; Luxmoore, I J; Houston, P A; Ranalli, F; Wang, T; Parbrook, P J; Uren, M J; Wallis, D J; Martin, T

    2009-01-01

    A SiCl 4 /SF 6 dry etch plasma recipe is presented giving a selectivity of 14:1 between GaN and AlGaN. Using a leakage test structure, which enables bulk and surface leakage components to be identified independently, the optimized recipe is compared to an un-etched sample and devices recessed using a Cl 2 /Ar/O 2 -based plasma chemistry. Devices etched using the SiCl 4 /SF 6 recipe demonstrated reduced bulk and surface leakage currents when operated over a wide range of temperatures. Consequently the SiCl 4 /SF 6 recipe is identified as most suitable for the fabrication of gate recessed AlGaN/GaN HEMTs

  9. 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.

  10. Structural properties of (GaIn)(AsN)/GaAs MQW structures grown by MOVPE

    International Nuclear Information System (INIS)

    Giannini, C.; Carlino, E.; Tapfer, L.; Hoehnsdorf, F.; Koch, J.; Stolz, W.

    2000-01-01

    In this work, the authors investigate the structural properties of (GaIn)(AsN)/GaAs multiple quantum wells (MQW) grown at low temperature by metalorganic vapor phase epitaxy. The structural properties, in particular the In- and N-incorporation, the lattice strain (strain modulation), the structural perfection of the metastable (GaIn)(AsN) material system and the structural quality of the (GaIn)(AsN)/GaAs interfaces are investigated by means of high-resolution x-ray diffraction, transmission electron microscopy (TEM), and secondary ion mass spectrometry. They demonstrate that (GaIn)(AsN) layers of high structural quality can be fabricated up to lattice mismatches of 4%. The experiments reveal that N and In atoms are localized in the quaternary material and no evidences of In-segregation or N-interdiffusion could be found. TEM analyses reveal a low defect density in the highly strained layers, but no clustering or interface undulation could be detected. High-resolution TEM images show that (GaIn)(AsN)/GaAs interfaces are slightly rougher than GaAs/(GaIn)(AsN) ones

  11. Photovoltaic response of InGaN/GaN multi-quantum well solar cells enhanced by inserting thin GaN cap layers

    Energy Technology Data Exchange (ETDEWEB)

    Yang, J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Zhao, D.G., E-mail: dgzhao@red.semi.ac.cn [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Jiang, D.S.; Chen, P.; Zhu, J.J.; Liu, Z.S.; Le, L.C.; He, X.G.; Li, X.J. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Yang, H. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, PO BOX 912, Beijing 100083 (China); Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Zhang, Y.T.; Du, G.T. [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130023 (China)

    2015-06-25

    Highlights: • The spectral response of InGaN/GaN MQW solar cells with different LT-cap layer thicknesses was investigated. • Inserting a 0.75 nm-thick LT-cap layer can remarkably improve photovoltaic response of InGaN/GaN MQW solar cells. • A macroscopic optical method was used to investigate the microscopic localization effect and defect density in InGaN QW. • Strong localization effect in InGaN QW is harmful for the formation of high efficiency InGaN/GaN MQW solar cells. - Abstract: Structural properties and photovoltaic response of InGaN/GaN multi-quantum well (MQW) solar cells with low temperature grown GaN cap (LT-cap) layers were investigated. It is found that inserting a thin LT-cap layer (around 0.75 nm) between each InGaN quantum well (QW) and GaN quantum barrier (QB) can remarkably improve photovoltaic response of InGaN/GaN MQW solar cells. This is attributed to the increased optical absorption of InGaN QWs due to higher indium content and thicker InGaN QWs thickness when LT-cap layers are added. However, if the LT-cap layer is too thick, the localization effect is enhanced and the defect density of InGaN QW layers will increase too much. Both of them will result in a reduced photovoltaic response of InGaN/GaN MQW solar cells.

  12. Barrier layer engineering: Performance evaluation of E-mode InGaN/AlGaN/GaN HEMT

    Science.gov (United States)

    Majumdar, Shubhankar; Das, S.; Biswas, D.

    2015-08-01

    Impact on DC characteristics of InGaN/AlGaN/GaN HEMT due to variation in the hetero-structure parameters i.e. molar fraction of Al and thickness of AlGaN barrier layer is presented in this paper. Gate controllability over the channel is dependent on barrier layer thickness, and molar fraction has an impact on band offset and 2DEG, which further affects the current. HEMT device that is simulated in SILVACO has InGaN cap layer of 2 nm thickness with 15% In molar fraction, variation of Al percentage and thickness of the AlGaN barrier layer are taken as 15-45% and 5-20nm, respectively. A tremendous change in threshold voltage (Vth), maximum transconductance (Gmmax) and subthreshold swing is found due to variation in hetero-structure parameter of barrier layer and the values are typically 1.3-0.1 V, 0.6-0.44 S/mm and 75-135 mV/dec respectively.

  13. Misfit dislocation-related deep levels in InGaAs/GaAs and GaAsSb/GaAs p-i-n heterostructures and the effect of these on the relaxation time of nonequilibrium carriers

    Science.gov (United States)

    Sobolev, M. M.; Soldatenkov, F. Yu.; Shul'pina, I. L.

    2018-04-01

    A study of deep levels in InGaAs/GaAs and GaAsSb/GaAs p0-i-n0 heterostructures with misfit dislocations and identification of the effective defects responsible for the significant (by up to a factor of 100) decrease in the relaxation time of nonequilibrium carriers in the base layers (and in the related reverse recovery time) of InGaAs/GaAs and GaAsSb/GaAs high-voltage power p-i-n diodes is reported. Experimental capacitance-voltage characteristics and deep-level transient spectroscopy spectra of p+-p0-i-n0-n+ homostructures based on undoped GaAs layers without misfit dislocations and InGaAs/GaAs and GaAsSb/GaAs heterostructures with a homogeneous network of misfit dislocations, all grown by liquid-phase epitaxy, are analyzed. Acceptor defects with deep levels HL2 and HL5 are identified in GaAs epitaxial p0 and n0 layers. Dislocation-related electron and hole deep traps designated as ED1 and HD3 are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The effective recombination centers in the heterostructure layers, to which we attribute the substantial decrease in the relaxation time of nonequilibrium carriers in the base layers of p-i-n diodes, are dislocation-related hole traps that are similar to HD3 and have the following parameters: thermal activation energy Et = 845 meV, carrier capture cross-section σp = 1.33 × 10-12 cm2, concentration Nt = 3.80 × 1014 cm-3 for InGaAs/GaAs and Et = 848 meV, σp = 2.73 × 10-12 cm2, and Nt = 2.40 × 1014 cm-3 for the GaAsSb/GaAs heterostructure. The relaxation time of the concentration of nonequilibrium carriers in the presence of dislocation-related deep acceptor traps similar to HD3 was estimated to be 1.1 × 10-10 and 8.5 × 10-11 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 8.9 × 10-7 s for the GaAs homostructure. These data correspond to the relaxation times of nonequilibrium carriers in the base layers of GaAs, InGaAs/GaAs, and GaAsSb/GaAs high-voltage power p-i-n diodes.

  14. AlGaN/GaN heterostructures with an AlGaN layer grown directly on reactive-ion-etched GaN showing a high electron mobility (>1300 cm2 V-1 s-1)

    Science.gov (United States)

    Yamamoto, Akio; Makino, Shinya; Kanatani, Keito; Kuzuhara, Masaaki

    2018-04-01

    In this study, the metal-organic-vapor-phase-epitaxial growth behavior and electrical properties of AlGaN/GaN structures prepared by the growth of an AlGaN layer on a reactive-ion-etched (RIE) GaN surface without regrown GaN layers were investigated. The annealing of RIE-GaN surfaces in NH3 + H2 atmosphere, employed immediately before AlGaN growth, was a key process in obtaining a clean GaN surface for AlGaN growth, that is, in obtaining an electron mobility as high as 1350 cm2 V-1 s-1 in a fabricated AlGaN/RIE-GaN structure. High-electron-mobility transistors (HEMTs) were successfully fabricated with AlGaN/RIE-GaN wafers. With decreasing density of dotlike defects observed on the surfaces of AlGaN/RIE-GaN wafers, both two-dimensional electron gas properties of AlGaN/RIE-GaN structures and DC characteristics of HEMTs were markedly improved. Since dotlike defect density was markedly dependent on RIE lot, rather than on growth lot, surface contaminations of GaN during RIE were believed to be responsible for the formation of dotlike defects and, therefore, for the inferior electrical properties.

  15. Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs) Photoconductive Semiconductor Switch (PCSS) Fabrication

    Science.gov (United States)

    2016-09-27

    ARL-TR-7819 ● SEP 2016 US Army Research Laboratory Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs...Laboratory Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs) Photoconductive Semiconductor Switch (PCSS) Fabrication by...Report 3. DATES COVERED (From - To) January 2016–September 2016 4. TITLE AND SUBTITLE Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs

  16. Growth and properties of the MOVPE GaAs/InAs/GaAsSb quantum dot structures

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Oswald, Jiří; Pangrác, Jiří; Kuldová, Karla; Zíková, Markéta; Vyskočil, Jan; Hulicius, Eduard

    2016-01-01

    Roč. 480, Jan (2016), 14-22 ISSN 0921-4526 R&D Projects: GA ČR GA13-15286S; GA ČR(CZ) GP14-21285P; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : quantum dot * band alignment * InAs/GaAs * GaAsSb * MOVPE * luminescence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2016

  17. 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.

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

    KAUST Repository

    Mughal, Asad J.

    2017-11-27

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

  19. 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.

  20. Data processing system of GA and PPPL

    International Nuclear Information System (INIS)

    Oshima, Takayuki

    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)

  1. Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

    Science.gov (United States)

    Zheng, Nan; Ahrenkiel, S. Phillip

    2017-07-01

    Metamorphic growth presents routes to novel nanomaterials with unique properties that may be suitable for a range of applications. We discuss self-assembled, epitaxial nanowires formed during metalorganic chemical vapor deposition of metamorphic GaAs/GaPAs short-period superlattices. The heterostructures incorporate strain-engineered GaPAs compositional grades on 6°-B miscut GaAs substrates. Lateral diffusion within the SPS into vertically aligned, three-dimensional columns results in nanowires extending along A directions with a lateral period of 70-90 nm. The microstructure is probed by transmission electron microscopy to confirm the presence of coherent GaAs nanowires within GaPAs barriers. The compositional profile is inferred from analysis of {200} dark-field image contrast and lattice images.

  2. Multi-bands photoconductive response in AlGaN/GaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G.; Rong, X.; Xu, F. J.; Tang, N. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Wang, X. Q., E-mail: wangshi@pku.edu.cn; Shen, B., E-mail: bshen@pku.edu.cn [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Fu, K.; Zhang, B. S. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Ruoshui Road 398, 215123 Suzhou (China); Hashimoto, H.; Yoshikawa, A. [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Ge, W. K. [Department of Physics, Tsinghua University, Beijing 100871 (China)

    2014-04-28

    Based on the optical transitions among the quantum-confined electronic states in the conduction band, we have fabricated multi-bands AlGaN/GaN quantum well infrared photodetectors. Crack-free AlGaN/GaN multiple quantum wells (MQWs) with atomically sharp interfaces have been achieved by inserting an AlN interlayer, which releases most of the tensile strain in the MQWs grown on the GaN underlayer. With significant reduction of dark current by using thick AlGaN barriers, photoconductive responses are demonstrated due to intersubband transition in multiple regions with center wavelengths of 1.3, 2.3, and 4 μm, which shows potential applications on near infrared detection.

  3. Formation of columnar (In,Ga)As quantum dots on GaAs(100)

    International Nuclear Information System (INIS)

    He, J.; Noetzel, R.; Offermans, P.; Koenraad, P.M.; Gong, Q.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

    2004-01-01

    Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs/InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced

  4. A Ga 2O 3 passivation technique compatible with GaAs device processing

    Science.gov (United States)

    Hong, M.; Passlack, M.; Mannaerts, J. P.; Harris, T. D.; Schnoes, M. L.; Opila, R. L.; Krautter, H. W.

    1997-04-01

    Electronic and structural properties of ex-situ fabricated Ga 2O 3GaAs interfaces have been investigated. The fabrication comprises thermal desorption of native oxide and subsequent Ga 2O 3 film deposition on (100) GaAs wafers in ultra-high vacuum. Interfacial x-ray photoelectron spectroscopy revealed the absence of As xO y indicating thermodynamic stability of the oxide-GaAs interface. A low interface recombination velocity S of 9000 cm/s equivalent to an interface state density Dit in the upper 10 10 cm -2 eV -1 range has been inferred. The technique provides excellent passivation for GaAs wafers or surfaces exposed to room air and/or processing environments during fabrication of devices such as FETs, HBTs, etc.

  5. Electrical characterization of InGaN/GaN quantum dots by deep level transient spectroscopy

    International Nuclear Information System (INIS)

    Kim, J.S.; Kim, E.K.; Kim, H.J.; Yoon, E.; Park, I.W.; Park, Y.J.

    2004-01-01

    We have investigated the electrical property of InGaN quantum dots (QDs) embedded in GaN layer using capacitance-voltage and deep-level transient spectroscopy (DLTS) measurements. The apparent activation energy was observed 0.43 eV below the conduction band edge of barrier layers in InGaN/GaN QDs system. The capture barrier height of InGaN QDs was measured more than about 0.17 eV, showing the existence of strain between QDs and barrier layers. Thus, the bound state of QDs was estimated as 0.26 eV apart from the conduction band edge of the GaN. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Mid-infrared Photoconductive Response in AlGaN/GaN Step Quantum Wells

    Science.gov (United States)

    Rong, X.; Wang, X. Q.; Chen, G.; Zheng, X. T.; Wang, P.; Xu, F. J.; Qin, Z. X.; Tang, N.; Chen, Y. H.; Sang, L. W.; Sumiya, M.; Ge, W. K.; Shen, B.

    2015-09-01

    AlGaN/GaN quantum structure is an excellent candidate for high speed infrared detectors based on intersubband transitions. However, fabrication of AlGaN/GaN quantum well infrared detectors suffers from polarization-induced internal electric field, which greatly limits the carrier vertical transport. In this article, a step quantum well is proposed to attempt solving this problem, in which a novel spacer barrier layer is used to balance the internal electric field. As a result, a nearly flat band potential profile is obtained in the step barrier layers of the AlGaN/GaN step quantum wells and a bound-to-quasi-continuum (B-to-QC) type intersubband prototype device with detectable photocurrent at atmosphere window (3-5 μm) is achieved in such nitride semiconductors.

  7. Anisotropy of mosaic structure of GaAsP layers grown on GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    Saka, T. [Daido Institute of Technology, 10-3, Takiharu-cho, Minami-ku, Nagoya 457-8530 (Japan); Kato, T. [Daido Steel Co. Ltd., 2-30, Daido-cho, Minami-ku, Nagoya 457-8545 (Japan); Jin, X.G.; Tanioku, M.; Ujihara, T.; Takeda, Y. [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yamamoto, N.; Nakagawa, Y.; Mano, A.; Okumi, S.; Yamamoto, M.; Nakanishi, T. [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Horinaka, H.; Matsuyama, T. [Faculty of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai 599-8531 (Japan); Yasue, T.; Koshikawa, T. [Fundamental Electronics Research Institute, Osaka Electro-Communication University, 18-8, Hatsu-cho, Neyagawa 572-8530 (Japan)

    2009-08-15

    The crystalline structure of GaAsP layers grown on GaAs and GaP(001) substrates, used for spin polarized photocathodes, has been investigated by X-ray diffraction. The layers on the GaAs substrate possess a mosaic structure observable by X-ray topography and consist of many large blocks. The mosaicity is anisotropic and the distribution of the mosaic is restricted within the (110) plane, and the blocks zigzag around the [110] direction. The layer grown on the GaP substrate was uniform and no mosaic was observed in the topographs. The results indicate that different mechanisms of strain release occur in GaAsP layers for tensile and compressive strains. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  8. 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.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    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 In 0.25 Ga 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 0.25 Ga 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%.

  10. 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%.

  11. Metamagnetism in Ce(Ga,Al)2

    Indian Academy of Sciences (India)

    Abstract. Effect of Al substitution on the magnetic properties of Ce(Ga1−x Alx )2 (x = 0, 0.1 and. 0.5) system has been studied. The magnetic state of CeGa2 is found to be FM with a TC of 8 K, whereas the compounds with x =0.1 and 0.5 are AFM and possess TN of about 9 K. These two com- pounds undergo metamagnetic ...

  12. Modeling and Simulation of Monolithic AlGaAs/InGaAs Tandem Solar Cell

    Directory of Open Access Journals (Sweden)

    Samia SLIMANI

    2015-06-01

    Full Text Available Employing conventional III-V junctions we report a classical calculation of conduction and valence band edge and the electron and hole densities. It is shown that the optimum performance can be achieved by employing AlGaAs /AlGaAs/InGaAs monolithic cascade solar cells, we have established these calculations by solving the Poisson equation within the framework of the Nextnano.

  13. Investigation of localization effect in GaN-rich InGaN alloys and ...

    Indian Academy of Sciences (India)

    The temperature-dependent PL properties of GaN-rich InGa1−N alloys is investigated and -shaped temperature dependence is observed in all InGaN samples. It is found that the origin of localization effect in samples A and B are different from that in sample C. For samples A and B, In content fluctuations should be the ...

  14. 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, these d......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...

  15. Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices

    Science.gov (United States)

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Osinsky, A. V.; Norris, P. E.; Pearton, S. J.; Van Hove, J.; Wowchak, A.; Chow, P.

    2001-12-01

    Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices are compared to those of similarly doped p-GaN films. It is shown that modulation doping increases the sheet hole concentration by several times. In p-AlGaN/GaN superlattices grown on GaN underlayers, this increase is accompanied by a significant increase in hole mobility which results in a remarkable decrease in sheet resistivity of the structure compared to p-GaN films and this decrease in sheet resistivity should hold up to temperatures exceeding 350 °C. For superlattices prepared on AlGaN underlayers, the mobility decreases compared to p-GaN. In such superlattices, one also observes a strong redshift and a strong broadening of the band edge luminescence peak coming most probably from increased mosaicity and strain which would also explain the observed deterioration of mobility. The magnitude of the redshift in the position of the band edge luminescence band slightly increased upon application of reverse bias which is interpreted as a manifestation of quantum-confined Stark effect.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-07-15

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

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

    Science.gov (United States)

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

    2014-08-07

    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/Al(0.25)Ga(0.75)N/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 × 10(13) 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

  18. Interface electron traps and capacitance characteristics of AlGaN/GaN

    International Nuclear Information System (INIS)

    Osvald, J.

    2012-01-01

    We simulated the charge transport in heterostructures by well-known drift-diffusion approximation. Continuity equations were solved self-consistently with the Poisson equation and we received the electric potential and the charge concentration in every point of the whole device. The AlGaN/GaN structure consisted of 25 nm thick AlGaN barrier layer and 75 nm thick GaN buffer layer. Doping concentration of AlGaN barrier layer was assumed to be 1 · 10 18 cm -3 and for GaN buffer layer we considered two doping concentrations assumed, 1 · 10 17 cm -3 , and 1 · 10 16 cm -3 , the sheet concentration of positive piezoelectric charge at the AlGaN/GaN interface responsible for the 2DEG formation was set to 8 · 10 12 cm -2 . Schottky barrier height at the metal/AlGaN interface was chosen to be 1.3 V. (authors)

  19. 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....

  20. GA-4/GA-9 honeycomb impact limiter tests and analytical model

    International Nuclear Information System (INIS)

    Koploy, M.A.; Taylor, C.S.

    1991-01-01

    General Atomics (GA) has a test program underway to obtain data on the behavior of a honeycomb impact limiter. The program includes testing of small samples to obtain basic information, as well as testing of complete 1/4-scale impact limiters to obtain load-versus-deflection curves for different crush orientations. GA has used the test results to aid in the development of an analytical model to predict the impact limiter loads. The results also helped optimize the design of the impact limiters for the GA-4 and GA-9 Casks

  1. Exploring the radiosynthesis and in vitro characteristics of [68Ga]Ga-DOTA-Siglec-9

    DEFF Research Database (Denmark)

    Jensen, Svend Borup; Käkelä, Meeri; Jødal, Lars

    2017-01-01

    Vascular adhesion protein-1 (VAP-1) is a leukocyte homing-associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283-297 of sialic acid-binding IgG-like lectin 9...... to previously published methods. A simple, robust radiosynthesis of [68 Ga]Ga-DOTA-Siglec-9 with a yield of 62% (non-decay corrected) was identified, it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [68 Ga]Ga-DOTA-Siglec-9 were...

  2. Meningiomas: A Comparative Study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for Molecular Imaging in Mice

    Science.gov (United States)

    Soto-Montenegro, María Luisa; Peña-Zalbidea, Santiago; Mateos-Pérez, Jose María; Oteo, Marta; Romero, Eduardo; Morcillo, Miguel Ángel; Desco, Manuel

    2014-01-01

    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. PMID:25369268

  3. Fabrication of vertical GaN/InGaN heterostructure nanowires using Ni-Au bi-metal catalysts.

    Science.gov (United States)

    Ha, Ryong; Kim, Sung-Wook; Choi, Heon-Jin

    2013-06-26

    We have fabricated the vertically aligned coaxial or longitudinal heterostructure GaN/InGaN nanowires. The GaN nanowires are first vertically grown by vapor-liquid-solid mechanism using Au/Ni bi-metal catalysts. The GaN nanowires are single crystal grown in the [0001] direction, with a length and diameter of 1 to 10 μm and 100 nm, respectively. The vertical GaN/InGaN coaxial heterostructure nanowires (COHN) are then fabricated by the subsequent deposition of 2 nm of InxGa1-xN shell on the surface of GaN nanowires. The vertical GaN/InGaN longitudinal heterostructure nanowires (LOHN) are also fabricated by subsequent growth of an InGaN layer on the vertically aligned GaN nanowires using the catalyst. The photoluminescence from the COHN and LOHN indicates that the optical properties of GaN nanowires can be tuned by the formation of a coaxial or longitudinal InGaN layer. Our study demonstrates that the bi-metal catalysts are useful for growing vertical as well as heterostructure GaN nanowires. These vertically aligned GaN/InGaN heterostructure nanowires may be useful for the development of high-performance optoelectronic devices.

  4. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    International Nuclear Information System (INIS)

    Li Yanbo; Zhang Yang; Zhang Yuwei; Wang Baoqiang; Zhu Zhanping; Zeng Yiping

    2012-01-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (Ga Sb ) defect.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  7. 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.

  8. Electrical characteristics of AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes irradiated with protons

    Science.gov (United States)

    Sin, Yongkun; Presser, Nathan; Foran, Brendan; LaLumondiere, Stephen; Lotshaw, William; Moss, Steven C.

    2014-03-01

    AlGaN-GaN high electron mobility transistors (HEMTs) are most suitable for commercial and military applications requiring high voltage, high power, and high efficiency operation. In recent years, leading AlGaN HEMT manufacturers have reported encouraging reliability of these devices, but their long-term reliability especially in the space environment still remains a major concern. In addition, degradation mechanisms in AlGaN HEMT devices are still not well understood, and a large number of traps and defects present both in the bulk and at the surface lead to undesirable characteristics. Study of reliability and radiation effects of AlGaN-GaN HEMTs is therefore necessary before GaN HEMT technology is successfully employed in satellite communication systems. For the present study, we investigated electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes irradiated with protons. We studied two types of MOCVD-grown AlGaN HEMTs on semi-insulating SiC substrates (HEMT-1 and HEMT-2) as well as MOCVD-grown Al0.27Ga 0.73N Schottky diodes on conducting SiC substrates. Our HEMT-1 structure consisted of a GaN cap, AlGaN/AlN barrier, and 2 μm GaN buffer layers. Our HEMT-2 structure consisting of undoped AlGaN barrier and GaN buffer layers grown on an AlN nucleation layer showed a charge sheet density of ~1013/cm2 and a Hall mobility of ~1500 cm2 /V.sec. Our HEMT-1 devices had a Pt-Au Schottky gate length of 0.2 μm, a total gate width of 200-400 μm periphery, and SiNx passivation. Electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes were compared before and after they were proton irradiated with different energies and fluences. Current-mode deep level transient spectroscopy (DLTS) and capacitance-mode DLTS were employed to study pre-proton irradiation trap characteristics in the AlGaN-GaN HEMTs and AlGaN Schottky diodes, respectively. Focused ion beam (FIB) was employed to prepare both cross-sectional and plan view TEM samples for defect

  9. Determination of 68Ga production parameters by different reactions ...

    Indian Academy of Sciences (India)

    Gallium-68 (1/2 = 68 min, + = 89%) is an important positron-emitting radionuclide for positron emission tomography and used in nuclear medicine for diagnosing tumours. This study gives a suitable reaction to produce 68Ga. Gallium-68 excitation function via 68Zn(, ) 68Ga, 68Zn(, 2) 68Ga, 70Zn(, 3) 68Ga and ...

  10. Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AlGaN/GaN heterostructures using capacitance deep level optical spectroscopy

    OpenAIRE

    Armstrong, A; Chakraborty, A; Speck, J S; DenBaars, S P; Mishra, U K; Ringel, S A

    2006-01-01

    Deep levels were observed using capacitance deep level optical spectroscopy (DLOS) in an AlGaN/GaN heterostructure equivalent to that of a heterojunction field effect transistor. Band gap states were assigned to either the AlGaN or GaN regions by comparing the DLOS spectra in accumulation and pinch-off modes, where the former reflects both AlGaN- and GaN-related defects, and the latter emphasizes defects residing in the GaN. A band gap state at E-c-3.85 eV was unambigu...

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

    International Nuclear Information System (INIS)

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

    2013-01-01

    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

  12. Characterization of GaN/AlGaN epitaxial layers grown by ...

    Indian Academy of Sciences (India)

    of the native substrate, GaN epitaxial layers are generally grown on sapphire or. SiC substrate with lattice and thermal mismatch. Growth of GaN epitaxial layers on such substrates, by using a low-temperature nucleation layer demonstrated a good crystal quality [4]. Remarkable improvement in epitaxial material quality is.

  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. Sub-monolayer Deposited InGaAs/GaAs Quantum Dot Heterostructures and Lasers

    DEFF Research Database (Denmark)

    Xu, Zhangcheng

    2004-01-01

    are two different methods of growing self-assembled QDs. In the case of SK growth, which has been widely used for lattice mis-matched materials, such as In(Ga)As/Ga(Al)As, coherent three dimensional (3D) islands form on top of a wetting layer to relax the strain energy. However,in the case of SML...

  15. A localized orbital description of ideal vacancies in GaP and GaSb

    International Nuclear Information System (INIS)

    Erbarut, E.; Tomak, M.

    1986-10-01

    Gaussian orbitals of s and p symmetry and an empirical pseudopotential Hamiltonian is employed for the study of electronic structures of ideal vacancies in GaP and GaSb. A reasonably accurate description of band structures and densities of states are attained. (author)

  16. Integrated photonic platform based on semipolar InGaN/GaN multiple section laser diodes

    KAUST Repository

    Shen, Chao

    2017-11-30

    The challenges to realizing III-nitride photonic integrated circuit (PIC) are discussed. Utilizing InGaN-based multi-section laser diode (LD) on semipolar GaN substrate, the seamless on-chip integration of III-nitride waveguide photodetector (WPD) in the visible regime has been demonstrated.

  17. Misfit dislocation reduction in InGaAs epilayers grown on porous GaAs substrates

    Czech Academy of Sciences Publication Activity Database

    Dimitrakopulos, G.P.; Bazioti, C.; Grym, Jan; Gladkov, Petar; Hulicius, Eduard; Pangrác, Jiří; Pacherová, Oliva; Komninou, Ph.

    2014-01-01

    Roč. 306, Jul (2014), s. 89-93 ISSN 0169-4332 R&D Projects: GA MŠk 7AMB12GR034 Institutional support: RVO:68378271 ; RVO:67985882 Keywords : compound semiconductors * InGaAs * porous substrate * misfit dislocations * strain Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.711, year: 2014

  18. Measurement of strain in InGaN/GaN nanowires and nanopyramids

    DEFF Research Database (Denmark)

    Stankevic, Tomas; Mickevicius, Simas; Nielsen, Mikkel Schou

    2015-01-01

    the individual facet planes. The strained lattice constants were found from the positions of the Bragg peaks. Vegard's law and Hooke's law for an anisotropic medium were applied in order to find the composition and strain in the InGaN shells. A range of nanowire samples with different InGaN shell thicknesses...

  19. Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

    International Nuclear Information System (INIS)

    Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

    2010-01-01

    Molecular-Beam Epitaxy growth of multiple In 0.4 Ga 0.6 As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4 Ga 0.6 As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4 Ga 0.6 As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

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

    KAUST Repository

    Al-Jabr, Ahmad

    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.

  1. 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...

  2. 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...

  3. Deep defects in GaN/AlGaN/SiC hererostructures

    Czech Academy of Sciences Publication Activity Database

    Kindl, Dobroslav; Hubík, Pavel; Krištofik, Jozef; Mareš, Jiří J.; Výborný, Zdeněk; Leys, M.R.; Boeykens, S.

    2009-01-01

    Roč. 105, č. 9 (2009), 093706/1-093706/8 ISSN 0021-8979 R&D Projects: GA ČR GA202/07/0525 Institutional research plan: CEZ:AV0Z10100521 Keywords : nitrides * silicon carbide * deep levels * DLTS Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.072, year: 2009

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

    International Nuclear Information System (INIS)

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

    2017-01-01

    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 Al 0.5 Ga 0.5 N 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. (paper)

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

    International Nuclear Information System (INIS)

    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 × 10 15 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. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

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

    Science.gov (United States)

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

    2012-03-01

    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.

  7. AlGaN/InGaN Nitride Based Modulation Doped Field Effect Transistor

    National Research Council Canada - National Science Library

    Blair, S

    2003-01-01

    The goal of the proposed work is to investigate the potential advantages of the InGaN channel as a host of the 2DEG and to address the material related problems facing this ternary alloy in the AlGaN...

  8. Investigation of Photovoltaic Properties of Single Core-Shell GaN/InGaN Wires.

    Science.gov (United States)

    Messanvi, A; Zhang, H; Neplokh, V; Julien, F H; Bayle, F; Foldyna, M; Bougerol, C; Gautier, E; Babichev, A; Durand, C; Eymery, J; Tchernycheva, M

    2015-10-07

    We report the investigation of the photovoltaic properties of core-shell GaN/InGaN wires. The radial structure is grown on m-plane {11̅00} facets of self-assembled c̅-axis GaN wires elaborated by metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates. The conversion efficiency of wires with radial shell composed of thick In0.1Ga0.9N layers and of 30× In0.18Ga0.82N/GaN quantum wells are compared. We also investigate the impact of the contact nature and layout on the carrier collection and photovoltaic performances. The contact optimization results in an improved conversion efficiency of 0.33% and a fill factor of 83% under 1 sun (AM1.5G) on single wires with a quantum well-based active region. Photocurrent spectroscopy demonstrates that the response ascribed to the absorption of InGaN/GaN quantum wells appears at wavelengths shorter than 440 nm.

  9. AlGaN/GaN-based HEMT on SiC substrate for microwave ...

    Indian Academy of Sciences (India)

    The AlGaN/GaN-based high electron mobility transistors (HEMTs) are attracting much research interest worldwide because of their high density of states (DOS), high elec- tron saturation drift velocity, large band gap, high breakdown voltage, high electric field. DOI: 10.1007/s12043-012-0290-9; ePublication: 20 June 2012.

  10. 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

  11. Sharp interfaces in p+-AlGaAs/n-GaAs epitaxial structures obtained by MOCVD

    Directory of Open Access Journals (Sweden)

    Vakiv N. M.

    2014-06-01

    Full Text Available The complexity of forming sharp and high-quality boundaries in p+AlGaAs/n-GaAs systems by MOCVD method is caused by differing on 80—120°С optimal crystallization temperature of GaAs layers and n-AlGaAs solid solutions. A method of forming qualitative hetero boundaries under conditions of continuous growth at changing crystallization temperature from 600—700°C has been developed. It has been determined that the crystallization of p+-AlGaAs: Zn solid solution layer on the surface of n-GaAs:Si layer, with increasing the crystallization temperature in the temperature range of 600—760°C at a rate 8—10 °C/min allows to crystallize sharp impurity boundary between the layers of p- and n-type conductivity. The method of forming sharp hetero boundaries in p-GaAs:Zn/n-GaAs:Si systems can be used for manufacturing wide range of epitaxial structures.

  12. 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.

  13. Threshold Voltage Instability in Al2O3/GaN/AlGaN/GaN Metal-Insulator-Semiconductor High-Electron Mobility Transistors

    Science.gov (United States)

    Huang, Sen; Yang, Shu; Roberts, John; Chen, Kevin J.

    2011-11-01

    The threshold voltage (Vth) instability in GaN-based metal-insulator-semiconductor high-electron mobility transistors (MIS-HEMTs) with 15-nm atomic-layer-deposited (ALD) Al2O3 as gate dielectrics is systematically investigated by dc current-voltage (I-V), high-frequency capacitance-voltage (C-V) (HFCV), and quasi-static C-V (QSCV) characterizations. Both Al2O3/GaN/AlGaN/GaN MIS diode and GaN/AlGaN/GaN Schottky diode only exhibit tiny threshold-voltage hysteresis (ΔVth) (HEMTs is thus studied by increasing the maximum VGS (VGSmax) in the measurement of transfer characteristics. Significant positive Vth shift occurred once the VGSmax exceeds +1 V, while such Vth-instability is still absent in Schottky-gate AlGaN/GaN HEMTs. It is suggested that the acceptor-like deep states at Al2O3/GaN interface account for the Vth-instability in Al2O3/GaN/AlGaN/GaN MIS-HEMTs. As the filling and emission processes of these interface states are slow, they are successfully captured by low-frequency QSCV techniques.

  14. Improved light output power in GaN-based vertical light-emitting diodes with p-AlInGaN/GaN superlattices

    International Nuclear Information System (INIS)

    Kim, Su Jin; Son, Sung Hun; Kim, Tae Geun

    2012-01-01

    In this paper, we report the effect of p-type AlGaInN/GaN superlattices (SLs) as electron blocking layers (EBLs) on the optical properties of vertical light-emitting diodes (VLEDs). Using p-AlGaInN/GaN SLs in VLEDs, we have achieved significant improvements in the output power and the external quantum efficiency (EQE) as compared to VLEDs using p-AlGaInN EBL and p-AlGaN EBL. The forward voltages at 350 mA were calculated to be 4.1, 4.3, and 4.4 V for VLEDs with p-AlInGaN/GaN SLs, p-AlInGaN, and p-AlGaN EBLs, respectively. When p-AlInGaN/GaN SLs were inserted as the EBLs, the light-output power and the EQE were also improved by 16.8% and 17.3% at 350 mA, respectively, as compared to those with p-AlGaN EBLs.

  15. 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.

  16. 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.)

  17. The Effect of the number of InGaN/GaN pairs on the photoelectrochemical properties of InGaN/GaN multi quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Hyojung; Park, Jun-Beom [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Fujii, Katsushi [Institute of Environmental Science and Technology, The University of Kitakyushu, Kitakyushu, Fukuoka (Japan); Lee, Hyo-Jong [Materials Science and Engineering, Dong-A University, Busan 49315 (Korea, Republic of); Lee, Sang-Hyun [Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Joellabuk-do 55324 (Korea, Republic of); Ryu, Sang-Wan; Lee, June Key [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Ha, Jun-Seok, E-mail: jsha@jnu.ac.kr [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of)

    2017-04-15

    Highlights: • The 1–5 period InGaN/GaN quantum well (QW) structures were grown on sapphire. • The photoelectrochemical properties of these structures were investigated. • The saturated photocurrent density increased with increasing number of QW pairs. • But, it was different in the stability of the photoanode. • We reported the reason for this difference. - Abstract: In this study, the effects of the number of quantum well (QW) pairs on the photoelectrochemical (PEC) properties of InGaN/GaN multi-QW structures (MQWs) were investigated. MQW samples were grown using metal-organic chemical vapor deposition, and their structural characteristics were confirmed by X-ray diffraction measurements. The photoluminescence measurements revealed that the optical properties of MQWs may be related to the PEC properties. The cyclic voltammetry data revealed that the saturated photocurrent density increased with increasing number of QW pairs; the photocurrent density of MQW5 was twice that of an nGaN reference. However, in the chronoamperometry measurement of the photoanode stability, MQWs with 3 QWs displayed the highest photocurrent stability, although the saturated photocurrent density was highest for MQW5. This was also confirmed by field-emission scanning electron microscopy of the surface morphology after PEC measurements. The stability and photocurrent density may be attributed to the quality of crystallinity of the MQWs.

  18. Ga-67 imaging in pediatric oncology

    International Nuclear Information System (INIS)

    Edeling, C.J.

    1983-01-01

    One hundred sixty-nine children suspected of having malignant disease were examined by Ga-67 scintigraphy. In 99 children with untreated diseases at the time of examination, abnormal accumulation of Ga-67 was found in 51 patients, including 40 with malignant tumor. Forty-three negative results were obtained in children with benign disorders. Five false-negative results were obtained in patients with neuroblastoma of the adrenal gland. In 70 children with malignant diseases treated before the examination, abnormal accumulation of Ga-67 was seen in 40 patients, including 38 with malignant disease and two with no clinical evidence of recurrence. Normal results were obtained in 30 patients, including 11 still suffering from malignant disease. The results of Ga-67 scintigraphy in all of the children were evaluated qualitatively. For the final diagnosis of malignant disease, diagnostic specificity was 86% and diagnostic sensitivity 79%. The prevalence of malignant disease was 56%. It is concluded that Ga-67 scintigraphy should be used for primary visualization and control of malignant tumors in children

  19. 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.)

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

    International Nuclear Information System (INIS)

    Talon, M.; Zeevaart, J.A.D.; Koornneef, M.

    1990-01-01

    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 53 , GA 44 , GA 19 , GA 17 , GA 20 , GA 1 , GA 29 , and GA 8 ), six are members of the early-3-hydroxylation pathway (GA 37 , GA 27 , GA 36 , GA 13 , GA 4 , and GA 34 ), and the remaining six are members of the non-3,13-hydroxylation pathway (GA 12 , GA 15 , GA 24 , GA 25 , GA 9 , and GFA 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 9 in the ga4 mutant, indicate that GA 9 is not active in Arabidopsis, but it must be 3β-hydroxytlated to GA 4 to become bioactive. It is concluded that the reduced levels of the 3β-hydroxy-GAs, GA 1 and GA 4 , are the cause of the semidwarf growth habit of both mutants

  1. 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...

  2. 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.

  3. 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

  4. Orbital Contribution in 5f itinerant antiferromagnet UNiGa5 and UPtGa_5

    Science.gov (United States)

    Kaneko, Koji; Metoki, Naoto; Tokiwa, Yoshihumi; Haga, Yoshinori; Ishii, Yoshinobu; Bernhoeft, Nicholas; Lander, Gerard H.; O¯nuki, Yoshichika

    2003-03-01

    UNiGa5 and UPtGa5 which are isostructural to the heavy fermion superconductor PuCoGa5 exhibit itinerant antiferromagnetism with T_N=86 K and 26 K, respectively. Note that the nearest neighbor coupling of magnetic moments within the (0 0 1) plane is different between these iso-electronic compounds. In this work, the itinerant antiferromagnetism of UNiGa5 and UPtGa5 were studied in terms of magneto-striction and magnetic form factors. The neutron diffraction reveals the existence of remarkable magneto-strictions around T_N, indicating the large spin-orbit coupling in this system. The magnetic form factors of both compounds show that the orbital moments are quenched systematically corresponding to their behavior in the magnetic susceptibility. The result indicates the important role of orbital moment on the itinerancy of 5f electron in this system.

  5. Optimization of the GaAs et GaAs/Si annealing using halogen lamp flashes

    International Nuclear Information System (INIS)

    Blanck, H.

    1989-01-01

    The aim of the work is to check whether the flash annealing of GaAs and GaAs/Si, using halogen lamps, allows an improvement in the results obtained by usual methods. The electrical activation, defects behavior and results uniformity are studied. The results on the activation and diffusion of implanted impurities are shown to be equivalent to those obtained with classical annealing methods. However, residual impurities (or defects) diffusion phenomena are restrained by the flash annealing technique. The Hall effect cartographic measurements showed an improvement of the uniformity of the implanted coating surface resistance. Flash annealing is a suitable method for the Si activation in GaAs. It allows an improvement of the GaAs results obtained with standard techniques, as well as the formation, by means of ion implantation, of active zones in the GaAs/Si layers [fr

  6. Biaxially stressed excitons in GaAs/AlGaAs quantum wells grown on Si substrates

    Science.gov (United States)

    Jagannath, C.; Zemon, S.; Norris, P.; Elman, B. S.

    1987-10-01

    Photoluminescence and photoluminescence excitation spectroscopies are utilized to study excitons in GaAs/AlGaAs quantum wells (QW's) fabricated by molecular beam epitaxy on a GaAs buffer layer grown on a Si substrate. The buffer layer was grown by metalorganic vapor phase epitaxy. The experimental results are understood in terms of a uniform biaxial tension of approximately 3 kbar present in the plane of growth for both the QW's and the GaAs buffer. An important consequence of the biaxial tension is that for QW's with well widths larger than about 15 nm the light-hole and heavy-hole subbands cross each other in energy, resulting in a light-hole exciton energy lower than that of the heavy-hole exciton, opposite to the case of QW's grown on GaAs substrates.

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

    International Nuclear Information System (INIS)

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

    2001-01-01

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

  8. GaInP/GaP quantum dots: a material for OEIC on silicon substrates

    Science.gov (United States)

    Lee, Jong Won; Schremer, Alfred T.; Shealy, James R.; Ballantyne, Joseph M.

    1997-12-01

    Realization of optoelectronic integrated circuits on silicon substrates has many difficulties, one of which is depositing high quality light-emitting material on the silicon surface. A desirable depositing method from a manufacturing point of view is chemical vapor deposition. Because there are currently no light emitting semiconductor alloys lattice-matched to silicon, epitaxial growth of III-V compound devices on Si has required a lattice constant engineering step such as wafer bonding or thick buffer layer growth. Growth of GaInP/GaP strain-induced quantum dots offers an opportunity to grow single crystal light-emitting devices monolithically on silicon substrates without lattice constant engineering steps, since single crystal GaP can be grown on silicon. In this presentation, progress on MOCVD growth of GaInP/GaP quantum dots and its device applications are reviewed.

  9. Fabrication of vertical GaN/InGaN heterostructure nanowires using Ni-Au bi-metal catalysts

    OpenAIRE

    Ha, Ryong; Kim, Sung-Wook; Choi, Heon-Jin

    2013-01-01

    We have fabricated the vertically aligned coaxial or longitudinal heterostructure GaN/InGaN nanowires. The GaN nanowires are first vertically grown by vapor?liquid-solid mechanism using Au/Ni bi-metal catalysts. The GaN nanowires are single crystal grown in the [0001] direction, with a length and diameter of 1 to 10 ?m and 100 nm, respectively. The vertical GaN/InGaN coaxial heterostructure nanowires (COHN) are then fabricated by the subsequent deposition of 2 nm of InxGa1-xN shell on the sur...

  10. 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.

  11. 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)

  12. N-polar GaN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor formed on sapphire substrate with minimal step bunching

    Science.gov (United States)

    Prasertsuk, Kiattiwut; Tanikawa, Tomoyuki; Kimura, Takeshi; Kuboya, Shigeyuki; Suemitsu, Tetsuya; Matsuoka, Takashi

    2018-01-01

    The metal-insulator-semiconductor (MIS) gate N-polar GaN/AlGaN/GaN high-electron-mobility transistor (HEMT) on a (0001) sapphire substrate, which can be expected to operate with lower on-resistance and more easily work on the pinch-off operation than an N-polar AlGaN/GaN HEMT, was fabricated. For suppressing the step bunching and hillocks peculiar in the N-polar growth, a sapphire substrate with an off-cut angle as small as 0.8° was introduced and an N-polar GaN/AlGaN/GaN HEMT without the step bunching was firstly obtained by optimizing the growth conditions. The previously reported anisotropy of transconductance related to the step was eliminated. The pinch-off operation was also realized. These results indicate that this device is promising.

  13. 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

    obstruction-free transport of holes and the highest possible barrier height for electrons are found. The optimal compositions of both compounds ((InAlGaAs)-Al-0.232-Ga-0.594-As-0.174/(AlGaAs)-Ga-0.355-As-0.645) at which the flux of electrons across the barrier is at a minimum are determined with consideration...

  14. 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...... the existence of magnetostrictive nanoclusters spaced at similar to 15 nm apart that have a different magnetization than the A2 matrix. Combining the SANS results and the magnetization orientation obtained from the magnetic domain images using a Kerr microscope, it appears that the nanoclusters contribute...

  15. 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.

  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. 75 FR 23577 - Airworthiness Directives; GA 8 Airvan (Pty) Ltd Models GA8 and GA8-TC320 Airplanes

    Science.gov (United States)

    2010-05-04

    ... the specified products. The Australian AD clarifies the applicability of the AD to include Model GA8... the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. For the reasons discussed above, I certify that this AD...

  18. Selected Ga-68-siderophores versus Ga-68-colloid and Ga-68-citrate: biodistribution and small animal imaging in mice

    Czech Academy of Sciences Publication Activity Database

    Petřík, M.; Vlčková, A.; Nový, Z.; Urbánek, Lubor; Haas, H.; Decristoforo, C.

    2015-01-01

    Roč. 159, č. 1 (2015), s. 60-66 ISSN 1213-8118 R&D Projects: GA MŠk(CZ) LO1304 Institutional support: RVO:61389030 Keywords : gallium-68 * siderophores * colloid Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 0.924, year: 2015

  19. 75 FR 52253 - Airworthiness Directives; GA 8 Airvan (Pty) Ltd Models GA8 and GA8-TC320 Airplanes

    Science.gov (United States)

    2010-08-25

    ... Authority (CASA), which is the aviation authority for Australia, has issued AD/GA8/3, Amdt 2, dated August... order to follow FAA policies. Any such differences are described in a separate paragraph of the AD... the overall regulatory, economic, environmental, and energy aspects of this AD. We will consider all...

  20. High Excitation Density Effects in Plasmonic GaAs-AlGaAs-GaAs Core-Shell Nanowires

    Science.gov (United States)

    Kaveh-Baghbadorani, Masoud; Gao, Qiang; Jagadish, Chennupati; Wagner, Hans-Peter

    We investigate the near-band emission of highly exited hybrid plasmonic GaAs-AlGaAs-GaAs core-shell nanowire (NW) heterostructures using time integrated (TI) photoluminescence (PL) measurements. The plasmonic structures are composed of 130 nm diameter zincblende NWs, either as bare NWs lying on an Au coated glass substrate or as Au coated NWs lying on a bare glass substrate. Intensity-dependent PL measurements on bare and plasmonic NW samples at high excitation densities reveal electron-hole-plasma (EHP) recombination. The EHP band shows a super-linear increase with increasing excitation intensity suggesting amplified spontaneous emission (ASE) at a threshold power density of around 60 microJ/cm2. Plasmonic NW samples excited above the threshold fluence reveal a weakly resolved sub-structure within the broad EHP band. The emerging sub-bands have a bandwidth which is by a factor of around 3 smaller than the width of the EHP background and are tentatively attributed to plasmonic lasing modes. This interpretation is supported by the fact that photonic lasing from 130 nm diameter thin uncoated GaAs NWs is theoretically not possible and that no sub-structure in the EHP band has been observed on bare nanowires.

  1. Microstructure of (Ga,Mn)As/GaAs digital ferromagnetic heterostructures

    International Nuclear Information System (INIS)

    Kong, X.; Trampert, A.; Guo, X.X.; Kolovos-Vellianitis, D.; Daeweritz, L.; Ploog, K.H.

    2005-01-01

    We report on the microstructure of (Ga,Mn)As digital ferromagnetic heterostructures grown on GaAs (001) substrates by low-temperature molecular-beam epitaxy. The Mn concentration and the As 4 /Ga beam equivalent pressure (BEP) ratio are varied in the samples containing periods of Mn sheets separated by thin GaAs spacer layers. Transmission electron microscopy studies reveal that decreasing the Mn doping concentration and reducing the BEP ratio lead to smaller composition fluctuations of Mn and more homogeneous (Ga,Mn)As layers with abrupt interfaces. Planar defects are found as the dominant defect in these heterostructures and their density is related to the magnitude of the composition fluctuation. These defects show a noticeable anisotropy in the morphologic distribution parallel to the orthogonal [110] and [110] direction. Along the [110] direction, they are stacking faults, which are preferentially formed in V-shaped pairs and nucleate at the interfaces between (Ga,Mn)As and GaAs layers. Along the [110] direction, the planar defects are isolated thin twin lamellae. The character of the planar defects and their configuration are analyzed in detail

  2. 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

  3. Compositional and structural characterisation of GaSb and GaInSb

    International Nuclear Information System (INIS)

    Corregidor, V.; Alves, E.; Alves, L.C.; Barradas, N.P.; Duffar, Th.; Franco, N.; Marques, C.; Mitric, A.

    2005-01-01

    Low band gap III-V semiconductors are researched for applications in thermophotovoltaic technology. GaSb crystal is often used as a substrate. Ga 1-x In x Sb is also a promising substrate material, because its lattice parameters can be adjusted by controlling x. We used a new method to synthesise GaSb and GaInSb, in which a high frequency alternate magnetic field is used to heat, to melt and to mix the elements. We present a compositional and structural characterisation of the materials using a combination of complementary techniques. Rutherford backscattering was used to determine accurately the composition of the GaSb. With proton induced X-ray emission in conjunction with a 3 x 3 μm 2 micro-beam we studied the homogeneity of the samples. Structural analysis and phase identification were done with X-ray diffraction. The results for GaSb show a homogeneous composition while the GaInSb samples were found to be strongly heterogeneous at the end of the ingot. The ingots produced are competitive feed material, when compared to other growth techniques, to be used in a second step for the production of good quality ternary crystals

  4. Atmospheric pressure-MOVPE growth of GaSb/GaAs quantum dots

    Science.gov (United States)

    Tile, Ngcali; Ahia, Chinedu C.; Olivier, Jaco; Botha, Johannes Reinhardt

    2018-04-01

    This study focuses on the growth of GaSb/GaAs quantum dots (QD) using an atmospheric pressure MOVPE system. For the best uncapped dots, the average dot height, base diameter and density are 5 nm, 45 nm and 4.5×1010 cm-2, respectively. Capping of GaSb QDs at high temperatures caused flattening and formation of thin inhomogeneous GaSb layer inside GaAs resulting in no obvious QD PL peak. Capping at low temperatures lead to the formation of dot-like features and a wetting layer (WL) with distinct PL peaks for QD and WL at 1097 nm and 983 nm respectively. Some of the dot-like features had voids. An increase in excitation power caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending leading to triangular potential wells, typical of type-II alignment between GaAs and strained GaSb. Variable temperature PL measurements of the QD sample showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the temperature increased.

  5. Electronic states in modulation doped p-AlGaN/GaN superlattices

    Science.gov (United States)

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Osinsky, A. V.; Norris, P. E.; Pearton, S. J.; Van Hove, J.; Wowchack, A. M.; Chow, P. P.

    2001-10-01

    The properties of p-AlGaN/GaN modulation doped superlattices (SLs) prepared by molecular beam epitaxy were studied by means of conductivity versus temperature, admittance spectroscopy, photoinduced current spectroscopy, microcathodoluminescence (MCL) spectra measurements, and measurements of effective diffusion lengths. It is shown that in SLs grown on GaN underlayers the sheet resistivity is about two orders of magnitude lower than for reference p-GaN films and the resistivity of SLs remains lower up to temperatures of about 350 °C. For SLs grown on AlGaN underlayers the gain in resistivity is much more moderate and certain advantages in using such SLs are envisaged only for temperatures below room temperature. The reason for this lower gain is a considerable decrease in hole mobility compared to p-GaN. The effect is somewhat tentatively attributed to worse crystalline perfection of these SLs. It is also shown that such SLs are characterized by a strongly broadened MCL peak and the presence of additional hole traps with activation energy of about 0.4 eV. Despite that, the photosensitivity and MCL intensity of these SLs are much better than for reference p-GaN samples.

  6. InGaN LEDs prepared on β-Ga2O3 (-201) substrates

    Science.gov (United States)

    Iizuka, Kazuyuki; Morishima, Yoshikatsu; Kuramata, Akito; Shen, Yu-Jiun; Tsai, Chang-Yu; Su, Ying-Yong; Liu, Gavin; Hsu, Ta-Cheng; Yeh, J. H.

    2015-03-01

    We fabricated InGaN LEDs prepared on β-Ga2O3 (201) single-crystal substrates. The substrates were produced by using the edge-defined film-fed growth (EFG) method. A Si-doped GaN epitaxial layer was grown on an electrically conductive β-Ga2O3 (201) substrate by metal organic chemical vapor deposition (MOCVD). The full-width at half maximum (FWHM) of (0002) and (101 1) X-ray rocking curves (XRCs) of the Si-doped GaN layer were 220 arcsec and 223 arcsec, respectively. The dark spot density measured by cathode luminescence (CL) was approximately 1.5×108 cm-2. The crystalline quality was equal to that of GaN layer on sapphire. We fabricated a vertical LED in the p-side down configuration. The peak wavelength was approximately 450 nm. The p-contact metal area was 300 ×300 μm2. The light output power did not saturate at 1000 A/cm2. This device characteristic indicates the great potential of Ga2O3 for use in high-power LEDs.

  7. Microwave-assisted synthesis of submicrometer GaO(OH) and Ga2O3 rods

    Science.gov (United States)

    Patra, Chitta Ranjan; Mastai, Yitzhak; Gedanken, Aharon

    2004-10-01

    Submicrometer sized gallium oxide hydroxide (GaO(OH)) and gallium oxide (Ga2O3) rods have been successfully fabricated on a large scale by refluxing an aqueous solution of Ga(NO3)3 and NH4OH in a simple domestic microwave oven (DMO). The structures, morphologies, compositions and physical properties of the as-synthesized and calcined products have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), selected area energy dispersive X-ray spectroscopy (SAEDS), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and energy dispersive X-ray (EDX) analysis. TEM images show that submicrometer sized as-synthesized Ga O(OH) rods have diameters of 0.3-0.5 μm and lengths of 3.2-3.5 μm. The calcined product consists of submicrometer rods with diameters of 0.4-0.5 μm and lengths of 5-5.5 μm. XRD, EDX and SAED analysis together indicate that the as-synthesized product has an orthorhombic gallium oxide hydroxide (GaO(OH)) crystal structure, and that the calcined product is rhombohedral Ga2O3. A possible mechanism for the formation of submicrometer sized GaO(OH) rods is discussed briefly.

  8. Performance improvement of junctionless field effect transistors using p-GaAs/AlGaAs heterostructure

    Science.gov (United States)

    Bajelan, F.; Goharrizi, A. Yazdanpanah; Faez, R.; Darvish, G.

    2017-10-01

    The performance analysis of junctionless (JL) gate-all-around (GAA) metal oxide semiconductor field effect transistors (MOSFETs) is investigated using the Non-Equilibrium Green's Function (NEGF) formalism. The main problem of JL transistors is found to be the OFF-state current. In the present work, the OFF-state current of such devices is decreased by choosing channel materials with a large band gap and heavy effective mass. Our simulation results show that the OFF-state current of JL transistors with p-type GaAs is less than that of n-type GaAs. Plus, the heterostructure (HES) channel is proposed in this study for improving the device characteristics of JL-FETs as compared to homostructure (HOS). Therefore, p-type GaAs and GaAs/AlGaAs are used as the channel material for HOS and HES devices, respectively. The simulation is performed for different thicknesses of GaAs and AlGaAs with a fixed diameter of 5 nm for the nanowire. It is shown that the optimum electronic characteristics of HES devices is achieved when the thicknesses of GaAs and AlGaAs layers are chosen to be 0.5 nm and 4 nm, respectively. OFF-state current (IOFF) of 5.32 × 10-16 A, ON-state current (ION) of 6.44 × 10-6 A, ON/OFF current ratio (ION/IOFF) of 1.21 × 1010, subthreshold slope (SS) of 60.8 mV/dec, drain induced barrier lowering (DIBL) of 4.6 mV/V, and threshold voltage (VTH) of 330 mV are obtained for the proposed HES JL-GAA-FET.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

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

  10. 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.

  11. A new theoretical approach to adsorption desorption behavior of Ga on GaAs surfaces

    Science.gov (United States)

    Kangawa, Y.; Ito, T.; Taguchi, A.; Shiraishi, K.; Ohachi, T.

    2001-11-01

    We propose a new theoretical approach for studying adsorption-desorption behavior of atoms on semiconductor surfaces. The new theoretical approach based on the ab initio calculations incorporates the free energy of gas phase; therefore we can calculate how adsorption and desorption depends on growth temperature and beam equivalent pressure (BEP). The versatility of the new theoretical approach was confirmed by the calculation of Ga adsorption-desorption transition temperatures and transition BEPs on the GaAs(0 0 1)-(4×2)β2 Ga-rich surface. This new approach is feasible to predict how adsorption and desorption depend on the growth conditions.

  12. Electrical properties of Ga ion beam implanted GaAs epilayer

    International Nuclear Information System (INIS)

    Hirayama, Yoshiro; Okamoto, Hiroshi

    1985-01-01

    Resistivity enhancement by 5 orders or more was realized by Ga focused ion beam implantation into n + and p + GaAs epilayers. For originally n + epilayers, this resistivity enhancement is maintained after annealing as high as 800 deg C. However this enhancement disappears after annealing at above 650 deg C for p + epilayer. This property makes GaAs high resistive only in a limited area whose minimum dimension is 0.1 μm or less, and is attractive for a device fabrication process to electrically isolate integrated elements. (author)

  13. Photocurrent Cancellation Due to Barrier Asymmetry in GaAs/AlGaAs Heterostructure Infrared Detectors

    Science.gov (United States)

    2014-05-01

    response time. The III-V compounds of gallium arsenide and aluminum 9 gallium arsenide (AlGaAs) are the principle materials used in this study of...negative and positive applied bias, and shows increasing potential offset with increasing aluminum fraction of the AlxGa1- 1. REPORT DATE (DD-MM-YYYY) 4...negative and positive applied bias, and shows increasing potential offset with increasing aluminum fraction of the AlxGa1-xAs barriers.This barrier

  14. Defect Structure of High-Temperature-Grown GaMnSb/GaSb

    International Nuclear Information System (INIS)

    Romanowski, P.; Bak-Misiuk, J.; Dynowska, E.; Domagala, J.Z.; Wojciechowski, T.; Jakiela, R.; Sadowski, J.; Barcz, A.; Caliebe, W.

    2010-01-01

    GaMnSb/GaSb(100) layers with embedded MnSb inclusions have been grown at 720 K using MBE technique. This paper presents the investigation of the defect structure of Ga1-xMnxSb layers with different content of manganese (up to x = 0.07). X-ray diffraction method using conventional and synchrotron radiation was applied. Dimensions and shapes of inclusions were detected by scanning electron microscopy. Depth profiles of elements were measured using secondary ion mass spectroscopy technique. (authors)

  15. 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.

  16. Theoretical modelling of quaternary GaInAsSb/GaAs self-assembled quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Llorens, J M; Taboada, A G; Ripalda, J M; Alonso-Alvarez, D; Alen, B; Martin-Sanchez, J; Garcia, J M; Gonzalez, Y [IMM-Instituto de Microelectronica de Madrid, (CNM-CSIC), Isaac Newton 8, PTM, E-28760 Tres Cantos, Madrid (Spain); Sanchez, A M [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Beltran, A M; Galindo, P L; Molina, S I, E-mail: jose.llorens@imm.cnm.csic.e [Universidad de Cadiz, Puerto Real, 11510 Cadiz (Spain)

    2010-09-01

    InAs/GaAs quantum dots exposed to Sb after growth exhibit spectral changes. We study in the present paper an idealized nanostructure consisting of a homogeneous distribution of the quaternary GaInAsSb surrounded by a barrier of GaAs. We find that the valence band offset is a critical parameter in modelling its electronic structure. Depending on this value, we predict a transition from type-I to type-II band alignment at a different Sb concentration. The addition of Sb to reduce the transition energy while keeping a type-I alignment is only of benefit at low Sb concentration.

  17. The role of Ga in the acetylene adsorption on PdGa intermetallic

    Science.gov (United States)

    Sandoval, M.; Bechthold, P.; Orazi, V.; González, E. A.; Juan, A.; Jasen, P. V.

    2018-03-01

    We performed density functional calculation of the acetylene hydrogenation reaction on the PdGa(110) surface. The reaction C2H2+H2 → C2H4 is modeled and understood in terms of chemical bonding change. The evolution of electronic structure and electron density plot also shed more light on the role of Pd, Ga and C2H2 during the hydrogenation reactions. This new way of looking at a particular chemical reaction includes the changes in bond order in the different reaction steps. As mentioned before the role of Ga is revealed as a part of the active site and not a single spacer.

  18. Parity Measurements in the 70Ga Nucleus

    Science.gov (United States)

    Venegas Vargas, D. C.; Haring-Kaye, R. A.; Jones, K. D.; Le, K. Q.; Harbin, B. L.; Döring, J.; Abromeit, B.; Dungan, R.; Lubna, R.; Tabor, S. L.; Tai, P.-L.; Tripati, Vandana; Vonmoss, J. M.; Morrow, S. I.

    2017-09-01

    The odd-odd 70Ga nucleus was studied at high spin after being produced at Florida State University using the 62Ni(14C,αpn) fusion-evaporation reaction at a beam energy of 50 MeV. The resulting γ rays were detected in coincidence using an array of Compton-suppressed Ge detectors consisting of three Clover detectors and seven single-crystal detectors. The linear polarizations of eight γ-ray transitions in 70Ga were measured by comparing their scattering yields within a Clover detector in the parallel and perpendicular directions relative to the beam axis, under the requirement that at least one other γ ray in 70Ga was recorded by a single-crystal detector in the array. As a result of these measurements, the parities of six states were confirmed and those of two other states were established for the first time based on a comparison of the experimental polarizations with the predicted ones determined from known spin assignments. The resulting level spectrum of 70Ga shows both similarities and differences with the predictions of previous shell-model calculations. This work was supported by the U.S. National Science Foundation and the Ohio Wesleyan University Summer Science Research Program.

  19. European Frontiers in RF GaN

    NARCIS (Netherlands)

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

    2015-01-01

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

  20. Metamagnetism in Ce(Ga,Al)2

    Indian Academy of Sciences (India)

    Metamagnetism in Ce(Ga,Al)2. K G SURESH1,∗. , S RADHA2 and A K NIGAM3. 1Department of Physics, Indian Institute of Technology, Mumbai 400 076, India. 2Department of Physics, Mithibai College, Mumbai 400 056, India. 3Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India. ∗.

  1. 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.

  2. Ga-67 uptake post cesarean section

    International Nuclear Information System (INIS)

    Lopez, O.L.; Maisano, E.R.

    1984-01-01

    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

  3. 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...... consistent with its cubic crystal structure which supports the reliability of the experimental data. In addition, the (71)Ga and (27)Al isotropic chemical shifts for YGG and YAG give further support to the linear correlation observed earlier between (71)Ga and (27)Al isotropic chemical shifts....

  4. Anisotropic magnetoresistance components in (Ga,Mn)As

    Czech Academy of Sciences Publication Activity Database

    Rushforth, A.W.; Výborný, Karel; King, C.S.; Edmonds, K. W.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.; Irvine, A.C.; Vašek, Petr; Novák, Vít; Olejník, Kamil; Sinova, J.; Jungwirth, Tomáš; Gallagher, B. L.

    2007-01-01

    Roč. 99, č. 14 (2007), 147207/1-147207/4 ISSN 0031-9007 R&D Projects: GA ČR GA202/05/0575; GA ČR GA202/04/1519; GA ČR GEFON/06/E002; GA MŠk LC510 Grant - others:UK(GB) GR/S81407/01 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductors * anisotropic magnetoresistence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 6.944, year: 2007

  5. Electronic properties of GaV 4 S 8

    Indian Academy of Sciences (India)

    ... different in GaV4S8-1 and GaV4S8-2. This statement is strongly supported by the calculated bandwidth per cluster in GaV4S8 (∼0.342 eV in GaV4S8-1 and ∼0.374 eV in GaV4S8-2). A negative magnetoresistance (MR) is also found around 43 K in GaV4S8-2 at 6.0 T magnetic field associated with structural transition.

  6. Huge tunnelling anisotropic magnetoresistance in (Ga,Mn)As nanoconstrictions

    Czech Academy of Sciences Publication Activity Database

    Giddings, A.D.; Makarovsky, O. N.; Khalid, M.N.; Yasin, S.; Edmonds, K. W.; Campion, R. P.; Wunderlich, J.; Jungwirth, Tomáš; Williams, D.A.; Gallagher, B. L.; Foxon, C. T.

    2008-01-01

    Roč. 10, č. 8 (2008), 085004/1-085004/9 ISSN 1367-2630 R&D Projects: GA ČR GEFON/06/E002; GA MŠk LC510; GA ČR GA202/05/0575; GA ČR GA202/04/1519 EU Projects: European Commission(XE) 015728 - NANOSPIN Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductor * nanoconstriction * tunneling anisotropic magnetoresistance , Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.440, year: 2008

  7. Domain walls in (Ga,Mn)As diluted magnetic semiconductor

    Czech Academy of Sciences Publication Activity Database

    Sugawara, A.; Kasai, H.; Tonomura, A.; Brown, P.D.; Campion, R. P.; Edmonds, K. W.; Gallagher, B. L.; Zemen, Jan; Jungwirth, Tomáš

    2008-01-01

    Roč. 100, č. 4 (2008), 047202/1-047202/4 ISSN 0031-9007 R&D Projects: GA MŠk LC510; GA ČR GEFON/06/E002; GA ČR GA202/05/0575; GA ČR GA202/04/1519 EU Projects: European Commission(XE) 015728 - NANOSPIN Institutional research plan: CEZ:AV0Z10100521 Keywords : dilute ferromagnetic semiconductor * Néel domain walls * electron holography * Landau-Lifshitz-Gilbert simulation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.180, year: 2008

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

    International Nuclear Information System (INIS)

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

    2011-01-01

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

  9. 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.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    Highlights: • High quality InGaAsP material with a bandgap of 1.0 eV was grown by MBE. • Room-temperature wafer-bonded GaInP/GaAs/InGaAsP SCs were fabricated. • An efficiency of 30.3% of wafer-bonded triple-junction SCs was obtained. - Abstract: 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Wen-xian; Dai, Pan; Ji, Lian; Tan, Ming; Wu, Yuan-yuan [Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Uchida, Shiro [Department of Mechanical Science and Engineering Faculty of Engineering, Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, Chiba 275-0016 (Japan); Lu, Shu-long, E-mail: sllu2008@sinano.ac.cn [Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China); Yang, Hui [Key Lab of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (CAS), Suzhou 215123 (China)

    2016-12-15

    Highlights: • High quality InGaAsP material with a bandgap of 1.0 eV was grown by MBE. • Room-temperature wafer-bonded GaInP/GaAs/InGaAsP SCs were fabricated. • An efficiency of 30.3% of wafer-bonded triple-junction SCs was obtained. - Abstract: 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.

  12. Wavelength Red-Shift of Long Wavelength InGaN/GaN Multi-Quantum Well by Using an InGaN Underlying Layer

    International Nuclear Information System (INIS)

    Li-Rong, Huang; Feng, Wen; Liang-Zhu, Tong; De-Xiu, Huang

    2009-01-01

    Long-wavelength GaN based light-emitting diodes are of importance in full color displays, monolithic white light- emitting diodes and solid-state lighting, etc. However, their epitaxial growth faces great challenges because high indium (In) compositions of InGaN are difficult to grow. In order to enhance In incorporation and lengthen the emission wavelength of a InGaN/GaN multi-quantum well (MQW), we insert an InGaN underlying layer underneath the MQW. InGaN/GaN MQWs with various InGaN underlying layers, such as graded In y Ga 1−y N material with linearly increasing In content, or In y Ga 1−y N with fixed In content but different thicknesses, are grown by metal-organic chemical vapor deposition. Experimental results demonstrate the enhancement of In incorporation and the emission wavelength redshift by the insertion of an InGaN underlying layer. (cross-disciplinary physics and related areas of science and technology)

  13. Optical and structural characteristics of high indium content InGaN/GaN multi-quantum wells with varying GaN cap layer thickness

    Energy Technology Data Exchange (ETDEWEB)

    Yang, J.; Zhao, D. G., E-mail: dgzhao@red.semi.ac.cn; Jiang, D. S.; Chen, P.; Zhu, J. J.; Liu, Z. S.; Le, L. C.; Li, X. J.; He, X. G. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Liu, J. P. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Yang, H. [State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Zhang, Y. T.; Du, G. T. [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130023 (China)

    2015-02-07

    The optical and structural properties of InGaN/GaN multi-quantum wells (MQWs) with different thicknesses of low temperature grown GaN cap layers are investigated. It is found that the MQW emission energy red-shifts and the peak intensity decreases with increasing GaN cap layer thickness, which may be partly caused by increased floating indium atoms accumulated at quantum well (QW) surface. They will result in the increased interface roughness, higher defect density, and even lead to a thermal degradation of QW layers. An extra growth interruption introduced before the growth of GaN cap layer can help with evaporating the floating indium atoms, and therefore is an effective method to improve the optical properties of high indium content InGaN/GaN MQWs.

  14. Study on ECR dry etching and selective MBE growth of AlGaN/GaN for fabrication of quantum nanostructures on GaN (0001) substrates

    International Nuclear Information System (INIS)

    Oikawa, Takeshi; Ishikawa, Fumitaro; Sato, Taketomo; Hashizume, Tamotsu; Hasegawa, Hideki

    2005-01-01

    This paper attempts to form AlGaN/GaN quantum wire (QWR) network structures on patterned GaN (0001) substrates by selective molecular beam epitaxy (MBE) growth. Substrate patterns were prepared along - and -directions by electron cyclotron resonance assisted reactive-ion beam etching (ECR-RIBE) process. Selective growth was possible for both directions in the case of GaN growth, but only in the -direction in the case of AlGaN growth. A hexagonal QWR network was successfully grown on a hexagonal mesa pattern by combining the -direction and two other equivalent directions. AFM observation confirmed excellent surface morphology of the grown network. A clear cathodoluminescence (CL) peak coming from the embedded AlGaN/GaN QWR structure was clearly identified

  15. 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)

  16. Electron-beam-induced segregation in InGaN/GaN multiple-quantum wells

    International Nuclear Information System (INIS)

    O'Neill, J.P.; Ross, I.M.; Cullis, A.G.; Wang, T.; Parbrook, P.J.

    2003-01-01

    We report a study of the morphology and composition of In x Ga 1-x N/GaN multiple-quantum-well structures and their sensitivity to electron-beam damage. We have employed high-resolution transmission electron microscopy, energy dispersive x-ray analysis, and scanning transmission electron microscopy. Microstructural analysis was performed to investigate the dynamical effects of electron-beam irradiation on the relative indium distribution within the quantum wells. Exposure to relatively low incident beam illumination, corresponding to current densities at the specimen of ∼100 pA/cm 2 , was found to induce significant nanoclustering of indium within the multiple-quantum wells. These findings highlight the need for caution when reporting the presence of indium-rich clusters within InGaN/GaN multiple-quantum wells studied in the transmission electron microscope

  17. Fabrication of MnGa/GaAs contacts for optoelectronics and spintronics applications

    Energy Technology Data Exchange (ETDEWEB)

    Dorokhin, M. V., E-mail: dorokhin@nifti.unn.ru [Lobachevsky State University, Physical–Technical Research Institute (Russian Federation); Pavlov, D. A.; Bobrov, A. I. [Lobachevsky State University, Physical Department (Russian Federation); Danilov, Yu. A.; Lesnikov, V. P.; Zvonkov, B. N.; Zdoroveyshchev, A. V. [Lobachevsky State University, Physical–Technical Research Institute (Russian Federation); Kudrin, A. V. [Lobachevsky State University, Physical Department (Russian Federation); Demina, P. B. [Lobachevsky State University, Physical–Technical Research Institute (Russian Federation); Usov, Yu. V.; Nikolichev, D. E.; Kryukov, R. N.; Zubkov, S. Yu. [Lobachevsky State University, Physical Department (Russian Federation)

    2016-11-15

    The crystal structure, composition, and magnetic, and electric-transport properties of Mn{sub x}Ga{sub y} layers deposited onto a GaAs surface by pulsed laser deposition in a hydrogen atmosphere, pulsed laser deposition in vacuum, and electron-beam evaporation in vacuum are investigated. It is shown that the features of each technique affect the composition and crystal structure of the formed layers, and the degree of abruptness and crystalline quality of the heterointerface. Apparently, the composition and crystal structure are responsible for modification of the ferromagnetic properties. The defects in the heterointerface affect the properties of the Mn{sub x}Ga{sub y}/GaAs diode structure, in particular, the height of the Schottky diode potential barrier.

  18. Transmission electron microscopy of AlGaAs/GaAs quantum cascade laser structures.

    Science.gov (United States)

    Walther, T; Krysa, A B

    2017-12-01

    Quantum cascade lasers can be efficient infrared radiation sources and consist of several hundreds of very thin layers arranged in stacks that are repeated periodically. Both the thicknesses of the individual layers as well as the period lengths need to be monitored to high precision. Different transmission electron microscopy methods have been combined to analyse AlGaAs/GaAs quantum cascade laser structures in cross-section. We found a small parabolic variation of the growth rate during deposition, affecting the stack periodicity and a reduced aluminium content of the AlGaAs barriers, whereas their widths as well as those of the GaAs quantum wells agreed with the nominal values within one atomic layer. Growth on an offcut substrate led to facets and steps at the interfaces. © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society.

  19. Raman Scattering and Surface Photovoltage Spectroscopy Studies of InGaAs/GaAs Radial Superlattices

    Science.gov (United States)

    Angelova, T.; Cros, A.; Ivanov, Ts.; Donchev, V.; Cantarero, A.; Shtinkov, N.; Deneke, Ch.; Schmidt, O. G.

    2011-12-01

    In this work we get insight into the multilayer structure of rolled-up microtube radial superlattices (RSLs) by the study of the optical and folded acoustic phonon modes of individual microtubes. Raman results show shifts of the InGaAs and GaAs related longitudinal optical modes that can be related to the strain state of the tubes. The folding of the acoustic modes has been related with the periodicity of the artificial superlattice formed by the multiple turns of the heterostructures. Information on the electronic structure and optical transitions of RSLs has been obtained by surface photovoltage spectroscopy. Room temperature spectra reveal several electronic transitions with energies below 1.3 eV. These transitions have been identified as originating from defect levels at the interfaces, as well as from the RSLs and the In0.215Ga0.785As/GaAs quantum well in the unfolded regions of the sample.

  20. Four-junction AlGaAs/GaAs laser power converter

    Science.gov (United States)

    Huang, Jie; Sun, Yurun; Zhao, Yongming; Yu, Shuzhen; Dong, Jianrong; Xue, Jiping; Xue, Chi; Wang, Jin; Lu, Yunqing; Ding, Yanwen

    2018-04-01

    Four-junction AlGaAs/GaAs laser power converters (LPCs) with n+-GaAs/p+-Al0.37Ga0.63As heterostructure tunnel junctions (TJs) have been designed and grown by metal-organic chemical vapor deposition (MOCVD) for converting the power of 808 nm lasers. A maximum conversion efficiency η c of 56.9% ± 4% is obtained for cells with an aperture of 3.14 mm2 at an input laser power of 0.2 W, while dropping to 43.3% at 1.5 W. Measured current–voltage (I–V) characteristics indicate that the performance of the LPC can be further improved by increasing the tunneling current density of TJs and optimizing the thicknesses of sub-cells to achieve current matching in LPC. Project financially supported by the National Natural Science Foundation of China (No. 61376065) and Zhongtian Technology Group Co. Ltd.

  1. Effect of Passivation on Microwave Power Performances of AlGaN/GaN/Si HEMTs

    Directory of Open Access Journals (Sweden)

    H. MOSBAHI

    2014-05-01

    Full Text Available This paper reports on the use of plasma assisted molecular beam epitaxy of AlGaN/GaN high electron mobility transistors (HEMTs grown on silicon substrate. Surface passivation effects on AlGaN/GaN HEMTs were studied using SiO2/SiN dielectric layers grown by plasma enhanced chemical vapor deposition. The direct current measurement, pulsed characteristics and microwave small-signal characteristics were studied before and after passivation. An improvement of drain-source current density and the extrinsic transconductance was observed on the passivated HEMTs when compared with the unpassivated HEMTs. An enhancement of cut-off frequency (ft and maximum power gain (fmax was also observed for the devices with full SiO2/SiN passivation. A good correlation is found between pulsed and power measurements.

  2. Whispering gallery mode lasing from InGaN/GaN quantum well microtube.

    Science.gov (United States)

    Li, Yufeng; Feng, Lungang; Su, Xilin; Li, Qiang; Yun, Feng; Yuan, Ge; Han, Jung

    2017-07-24

    In this work, we have successfully fabricated microtubes by strain-induced self-rolling of a InGaN/GaN quantum wells nanomembrane. Freestanding quantum wells microtubes, with a diameter of 6 µm and wall thickness of 50 nm, are formed when the coherently strained InGaN/GaN quantum wells heterostructure is selectively released from the hosting substrate. Periodic oscillations due to whispering-gallery modes resonance were found superimposed on photoluminescence spectra even at low optical excitation power. With increasing pumping power density, the microtube is characterized by a stimulated emission with a threshold as low as 415 kW/cm 2 . Such emission shows predominant TM polarization parallel to the microtube axis.

  3. Development of methods for the purification of 67Ga and 68Ga for biomolecules labeling

    International Nuclear Information System (INIS)

    Costa, Renata Ferreira

    2012-01-01

    For more than fifty years, the long-lived 68 Ge/ 68 Ga generators have been in development, obtaining 68 Ga without the need of having in house cyclotron, which is a considerable convenience for PET centers that have no nearby cyclotrons. 68 Ga decays 89% by positron emission and low photon emission (1077 keV) and the physical half life of 67.7 minutes is compatible with the pharmacokinetics of low biomolecular weight substances like peptides and antibody fragments. Moreover, its established metallic chemistry allows it to be stably bound to the carrier peptide sequence via a suitable bifunctional chelator, such as DOTA. All these reasons together with the technology of PET/CT allowed advances in molecular imaging, in particular in the diagnosis of neuroendocrine diseases. However, the eluate from the commercial 68 Ge/ 68 Ga generators still contains high levels of long lived 68 Ge, besides other metallic impurities, which competes with 68 Ga with a consequent reduction of the labeling yield of biomolecules, such as Fe 3+ and Zn 2+ . Thus, the lower the amount of impurities in the eluate, the competition between the radiolabeled and unlabeled peptide by the receptor will be smaller and the quality of imaging will be better, a subsequent purification step is needed after the generator elution. The aim of this work is to evaluate different purifications methods of 68 Ga to label biomolecules, with emphasis on the study of the chemical impurities contained in the eluate and to develop a new purification method. Several purification methods were studied. Many cationic resin were tested simulating the commercial process. 68 Ga is adsorbed in cationic resin, which is not commercial available and eluted in acid/acetone solution. The use of minor particles of cationic resin AG50W-X4 (200-400 mesh) showed the best results. An innovate method was the extraction chromatography, which is based on the absorption of diisopropyl ether in XAD 16 and 68 Ga recovery in deionized

  4. 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.

  5. 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.

  6. Selective area deposition of diamond films on AlGaN/GaN heterostructures

    Czech Academy of Sciences Publication Activity Database

    Ižák, Tibor; Babchenko, Oleg; Jirásek, Vít; Vanko, G.; Vallo, M.; Vojs, M.; Kromka, Alexander

    2014-01-01

    Roč. 250, č. 12 (2014), 2574-2580 ISSN 0370-1972 R&D Projects: GA ČR(CZ) GP14-16549P Institutional support: RVO:68378271 Keywords : circular high electron mobility transistors * diamond films * GaN substrates * microwave chemical vapor deposition * selective area deposition Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.489, year: 2014

  7. Auger recombination suppression and band alignment in GaAsBi/GaAs heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hild, K.; Batool, Z.; Jin, S. R.; Hossain, N.; Marko, I. P.; Sweeney, S. J. [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, GU2 7XH (United Kingdom); Hosea, T. JC. [1 Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, GU2 7XH, UK and also, Ibnu Sina Institute, Universiti Teknologi Malaysia, Johor Bahru, 81310 (Malaysia); Lu, X. [Department of Electrical and Computer Engineering, University of Victoria, Victoria BC, V8W 3P6, Canada and now VarianSemiconductor Equipment Associates, Gloucester, MA 01930 (United States); Tiedje, T. [Department of Electrical and Computer Engineering, University of Victoria, Victoria BC, V8W 3P6 (Canada)

    2013-12-04

    Using a combination of experimental and theoretical techniques we present the dependence of the bandgap E{sub g} and the spin orbit splitting energy Δ{sub so}, with Bi concentration in GaAsBi/GaAs samples. We find that the concentration at which Δ{sub so},> E{sub g} occurs at 9%. Both spectroscopic as well as first device results indicate a type I alignment.

  8. 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...... is observed at temperatures lower than the critical point and can be interpreted in terms of the collective behavior of interwell excitions....

  9. Graded GaAsSb strain reducing layers covering InAs/GaAs quantum dots

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Zíková, Markéta; Pangrác, Jiří; Oswald, Jiří; Kuldová, Karla; Vyskočil, Jan; Hulicius, Eduard

    2013-01-01

    Roč. 370, MAY (2013), s. 303-306 ISSN 0022-0248 R&D Projects: GA ČR GAP102/10/1201 Institutional research plan: CEZ:AV0Z10100521 Keywords : band alignment * photoluminescence * strain reducing layer * quantum dot * MOVPE * InAs/GaAs Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.693, year: 2013

  10. 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.

  11. 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.

  12. Temperature-dependent stress in diamond-coated AlGaN/GaN heterostructures

    Czech Academy of Sciences Publication Activity Database

    Ižák, Tibor; Jirásek, Vít; Vanko, G.; Dzuba, J.; Kromka, Alexander

    2016-01-01

    Roč. 106, Sep (2016), s. 305-312 ISSN 0264-1275 R&D Projects: GA ČR(CZ) GP14-16549P Grant - others:AV ČR(CZ) SAV-16-02 Program:Bilaterální spolupráce Institutional support: RVO:68378271 Keywords : thermally induced stress * Raman spectroscopy * polycrystalline diamond film * GaN Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.364, year: 2016

  13. Magnetoresistance of individual ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires

    OpenAIRE

    Butschkow, Christian H.; Reiger, Elisabeth; Geißler, Stefan; Rudolph, Andreas; Soda, Marcello; Schuh, Dieter; Woltersdorf, Georg; Wegscheider, Werner; Weiss, Dieter

    2011-01-01

    We investigate, angle dependent, the magnetoresistance (MR) of individual self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic temperatures. The shape of the MR traces and the observed strong anisotropies in transport can be ascribed to the interplay of the negative magnetoresistance effect and a strong uniaxial anisotropy with the magnetic easy direction pointing along the wire axis. The magnetoresistance can be well described by a quantitative analysis based on the ...

  14. Light-hole conduction in InGaAs/GaAs strained-layer superlattices

    International Nuclear Information System (INIS)

    Schirber, J.E.; Fritz, I.J.; Dawson, L.R.

    1985-01-01

    We report the first observation of light-hole band carriers in In/sub 0.2/Ga/sub 0.8/As/GaAs strained-layer superlattices by direct measurements of their effective mass (m*m/sub o/ = 0.14) using oscillatory magnetoresistance data. Preferential population of light-hole states, due to splitting of the degenerate bulk valence bands by built-in strain, allows this direct observation

  15. 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.

  16. Optical displacement measurement with GaAs/AlGaAs-based monolithically integrated Michelson interferometers

    OpenAIRE

    Hofstetter, Daniel; Zappe, H. P.; Dändliker, René

    2008-01-01

    Two monolithically integrated optical displacement sensors fabricated in the GaAs/AlGaAs material system are reported. These single-chip microsystems are configured as Michelson interferometers and comprise a distributed Bragg reflector (DBR) laser, photodetectors, phase shifters, and waveguide couplers. While the use of a single Michelson interferometer allows measurement of displacement magnitude only, a double Michelson interferometer with two interferometer signals in phase quadrature als...

  17. 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

  18. Growth of dilute nitride GaAsN/GaAs heterostructure nanowires on Si substrates.

    Science.gov (United States)

    Araki, Yoshiaki; Yamaguchi, Masahito; Ishikawa, Fumitaro

    2013-02-15

    The concept of band engineering dilute nitride semiconductors into nanowires is introduced. Using plasma-assisted molecular beam epitaxy, dilute nitride GaAsN/GaAs heterostructure nanowires are grown on silicon (111) substrates. Growth of the nanowires under high As overpressure results in a regular wire diameter of 350 nm with a length exceeding 3 μm. The GaAsN/GaAs nanowires show characteristics including favorable vertical alignment, hexagonal cross-sectional structure with {110} facets, regions of wurtzite and zinc-blende phases, and a core-shell-type heterostructure. The nanowires are composed of GaAsN shells containing up to 0.3% nitrogen surrounding GaAs cores. Panchromatic cathodoluminescence images show intensity modulation along the length of the nanowires that is possibly related to the interfaces of wurtzite/zinc-blende regions. Photoluminescence with peak wavelengths between 870 and 920 nm is clearly observed at room temperature. The spectral red shift depends on the amount of introduced nitrogen. These results reveal a method for precise lattice and band engineering of nanowires composed of dilute nitride semiconductors.

  19. GaAs-AlGaAs core-shell nanowire lasers on silicon: invited review

    Science.gov (United States)

    Koblmüller, Gregor; Mayer, Benedikt; Stettner, Thomas; Abstreiter, Gerhard; Finley, Jonathan J.

    2017-05-01

    Semiconductor nanowire (NW) lasers provide significant potential to create a new generation of lasers and on-chip coherent light sources by virtue of their ability to operate as single mode optical waveguides at the nanoscale. Due to their unique geometry, a major benefit lies also in the feasibility for direct integration on silicon (Si), enabling III-V-on-Si NW lasers that could fuel applications in optical interconnects and data communication. In this review, we describe the state-of-the-art and recent progress in GaAs-AlGaAs based NW lasers emitting in the near infrared (NIR) spectral region, with a specific emphasis on integration on a Si platform. First, we explore design rules for the photonic properties in GaAs NW waveguides based on finite difference time domain calculations. The lasing characteristics of GaAs-AlGaAs core-shell NW lasers are then investigated under various different optical pumping schemes ranging from pulsed to continuous wave excitation. We further review recent activities on the realization of low-dimensional quantum heterostructures inside NW cavities as a means to tune lasing wavelength, gain and threshold properties. Ultimately, we describe schemes for monolithic integration of GaAs-based NW lasers directly on Si and show how such vertical nanocavity lasers are excellent candidates for low-threshold lasing, high spontaneous emission coupling (high β-factor lasers), and ultrafast emission characteristics.

  20. Carrier extraction behaviour in type II GaSb/GaAs quantum ring solar cells

    International Nuclear Information System (INIS)

    Fujita, Hiromi; James, Juanita; Carrington, Peter J; Marshall, Andrew R J; Krier, Anthony; Wagener, Magnus C; Botha, Johannes R

    2014-01-01

    The introduction of quantum dot (QD) or quantum ring (QR) nanostructures into GaAs single-junction solar cells has shown enhanced photo-response above the GaAs absorption edge, because of sub-bandgap photon absorption. However, to further improve solar cell performance a better understanding of the mechanisms of photogenerated carrier extraction from QDs and QRs is needed. In this work we have used a direct excitation technique to study type II GaSb/GaAs quantum ring solar cells using a 1064 nm infrared laser, which enables us to excite electron–hole pairs directly within the GaSb QRs without exciting the GaAs host material. Temperature and laser intensity dependence of the current–voltage characteristics revealed that the thermionic emission process produced the dominant contribution to the photocurrent and accounts for 98.9% of total photocurrent at 0 V and 300 K. Although the tunnelling process gives only a low contribution to the photocurrent, an enhancement of the tunnelling current was clearly observed when an external electric field was applied. (paper)

  1. High-capacity, high-strength trailer designs for the GA-4/GA-9 casks

    International Nuclear Information System (INIS)

    Rickard, N.D.; Kissinger, J.A.; Taylor, C.; Zimmer, A.

    1991-01-01

    General Atomics (GA) is developing final designs for two dedicated legal-weight trailers to transport the GA-4 and GA-9 Spent-Fuel Casks. The basic designs for these high-capacity, high-strength trailers are essentially identical except for small modifications to account for the differences in cask geometry. The authors are designing both trailers to carry a 55,000 lb (24,900 kg) payload and to withstand a 2.5 g vertical design load. The GA-4 and GA-9 trailers are designed for significantly higher loads than are typical commercial semitrailers, which are designed to loads in the range of 1.7 to 2.0 g. To meet the federal gross vehicle weight limit for legal-weight trucks, GA has set a target design weight for the trailers of 9000 lb (4080 kg). This weight includes the personnel barrier, cask tiedowns, and impact limiter removal and storage system. Based on the preliminary trailer designs, the final design weight will to be very close to this target weight

  2. Recent advancements in monolithic AlGaAs/GaAs solar cells for space applications

    Science.gov (United States)

    Wickham, K. R.; Chung, B.-C.; Klausmeier-Brown, M.; Kuryla, M. S.; Ristow, M. Ladle; Virshup, G. F.; Werthen, J. G.

    1991-01-01

    High efficiency, two terminal, multijunction AlGaAs/GaAs solar cells were reproducibly made with areas of 0.5 sq cm. The multiple layers in the cells were grown by Organo Metallic Vapor Phase Epitaxy (OMVPE) on GaAs substrates in the n-p configuration. The upper AlGaAs cell has a bandgap of 1.93 eV and is connected in series to the lower GaAs cell (1.4 eV) via a metal interconnect deposited during post-growth processing. A prismatic coverglass is installed on top of the cell to reduce obscuration caused by the gridlines. The best 0.5 sq cm cell has a two terminal efficiency of 23.0 pct. at 1 sun, air mass zero (AM0) and 25 C. To date, over 300 of these cells were grown and processed for a manufacturing demonstration. Yield and efficiency data for this demonstration are presented. As a first step toward the goal of a 30 pct. efficient cell, a mechanical stack of the 0.5 sq cm cells described above, and InGaAsP (0.95 eV) solar cells was made. The best two terminal measurement to date yields an efficiency of 25.2 pct. AM0. This is the highest reported efficiency of any two terminal, 1 sun space solar cell.

  3. 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%.

  4. GaN-based LEDs grown by molecular beam epitaxy

    Science.gov (United States)

    Averbeck, Robert; Graber, A.; Tews, H.; Bernklau, D.; Barnhoefer, Ulrich; Riechert, Henning

    1998-04-01

    We report on the growth of GaN, InGaN and GaN/InGaN/GaN pn- junctions grown on sapphire by RF-plasma assisted MBE. MBE allows us to grow high quality nitrides with growth rates around 1 micrometers /h at relatively low temperatures. Thereby p- type doping with Mg and the incorporation of In in InGaN are greatly facilitated. Device-typical n- and p-type doping levels yield room temperature mobilities of 220 cm2/Vs and 10 cm2/Vs, respectively. InGaN with In contents of more than 40 percent is readily achieved. LEDs fabricated from heterostructures with a 4 nm InGaN layer show bright blue or green electroluminescence depending on the In content. Various effects in the electroluminescence caused by fluctuations in the conduction and valence band will be discussed, the most striking one a reduction in linewidth with increasing temperature.

  5. 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.

  6. Control of Ga-oxide interlayer growth and Ga diffusion in SiO2/GaN stacks for high-quality GaN-based metal–oxide–semiconductor devices with improved gate dielectric reliability

    Science.gov (United States)

    Yamada, Takahiro; Watanabe, Kenta; Nozaki, Mikito; Yamada, Hisashi; Takahashi, Tokio; Shimizu, Mitsuaki; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2018-01-01

    A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal–oxide–semiconductor (MOS) devices was developed. The direct chemical vapor deposition of SiO2 films on GaN substrates forming Ga-oxide interlayers was carried out to fabricate SiO2/GaO x /GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state densities below 1010 cm‑2 eV‑1 were obtained by postdeposition annealing, Ga diffusion into overlying SiO2 layers severely degraded the dielectric breakdown characteristics. However, this problem was found to be solved by rapid thermal processing, leading to the superior performance of the GaN-MOS devices in terms of interface quality, insulating property, and gate dielectric reliability.

  7. 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

  8. 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

  9. Improved interface properties of GaN-based metal-oxide-semiconductor devices with thin Ga-oxide interlayers

    Science.gov (United States)

    Yamada, Takahiro; Ito, Joyo; Asahara, Ryohei; Watanabe, Kenta; Nozaki, Mikito; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2017-06-01

    The impact of thin Ga-oxide (GaOx) interlayers on the electrical properties of GaN-based metal-oxide-semiconductor (MOS) devices was systematically investigated. Thin thermal oxides formed at around 900 °C were found to be beneficial for improving the electrical properties of insulator/GaN interfaces, despite the fact that thermal oxidation of GaN surfaces at high temperatures proceeds by means of grain growth. Consequently, well-behaved capacitance-voltage characteristics of SiO2/GaOx/n-GaN stacked MOS capacitors with an interface state density (Dit) as low as 1.7 × 1011 cm-2 eV-1 were demonstrated. Moreover, the Dit value was further reduced for the SiO2/GaOx/GaN capacitor with a 2-nm-thick sputter-deposited GaOx interlayer. These results clearly indicate the intrinsically superior nature of the oxide/GaN interfaces and provide plausible guiding principles for fabricating high-performance GaN-MOS devices with thin GaOx interlayers.

  10. Interface States in AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors

    International Nuclear Information System (INIS)

    Feng Qian; Du Kai; Li Yu-Kun; Shi Peng; Feng Qing

    2013-01-01

    Frequency-dependent capacitance and conductance measurements are performed on AlGaN/GaN high electron mobility transistors (HEMTs) and NbAlO/AlGaN/GaN metal-insulator-semiconductor HEMTs (MISHEMTs) to extract density and time constants of the trap states at NbAlO/AlGaN interface and gate/AlGaN interface with the gate-voltage biased into the accumulation region and that at the AlGaN/GaN interface with the gate-voltage biased into the depletion region in different circuit models. The measurement results indicate that the trap density at NbAlO/AlGaN interface is about one order lower than that at gate/AlGaN interface while the trap density at AlGaN/GaN interface is in the same order, so the NbAlO film can passivate the AlGaN surface effectively, which is consistent with the current collapse results

  11. Gallium isotope fractionation during Ga adsorption on calcite and goethite

    Science.gov (United States)

    Yuan, Wei; Saldi, Giuseppe D.; Chen, JiuBin; Vetuschi Zuccolini, Marino; Birck, Jean-Louis; Liu, Yujie; Schott, Jacques

    2018-02-01

    Gallium (Ga) isotopic fractionation during its adsorption on calcite and goethite was investigated at 20 °C as a function of the solution pH, Ga aqueous concentration and speciation, and the solid to solution ratio. In all experiments Ga was found to be enriched in light isotopes at the solid surface with isotope fractionation △71Gasolid-solution up to -1.27‰ and -0.89‰ for calcite and goethite, respectively. Comparison of Ga isotopic data of this study with predictions for 'closed system' equilibrium and 'Rayleigh fractionation' models indicates that the experimental data are consistent with a 'closed system' equilibrium exchange between the fluid and the solid. The results of this study can be interpreted based on Ga aqueous speciation and the structure of Ga complexes formed at the solid surfaces. For calcite, Ga isotope fractionation is mainly triggered by increased Ga coordination and Ga-O bond length, which vary respectively from 4 and 1.84 Å in Ga(OH)4- to 6 and 1.94 Å in the >Ca-O-GaOH(OH2)4+ surface complex. For goethite, despite the formation of Ga hexa-coordinated >FeOGa(OH)20 surface complexes (Ga-O distances of 1.96-1.98 Å) both at acid and alkaline pH, a similar extent of isotope fractionation was found at acid and alkaline pH, suggesting that Ga(OH)4- is preferentially adsorbed on goethite for all investigated pH conditions. In addition, the observed decrease of Ga isotope fractionation magnitude observed with increasing Ga surface coverage for both calcite and goethite is likely related to the formation of Ga surface polymers and/or hydroxides with reduced Ga-O distances. This first study of Ga isotope fractionation during solid-fluid interactions suggests that the adsorption of Ga by oxides, carbonates or clay minerals could yield significant Ga isotope fractionation between secondary minerals and surficial fluids including seawater. Ga isotopes thus should help to better characterize the surficial biogeochemical cycles of gallium and its

  12. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

    Unknown

    of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is compa- rable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on ...

  13. Gallium-containing Heusler phases ScRh{sub 2}Ga, ScPd{sub 2}Ga, TmRh{sub 2}Ga and LuRh{sub 2}Ga. Magnetic and solid state NMR-spectroscopic characterization

    Energy Technology Data Exchange (ETDEWEB)

    Heletta, Lukas; Seidel, Stefan; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Benndorf, Christopher [Leipzig Univ. (Germany). Inst. fuer Mineralogie, Kristallographie und Materialwissenschaften; Eckert, Hellmut [Muenster Univ. (Germany). Inst. fuer Physikalische Chemie; Sao Paulo Univ., Sao Carlos (Brazil). Inst. of Physics

    2017-10-01

    The gallium-containing Heusler phases ScRh{sub 2}Ga, ScPd{sub 2}Ga, TmRh{sub 2}Ga and LuRh{sub 2}Ga have been synthesized by arc-melting of the elements followed by different annealing sequences to improve phase purity. The samples have been studied by powder X-ray diffraction. The structures of Lu{sub 0.97}Rh{sub 2}Ga{sub 1.03} (Fm3m, a=632.94(5) pm, wR2=0.0590, 46 F{sup 2} values, seven variables) and Sc{sub 0.88}Rh{sub 2}Ga{sub 1.12} (a=618.91(4) pm, wR2=0.0284, 44 F{sup 2} values, six variables) have been refined from single crystal X-ray diffractometer data. Both gallides show structural disorder through Lu/Ga and Sc/Ga mixing. Temperature dependent magnetic susceptibility measurements showed Pauli paramagnetism for ScRh{sub 2}Ga, ScPd{sub 2}Ga, and LuRh{sub 2}Ga and Curie-Weiss paramagnetism for TmRh{sub 2}Ga. {sup 45}Sc and {sup 71}Ga solid state MAS NMR spectroscopic investigations of the Sc containing compounds confirmed the site mixing effects typically observed for Heusler phases. The data indicate that the effect of mixed Sc/Ga occupancy is significantly stronger in ScRh{sub 2}Ga than in ScPd{sub 2}Ga.

  14. Mn doped GaN thin films and nanoparticles

    Czech Academy of Sciences Publication Activity Database

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

    2012-01-01

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

  15. Interlayer exchange coupling in (Ga,Mn)As based multilayers

    Czech Academy of Sciences Publication Activity Database

    Giddings, A.D.; Jungwirth, Tomáš; Gallagher, B. L.

    2006-01-01

    Roč. 3, č. 12 (2006), s. 4070-4073 ISSN 1610-1634 R&D Projects: GA ČR GA202/05/0575; GA AV ČR(CZ) IAA100100530; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductors * standing-wave fluorescence * x-ray diffraction Subject RIV: BM - Solid Matter Physics ; Magnetism

  16. Dislocation mechanism of twinning in Ni-Mn-Ga

    Czech Academy of Sciences Publication Activity Database

    Zárubová, Niva; Ge, Y.; Gemperlová, Juliana; Gemperle, Antonín; Hannula, S.-P.

    2012-01-01

    Roč. 5, č. 1 (2012), "1250006-1"-"1250006-4" ISSN 1793-6047 R&D Projects: GA ČR GAP107/10/0824; GA ČR(CZ) GAP107/11/0391; GA AV ČR IAA100100920 Institutional research plan: CEZ:AV0Z10100520 Keywords : Ni-Mn-Ga shape memory alloy * martensitic transformation * in situ TEM straining Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.270, year: 2012

  17. Tuning high frequency magnetic properties and damping of FeGa, FeGaN and FeGaB thin films

    Directory of Open Access Journals (Sweden)

    Derang Cao

    2017-11-01

    Full Text Available A series of FeGa, FeGaN and FeGaB films with varied oblique angles were deposited by sputtering method on silicon substrates, respectively. The microstructure, soft magnetism, microwave properties, and damping factor for the films were investigated. The FeGa films showed a poor high frequency magnetic property due to the large stress itself. The grain size of FeGa films was reduced by the additional N element, while the structure of FeGa films was changed from the polycrystalline to amorphous phase by the involved B element. As a result, N content can effectively improve the magnetic softness of FeGa film, but their high frequency magnetic properties were still poor both when the N2/Ar flow rate ratio is 2% and 5% during the deposition. The additional B content significantly led to the excellent magnetic softness and the self-biased ferromagnetic resonance frequency of 1.83 GHz for FeGaB film. The dampings of FeGa films were adjusted by the additional N and B contents from 0.218 to 0.139 and 0.023, respectively. The combination of these properties for FeGa films are helpful for the development of magnetostrictive microwave devices.

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

    International Nuclear Information System (INIS)

    Pérez-Tomás, A.; Fontserè, A.; Llobet, J.; Placidi, M.; Rennesson, S.; Chenot, S.; Moreno, J. C.; Cordier, Y.; Baron, N.

    2013-01-01

    The vertical bulk (drain-bulk) current (I 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 db (25–300 °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 a ), the (soft or destructive) vertical breakdown voltage (V 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 a = 0.35 eV at T = 25–300 °C; V B = 840 V), GaN-on-sapphire follows the trap assisted mechanism (E a = 2.5 eV at T > 265 °C; V B > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (E a = 0.35 eV at T > 150 °C; V B = 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored.

  19. Elimination of V-shaped pits in InGaN/GaN/AlN/GaN heterostructure by metal modulation growth technique

    Science.gov (United States)

    Chakraborty, Apurba; Bag, Ankush; Mukhopadhyay, Partha; Ghosh, Saptarsi; Biswas, Dhrubes

    2018-03-01

    In this paper, we have demonstrated the growth process of higher Indium content indium gallium nitride (InGaN) epitaxial layer of InGaN/GaN/AlN/GaN heterostructure without any V-shaped pits formation on the growth surface. The epitaxial InGaN with In fraction of 16%, 22% and 26% has been grown by using metal modulation growth scheme. The direct growth of relaxed InGaN structures with In content of 16% and 22% on GaN/AlN/GaN periodic layer shows higher density of V-shaped pits on the surface, as the InGaN epilayer is experienced to higher lattice relaxation and threading dislocation density. But for the 26% In mole heterostructure, the V pits are mitigated by varying the Indium fraction from 16% to 26% via 22% in bottom to top direction of the structure. The FESEM images have also confirmed the absence of any pits formation in 26% In content InGaN heterostructure, which is due to the lesser lattice relaxation and threading dislocation density. The different contents of Indium are confirmed by room temperature photoluminescence and XRD measurements.

  20. Design and comparison of GaAs, GaAsP and InGaAlAs quantum-well active regions for 808-nm VCSELs.

    Science.gov (United States)

    Zhang, Yan; Ning, Yongqiang; Zhang, Lisen; Zhang, Jinsheng; Zhang, Jianwei; Wang, Zhenfu; Zhang, Jian; Zeng, Yugang; Wang, Lijun

    2011-06-20

    Vertical-cavity surface-emitting lasers emitting at 808 nm with unstrained GaAs/Al0.3Ga0.7As, tensilely strained GaAs(x)P(1-x)/Al0.3Ga0.7As and compressively strained In(1-x-y)Ga(x)Al(y)As/Al0.3Ga0.7As quantum-well active regions have been investigated. A comprehensive model is presented to determine the composition and width of these quantum wells. The numerical simulation shows that the gain peak wavelength is near 800 nm at room temperature for GaAs well with width of 4 nm, GaAs0.87P0.13 well with width of 13 nm and In0.14Ga0.74Al0.12As well with width of 6 nm. Furthermore, the output characteristics of the three designed quantum-well VCSELs are studied and compared. The results indicate that In0.14Ga0.74Al0.12As is the most appropriate candidate for the quantum well of 808-nm VCSELs.

  1. 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.

  2. Phase transition induced anelasticity in Fe–Ga alloys with 25 and 27%Ga

    Energy Technology Data Exchange (ETDEWEB)

    Golovin, I.S., E-mail: i.golovin@misis.ru [National University of Science and Technology “MISIS”, Leninsky ave. 4, 119049, Moscow (Russian Federation); Balagurov, A.M., E-mail: bala@nf.jinr.ru [Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980, Dubna (Russian Federation); Bobrikov, I.A. [Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980, Dubna (Russian Federation); Palacheva, V.V. [National University of Science and Technology “MISIS”, Leninsky ave. 4, 119049, Moscow (Russian Federation); Cifre, J. [Universitat de les Illes Balears, Ctra. De Valldemossa, km.7.5, E-07122, Palma de Mallorca (Spain)

    2016-08-05

    Neutron diffraction and mechanical spectroscopy techniques were applied to study phase transitions in Fe–Ga alloys with 25 and 27 at.% Ga. The following sequences of phase transitions at continuous heating and subsequent cooling in the 20–900 °C temperature range were recorded: D0{sub 3} → L1{sub 2} (limited amount) → A2(B2) was recorded at heating and A2(B2) → D0{sub 3} at cooling for Fe-24.8Ga alloy, and the D0{sub 3} → L1{sub 2} → D0{sub 19} → A2(B2) was recorded at heating and A2(B2) → L1{sub 2} at cooling for Fe-27.4Ga alloy. Thus, the difference in 2.6 at.%Ga between two studied compositions with D0{sub 3} structure leads to their different structures after heating to 900 °C. These transition sequences determine different temperature dependencies of elastic and anelastic properties. The D0{sub 3} → A2(B2) transition (in Fe-25Ga) does not lead to a well-pronounced anelastic effect, in contrast the D0{sub 3} → L1{sub 2} transition (in Fe-27Ga) generates internal stresses due to a different rate of an increase in the lattice parameter with temperature and leads to a well-pronounced transient internal friction effect. - Highlights: • Neutron diffraction technique is used to study in situ phase transitions in Fe-25 and 27 at.% Ga. • D0{sub 3} → L1{sub 2} → D0{sub 19} → A2/B2 transitions were recorded at instant heating in Fe-27 at.% Ga. • D0{sub 3} → L1{sub 2} (limited amount) → A2(B2) was recorded at instant heating in Fe-25 at.% Ga • The D0{sub 3} → L1{sub 2} transition generates internal stresses and leads to elastic and anelastic response.

  3. Mercury(II) selective sensors based on AlGaN/GaN transistors

    International Nuclear Information System (INIS)

    Asadnia, Mohsen; Myers, Matthew; Akhavan, N.D.; O'Donnell, Kane; Umana-Membreno, Gilberto A.; Mishra, U.K.; Nener, Brett; Baker, Murray; Parish, Giacinta

    2016-01-01

    This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg 2+ . This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg 2+ concentrations. At pH 2.8 in a 10 −2  M KNO 3 ion buffer, a detection limit below 10 −8  M and a linear response range between 10 −8  M-10 −4  M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10 −7  M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10 −7  M and 10 −6  M in 10 −2  M Cd(NO 3 ) 2 and 10 −2  M Pb(NO 3 ) 2 ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg 2+ solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices. - Highlights: • This work is the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. • The sensor utilised an AlGaN/GaN transistor by functionalising the gate area with a polyvinyl chloride (PVC) based membrane. • The sensor showed a rapid and linear response between 10 −8 M-10 −4 M for Hg 2+ detection at pH 2.8 in a 10 −2 M KNO 3 ion buffer. • Detection limits of approximately 10 −7 M and 10 −6 M in 10 −2 M Cd(NO 3 ) 2 and 10 −2 M Pb(NO 3 ) 2 ion buffers

  4. Preparation and characterization of GA/RDX nanostructured ...

    Indian Academy of Sciences (India)

    Thenhexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was added and trapped in the nano-porous three-dimensional networks of GA to obtain a novel GA/RDX nanostructured energetic composite. The composition, morphology andstructure of the obtained GA/RDX nanostructured energetic composite were characterized by ...

  5. Preparation and characterization of GA/RDX nanostructured ...

    Indian Academy of Sciences (India)

    The results showed that GA could be a perfect aerogel matrix for the fabrication of GA/RDX nanostructured energetic composite due to itsunique nano-porous structure and attributes. It was also demonstrated that RDX homogeneously disperses in the asprepared GA/RDX nanostructured energetic composite at nanometric ...

  6. Preparation and characterization of GA/RDX nanostructured ...

    Indian Academy of Sciences (India)

    GA showed promising catalytic effects for the thermal decomposition of RDX. ... and extremely small feature sizes exhibit structure- and size-dependent properties, including thermal ..... Nitrogen adsorption–desorption isotherms for GA and GA/RDX nanostructured energetic composites. The results of specific surface area ...

  7. Magnetic ordering in TmGa

    DEFF Research Database (Denmark)

    Cadogan, J.M.; Stewart, G.A.; Muños Pérez, S.

    2014-01-01

    We have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and 169Tm Mössbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order...... to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) μB at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) μB. The 169Tm hyperfine magnetic field...

  8. Viscosity of Ga-Li liquid alloys

    Science.gov (United States)

    Vidyaev, Dmitriy; Boretsky, Evgeny; Verkhorubov, Dmitriy

    2018-03-01

    The measurement of dynamic viscosity of Ga-Li liquid alloys has been performed using low-frequency vibrational viscometer at five temperatures in the range 313-353 K and four gallium-based dilute alloy compositions containing 0-1.15 at.% Li. It was found that the viscosity of the considered alloys increases with decreasing temperature and increasing lithium concentration in the above ranges. It was shown that dependence of the viscosity of Ga-Li alloys in the investigated temperature range has been described by Arrhenius equation. For this equation the activation energy of viscous flow and pre-exponential factor were calculated. This study helped to determine the conditions of the alkali metals separating process in gallam-exchange systems.

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

    International Nuclear Information System (INIS)

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

    2011-01-01

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

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

    Science.gov (United States)

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

    2017-11-01

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

  11. Current collapse modeling in AlGaN/GaN HEMT using small signal equivalent circuit for high power application

    Science.gov (United States)

    Nirmal, D.; Arivazhagan, L.; Fletcher, A. S. Augustine; Ajayan, J.; Prajoon, P.

    2018-01-01

    In this paper, the drain current collapse in AlGaN/GaN High Electron Mobility Transistor (HEMT) with field plate engineering is investigated. A small signal equivalent circuit of AlGaN/GaN HEMT is developed and a new drain current model is derived. This model is useful to correlate the impact of intrinsic capacitance and conductance on drain current collapse. The proposed device suppressed the current collapse phenomena by 10% compared with the conventional AlGaN/GaN HEMT. Moreover, the DC characteristics of the simulated device shows a drain current of 900 mA/mm, breakdown voltage of 291 V and transconductance of 175 mS/mm. Besides, the intrinsic capacitance and conductance parameters are extracted and its impact on drain current is analysed. Finally, the simulation results obtained were in compliance with the derived mathematical model of AlGaN/GaN HEMT.

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

    Directory of Open Access Journals (Sweden)

    Bhishma Pandit

    2016-06-01

    Full Text Available 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.

  13. Towards InAs/InGaAs/GaAs Quantum Dot Solar Cells Directly Grown on Si Substrate

    Directory of Open Access Journals (Sweden)

    Bilel Azeza

    2015-07-01

    Full Text Available This paper reports on an initial assessment of the direct growth of In(GaAs/GaAs quantum dots (QDs solar cells on nanostructured surface Si substrate by molecular beam epitaxy (MBE. The effect of inserting 40 InAs/InGaAs/GaAs QDs layers in the intrinsic region of the heterojunction pin-GaAs/n+-Si was evaluated using photocurrent spectroscopy in comparison with pin-GaAs/n+-Si and pin-GaAs/GaAs without QDs. The results reveal the clear contribution of the QDs layers to the improvement of the spectral response up to 1200 nm. The novel structure has been studied by X ray diffraction (XRD, photoluminescence spectroscopy (PL and transmission electron microscopy (TEM. These results provide considerable insights into low cost III-V material-based solar cells.

  14. Excitonic transitions in homoepitaxial GaN

    Energy Technology Data Exchange (ETDEWEB)

    Martinez-Criado, G.; Cros, A.; Cantarero, A. [Materials Science Inst. and Dept. of Applied Physics, Univ. of Valencia (Spain); Miskys, C.R.; Ambacher, O.; Stutzmann, M. [Technische Univ. Muenchen, Garching (Germany). Walter-Schottky-Inst. fuer Physikalische Grundlagen der Halbleiterelektronik

    2001-11-08

    The photoluminescence spectrum of a high quality homoepitaxial GaN film has been measured as a function of temperature. As temperature increases the recombination of free excitons dominates the spectra. Their energy shift has successfully fitted in that temperature range by means of the Bose-Einstein expression instead of Varshni's relationship. Values for the parameters of both semi-empirical relations describing the energy shift are reported and compared with the literature. (orig.)

  15. Metamagnetism in Ce (Ga, Al) 2

    Indian Academy of Sciences (India)

    Strongly Correlated Electron Systems Volume 58 Issue 5-6 May-June 2002 pp 769-771 ... 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 ...

  16. Magnetotransport study on AlInN/(GaN)/AlN/GaN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Bayrakli, Aydin [Faculty of Engineering, Department of Physics Engineering, Hacettepe University, Ankara (Turkey); Undersecretariate for Defence Industries (SSM), Balgat, Ankara (Turkey); Arslan, Engin; Kazar, Oezguer; Cakmak, Hueseyin [Nanotechnology Research Center-NANOTAM, Bilkent University, Ankara (Turkey); Firat, Tezer; Oezcan, Sadan [Faculty of Engineering, Department of Physics Engineering, Hacettepe University, Ankara (Turkey); Oezbay, Ekmel [Nanotechnology Research Center-NANOTAM, Bilkent University, Ankara (Turkey); Departments of Physics and Electrical and Electronics Engineering, Bilkent University, Ankara (Turkey)

    2012-06-15

    We report the effect of a thin GaN (2 nm) interlayer on the magnetotransport properties of AlInN/AlN/GaN-based heterostructures. Two samples were prepared (Sample A: AlInN/AlN/GaN and sample B: AlInN/GaN/AlN/GaN). Van der Pauw and Hall measurements were performed in the 1.9-300 K temperature range. While the Hall mobilities were similar at room temperature (RT), sample B had nearly twice as large Hall mobility as sample A at the lowest temperature; 679 and 889 cm{sup 2}/Vs at RT and 1460 and 3082 cm{sup 2}/Vs at 1.9 K for samples A and B. At 1.9-10 K, the longitudinal magnetoresistance was measured up to 9 T, in turn revealing Shubnikov-de Haas (SdH) oscillations. The carrier concentration, effective mass and quantum mobility of the two-dimensional electron gas (2DEG) were determined from SdH oscillations. At 1.9 K, the 2DEG concentration of sample B was nearly seven times larger than of sample A (1.67 x 10{sup 13}/cm{sup 2} vs. 0.24 x 10{sup 13}/cm{sup 2}). On the contrary, the quantum mobility was changed adversely nearly three times (sample B 2500 cm{sup 2}/Vs and sample A 970 cm{sup 2}/Vs). The increase of the 2DEG concentration was attributed to the existence of the GaN interlayer, which has strengthened the spontaneous polarization difference between the AlInN and GaN layers of the heterostructure. Hence, the stronger electric field at the 2DEG region bent the conduction band profile downwards and consequently the quantum mobility decreased due to the increased interface roughness scattering. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Durability testing of the high-capacity GA-4/GA-9 trailer

    International Nuclear Information System (INIS)

    Zimmer, A.

    1993-01-01

    General Atomics (GA) is under contract to the US Department of Energy (DOE), Idaho Field Office, to develop two legal-weight truck from-reactor spent-fuel shipping casks with trailers. GA is developing these high capacity transport systems to support the Office of Civilian Radioactive Waste Management's (OCRWM) mission to transport spent fuel from reactors to a permanent disposal site. GA's goal is to maximize the number of fuel assemblies that the transport system can safely carry. The GA-4 Cask is being designed to transport four pressurized-water-reactor (PWR) spent-fuel assemblies, and the GA-9 Cask is being designed to transport nine boiling-water-reactor (BWR) spent-fuel assemblies. The use of these high-capacity transport systems will have a large benefit to-public safety since the number of legal-weight truck shipments will be reduced by at least a factor of four over existing spent-fuel shipping cask systems. Achieving these capacities requires that the weight of each component of the transport system. i.e., cask, trailer and tractor, be minimized. The weight of the trailer is of particular importance. With a high load-to-weight ratio, the durability and reliability of the trailer become significant factors in the success of the transport system. In order to verify that the trailer design will meet the durability and performance requirements to safely transport spent-fuel, GA has planned an extensive testing program. The testing program includes non-destructive examination (NDE) of the trailer welds, operational testing, a static load test, an over-the-road performance test, and a test to verify the durability of the trailer up to its 1,000,000-mile design life. Since a prototype cask will not be available for the testing, GA designed and built a dummy payload that simulates the correct weight distribution and approximates the dynamic response of the prototype cask

  18. 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.

  19. Unintentional doping in GaN.

    Science.gov (United States)

    Zhu, Tongtong; Oliver, Rachel A

    2012-07-21

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

  20. GaAsSb/InAs/(In)GaAs type II quantum dots for solar cell applications

    Czech Academy of Sciences Publication Activity Database

    Vyskočil, Jan; Hospodková, Alice; Petříček, Otto; Pangrác, Jiří; Zíková, Markéta; Oswald, Jiří; Vetushka, Aliaksi

    2017-01-01

    Roč. 464, Apr (2017), s. 64-68 ISSN 0022-0248 R&D Projects: GA ČR(CZ) GP14-21285P; GA MŠk LO1603 Institutional support: RVO:68378271 Keywords : InAs * GaAsSb * InGaAs * quantum dot * solar cells Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

  1. InGaN/GaN Structures: Effect of the quantum well number on the cathodoluminescent properties

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Hubáček, Tomáš; Oswald, Jiří; Pangrác, Jiří; Kuldová, Karla; Hývl, Matěj; Dominec, Filip; Ledoux, G.; Dujardin, C.

    (2017), s. 1-5, č. článku 1700464. ISSN 0370-1972 R&D Projects: GA MŠk LM2015087; GA MŠk(CZ) LO1603; GA ČR GA16-11769S EU Projects: European Commission(XE) 690599 - ASCIMAT Institutional support: RVO:68378271 Keywords : MOVPE * nitrides * scintillator * quantum well * cathodoluminescence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.674, year: 2016

  2. Mn-doped Ga(As,P) and (Al,Ga)As ferromagnetic semiconductors: electronic structure calculations

    Czech Academy of Sciences Publication Activity Database

    Mašek, Jan; Kudrnovský, Josef; Máca, František; Sinova, J.; MacDonald, A. H.; Champion, R.P.; Gallagher, B. L.; Jungwirth, Tomáš

    2007-01-01

    Roč. 75, č. 4 (2007), 045202/1-045202/6 ISSN 1098-0121 R&D Projects: GA ČR GA202/05/0575; GA ČR GA202/04/0583 Institutional research plan: CEZ:AV0Z10100521; CEZ:AV0Z10100520 Keywords : ferromagnetic semiconductors * electronic structure calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.172, year: 2007

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

    KAUST Repository

    Majid, Mohammed Abdul

    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.

  4. Effect of neutron irradiation on characteristics of power ІnGaN/GaN light-emitting diodes

    Directory of Open Access Journals (Sweden)

    A. I. Vlasenko

    2015-12-01

    Full Text Available Effect of the reactor fast neutron flux (E = 2 MeV, Ф = 2⋅1014 n/cm2 on the current-voltage, capacitance-voltage characteristics, the electroluminescence intensity of power ІnGaN/GaN LEDs on the SіC and AuSn/Si substrates are studied. It was revealed that radiation hardness of InGaN/GaN heterostructures depend on the substrate.

  5. Multilayered InGaN/GaN structure vs. single InGaN layer for solar cell applications: A comparative study

    International Nuclear Information System (INIS)

    El Gmili, Y.; Orsal, G.; Pantzas, K.; Moudakir, T.; Sundaram, S.; Patriarche, G.; Hester, J.; Ahaitouf, A.; Salvestrini, J.P.; Ougazzaden, A.

    2013-01-01

    We report a comparison of the morphological, structural and optical properties of both InGaN single-layer and multilayered structures, the latter consisting of periodic thin GaN interlayers inserted during InGaN growth. It is shown that such a structure suppresses the In concentration fluctuations and corresponding different states of strain relaxation with depth, both detrimental to solar cell applications. Measurements performed by X-ray diffraction, cathodoluminescence and photoluminescence demonstrate that this multilayer growth is a promising approach to increase both the InGaN layer total thickness and In content in InGaN epilayers. As an example, single-phase 120 nm thick InGaN with 14.3% In content is obtained and found to possess high structural quality

  6. 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.

  7. GaSb/GaP compliant interface for high electron mobility AlSb/InAs heterostructures on (001) GaP

    International Nuclear Information System (INIS)

    El Kazzi, S.; Desplanque, L.; Coinon, C.; Wallart, X.; Wang, Y.; Ruterana, P.

    2010-01-01

    We report on the epitaxial growth of an AlSb/InAs heterostructure on a (001) GaP substrate. We investigate the conditions for the most efficient relaxation of GaSb islands on GaP. In particular, we show that the GaP surface treatment and the growth temperature are crucial for the formation of a two-dimensional periodic array of 90 deg. misfit dislocations at the episubstrate interface. With this relaxation process, an AlSb/InAs heterostructure exhibiting a room temperature mobility of 25 500 cm 2 V -1 s -1 on GaP is demonstrated. This result paves the way to the integration of Sb-based devices on Si substrates through the use of GaP/Si templates.

  8. Propriétés électriques d'hétérostructures a-GaAs/c-GaAs(n) et de structures de type MIS a-GaAsN/c-GaAs(n)

    Science.gov (United States)

    Aguir, K.; Fennouh, A.; Carchano, H.; Lollman, D.

    1995-10-01

    Heterojunctions were fabricated by deposit of amorphous GaAs and GaAsN on c-GaAs. I(V) and C(V) measurements were performed to determine electrical properties of these structures. The a-GaAs/c-GaAs(n) heterojunctions present a p-n junction like behaviour. The characteristics of the a-GaAsN/c-GaAs(n) heterojunctions present a MIS like structure behaviour with some imperfections. A fixed positive charge was detected and a density of interface states of about 10^{11} eV^{-1}cm^{-2} was evaluated. L'étude porte sur des couches minces de GaAs et de GaAsN amorphes déposées par pulvérisation cathodique RF réactive sur des substrats de GaAs cristallin. Les caractéristiques électriques I(V) et C(V) ont été mesurées. Les hétérojonctions a-GaAs/c-GaAs(n) présentent un effet redresseur. Cet effet laisse place à une caractéristique symétrique avec une forte atténuation de l'intensité du courant pour les structures a-GaAsN/cGaAs(n). Les structures réalisées ont alors un comportement semblable à celui d'une structure MIS imparfaite. L'existence d'une charge positive fixe dans le a-GaAsN a été mise en évidence. La densité des états d'interface au milieu de la bande interdite est évaluée à quelques 10^{11} cm^{-2}eV^{-1}.

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

    International Nuclear Information System (INIS)

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

    2015-01-01

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

  10. Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

    Science.gov (United States)

    Grady, R.; Bayram, C.

    2017-07-01

    In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al X Ga(1-X)N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al X Ga(1-X)N/GaN heterojunction is formed through intentional δ-doping part of the Al X Ga(1-X)N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al X Ga(1-X)N barrier; δ-doping location (within the Al X Ga(1-X)N barrier), δ-doped Al X Ga(1-X)N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al X Ga(1-X)N barrier results in a normally-off behavior whereas Al X Ga(1-X)N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology.

  11. Isolating GaSb Membranes Grown Metamorphically on GaAs Substrates Using Highly Selective Substrate Removal Etch Processes

    Science.gov (United States)

    Renteria, E. J.; Muniz, A. J.; Addamane, S. J.; Shima, D. M.; Hains, C. P.; Balakrishnan, G.

    2015-05-01

    The etch rates of NH4OH:H2O2 and C6H8O7:H2O2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH4OH:H2O2 solution has a greater etch rate differential for the GaSb/GaAs material system than C6H8O7:H2O2 solution. The selectivity of NH4OH:H2O2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11,000 ± 2000, whereas that of C6H8O7:H2O2 has been measured up to 143 ± 2. The etch contrast has been verified by isolating 2- μm-thick GaSb epilayers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high- resolution x-ray diffraction and atomic force microscopy.

  12. Fabrication and improvement of nanopillar InGaN/GaN light-emitting diodes using nanosphere lithography

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Ou, Yiyu; Zhan, Teng

    2015-01-01

    Surface-patterning technologies have enabled the improvement of currently existinglight-emitting diodes (LEDs) and can be used to overcome the issue of low quantum efficiency ofgreen GaN-based LEDs. We have applied nanosphere lithography to fabricate nanopillars onInGaN∕GaN quantum-well LEDs. By ...

  13. Influence of strain relaxation on the optical properties of InGaN/GaN multiple quantum well nanorods

    International Nuclear Information System (INIS)

    Wang, Q; Bai, J; Gong, Y P; Wang, T

    2011-01-01

    Optical investigation has been carried out on InGaN/GaN nanorod structures with different indium compositions, fabricated from InGaN/GaN multiple quantum well (MQW) epitaxial wafers using a self-organized nickel nano-mask and subsequent dry etching techniques. In comparison with the as-grown InGaN/GaN MQWs, the internal quantum efficiencies of the nanorods are significantly improved, in particular, for the green InGaN/GaN nanorods with a high indium composition, the internal quantum efficiency is enhanced by a factor of 8, much larger than the enhancement factor of 3.4 for the blue InGaN/GaN nanorods. X-ray reciprocal space mapping (RSM) measurements have been performed in order to quantitatively evaluate the stain relaxation in the nanorods, demonstrating that the majority of strain in InGaN/GaN MQWs can be relaxed as a result of fabrication into nanorods. The excitation-power-dependent photoluminescence measurements have also clearly shown that a significant reduction in the strain-induced quantum confined stark effect has occurred to the nanorod structures.

  14. 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.

  15. GaAsSb/InGaAs heterojunction tunnel field-effect transistors with a heterogeneous channel

    Science.gov (United States)

    Lin, Chun-Wei; Chen, Hung-Ru; Yu, Yu-Tzu; Hsin, Yue-Ming

    2018-03-01

    This study presents a new structure to improve off-state current and ambipolar conduction in GaAsSb/InGaAs heterojunction tunnel field-effect transistors (HTFET). A GaAsSb/InGaAs heterogeneous channel was proposed to form p-GaAsSb/i-InGaAs junction at the source side and i-GaAsSb/n-InGaAs junction at the drain side. In the off-state bias condition, the band offsets of GaAsSb/InGaAs in the channel can prevent electrons tunneling to the drain side to reduce the leakage current and ambipolar conduction. Through simulation, heterogeneous channel HTFETs demonstrate that the off-state current can be reduced by four orders of magnitude and still demonstrate a high on-state current compared with GaAsSb/InGaAs HTFETs. As a result, the proposed heterogeneous channel HTFET exhibits suppressed ambipolar conduction even when the drain doping is as high as 1 × 1019 cm‑3.

  16. Characterization and technology of AlGaAs/GaAs phototransistor with double delta-doped base

    International Nuclear Information System (INIS)

    Radziewicz, D.; Sciana, B.; Pucicki, D.; Zborowska-Lindert, I.; Kovac, J.; Skriniarova, J.; Vincze, A.

    2011-01-01

    This work describes the fabrication and measurements of n-p-n AlGaAs/GaAs heterojunction phototransistor with double Zn-delta-doped 50 nm - thick GaAs base region. Parameters of the particular transistor epilayers were optimized by computer simulations using Silvaco Atlas program. (authors)

  17. 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

  18. Growth of GaP and AlGaP on GaP(1 1 1)B using gas-source molecular-beam-epitaxy

    Science.gov (United States)

    Barakat, J.-B.; Dadgostar, S.; Hestroffer, K.; Bierwagen, O.; Trampert, A.; Hatami, F.

    2017-11-01

    We present an initial study of the influence of the growth parameters on the surface morphology and on the interface quality of homoepitaxial GaP(1 1 1) and heteroepitaxial GaP/AlGaP(1 1 1) grown on GaP(1 1 1)B substrates using Gas-Source Molecular Beam Epitaxy (GSMBE). Three different surface reconstructions are identified in the RHEED patterns during the growth runs. The Root Mean Square (RMS) surface roughness measured post-growth by AFM ranges from 3 to 10 nm over 10 × 10 μm2 areas, for a film thickness of 100-600 nm. The results of 2θ-ω XRD scans on (1 1 1) and (3 1 1) planes reveal a stacking disorder in the AlGaP layer and further XRD phi-scan measurements on GaP (3 1 1) show strong peaks with 3-fold rotational symmetry and additional of 3-fold weak peaks indicating only a negligible fraction of the twinned crystal orientation in the substrate. TEM images of these samples show a smooth interface between the AlGaP layer and GaP substrate, and reveal the presence of a high density of extended defects such as stacking faults, twinning and dislocations lines in AlGaP layer whereas the GaP layer appears as pure Zinc-Blende. Further TEM analysis reveals composition and local strain variations for GaP/AlGaP samples associated with an undulated surface.

  19. Synthesis of GaAs quantum dots on Si-layers on AlGaAs films grown on GaAs(100) substrates

    International Nuclear Information System (INIS)

    Mendez-Garcia, V. H.; Zamora-Peredo, L.; Saucedo-Zeni, N.

    2002-01-01

    In this work we report a novel method for obtaining GaAs quantum dots by molecular beam epitaxy (MBE) on an AlGaAs underlying film. We propose to use a Si monolayer (ML) grown on AlGaAs, in order to induce a 3D nucleation during the GaAs overgrowth. The samples were prepared in a Riber 32P MBE system employing undoped Si-GaAs(100) substrates. First, a 500 nm thick layer of Al x Ga 1-x As was grown with a nominal concentration x=0.35. Several samples were grown in order to analyze the effects of changing the Si interlayer thickness, and the amount of GaAs overgrowth, on the final structures. Previous to the Si-exposure, the AlGaAs presented a (1x3) surface reconstruction which gradually turned to a (3x1) structure when the Si-thickness was 1 ML, as observed in the reflection high-energy electron diffraction (RHEED) patterns. When the GaAs overgrowth started on this surface, transmission RHEED spots appeared and showed a considerable increase in intensity until reaching a maximum. This behavior is typical from a 3D island growth. If the GaAs overgrowth continues, the initial streaky RHEED patterns recovered indicating a 2D-growth. Thus, we prepared a sample stopping the GaAs overgrowth at the time when the diffraction 3D spot reached the maximum intensity, equivalent to 2ML of GaAs. The sample surface was analyzed in air by atomic force microscopy (AFM). Islands of 1.5 nm-height and 20x20 nm of base were clearly observed, these dimensions are suitable for applications in quantum dots. (Authors)

  20. Properties of (Ga,Mn)As codoped with Li

    Science.gov (United States)

    Miyakozawa, Shohei; Chen, Lin; Matsukura, Fumihiro; Ohno, Hideo

    2014-06-01

    We grow Li codoped (Ga,Mn)As layers with nominal Mn composition up to 0.15 by molecular beam epitaxy. The layers before and after annealing are characterized by x-ray diffraction, transport, magnetization, and ferromagnetic resonance measurements. The codoping with Li reduces the lattice constant and electrical resistivity of (Ga,Mn)As after annealing. We find that (Ga,Mn)As:Li takes similar Curie temperature to that of (Ga,Mn)As, but with pronounced magnetic moments and in-plane magnetic anisotropy, indicating that the Li codoping has nontrivial effects on the magnetic properties of (Ga,Mn)As.

  1. Recovery of electron irradiated V-Ga alloys

    International Nuclear Information System (INIS)

    Leguey, T.; Monge, M.; Pareja, R.; Hodgson, E.R.

    2000-01-01

    The recovery characteristics of electron-irradiated V-Ga alloys with 1.2 and 4.6 at.% Ga have been investigated by positron annihilation spectroscopy (PAS). It is found that vacancies created by electron irradiation become mobile in these alloys at ∼293 K. This temperature is noticeably lower than that in pure V and V-Ti alloys. The vacancies aggregate into microvoids in V-4.6Ga, but do not in V-1.2Ga. The results indicate that vacancies are bound to Ga-interstitial impurity pairs

  2. 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.

  3. Resonant Raman characterization of InAlGaN/GaN heterostructures

    International Nuclear Information System (INIS)

    Cros, A.; Cantarero, A.; Pelekanos, N.T.; Georgakilas, A.; Pomeroy, J.; Kuball, M.

    2006-01-01

    InAlGaN/GaN heterostructures and thin films with In composition ranging from 0.03 to 0.1 are characterized by means of Raman scattering excited at various energies in the ultra violet range, tuning the laser excitation energy through the band gap of In x Al y Ga 1-x-y N. It is shown that the addition of In to the Al y Ga 1-y N alloy diminishes considerably the vibration energy of the A 1 (LO) phonon mode. The phonon line is asymmetric on the low energy side, and the asymmetry increases with In content, while the main peak shifts to lower energies. A shift of the phonon energy has also been observed when the excitation energy is close to the absorption edge of the In x Al y Ga 1-x-y N layer. The nature of this shift is discussed in relation with intrinsic and extrinsic inhomogeneities in the quaternary alloy. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Resonant Raman characterization of InAlGaN/GaN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Cros, A.; Cantarero, A. [Institut de Ciencia dels Materials, Universitat de Valencia, 46071 Valencia (Spain); Pelekanos, N.T.; Georgakilas, A. [Microelectronics Research Group, FORTH/IESL and University of Crete, P.O. Box 1527, 71110 Heraklion, Crete (Greece); Pomeroy, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)

    2006-06-15

    InAlGaN/GaN heterostructures and thin films with In composition ranging from 0.03 to 0.1 are characterized by means of Raman scattering excited at various energies in the ultra violet range, tuning the laser excitation energy through the band gap of In{sub x}Al{sub y}Ga{sub 1-x-y}N. It is shown that the addition of In to the Al{sub y}Ga{sub 1-y}N alloy diminishes considerably the vibration energy of the A{sub 1}(LO) phonon mode. The phonon line is asymmetric on the low energy side, and the asymmetry increases with In content, while the main peak shifts to lower energies. A shift of the phonon energy has also been observed when the excitation energy is close to the absorption edge of the In{sub x}Al{sub y}Ga{sub 1-x-y}N layer. The nature of this shift is discussed in relation with intrinsic and extrinsic inhomogeneities in the quaternary alloy. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Optical AND operation in n-AlGaAs/GaAs heterojunction field effect transistor

    Science.gov (United States)

    Kawazu, T.; Noda, T.; Sakuma, Y.

    2018-02-01

    The near-infrared photoresponses of an n-AlGaAs/GaAs heterojunction field-effect transistor (FET) were investigated for the irradiation of two lights: (A) a laser beam with the energy above the Schottky-barrier which uniformly illuminates the gate region and (B) a laser beam with the energy above the GaAs bandgap which locally illuminates the ungate region. We measured a lateral photocurrent in the two dimensional electron gas (2DEG) channel at the n-AlGaAs/GaAs heterojunction and found that the FET acts as an optical AND element; the lateral photocurrent is generated only when both the light A and B simultaneously illuminate the FET. The lateral current flows from left to right when the left side of the FET is illuminated with the light B, while the right side irradiation leads to the current from right to left. The experimental findings are well explained by a theory based on the current-continuity equation, where the lateral current in the 2DEG channel is driven by an asymmetric electron transfer resulting from the simultaneous irradiation of the light A and B.

  6. 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...

  7. 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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Strain analysis of InGaN/GaN multi quantum well LED structures

    Energy Technology Data Exchange (ETDEWEB)

    Sebnem Cetin, S.; Kemal Oeztuerk, M.; Oezcelik, S. [Department of Physics, Science Faculty, Gazi University, Ankara (Turkey); Photonics Application and Research Center, Gazi University, Ankara (Turkey); Oezbay, E. [Nanotechnology Research Center, Department of Physics, Department of Electrical and Electronics Engineering, Bilkent, Ankara (Turkey)

    2012-08-15

    Five period InGaN/GaN multi quantum well (MQW) light emitting diode (LED) structures were grown by a metalorganic chemical vapor deposition (MOCVD) system on c-plane sapphire. The structural characteristics as a strain-stress analysis of hexagonal epilayers MQWs were determined by using nondestructive high resolution x-ray diffraction (HRXRD) in detail. The strain/stress analysis in AlN, GaN, and InGaN thin films with a variation of the In molar fraction in the InGaN well layers was conducted based on the precise measurement of the lattice parameters. The a- and c-lattice parameters of the structures were calculated from the peak positions obtained by rocking the theta axis at the vicinity of the symmetric and asymmetric plane reflection angles, followed by the in-plane and out-of-plane strains. The biaxial and hydrostatic components of the strain were extracted from the obtained a- and c-direction strains values. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Al composition dependent structural and electrical properties of InAlGaN/GaN heterostructures

    International Nuclear Information System (INIS)

    Nagarajan, S; Kumar, M Senthil; Choi, Y J; Chung, S J; Hong, C-H; Suh, E-K

    2007-01-01

    InAlGaN/GaN heterostructures with various Al compositions have been grown on sapphire substrate using the metal organic chemical vapour deposition technique. The solid-to-gas phase ratio indicates a high Al incorporation efficiency. Atomic force microscopy reveals a smooth surface with the formation of hexagonal pits. The size and the density of the hexagonal pits increase with increasing Al mole fraction. The Hall effect and the capacitance-voltage (C-V) studies show the formation of a two-dimensional electron gas (2DEG) at the InAlGaN/GaN interface. A relatively higher Hall sheet carrier density compared with the 2DEG density estimated from the C-V profile indicates parallel conduction via the underlying GaN layer. It is observed that the 2DEG density decreases as a function of the Al composition and these results are discussed based on the increasing depth of the hexagonal pit and the background donor density

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

    International Nuclear Information System (INIS)

    Krueger, David

    2009-01-01

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  11. Quantum well intermixing and radiation effects in InGaN/GaN multi quantum wells

    Science.gov (United States)

    Lorenz, K.; Redondo-Cubero, A.; Lourenço, M. B.; Sequeira, M. C.; Peres, M.; Freitas, A.; Alves, L. C.; Alves, E.; Leitão, M. P.; Rodrigues, J.; Ben Sedrine, N.; Correia, M. R.; Monteiro, T.

    2016-02-01

    Compositional grading of InGaN/GaN multi quantum wells (QWs) was proposed to mitigate polarization effects and Auger losses in InGaN-based light emitting diodes [K. P. O'Donnell et al., Phys. Status Solidi RRL 6 (2012) 49]. In this paper we are reviewing our recent attempts on achieving such gradient via quantum well intermixing. Annealing up to 1250 °C resulted in negligible interdiffusion of QWs and barriers revealing a surprising thermal stability well above the typical MOCVD growth temperatures. For annealing at 1400 °C results suggest a decomposition of the QWs in regions with high and low InN content. The defect formation upon nitrogen implantation was studied in detail. Despite strong dynamic annealing effects, which keep structural damage low, the created defects strongly quench the QW luminescence even for low implantation fluences. This degradation could not be reversed during thermal annealing and is hampering the use of implantation induced quantum well intermixing in InGaN/GaN structures.

  12. InGaAs-GaAs strained layer quantum well heterostructure lasers

    Science.gov (United States)

    Coleman, J. J.; York, P. K.; Beernink, K. J.; Waters, R. G.

    1990-05-01

    InGaAs-GaAs strained layer quantum well heterostructure lasers offer availability of emission wavelengths in the range of 0.9-1.1 micron, otherwise largely inaccessible with semiconductor diode lasers. Here, InGaAs-GaAs strained layer lasers and laser arrays grown by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) are described. The growth conditions for preparing these strained layer structures by MOCVD are presented, and time zero characterization of oxide defined stripe broad area lasers is outlined as a function of InGaAs layer composition and thickness, relative to the critical thickness. Various structures, grown throughout the 0.9-1.1-micron wavelength range and having In mole fractions from x = 0 - 0.50, are shown to have low broad area threshold current densities (Jth less than 200 A/sq cm) and other characteristics of unstrained quantum well heterostructure lasers. Recent results indicating highly reliable CW operation of oxide stripe strained quantum well heterostructure lasers are reviewed.

  13. Emission wavelength red-shift by using ;semi-bulk; InGaN buffer layer in InGaN/InGaN multiple-quantum-well

    Science.gov (United States)

    Alam, Saiful; Sundaram, Suresh; Li, Xin; El Gmili, Youssef; Elouneg-Jamroz, Miryam; Robin, Ivan Christophe; Patriarche, Gilles; Salvestrini, Jean-Paul; Voss, Paul L.; Ougazzaden, Abdallah

    2017-12-01

    We report an elongation of emission wavelength by inserting a ∼70 nm thick high quality semi-bulk (SB) InyGa1-yN buffer layer underneath the InxGa1-xN/InyGa1-yN (x > y) multi-quantum-well (MQW).While the MQW structure without the InGaN SB buffer is fully strained on the n-GaN template, the MQW structure with the buffer has ∼15% relaxation. This small relaxation along with slight compositional pulling induced well thickness increase of MQW is believed to be the reason for the red-shift of emission wavelength. In addition, the SB InGaN buffer acts as an electron reservoir and also helps to reduce the Quantum Confined Stark Effect (QCSE) and thus increase the emission intensity. In this way, by avoiding fully relaxed buffer induced material degradation, a longer emission wavelength can be achieved by just using InGaN SB buffer while keeping all other growth conditions the same as the reference structure. Thus, a reasonably thick fully strained or very little relaxed InGaN buffer, which is realized by ;semi-bulk; approach to maintain good InGaN material quality, can be beneficial for realizing LEDs, grown on top of this buffer, emitting in the blue to cyan to green regime without using excess indium (In).

  14. Calorimetric measurement of the intermetallic compounds Cr{sub 3}Ga and CrGa{sub 4} and thermodynamic assessment of the (Cr-Ga) system

    Energy Technology Data Exchange (ETDEWEB)

    Belgacem-Bouzida, A. [Laboratoire d' etude Physico-Chimique des Materiaux, Departement de Physique, Faculte des Sciences, Universite de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria)]. E-mail: bouzida.aissa@caramail.com; Djaballah, Y. [Laboratoire d' etude Physico-Chimique des Materiaux, Departement de Physique, Faculte des Sciences, Universite de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria)]. E-mail: djaballah.y@caramail.com; Notin, M. [Laboratoire de Chimie du Solide Mineral, Faculte des Sciences, Universite Henri Poincare Nancy I, B.P. 239, F-54506 Vandoeuvre-les-Nancy Cedex (France)

    2005-07-19

    The enthalpies of formation have been measured for the two binary compounds Cr{sub 3}Ga and CrGa{sub 4} richest and least rich in chromium of the (Cr-Ga) system. We have used two types of calorimetric method: direct reaction and progressive precipitation calorimetry. Thermodynamic optimizations for the binary (Cr-Ga) system using Calphad method are investigated and a set of parameters describing the Gibbs energy of the different phases is given, the phase diagram has been also calculated and presented.

  15. White emission by self-regulated growth of InGaN/GaN quantum wells on in situ self-organized faceted n-GaN islands

    International Nuclear Information System (INIS)

    Fang Zhilai

    2011-01-01

    The in situ self-organization of three-dimensional n-GaN islands of distinct sidewall faceting was realized by initial low V/III ratio growth under high reactor pressure followed by variations of the V/III ratio and reactor pressure. The naturally formed faceted islands with top and sidewall facets of various specific polar angles may serve as an ideal template for self-regulated growth of the InGaN/GaN multiple quantum wells (MQWs), i.e. the growth behavior is specific polar angle dependent. Further, the growth behavior and luminescence properties of the InGaN/GaN MQWs on various facets of different specific polar angles are directly compared and discussed. Tetrachromatic white emissions (blue, cyan, green, and red) from single-chip phosphor-free InGaN/GaN MQWs are realized by color tuning through island shaping, shape variations, and self-regulated growth of the InGaN/GaN MQWs.

  16. 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.

  17. Reactive codoping of GaAlInP compound semiconductors

    Science.gov (United States)

    Hanna, Mark Cooper [Boulder, CO; Reedy, Robert [Golden, CO

    2008-02-12

    A GaAlInP compound semiconductor and a method of producing a GaAlInP compound semiconductor are provided. The apparatus and method comprises a GaAs crystal substrate in a metal organic vapor deposition reactor. Al, Ga, In vapors are prepared by thermally decomposing organometallic compounds. P vapors are prepared by thermally decomposing phospine gas, group II vapors are prepared by thermally decomposing an organometallic group IIA or IIB compound. Group VIB vapors are prepared by thermally decomposing a gaseous compound of group VIB. The Al, Ga, In, P, group II, and group VIB vapors grow a GaAlInP crystal doped with group IIA or IIB and group VIB elements on the substrate wherein the group IIA or IIB and a group VIB vapors produced a codoped GaAlInP compound semiconductor with a group IIA or IIB element serving as a p-type dopant having low group II atomic diffusion.

  18. 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).

  19. [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.

  20. In0.5Ga0.5As self-assembled quantum dots on GaP/Si

    Science.gov (United States)

    Song, Yuncheng

    This thesis focuses on demonstrating monolithic integration of III-V optoelectronic devices with Si by means of GaP on Si templates. Though high-quality epitaxial GaP on Si has been developed, GaP itself is not useful for most photonic applications due to its indirect bandgap. Historically, deep level impurities have allowed the realization of GaP light emitting diodes (LEDs), but these devices had low efficiency and the gain was insufficient for laser action. The lattice matched dilute nitride material Ga(NAsP) is an option for direct bandgap material on GaP, but N-related point defects make the material challenging to grow. InxGa1--xAs self-assembled quantum dots (SAQDs) grown on GaP offer another path to integration of direct-bandgap III-V material onto Si. The use of InxGa 1--xAs allows access to a wide range of bulk bandgaps (1.42-0.36 eV for x=0-1) and the potential for great flexibility in emission wavelength from visible to near-infrared. While chip-to-chip optical communication remains a goal, a range of sensing applications could also benefit from the direction integration of Si electronics with light sources. Sample growth was carried out by solid-source molecular beam epitaxy (MBE) using conditions similar to those used for the well-known case of InAs/GaAs SAQDs. SAQD formation was through Stranski--Krastanov (S-K) growth mode, as evidenced by reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM). Cross-sectional transmission microscopy (XTEM) with several two-beam conditions confirmed that both the SAQDs and the GaP cap layer were free of dislocations. Intense photoluminescence was visible from the quantum dots at both 80 K and room temperature to the unaided eye in ambient lighting. The photoluminescence results also showed that emission energy can be controlled by varying the In0.5Ga0.5As deposition thickness. The commercial availability of high-quality GaP/Si templates enabled research on In0.5Ga0.5As/Ga

  1. Piezoelectric potential in axial (In,Ga)N/GaN nanowire heterostructures

    Science.gov (United States)

    Kaganer, Vladimir M.; Marquardt, Oliver; Brandt, Oliver

    2016-04-01

    We derive analytic expressions for the built-in electrostatic potential arising from piezo- and pyroelectricity in a cylindrical axial In x Ga{}1-xN/GaN nanowire (NW) heterostructure. Our simulations show that, for sufficiently thin NWs, a significant reduction of the built-in potential is reached in comparison to the planar heterostructure of the same In content, thickness, and orientation. This specific feature of axial NW heterostructures makes the aspect ratio of the embedded In x Ga{}1-xN disks an important additional degree of freedom to control the recombination energies. We furthermore show that the magnitude of the polarization potential decreases again above a certain value of the aspect ratio and that the extrema of the potential move from the central axis of the NW towards the side facets when the thickness of the disk is increased.

  2. Graphene in ohmic contact for both n-GaN and p-GaN

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, Haijian; Liu, Zhenghui; Shi, Lin; Xu, Gengzhao; Fan, Yingmin; Huang, Zengli [Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); Wang, Jianfeng; Ren, Guoqiang; Xu, Ke, E-mail: kxu2006@sinano.ac.cn [Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); Suzhou Nanowin Science and Technology Co., Ltd., Suzhou 215123 (China)

    2014-05-26

    The wrinkles of single layer graphene contacted with either n-GaN or p-GaN were found both forming ohmic contacts investigated by conductive atomic force microscopy. The local I–V results show that some of the graphene wrinkles act as high-conductive channels and exhibiting ohmic behaviors compared with the flat regions with Schottky characteristics. We have studied the effects of the graphene wrinkles using density-functional-theory calculations. It is found that the standing and folded wrinkles with zigzag or armchair directions have a tendency to decrease or increase the local work function, respectively, pushing the local Fermi level towards n- or p-type GaN and thus improving the transport properties. These results can benefit recent topical researches and applications for graphene as electrode material integrated in various semiconductor devices.

  3. Structural characterisation of GaAlN/GaN HEMT heterostructures

    International Nuclear Information System (INIS)

    Sarazin, N.; Durand, O.; Magis, M.; Di Forte Poisson, M.-A.; Di Persio, J.

    2006-01-01

    (GaN/GaAlN/GaN)//Al 2 O 3 (00.1) HEMT heterostructures have been studied by X-ray scattering techniques, transmission electron microscopy and atomic force microscopy. X-ray reflectometry has been used to determine with a high accuracy both the individual layer thicknesses and the interfacial roughness, in spite of the weak electronic density contrast between layers. From the Fourier inversion method and using a simulation software, the roughness of the interface corresponding to the two-dimensional electron gas location has been determined equal to 0.5 nm. Both high resolution X-ray diffraction and transmission electron microscopy experiments have shown the excellent crystallinity of the heterostructures. Finally, the surface morphology has been inferred using atomic force microscopy experiments

  4. 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.

  5. Optical and structural properties of MOVPE-grown GaInSb/GaSb quantum wells

    International Nuclear Information System (INIS)

    Wagener, Viera; Olivier, E.J.; Botha, J.R.

    2009-01-01

    This paper reports on the optical and structural properties of strained type-I Ga 1-x In 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 1-x In 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 (∼2 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.

  6. 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.

  7. Photocapacitance study of type-II GaSb/GaAs quantum ring solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wagener, M. C.; Botha, J. R. [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth (South Africa); Carrington, P. J.; Krier, A. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom)

    2014-01-07

    In this study, the density of states associated with the localization of holes in GaSb/GaAs quantum rings are determined by the energy selective charging of the quantum ring distribution. The authors show, using conventional photocapacitance measurements, that the excess charge accumulated within the type-II nanostructures increases with increasing excitation energies for photon energies above 0.9 eV. Optical excitation between the localized hole states and the conduction band is therefore not limited to the Γ(k = 0) point, with pseudo-monochromatic light charging all states lying within the photon energy selected. The energy distribution of the quantum ring states could consequently be accurately related from the excitation dependence of the integrated photocapacitance. The resulting band of localized hole states is shown to be well described by a narrow distribution centered 407 meV above the GaAs valence band maximum.

  8. 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.)

  9. 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.

  10. 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.

  11. (In)GaSb/AlGaSb quantum wells grown on Si substrates

    International Nuclear Information System (INIS)

    Akahane, Kouichi; Yamamoto, Naokatsu; Gozu, Shin-ichiro; Ueta, Akio; Ohtani, Naoki

    2007-01-01

    We have successfully grown GaSb and InGaSb quantum wells (QW) on a Si(001) substrate, and evaluated their optical properties using photoluminescence (PL). The PL emissions from the QWs at room temperature were observed at around 1.55 μm, which is suitable for fiber optic communications systems. The measured ground state energy of each QW matched well with the theoretical value calculated by solving the Schroedinger equation for a finite potential QW. The temperature dependence of the PL intensity showed large activation energy (∼ 77.6 meV) from QW. The results indicated that the fabricated QW structure had a high crystalline quality, and the GaSb QW on Si for optical devices operating at temperatures higher than room temperature will be expected

  12. Materials for LiGA and LiGA-based microsystems

    International Nuclear Information System (INIS)

    Hormes, J.; Goettert, J.; Lian, K.; Desta, Y.; Jian, L.

    2003-01-01

    The LiGA technique that has been developed for the inexpensive mass fabrication of microdevices consists of three basic processes: X-ray lithography, electroforming and moulding. In each of these steps the properties of the used materials and the process parameters are strongly correlated to each other. Thus, optimizing processes requires detailed knowledge of the materials properties especially as the LiGA technique offers an extremely broad variety of materials (polymers, metals, alloys, ceramics) for the fabrication of three-dimensional microstructures. When it comes to specific applications of LiGA devices, it is often desirable to tailor the properties of materials and surfaces e.g. in respect to mechanical properties, optical properties, thermo- and electrochemical stability and biocompatibility. Again, a detailed knowledge of the properties of the various materials is crucial to optimize these tasks, keeping in mind that these properties on the microscale can differ from those of bulk materials

  13. Iron clustering in GaSe epilayers grown on GaAs(111)B

    International Nuclear Information System (INIS)

    Moraes, A R de; Mosca, D H; Mattoso, N; Guimaraes, J L; Klein, J J; Schreiner, W H; Souza, P E N de; Oliveira, A J A de; Vasconcellos, M A Z de; Demaille, D; Eddrief, M; Etgens, V H

    2006-01-01

    In this paper we report on the structural, morphological and magnetic properties of semiconducting GaSe epilayers, grown by molecular beam epitaxy, doped to different iron contents (ranging from 1 to 22 at.% Fe). Our results indicate that iron forms metallic Fe nanoparticles with diameters ranging from 1 to 20 nm embedded in the crystalline GaSe matrix. The Fe incorporation proceeds by segregation and agglomeration and induces a progressive disruption of the lamellar GaSe epilayers. The magnetization as a function of the temperature for zero-field cooling with the magnetic field parallel to the surface of the sample provides evidence of superparamagnetic behaviour of the nanoparticles. Cathodoluminescence experiments performed at room temperature reveal semiconducting behaviour even for samples with Fe concentrations as high as 20 at.%

  14. 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.

  15. Graphene in ohmic contact for both n-GaN and p-GaN

    International Nuclear Information System (INIS)

    Zhong, Haijian; Liu, Zhenghui; Shi, Lin; Xu, Gengzhao; Fan, Yingmin; Huang, Zengli; Wang, Jianfeng; Ren, Guoqiang; Xu, Ke

    2014-01-01

    The wrinkles of single layer graphene contacted with either n-GaN or p-GaN were found both forming ohmic contacts investigated by conductive atomic force microscopy. The local I–V results show that some of the graphene wrinkles act as high-conductive channels and exhibiting ohmic behaviors compared with the flat regions with Schottky characteristics. We have studied the effects of the graphene wrinkles using density-functional-theory calculations. It is found that the standing and folded wrinkles with zigzag or armchair directions have a tendency to decrease or increase the local work function, respectively, pushing the local Fermi level towards n- or p-type GaN and thus improving the transport properties. These results can benefit recent topical researches and applications for graphene as electrode material integrated in various semiconductor devices.

  16. 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.

  17. Molecular Beam Epitaxy of GaSb on GaAs Substrates with AlSb Buffer Layers

    International Nuclear Information System (INIS)

    Zhi-Qiang, Zhou; Ying-Qiang, Xu; Rui-Ting, Hao; Bao, Tang; Zheng-Wei, Ren; Zhi-Chuan, Niu

    2009-01-01

    We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using AlSb buffer layers. Optimization of AlSb growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of AlSb layers are found to be 450° C and 2.1 nm, respectively. A rms surface roughness of 0.67nm over 10 × 10 μm 2 is achieved as a 0.5μm GaSb film is grown under optimized conditions

  18. Photoelectrochemical studies of InGaN/GaN MQW photoanodes

    Science.gov (United States)

    Butson, Joshua; Reddy Narangari, Parvathala; Krishna Karuturi, Siva; Yew, Rowena; Lysevych, Mykhaylo; Tan, Hark Hoe; Jagadish, Chennupati

    2018-01-01

    The research interest in photoelectrochemical (PEC) water splitting is ever growing due to its potential to contribute towards clean and portable energy. However, the lack of low energy band gap materials with high photocorrosion resistance is the primary setback inhibiting this technology from commercialisation. The ternary alloy InGaN shows promise to meet the photoelectrode material requirements due to its high chemical stability and band gap tunability. The band gap of InGaN can be modulated from the UV to IR regions by adjusting the In concentration so as to absorb the maximum portion of the solar spectrum. This paper reports on the influence of In concentration on the PEC properties of planar and nanopillar (NP) InGaN/GaN multi-quantum well (MQW) photoanodes, where NPs were fabricated using a top-down approach. Results show that changing the In concentration, while having a minor effect on the PEC performance of planar MQWs, has an enormous impact on the PEC performance of NP MQWs, with large variations in the photocurrent density observed. Planar photoanodes containing MQWs generate marginally lower photocurrents compared to photoanodes without MQWs when illuminated with sunlight. NP MQWs with 30% In generated the highest photocurrent density of 1.6 mA cm-2, 4 times greater than that of its planar counterpart and 1.8 times greater than that of the NP photoanode with no MQWs. The InGaN/GaN MQWs also slightly influenced the onset potential of both the planar and NP photoanodes. Micro-photoluminescence, diffuse reflectance spectroscopy and IPCE measurements are used to explain these results.

  19. Gamma-gamma angular correlations in the 71 Ga and 69 Ga nuclei

    International Nuclear Information System (INIS)

    Bairrio Nuevo Junior, A.

    1975-01-01

    The directional correlations of v-transitions in 71 Ga and 69 Ga have been measured from the decay of 71 Z n and 69 Ge respectively using a Ge(Li)-NaI (f pound) gamma spectrometer. Spin assignments to the levels in Ga at 390(1/2), 487 (5/2 ) , 512(3/2 ) , 964(5/2 ) , 1107(7/2 ) , 1494(9/2*) and 2247 KeV(7/2 ), and 69 Ga at 318(1/2) , 574(5/2) , 872(3/2), 1106(5/2 , 3/2 ) , 1336(7/2 ) , and 1923 KeV(7/2) confirm the results of previous studies on these nuclei . The multipole mixing ratios 6(E2/M1) for several γ-transitions in both nuclei have been determined from the present angular correlation data. The results are: 6(121) - -0.2 * 6(142) * 0.04 - - 0.04, 6(386) = -0.003 - 0.014, 6(487) = 0.04 - 0.07, 5(512) - -0.14 - 0.10, 6(620) = 1.3 * j j and, 6(753) - 0.00 - 0.01 and 6(964) = 0.6 + Q 9 for transitions i n 71 Ga and 6(234) much greater than 0.28 - 0.04 or 0.08 - 0.02, 6(587) - -1.1 - 0.08, 6(1051) much greater than 0.0 - 0.10 and 6(1349) - 0.13 - 0.03 for transitions in 69 Ga . The experimental results are discussed in terms of various nuclear models which are applicable for the odd-A nuclei in this mass region. (author)

  20. Mercury(II) selective sensors based on AlGaN/GaN transistors.

    Science.gov (United States)

    Asadnia, Mohsen; Myers, Matthew; Akhavan, N D; O'Donnell, Kane; Umana-Membreno, Gilberto A; Mishra, U K; Nener, Brett; Baker, Murray; Parish, Giacinta

    2016-11-02

    This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg 2+ . This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg 2+ concentrations. At pH 2.8 in a 10 -2  M KNO 3 ion buffer, a detection limit below 10 -8  M and a linear response range between 10 -8  M-10 -4  M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10 -7  M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10 -7  M and 10 -6  M in 10 -2  M Cd(NO 3 ) 2 and 10 -2  M Pb(NO 3 ) 2 ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg 2+ solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices. Crown Copyright © 2016. Published by Elsevier B.V. All rights reserved.

  1. III-Nitrides growth and AlGaN/GaN heterostructures on ferroelectric materials

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kyoung-Keun [Georgia Institute of Technology, School of Electrical and Computer Engineering, 777 Atlantic Dr., Atlanta, GA 30332 (United States); Namkoong, Gon [Old Dominion University, Department of Electrical and Computer Engineering, Norfolk, VA 23529 (United States); Madison, Shannon M. [Georgia Institute of Technology, School of Electrical and Computer Engineering, 777 Atlantic Dr., Atlanta, GA 30332 (United States); Ralph, Stephen E. [Georgia Institute of Technology, School of Electrical and Computer Engineering, 777 Atlantic Dr., Atlanta, GA 30332 (United States); Doolittle, W. Alan [Georgia Institute of Technology, School of Electrical and Computer Engineering, 777 Atlantic Dr., Atlanta, GA 30332 (United States)]. E-mail: alan.doolittle@ece.gatech.edu; Losurdo, Maria [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, Department of Chemistry, University of Bari, via Orabona, 4 70126 Bari (Italy); Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, Department of Chemistry, University of Bari, via Orabona, 4 70126 Bari (Italy); Cho, Hyung Koun [Department of Materials Science and Engineering, Sung Kyun Kwan University, Suwon 440-746 (Korea, Republic of)

    2007-06-15

    The growth of III-nitrides on the ferroelectric materials lithium niobate (LN) and lithium tantalate (LT) via molecular beam epitaxy (MBE) using rf plasma source has been investigated. We have found that gallium nitride (GaN) epitaxial layers have a crystalline relationship with lithium niobate (tantalate) as follows: (0 0 0 1) GaN || (0 0 0 1) LN (LT) with [10-10] GaN || [11-20] LN (LT). The surface stability of LN and LT substrates has been monitored by in situ spectroscopic ellipsometry in the vacuum chamber. Three different temperature zones have been discerned; surface degas and loss of OH group (100-350 deg. C); surface segregation/accumulation of Li and O-species (400-700 deg. C); surface evaporation of O-species and Li desorption (over 750 deg. C). However, LT shows only surface degassing in the range of 100-800 deg. C. Therefore, congruent LN substrates were chemically unstable at the growth temperature of 550-650 deg. C, and therefore developed an additional phase of Li-deficient lithium niobate (LiNb{sub 3}O{sub 8}) along with lithium niobate (LiNbO{sub 3}), confirmed by X-ray diffraction. On the other hand, LT showed better chemical stability at these temperatures, with no additional phase development. The structural quality of GaN epitaxial layers has shown slight improvement on LT substrates over LN substrates, according to X-ray diffraction. Herein, we demonstrate AlGaN/GaN heterostructure devices on ferroelectric materials that will allow future development of multifunctional electrical and optical applications.

  2. 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.

  3. Degradation of 2DEG transport properties in GaN-capped AlGaN/GaN heterostructures at 600 °C in oxidizing and inert environments

    Science.gov (United States)

    Hou, Minmin; Jain, Sambhav R.; So, Hongyun; Heuser, Thomas A.; Xu, Xiaoqing; Suria, Ateeq J.; Senesky, Debbie G.

    2017-11-01

    In this paper, the electron mobility and sheet density of the two-dimensional electron gas (2DEG) in both air and argon environments at 600 °C were measured intermittently over a 5 h duration using unpassivated and Al2O3-passivated AlGaN/GaN (with 3 nm GaN cap) van der Pauw test structures. The unpassivated AlGaN/GaN heterostructures annealed in air showed the smallest decrease (˜8%) in 2DEG electron mobility while Al2O3-passivated samples annealed in argon displayed the largest drop (˜70%) based on the Hall measurements. Photoluminescence and atomic force microscopy showed that minimal strain relaxation and surface roughness changes have occurred in the unpassivated samples annealed in air, while those with Al2O3 passivation annealed in argon showed significant microstructural degradations. This suggests that cracks developed in the samples annealed in air were healed by oxidation reactions. To further confirm this, Auger electron spectroscopy was conducted on the unpassivated samples after the anneal in air and results showed that extra surface oxides have been generated, which could act as a dislocation pinning layer to suppress the strain relaxation in AlGaN. On the other hand, similar 2DEG sheet densities were observed in passivated and unpassivated AlGaN/GaN samples at the end of the 5-h anneal in air or argon due to the combined impact of strain relaxation and changes in the ionized electronic states. The results support the use of unpassivated GaN-capped AlGaN/GaN heterostructures as the material platform for high-temperature electronics and sensors used in oxidizing environmental conditions.

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

    International Nuclear Information System (INIS)

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

    2015-01-01

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

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

    Science.gov (United States)

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

    2015-08-01

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

  6. 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.

  7. InGaAsP/InGaAs tandem photovoltaic devices for four-junction solar cells

    International Nuclear Information System (INIS)

    Zhao Yongming; Dong Jianrong; Li Kuilong; Sun Yurun; Zeng Xulu; He Yang; Yu Shuzhen; Yang Hui

    2015-01-01

    Lattice-matched InGaAs(P) photovoltaic devices were grown on InP substrates by metal-organic chemical vapor deposition. InGaAsP/InGaAs (1.07/0.74 eV) dual-junction (DJ) solar cells were fabricated and characterized by quantum efficiency and I–V measurements. The open circuit voltage, short circuit current density, fill factor, and efficiency of InGaAsP/InGaAs DJ solar cell are 0.977 V, 10.2 mA/cm 2 , 80.8%, and 8.94%, respectively, under one sun illumination of the AM 1.5D spectrum. For the InGaAsP/InGaAs DJ solar cell, with increasing concentration, the conversion efficiency first increases steadily and reaches 13% around 280 suns, and finally decreases due to the drop in fill factor at higher concentration ratios. These experimental results demonstrate the promising prospect of GaInP/GaAs/InGaAsP/InGaAs four-junction solar cells. (paper)

  8. Growth initiation processes for GaAs and AlGaAs in CBE

    International Nuclear Information System (INIS)

    Hill, D.

    2002-01-01

    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 between 510-610 deg C with arsine (AsH 3 ) thermally cracked to As 2 , triethylgallium (TEGa), trimethylgallium (TMGa), trimethylaminealane (TMAA) and diethylmethylaminealane (DEMAA) at high III:V BEP ratios reveals that the transition from 'pre-growth' to 'in-growth' reconstructions is not as straightforward as that for lower III:V BEP ratio growth. Instead of the reconstruction changing directly to the usual 2x4 'in-growth' reconstruction over 1-2 seconds it passes through several other transient reconstructions over a period of up to and greater than 60s, firstly the Ga rich 4x2 then several other 2x4 As-stable reconstructions. It has been shown that at the III:V BEP ratios and substrate temperatures used in this work growth is taking place in a transitional area of the phase diagram for 'in-growth' reconstructions. At higher III:V BEP ratio growth the transition is believed to be direct, from the 'pre-growth' reconstruction to a 4x2 Ga-rich 'in-growth' reconstruction. The surfaces grown with any of the precursors are initially saturated with Ga and then as the As coverage gradually increases the reconstructions change until enough As is present on the surface for usual 2x4 '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

  9. Local spin valve effect in lateral (Ga,MnAs/GaAs spin Esaki diode devices

    Directory of Open Access Journals (Sweden)

    M. Ciorga

    2011-06-01

    Full Text Available We report here on a local spin valve effect observed unambiguously in lateral all-semiconductor all-electrical spin injection devices, employing p+ −(Ga,MnAs/n+ −GaAs Esaki diode structures as spin aligning contacts. We discuss the observed local spin-valve signal as a result of the interplay between spin-transport-related contribution and the tunneling anisotropic magnetoresistance of the magnetic contacts. The magnitude of the spin-related magnetoresistance change is equal to 30 Ω which is twice the magnitude of the measured non-local signal.

  10. Two-dimensional electron transport in AlGaN/GaN heterostructures

    International Nuclear Information System (INIS)

    Tan Renbing; Xu Wen; Zhou Yu; Zhang Xiaoyu; Qin Hua

    2012-01-01

    We present a theoretical study of electron transport properties of two-dimensional electron gas in AlGaN/GaN heterostructures. By assuming a drifted Fermi-Dirac distribution and taking into account all major scattering mechanisms, including polar optical and acoustic phonons, background impurities, dislocation and interface roughness, the momentum- and energy-balance equations derived from Boltzmann equation are solved self-consistently. The dependence of the electron drift velocity and electron temperature as a function of the applied electric field are obtained and discussed.

  11. Two-dimensional electron transport in AlGaN/GaN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Tan Renbing [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China); Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Graduate University of Chinese Academy of Sciences, Beijing 100049 (China); Xu Wen, E-mail: wenxu_issp@yahoo.cn [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Zhou Yu; Zhang Xiaoyu [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China); Qin Hua, E-mail: hqin2007@sinano.ac.cn [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215125 (China)

    2012-11-01

    We present a theoretical study of electron transport properties of two-dimensional electron gas in AlGaN/GaN heterostructures. By assuming a drifted Fermi-Dirac distribution and taking into account all major scattering mechanisms, including polar optical and acoustic phonons, background impurities, dislocation and interface roughness, the momentum- and energy-balance equations derived from Boltzmann equation are solved self-consistently. The dependence of the electron drift velocity and electron temperature as a function of the applied electric field are obtained and discussed.

  12. Stability of AlGaN/GaN heterostructures after hydrogen plasma treatment

    Czech Academy of Sciences Publication Activity Database

    Babchenko, O.; Dzuba, J.; Lalinský, T.; Vojs, M.; Vincze, A.; Ižák, Tibor; Vanko, G.

    2017-01-01

    Roč. 395, Feb (2017), s. 92-97 ISSN 0169-4332 R&D Projects: GA ČR(CZ) GP14-16549P Grant - others:AV ČR(CZ) SAV-16-02 Program:Bilaterální spolupráce Institutional support: RVO:68378271 Keywords : AIGaN/GaN heterostructure * hydrogen plasma * SIMS * TLM * HEMT Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.387, year: 2016

  13. Spin Dynamics in (111) GaAs/AlGaAs Undoped Asymmetric Quantum Wells

    International Nuclear Information System (INIS)

    Wang Gang; Ye Hui-Qi; Shi Zhen-Wu; Wang Wen-Xin; Liu Bao-Li; Xavier Marie; Andrea Balocchi; Thierry Amand

    2012-01-01

    The electron spin dynamics is investigated by the time-resolved Kerr rotation technique in a pair of special GaAs/AlGaAs asymmetric quantum well samples grown on (111)-oriented substrates, whose structures are the same except for their opposite directions of potential asymmetry. A large difference of spin lifetimes between the two samples is observed at low temperature. This difference is interpreted in terms of a cancellation effect between the Dresselhaus spin-splitting term in the conduction band and another term induced by interface inversion asymmetry. The deviation decreases with the increasing temperature, and almost disappears when T > 100 K because the cubic Dresselhaus term becomes more important

  14. Photoluminescence and magnetophotoluminescence studies in GaInNAs/GaAs quantum wells

    Science.gov (United States)

    Segura, J.; Garro, N.; Cantarero, A.; Miguel-Sánchez, J.; Guzmán, A.; Hierro, A.

    2007-04-01

    We investigate the effects of electron and hole localization in the emission of a GaInNAs/GaAs single quantum well at low temperatures. Photoluminescence measurements varying the excitation density and under magnetic fields up to 14 T have been carried out. The results indicate that electrons are strongly localized in these systems due to small fluctuations in the nitrogen content of the quaternary alloy. The low linear diamagnetic shift of the emission points out the weakness of the Coulomb correlation between electrons and holes and suggests an additional partial localization of the holes.

  15. Pressure-dependent shallow donor binding energy in InGaN/GaN square QWWs

    International Nuclear Information System (INIS)

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

    2013-01-01

    Using a variational approach, we perform a theoretical study of hydrostatic pressure effect on the ground-state of axial hydrogenic shallow-donor impurity binding energy in InGaN/GaN square quantum well wire (SQWWs) as a function of the side length within the effective-mass scheme and finite potential barrier. The pressure dependence of wire length, effective mass, dielectric constant and potential barrier are taken into account. Numerical results show that: (i) the binding energy is strongly affected by the wire length and the external applied pressure and (ii) its maximum moves to the narrow wire in particular for height pressure.

  16. 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.

  17. Analysis of noise spectra in GaAs and GaN Schottky barrier diodes

    International Nuclear Information System (INIS)

    Pardo, D; Grajal, J; Mencía, B; Pérez, S; Mateos, J; González, T

    2011-01-01

    The Monte Carlo method is applied in this paper to characterize the noise spectra of GaAs and GaN Schottky barrier diodes operating under static and time varying conditions. We show the influence of the structure of the diode and working regimes on the noise spectrum of the diodes. Besides, the paper evaluates the capabilities of published analytical models to describe the noise spectra in Schottky diodes under time varying conditions. This is a further step toward the development of a design tool that integrates both the electrical response and the intrinsic noise generated in the devices

  18. Multi-bias capacitance voltage characteristic of AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Pu Yan; Wang Liang; Yuan Tingting; Ouyang Sihua; Pang Lei; Liu Guoguo; Luo Weijun; Liu Xinyu

    2010-01-01

    The method of multi-bias capacitance voltage measurement is presented. The physical meaning of gate-source and gate-drain capacitances in AlGaN/GaN HEMT and the variations in them with different bias conditions are discussed. A capacitance model is proposed to reflect the behaviors of the gate-source and gate-drain capacitances, which shows a good agreement with the measured capacitances, and the power performance obtains good results compared with the measured data from the capacitance model. (semiconductor devices)

  19. Multi-bias capacitance voltage characteristic of AlGaN/GaN HEMT

    Energy Technology Data Exchange (ETDEWEB)

    Pu Yan; Wang Liang; Yuan Tingting; Ouyang Sihua; Pang Lei; Liu Guoguo; Luo Weijun; Liu Xinyu, E-mail: puyan_66721@hotmail.co [Key Laboratory of Microelectronics Device and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)

    2010-10-15

    The method of multi-bias capacitance voltage measurement is presented. The physical meaning of gate-source and gate-drain capacitances in AlGaN/GaN HEMT and the variations in them with different bias conditions are discussed. A capacitance model is proposed to reflect the behaviors of the gate-source and gate-drain capacitances, which shows a good agreement with the measured capacitances, and the power performance obtains good results compared with the measured data from the capacitance model. (semiconductor devices)

  20. Small signal modeling of AlGaN/GaN HEMTs with consideration of CPW capacitances

    International Nuclear Information System (INIS)

    Du Jiangfeng; Wang Kang; Yin Chenggong; Liu Yang; Yu Qi; Xu Peng; Feng Zhihong; Dun Shaobo

    2015-01-01

    Given the coplanar waveguide (CPW) effect on AlGaN/GaN high electron mobility transistors at a high frequency, the traditional equivalent circuit model cannot accurately describe the electrical characteristics of the device. The admittance of CPW capacitances is large when the frequency is higher than 40 GHz; its impact on the device cannot be ignored. In this study, a small-signal equivalent circuit model considering CPW capacitance is provided. To verify the model, S-parameters are obtained from the modeling and measurements. A good agreement is observed between the simulation and measurement results, indicating the reliability of the model. (paper)

  1. SEMICONDUCTOR DEVICES Multi-bias capacitance voltage characteristic of AlGaN/GaN HEMT

    Science.gov (United States)

    Yan, Pu; Liang, Wang; Tingting, Yuan; Sihua, Ouyang; Lei, Pang; Guoguo, Liu; Weijun, Luo; Xinyu, Liu

    2010-10-01

    The method of multi-bias capacitance voltage measurement is presented. The physical meaning of gate—source and gate—drain capacitances in AlGaN/GaN HEMT and the variations in them with different bias conditions are discussed. A capacitance model is proposed to reflect the behaviors of the gate—source and gate—drain capacitances, which shows a good agreement with the measured capacitances, and the power performance obtains good results compared with the measured data from the capacitance model.

  2. 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...... lifetime and spin detection efficiency (22 +/- 4%). This work builds on existing studies on off-stoichiometric Heusler injectors into similar light-emitting-diode structures. The role of injector stoichiometry can therefore be quantitatively assessed with the result that the spin injection efficiency...

  3. 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.

  4. Terahertz-radiation generation and detection in low-temperature-grown GaAs epitaxial films on GaAs (100) and (111)A substrates

    Energy Technology Data Exchange (ETDEWEB)

    Galiev, G. B.; Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru [Russian Academy of Sciences, Institute of Ultrahigh-Frequency Semiconductor Electronics (Russian Federation); Buriakov, A. M.; Bilyk, V. R.; Mishina, E. D. [Moscow Technological University “MIREA” (Russian Federation); Klimov, E. A. [Russian Academy of Sciences, Institute of Ultrahigh-Frequency Semiconductor Electronics (Russian Federation); Vasil’evskii, I. S. [National Research Nuclear University “MEPhI” (Russian Federation); Maltsev, P. P. [Russian Academy of Sciences, Institute of Ultrahigh-Frequency Semiconductor Electronics (Russian Federation)

    2017-04-15

    The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity of the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.

  5. Real-time studies of In-adlayer during PAMBE of InGaN/GaN MQWs

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Tong-Ho; Yoon, Inho; Brown, April [Department of Electrical and Computer Engineering, Duke University, 27708 Durham, NC (United States); Losurdo, Maria; Bruno, Giovanni [Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR, via Orabona 4, 70126 Bari (Italy); Choi, Soojeong [Materials Department, University of California, 93106 Santa Barbara, CA (United States)

    2012-03-15

    The control of In adlayer during plasma-assisted molecular beam epitaxy (PAMBE) of InGaN/GaN multiquantum wells (MQWs) is critical to achieve good structural and optical properties. This contribution focuses on the investigation by real-time spectroscopic ellipsometry, corroborated by reflection high energy electron diffraction (RHEED), of In adlayer during the PAMBE growth of InGaN/GaN MQWs. The ellipsometric data reveal In accumulation during InGaN growth, which results in thicker quantum well than designed. We address the effect of the indium adlayer on the growth of InGaN/GaN with an indium composition between 7% and 13%, and on their optical and structural properties determined by high-resolution X-ray diffraction and photoluminescence. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Molecular beam epitaxy of AlSb on GaAs and GaSb on AlSb films

    International Nuclear Information System (INIS)

    Gotoh, H.; Sasamoto, K.; Kuroda, S.; Kimata, M.

    1983-01-01

    Single crystalline AlSb films are successfully grown, by MBE on GaAs substrates at temperatures higher than 400 0 C. The surface gives a C(2 x 6) structure under Sb stabilized conditions. Undoped AlSb is p-type with resistivities of 10 2 to 10 3 Ωcm. Then, GaSb films are grown on AlSb/GaAs. It can be seen, from RHEED observation that the interface between AlSb and GaSb is very smooth, and the layer growth continues at the interface. Fabricating that structure improves the properties of GaSb in comparison with those of GaSb directly grown on GaAs by the relaxation of lattice mismatch. (author)

  7. Ion implanted GaAs microwave FET's

    Science.gov (United States)

    Gill, S. S.; Blockley, E. G.; Dawsey, J. R.; Foreman, B. J.; Woodward, J.; Ball, G.; Beard, S. J.; Gaskell, J. M.; Allenson, M. B.

    1988-06-01

    The combination of ion implantation and photolithographic patterning techniques was applied to the fabrication of GaAs microwave FETs to provide a large number of devices having consistently predictable dc and high frequency characteristics. To validate the accuracy and repeatability of the high frequency device parameters, an X-band microwave circuit was designed and realized. The performance of this circuit, a buffered amplifier, is very close to the design specification. The availability of a large number of reproducible, well-characterized transistors enabled work to commence on the development of a large signal model for FETs. Work in this area is also described.

  8. Assessment of Ga2O3 technology

    Science.gov (United States)

    2016-09-15

    electronics application is the only driver for the technology at present. This type of electronics have a large commercial market , but there are...vol. 43, p. 7133, 2004. [119] A. J. Freeman, K. R. Poeppelmeier, T. O. Mason, R. P. H. Chang, and T. J. Marks, "Chemical and Thin-Film Strategies for...doped β-Ga2O3 single crystals," Applied Physics Letters, vol. 92, p. 201914, 2008. [138] R. A. Laudise, J. B. Mullin , B. Mutaftschiev, and K. Nassau

  9. Preliminary PET/CT Imaging with Somatostatin Analogs [68Ga]DOTAGA-TATE and [68Ga]DOTAGA-TOC.

    Science.gov (United States)

    Satpati, Drishty; Shinto, Ajit; Kamaleshwaran, K K; Sarma, Haladhar Dev; Dash, Ashutosh

    2017-12-01

    Somatostatin receptor positron emission tomography/X-ray computed tomography (SSTR-PET/CT) is a well-established technique for staging and detection of neuroendocrine tumors (NETs). Ga-68-labeled DOTA-conjugated octreotide analogs are the privileged radiotracers for diagnosis and therapeutic monitoring of NETs. Hence, we were interested in assessing the influence of promising, newer variant DOTAGA on the hydrophilicity, pharmacokinetics, and lesion pick-up of somatostatin analogs. Herein, the potential of ([ 68 Ga]DOTAGA, Tyr 3 , Thr 8 ) octreotide ([ 68 Ga]DOTAGA-TATE) and ([ 68 Ga]DOTAGA, Tyr 3 ) octreotide ([ 68 Ga]DOTAGA-TOC) as NET imaging agents has been investigated. Amenability of [ 68 Ga]DOTAGA-(TATE/TOC) to kit-type formulation has been demonstrated. Biodistribution studies were carried out in normal rats at 1 h post-injection (p.i.). [ 68 Ga]DOTAGA-(TATE/TOC) PET/CT scans were carried out in patients (70-170 MBq, 1 h p.i.) with histologically confirmed well-differentiated NETs. [ 68 Ga]DOTAGA-TATE exhibited hydrophilicity similar to [ 68 Ga]DOTA-TATE (log P = -3.51 vs -3.69) whereas [ 68 Ga]DOTAGA-TOC was more hydrophilic than [ 68 Ga]DOTA-TOC (log P = -3.27 vs -2.93). [ 68 Ga]DOTAGA-TATE and [ 68 Ga]DOTA-TATE showed almost identical blood and kidney uptake in normal rats whereas significantly fast clearance (p TOC also demonstrated rapid clearance from blood and kidneys (p TOC. The metastatic lesions in NET patients were well identified by [ 68 Ga]DOTAGA-TATE and [ 68 Ga]DOTAGA-TOC. The phenomenal analogy was observed between [ 68 Ga]DOTAGA-TATE and [ 68 Ga]DOTA-TATE as well as between [ 68 Ga]DOTAGA-TOC and [ 68 Ga]DOTA-TOC in biodistribution studies in rats. The good lesion detection ability of the two radiotracers indicates their potential as NET imaging radiotracers.

  10. Magnetic anisotropy in GaMnAs; Magnetische Anisotropie in GaMnAs

    Energy Technology Data Exchange (ETDEWEB)

    Daeubler, Joachim

    2009-07-02

    The goal of the present work was the detailed investigation of the impact of parameters like vertical strain, hole concentration, substrate orientation and patterning on the MA in GaMnAs. At first a method is introduced enabling us to determine the MA from angle-dependent magnetotransport measurements. This method was used to analyze the impact of vertical strain {epsilon}{sub zz} on the MA in a series of GaMnAs layers with a Mn content of 5% grown on relaxed InGaAs-templates. While hole concentration and Curie temperature were found to be unaffected by vertical strain, a significant dependence of the MA on {epsilon}{sub zz} was found. The most pronounced dependence was observed for the anisotropy parameter B{sub 2} {sub perpendicular} {sub to}, representing the intrinsic contribution to the MA perpendicular to the layer plane. For this parameter a linear dependence on {epsilon}{sub zz} was found, resulting in a strain-induced transition of the magnetic easy axis with increasing strain from in-plane to out-of-plane at {epsilon}{sub zz} {approx} -0.13%. Post-growth annealing of the samples leads to an outdiffusion and/or regrouping of the highly mobile Mn interstitial donor defects, resulting in an increase in both p and T{sub C}. For the annealed samples, the transition from in-plane to out-of-plane easy axis takes place at {epsilon}{sub zz} {approx} -0.07%. From a comparison of as-grown and annealed samples, B{sub 2} {sub perpendicular} {sub to} was found to be proportional to both p and {epsilon}{sub zz}, B{sub 2} {sub perpendicular} {sub to} {proportional_to} p .{epsilon}{sub zz}. To study the influence of substrate orientation on the magnetic properties of GaMnAs, a series of GaMnAs layers with Mn contents up to 5% was grown on (001)- and (113)A-oriented GaAs substrates. The hole densities and Curie temperatures, determined from magnetotransport measurements, are drastically reduced in the (113)A layers. The differences in the magnetic properties of (113)A- and

  11. 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.

  12. 67Ga-emission computed tomography in bronchogenic carcinoma

    International Nuclear Information System (INIS)

    Ichiya, Yuichi; Oshiumi, Yoshihiko; Kuwabara, Yasuo; Wada, Makoto; Ayabe, Zenji; Matsuura, Keiichi

    1982-01-01

    Both conventional 67 Ga scintigraphy and 67 Ga emission computed tomography (ECT) were performed in 36 patients with bronchogenic carcinoma to evaluate clinical significance of 67 Ga-ECT as an adjunctive method. Each patient received 111 -- 185 MBq (3 -- 5 mCi) of 67 Ga-citrate intravenously. A rotation #betta# camera (Shimadzu LFOV-E) was used for ECT study, and a #betta# camera (Searle LFOV) was used for conventional scintigraphy. The detectability of 67 Ga scintigraphy with ECT in primary tumors and regional lymph node metastases was compared retrospectively with that of conventional 67 Ga scintigraphy alone. There was little improvement in detection of primary and metastatic lesions by adding 67 Ga-ECT. Only 3 primary tumors were demonstrated more distinctly by 67 Ga-ECT. However, there was no lesion which was detected only by 67 Ga-ECT. Our data indicate that inclusion of 67 Ga-ECT in the routine examination is unnecessary in cases with bronchogenic carcinoma. (author)

  13. GaN Micromechanical Resonators with Meshed Metal Bottom Electrode

    Science.gov (United States)

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

    2015-01-01

    This work describes a novel architecture to realize high-performance gallium nitride (GaN) bulk acoustic wave (BAW) resonators. The method is based on the growth of a thick GaN layer on a metal electrode grid. The fabrication process starts with the growth of a thin GaN buffer layer on a Si (111) substrate. The GaN buffer layer is patterned and trenches are made and refilled with sputtered tungsten (W)/silicon dioxide (SiO2) forming passivated metal electrode grids. GaN is then regrown, nucleating from the exposed GaN seed layer and coalescing to form a thick GaN device layer. A metal electrode can be deposited and patterned on top of the GaN layer. This method enables vertical piezoelectric actuation of the GaN layer using its largest piezoelectric coefficient (d33) for thickness-mode resonance. Having a bottom electrode also results in a higher coupling coefficient, useful for the implementation of acoustic filters. Growth of GaN on Si enables releasing the device from the frontside using isotropic xenon difluoride (XeF2) etch and therefore eliminating the need for backside lithography and etching. PMID:28787997

  14. Understanding GaN/InGaN core–shell growth towards high quality factor whispering gallery modes from non-polar InGaN quantum wells on GaN rods

    Science.gov (United States)

    Tessarek, C.; Rechberger, S.; Dieker, C.; Heilmann, M.; Spiecker, E.; Christiansen, S.

    2017-12-01

    GaN microrods are used as a basis for subsequent InGaN quantum well (QW) and quantum dot deposition by metal-organic vapor phase epitaxy. The coverage of the shell along the sidewall of rods is dependent on the rod growth time and a complete coverage is obtained for shorter rod growth times. Transmission electron microscopy measurements are performed to reveal the structural properties of the InGaN layer on the sidewall facet and on the top facet. The presence of layers in the microrod and on the microrod surface will be discussed with respect to GaN and InGaN growth. A detailed model will be presented explaining the formation of multiple SiN layers and the partial and full coverage of the shell around the core. Cathodoluminescence measurements are performed to analyze the InGaN emission properties along the microrod and to study the microresonator properties of such hexagonal core–shell structures. High quality factor whispering gallery modes with Q∼ 1200 are reported for the first time in a GaN microrod/InGaN non-polar QW core–shell geometry. The GaN/InGaN core–shell microrods are expected to be promising building blocks for low-threshold laser diodes and ultra-sensitive optical sensors.

  15. Understanding GaN/InGaN core-shell growth towards high quality factor whispering gallery modes from non-polar InGaN quantum wells on GaN rods.

    Science.gov (United States)

    Tessarek, C; Rechberger, S; Dieker, C; Heilmann, M; Spiecker, E; Christiansen, S

    2017-12-01

    GaN microrods are used as a basis for subsequent InGaN quantum well (QW) and quantum dot deposition by metal-organic vapor phase epitaxy. The coverage of the shell along the sidewall of rods is dependent on the rod growth time and a complete coverage is obtained for shorter rod growth times. Transmission electron microscopy measurements are performed to reveal the structural properties of the InGaN layer on the sidewall facet and on the top facet. The presence of layers in the microrod and on the microrod surface will be discussed with respect to GaN and InGaN growth. A detailed model will be presented explaining the formation of multiple SiN layers and the partial and full coverage of the shell around the core. Cathodoluminescence measurements are performed to analyze the InGaN emission properties along the microrod and to study the microresonator properties of such hexagonal core-shell structures. High quality factor whispering gallery modes with [Formula: see text] are reported for the first time in a GaN microrod/InGaN non-polar QW core-shell geometry. The GaN/InGaN core-shell microrods are expected to be promising building blocks for low-threshold laser diodes and ultra-sensitive optical sensors.

  16. GaN based nanorods for solid state lighting

    Science.gov (United States)

    Li, Shunfeng; Waag, Andreas

    2012-04-01

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

  17. Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values

    International Nuclear Information System (INIS)

    Ma Xiao-Hua; Zhang Ya-Man; Chen Wei-Wei; Wang Xin-Hua; Yuan Ting-Ting; Pang Lei; Liu Xin-Yu

    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. The HEMT with a thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage (BV off ). Device simulation indicates that thickening the 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 BV off in the 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 BV off in AlGaN/GaN HEMTs. (paper)

  18. Interface traps contribution to capacitance of Al2O3/(GaN)AlGaN/GaN heterostructures at low frequencies

    Science.gov (United States)

    Osvald, J.

    2017-09-01

    Influence of interface traps at Al2O3/(GaN)/AlGaN interface on low and high frequency capacitance of Al2O3/(GaN)/AlGaN/GaN heterostructure capacitor was studied. New features were observed in the capacitance curves. Obtained experimental results were modeled and simulated and accordance with the experiment has been obtained. For lower frequencies a new capacitance peak in the depletion and increase of the capacitance in a plateau region were measured. The capacitance peak in the depletion region was successfully explained by a capacitance response of the interface traps with U-shape density distribution. On the other hand the increase of the capacitance plateau was modeled by the homogeneous interface trap distribution. We assume that the traps located near the band edges having the highest density are able to respond to the low frequency measuring.

  19. Fast and slow traps in Al2O3/(GaN)/AlGaN/GaN heterostructures studied by conductance technique

    Science.gov (United States)

    Osvald, J.

    2018-03-01

    Influence of interface traps at Al2O3/(GaN)/AlGaN interface at low and high frequency on equivalent parallel conductance of Al2O3/(GaN)/AlGaN/GaN heterostructure capacitor was studied. By the conductance measurements two types of traps were identified in the measured structure. The traps differ in time constants by more than one order in magnitude. Fast traps with low time constants have narrow energy distribution and are probably located in the semiconductor energy gap close to the insulator semiconductor interface. Slow traps have wider distribution and are assumed to be directly at the insulator semiconductor interface. The presence of the fast traps which are able to respond to external ac signal is given into connection with the recently published increase of the structure capacitance in the plateau region with decreasing frequency.

  20. Optical tunability of magnetic polaron stability in single-Mn doped bulk GaAs and GaAs/AlGaAs quantum dots

    Science.gov (United States)

    Qu, Fanyao; Moura, Fábio Vieira; Alves, Fabrizio M.; Gargano, Ricardo

    2013-03-01

    Optical control of magnetic property of a magnetic polaron (MP) in Mn-doped bulk GaAs and GaAs/AlGaAs quantum dots (QDs) have been studied. We have developed basis optimization technique for the method of linear combination of atomic orbitals (LCAOs), which significantly improve the accuracy of the conventional LCAO calculation. We have demonstrated that a monochromatic, linearly polarized, intense pulsed laser field induces a collapse of the MP and an ionization of Mn-acceptor in Mn-doped GaAs materials due to a dichotomy of hole wave function. We find this optical tunability of MP stability can be adjusted by confinement introduced in GaAs QDs.

  1. InGaN stress compensation layers in InGaN/GaN blue LEDs with step graded electron injectors

    Science.gov (United States)

    Sheremet, V.; Gheshlaghi, N.; Sözen, M.; Elçi, M.; Sheremet, N.; Aydınlı, A.; Altuntaş, I.; Ding, K.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

    2018-04-01

    We investigate the effect of InGaN stress compensation layer on the properties of light emitting diodes based on InGaN/GaN multiple quantum well (MQW) structures with step-graded electron injectors. Insertion of an InGaN stress compensation layer between n-GaN and the step graded electron injector provides, among others, strain reduction in the MQW region and as a result improves epitaxial quality that can be observed by 15-fold decrease of V-pit density. We observed more uniform distribution of In between quantum wells in MQW region from results of electro- and photoluminescence measurement. These structural improvements lead to increasing of radiant intensity by a factor of 1.7-2.0 and enhancement of LED efficiency by 40%.

  2. 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.

  3. Magneto-transport studies of GaSb/InAs/GaSb double heterostructures Semiconductors

    CERN Document Server

    Takashina, K

    2002-01-01

    The electrical transport properties of GaSb/lnAs/GaSb double-heterostructures are examined experimentally. The structures are studied at low temperatures and high magnetic field. InAs/GaSb is a crossed-gap system where the conduction band minimum of InAs lies lower in energy than the valence band maximum of GaSb. The samples examined exploit this property to contain two-dimensional layers of electrons and holes. A description of the general electrical magneto-transport properties is given. Effects due to anticrossing behaviour between the electron and hole dispersion relations are demonstrated and discussed. It is shown that the anticrossing can lead to a non-monotonic temperature dependence of the resistivity. Under quantum Hall conditions, the system displays two types of behaviour. An insulating behaviour where both Hall and diagonal conductivities become vanishingly small, and a more conventional metallic behaviour where the Hall resistance is quantized and the diagonal resistivity disappears. It is found...

  4. Recessed insulator and barrier AlGaN/GaN HEMT: A novel structure ...

    Indian Academy of Sciences (India)

    In this study, a gallium nitride (GaN) high electron mobility transistor (HEMT) with recessed insulator and barrier is reported. In the proposed structure, insulator is recessed into the barrier at the drain side and barrier is recessed into the buffer layer at the source side. We study important device characteristics such as electric ...

  5. Cascaded Ga1-xAlxAs/GaAs solar cell with graded i-region

    Science.gov (United States)

    Mil'shtein, Sam; Halilov, Samed

    2018-02-01

    In current study we designed p-i-n junction with extended intrinsic layer, where linearly graded Alx Ga1-x As presents variable energy gap so needed for effective harvesting of sun radiation. The design realization involves two regions of compositional structure in the stacking direction. The top AlxGa1-xAs layer of 1 um total thickness has stoichiometric structure x=0.3-0.2d, where depth d runs from 0 to 1 um, topmost 200 nm of which is Be-doped. Bottom AlxGa1-xAs layer of 3 um total thickness has a variable composition of x=0.133-0.033d, d runs from 1 to 4 um, the very bottom of which with 10 nm thickness is Si-doped. On the top surface, there is a 50 nm layer of p+ doped GaAs as a spacer for growing AuGe/Ni anode electrode of 20% surface area, the bottom is coated with AuGe/Ni cathode electrode. The designed cell demonstrates 89% fill factor and 30% conversion efficiency without anti-reflection coating.

  6. Cross-sectional scanning tunneling microscopy of Ga1-xMnxAs/GaAs Heterostructures

    Science.gov (United States)

    Roushan, Pedram; Richardella, Anthony; Mack, Shawn; Awschalom, David; Yazdani, Ali

    2008-03-01

    We have used a cryogenic scanning tunneling microscope (STM) to perform cross-sectional imaging studies of GaMnAs heterostructures. The heterostructures, consisting of a p-type buffer followed by a 3% Mn doped layer, were grown on a n-type GaAs substrate by molecular-beam epitaxy and cleaved in situ for STM measurements. The topographic measurements on the GaMnAs layer showed a variety of long range electronic structure modulations on the order of a few nm due to high level of disorder and compensation. Combining bias-dependent imaging and spectroscopy, we have used the STM to identify electronic features due to Mn dopants and other defects. In particular, we find that Mn dopants on the top most layer act as deep acceptors and exhibits similar topographic and spectroscopic features as our previous work [1] on Mn adatoms substituted into GaAs using STM manipulation techniques. [1] D. Kitchen, A. Richardella, J-M. Tang, M. Flatte, A. Yazdani, Nature 442, 436--439 (2006)

  7. Analysis of the thermal behavior of AlGaN/GaN HEMTs

    International Nuclear Information System (INIS)

    Russo, Salvatore; D’Alessandro, Vincenzo; Costagliola, Maurizio; Sasso, Grazia; Rinaldi, Niccolò

    2012-01-01

    Highlights: ► The thermal behavior of advanced multifinger AlGaN/GaN HEMTs grown on SiC is analyzed. ► The study is performed through accurate FEM simulations and DC/dynamic measurements. ► The FEM analysis is supported by an in-house tool devised for a smart mesh generation. ► Illustrative technology/layout guidelines to minimize the thermal issues are provided. - Abstract: The thermal behavior of state-of-the-art multifinger AlGaN/GaN HEMTs grown on SiC is thoroughly analyzed under steady-state and dynamic conditions. Accurate 3-D FEM simulations – based on a novel in-house tool devised to automatically build the device mesh – are performed using a commercial software to explore the influence of various layout and technological solutions on the temperature field. An in-house routine is employed to determine the Foster/Cauer networks suited to describe the dynamic heat propagation through the device structure. To conclude, various experimental techniques are employed to assess the thermal resistance and to allow the monitoring of the thermal impedance versus time of the transistors under test.

  8. Gate metal dependent electrical characteristics of AlGaN/GaN HEMTs

    Energy Technology Data Exchange (ETDEWEB)

    Koo, Sang-Mo, E-mail: smkoo@kw.ac.kr; Kang, Min-Seok, E-mail: hyde0220@gmail.com

    2014-10-15

    Highlights: • We investigated transfer characteristics of AlGaN/GaN high electron mobility transistors. • We demonstrate the effect of the barrier height of Schottky gate metals. • The conduction mechanisms examine by comparing the experimental results with numerical simulations. • 2-DEG concentration depends on the barrier height of Schottky gate metals. - Abstract: We investigated transfer characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) and the effect of the barrier height of Schottky gate metals. It is found that the threshold voltage of the HEMT structures with the Ni Schottky contact shows a positive shift compared to that of the Ti Schottky contacts (ΔV{sub th} = 2.9 V). The maximum saturation current of the HEMT structures with the Ti Schottky contact (∼1.4 × 10{sup 7} A/cm{sup 2}) is found to be ∼2.5 times higher than that of the Ni Schottky contact (2.9 × 10{sup 7} A/cm{sup 2}). The conduction mechanisms have been examined by comparing the experimental results with numerical simulations, which confirm that the increased barrier height is mainly attributed to the reduction of 2-DEG concentration.

  9. Efficient yellow and green emitting InGaN/GaN nanostructured QW materials and LEDs

    International Nuclear Information System (INIS)

    Nakajima, Yoshitake; Lin, Yenting; Dapkus, Paul Daniel

    2016-01-01

    Efficient green emitting LEDs and monolithic white light emitting LEDs require the extension of the range of efficient light emission in the GaN/InGaN materials system. We demonstrate high efficiency green and yellow light emitting multiple quantum well (MQW) structures grown on GaN nanostripe templates. The structures show promise for realizing high efficiency phosphor - free white LEDs. The nanostripe dimensions range from 100 to 300 nm and have separations that range from 300 nm to 1 μm. The MOCVD growth conditions strongly affect surfaces expressed in the GaN nanostripes whose sidewalls can be controlled to be nearly vertical or inclined and intersecting. Single quantum well (QW) structures are grown on these different stripes. Photoluminescence (PL) measurement shows that QW grown on stripes with the {10-11} surfaces and triangular shape emit the longest peak wavelength and highly efficient PL emission peak wavelengths as long as 570 nm are realized. PL and electroluminescence (EL) spectra show narrow linewidth that is comparable to the planar case and CL studies further demonstrate the uniform emission wavelength along the sidewalls of the structures. Finally, we have grown and fabricated green emitting LEDs on {10-11} faceted nanostripes with promising device characteristics. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. AlGaN/GaN heterostructure field-effect transistors regrown on nitrogen implanted templates

    International Nuclear Information System (INIS)

    Witte, W; Reuters, B; Fahle, D; Behmenburg, H; Hahn, H; Kalisch, H; Heuken, M; Vescan, A; Wang, K R; Trampert, A; Holländer, B

    2013-01-01

    We demonstrate the application of nitrogen (N) implantation in GaN as a current-blocking layer. In a first step, vertical current-blocking behavior was confirmed by processing quasi-vertical Schottky diodes with full-area N-implantation. The leakage current was only 10 −6 A cm −2 in forward and reverse directions. Also, the regrowth of AlGaN/GaN heterostructure field-effect transistors on N-implanted and, for reference, non-implanted GaN templates is demonstrated. Even though a decrease in the mobility and sheet carrier density of the two-dimensional electron gas was observed, excellent off-state properties were achieved. Regrown devices exhibited leakage currents as low as 10 −7 mA mm −1 , showing very good quality of the regrowth interface. However, a detailed analysis with pulsed I–V and C–V measurements suggest an increased presence of traps due to regrowth, especially on N-implanted templates. (paper)

  11. Epitaxy of (Ga,Mn)As; Epitaxie von (Ga,Mn)As

    Energy Technology Data Exchange (ETDEWEB)

    Utz, Martin

    2012-09-14

    The focus of this work lies on the enhancement of the magnetic properties of the ferromagnetic semiconductor Gallium manganese arsenide (GaMnAs), which is a basic material for the research in spintronics: It is told, how a high sample reproducibility and a strong control over the growth process can be gained by applying band edge spectroscopy and a special procedure for the material flux calibration. Also the most important methods for the electrical characterization of GaMnAs are discussed in a critical manner by showing that the anomalous Hall Effect contributes significantly to the Hall resistance even at room temperature and that Novak's method for the termination of the Curie-temperature provides correct values for layers with low defect concentration. Furthermore it is reported on the considerable enlargement of the useable parameter space of GaMnAs which was enabled by the enhanced control over the growth process: It was possible to grow layers with a very high Manganese content of 22% and Curie temperatures of 172 K and even once were produced which showed a strong magnetic moment despite an insulating behaviour at low temperatures. A last key aspect is the growth and characterization of ultra-thin GaMnAs layers, giving prospects for gating experiments or experiments on the proximity effect as these layers combine high Curie temperatures with insulating behaviour.

  12. Comprehensive analyses of core-shell InGaN/GaN single nanowire photodiodes

    Science.gov (United States)

    Zhang, H.; Guan, N.; Piazza, V.; Kapoor, A.; Bougerol, C.; Julien, F. H.; Babichev, A. V.; Cavassilas, N.; Bescond, M.; Michelini, F.; Foldyna, M.; Gautier, E.; Durand, C.; Eymery, J.; Tchernycheva, M.

    2017-12-01

    Single nitride nanowire core/shell n-p photodetectors are fabricated and analyzed. Nanowires consisting of an n-doped GaN stem, a radial InGaN/GaN multiple quantum well system and a p-doped GaN external shell were grown by catalyst-free metal-organic vapour phase epitaxy on sapphire substrates. Single nanowires were dispersed and the core and the shell regions were contacted with a metal and an ITO deposition, respectively, defined using electron beam lithography. The single wire photodiodes present a response in the visible to UV spectral range under zero external bias. The detector operation speed has been analyzed under different bias conditions. Under zero bias, the  -3 dB cut-off frequency is ~200 Hz for small light modulations. The current generation was modeled using non-equilibrium Green function formalism, which evidenced the importance of phonon scattering for carrier extraction from the quantum wells.

  13. Nonpolar InGaN/GaN Core-Shell Single Nanowire Lasers.

    Science.gov (United States)

    Li, Changyi; Wright, Jeremy B; Liu, Sheng; Lu, Ping; Figiel, Jeffrey J; Leung, Benjamin; Chow, Weng W; Brener, Igal; Koleske, Daniel D; Luk, Ting-Shan; Feezell, Daniel F; Brueck, S R J; Wang, George T

    2017-02-08

    We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.

  14. Investigation of localization effect in GaN-rich InGaN alloys and ...

    Indian Academy of Sciences (India)

    localization effect, while the localization effect can be attributed to In-rich clusters and metallic indium inclusions for sample C. In addition, the band-tail model is modified and the modified band-tail model is used to investigate the degree of localization effect in the three samples. Keywords. InGaN; localization effect ...

  15. Numerical simulation of anisotropic elastic fields of a GaAs/GaAs twist boundary

    Energy Technology Data Exchange (ETDEWEB)

    Madani, Salah; Outtas, Toufik; Adami, Lahbib [Departement de Mecanique, Faculte des Sciences de l' Ingenieur, University of Batna, Avenue Chahid Boukhlouf, 05000 Batna (Algeria)

    2007-09-15

    Self-assembled nanostructures are particularly interesting for optoelectronic and photonic applications, especially on silicon and GaAs substrates. Nevertheless, their long-range spatial distribution is random, their density is difficult to control, their size distribution can be large and their shapes can be different. By overcoming these drawbacks, it should be possible to improve the performances of existing devices or to fabricate new ones. This work studies the possibility to order on a long range self-assembled nanostructures on a GaAs substrate, by means of the elastic fields induced at the surface by shallowly buried periodic dislocation networks. The needed strain and stress fields, generated by a square network of screw dislocations located between a finite layer of GaAs bonded onto a semi-infinite GaAs substrate, are calculated using anisotropic elasticity. The results obtained are compared to those obtained using isotropic elasticity. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Multilayers of GaAs/Mn deposited on a substrate of GaAs (001)

    Energy Technology Data Exchange (ETDEWEB)

    Bernal-Salamanca, M; Pulzara-Mora, A; Rosales-Rivera, A [Laboratorio de Magnetismo y Materiales Avanzados, Universidad Nacional de Colombia, Sede Manizales, A.A. 127 (Colombia); Molina-Valdovinos, S; Melendez-Lira, M [Physics Department, Centro de Investigacion y Estudios Avanzados del IPN, Av. IPN No. 2508, Apartado Postal 14-740, 07000 Mexico D.F (Mexico); Lopez-Lopez, M, E-mail: aopulzaram@unal.edu.c [Centro de Fisica Aplicada y Tecnologia Avanzada, Universidad Nacional Autonoma de Mexico, Apartado Postal 1-1010, Queretaro 76000 (Mexico)

    2009-05-01

    In this work GaAs/Mn multilayers were deposited on GaAs (001) substrates by R.F magnetron sputtering technique, varying the deposition time (tg). Scanning electron and atomic force Microscopy studies were realized on the surface of the samples in order to determine the morphology and average roughness. X-ray diffraction spectra show that our samples tend to do amorphous. Raman spectroscopy at room temperature was employed to analyze the structural properties of the samples. We found that for a GaAs film taken as reference, the Raman spectra is dominated by the transverse (TO) and longitudinal (LO) modes located at 266 cm{sup -1} and 291 cm{sup -1}, respectively. However, for the GaAs/Mn multilayers the TO and LO modes decrease dramatically, and the Mn Raman modes in the range of 100 cm{sup -1} and 250 cm{sup -1} are evidenced. Additional new peaks located around 650 and 690 cm {sup -1} are only observed for the samples with high Mn content. By using the mass reduced model we estimate that the Mn related peaks are located at 650.2 cm{sup -1} and 695.2 cm{sup -1}, in good agreement with the experimental data, these peaks are correlated with excitations due to (Mn){sub m}As{sub n} localized structures.

  17. Sensing by means of nonlinear optics with functionalized GaAs/AlGaAs photonic crystals.

    Science.gov (United States)

    Estephan, Elias; Bajoni, Daniele; Saab, Marie-Belle; Cloitre, Thierry; Aulombard, Roger; Larroque, Christian; Andreani, Lucio Claudio; Liscidini, Marco; Malvezzi, Andrea Marco; Gergely, Csilla

    2010-06-15

    We report on specific functionalization of GaAs/AlGaAs photonic structures for molecular sensing via the optical second harmonic generation signal in the visible range exhibited by these nanostructures. Functionalization has been achieved by peptides selected by the phage display technology, revealing specific recognition for semiconducting surfaces. These small peptides when biotinylated serve for controlled placement of biotin onto the substrate to capture then streptavidin. Functionalization (with biotinylated peptide) and molecular recognition (of streptavidin) events both result in enhancing the nonlinear optical response of the samples. Adsorption and infiltration of biomolecules into the GaAs/AlGaAs photonic structure were monitored by atomic force and scanning electron microscopy combined with Energy Dispersive X-ray spectroscopy. We demonstrate that once functionalized with specific peptides, photonic structures could be used as miniature biosensors down to femtomolar detection sensitivity, by monitoring changes in the second harmonic signal when molecules are captured. Our results prove the outstanding sensitivity of the nonlinear approach in biosensing with photonic crystal waveguides as compared to linear absorption techniques on the same samples. The present work is expected to pioneer development of a new class of extremely small affinity-based biosensors with high sensitivity and demonstrates that photonic structures support device functionality that includes strongly confined and localized nonlinear radiation emission and detection processes.

  18. METABOLISM OF [14C]GA19 AND [14C]GA53 BY ECOTYPES OF ...

    African Journals Online (AJOL)

    ADMIN

    night periods. The most abundant metabolite was [14C]GA19 (10% of the activity in the samples). Key words/phrases: Conjugation, ecotype, gibberellins, metabolism, radioactivity. Abbreviations: [14C]GAx, radioactive carbon labelled gibberellin x; LD, long day; SD, Short day; 1SD, one short day; 4SD, four short days; HPLC ...

  19. AlGaAs/InGaAlP tunnel junctions for multijunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    SHARPS,P.R.; LI,N.Y.; HILLS,J.S.; HOU,H.; CHANG,PING-CHIH; BACA,ALBERT G.

    2000-05-16

    Optimization of GaInP{sub 2}/GaAs dual and GaInP{sub 2}/GaAs/Ge triple junction cells, and development of future generation monolithic multi-junction cells will involve the development of suitable high bandgap tunnel junctions. There are three criteria that a tunnel junction must meet. First, the resistance of the junction must be kept low enough so that the series resistance of the overall device is not increased. For AMO, 1 sun operation, the tunnel junction resistance should be below 5 x 10{sup {minus}2} {Omega}-cm. Secondly, the peak current density for the tunnel junction must also be larger than the J{sub sc} of the cell so that the tunnel junction I-V curve does not have a deleterious effect on the I-V curve of the multi-junction device. Finally, the tunnel junction must be optically transparent, i.e., there must be a minimum of optical absorption of photons that will be collected by the underlying subcells. The paper reports the investigation of four high bandgap tunnel junctions grown by metal-organic chemical vapor deposition.

  20. Magnetic ordering in TmGa.

    Science.gov (United States)

    Cadogan, J M; Stewart, G A; Muñoz Pérez, S; Cobas, R; Hansen, B R; Avdeev, M; Hutchison, W D

    2014-03-19

    We have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and (169)Tm Mössbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an incommensurate antiferromagnetic structure described by the propagation vector k1 = [0 0.275(2) 0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) μB at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) μB. The (169)Tm hyperfine magnetic field at 5 K is 631(1) T.

  1. 66Ga ground state β spectrum

    DEFF Research Database (Denmark)

    Severin, Gregory; Knutson, L. D.; Voytas, P. A.

    2014-01-01

    The ground state branch of the β decay of 66Ga is an allowed Fermi (0+ → 0+) transition with a relatively high f t value. The large f t and the isospin-forbidden nature of the transition indicates that the shape of the β spectrum of this branch may be sensitive to higher order contributions...... to the decay. Two previous measurements of the shape have revealed deviations from an allowed spectrum but disagree about whether the shape factor has a positive or negative slope. As a test of a new iron-free superconducting β spectrometer, we have measured the shape of the ground state branch of the 66Ga β...... spectrum above a positron energy of 1.9 MeV. The spectrum is consistent with an allowed shape, with the slope of the shape factor being zero to within ±3 × 10−3 per MeV. We have also determined the endpoint energy for the ground state branch to be 4.1535 ± 0.0003 (stat.) ±0.0007 (syst.) MeV, in good...

  2. Hot-electron real-space transfer and longitudinal transport in dual AlGaN/AlN/{AlGaN/GaN} channels

    International Nuclear Information System (INIS)

    Šermukšnis, E; Liberis, J; Matulionis, A; Avrutin, V; Ferreyra, R; Özgür, Ü; Morkoç, H

    2015-01-01

    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 Al 0.3 Ga 0.7 N/AlN/{Al 0.15 Ga 0.85 N/GaN} structure with a composite channel of Al 0.15 Ga 0.85 N/GaN, where the electrons with a sheet density of 1.4 × 10 13 cm −2 , estimated from the Hall effect measurements, are confined. The equilibrium electrons are situated predominantly in the Al 0.15 Ga 0.85 N 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 > 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 > 8 kV cm −1 . In this range of fields, the longitudinal current exceeds the values measured for a mono channel reference Al 0.3 Ga 0.7 N/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. (paper)

  3. Mercury(II) selective sensors based on AlGaN/GaN transistors

    Energy Technology Data Exchange (ETDEWEB)

    Asadnia, Mohsen, E-mail: mohsen.asadnia@mq.edu.au [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Department of Engineering, Macquarie University, NSW 2109 (Australia); Myers, Matthew [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); CSIRO Energy Flagship, Kensington, Western Australia 6151 (Australia); Akhavan, N.D. [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); O' Donnell, Kane [Department of Imaging and Applied Physics, Curtin University, Bentley, Western Australia 6102 (Australia); Umana-Membreno, Gilberto A. [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Mishra, U.K. [Electrical and Computer Engineering Department, University of California, Santa Barbara, CA 93106 (United States); Nener, Brett [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Baker, Murray [School of Chemistry and Biochemistry, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia); Parish, Giacinta [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy., Crawley, Western Australia 6009 (Australia)

    2016-11-02

    This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg{sup 2+}. This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg{sup 2+} concentrations. At pH 2.8 in a 10{sup −2} M KNO{sub 3} ion buffer, a detection limit below 10{sup −8} M and a linear response range between 10{sup −8} M-10{sup −4} M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10{sup −7} M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10{sup −7} M and 10{sup −6} M in 10{sup −2} M Cd(NO{sub 3}){sub 2} and 10{sup −2} M Pb(NO{sub 3}){sub 2} ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg{sup 2+} solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices. - Highlights: • This work is the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. • The sensor utilised an AlGaN/GaN transistor by functionalising the gate area with a polyvinyl chloride (PVC) based membrane. • The sensor showed a rapid and linear response between 10{sup −8} M-10{sup −4} M for Hg{sup 2+} detection at pH 2.8 in a 10{sup −2} M KNO{sub 3} ion buffer. • Detection limits of

  4. Evidence of type-II band alignment at the ordered GaInNP to GaAs heterointerface

    International Nuclear Information System (INIS)

    Hsu, H.P.; Huang, Y.N.; Huang, Y.S.; Sitarek, P.; Tiong, K.K.; Tu, C.W.

    2009-01-01

    Polarized piezoreflectance (PzR) and photoreflectance (PR) are employed to study band alignment in Ga 0.46 In 0.54 N y P 1-y /GaAs heterostructures grown by gas-source molecular-beam epitaxy. The features near the band edge of Ga 0.46 In 0.54 N y P 1-y show strong polarization dependence, indicating the existence of some degree of ordering of these samples. The PR spectra exhibit Franz-Keldysh Oscillations (FKOs) above the band edge of GaAs. The electric fields in the GaAs region are evaluated by analyzing the FKOs and found to decrease with increasing nitrogen content. The type-II band alignment at the Ga 0.46 In 0.54 N y P 1-y /GaAs interface is concluded for the alloys with nitrogen content y larger than 0.5% based on the appearance of additional features below band edge of GaAs. These features are attributed to the spatially indirect type-II transitions in the vicinity of interface region between Ga 0.46 In 0.54 N y P 1-y and GaAs. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. 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).

  6. Structural changes during annealing of GaInAsN

    International Nuclear Information System (INIS)

    Kurtz, Sarah; Webb, J.; Gedvilas, L.; Friedman, D.; Geisz, J.; Olson, J.; King, R.; Joslin, D.; Karam, N.

    2001-01-01

    The alloy GaInAsN has great potential as a lower-band-gap material lattice matched to GaAs, but there is little understanding of what causes its poor optoelectronic properties and why these improve with annealing. This study provides information about the structural changes that occur when GaInAsN is annealed. The Fourier transform infrared spectra exhibit two primary features: a triplet at ∼470 cm-1 (Ga--N stretch) and two or three bands at ∼3100 cm-1 (N--H stretch). The change in the Ga--N stretch absorption can be explained if the nitrogen environment is converted from NGa 4 to NInGa 3 after annealing. The N--H stretch is also changed after annealing, implying a second, and unrelated, structural change

  7. Epitaxial growth on porous GaAs substrates

    Czech Academy of Sciences Publication Activity Database

    Grym, Jan; Nohavica, Dušan; Gladkov, Petar; Hulicius, Eduard; Pangrác, Jiří; Piksová, K.

    2013-01-01

    Roč. 16, č. 1 (2013), s. 59-64 ISSN 1631-0748 R&D Projects: GA ČR GAP102/10/1201; GA ČR GAP108/10/0253 Institutional support: RVO:67985882 ; RVO:68378271 Keywords : Electrochemical etching * Porous semiconductors * Epitaxial growth * GaAs Subject RIV: BH - Optics, Masers, Lasers; JA - Electronics ; Optoelectronics, Electrical Engineering (FZU-D) Impact factor: 1.483, year: 2013

  8. Diffusion measurements of 67Ga in polycrystalline magnesium

    Czech Academy of Sciences Publication Activity Database

    Stloukal, Ivo; Čermák, Jiří

    237-240, - (2005), s. 1287-1292 ISSN 1012-0386. [DIMAT 2004 /6./. Krakow, 18.07.2004-23.07.2004] R&D Projects: GA ČR(CZ) GA106/01/0384 Grant - others:GA AV ČR(CZ) Z20419004-I003 Institutional research plan: CEZ:AV0Z2041904 Keywords : magnesium * volume diffusion * grain boundary diffusion Subject RIV: BJ - Thermodynamics Impact factor: 0.483, year: 2005

  9. Timing performance of ZnO: Ga nanopowder composite scintillators

    Czech Academy of Sciences Publication Activity Database

    Turtos, R.M.; Gundacker, S.; Lucchini, M.T.; Procházková, L.; Čuba, V.; Burešová, H.; Mrázek, Jan; Nikl, Martin; Lecoq, P.; Auffray, E.

    2016-01-01

    Roč. 10, č. 11 (2016), s. 843-847 ISSN 1862-6254 R&D Projects: GA ČR GA13-09876S EU Projects: European Commission(XE) 690599 - ASCIMAT Grant - others:COST(XE) TD1401 Institutional support: RVO:67985882 ; RVO:68378271 Keywords : nanocrystals * coincidence time resolution * scintillators ZnO:Ga Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering; BM - Solid Matter Physics ; Magnetism (FZU-D) Impact factor: 3.032, year: 2016

  10. 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.

  11. Anisotropic magnetoresistance of GaMnAs ferromagnetic semiconductors

    Czech Academy of Sciences Publication Activity Database

    Vašek, Petr; Svoboda, Pavel; Novák, Vít; Cukr, Miroslav; Výborný, Karel; Jurka, Vlastimil; Stuchlík, Jiří; Orlita, Milan; Maude, D. K.

    2010-01-01

    Roč. 23, č. 6 (2010), 1161-1163 ISSN 1557-1939 R&D Projects: GA AV ČR KAN400100652; GA MŠk MEB020928 Grant - others:EU EuroMagNET II(XE) Egide 19535NF Institutional research plan: CEZ:AV0Z10100521 Keywords : GaMnAs * anisotropic magnetoresistance * hydrogenation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.014, year: 2010

  12. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

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

  13. Properties of GaP/ZnO heterostructures for photovoltaics

    International Nuclear Information System (INIS)

    Kovac, J.; Buc, D.; Brath, T.; Kovac, J. jr.; Caplovicova, M.; Elias, P.; Hasenohrl, S.; Novak, J.

    2012-01-01

    In this paper, we discuss the deposition of ZnO thin layers on GaP substrate and GaP nanowires by RF magnetron sputtering and their influence on the structural properties. The main goal of this work is to find the optimal technology for deposition very thin ZnO layers by RF magnetron sputtering with defined parameters to cover round GaP nanowires surface prepared by MOVPE technology. (authors)

  14. Combined vertically correlated InAs and GaAsSb quantum dots separated by triangular GaAsSb barrier

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Oswald, Jiří; Pangrác, Jiří; Zíková, Markéta; Kubištová, Jana; Komninou, Ph.; Kioseoglou, J.; Kuldová, Karla; Hulicius, Eduard

    2013-01-01

    Roč. 114, č. 17 (2013), "174305-1"-"174305-5" ISSN 0021-8979 R&D Projects: GA ČR GA13-15286S; GA MŠk 7AMB12GR034; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : quantum dots * metal-organic vapor phase epitaxy * InAs * GaAs * GaAsSb Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.185, year: 2013

  15. Growth of InAs/GaAs quantum dots covered by GaAsSb in multiple structures studied by reflectance anisotropy spectroscopy

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Pangrác, Jiří; Vyskočil, Jan; Zíková, Markéta; Oswald, Jiří; Komninou, Ph.; Hulicius, Eduard

    2015-01-01

    Roč. 414, Mar (2015), s. 156-160 ISSN 0022-0248 R&D Projects: GA ČR(CZ) GP14-21285P; GA ČR GA13-15286S; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : MOVPE * InAs/GaAs MQD * GaAsSb SRL * RAS Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.462, year: 2015

  16. Quantum efficiency of GaN photocathode under different illumination

    Science.gov (United States)

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

    2011-07-01

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

  17. Annealing of GaN under high pressure of nitrogen

    CERN Document Server

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

    2002-01-01

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

  18. P-type doping of GaN

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Raechelle Kimberly [Univ. of California, Berkeley, CA (United States)

    2000-04-01

    After implantation of As, As + Be, and As + Ga into GaN and annealing for short durations at temperatures as high as 1500 C, the GaN films remained highly resistive. It was apparent from c-RBS studies that although implantation damage did not create an amorphous layer in the GaN film, annealing at 1500 C did not provide enough energy to completely recover the radiation damage. Disorder recovered significantly after annealing at temperatures up to 1500 C, but not completely. From SIMS analysis, oxygen contamination in the AIN capping layer causes oxygen diffusion into the GaN film above 1400 C. The sapphire substrate (A1203) also decomposed and oxygen penetrated into the backside of the GaN layer above 1400 C. To prevent donor-like oxygen impurities from the capping layer and the substrate from contaminating the GaN film and compensating acceptors, post-implantation annealing should be done at temperatures below 1500 C. Oxygen in the cap could be reduced by growing the AIN cap on the GaN layer after the GaN growth run or by depositing the AIN layer in a ultra high vacuum (UHV) system post-growth to minimize residual oxygen and water contamination. With longer annealing times at 1400 C or at higher temperatures with a higher quality AIN, the implantation drainage may fully recover.

  19. Interaction of GaN epitaxial layers with atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Losurdo, M.; Giangregorio, M.M.; Capezzuto, P.; Bruno, G.; Namkoong, G.; Doolittle, W.A.; Brown, A.S

    2004-08-15

    GaN surface passivation processes are still under development and among others hydrogen treatments are investigated. In this study, we use non-destructive optical and electrical probes such as spectroscopic ellipsometry (SE) and surface potential Kelvin probe microscopy (SP-KPM) in conjunction with non-contact atomic force microscopy (AFM) for the study of the different reactivity of Ga-polar and N-polar GaN epitaxial layers with atomic hydrogen. The GaN epitaxial layers are grown by molecular beam epitaxy on sapphire (0 0 0 1) substrates, and GaN and AlN buffer layers are used to grow N-polar and Ga-polar films, respectively. The atomic hydrogen is produced by a remote rf (13.56 MHz) H{sub 2} plasma in order to rule out any ion bombardment of the GaN surface and make the interaction chemical. It is found that the interaction of GaN surfaces with atomic hydrogen depends on polarity, with N-polar GaN exhibiting greater reactivity. Furthermore, it is found that atomic hydrogen is effective in the passivation of grain boundaries and surface defects states.

  20. Inverse spin Hall effect in Pt/(Ga,Mn)As

    Science.gov (United States)

    Nakayama, H.; Chen, L.; Chang, H. W.; Ohno, H.; Matsukura, F.

    2015-06-01

    We investigate dc voltages under ferromagnetic resonance in a Pt/(Ga,Mn)As bilayer structure. A part of the observed dc voltage is shown to originate from the inverse spin Hall effect. The sign of the inverse spin Hall voltage is the same as that in Py/Pt bilayer structure, even though the stacking order of ferromagnetic and nonmagnetic layers is opposite to each other. The spin mixing conductance at the Pt/(Ga,Mn)As interface is determined to be of the order of 1019 m-2, which is about ten times greater than that of (Ga,Mn)As/p-GaAs.

  1. Structural transformations in quenched Fe-Ga alloys

    International Nuclear Information System (INIS)

    Lograsso, T.A.; Ross, A.R.; Schlagel, D.L.; Clark, A.E.; Wun-Fogle, M.

    2003-01-01

    It has been speculated that the large increase in magnetostriction in Fe-Ga alloys results from local short-range ordering of the Ga atoms along specific crystallographic directions in the disordered Fe structure. The structural transitions associated with different cooling rates from the high temperature disordered state were investigated with X-ray diffraction of oriented single crystals of Fe-19 at% Ga. Results are presented for long-range ordering during slow cooling and indirect evidence of local short-range ordering of Ga atoms in the disordered state when the alloys are quenched is also presented. In the latter case, the short-range ordering of Ga atoms leads to a tetragonal distortion of the lattice. The dependence of the magnetostrictive response of Fe-Ga alloys on thermal history has been found to be directly related to these structural transformations in Fe-19 at% Ga alloys and experimental support for the proposed magnetostriction model based on Ga-Ga pairing along [100] crystallographic directions is presented

  2. Ultrasensitive detection of Hg2+ using oligonucleotide-functionalized AlGaN/GaN high electron mobility transistor

    International Nuclear Information System (INIS)

    Cheng, Junjie; Li, Jiadong; Miao, Bin; Wu, Dongmin; Wang, Jine; Pei, Renjun; Wu, Zhengyan

    2014-01-01

    An oligonucleotide-functionalized ion sensitive AlGaN/GaN high electron mobility transistor (HEMT) was fabricated to detect trace amounts of Hg 2+ . The advantages of ion sensitive AlGaN/GaN HEMT and highly specific binding interaction between Hg 2+ and thymines were combined. The current response of this Hg 2+ ultrasensitive transistor was characterized. The current increased due to the accumulation of Hg 2+ ions on the surface by the highly specific thymine-Hg 2+ -thymine recognition. The dynamic linear range for Hg 2+ detection has been determined in the concentrations from 10 −14 to 10 −8 M and a detection limit below 10 −14 M level was estimated, which is the best result of AlGaN/GaN HEMT biosensors for Hg 2+ detection till now.

  3. Impact of the Ga/In ratio on the N incorporation into (In,Ga)(As,N) quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Gargallo-Caballero, R.; Guzman, A.; Ulloa, J. M.; Hierro, A. [Instituto de Sistemas Optoelectronicos y Microtecnologia (ISOM)-Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Hopkinson, M. [Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S1 3JD (United Kingdom); Luna, E.; Trampert, A. [Paul Drude Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2012-04-15

    In this work, we demonstrate the dependence of the nitrogen incorporation on the Ga/In content into (In,Ga)(As,N) quantum dots (QDs) grown on GaAs (100) by radio-frequency plasma assisted molecular beam epitaxy (MBE). Morphological analysis by atomic force microscopy and cross-sectional transmission electron microscopy, together with an estimation of the transition thickness, monitored in situ during the growth, predict a maximum in the N incorporation for 30% Ga content. This result is confirmed by photoluminescence measurements of the as-grown and post-growth annealed samples. We attribute this behavior to a trade off between two mechanisms depending on the Ga/In content: one related to the stability of the Ga-N bond, and the other related to the surface strain and/or In segregation.

  4. Tunneling induced electron transfer in SiNx/AlGaN/GaN based metal-insulator-semiconductor structures

    International Nuclear Information System (INIS)

    Wang, M.J.; Shen, B.; Wang, Y.; Huang, S.; Xu, F.J.; Xu, J.; Qin, Z.X.; Yang, Z.J.; Zhang, G.Y.

    2007-01-01

    Tunneling induced electron transfer in SiN x /Al 0.22 Ga 0.78 N/GaN based metal-insulator-semiconductor (MIS) structures has been investigated by means of capacitance-voltage (C-V) measurements at various temperatures. Large clock-wise hysteresis window in C-V profiles indicates the injection of electrons from the two-dimensional electron gas (2DEG) channel to the SiN x layer. Depletion of the 2DEG at positive bias in the negative sweeping direction indicates that the charges injected have a long decay time, which was also observed in the recovery process of the capacitance after injection. The tunneling induced electron transfer effect in SiN x /Al 0.22 Ga 0.78 N/GaN based MIS structure opens up a way to design Al x Ga 1-x N/GaN based variable capacitors and memory devices

  5. Diffraction anomalous fine-structure study of strained Ga1-xInxAs on GaAs(001)

    International Nuclear Information System (INIS)

    Woicik, J.C.; Cross, J.O.; Bouldin, C.E.; Ravel, B.; Pellegrino, J.G.; Steiner, B.; Bompadre, S.G.; Sorensen, L.B.; Miyano, K.E.; Kirkland, J.P.

    1998-01-01

    Diffraction anomalous fine-structure measurements performed at both the Ga and As K edges have determined the Ga-As bond length to be 2.442±0.005thinsp Angstrom in a buried, 213-Angstrom-thick Ga 0.785 In 0.215 As layer grown coherently on GaAs(001). This bond length corresponds to a strain-induced contraction of 0.013±0.005thinsp Angstrom relative to the Ga-As bond length in bulk Ga 1-x In x As of the same composition. Together with recent extended x-ray-absorption fine-structure measurements performed at the In K edge [Woicik et al., Phys. Rev. Lett. 79, 5026 (1997)], excellent agreement is found with the uniform bond-length distortion model for strained-layer semiconductors on (001) substrates. copyright 1998 The American Physical Society

  6. Optimum Design of ARC-less InGaP/GaAs DJ Solar Cell with Hetero Tunnel Junction

    Science.gov (United States)

    Abbasian, Sobhan; Sabbaghi-Nadooshan, Reza

    2018-03-01

    The operation of hetero In0.49Ga0.51P-Al0.7Ga0.3As tunnel diodes has been evaluated, and an approach for optimizing the back surface field (BSF) layer of a InGaP/GaAs dual-junction (DJ) solar cell developed. The results show that the hetero In0.49Ga0.51P-Al0.7Ga0.3As tunnel diode transferred more electrons and holes and showed less recombination between the top and bottom cells with increased efficiency (η) in the InGaP/GaAs DJ solar cell. To achieve higher open-circuit voltage (V oc), GaAs semiconductor was investigated to match with Al0.52In0.48P with bandgap of 2.4 eV, and replacement of the bottom cell in the InGaP/GaAs DJ solar cell with such an Al0.52In0.48P-GaAs heterojunction increased the photogeneration in this region. In the next step, addition of a BSF layer to the top cell required two BSF layers in the bottom cell to optimize the short-circuit current (J sc) and η. The thickness and doping of the BSF layers were increased to obtain the highest η for the cell. The proposed structure was then compared with previous works. The proposed structure yielded V oc = 2.46 V, J sc = 30 mA/cm2, fill factor (FF) = 88.61%, and η = 65.51% under AM1.5 (1 sun) illumination.

  7. Abnormal Endogenous Repression of GA Signaling in a Seedless Table Grape Cultivar with High Berry Growth Response to GA Application

    Directory of Open Access Journals (Sweden)

    Atiako K. Acheampong

    2017-05-01

    Full Text Available Gibberellin (GA application is routinely used in the table grape industry to increase berry size and cluster length. Although grapevine cultivars show a wide range of growth responsiveness to GA3 application, the reasons for these differences is unclear. To shed light on this issue, two commercial grapevine cultivars with contrasting berry response to GA were selected for comparative analysis, in which we tested if the differences in response: (1 is organ-specific or cultivar-related; (2 will be reflected in qualitative/quantitative differences in transcripts/proteins of central components of GA metabolism and signaling and levels of GA metabolites. Our results showed that in addition to the high response of its berries to GA, internodes and rachis of cv. Black finger (BF presented a greater growth response compared to that of cv. Spring blush (SB. In agreement, the results exposed significant quantitative differences in GA signaling components in several organs of both cultivars. Exceptionally higher level of all three functional VvDELLA proteins was recorded in young BF organs, accompanied by elevated VvGID1 expression and lower VvSLY1b transcripts. Absence of seed traces, low endogenous GA quantities and lower expression of VvGA20ox4 and VvGA3ox3 were also recorded in berries of BF. Our results raise the hypothesis that, in young organs of BF, low expression of VvSLY1b may be responsible for the massive accumulation of VvDELLA proteins, which then leads to elevated VvGID1 levels. This integrated analysis suggests causal relationship between endogenous mechanisms leading to anomalous GA signaling repression in BF, manifested by high quantities of VvDELLA proteins, and greater growth response to GA application.

  8. Self-consistent vertical transport calculations in AlxGa1-xN/GaN based resonant tunneling diode

    Science.gov (United States)

    Rached, A.; Bhouri, A.; Sakr, S.; Lazzari, J.-L.; Belmabrouk, H.

    2016-03-01

    The formation of two-dimensional electron gases (2DEGs) at AlxGa1-xN/GaN hexagonal double-barriers (DB) resonant tunneling diodes (RTD) is investigated by numerical self-consistent (SC) solutions of the coupled Schrödinger and Poisson equations. Spontaneous and piezoelectric effects across the material interfaces are rigorously taken into account. Conduction band profiles, band edges and corresponding envelope functions are calculated in the AlxGa1-xN/GaN structures and likened to those where no polarization effects are included. The combined effect of the polarization-induced bound charge and conduction band offsets between the hexagonal AlGaN and GaN results in the formation of 2DEGs on one side of the DB and a depletion region on the other side. Using the transfer matrix formalism, the vertical transport (J-V characteristics) in AlGaN/GaN RTDs is calculated with a fully SC calculation in the ballistic regime. Compared to standard calculations where the voltage drop along the structure is supposed to be linear, the SC method leads to strong quantitative changes in the J-V characteristics showing that the applied electric field varies significantly in the active region of the structure. The influences of the aluminum composition and the GaN(AlGaN) thickness layers on the evolution of the current characteristics are also self-consistently investigated and discussed. We show that the electrical characteristics are very sensitive to the potential barrier due to the interplay between the potential symmetry and the barrier height and width. More interestingly, we demonstrate that the figures of merit namely the peak-to-valley ratio (PVR) of GaN/AlGaN RTDs can be optimized by increasing the quantum well width.

  9. An inverted AlGaAs/GaAs patterned-Ge tunnel junction cascade concentrator solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Venkatasubramanian, R. (Research Triangle Inst., Research Triangle Park, NC (United States))

    1993-01-01

    This report describes work to develop inverted-grown Al[sub 0.34]Ga[sub 0.66]As/GaAs cascades. Several significant developments are reported on as follows: (1) The AM1.5 1-sun total-area efficiency of the top Al[sub 0.34]Ga[sub 0.66]As cell for the cascade was improved from 11.3% to 13.2% (NREL measurement [total-area]). (2) The cycled'' organometallic vapor phase epitaxy growth (OMVPE) was studied in detail utilizing a combination of characterization techniques including Hall-data, photoluminescence, and secondary ion mass spectroscopy. (3) A technique called eutectic-metal-bonding (EMB) was developed by strain-free mounting of thin GaAs-AlGaAs films (based on lattice-matched growth on Ge substrates and selective plasma etching of Ge substrates) onto Si carrier substrates. Minority-carrier lifetime in an EMB GaAs double-heterostructure was measured as high as 103 nsec, the highest lifetime report for a freestanding GaAs thin film. (4) A thin-film, inverted-grown GaAs cell with a 1-sun AM1.5 active-area efficiency of 20.3% was obtained. This cell was eutectic-metal-bonded onto Si. (5) A thin-film inverted-grown, Al[sub 0.34]Ga[sub 0.66]As/GaAs cascade with AM1.5 efficiency of 19.9% and 21% at 1-sun and 7-suns, respectively, was obtained. This represents an important milestone in the development of an AlGaAs/GaAs cascade by OMVPE utilizing a tunnel interconnect and demonstrates a proof-of-concept for the inverted-growth approach.

  10. Metabolism of [ 14 C]GA 19 and [ 14 C]GA 53 by ecotypes of Betula ...

    African Journals Online (AJOL)

    Continuing with this line of research, we studied the metabolism of 14C-labelled GA19 and GA53. [14C]GA19 and [14C] A53 were applied to the apices of the northern ecotype (67º N) and to the leaves of the southern ecotype (64º N) of Betula pendula Roth. under different photoperiods and at different times in order to ...

  11. Isolating GaSb membranes grown metamorphically on GaAs substrates using highly selective substrate removal etch processes

    Energy Technology Data Exchange (ETDEWEB)

    Lavrova, Olga [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering. Center for High Technology Materials; Balakrishnan, Ganesh [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering. Center for High Technology Materials

    2017-02-24

    The etch rates of NH4OH:H2O2 and C6H8O7:H2O2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH4OH:H2O2 solution has a greater etch rate differential for the GaSb/GaAs material system than C6H8O7:H2O2 solution. The selectivity of NH4OH:H2O2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11471 ± 1691 whereas that of C6H8O7:H2O2 has been measured up to 143 ± 2. The etch contrast has been verified by isolating 2 μm thick GaSb epi-layers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high-resolution X-Ray diffraction (HR-XRD) and atomic force microscopy (AFM).

  12. Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

    International Nuclear Information System (INIS)

    Grady, R; Bayram, C

    2017-01-01

    In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al X Ga (1−X) N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al X Ga (1−X) N/GaN heterojunction is formed through intentional δ -doping part of the Al X Ga (1−X) N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al X Ga (1−X) N barrier; δ -doping location (within the Al X Ga (1−X) N barrier), δ-doped Al X Ga (1−X) N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al X Ga (1−X) N barrier results in a normally-off behavior whereas Al X Ga (1−X) N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology. (paper)

  13. Conduction electrons in acceptor-doped GaAs/GaAlAs heterostructures: a review

    International Nuclear Information System (INIS)

    Zawadzki, Wlodek; Raymond, Andre; Kubisa, Maciej

    2016-01-01

    We review magneto-optical and magneto-transport effects in GaAs/GaAlAs heterostructures doped in GaAlAs barriers with donors, providing two-dimensional (2D) electron gas (2DEG) in GaAs quantum wells (QWS), and additionally doped with smaller amounts of acceptors (mostly Be atoms) in the vicinity of 2DEG. One may also deal with residual acceptors (mostly C atoms). The behavior of such systems in the presence of a magnetic field differs appreciably from those doped in the vicinity of 2DEG with donors. Three subjects related to the acceptor-doped heterostructures are considered. First is the problem of bound states of conduction electrons confined to the vicinity of negatively charged acceptors by the joint effect of a QW and an external magnetic field parallel to the growth direction. A variational theory of such states is presented, demonstrating that an electron turning around a repulsive center has discrete energies above the corresponding Landau levels. Experimental evidence for the discrete electron energies comes from the work on interband photo-magneto-luminescence, intraband cyclotron resonance and quantum magneto-transport (the Quantum Hall and Shubnikov–de Haas effects). An electron rain-down effect at weak electric fields and a boil-off effect at strong electric fields are introduced. It is demonstrated, both theoretically and experimentally, that a negatively charged acceptor can localize more than one electron. The second subject describes experiment and theory of asymmetric quantized Hall and Shubnikov–de Haas plateaus in acceptor-doped GaAs/GaAlAs heterostructures. It is shown that the main features of the plateau asymmetry can be attributed to asymmetric density of Landau states in the presence of acceptors. However, at high magnetic fields, the rain-down effect is also at work. The third subject deals with the so-called disorder modes (DMs) in the cyclotron resonance of conduction electrons. The DMs originate from random distributions of

  14. Influence of InGaN layer growth temperature on luminescence properties of InGaN/GaN multiple quantum wells

    Science.gov (United States)

    Wang, Xiaowei; Yang, Jing; Zhao, Degang; Jiang, Desheng; Liu, Zongshun; Liu, Wei; Liang, Feng; Liu, Shuangtao; Xing, Yao; Wang, Wenjie; Li, Mo

    2018-02-01

    Optical investigation was performed on InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition (MOCVD) with different temperatures. It is found that the emission intensity decreases abruptly when the growth temperature of InGaN QW decreases from 710 to 670 °C. The XRD measurements show that a poorer quality interface between the QW layers could decrease the emission quite a bit when the growth temperature is lower. In addition, due to the weakening surface mobility of adatoms, the localization states accompanied with defects are distributed more inhomogeneous at lower growth temperature, which is also responsible for the low emission intensity.

  15. Electron-hole transition in spherical QD-QW nanoparticles based on GaN∣(In,Ga)N∣GaN under hydrostatic pressure

    International Nuclear Information System (INIS)

    El Ghazi, Haddou; Jorio, Anouar

    2013-01-01

    Within the framework of effective-mass approximation and finite parabolic potential confinement barrier in which two confinement parameters are taking account, the electron (hole) energy and the ground-state electron-hole (e−h) transition in Core∣well∣shell (GaN|In x Ga 1−x N|GaN) spherical QD-QW nanoparticles are investigated as a function of the inner and the outer radii under externally applied hydrostatic pressure. The pressure dependencies of the effective-mass and the QD radius are taking into account. The results we obtained are in quite good agreement with the theoretical and the experimental findings

  16. In situ neutron powder diffraction of the formation of SrGa2D2, and hydrogenation behavior of YbGa2 and EuGa2.

    Science.gov (United States)

    Wenderoth, Patrick; Kohlmann, Holger

    2013-09-16

    The hydrogenation behavior of the Zintl phases MGa2 (M = Sr, Eu, Yb) was investigated. Upon being heated under 50 bar of hydrogen gas pressure, SrGa2 starts forming the polyanionic hydride SrGa2H2 at 125 °C as observed by in situ differential scanning calorimetry (DSC) and ex situ X-ray powder diffraction. The deuteration of SrGa2 was studied by in situ neutron powder diffraction at temperatures up to 300 °C in the pressure range of 50 ≤ p(D2) ≤ 61 bar with a time resolution of two minutes. Neither incorporation of deuterium into the interstitials of the crystal structure of SrGa2 nor any other intermediate of the reaction was observed. No significant variation in positional or occupational parameters as refined by the Rietveld method was observed for the deuteride SrGa2D2 under various temperature and pressure conditions (e.g., at T = 299 °C, p(D2) = 60 bar, space group P3m1, a = 4.4098(2) Å, c = 4.7429(3) Å, Sr in 1a, 0 0 0; Ga in 2d, 1/3 2/3 0.474(1); D in 2d, 1/3 2/3 0.120(2)). In situ DSC complemented by ex situ X-ray powder diffraction revealed that EuGa2 and YbGa2 do not form polyanionic hydrides in the investigated temperature-pressure ranges (20 °C ≤ T ≤ 220 °C, 5 bar ≤ p ≤ 54 bar). Instead binary hydrides and gallium-rich intermetallics are formed. The first refined crystal structural data are presented for YbGa6 in the tetragonal PuGa6-type structure (space group P4/nbm (No. 125), a = 6.0890(3) Å, c = 7.6562(4) Å, Yb in 2c, 3/4 1/4 0; Ga1 in 8m, 0.4750(4) 0.5250(4) 0.3377(4); Ga2 in 4g, 1/4 1/4 0.1691(5)).

  17. High mobility two-dimensional hole gases in GaAs/AlGaAs heterostructures; Hochbewegliche zweidimensionale Lochsysteme in GaAs/AlGaAs Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Gerl, Christian

    2009-10-14

    This thesis outlines the fabrication of high mobility two-dimensional hole-gases (2DHG) in GaAs/AlGaAs heterostructures with molecular beam epitaxy (MBE) and their characterization with magnetotransport measurements at low temperatures between 4 K and 30 mK. Here the optimization of the carrier mobility is focused. This will be achieved by introducing a novel carbon-filament doping source, with which contaminations of the MBE system and therefore in the grown layers can be reduced and by vary the band structure design to minimize scattering processes. With the help of these actions, hole mobilities above 1 E6 cm{sup 2}/Vs are achievable, what reflects an increase of factor 3 in the (001)- and factor 6.5 in the (110)- oriented transport plane compared to common 2DHGs. Furthermore states of the fractional Quantum Hall Effect can be observed in these 2DHGs, only visible in n-doped 2D systems so fare. Magnetotransport measurements on 2DHGs with aluminum gates reveal a hysteretic behavior of the carrier density with respect to the gate potential which can be attributed to the incorporation mechanisms of carbon atoms as acceptor. Temperature dependent magnetotransport measurements allow the evaluation of effective mass and quantum scattering time as well as the dependence of these parameters from the band structure design. In these experiments an aperiodic behavior of the Shubnikov-de Haas oscillations can be observed in the inverse magnetic field, which is attributed to the position of the fermi energy in the immediate vicinity of crossing regions of the complex Landau fan of 2DHGs. (orig.)

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

    DEFF Research Database (Denmark)

    van Capel, P. J. S.; Turchinovich, Dmitry; Porte, Henrik

    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 origin in ultrafast dynamical screening of the built-in piezoelectric field in the MQWs. The measured...

  19. Transient photoconductivity in InGaN/GaN multiple quantum wells, measured by time-resolved terahertz spectroscopy

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    2009-01-01

    Terahertz conductivity of InGaN/GaN MQWs was studied by time-resolved terahertz spectroscopy. Restoration of the built-in piezoelectric field leads to a nonexponential carrier density decay. Terahertz conductivity spectrum is described by the Drude-Smith......Terahertz conductivity of InGaN/GaN MQWs was studied by time-resolved terahertz spectroscopy. Restoration of the built-in piezoelectric field leads to a nonexponential carrier density decay. Terahertz conductivity spectrum is described by the Drude-Smith...

  20. Reduced pressure MOVPE growth and characterization of GaAs/GaAlAs heterostructures using a triethylgallium source

    Science.gov (United States)

    Norris, P.; Black, J.; Zemon, S.; Lambert, G.

    1984-09-01

    The technologically important GaAs/GaAlAs materials system has been explored via reduced pressure MOVPE using a triethylgallium source. The growth system was designed for rapid responsein order to attain sharp interfaces and is load-locked to minimize contamination from atmospheric sources. GaAs/GaAlAs epilayers have been grown over the temperature range 625-750°C at pressure between 25 and 100 Torr. Photoluminescence (PL) measurements on GaAs and GaAlAs show sharp excitonic structure indicative of high purity. Hall and C - V carrier concentration profiling results confirm this. These high purity GaAs epilayers exhibit evidence of residual Mg acceptors and GaAlAs has a high radiative efficiency due to the use of an In-Ga-Al eutectic trap. Controlled doping experiments on multilayer structures have been performed using a SiH 4 dopant source and wide range dilution system. Epilayer surfaces are essentially featureless under interference contrast microscopic examination; however, "oval defects" originating at epilayer interfaces are still observed. Multiple quantum well (MQW) structures have been fabricated, without growth interruption, as a diagnostic aid in evaluating MOVPE system dynamic response. PL characterization of MQW structures with 6.5 nm well widths indicate high-quality abrupt heterointerfaces.

  1. Theoretical studies of optical gain tuning by hydrostatic pressure in GaInNAs/GaAs quantum wells

    International Nuclear Information System (INIS)

    Gladysiewicz, M.; Wartak, M. S.; Kudrawiec, R.

    2014-01-01

    In order to describe theoretically the tuning of the optical gain by hydrostatic pressure in GaInNAs/GaAs quantum wells (QWs), the optical gain calculations within kp approach were developed and applied for N-containing and N-free QWs. The electronic band structure and the optical gain for GaInNAs/GaAs QW were calculated within the 10-band kp model which takes into account the interaction of electron levels in the QW with the nitrogen resonant level in GaInNAs. It has been shown that this interaction increases with the hydrostatic pressure and as a result the optical gain for GaInNAs/GaAs QW decreases by about 40% and 80% for transverse electric and transverse magnetic modes, respectively, for the hydrostatic pressure change from 0 to 40 kilobars. Such an effect is not observed for N-free QWs where the dispersion of electron and hole energies remains unchanged with the hydrostatic pressure. This is due to the fact that the conduction and valence band potentials in GaInAs/GaAs QW scale linearly with the hydrostatic pressure

  2. Quantitative and depth-resolved deep level defect distributions in InGaN/GaN light emitting diodes.

    Science.gov (United States)

    Armstrong, A; Henry, T A; Koleske, D D; Crawford, M H; Lee, S R

    2012-11-05

    Deep level defects in the multi-quantum well (MQW) region of InGaN/GaN light emitting diodes (LEDs) were investigated. InGaN quantum well and GaN quantum barrier defect states were distinguished using bias-dependent steady-state photocapacitance and deep level optical spectroscopy, and their possible physical origin and potential impact on LED performance is considered. Lighted capacitance-voltage measurements provided quantitative and nanoscale depth profiling of the deep level concentration within the MQW region. The concentration of every observed deep level varied strongly with depth in the MQW region, which indicates evolving mechanisms for defect incorporation during MQW growth.

  3. Linear Rashba Model of a Hydrogenic Donor Impurity in GaAs/GaAlAs Quantum Wells

    Directory of Open Access Journals (Sweden)

    Li Shu-Shen

    2008-01-01

    Full Text Available Abstract The Rashba spin-orbit splitting of a hydrogenic donor impurity in GaAs/GaAlAs quantum wells is investigated theoretically in the framework of effective-mass envelope function theory. The Rashba effect near the interface between GaAs and GaAlAs is assumed to be a linear relation with the distance from the quantum well side. We find that the splitting energy of the excited state is larger and less dependent on the position of the impurity than that of the ground state. Our results are useful for the application of Rashba spin-orbit coupling to photoelectric devices.

  4. Detection of prostate-specific antigen with biomolecule-gated AlGaN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Li, Jia-dong; Miao, Bin; Wei, Xiao-wei; Xie, Jie; Wu, Dong-min; Cheng, Jun-jie; Zhang, Jin-cheng; Zhang, Zhi-qiang

    2014-01-01

    In order to improve the sensitivity of AlGaN/GaN high electron mobility transistor (HEMT) biosensors, a simple biomolecule-gated AlGaN/GaN HEMT structure was designed and successfully fabricated for prostate specific antigen (PSA) detection. UV/ozone was used to oxidize the GaN surface and then a 3-aminopropyl trimethoxysilane (APTES) self-assembled monolayer was bound to the sensing region. This monolayer serves as a binding layer for attachment of the prostate specific antibody (anti-PSA). The biomolecule-gated AlGaN/GaN HEMT sensor shows a rapid and sensitive response when the target prostate-specific antigen in buffer solution was added to the antibody-immobilized sensing area. The current change showed a logarithm relationship against the PSA concentration from 0.1 pg/ml to 0.993 ng/ml. The sensitivity of 0.215% is determined for 0.1 pg/ml PSA solution. The above experimental result of the biomolecule-gated AlGaN/GaN HEMT biosensor suggested that this biosensor might be a useful tool for prostate cancer screening. (paper)

  5. AlGaInP/GaAs Tandem Solar Cells for Power Conversion at 400 degrees C and High Concentration

    Energy Technology Data Exchange (ETDEWEB)

    Steiner, Myles A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Perl, Emmett [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Simon, John D [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Friedman, Daniel J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sharps, Paul [SolAero Technologies Corp.; McPheeters, Claiborne [SolAero Technologies Corp.; Lee, Minjoo L. [University of Illinois at Urbana-Champaign

    2017-09-06

    We demonstrate dual junction (Al)GaInP/GaAs solar cells that are designed to operate at 400 degrees C and 1000X concentration in a hybrid photovoltaic-solar thermal concentrator system. The cells have a front metallization and anti-reflection coating that are stable under 400 degrees C operation. We show how the cell performance degrades with increasing aluminum compositions in the top cell. Our best cell is a GaInP/GaAs tandem that demonstrated 15+/-1% efficiency at 400 degrees C over a concentration range of 300-1000 suns, with several pathways to improved performance.

  6. Long wavelength MSM photodetectors fabricated on InGaNAs

    Science.gov (United States)

    Gouin, François; Noad, Julian; Higgins, Erle; Coulas, David

    2006-02-01

    Recently there has been a great deal of interest in the growth of dilute nitride quaternary alloys, such as InGaNAs, on GaAs substrates for the fabrication of GaAs-based components and optoelectronic integrated circuits. The addition of indium to the binary compound GaAs produces a ternary with a lower bandgap and larger lattice constant. The incorporation of nitrogen in this ternary further decreases the bandgap while reducing the lattice constant. This makes it possible to grow material lattice-matched to a GaAs substrate but with a narrower bandgap offering the possibility of growing materials suitable for opto-electronic devices on a GaAs substrate while operating at wavelengths used in long-distance optical communications. These devices can then be integrated with mature GaAs device technologies (MESFET, HBT) in photoreceivers and receivers/transmitters for improved functionality and reliability, lower cost, reduced size, etc. We have fabricated metal-semiconductor-metal (MSM) photodetectors on 1-μm thick In .1Ga .9N .03As .97 epilayers, a composition that results in a bandgap in the 1.3 μm region. We report on the DC characteristics, frequency dependence and wavelength dependence of the photoresponse. The results are compared to MSMs fabricated on GaAs. The temporal response is not as fast as that of GaAs MSMs and may be related to low carrier mobility. This shortcoming has been reported as the cause for the lower-than-expected efficiency of solar cells fabricated using this quarternary. The effect of growth conditions and thermal processing on detector characteristics such as bandwidth and dark current were investigated. The challenges associated with the use of InGaNAs in photodetectors (such as defects, response speed, requirement for thermal anneal) will be discussed.

  7. Current steering effect of GaN nanoporous structure

    International Nuclear Information System (INIS)

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

    2014-01-01

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

  8. GaSb-related materials for TPV cells

    Science.gov (United States)

    Mauk, M. G.; Andreev, V. M.

    2003-05-01

    A survey of materials options and technologies for GaSb-related thermophotovoltaic (TPV) cells is presented, followed by an overview of device design principles and issues. This device technology has been developed for thermal-to-electric generator systems with thermal emitter infrared sources operated in the 1000-1200 °C range. Significant results for the growth, material characterization and device performance of TPV cells based on InGaAsSb, InGaSb, AlGaAsSb and InAsSbP fabricated by LPE, MOCVD, MBE and diffusion methods are reviewed. For single-junction TPV cells, epitaxial heterostructures with a ~0.53 eV bandgap InGaAsSb base layer and wide-bandgap AlGaAsSb or GaSb window/cladding layers (all closely lattice matched to a GaSb substrate) represent the state of the art. As an alternative, a low-cost Zn-diffusion technology for fabrication of InGaAsSb p-n homojunction structures has been developed for producing the high efficiency TPV cells. External quantum yields as high as 90% at wavelengths (around 2000 nm wavelength), and response edges to about 2400 nm wavelength have been obtained with these TPV cells. Multijunction tandem TPV devices based on GaSb top cells and InGaAsSb bottom cells provide even higher performance. TPV cells based on InAsSbP, also reviewed here, have spectral responses in wavelengths in the 2.5-3.5 mum range, and thus provide a means for utilizing radiation from thermal emitters with lower temperatures.

  9. Radiation effects in pigtailed GaAs and GaA1As LEDs

    International Nuclear Information System (INIS)

    Barnes, C.E.

    1981-06-01

    Permanent and transient radiation effects have been studied in Plessey pigtailed, high radiance GaAs and GaAlAs LEDs using neutron, gamma ray and X-ray sources. The radiation-induced source of degradation in these devices was determined by also examining both bare, unpigtailed LEDs and separate samples of the Corning fibers used as pigtails. No transient effects were observed in the unpigtailed LEDs during either pulsed neutron or X-ray exposure. In contrast, the Corning doped silica fibers exhibited strong transient attenuation following pulsed X-ray bombardment. Permanent neutron damage in these pigtailed LEDs consisted essentially of light output degradation in the LED itself. Permanent gamma ray effects due to a Co-60 irradiation of 1 megarad were restricted to a small increase in attenuation in the fiber. The two primary radiation effects were then transient attenuation in the fiber pigtail and permanent neutron-induced degradation of the LED

  10. Radial multiple quantum well GaAs/AlGaAs heterostructure formed in nanowires

    Science.gov (United States)

    Tito, M. A.; Tavares, B. G. M.; Arakaki, H.; de Souza, C. A.; Pusep, Yu A.

    2016-12-01

    Optical emission of the heterostructured GaAs/AlGaAs core/shell nanowires with a multiple quantum well structure of the shell was found dominant by spatially indirect recombination of the electrons in the NW core with the photoexcited holes confined in the QWs of the shell. Multiple photoluminescence peak structure corresponding to the contributions of the individual quantum wells was observed. Numerical calculations of the confined hole eigenstate energies allowed for determination of the characteristic parameters of the studied nanowires, such as the surface depletion potential, intrinsic electron concentration and the actual widths of the quantum wells and the barriers formed in the nanowire shell. The presented data suggest formation of highly uniform cylinder symmetry two-dimensional quantum wells embedded in the nanowire shell.

  11. Harsh photovoltaics using InGaN/GaN multiple quantum well schemes

    KAUST Repository

    Lien, Derhsien

    2015-01-01

    Harvesting solar energy at extremely harsh environments is of practical interest for building a self-powered harsh electronic system. However, working at high temperature and radiative environments adversely affects the performance of conventional solar cells. To improve the performance, GaN-based multiple quantum wells (MQWs) are introduced into the solar cells. The implementation of MQWs enables improved efficiency (+0.52%/K) and fill factor (+0.35%/K) with elevated temperature and shows excellent reliability under high-temperature operation. In addition, the GaN-based solar cell exhibits superior radiation robustness (lifetime >30 years under solar storm proton irradiation) due to their strong atomic bonding and direct-bandgap characteristics. This solar cell employing MQW nanostructures provides valuable routes for future developments in self-powered harsh electronics.

  12. Investigation of InGaN/GaN laser degradation based on luminescence properties

    International Nuclear Information System (INIS)

    Wen, Pengyan; Zhang, Shuming; Liu, Jianping; Li, Deyao; Zhang, Liqun; Sun, Qian; Tian, Aiqin; Zhou, Kun; Yang, Hui; Zhou, Taofei

    2016-01-01

    Degradation of InGaN/GaN laser diode (LD) is investigated based on the luminescence properties. Gradual degradation of the LD is presented with the threshold current increase and the slope efficiency decrease. The cathodoluminescence and photoluminescence characterizations of the LD show a dislocation independent degradation of the active region under the ridge. Detailed studies on the temperature-dependent micro-photoluminescence and the electroluminescence indicate that the degradation of the LD is attributed to the generation of non-radiative recombination centers in the local multiple quantum well regions with lower indium content. The activation energy of the non-radiative recombination centers is about 10.2 meV.

  13. Investigation of InGaN/GaN laser degradation based on luminescence properties

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Pengyan; Zhang, Shuming, E-mail: smzhang2010@sinano.ac.cn; Liu, Jianping; Li, Deyao; Zhang, Liqun; Sun, Qian; Tian, Aiqin; Zhou, Kun; Yang, Hui [Key Laboratory of Nanodevices and Applications, Chinese Academy of Sciences, Suzhou 215123 (China); Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Zhou, Taofei [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China)

    2016-06-07

    Degradation of InGaN/GaN laser diode (LD) is investigated based on the luminescence properties. Gradual degradation of the LD is presented with the threshold current increase and the slope efficiency decrease. The cathodoluminescence and photoluminescence characterizations of the LD show a dislocation independent degradation of the active region under the ridge. Detailed studies on the temperature-dependent micro-photoluminescence and the electroluminescence indicate that the degradation of the LD is attributed to the generation of non-radiative recombination centers in the local multiple quantum well regions with lower indium content. The activation energy of the non-radiative recombination centers is about 10.2 meV.

  14. AlGaAs/GaAs laser diode bars (λ = 808 nm) with improved thermal stability

    International Nuclear Information System (INIS)

    Marmalyuk, A A; Ladugin, M A; Andreev, A Yu; Telegin, K Yu; Yarotskaya, I V; Meshkov, A S; Konyaev, V P; Sapozhnikov, S M; Lebedeva, E I; Simakov, V A

    2013-01-01

    Two series of AlGaAs/GaAs laser heterostructures have been grown by metal-organic vapour phase epitaxy, and 808-nm laser diode bars fabricated from the heterostructures have been investigated. The heterostructures differed in waveguide thickness and quantum well depth. It is shown that increasing the barrier height for charge carriers in the active region has an advantageous effect on the output parameters of the laser sources in the case of the heterostructures with a narrow symmetric waveguide: the slope of their power – current characteristics increased from 0.9 to 1.05 W A -1 . Thus, the configuration with a narrow waveguide and deep quantum well is better suited for high-power laser diode bars under hindered heat removal conditions. (lasers)

  15. AlGaAs/GaAs laser diode bars (λ = 808 nm) with improved thermal stability

    Energy Technology Data Exchange (ETDEWEB)

    Marmalyuk, A A; Ladugin, M A; Andreev, A Yu; Telegin, K Yu; Yarotskaya, I V; Meshkov, A S; Konyaev, V P; Sapozhnikov, S M; Lebedeva, E I; Simakov, V A [Open Joint-Stock Company M.F. Stel' makh Polyus Research Institute, Moscow (Russian Federation)

    2013-10-31

    Two series of AlGaAs/GaAs laser heterostructures have been grown by metal-organic vapour phase epitaxy, and 808-nm laser diode bars fabricated from the heterostructures have been investigated. The heterostructures differed in waveguide thickness and quantum well depth. It is shown that increasing the barrier height for charge carriers in the active region has an advantageous effect on the output parameters of the laser sources in the case of the heterostructures with a narrow symmetric waveguide: the slope of their power – current characteristics increased from 0.9 to 1.05 W A{sup -1}. Thus, the configuration with a narrow waveguide and deep quantum well is better suited for high-power laser diode bars under hindered heat removal conditions. (lasers)

  16. Grin-parabolic optical cavity characteristic study in AlGaAs-GaAs laser

    International Nuclear Information System (INIS)

    Martin A, J.A.; Diaz A, P.; Garcia R, F.

    1994-01-01

    In this paper we study theoretically the characteristics of a GaAs-AlGaAs laser transverse optical cavity with a parabolic graded variation of the refractive index (GRIN-SCH). We give an exact solution of the wave equation and analyze the near field distribution as well as the values of the effective refractive index of the fundamental mode. The condition for a mono mode optical cavity are also deduced. The behavior of the confinement factor and the far field in the plane perpendicular to the active region are reported. The results for the GRIN-SCH structure are compared with a similar SCH-straight laser transverse optical cavity. (Author) 11 refs

  17. Temperature dependent optical properties of stacked InGaAs/GaAs quantum rings

    Energy Technology Data Exchange (ETDEWEB)

    Ouerghui, W. [Unite de Recherche Des Physiques des Semiconducteurs et Capteurs, Institut Preparatoire aux Etudes Scientifiques et Techniques, La Marsa 2070, Tunis (Tunisia)], E-mail: ouerghuiwalid@yahoo.fr; Martinez-Pastor, J.; Gomis, J. [Instituto de Ciencia de los Materials, Universidad de Valencia, P.O. Box 22085, 46071 Valencia (Spain); Maaref, M. [Unite de Recherche Des Physiques des Semiconducteurs et Capteurs, Institut Preparatoire aux Etudes Scientifiques et Techniques, La Marsa 2070, Tunis (Tunisia); Granados, D.; Garcia, J.M. [Instituto de Microelectronica de Madrid, Isaac newton 8, 28760 Tres Cantos, Madrid (Spain)

    2008-07-01

    In this paper we describe the results of temperature dependent photoluminescence intensity and decay time measurements of In(Ga)As/GaAs quantum rings where the depth of barrier is varied from sample to sample. The activation energy found for the reduction of the exciton decay time as a function of the temperature is approximately half the value of the thermionic escape energy of excitons. The temperature dependant behaviour is ascribed to the carriers lost via the excited state to the WL. The time resolved PL study indicates that thermal escape mechanisms is not so affected by reducing the spacer thickness, but it's influenced essentially by the excited state recombination.

  18. Composition Related Electrical Active Defect States of InGaAs and GaAsN

    Directory of Open Access Journals (Sweden)

    Arpad Kosa

    2017-01-01

    Full Text Available This paper discusses results of electrically active defect states - deep energy level analysis in InGaAs and GaAsN undoped semiconductor structures grown for solar cell applications. Main attention is focused on composition and growth condition dependent impurities and the investigation of their possible origins. For this purpose a widely utilized spectroscopy method, Deep Level Transient Fourier Spectroscopy, was utilized. The most significant responses of each sample labelled as InG2, InG3 and NG1, NG2 were discussed in detail and confirmed by simulations and literature data. The presence of a possible dual conduction type and dual state defect complex, dependent on the In/N composition, is reported. Beneficial characteristics of specific indium and nitrogen concentrations capable of eliminating or reducing certain point defects and dislocations are stated.

  19. Microwave characterization and modeling of GaAs/AlGaAs heterojunction bipolar transistors

    Science.gov (United States)

    Simons, Rainee N.; Romanofsky, Robert R.

    1987-01-01

    The characterization and modeling of a microwave GaAs/AlGaAs heterojunction Bipolar Transistor (HBT) are discussed. The de-embedded scattering parameters are used to derive a small signal lumped element equivalent circuit model using EEsof's Touchstone software package. Each element in the equivalent circuit model is shown to have its origin within the device. The model shows good agreement between the measured and modeled scattering parameters over a wide range of bias currents. Further, the MAG (maximum available power gain) and the h sub 21 (current gain) calculated from the measured data and those predicted by the model are also in good agreement. Consequently, the model should also be capable of predicting the f sub max and the f sub T of other HBTs.

  20. Evaluation of the two-photon absorption characteristics of GaSb/GaAs quantum rings

    Energy Technology Data Exchange (ETDEWEB)

    Wagener, M. C.; Botha, J. R. [Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth 6031 (South Africa); Carrington, P. J. [Department of Electronic and Electrical Engineering, University College London, London (United Kingdom); Krier, A. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom)

    2014-07-28

    The optical parameters describing the sub-bandgap response of GaSb/GaAs quantum rings solar cells have been obtained from photocurrent measurements using a modulated pseudo-monochromatic light source in combination with a second, continuous photo-filling source. By controlling the charge state of the quantum rings, the photoemission cross-sections describing the two-photon sub-bandgap transitions could be determined independently. Temperature dependent photo-response measurements also revealed that the barrier for thermal hole emission from the quantum rings is significantly below the quantum ring localisation energy. The temperature dependence of the sub-bandgap photo-response of the solar cell is also described in terms of the photo- and thermal-emission characteristics of the quantum rings.

  1. Electron irradiation of near-UV GaN/InGaN light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Lee, In-Hwan; Cho, Han-Su [Department of Materials Science and Engineering, Korea University, Seoul (Korea, Republic of); Polyakov, Alexander Y.; Smirnov, N.B.; Shchemerov, I.V.; Zinovyev, R.A.; Didenko, S.I.; Lagov, P.B. [National University of Science and Technology MISiS, Moscow (Russian Federation); Shmidt, N.M.; Shabunina, E.I. [Ioffe Physico-Technical Institute, St. Petersburg (Russian Federation); Tal' nishnih, N.A. [Submicron Heterostructures for Microelectronics Research and Engineering Center, St. Petersburg (Russian Federation); Hwang, Sung-Min [Soft-Epi, Inc., Opo-ro 240, Gwangju-si, Gyeonggi-do (Korea, Republic of); Pearton, S.J. [Department of Materials Science and Engineering, University of Florida, Gainesville, FL (United States)

    2017-10-15

    Irradiation with 6 MeV electrons of near-UV (peak wavelength 385-390 nm) multi-quantum-well (MQW) GaN/InGaN light emitting diodes (LEDs) causes an increase in density of deep electron traps near E{sub c} -0.8 and E{sub c} -1 eV, and correlates to a 90% decrease of electroluminescence (EL) efficiency after a fluence of 1.1 x 10{sup 16} cm{sup -2}. The likely origin of the EL efficiency decrease is this increase in concentration of the E{sub c} -0.8 eV and E{sub c} -1 eV traps. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Photocapacitance characteristics of (In,Ga)N/GaN MQW structures

    International Nuclear Information System (INIS)

    Rivera, C.; Pau, J.L.; Munoz, E.; Ive, T.; Brandt, O.

    2006-01-01

    Photocapacitance techniques have been used to study the electronic properties of (In,Ga)N/GaN quantum wells (QWs). Negative differential capacitance (NDC) features were observed at room temperature for the first time in capacitance-voltage (C-V) experiments under optical excitation. A detailed analysis of the results seems to indicate that charge accumulation in quantum dot-like structures embedded in the QWs could be responsible of such behaviour. Polarization field effects present in these structures are detected through C-V hysteresis, allowing to estimate built-in electric fields as high as 1.9 MV/cm in 14% In QWs. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  3. Study of electrical properties of AlGaN/GaN structures by capacitance method

    International Nuclear Information System (INIS)

    Sebok, J.; Stuchlikova, L.; Pechacek, J.; Petrus, M.; Kovac, J.; Nemec, M.; Harmatha, L.; Skriniarova, J.; Pisecny, P.

    2011-01-01

    This work deals with study of electrical properties of AlGaN/GaN Schottky structures by capacitance method (CV, Ct and DLTS). Cross point (independent on temperature depth) around -1.2 V range was observed. The position of hetero-structure's interface set by the maximum of concentration profile was determined to 23 nm below the surface. Five hole-like deep energy levels (HL1 - HL5) have been identified from measured DLTFS spectra and capacitance transient. Basic parameters of these defects and comparison with the parameters set out in publications are described in the summary table (Tab. 1). The exact origin of this deep level remains an open question similarly as published in [7 - 10] and will be subjected for further investigations with complementary electrical and structural methods. (authors)

  4. Capacitance and conductance dispersion in AlGaN/GaN heterostructure

    International Nuclear Information System (INIS)

    Yan Dawei; Wang Fuxue; Zhu Zhaomin; Cheng Jianmin; Gu Xiaofeng

    2013-01-01

    The dispersion mechanism in Al 0.27 Ga 0.73 N/GaN heterostructure was investigated using frequency-dependent capacitance and conductance measurements. It was found that the significant capacitance and conductance dispersion occurred primarily for measurement frequency beyond ∼ 100 kHz before the channel cutoff at the interface, suggesting that the vertical polarization electrical field under the gate metal should be closely related with the observed dispersive behavior. According to the Schottky—Read—Hall model, a traditional trapping mechanism cannot be used to explain our result. Instead, a piezoelectric polarization strain relaxation model was adopted to interpret the dispersion. By fitting the obtained capacitance data, the corresponding characteristic time and charge density were determined ∼10 −8 s and ∼ 5.26 × 10 12 cm −2 respectively, in good agreement with the conductance data and theoretical prediction. (semiconductor devices)

  5. Small-signal model parameter extraction for AlGaN/GaN HEMT

    Science.gov (United States)

    Le, Yu; Yingkui, Zheng; Sheng, Zhang; Lei, Pang; Ke, Wei; Xiaohua, Ma

    2016-03-01

    A new 22-element small signal equivalent circuit model for the AlGaN/GaN high electron mobility transistor (HEMT) is presented. Compared with the traditional equivalent circuit model, the gate forward and breakdown conductions (G gsf and G gdf) are introduced into the new model to characterize the gate leakage current. Additionally, for the new gate-connected field plate and the source-connected field plate of the device, an improved method for extracting the parasitic capacitances is proposed, which can be applied to the small-signal extraction for an asymmetric device. To verify the model, S-parameters are obtained from the modeling and measurements. The good agreement between the measured and the simulated results indicate that this model is accurate, stable and comparatively clear in physical significance.

  6. Small-signal model parameter extraction for AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Yu Le; Zhang Sheng; Ma Xiaohua; Zheng Yingkui; Pang Lei; Wei Ke

    2016-01-01

    A new 22-element small signal equivalent circuit model for the AlGaN/GaN high electron mobility transistor (HEMT) is presented. Compared with the traditional equivalent circuit model, the gate forward and breakdown conductions (G gsf and G gdf ) are introduced into the new model to characterize the gate leakage current. Additionally, for the new gate-connected field plate and the source-connected field plate of the device, an improved method for extracting the parasitic capacitances is proposed, which can be applied to the small-signal extraction for an asymmetric device. To verify the model, S-parameters are obtained from the modeling and measurements. The good agreement between the measured and the simulated results indicate that this model is accurate, stable and comparatively clear in physical significance. (paper)

  7. Effect of annealing on sheet carrier density of AlGaN/GaN HEMT structure

    Science.gov (United States)

    Chen, Nie-Chuan; Tseng, Chien-Yuan; Lin, Hsin-Tung

    2009-01-01

    The effects of surface state on sheet carrier density in the Al 0.17Ga 0.83N/GaN heterostructure were investigated. The sheet carrier density obtained by Hall measurement was 1.803×10 13 e/cm 2. However, this value was inconsistent with the capacitance-voltage ( C- V) measurements. This carrier density varied with the surface conditions of the samples that were prepared for Hall and C- V measurements. To study further the effects of the surface conditions on the sheet carrier densities, the samples were annealed at various temperatures and then characterized by Hall and work function measurements. The carrier densities increased with annealing temperatures. Meanwhile, the work functions decreased. Accordingly, the relationship between the surface states and the sheet carrier densities was determined.

  8. Small signal modeling of AlGaN/GaN HEMTs with consideration of CPW capacitances

    Science.gov (United States)

    Jiangfeng, Du; Peng, Xu; Kang, Wang; Chenggong, Yin; Yang, Liu; Zhihong, Feng; Shaobo, Dun; Qi, Yu

    2015-03-01

    Given the coplanar waveguide (CPW) effect on AlGaN/GaN high electron mobility transistors at a high frequency, the traditional equivalent circuit model cannot accurately describe the electrical characteristics of the device. The admittance of CPW capacitances is large when the frequency is higher than 40 GHz; its impact on the device cannot be ignored. In this study, a small-signal equivalent circuit model considering CPW capacitance is provided. To verify the model, S-parameters are obtained from the modeling and measurements. A good agreement is observed between the simulation and measurement results, indicating the reliability of the model. Project supported by the National Natural Science Foundation of China (Nos. 61376078, 61274086) and the Fundamental Research Funds for the Central Universities of China (No. ZYGX2012J041).

  9. Ultrafast dynamics of type-II GaSb/GaAs quantum dots

    International Nuclear Information System (INIS)

    Komolibus, K.; Piwonski, T.; Gradkowski, K.; Reyner, C. J.; Liang, B.; Huffaker, D. L.; Huyet, G.; Houlihan, J.

    2015-01-01

    In this paper, room temperature two-colour pump-probe spectroscopy is employed to study ultrafast carrier dynamics in type-II GaSb/GaAs quantum dots. Our results demonstrate a strong dependency of carrier capture/escape processes on applied reverse bias voltage, probing wavelength and number of injected carriers. The extracted timescales as a function of both forward and reverse bias may provide important information for the design of efficient solar cells and quantum dot memories based on this material. The first few picoseconds of the dynamics reveal a complex behaviour with an interesting feature, which does not appear in devices based on type-I materials, and hence is linked to the unique carrier capture/escape processes possible in type-II structures

  10. Spin relaxation in InGaN quantum disks in GaN nanowires

    KAUST Repository

    Banerjee, Animesh

    2011-12-14

    The spin relaxation time of photoinduced conduction electrons has been measured in InGaN quantum disks in GaN nanowires as a function of temperature and In composition in the disks. The relaxation times are of the order of ∼100 ps at 300 K and are weakly dependent on temperature. Theoretical considerations show that the Elliott-Yafet scattering mechanism is essentially absent in these materials and the results are interpreted in terms of the D\\'yakonov-Perel\\' relaxation mechanism in the presence of Rashba spin-orbit coupling of the wurtzite structure. The calculated spin relaxation times are in good agreement with the measured values. © 2011 American Chemical Society.

  11. Quantum transport in low-dimensional AlGaN/GaN systems

    International Nuclear Information System (INIS)

    Spirito, D.; Frucci, G.; Di Gaspare, A.; Di Gaspare, L.; Giovine, E.; Notargiacomo, A.; Roddaro, S.; Beltram, F.; Evangelisti, F.

    2011-01-01

    In this work, we investigated the magnetotransport properties of a two dimensional electron gas hosted in an AlGaN/AlN/GaN heterostructure and one-dimensional devices fabricated on it. At cryogenic temperature, high mobility and long mean free path is achieved, allowing ballistic transport experiments. Longitudinal resistivity measured in Hall bar geometry shows well-developed Shubnikov–de Haas oscillations with amplitude modulation. Amongst possible mechanisms, the zero-field spin splitting may be the origin of the observed effects. Split gate quantum point contacts were fabricated by electron beam lithography. Linear conductance measurements at zero magnetic field show clear quantized conductance plateaus at 2e 2 /h and 4e 2 /h. Non-perfectly quantized conductance values are found for higher plateaus, suggesting the presence of impurity scattering.

  12. InGaN/GaN core/shell nanowires for visible to ultraviolet range photodetection

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Hezhi; Lavenus, Pierre; Julien, Francois H.; Tchernycheva, Maria [Institut d' Electronique Fondamentale, UMR CNRS 8622, Universite Paris Sud 11, 91405, Orsay (France); Messanvi, Agnes [Institut d' Electronique Fondamentale, UMR CNRS 8622, Universite Paris Sud 11, 91405, Orsay (France); Universite Grenoble Alpes, 38000, Grenoble (France); CEA, INAC-SP2M, ' ' Nanophysique et semiconducteurs' ' Group, 38000, Grenoble (France); Durand, Christophe; Eymery, Joel [Universite Grenoble Alpes, 38000, Grenoble (France); CEA, INAC-SP2M, ' ' Nanophysique et semiconducteurs' ' Group, 38000, Grenoble (France); Babichev, Andrey [ITMO University, 197101, St. Petersburg (Russian Federation); Ioffe Institute, Polytekhnicheskaya 26, 194021, St. Petersburg (Russian Federation)

    2016-04-15

    We report on the fabrication and characterization of single nitride nanowire visible-to-ultraviolet p-n photodetectors. Nitride nanowires containing 30 InGaN/GaN radial quantum wells with 18% indium fraction were grown by catalyst-free metal-organic vapour phase epitaxy. Single nanowires were contacted using optical lithography. As expected for a radial p-n junction, the current-voltage (I-V) curves of single wire detectors show a rectifying behavior in the dark and a photocurrent under illumination. The detectors present a response in the visible to UV spectral range starting from 2.8 eV. The peak responsivity is 0.17 A/W at 3.36 eV. The on-off switching time under square light pulses is found to be below 0.1 s. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Capacitance spectroscopy on n-type GaNAs/GaAs embedded quantum structure solar cells

    Science.gov (United States)

    Venter, Danielle; Bollmann, Joachim; Elborg, Martin; Botha, J. R.; Venter, André

    2018-04-01

    In this study, both deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) have been used to study the properties of electrically active deep level centers present in GaNAs/GaAs quantum wells (QWs) embedded in p-i-n solar cells. The structures were grown by molecular beam epitaxy (MBE). In particular, the electrical properties of samples with Si (n-type) doping of the QWs were investigated. DLTS revealed four deep level centers in the material, whereas only three were detected by AS. NextNano++ simulation software was used to model the sample band-diagrams to provide reasoning for the origin of the signals produced by both techniques.

  14. Efficient InGaP/GaAs DJ solar cell with double back surface field layer

    Directory of Open Access Journals (Sweden)

    G.P. Mishra

    2015-09-01

    Full Text Available An effective and optimised BSF layer is an important layer in both single junction and multijunction solar cells. In this work the use of the double layer BSF for top cell with their varied thicknesses is investigated on GaInP/GaAs DJ solar cell using the computational numerical modelling TCAD tool Silvaco ATLAS. The detail photo-generation rates are determined. The major modelling stages are described and the simulation results are validated with published experimental data in order to describe the accuracy of our results produced. For this optimized cell structure, the maximum Jsc = 17.33 mA/cm2, Voc = 2.66 V, and fill factor (FF = 88.67% are obtained under AM1.5G illumination, exhibiting a maximum conversion efficiency of 34.52% (1 sun and 39.15% (1000 suns.

  15. Characteristics of GaAs/AlGaAs-doped channel MISFET's at cryogenic temperatures

    International Nuclear Information System (INIS)

    Laskar, J.; Kolodzey, J.; Ketterson, A.A.; Adesida, I.; Cho, A.Y.

    1990-01-01

    The authors present high-frequency measurements at cryogenic temperatures to 125 K of 0.3-μm gate length GaAs/Al 0.3 Ga 0.7 As metal insulator semiconductor field-effect transistors (MISFET's) with a doped channel. Experimental results demonstrate significant improvement in performance including an increase in the maximum frequency of oscillation f max from 70 to 81 GHz and an increase in the unity current gain cutoff frequency f T from 46 to 57 GHz. Independently determined decreases in electron mobility and increases in electron velocity under similar conditions lead to the conclusion that carrier velocity and not mobility controls transport in these devices. These results show the high-speed potential of doped channel MISFET's at both room temperature and cryogenic temperatures

  16. InGaP/InGaAs field-effect transistor typed hydrogen sensor

    Science.gov (United States)

    Tsai, Jung-Hui; Liou, Syuan-Hao; Lin, Pao-Sheng; Chen, Yu-Chi

    2018-02-01

    In this article, the Pd-based mixture comprising silicon dioxide (SiO2) is applied as sensing material for the InGaP/InGaAs field-effect transistor typed hydrogen sensor. After wet selectively etching the SiO2, the mixture is turned into Pd nanoparticles on an interlayer. Experimental results depict that hydrogen atoms trapped inside the mixture could effectively decrease the gate barrier height and increase the drain current due to the improved sensing properties when Pd nanoparticles were formed by wet etching method. The sensitivity of the gate forward current from air (the reference) to 9800 ppm hydrogen/air environment approaches the high value of 1674. Thus, the studied device shows a good potential for hydrogen sensor and integrated circuit applications.

  17. Faraday rotation in multiple quantum wells of GaAs/AlGaAs

    International Nuclear Information System (INIS)

    Dudziak, E.; Bozym, J.; Prochnik, D.; Wasilewski, Z.R.

    1996-01-01

    We report on the results of first measurements on the Faraday rotation of modulated n-doped multiple quantum wells of GaAs/Al x Ga 1-x As (x = 0.312). The measurements have been performed in the magnetic fields up to 13 T at the temperature of 2 K, in the spectral region of interband transitions. A rich structure of magneto-excitons has been found in the measured spectra. Faraday rotation (phase) measurements are proposed as an alternative method to the photoluminescence excitation for investigations of magneto-excitons in quantum wells. The dependence of measured Faraday rotation on magnetic field and hypothetical connections with quantum Hall effect are also discussed. (author)

  18. Double-scaled disorder in Ga(N,As,P)/GaP multiquantum wells

    International Nuclear Information System (INIS)

    Karcher, C.; Jandieri, K.; Kunert, B.; Fritz, R.; Volz, K.; Stolz, W.; Gebhard, F.; Baranovskii, S.D.; Heimbrodt, W.

    2013-01-01

    The compositional dependence of the properties of metastable Ga(N,As,P) has been characterized optically by means of temperature dependent absorptive and emissive techniques. By assuming a two-scaled disorder within the alloy caused by microscopic composition fluctuations on the one hand and a fluctuation of strain fields or the well width on the other hand, Monte Carlo simulations of the carrier dynamics are in good agreement with the experimental findings. The compositional dependence further reveals an increase of disorder with decreasing nitrogen content. - Highlights: ► Temperature dependent spectral dataset of two Ga(N,As,P)/ MQWs with varying composition. ► High resolution TEM study revealing height fluctuations within the triple QWs. ► Two distinct scales of disorder corresponding to two spatial length scales. ► Almost perfect Monte-Carlo simulations of the experimental findings. ► Theoretical explanation of the discovered reduction of disorder with increasing N.

  19. Mitigating Structural Defects in Droop-Minimizing InGaN/GaN Quantum Well Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Zhibo; Chesin, Jordan; Singh, Akshay; Nelson, Erik; Wildeson, Isaac; Deb, Parijat; Armstrong, Andrew; Stach, Eric; Gradecak, Silvija

    2016-12-01

    Modern commercial InGaN/GaN blue LEDs continue to suffer from efficiency droop, a reduction in efficiency with increasing drive current. External quantum efficiency (EQE) typically peaks at low drive currents (< 10 A cm2) and drops monotonically at higher current densities, falling to <85% of the peak EQE at a drive current of 100 A cm2. Mitigating droop-related losses will yield tremendous gains in both luminous efficacy (lumens/W) and cost (lumens/$). Such improvements are critical for continued large-scale market penetration of LED technologies, particularly in high-power and high flux per unit area applications. However, device structures that reduce droop typically require higher indium content and are accompanied by a corresponding degradation in material quality which negates the droop improvement via enhanced Shockley-Read-Hall (SRH) recombination. In this work, we use advanced characterization techniques to identify and classify structural defects in InGaN/GaN quantum well (QW) heterostructures that share features with low-droop designs. Using aberration-corrected scanning transmission electron microscopy (Cs-STEM), we find the presence of severe well width fluctuations (WWFs) in a number of low droop device architectures. However, the presence of WWFs does not correlate strongly with external quantum efficiency nor defect densities measured via deep level optical spectroscopy (DLOS). Hence, performance losses in the heterostructures of interest are likely dominated by nanoscale point or interfacial defects rather than large-scale extended defects.

  20. Preparation and properties of thick intentionally undopted GaInP/GaAs layers

    Czech Academy of Sciences Publication Activity Database

    Nohavica, Dušan; Gladkov, Petar; Žďánský, Karel; Pospíšil, S. (ed.); Smith, K.M. (ed.); Wilhelm, I. (ed.)

    1999-01-01

    Roč. 434, No 1 Special Issue (1999), s. 164-168 ISSN 0168-9002. [International Workshop on Gallium Arsenide and Related Compounds /6./. Prague, 22.06.1998-26.06.1998] R&D Projects: GA AV ČR IAA1010807 Institutional research plan: CEZ:AV0Z2067918 Keywords : III-V semiconductors * photoluminescence * semiconductor doping Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.921, year: 1999

  1. Unconstrained Heterogeneous Colloidal Quantum Dots Embedded in GaAs/GaSb Nanovoids

    Science.gov (United States)

    2014-04-17

    fabrication. Etching on a nanoscale is presently achieved through e-beam lithography, scanning-tunneling-microscopy-assisted lithography, optical ...as the As and the Sb sources. Operating temperatures were 900 C and 950 C, resulting in As2 and Sb2, respectively. A pyrometer was used to measure...because of it, GaAs absorbed the excitation wavelength of the QDs to reduce the apparent QE. Sapphire, on the other hand, has a wide optical

  2. Optical and acoustic phonon modes in strained InGaAs/GaAs rolled up tubes

    Science.gov (United States)

    Angelova, T.; Shtinkov, N.; Ivanov, Ts.; Donchev, V.; Cantarero, A.; Deneke, Ch.; Schmidt, O. G.; Cros, A.

    2012-05-01

    Rolled-up semiconductor tubes of various diameters made of alternating In0.215Ga0.785As/GaAs layers have been investigated by means of Raman scattering. The optical and acoustic phonon modes of individual tubes have been studied and compared with the characteristics of the surrounding material. After tube formation, the frequency of the phonon modes shifts with respect to the as-grown material and disorder activated modes are observed. The frequency shifts are related to the residual strain in the tubes through the deformation potential approximation. Good agreement with atomistic valence force field simulations and x-ray micro-diffraction measurements is found. By comparison with x-ray data, a Raman strain constant K = 0.65 is proposed for In0.215Ga0.785As. In the low frequency range, acoustic mode doublets are observed on the tubes that are absent in the surrounding material. They show clear evidence of the formation of periodic superlattices after the rolling-up process, and give insight into the quality of their interfaces.

  3. Emergence of localized states in narrow GaAs/AlGaAs nanowire quantum well tubes.

    Science.gov (United States)

    Shi, Teng; Jackson, Howard E; Smith, Leigh M; Jiang, Nian; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Zheng, Changlin; Etheridge, Joanne

    2015-03-11

    We use low-temperature photoluminescence, photoluminescence excitation, and photoluminescence imaging spectroscopy to explore the optical and electronic properties of GaAs/AlGaAs quantum well tube (QWT) heterostructured nanowires (NWs). We find that GaAs QWTs with widths >5 nm have electronic states which are delocalized and continuous along the length of the NW. As the NW QWT width decreases from 5 to 1.5 nm, only a single electron state is bound to the well, and no optical excitations to a confined excited state are present. Simultaneously, narrow emission lines (fwhm points along the length of the NW. We find that these quantum-dot-like states broaden at higher temperatures and quench at temperatures above 80 K. The lifetimes of these localized states are observed to vary from dot to dot from 160 to 400 ps. The presence of delocalized states and then localized states as the QWTs become more confined suggests both opportunities and challenges for possible incorporation into quantum-confined device structures.

  4. Electron states at electrolyte/n-GaN and electrolyte/n-InGaN interfaces

    International Nuclear Information System (INIS)

    Rudinsky, M. E.; Gutkin, A. A.; Brunkov, P. N.

    2012-01-01

    The differential capacitance and differential active conductance of rectifying contacts of n-GaN and n-In x Ga 1−x N (x ≈ 0.15) with an electrolyte (0.2 M aqueous solutions of NaOH, NaCl, or HCl) have been studied. It was found that electron states with energies corresponding to the upper half of the energy gap of a semiconductor exist at the interface between these semiconductors and a NaOH solution. The density and characteristic recharging time of states noticeably contributing to the differential capacitance and differential active conductance at probe-voltage frequencies of 0.3–1 kHz grow with their binding energy and, for states lying at 0.15–0.3 eV below the conduction-band bottom of n-GaN, fall within the ranges 10 12 –2 × 10 13 cm −2 eV −1 and 10 −4 –10 −2 s, respectively. For contacts with NaCl and HCl solutions, there are no states of this kind. It is assumed that the observed states are related to the adsorption of hydroxyl groups.

  5. AlGaN/GaN-based HEMTs for electrical stimulation of neuronal cell cultures

    International Nuclear Information System (INIS)

    Witte, H; Warnke, C; Krost, A; Voigt, T; De Lima, A; Ivanov, I; Vidakovic-Koch, T R; Sundmacher, K

    2011-01-01

    Unipolar source-drain voltage pulses of GaN/AlGaN-high electron mobility transistors (HEMTs) were used for stimulation of cultured neuronal networks obtained from embryonic rat cerebral cortex. The HEMT sensor was grown by metal organic vapour phase epitaxy on a 2 inch sapphire substrate consisting of 10 single HEMTs concentrically arranged around the wafer centre. Electrolytic reactions between the HEMT sensor surface and the culture medium were not detected using cyclic voltammetry. During voltage pulses and resulting neuronal excitation, capacitances were recharged giving indications of the contributions of the AlGaN and AlO x isolation layers between the two-dimensional electron gas channel and the neuron culture. The resulting threshold current for stimulation of neuron activity strongly depended on the culture and HEMT position on the sensor surface under consideration which was caused by different impedances of each neuron culture and position within the culture. The differences of culture impedances could be explained by variations of composition, thickness and conductivity of the culture areas.

  6. AlGaN/GaN-based HEMTs for electrical stimulation of neuronal cell cultures

    Science.gov (United States)

    Witte, H.; Warnke, C.; Voigt, T.; de Lima, A.; Ivanov, I.; Vidakovic-Koch, T. R.; Sundmacher, K.; Krost, A.

    2011-09-01

    Unipolar source-drain voltage pulses of GaN/AlGaN-high electron mobility transistors (HEMTs) were used for stimulation of cultured neuronal networks obtained from embryonic rat cerebral cortex. The HEMT sensor was grown by metal organic vapour phase epitaxy on a 2 inch sapphire substrate consisting of 10 single HEMTs concentrically arranged around the wafer centre. Electrolytic reactions between the HEMT sensor surface and the culture medium were not detected using cyclic voltammetry. During voltage pulses and resulting neuronal excitation, capacitances were recharged giving indications of the contributions of the AlGaN and AlOx isolation layers between the two-dimensional electron gas channel and the neuron culture. The resulting threshold current for stimulation of neuron activity strongly depended on the culture and HEMT position on the sensor surface under consideration which was caused by different impedances of each neuron culture and position within the culture. The differences of culture impedances could be explained by variations of composition, thickness and conductivity of the culture areas.

  7. Numerical simulation of local doped barrier layer AlGaN/GaN HEMTs

    Science.gov (United States)

    Fu, Wenli; Xu, Yuehang; Yan, Bo; Zhang, Bin; Xu, Ruimin

    2013-08-01

    A GaN HEMT with local doped barrier layer is proposed in this paper. The DC and RF characteristics of the proposed GaN HEMT structure is analyzed by using 2D numerical simulation. The results show that the breakdown voltage is 23% larger than that of the entire doped barrier layer structure due to the extension of depletion layer width between gate and drain electrodes, which reduces the electric field peak value at the right corner of the gate. A theoretical maximum output power density of 16.2 W/mm has been achieved, which is ∼34% larger than that of the entire doped barrier layer structure, and 7% larger than that of the unintentionally doped barrier layer structure. And the RF simulation results show that the proposed GaN HEMT also improved the maximum stable gain (MSG) by 0.8 dB up to 25 GHz due to the decrease of the gate-drain capacitance compared to the unintentionally doped and entire doped barrier layer structures.

  8. Optical investigation of spin injection from (Ga,Mn)As into n-GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Endres, Bernhard; Sperl, Matthias; Utz, Martin; Schuh, Dieter; Einwanger, Andreas; Ciorga, Mariusz; Back, Christian; Bayreuther, Guenther [Universitaet Regensburg (Germany)

    2011-07-01

    Spin injection from a Ga(Mn,As) contact into a n-GaAs channel through an Esaki diode structure was investigated. Details of the layer structure are described in Ref 1. After lithographic patterning the spin polarization in the GaAs was measured by p-MOKE at low temperatures across a cleaved edge as described in Ref. 2. From the distribution of the spin polarization below the injecting contact the spin diffusion length and the drift dependent spin decay length can be estimated, which are important parameters for the calculation of the spin lifetime from Hanle-measurements. However, several contributions to the Hanle curves as the stray field, dynamic nuclear polarization and a tilted magnetization of the injector make the calculation of the spin lifetime more complex. In this contribution the different parameters of the sample are characterized by fitting experimental data with a one-dimensional drift-diffusion equation. A spin diffusion length of about 5 {mu}m and a spin lifetime of 10 ns was observed.

  9. Low-noise AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor recessed by electron cyclotron resonance plasma etching

    CERN Document Server

    Lee, J H; Lee, C W; Yoon, H S; Park, B S; Park, C S

    1999-01-01

    GaAs pseudomorphic high electron mobility transistor recessed by electron cyclotron resonance (ECR) plasma etching have been investigated. We used a BCl sub 3 /SF sub 6 gas mixture to implement the gate recess process. We obtained a uniformity of the threshold voltage to within 50 mV in 3-inch wafers. The GaAs PHEMTs with a 0.2-mu m gate length recessed by the ECR plasma exhibited a minimum noise figure (NF sub m sub i sub n) as low as 0.26 dB with an associated gain (G sub a) of 13 dB at 12 GHz. At 18 GHz, the NF sub m sub i sub n was 0.47 dB with a Ga of 11.66 dB. These results suggest that the ECR plasma etching process reported here is suitable as a manufacturing process for gate recess of a GaAs PHEMT.

  10. Second harmonic generation from photonic structured GaN nanowalls

    Energy Technology Data Exchange (ETDEWEB)

    Soya, Takahiro; Inose, Yuta; Kunugita, Hideyuki; Ema, Kazuhiro; Yamano, Kouji; Kikuchi, Akihiko; Kishino, Katsumi, E-mail: t-soya@sophia.ac.j [Department of Engineering and Applied Sciences, Sophia University 7-1, Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan)

    2009-11-15

    We observed large enhancement of reflected second harmonic generation (SHG) using the one-dimensional photonic effect in regularly arranged InGaN/GaN single-quantum-well nanowalls. Using the effect when both fundamental and SH resonate with the photonic mode, we obtained enhancement of about 40 times compared with conditions far from resonance.

  11. GaN:Co epitaxial layers grown by MOVPE

    Czech Academy of Sciences Publication Activity Database

    Šimek, P.; Sedmidubský, D.; Klímová, K.; Mikulics, M.; Maryško, Miroslav; Veselý, M.; Jurek, Karel; Sofer, Z.

    2015-01-01

    Roč. 44, Mar (2015), 62-68 ISSN 0022-0248 R&D Projects: GA ČR GA13-20507S Institutional support: RVO:68378271 Keywords : doping * metalorganic vapor phase epitaxy * cobalt * gallium compounds * nitrides * magnetic materials spintronics Subject RIV: CA - Inorganic Chemistry Impact factor: 1.462, year: 2015

  12. Ga-67 citrate scan in vascular graft infection

    Energy Technology Data Exchange (ETDEWEB)

    Banzo, I.; Quirce, R.; Serrano, J.; Jimenez, J.; Tabuenca, O.; Carril, J.M. (Hospital Universitario Valdecilla, Santander (Spain))

    1992-11-01

    The clinical utility of the Ga-67 scan has been studied in 9 patients with clinical suspicion of vascular graft infection. Eleven grafts were analyzed: 4 aortobifemoral, 2 iliofemoral, 3 femoropopliteal, 1 axillofemoral, and 1 axillobifemoral. The Ga-67 scan was positive in 8 grafts with bacteriological proof of infection and negative in 3 grafts in which infection was ruled out by clinical follow-up. A Ga-67 scan also demonstrated the spread of infection to the thigh in two patients and to the pelvis in another two patients. In 4 patients CT was performed. The CT findings included graft thrombosis, perigraft fluid collection and thickened graft wall. No discrepancies were found between the CT scan and Ga-67 scan. In three patients a control Ga-67 scan was carried out after specific antibiotic and surgical treatment. Two of these showed increased Ga-67 uptake and spreading of infection along the graft; in the other patient, a Ga-67 scan revealed normalization after resolution of an abdominal abscess. In conclusion, the Ga-67 scan proved useful in the diagnosis of vascular graft infection, the definition of location of the extent of the disease and in the evaluation of the efficiency of treatment. (author).

  13. 75 FR 4269 - Establishment of Class E Airspace; Clayton, GA

    Science.gov (United States)

    2010-01-27

    ... September 14, 2009 that establishes Class E Airspace at Heaven's Landing Airport, Clayton, GA. DATES... DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 71 [Docket No. FAA-2009-0605; Airspace Docket No. 09-ASO-19] Establishment of Class E Airspace; Clayton, GA AGENCY: Federal...

  14. Panel fabrication utilizing GaAs solar cells

    Science.gov (United States)

    Mardesich, N.

    1984-01-01

    The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

  15. Feasibility and availability of 68Ga-labelled peptides

    International Nuclear Information System (INIS)

    Decristoforo, Clemens; Pickett, Roger D.; Verbruggen, Alfons

    2012-01-01

    68 Ga has attracted tremendous interest as a radionuclide for PET based on its suitable half-life of 68 min, high positron emission yield and ready availability from 68 Ge/ 68 Ga generators, making it independent of cyclotron production. 68 Ga-labelled DOTA-conjugated somatostatin analogues, including DOTA-TOC, DOTA-TATE and DOTA-NOC, have driven the development of technologies to provide such radiopharmaceuticals for clinical applications mainly in the diagnosis of somatostatin receptor-expressing tumours. We summarize the issues determining the feasibility and availability of 68 Ga-labelled peptides, including generator technology, 68 Ga generator eluate postprocessing methods, radiolabelling, automation and peptide developments, and also quality assurance and regulatory aspects. 68 Ge/ 68 Ga generators based on SnO 2 , TiO 2 or organic matrices are today routinely supplied to nuclear medicine departments, and a variety of automated systems for postprocessing and radiolabelling have been developed. New developments include improved chelators for 68 Ga that could open new ways to utilize this technology. Challenges and limitations in the on-site preparation and use of 68 Ga-labelled peptides outside the marketing authorization track are also discussed. (orig.)

  16. Feasibility and availability of ⁶⁸Ga-labelled peptides.

    Science.gov (United States)

    Decristoforo, Clemens; Pickett, Roger D; Verbruggen, Alfons

    2012-02-01

    (68)Ga has attracted tremendous interest as a radionuclide for PET based on its suitable half-life of 68 min, high positron emission yield and ready availability from (68)Ge/(68)Ga generators, making it independent of cyclotron production. (68)Ga-labelled DOTA-conjugated somatostatin analogues, including DOTA-TOC, DOTA-TATE and DOTA-NOC, have driven the development of technologies to provide such radiopharmaceuticals for clinical applications mainly in the diagnosis of somatostatin receptor-expressing tumours. We summarize the issues determining the feasibility and availability of (68)Ga-labelled peptides, including generator technology, (68)Ga generator eluate postprocessing methods, radiolabelling, automation and peptide developments, and also quality assurance and regulatory aspects. (68)Ge/(68)Ga generators based on SnO(2), TiO(2) or organic matrices are today routinely supplied to nuclear medicine departments, and a variety of automated systems for postprocessing and radiolabelling have been developed. New developments include improved chelators for (68)Ga that could open new ways to utilize this technology. Challenges and limitations in the on-site preparation and use of (68)Ga-labelled peptides outside the marketing authorization track are also discussed.

  17. The development of integrated chemical microsensors in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    CASALNUOVO,STEPHEN A.; ASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; BACA,ALBERT G.; HIETALA,S.L.

    1999-11-01

    Monolithic, integrated acoustic wave chemical microsensors are being developed on gallium arsenide (GaAs) substrates. With this approach, arrays of microsensors and the high frequency electronic components needed to operate them reside on a single substrate, increasing the range of detectable analytes, reducing overall system size, minimizing systematic errors, and simplifying assembly and packaging. GaAs is employed because it is both piezoelectric, a property required to produce the acoustic wave devices, and a semiconductor with a mature microelectronics fabrication technology. Many aspects of integrated GaAs chemical sensors have been investigated, including: surface acoustic wave (SAW) sensors; monolithic SAW delay line oscillators; GaAs application specific integrated circuits (ASIC) for sensor operation; a hybrid sensor array utilizing these ASICS; and the fully monolithic, integrated SAW array. Details of the design, fabrication, and performance of these devices are discussed. In addition, the ability to produce heteroepitaxial layers of GaAs and aluminum gallium arsenide (AlGaAs) makes possible micromachined membrane sensors with improved sensitivity compared to conventional SAW sensors. Micromachining techniques for fabricating flexural plate wave (FPW) and thickness shear mode (TSM) microsensors on thin GaAs membranes are presented and GaAs FPW delay line and TSM resonator performance is described.

  18. Optical pumping of hot phonons in GaAs

    International Nuclear Information System (INIS)

    Collins, C.L.; Yu, P.Y.

    1982-01-01

    Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated

  19. High efficiency low cost GaAs/Ge cell technology

    Science.gov (United States)

    Ho, Frank

    1990-01-01

    Viewgraphs on high efficiency low cost GaAs/Ge cell technology are presented. Topics covered include: high efficiency, low cost GaAs/Ge solar cells; advantages of Ge; comparison of typical production cells for space applications; panel level comparisons; and solar cell technology trends.

  20. Interface defects in GaN/sapphire studied using Rutherford ...

    Indian Academy of Sciences (India)

    Abstract. GaN on sapphire was grown by MOCVD technique. Rutherford backscatter- ing spectra together with channeling along [0 0 0 1] axis were recorded to study the defects at the interface. Detailed calculation shows that the defects at GaN/sapphire interface are due to dislocations which are distributed into the whole ...