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Sample records for henka ga module

  1. Effect of PV module output power on module temperature; Taiyo denchi no shutsuryoku henka ga module hyomen ondo ni oyobosu eikyo

    Energy Technology Data Exchange (ETDEWEB)

    Hongo, T.; Kitamura, A. [Kansai Electric Power Co. Inc., Osaka (Japan); Igaki, K.; Mizumoto, T. [Kanden Kako Co. Inc., Osaka (Japan)

    1996-10-27

    Effect of the photovoltaic (PV) module output power variation on the module surface temperature has been investigated by field measurements. PV modules with capacity of 54 W were used for the temperature measurements. Three 2 kW-class PV systems were operated. T-type thermocouples were used for measuring temperatures. Measurement time intervals were 15 minutes, 30 minutes, 60 minutes, and 24 hours. Measurement period was between May 25, 1995 and June 25, 1996. The surface temperature increased during non-loaded PV output, and decreased during load-carrying PV output. Difference of the surface temperature between non-loaded PV output and load-carrying PV output was 3.5{degree}C at maximum through a year. The surface temperature was saturated within 30 minutes. When PV output was changed in 30 or 60 minutes interval, the variation of surface temperature was distinctly observed. When PV output was changed in 15 minutes interval, it was not observed distinctly. There was no difference of the surface temperatures during the time zones with less solar radiation, such as in the morning and evening, and at night. Except these time zones, difference of the surface temperatures was 3.5{degree}C at maximum. 4 figs.

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

    Science.gov (United States)

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

    1987-10-01

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

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

    Science.gov (United States)

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

    2010-02-01

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

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

    KAUST Repository

    Shen, Chao

    2015-10-04

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

  5. InGaAsP/InP DH Ridge Waveguide Phase Modulator with High Modulation Efficiency

    Institute of Scientific and Technical Information of China (English)

    Young; Tae; Byun; Hwa; Sun; Park; Sung; Jin; Kim; Deok; Ha; Woo; Jong; Chang; Yi; Yoshiaki; Nakano

    2003-01-01

    The P-p-n-N InGaAsP/InP ridge waveguide phase modulator has been fabricated and investigated at a wavelength of 1550nm. The phase modulation efficiency measured by the Fabry-Perot resonance method is as high as 34°/V·mm for TE mode. The QEO effect becomes dominant from - 4V to - 8V.

  6. InGaAsP/InP DH Ridge Waveguide Phase Modulator with High Modulation Efficiency

    Institute of Scientific and Technical Information of China (English)

    Young Tae Byun; Hwa Sun Park; Sung Jin Kim; Deok Ha Woo; Jong Chang Yi; Yoshiaki Nakano

    2003-01-01

    The P-p-n-N InGaAsP/InP ridge waveguide phase modulator has been fabricated and investigated at a wavelength of 1550nm. The phase modulation efficiency measured by the Fabry-Perot resonance method is as high as 34°/V.mm for TE mode. The QEO effect becomes dominant from -4V to -8V.

  7. A field induced guide-antiguide modulator of GaAs-AlGaAs

    Science.gov (United States)

    Huang, T. C.; Chung, Y.; Young, D. B.; Dagli, N.; Coldren, L. A.

    1991-01-01

    A guide-antiguide modulator of GaAs-AlGaAs using the electric-field-induced waveguide concept was demonstrated. The device was formed with a central waveguide electrode sandwiched between two antiguide electrodes on the surface of a p-i-n multiple quantum well (MQW). Switching between lateral guiding and antiguiding was accomplished by reverse biasing either the central electrode or the adjacent electrodes to increase the index beneath these respective regions. The on-off ratio was measured to be 20:1 with a propagation loss of the on-state of about 5 dB/mm.

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

    Institute of Scientific and Technical Information of China (English)

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

    2001-01-01

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

  9. InGaP DHBT for High Efficiency L-band T/R Module Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A fully monolithically integrated L-band T/R module using InGaP/GaAs-based HBTs (heterojunction bipolar transistors) for both the transmit and receive functions is...

  10. Complex dynamical behaviors in modulation-doped GaAs/AlxGa1-x As heterostructures

    Institute of Scientific and Technical Information of China (English)

    李国辉; 周世平; 徐得名

    2001-01-01

    We study dynamics of the forced modulation-doped GaAs/AIGaAs heterostructure devices. The coupled differential equations governing the dynamical behaviors are numerically simulated.Biased with an appropriate dc field, the system exhibits two states: spontaneous current oscillation and fixed points. By imposing an ac driving force, the dynamical system shows frequency locking,quasiperiodicity, and chaos, which are sensitive to the amplitude and frequency of the externally applied periodical microwave field. The basins of attraction of both ordinary attractors and strange attractors are presented.

  11. Electroluminescence from a forward-biased Schottky barrier diode on modulation Si {delta}-doped GaAs/InGaAs/AlGaAs heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, Adam; Witczak, P.; Twardowski, A.; Baranowski, J. M.

    2001-06-18

    Electroluminescence (EL) from a forward-biased Schottky barrier diode on modulation Si {delta}-doped pseudomorphic GaAs/InGaAs/AlGaAs heterostructure with high mobility electron gas is investigated in this work. It has been found that the EL from the InGaAs quantum well can be observed at temperatures up to 90 K. The EL line shape depends on the current density, which reflects the filling of the InGaAs channel with electrons. The total integrated EL intensity depends linearly on the current density. We propose that hole diffusion from an inversion layer at the Schottky barrier is responsible for the observed optical recombination with electrons in the InGaAs quantum well. {copyright} 2001 American Institute of Physics.

  12. GHz modulation enabled using large extinction ratio waveguide-modulator integrated with 404 nm GaN laser diode

    KAUST Repository

    Shen, Chao

    2017-01-30

    A 404-nm emitting InGaN-based laser diode with integrated-waveguide-modulator showing a large extinction ratio of 11.3 dB was demonstrated on semipolar (2021) plane GaN substrate. The device shows a low modulation voltage of −2.5 V and ∼ GHz −3 dB bandwidth, enabling 1.7 Gbps data transmission.

  13. Microstrain in modulation-doped Al sub x Ga sub 1 sub - sub x N/GaN heterostructures

    CERN Document Server

    Tan Wei Shi; Shen Bo; Cai Hong Ling; Wu Xiao Shan; Jiang Shu Sheng; Zheng Wen Li; Jia Quan Jie; Jiang Xiao Ming

    2002-01-01

    Modulation-doped Al sub x Ga sub 1 sub - sub x N/GaN heterostructures with various thickness of Si-doped n-Al sub 0 sub . sub 2 sub 2 Ga sub 0 sub . sub 7 sub 8 N barrier (n-AlGaN) were deposited on (0001)-oriented sapphire (alpha-Al sub 2 O sub 3) by MOCVD. The reciprocal space mappings (RSMs) of symmetric reflection (0002) and asymmetric reflection (1014) were measured with the methods of high resolution X-ray diffraction (HRXRD). The results indicate that the microstructure and strain status of barrier correlate to those of the i-GaN layer. The strained barrier starts to be relaxed while its thickness is larger than 750 Angstrom and the critical thickness t sub c is larger than 500 Angstrom. The barrier holds an 'abnormal' relaxation status, which probably results from the internal defects of n-AlGaN and the strain relaxation status at the i-GaN/alpha-Al sub 2 O sub 3 interfaces

  14. On-chip integration of InGaAs/GaAs quantum dot lasers with waveguides and modulators on silicon

    Science.gov (United States)

    Yang, Jun; Bhattacharya, Pallab; Qin, Guoxuan; Ma, Zhenqiang

    2008-02-01

    Compound-semiconductor-based photonic devices, including lasers and modulators, directly grown and on-chip integrated on Si substrates provide a promising approach for the realization of optical interconnects with CMOS compatibility. Utilizing quantum dots as efficient dislocation filters near the GaAs-Si interface, for the first time, we demonstrated high-performance InGaAs/GaAs quantum dot (QD) lasers on silicon with a relatively low threshold current (J th = 900 A/cm2), large small-signal modulation bandwidth of 5.5 GHz, and a high characteristic temperature (T 0 = 278 K). The integrated InGaAs QD lasers with quantum well (QW) electroabsorption modulators, achieved through molecular beam epitaxy (MBE) growth and regrowth, exhibit a coupling coefficient greater than 20% and a modulation depth ~100% at 5 V reverse bias. We achieved the monolithic integration of amorphous and crystalline silicon waveguides with quantum dot lasers by using plasma-enhanced-chemical-vapor-deposition (PECVD) and membrane transfer, respectively. Finally, preliminary results on the integration of QD lasers with Si CMOS transistors are presented.

  15. Optical investigation of InAs quantum dots inserted in AlGaAs/GaAs modulation doped heterostructure

    Science.gov (United States)

    Khmissi, H.; Baira, M.; Sfaxi, L.; Bouzaïene, L.; Saidi, F.; Bru-Chevallier, C.; Maaref, H.

    2011-03-01

    Optical properties of InAs quantum dots (QDs) inserted in AlGaAs/GaAs modulation doped heterostructure are investigated. To study the effect of carrier transfer behavior on the luminescence of self-assembled quantum dots, a series of sample has been prepared using molecular beam epitaxy (Riber 32 system) in which we have varied the thickness separating the delta dopage and the InAs quantum dots layer. Photoluminescence spectra show the existence of two peaks that can be attributed to transition energies from the ground state (E1-HH1) and the first excited state (E2-HH2). Two antagonist effects have been observed, a blue shift of the emission energies result from electron transferred from the AlGaAs/GaAs heterojunction to the InAs quantum dots and a red shift caused by the quantum confined Stark effect due to the internal electric field existing In the AlGaAs/GaAs heterojunction.

  16. Modulation transfer function characteristic of uniform-doping transmission-mode GaAs/GaAlAs photocathode

    Institute of Scientific and Technical Information of China (English)

    Ren Ling; Chang Ben-Kang

    2011-01-01

    The resolution characteristic can be obtained by the modulation transfer function(MTF)of a GaAs/GaAlAs photocathode.After establishing the theoretical model of GaAs(100)-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers,this paper calculates the trajectories of photoelectrons in a photocathode.Thus the distribution of photoelectron spots on the emit-face is obtained,which is namely the point spread function.The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function.The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length,and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration.Furthermore,the resolution is enhanced considerably by increasing the active-layer thickness,especially at high spatial frequencies.The best spatial resolution is 860 lp/mm,for the GaAs photocathode of doping concentration 1×1019cm-3,electron diffusion length 3.6 μm and the active-layer thickness 2 μm,under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode's resolution for preparing a high performance GaAs photocathode,and improve the resolution of a low light level image intensifier.

  17. 40 Gb/s AlGaInAs Electroabsorption Modulated Laser Module Based on Identical Epitaxial Layer Scheme

    Science.gov (United States)

    Cai, Peng-Fei; Sun, Chang-Zheng; Xiong, Bing; Wang, Jian; Zhang, Ming-Jun; Xu, Jian-Ming; Liu, Zhi-Zhi; Huang, Jin; Luo, Yi

    2007-07-01

    A 40 Gb/s transmitter module containing an AlGaInAs electroabsorption (EA) modulator monolithically integrated with a distributed feedback (DFB) semiconductor laser has been fabricated using identical epitaxial layer (IEL) approach. Low loss coaxial-to-coplanar waveguide (CPW) transition is designed and fabricated for the module. By improving the quality of the anti-reflection (AR) coating on the EA modulator facet and optimizing the structure of the CPW transmission line, resonances in the frequency response of the module have been effectively suppressed. The module exhibits a small signal modulation bandwidth over 35 GHz, and clear eye opening has been demonstrated under 40 Gb/s nonreturn-to-zero (NRZ) code modulation.

  18. InGaAsP Buried Channel Waveguide For Electroabsorption Modulation

    Science.gov (United States)

    Lin, S. C.; Chin, M. K.; Jing, X. L.; Walpita, L. M.; Yu, P. K. L.; Chang, W. S.

    1987-11-01

    External modulation of 1.3 μm laser light with LPE grown InGaAsP/InP buried channel waveguides is presented. The waveguide is compatible with single mode fiber and the planar structure has potential for monolithic integration. In this paper, a numerical analysis of electroabsorption (EA) modulation for the waveguide modulator shows interesting results which may help the design of this device.

  19. Fermi-edge singularity in photoluminescence spectra of modulation-doped AlGaAs/InGaAs/GaAs quantum wells

    Indian Academy of Sciences (India)

    K Gopalakrishna Naik; K S R K Rao; T Srinivasan; R Muralidharan

    2011-12-01

    The photoluminescence study of Fermi-edge singularity (FES) in modulation-doped pseudomorphic AlGa1–As/InGa1–As/GaAs quantum well (QW) heterostructures is presented. In the above QW structures the optical transitions between = 1 and = 2 electronic subband to the = 1 heavy hole subband (11 and 21 transitions, respectively) are observed with FES appearing as a lower energy shoulder to the 21 transition. The observed FES is attributed to the Fermi wave vector in the first electronic subband under the conditions of population of the second electronic subband. The FES appears at about 10 meV below 21 transition around 4.2 K. Initially it gets stronger with increasing temperature and becomes a distinct peak at about 20 K. Further increase in temperature quenches FES and reaches the base line at around 40 K.

  20. Design and Fabrication of 1.06 μm Resonant-Cavity Enhanced Reflective Modulator with GaInAs/GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    YANG Xiao-Hong; HAN Qin; NI Hai-Qiao; HUANG She-Song; DU Yun; PENG Hong-Ling; XIONG Yong-Hua; NIU Zhi-Chuan; WU Rong-Han

    2006-01-01

    A resonant-cavity enhanced reflective optical modulator is designed and fabricated, with three groups of three highly strained InGaAs/GaAs quantum wells in the cavity, for low voltage and high contrast ratio operation.The quantum wells are positioned in antinodes of the optical standing wave. The modulator is grown in a single growth step in an molecular beam epitaxy system, using GaAs/AlAs distributed Bragg reflectors as both the top and bottom mirrors. Results show that the reflection device has a modulation extinction of 3 dB at -4.5 V bias.

  1. Development of InGaAsSb Based Monolithic Interconnected Modules (MIMs)

    Science.gov (United States)

    Palmisiano, M. N.; Biefeld, R. M.; Cederberg, J. G.; Hafich, M. J.; Peake, G. M.

    2003-01-01

    The quaternary Sb-based materials are attractive for use in TPV devices due to the versatility associated with being able to grow InGaAsSb and AlGaAsSb material with a wide range of band gaps lattice matched to a GaSb substrate. Photodiodes (0.60 eV) consisting of an InGaAsSb p/n junction grown on GaSb were fabricated and characterized to establish baseline electrical performance of the material. In order to fabricate monolithic interconnected modules (MIMs) from these photodiodes using a conductive GaSb substrate, an electrical isolation layer must be added between the active layers and the substrate. For this purpose, AlGaAsSb cell isolation diodes (CIDs) were developed and characterized with respect to their ability to block current in reverse bias. These structures were combined in the first MIM structures grown and fabricated from Sb-based materials on GaSb substrates.

  2. Localized and collective magnetoplasmon excitations in AlGaN/GaN-based grating-gate terahertz modulators

    Science.gov (United States)

    Nogajewski, K.; Łusakowski, J.; Knap, W.; Popov, V. V.; Teppe, F.; Rumyantsev, S. L.; Shur, M. S.

    2011-11-01

    Magnetotransport and magnetooptics investigations of plasmon excitations in large-area grating-gate terahertz modulators based on AlGaN/GaN high-electron-mobility transistors with different grating-gate duty cycle are reported. We demonstrate that the effect of the gate potential on the ungated region extends beyond the conventional fringing effect distance, ranging over 250-350 nm instead of expected 26-30 nm. This phenomenon enables excitation of the localized gated magnetoplasmon modes only if the inter-finger spacing in the grating gate exceeds 350 nm. For narrower slits, only the collective gated magnetoplasmon modes extending over the entire period of the structure can be excited.

  3. Advanced photovoltaic power systems using tandem GaAs/GaSb concentrator modules

    Science.gov (United States)

    Fraas, L. M.; Kuryla, M. S.; Pietila, D. A.; Sundaram, V. S.; Gruenbaum, P. E.; Avery, J. E.; Dihn, V.; Ballantyne, R.; Samuel, C.

    1992-01-01

    In 1989, Boeing announced the fabrication of a tandem gallium concentrator solar cell with an energy conversion efficiency of 30 percent. This research breakthrough has now led to panels which are significantly smaller, lighter, more radiation resistant, and potentially less expensive than the traditional silicon flat plate electric power supply. The new Boeing tandem concentrator (BTC) module uses an array of lightweight silicone Fresnel lenses mounted on the front side of a light weight aluminum honeycomb structure to focus sunlight onto small area solar cells mounted on a thin back plane. This module design is shown schematically. The tandem solar cell in this new module consists of a gallium arsenide light sensitive cell with a 24 percent energy conversion efficiency stacked on top of a gallium antimonide infrared sensitive cell with a conversion efficiency of 6 percent. This gives a total efficiency 30 percent for the cell-stack. The lens optical efficiency is typically 85 percent. Discounting for efficiency losses associated with lens packing, cell wiring, and cell operating temperature still allows for a module efficiency of 22 percent which leads to a module power density of 300 Watts/sq. m. This performance provides more than twice the power density available from a single crystal silicon flat plate module and at least four times the power density available from amorphous silicon modules. The fact that the lenses are only 0.010 ft. thick and the aluminum foil back plane is only 0.003 ft. thick leads to a very lightweight module. Although the cells are an easy to handle thickness of 0.020 ft., the fact that they are small, occupying one-twenty-fifth of the module area, means that they add little to the module weight. After summing all the module weights and given the high module power, we find that we are able to fabricate BTC modules with specific power of 100 watts/kg.

  4. Novel electro-optical phase modulator based on GaInAs/InP modulation-doped quantum-well structures

    DEFF Research Database (Denmark)

    Thirstrup, C.

    1992-01-01

    A novel electro-optical phase modulator working at 1.55 µm is analyzed and proposed. It is shown by a numerical model that in a GaInAs/InP pn-nin-pn multiple-quantum-well waveguide structure, large optical phase modulation can be obtained at small intensity modulation and with improved performance...... compared to what is achieved in quantum confined Stark effect modulators of the same material system. The device proposed is based on a modulation of the quasi-Fermi energies of the electrons in the GaInAs quantum wells. This operational principle allows GHz modulation frequencies. Applied Physics Letters...

  5. The NF-YC–RGL2 module integrates GA and ABA signalling to regulate seed germination in Arabidopsis

    Science.gov (United States)

    Liu, Xu; Hu, Pengwei; Huang, Mingkun; Tang, Yang; Li, Yuge; Li, Ling; Hou, Xingliang

    2016-01-01

    The antagonistic crosstalk between gibberellic acid (GA) and abscisic acid (ABA) plays a pivotal role in the modulation of seed germination. However, the molecular mechanism of such phytohormone interaction remains largely elusive. Here we show that three Arabidopsis NUCLEAR FACTOR-Y C (NF-YC) homologues NF-YC3, NF-YC4 and NF-YC9 redundantly modulate GA- and ABA-mediated seed germination. These NF-YCs interact with the DELLA protein RGL2, a key repressor of GA signalling. The NF-YC–RGL2 module targets ABI5, a gene encoding a core component of ABA signalling, via specific CCAAT elements and collectively regulates a set of GA- and ABA-responsive genes, thus controlling germination. These results suggest that the NF-YC–RGL2–ABI5 module integrates GA and ABA signalling pathways during seed germination. PMID:27624486

  6. Development of GaAs Gunn Diodes and Their Applications to Frequency Modulated Continuous Wave Radar

    Science.gov (United States)

    Choi, Seok-Gyu; Han, Min; Baek, Yong-Hyun; Ko, Dong-Sik; Baek, Tae-Jong; Lee, Sang-Jin; Kim, Jin-Ho; Lee, Seong-Dae; Kim, Mi-Ra; Chae, Yeon-Sik; Kathalingam, Adaikalam; Rhee, Jin-Koo

    2010-11-01

    In this work, we have designed and fabricated the GaAs Gunn diodes for a 94 GHz waveguide voltage controlled oscillator (VCO) which is one of the important parts in a frequency modulated continuous wave (FMCW) radar application. For fabrication of the high power GaAs Gunn diodes, we adopted a graded gap injector which enhances the output power and conversion efficiency by effectively removing the dead-zone. We have measured RF characteristics of the fabricated GaAs Gunn diodes. The operating current, oscillation frequency, and output power of the fabricated GaAs Gunn diodes are presented as a function of the anode diameters. The operating current increases with anode diameters, whereas the oscillation frequency decreases. The higher oscillation frequency was obtained from 60 µm anode diameters of the fabricated Gunn GaAs diodes and higher power was obtained from 68 µm. Also, for application of the 94 GHz FMCW radar system, we have fabricated the 94 GHz waveguide VCO. From the fabricated GaAs Gunn diodes of anode diameter of 60 µm, we have obtained the improved VCO performance.

  7. High electron mobility of modulation doped GaAs after growing InP by solid source molecular beam epitaxy

    Institute of Scientific and Technical Information of China (English)

    SHU Yong-chun; PI Biao; LIN Yao-wang; XING Xiao-dong; YAO Jiang-hong; WANG Zhan-guo; XU Jing-jun

    2005-01-01

    Modulation-doped AlGaAs/GaAs structures were grown on GaAs(100) substrate by solid source molecular beam epitaxy (SSMBE) system. The factors which influence the electron mobility were investigated. After growing InP based materials, growth conditions were deteriorated, but by an appropriate method and using reasonaand growth conditions have been studied and optimized via Hall measurements. For a typical sample, 2.0 K electron served.

  8. Microwave-modulated reflectance spectroscopy in the GaAs/AlGaAs heterostructure%GaAs/AlGaAs异质结的微波调制反射谱

    Institute of Scientific and Technical Information of China (English)

    钱轩; 谷晓芳; 姬扬

    2011-01-01

    基于搭建的微波调制反射谱测量系统(MMRS),确定了GaAs/AlGaAs异质结构中价带空穴到二维电子系统(2DES)电子基态(GS)的跃迁.微波调制反射谱与温度的依赖关系表明,随着测量温度的升高,能带带隙发生了蓝移现象;而其与磁场的依赖关系表明,随着测量磁场的增大,能带带隙则发生了红移现象;它们均与GaAs/AlGaAs异质结构中价带空穴的带填充效应有关.基于Kramers-Kronig关系的理论模拟给出了和实验测量相似的结果.%A microwave-modulated reflectance spectroscopy (MMRS) measurement system was constructed.This MMRS technique was used to identify a transition from holes in valence band to electrons in the ground subband (GS) of the twodimensional electron system (2DES) formed in a GaAs/AlGaAs heterostructure sample.The temperature (T) dependence of the MMRS shows a blue shift of the energy gap with increasing T,while the magnetic field (B) dependence of the MMRS shows a red shift of the energy gap with increasing B.Both phenomena are attributed to the band-filling effect of holes in valence band in the GaAs/AlGaAs heterostructure.A theoretical simulation based on Kramers-Kronig relation was also presented which was similar with the experimental data.

  9. Two-Dimensional GaAs/AlGaAs Multiple Quantum Well Spatial Light Modulators

    Institute of Scientific and Technical Information of China (English)

    Qin Wang; Jan Borglind; Smilja Becanovic; Stéphane Junique; Daniel (A)gren; Bertrand Noharet; Linda H(o)glund; Olof (O)berg; Erik Petrini; Jan Y. Andersson; Hedda Malm

    2003-01-01

    Multiple quantum well spatial light modulators with 128x128 array in 38μm pitch are fabricated using two pproaches, one with an attachment of an optical substrate and another one without. These two fabrication processes are described and compared.

  10. Refraction index modulation induced with transverse electric field in double tunnel-coupled GaAs/AlGaAs quantum wells

    Science.gov (United States)

    Shumilov, A. A.; Vinnichenko, M. Ya; Balagula, R. M.; Vorobjev, L. E.; Firsov, D. A.; Kulagina, M. M.; Vasil'iev, A. P.; Duque, C. A.; Tiutiunnyk, A.; Akimov, V.; Restrepo, R. L.; Tulupenko, V. N.; Ter-Martirosyan, A. L.

    2015-11-01

    Modulation of refraction index under transverse electric field was studied in structures with multiple tunnel-coupled GaAs/AlGaAs quantum wells in the spectral range corresponding to intersubband light absorption. The change of refraction index in electric field was calculated using Kramers-Kronig relation and experimentally determined spectra of intersubband light absorption in equilibrium conditions and under transverse electric field.

  11. Electric field modulated half-metallicity of semichlorinated GaN nanosheets

    Science.gov (United States)

    Xiao, M. X.; Song, H. Y.; Ao, Z. M.; Xu, T. H.; Wang, L. L.

    2016-11-01

    Through density-functional theory calculations, we investigated the half-metallic properties of semichlorinated gallium nitride (Cl-GaN) nanosheets (NSs) under an electric field F. The results show that the electric field can modulate Cl-GaN NSs efficiently from ferromagnetic metals to half-metals. More interestingly, under a broad range of electric field intensity (-0.10~-1.30 V/Å), Cl-GaN NSs have the excellently half-metallic properties with the band gaps (3.71-0.96 eV) and maximal half-metallic gaps with 0.30 eV in spin-up states and metallic behaviors in spin-down states. Moreover, the total magnetic moment decreases (increases) depending on the negative (positive) F, mainly induced by the unpaired N atoms. Our studies demonstrate that the electronic and magnetic properties of GaN NSs can be delicately tuned by the combined surface modification and electric field, indicating the potential of GaN NSs for developing high-performance spintronic nanodevices.

  12. Phonon deformation potentials of hexagonal GaN studied by biaxial stress modulation

    Directory of Open Access Journals (Sweden)

    Jun-Yong Lu

    2011-09-01

    Full Text Available In this work, a biaxial stress modulation method, combining the microfabrication technique, finite element analysis and a weighted averaging process, was developed to study piezospectroscopic behavior of hexagonal GaN films, epitaxially grown by metalorganic chemical vapor deposition on c-sapphire and Si (111 substrates. Adjusting the size of patterned islands, various biaxial stress states could be obtained at the island centers, leading to abundant stress-Raman shift data. With the proposed stress modulation method, the Raman biaxial stress coefficients of E2H and A1 (LO phonons of GaN were determined to be 3.43 cm-1/GPa and 2.34 cm-1/GPa, respectively.

  13. Improved crystalline quality of N-polar GaN epitaxial layers grown with reformed flow-rate-modulation technology

    Science.gov (United States)

    Zhang, Heng; Zhang, Xiong; Wang, Shuchang; Wang, Xiaolei; Zhao, Jianguo; Wu, Zili; Dai, Qian; Yang, Hongquan; Cui, Yiping

    2017-01-01

    A reformed flow-rate-modulation technology was developed for the metalorganic vapor phase epitaxy (MOVPE) growth of the N-polar GaN epitaxial layers. To improve the crystalline quality of the N-polar GaN epitaxial layers, a GaN nucleation layer was grown at relatively low temperature with carefully-controlled pulsed supply of Ga source and showed diverse morphology with atomic force microscope (AFM). Furthermore, the electrical and optical properties of the grown N-polar GaN epitaxial layers were investigated extensively by means of Hall effect, photoluminescence (PL), and X-ray rocking curve (XRC) measurements. The characterization results revealed that as compared with the N-polar GaN epitaxial layer grown over the conventional GaN nucleation layer which was deposited with continuous supply of both N and Ga sources, the electrical and optical properties of the N-polar GaN epitaxial layer grown with optimized supply of Ga source for the GaN nucleation layer were significantly improved.

  14. Metalorganic chemical vapor phase epitaxy of narrow-band distributed Bragg reflectors realized by GaN:Ge modulation doping

    Science.gov (United States)

    Berger, Christoph; Lesnik, Andreas; Zettler, Thomas; Schmidt, Gordon; Veit, Peter; Dadgar, Armin; Bläsing, Jürgen; Christen, Jürgen; Strittmatter, André

    2016-04-01

    We report on metalorganic vapor phase epitaxy (MOVPE) of distributed Bragg reflectors (DBR) applying a periodic modulation of the GaN doping concentration only. The doping modulation changes the refractive index of GaN via the Burstein-Moss-effect. MOVPE growth of highly doped GaN:Ge and modulation of the dopant concentration by at least two orders of magnitude within few nanometers is required to achieve a refractive index contrast of 2-3%. Such modulation characteristic is achieved despite the presence of Ge memory effects and incorporation delay. We realized DBRs with up to 100 layer pairs by combining GaN:Ge with a nominal doping concentration of 1.6×1020 cm-3 as low-refractive index material with unintentionally doped GaN as high-refractive index layer. Scanning transmission electron microscope images reveal DBR structures with abrupt interfaces and homogenous layer thicknesses in lateral and vertical direction. Reflectance measurements of DBRs designed for the blue and near UV-spectral region show a narrow stopband with a maximum reflectivity of 85% at 418 nm and even 95% at 370 nm. InGaN/GaN multi-quantum well structures grown on top of such DBRs exhibit narrow emission spectra with linewidths below 3 nm and significantly increased emission intensity.

  15. InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

    Science.gov (United States)

    Aoki, Masahiro; Suzuki, Makoto; Sano, Hirohisa; Kawano, Toshihiro; Ido, Tatemi; Taniwatari, Tsuyoshi; Uomi, Kazuhisa; Takai, Atsushi

    1993-06-01

    Fabrication and basic characteristics of a new structure InGaAs/InGaAsP (MQW) electroabsorption modulator integrated with a distributed feedback (DFB) laser are presented. First, a fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. We have experimentally demonstrated both the efficient attenuation, the small hole pileup and small chirp characteristics of a discrete modular based on this MQW structure. We also made a study of the controllability of in-plane band-gap energy by the use of selective area metal-organic chemical vapor deposition aimed at one-step growth integration of modulators and lasers. We demonstrated a sufficient range for controllable quantum energy level and high quality of the selectively grown MQW lasers. By using this technique, the modulator was monolithically integrated with a same-material MQW DFB laser. Using a low capacitance semi-insulating buried-hetero structure, we achieved over 14-GHz modulation under high-light-output operations up to +10 dBm.

  16. Robust optical properties of sandwiched lateral composition modulation GaInP structure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; Min, Jung-Wook; Hwang, Hyeong-Yong; Jho, Young-Dahl; Lee, Yong Tak

    2016-12-26

    Double-hetero structure lateral composition modulated (LCM) GaInP and sandwiched LCM GaInP having the same active layer thickness were grown and their optical properties were compared. Sandwiched LCM GaInP showed robust optical properties due to periodic potential nature of the LCM structure, and the periodicity was undistorted even for thickness far beyond the critical layer thickness. A thick LCM GaInP structure with undistorted potential that could preserve the properties of native LCM structure was possible by stacking thin LCM GaInP structures interspaced with strain compensating GaInP layers. The sandwiched structure could be beneficial in realizing the LCM structure embedded high efficiency solar cells.

  17. Unveiling interfaces between In-rich and Ga-rich GaInP vertical slabs of laterally composition modulated structures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; Min, Jung-Wook; Lee, Yong-Tak

    2017-01-16

    We report changes at the interface between Ga-rich/In-rich GaInP vertical slabs in laterally composition modulated (LCM) GaInP as a function of the V/III ratio. The photoluminescence exhibits satellite peaks, indicating that the parasitic potential between the GaInP vertical slabs disappears as the V/III ratio decreases. However, a high V/III ratio leads to an abrupt interface, increasing the parasitic potential because of the phosphorus-amount-dependent diffusion of group-III atoms during growth. These results suggest that the V/III ratio is an important parameter that must be wisely chosen in designing optoelectronic devices incorporating LCM structure.

  18. Unveiling interfaces between In-rich and Ga-rich GaInP vertical slabs of laterally composition modulated structures

    Science.gov (United States)

    Park, Kwangwook; Kang, Seokjin; Ravindran, Sooraj; Min, Jung-Wook; Lee, Yong-Tak

    2017-02-01

    We report changes at the interface between Ga-rich/In-rich GaInP vertical slabs in laterally composition modulated (LCM) GaInP as a function of the V/III ratio. The photoluminescence exhibits satellite peaks, indicating that the parasitic potential between the GaInP vertical slabs disappears as the V/III ratio decreases. However, a high V/III ratio leads to an abrupt interface, increasing the parasitic potential because of the phosphorus-amount-dependent diffusion of group-III atoms during growth. These results suggest that the V/III ratio is an important parameter that must be wisely chosen in designing optoelectronic devices incorporating LCM structure.

  19. Photoluminescence of anti-modulation doped near-surface GaAs/AlGaAs single quantum well structures exposed to hydrogen plasma

    CERN Document Server

    Bumaj, Y A; Goldkhan, R; Shtajn, N; Golombek, A; Nakov, V; Cheng, T S

    2002-01-01

    The anti-modulation Si-doped GaAs/AlGaAs structures with near-surface single quantum wells grown by molecular-beam epitaxy were exposed to hydrogen plasma at 260 deg C and investigated by low-temperature photoluminescence, photoluminescence excitation and photoreflectance spectroscopy. After hydrogenation, the quenching of the exciton luminescence for the below AlGaAs band gap excitation due to the increase of electric field in the structure has been observed. The effect is consistent with unpinning of Fermi level from mid gap of nominally undoped (p-type) GaAs cap layer due to passivation of surface states by hydrogen without neutralization of shallow impurities in the epilayers

  20. Advanced digital modulation: Communication techniques and monolithic GaAs technology

    Science.gov (United States)

    Wilson, S. G.; Oliver, J. D., Jr.; Kot, R. C.; Richards, C. R.

    1983-01-01

    Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case.

  1. Impact of gain compression factor on modulation characteristics of InGaAs/GaAs self-assembled quantum dot lasers

    Science.gov (United States)

    Kariminezhad, Farzaneh; Rajaei, Esfandiar; Fali, Alireza; Mirzaei, Reyhaneh

    2016-12-01

    This paper investigates the influence of gain compression factor on the modulation response of InGaAs/GaAs self-assembled quantum dot laser based on rate equations. For different gain compression factors the output power-current characteristics, light emissions of quantum dot laser have been simulated and effect of gain compression factor changes on quantum dot laser is illustrated. Also, small and large-signal response of quantum dot lasers is studied and the impact of the gain compression factor is presented. It explains that increase of gain compression factor, decreases small-signal modulation characteristics, nevertheless, improves large-signal response of quantum dot lasers. It helps to generate better laser signal quality, higher eye and smaller jitter. The large-signal behavior of a laser diode determines its capability for digital data transfer. The modulation speed of quantum dot lasers is of specific importance if such lasers are considered for optical communication systems.

  2. Enhancement of minority carrier lifetime of GaInP with lateral composition modulation structure grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Park, K. W.; Ravindran, Sooraj; Kang, S. J.; Hwang, H. Y.; Jho, Y. D. [School of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Park, C. Y. [School of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Jo, Y. R.; Kim, B. J. [School of Material Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Lee, Y. T., E-mail: ytlee@gist.ac.kr [School of Information and Communications, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of)

    2014-07-28

    We report the enhancement of the minority carrier lifetime of GaInP with a lateral composition modulated (LCM) structure grown using molecular beam epitaxy (MBE). The structural and optical properties of the grown samples are studied by transmission electron microscopy and photoluminescence, which reveal the formation of vertically aligned bright and dark slabs corresponding to Ga-rich and In-rich GaInP regions, respectively, with good crystal quality. With the decrease of V/III ratio during LCM GaInP growth, it is seen that the band gap of LCM GaInP is reduced, while the PL intensity remains high and is comparable to that of bulk GaInP. We also investigate the minority carrier lifetime of LCM structures made with different flux ratios. It is found that the minority carrier lifetime of LCM GaInP is ∼37 times larger than that of bulk GaInP material, due to the spatial separation of electrons and holes by In-rich and Ga-rich regions of the LCM GaInP, respectively. We further demonstrate that the minority carrier lifetime of the grown LCM GaInP structures can easily be tuned by simply adjusting the V/III flux ratio during MBE growth, providing a simple yet powerful technique to tailor the electrical and optical properties at will. The exceptionally high carrier lifetime and the reduced band gap of LCM GaInP make them a highly attractive candidate for forming the top cell of multi-junction solar cells and can enhance their efficiency, and also make them suitable for other optoelectronics devices, such as photodetectors, where longer carrier lifetime is beneficial.

  3. Controllable GMR device in a δ-doped, magnetically and electrically modulated, GaAs /Alx Ga1-x As heterostructure

    Science.gov (United States)

    Shen, Li-Hua; Zhang, Gui-Lian; Yang, Duan-Chui

    2016-09-01

    We report on a theoretical study of giant magnetoresistance (GMR) effect in a δ-doped GaAs /Alx Ga1-x As heterostructure modulated by two stripes of ferromagnetic metal and a stripe of Schottky metal in parallel configuration. The δ-doping dependent transmission and conductance of the device are calculated. It is shown that a considerable giant magnetoresistance (GMR) effect exists in this structure. It is also shown that the magnetoresistance ratio (MR) can be switched by the δ-doping. The underlying physical mechanism of the results is analysed in light of δ-doping-dependent tunneling process in the device.

  4. Impact of gain compression on modulation response and dynamic properties of three state lasing InGaAs/GaAs quantum dot lasers

    Science.gov (United States)

    Shafieenezhad, Azam; Rajaei, Esfandiar; Yazdani, Saeed

    2016-04-01

    In this paper, we have theoretically studied dynamics of a semiconductor quantum dot (QD) laser for enhancing its small signal and large signal modulation as a function of compression gain. We have considered InGaAs/GaAs QD laser rate equations and solved this equation system numerically. We have revealed that a diminution in compression gain leads to an improvement in frequency bandwidth for this three state lasing system. We also have calculated turn on delay and output power that obviously indicates the effect of compression gain on relaxation oscillations.

  5. Characteristics of InAs/AlGaAs self-organized quantum dot modulation doped field effect transistors

    Science.gov (United States)

    Phillips, J.; Kamath, K.; Brock, T.; Bhattacharya, P.

    1998-06-01

    We have investigated the dc characteristics of InGaAs/AlGaAs modulation doped field effect transistors in which a layer of self-organized InAs quantum dots is inserted adjacent to the pseudomorphic quantum well channel. Distinct steps and a negative differential resistance are observed in the current-voltage characteristics at room temperature and lower temperatures. These are attributed to conduction through the bound states in the quantum dots.

  6. Surface supersaturation in flow-rate modulation epitaxy of GaN

    Science.gov (United States)

    Akasaka, Tetsuya; Lin, Chia-Hung; Yamamoto, Hideki; Kumakura, Kazuhide

    2017-06-01

    Hillocks on N-face GaN (000 1 bar) films are effectively eliminated by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rate of group-III sources are sequentially modulated under a constant supply of NH3. A hillock-free smooth surface obtained by group-III-source FME is attributed to the enhancement of step-flow growth. We found that a hillock originates from a micropipe and grows by spiral growth around the micropipe. The spiral growth rate rapidly decreases with decreasing the degree of surface supersaturation σ, while the step-flow growth rate decreases linearly. For group-III-source FME, wherein σ is lower than conventional continuous growth, the spiral growth rate could be lower than the step-flow growth one so that the formation of hillocks is suppressed.

  7. Phonon-Assisted Modulation of the Electron Collection Efficiency into InxGa1-xAs/GaAs Quantum Wells

    DEFF Research Database (Denmark)

    Borri, Paola; Gurioli, M.; Colocci, M.;

    1997-01-01

    The energy relaxation and the capture of free carriers in InxGa1-xAs/GaAs quantum wells have been investigated by means of continuous-wave and time-resolved photoluminescence for excitation energies tuned over a wide interval above the GaAs band-gap. The strong interaction between free electrons...... and longitudinal-optical phonons gives rise to a 42 meV-period modulation of the efficiency of carrier collection into the well and of the corresponding collection time. The energy position of the electronic level driving the capture into the well has been deduced from the data and does not coincide with any...... calculated energy level of the well structure. The capture time turns out to be at the limit of our time resolution (approximate to 20 ps), while the collection time oscillates with an amplitude of about 80 ps, because of the emission of acoustic phonons....

  8. Preparation of [(68)Ga]PSMA-11 for PET-CT imaging using a manual synthesis module and organic matrix based (68)Ge/(68)Ga generator.

    Science.gov (United States)

    Nanabala, Raviteja; Anees, Muhammed K; Sasikumar, Arun; Joy, Ajith; Pillai, M R A

    2016-08-01

    [(68)Ga]PSMA-11 is a relatively recently introduced radiopharmaceutical for PET-CT imaging of prostate cancer patients. The availability of (68)Ge/(68)Ga generator and PSMA-11 ligand from commercial sources is facilitating the production of the radiopharmaceutical in-house. This paper describes our experience on the preparation of ~200 batches of [(68)Ga]PSMA-11 for conducting PET-CT imaging in patients suspected/suffering from prostate cancer. The radiosynthesis of [(68)Ga]PSMA-11 was done in a hospital based nuclear medicine department using (68)Ge/(68)Ga generator and a manual synthesis module, both supplied by Isotope Technologies Garching (ITG), Germany. The production involved the reaction of 5μg (5.3nmol) of PSMA-11 ligand in 1 ml of 0.25M sodium acetate buffer with 4ml of (68)GaCl3 in 0.05M HCl for 5min at 105°C; followed by purification in a C18 cartridge and collection through a 0.22μm pore size filter. The radiochemical yields obtained were consistently high, 93.19%±3.76%, and there was hardly any batch failure. The radiochemical purity of the product was >99% and the product was stable for over 2h; however it was used in patients immediately after preparation. About 200 batches of [(68)Ga]PSMA-11 were prepared during the period and more than 300 patients received the tracer during the 14months of study. No adverse reaction was observed in any of the patients and the image qualities were consistent with literature reports. [(68)Ga]PSMA-11 with high radiochemical and radionuclidic purity is conveniently prepared by using a (68)Ge/(68)Ga generator and manual synthesis module. The radiochemical yields are very high; and activity sufficient for 3-4 patients can be prepared in a single batch; multiple batches can be done on the same day and when needed after a gap of 1.5-2h. Copyright © 2016 Elsevier Inc. All rights reserved.

  9. Monolithic strained-InGaAsP multiple-quantum-well lasers with integrated electroabsorption modulators for active mode locking

    Science.gov (United States)

    Sato, Kenji; Wakita, Koichi; Kotaka, Isamu; Kondo, Yasuhiro; Yamamoto, Mitsuo; Takada, Atsushi

    1994-07-01

    Active mode locking by monolithic lasers with integrated electroabsorption modulators using strained-InGaAsP multiple quantum wells is described. The electroabsorption modulator acts as a short optical gate when a sinusoidal voltage is driven at a deep bias point. Pulse widths as short as 2 ps have been obtained at a repetition rate of 16.3 GHz for a 2.5-mm-long monolithic laser.

  10. Spectral transmittance and module structure fitting for transmission-mode GaAs photocathodes

    Institute of Scientific and Technical Information of China (English)

    Zhao Jing; Chang Ben-Kang; Xiong Ya-Juan; Zhang Yi-Jun

    2011-01-01

    A transmission-mode GaAs photocathode includes four layers of glass, Si3N4, Gal-xAlxAs and GaAs. A gradientdoping photocathode sample was obtained by molecular beam epitaxy and its transmittance was measured by spectrophotometer from 600 nm to 1100 nm. The theoretical transmittance is derived and simulated based on the matrix formula for thin film optics. The simulation results indicate the influence of the transition layers and the three thin-film layers except glass on the transmittance spectra. In addition, a fitting coefficient needed for error modification enters into the fitted formula. The fitting results show that the relative error in the full spectrum reduces from 19.51% to 4.35% after the formula is modified. The coefficient and the thicknesses are gained corresponding to the minimum relative error, meanwhile each layer and total thin-film thickness deviation in the module can be controlled within 7%.The presence of glass layer roughness, layer interface effects and surface oxides is interpreted on the modification.

  11. Refractive index modulation based on excitonic effects in GaInAs-InP coupled asymmetric quantum wells

    DEFF Research Database (Denmark)

    Thirstrup, Carsten

    1995-01-01

    The effect of excitons in GaInAs-InP coupled asymmetric quantum wells on the refractive index modulation, is analyzed numerically using a model based on the effective mass approximation. It is shown that two coupled quantum wells brought in resonance by an applied electric field will, due...

  12. Non-Modulated Martensite Microstructure With Internal Nanotwins In Ni-Mn-Ga Alloys

    Directory of Open Access Journals (Sweden)

    Szczerba M.J.

    2015-09-01

    Full Text Available The self-accommodated non-modulated martensite of Ni-Mn-Ga single crystal was studied by transmission and scanning electron microscopy in the latter case using the electron backscatter diffraction technique. Three kinds of interfaces existing at different length scales were reported. The first, is the wavy and incoherent interface separating martensite variants observed on the micro-level with no-common crystallographic plane between them. The second is within a single martensite plate where the lattice rotates around one of the {110} pole to accommodate the interfacial curvature between martensite plates. Finally, at the nanoscale the third interface exists, a twin boundary separating internal nanotwins with the {112} type habit plane.

  13. Investigation of GaInNAs/GaAs quantum wells and vertical-cavity surface-emitting laser structures using modulated reflectance spectroscopy

    CERN Document Server

    Choulis, S A

    2001-01-01

    study on a representative InGaAs/GaAs/AlAs/AIGaAs as-grown VCSEL structure, using PR spectroscopy as a function of position on a non-uniform wafer. We also show how temperature dependent PR and the appropriate lineshape model can be used to obtain a full picture of the relative movements between the gain and the CM over the full range of temperature. This information allows calculating the material gain in the temperature range of interest, independent from the effect of the CM and also provides an alternative method for characterising the growth, which can be applied to uniform wafers. PR and non-destructive ER can be used to identify regions suitable for fabrication into devices. For this reason modulation spectroscopy can be very useful for industry to reject wafers where good alignment between the CM and the QW does not occur and can thus save on the time consuming and expensive fabrication procedures. We investigate the electronic band structure of device relevant GaInNAs/GaAs multiple quantum wells (MQW...

  14. Modulated switching current density and spin-orbit torques in MnGa/Ta films with inserting ferromagnetic layers

    Science.gov (United States)

    Meng, Kangkang; Miao, Jun; Xu, Xiaoguang; Wu, Yong; Xiao, Jiaxing; Zhao, Jianhua; Jiang, Yong

    2016-12-01

    We report modulated switching current density and spin-orbit torques (SOT) in MnGa/Ta films with inserting very thin Co2FeAl and Co layers. Ferromagnetic coupling has been found in MnGa/Co2FeAl/Ta, resulting in a decreased effective anisotropy field. On the contrary, in MnGa/Co/Ta, antiferromagnetic coupling plays a dominant role. The switching current density Jc in MnGa/Ta is 8.5 × 107 A/cm2. After inserting 0.8-nm-thick Co2FeAl and Co, theJc becomes 5 × 107 A/cm2 and 9 × 107 A/cm2, respectively. By performing adiabatic harmonic Hall voltage measurements, it is demonstrated that the inserted Co2FeAl layer has mainly enhanced the field-like torques, while in MnGa/Co/Ta the damping-like torques have been enhanced. Finally, the enhanced spin Hall effect (SHE) has also been studied using the spin Hall magnetoresistance measurement. The modulated Jc and SOT are ascribed to the combination of magnetic coupling, Rashba effect and SHE at the interfaces.

  15. Electrical spin injection in modulation-doped GaAs from an in situ grown Fe/MgO layer

    Energy Technology Data Exchange (ETDEWEB)

    Shim, Seong Hoon [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Physics, Korea University, Seoul 136-713 (Korea, Republic of); Kim, Hyung-jun [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Koo, Hyun Cheol [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-701 (Korea, Republic of); Lee, Yun-Hi [Department of Physics, Korea University, Seoul 136-713 (Korea, Republic of); Chang, Joonyeon, E-mail: presto@kist.re.kr [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Nanomaterials Science and Engineering, Korea University of Science and Technology, Daejeon 305-350 (Korea, Republic of)

    2015-09-07

    We study spin accumulation in n-doped GaAs that were electrically injected from Fe via MgO using three-terminal Hanle measurement. The Fe/MgO/GaAs structures were prepared in a cluster molecular beam epitaxy that did not require the breaking of the vacuum. We found the crystal orientation relationship of epitaxial structures Fe[100]//MgO[110]//GaAs[110] without evident defects at the interface. Control of depletion width and interface resistance by means of modulation doping improves spin injection, leading to enhanced spin voltage (ΔV) of 6.3 mV at 10 K and 0.8 mV even at 400 K. The extracted spin lifetime and spin diffusion length of GaAs are 220 ps and 0.77 μm, respectively, at 200 K. MgO tunnel barrier grown in situ with modulation doping at the interface appears to be promising for spin injection into GaAs.

  16. Field-dependent linewidths and photoluminescence energies in GaAs-AlGaAs multiquantum well modulators

    Science.gov (United States)

    Juang, F.-Y.; Singh, J.; Bhattacharya, P. K.; Bajema, K.; Merlin, R.

    1986-01-01

    Photoluminescence linewidths and transition energies have been measured in GaAs-AlGaAs multiple quantum wells with large (equal to or greater than 160 A) barrier widths as a function of applied transverse electric field. The experimental data agree well with values calculated by using a recently developed variational technique. It is apparent that heterointerface roughness is the dominant line broadening mechanism. The emission intensity decreases rapidly with field, principally due to carrier tunneling at high fields. At 80 kV/cm a shift of 20 meV in the emission energy is observed.

  17. Giant peak to valley ratio in a GaN based resonant tunnel diode with barrier width modulation

    Science.gov (United States)

    Sankaranarayanan, Sandeep; Saha, Dipankar

    2016-10-01

    A barrier width modulated GaN based resonant tunnel diode is theoretically proposed which exhibits a giant peak to valley current ratio as high as 60 and a high negative differential conductance (NDC) of 1.77 × 106 S/cm2 with very low valley current density of 3 mA/cm2. This is achieved by the unique characteristic of the device current which monotonically decreases for applied voltages greater than the valley voltage in our simulation window. This is in contrast to all the other negative differential conductance based devices which experience an immediate exponential increase in current after the NDC region. The proposed device is also the first bidirectional tunneling diode which shows negative differential conductance for both polarity of the applied bias which is normally not observed with the conventional GaN/AlGaN double barrier structures due to the strong asymmetry arising from the internal electric fields due to polarization. The unique characteristics of the device can be attributed to the use of a modulated barrier width which is made possible by a polarization modulating InGaN layer and efficient utilization of internal electric fields in III-nitrides.

  18. Intrinsic Limits of Electron Mobility in Modulation-Doped AlGaN/GaN 2D Electron Gas by Phonon Scattering

    Institute of Scientific and Technical Information of China (English)

    Liang Pang

    2014-01-01

    We theoretically present the intrinsic limits to electron mobility in the modulation-doped AlGaN/GaN two-dimensional electron gas (2DEG) due to effects including acoustic deformation potential (DP) scattering, piezoelectric scattering (PE), and polar-optic phonon scattering (POP). We find that DE and PE are the more significant limiting factors at intermediate temperatures of 40 K to 250 K, while POP becomes dominant as room temperature is approached. Detailed numerical results are presented for the change of electron mobility with respect to temperature and carrier density. We conclude that these three types of phonon scattering, which are generally determined by the material properties but not the technical processing, are hard limits to the 2DEG mobility.

  19. Polarization controlled quantum phase gate based on cross-phase modulation in GaAs/AlGaAs semiconductor quantum wells

    CERN Document Server

    Luo, Xiao-Qing; Fan, Heng; Liu, Wu-Ming

    2012-01-01

    We investigate the linear and nonlinear properties of the probe and signal optical pulses based on intersubband transitions in an asymmetric GaAs/AlGaAs double quantum wells. It shows that, in the presence of cross-phase modulation, a giant cross-Kerr nonlinearity and mutually matched group velocities of the probe and signal optical pulses can be achieved while realizing the suppression of linear and self-Kerr optical absorption synchronously. These characteristics serve to exhibit an all-optical two-qubit polarization controlled quantum phase gate within efficiently controllable photon-photon entanglement by semiconductor mediation. In addition, by using just polarizing beam and half-wave plates, we propose a practical experimental scheme to discriminate the maximally entangled polarization state of two-qubit through distinguishing two out of the four Bell states. This proposal potentially enables the realization of solid states mediated all-optical quantum computation and information processing.

  20. Er1.33Pt3Ga8: A modulated variant of the Er4Pt9Al24-structure type

    Science.gov (United States)

    Oswald, Iain W. H.; Gourdon, Olivier; Bekins, Amy; Evans, Jess; Treadwell, LaRico J.; Chan, Julia Y.; Macaluso, Robin T.

    2016-10-01

    Single crystals of Er1.33Pt3Ga8 were synthesized in a molten Ga flux. Er1.33Pt3Ga8 can be considered to be a modulated variant of the Er4Pt9Al24-structure type, where the partial occupancies are ordered. Indeed, the presence of weak satellite reflections indicates a complex organization and distribution of the Er and Ga atoms within the [ErGa] slabs. The structure has been solved based on single crystal X-ray diffraction data in the monoclinic superspace group X2/m(0β0)00 with a commensurate modulated vector q=1/3b*. Precession images also indicate diffusion in the perpendicular direction indicating a partial disorder of this arrangement from layer to layer. In addition, Er1.33Pt3Ga8 shows antiferromagnetic ordering at TN~5 K.

  1. The modulated structure of intermediate-valent CeCoGa

    Energy Technology Data Exchange (ETDEWEB)

    Niehaus, Oliver; Hoffmann, Rolf-Dieter; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie; Chevalier, Bernard [CNRS, Bordeaux Univ., Pessac (France). ICMCB, UPR 9048

    2016-05-01

    CeCoGa was synthesized by melting of the elements in an arc-melting furnace as well as in a sealed niobium tube in an induction furnace. A further annealing step improves the purity and crystallinity of the samples significantly. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Already at room temperature CeCoGa crystallizes in a superstructure of the HT-CeCoAl type. This superstructure can be described in the (3+1)D superspace group C2/m(α0γ)00; α=2/3, γ=1/3 with a temperature independent q-vector (Z=4). For the 300 K data (also for 90 K) the commensurate modulated structure could be refined with 1336 F{sup 2} values, 56 variables and residuals of wR=0.0348 for the main and wR=0.0605 for the satellites of 1{sup st} order [a=1101.7(1), b=436.0(1) and c=482.4(1) pm, β=103.2(1) ]. Furthermore a description in a transformed 3D supercell with the space group C2/m and Z=12 is possible. For the 90 K data this 3D supercell was refined with 1289 F{sup 2} values, 56 variables and a residual of wR=0.0409 [a=1618.8(1), b=435.3(1) and c=1094.1(1) pm, β=119.3(1) ]. The relation of the HT-CeCoAl type structure, the (3+1)D modulated and the 3D supercell structure are discussed on the basis of a group-subgroup relation. By thermal analysis and magnetic measurements the phase transition temperature to the HT-CeCoAl type structure is stated slightly above 475 K. Furthermore intermediate cerium valence was identified by the magnetic susceptibility.

  2. Differential absorption lidar measurements of atmospheric water vapor using a pseudonoise code modulated AlGaAs laser. Thesis

    Science.gov (United States)

    Rall, Jonathan A. R.

    1994-01-01

    Lidar measurements using pseudonoise code modulated AlGaAs lasers are reported. Horizontal path lidar measurements were made at night to terrestrial targets at ranges of 5 and 13 km with 35 mW of average power and integration times of one second. Cloud and aerosol lidar measurements were made to thin cirrus clouds at 13 km altitude with Rayleigh (molecular) backscatter evident up to 9 km. Average transmitter power was 35 mW and measurement integration time was 20 minutes. An AlGaAs laser was used to characterize spectral properties of water vapor absorption lines at 811.617, 816.024, and 815.769 nm in a multipass absorption cell using derivative spectroscopy techniques. Frequency locking of an AlGaAs laser to a water vapor absorption line was achieved with a laser center frequency stability measured to better than one-fifth of the water vapor Doppler linewidth over several minutes. Differential absorption lidar measurements of atmospheric water vapor were made in both integrated path and range-resolved modes using an externally modulated AlGaAs laser. Mean water vapor number density was estimated from both integrated path and range-resolved DIAL measurements and agreed with measured humidity values to within 6.5 percent and 20 percent, respectively. Error sources were identified and their effects on estimates of water vapor number density calculated.

  3. Low spectral modulation high-power output from a new AlGaAs superluminescent diode/optical amplifier structure

    Energy Technology Data Exchange (ETDEWEB)

    Alphonse, G.A.; Connolly, J.C.; Dinkel, N.A.; Palfrey, S.L.; Gilbert, D.B. (David Sarnoff Research Center, Princeton, New Jersey 08543-5300 (US))

    1989-11-27

    A double-heterojunction angled stripe AlGaAs device consisting of an index-guided ridge waveguide with gain-guided facet regions has produced cw output powers of 20 mW with less than 1% spectral modulation from a 300-{mu}m-long diode. These properties enable these devices to have important use in high-sensitivity fiber optic gyroscopes and as broadband traveling-wave optical amplifiers.

  4. Monolithic integration of an (Al)GaAs laser and an intracavity electroabsorption modulator using selective partial interdiffusion

    Science.gov (United States)

    O'Brien, S.; Shealy, J. R.; Wicks, G. W.

    1991-04-01

    The monolithic integration of an intracavity modulator with a multiple quantum well (Al)GaAs laser has been accomplished with the use of selective partial interdiffusion. Interdiffusion was used to create a blue-shifted and semitransparent modulator section in a ridge laser structure. In measuring the total optical output power from the devices, steady-state extinction ratios of 20 dB were measured at reverse biases of -4.6 and -3.6 V for modulator sections with lengths of 200 and 400 microns, respectively. Shifting of the lasing mode toward longer wavelengths was also observed making the structure useful as a tunable device and for frequency modulation applications.

  5. Effective masses of Quasi-2D electrons in InGaAs/GaAsSb modulation-doped heterostructures

    Science.gov (United States)

    Tanveer, Imtiaz; McCombe, Bruce; Detz, Hermann; Strasser, Gottfried

    2015-03-01

    The electronic properties of In0.53Ga0.47As/GaAs0.51Sb0.49 2D electron gas (2DEG) systems, in spite of their use in high power electronics, have not been extensively investigated. Recently, they have been suggested as potential materials for IR quantum devices such as quantum cascade lasers (QCL), and they also show a strong Rashba effect1,2. Here accurate values of the effective masses are important. Two remotely donor (Si)-doped samples grown by MBE with a 2DEG at the single heterostructure interface were studied by FIR magneto-transmission spectroscopy with a BOMEM FTIR spectrometer. The maximum mobilities (near 70 K) are 43,000 cm2/Vs and 36,000 cm2/Vs with corresponding carrier densities of 1.07 x 1012 cm-2 and 2.13 x 1012 cm-2, respectively. Cyclotron resonance measurements between 4T and 9T yielded m* = 0.0495m0 for the more heavily doped sample. Individual transmission profiles in this case showed broadening toward high-energy, which may be due to contributions to the overall absorption profile from higher occupied subbands. The lower density sample shows an energy vs B dependence that does not extrapolate to zero at B = 0. The origin of this behavior will be discussed. Work at UB supported in part by NSF DMR #1305770 and the Office of the Provost and at the TU Wien by the Austrian Science Fund (FWF): P26100-N27 (H2N) and F4909-N23 (NextLite).

  6. Modulation Spectroscopy of GaAs Covered by InAs Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    金鹏; 孟宪权; 张子旸; 李成明; 曲胜春; 徐波; 刘峰奇; 王占国; 李乙钢; 张存洲; 潘士宏

    2002-01-01

    Contactless electroreflectance has been employed at room temperature to study the Fermi level pinning atundoped-n+ GaAs surfaces covered by 1.6 and 1.8 monolayer (ML) InAs quantum dots (QDs). It is shownthat the 1.8 ML InAs QD moves the Fermi level at GaAs surface to the valence band maximum by about 70 meVcompared to bare GaAs, whereas 1.6 ML InAs on GaAs does not modify the Fermi level. It is corzfirmed thatthe modiffication of the 1.8 ML InAs deposition on the Fermi level at GaAs surface is due to the QDs, which aresurrounded by some oxidized InAs facets, rather than the wetting layer.

  7. Analysis of the modulation mechanisms of the electric field and breakdown performance in AlGaN/GaN HEMT with a T-shaped field-plate

    Science.gov (United States)

    Mao, Wei; Fan, Ju-Sheng; Du, Ming; Zhang, Jin-Feng; Zheng, Xue-Feng; Wang, Chong; Ma, Xiao-Hua; Zhang, Jin-Cheng; Hao, Yue

    2016-12-01

    A novel AlGaN/GaN high electron mobility transistor (HEMT) with a source-connected T-shaped field-plate (ST-FP HEMT) is proposed for the first time in this paper. The source-connected T-shaped field-plate (ST-FP) is composed of a source-connected field-plate (S-FP) and a trench metal. The physical intrinsic mechanisms of the ST-FP to improve the breakdown voltage and the FP efficiency and to modulate the distributions of channel electric field and potential are studied in detail by means of two-dimensional numerical simulations with Silvaco-ATLAS. A comparison to the HEMT and the HEMT with an S-FP (S-FP HEMT) shows that the ST-FP HEMT could achieve a broader and more uniform channel electric field distribution with the help of a trench metal, which could increase the breakdown voltage and the FP efficiency remarkably. In addition, the relationship between the structure of the ST-FP, the channel electric field, the breakdown voltage as well as the FP efficiency in ST-FP HEMT is analyzed. These results could open up a new effective method to fabricate high voltage power devices for the power electronic applications. Project supported by the National Natural Science Foundation of China (Grant Nos. 61574112, 61334002, 61306017, 61474091, and 61574110) and the Natural Science Basic Research Plan in Shaanxi Province, China (Grant No. 605119425012).

  8. Domain model for the magnetic shape-memory effect in non-modulated tetragonal Ni-Mn-Ga

    Energy Technology Data Exchange (ETDEWEB)

    Onisan, A T; Bogdanov, A N; Roessler, U K, E-mail: u.roessler@ifw-dresden.de [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany)

    2011-07-06

    We employ a general phenomenological domain theory for ferromagnetic shape memory (FSM) materials to model equilibrium domain states in martensites with tetragonal twin variants having axes ratios c/a > 1 and easy-plane magnetic anisotropy. The model is evaluated for realistic material parameters of non-modulated (NM) Ni{sub 2}MnGa alloys. Phase diagrams under competing external stresses and magnetic fields are presented that show regions of fully magnetized single-variant states and various multiphase regions. The theoretical elastic stresses that block single-variant states are found to be much smaller in NM than in the 5M structure of Ni{sub 2}MnGa alloys.

  9. Determination of the orientation relationship between austenite and incommensurate 7M modulated martensite in Ni-Mn-Ga alloys

    Energy Technology Data Exchange (ETDEWEB)

    Li, Z.B. [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China); Zhang, Y.D. [Laboratoire d' Etude des Microstructures et de Mecanique des Materiaux (LEM3), CNRS UMR 7239, Universite Paul Verlaine - Metz, 57045 Metz (France); Esling, C., E-mail: claude.esling@univ-metz.fr [Laboratoire d' Etude des Microstructures et de Mecanique des Materiaux (LEM3), CNRS UMR 7239, Universite Paul Verlaine - Metz, 57045 Metz (France); Zhao, X. [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China); Zuo, L., E-mail: lzuo@mail.neu.edu.cn [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819 (China)

    2011-04-15

    For Ni-Mn-Ga ferromagnetic shape memory alloys, a large magnetic-field-induced strain could be reached through the reorientation of martensitic variants in the martensite state. Owing to the collective and displacive nature of the austenite to martensite transformation, a certain orientation relationship (OR) between the parent and the product phase is required to minimize the transformation strain and the strain energy generated, which brings about self-accommodating groups of martensitic variants with specific orientation correlations. In this work, the microstructural and crystallographic characteristics of martensitic variants in a polycrystalline Ni{sub 50}Mn{sub 30}Ga{sub 20} alloy were investigated by electron backscatter diffraction analysis. With accurate orientation measurement on inherited martensitic variants, the local orientations of parent austenite grains were predicted using four classical OR for the martensitic transformation. Furthermore, a specific OR, namely the Pitsch relation with (1 0 1){sub A}//(1 2-bar 10-bar){sub 7M} and [1 0 1-bar]{sub A}//[10-bar 10-bar 1]{sub 7M}, was unambiguously determined by considering the magnitude of discontinuity between the lattices of the product and parent phases and the structural modulation of the incommensurate 7M modulated martensite. The present procedure to determine the OR, without recourse to the presence of retained austenite, is in general applicable to a variety of materials with modulated superstructure for insight into their martensitic transformation processes.

  10. Effects of electronic state modulation on the high-frequency response characteristics of GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Basanta Singh, N., E-mail: basanta_n@rediffmail.co [Department of Electronics and Communication Engineering, Manipur Institute of Technology, Imphal 795 004 (India); Deb, Sanjoy, E-mail: deb_sanjoy@yahoo.co [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700 032 (India); Sarkar, Subir Kumar, E-mail: su_sircir@yahoo.co.i [Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700 032 (India)

    2009-11-01

    The effect of electronic-state modulation on the high frequency response of GaAs quantum well with thin inserted barrier layer is studied. The carrier scattering by polar optic phonons, acoustic deformation potential and background ionized impurities are incorporated in the present calculations considering the carrier distribution to be heated drifted Fermi-Dirac distribution. Modified phonon spectra and modulated electron wave function give different values of form factor compared to bulk mode phonon. Mobility is found to be enhanced on insertion of thin layer inside the quantum well. The ac mobility and the phase lag increases with the increase in both the channel width and the 2D carrier concentration. Cutoff frequency, where ac mobility drops down to 0.707 of its low frequency value, is observed to be enhanced reflecting better high frequency response.

  11. The effect of δ-doping and modulation-doping on Si-doped high Al content n-AlxGa1-xN grown by MOCVD

    Institute of Scientific and Technical Information of China (English)

    Zhu Shaoxin; Yan Jianchang; Zeng Jianping; Zhang Ning; Si Zhao; Dong Peng; Li Jinmin

    2013-01-01

    The effect of periodic delta-doping and modulation-doping on high Al content n-AlxGa1-xN (x =0.55) epilayers grown by MOCVD has been investigated.Measured by XRD,AFM,contactless sheet resistance,and Hall-effect tests,δ-doped and modulation-doped n-AlxGa1-xN have better crystal quality,surface morphology and electrical properties as compared with uniformly-doped n-AlxGa1-xN.These improvements are attributed to the SiNx growth mask induced by δ-doping layers and the dislocation-blocking effect induced by both growth techniques.In addition,due to the broadened doping profile ascribed to enhanced dopant diffusion at high growth temperatures (1150 ℃) of n-Al0.55Ga0.45N,modulation-doped n-Al0.55Ga0.45N has similar properties as δ-doped n-Al0.55Ga0.45N.

  12. Magnetic field-modulated photo-thermo-electric effect in Fe/GaAs film

    Energy Technology Data Exchange (ETDEWEB)

    Qiao, Shuang; Liu, Jihong; Yan, Guoying; Wang, Shufang, E-mail: xinhuiz@semi.ac.cn, E-mail: sfwang@hbu.edu.cn; Fu, Guangsheng [Hebei Key Laboratory of Optic-Electronic Information and Materials, College of Physics Science and Technology, Hebei University, Baoding 071002 (China); Zhao, Jianhua; Zhang, Xinhui, E-mail: xinhuiz@semi.ac.cn, E-mail: sfwang@hbu.edu.cn [State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China)

    2015-11-02

    Ferromagnet/semiconductor heterostructure, such as Fe/GaAs, is always one of the key issues in spintronics due to its prerequisite for the realization of spin sensitive devices. In this letter, a lateral photoelectric effect (LPE) was observed in Fe/GaAs. Our results show that the sensitivity was not related to laser wavelength, but only proportional to laser power, suggesting that the lateral photovoltage was induced by photo-thermo-electric effect. Moreover, we also observe that the voltage signal increases with the increase in applied field due to decreasing scattering probability for spin-polarized electrons. Our finding of LPE adds another functionality to the Fe/GaAs system and will be useful in development of spin-polarized voltage devices.

  13. Improved two-dimensional electron mobility in asymmetric barrier delta-doped GaAs/AlGaAs modulation-doped field-effect transistor structures

    Science.gov (United States)

    Das, Sudhakar; Mohapatra, Meryleen; Nayak, Rasmita K.; Panda, Ajit K.; Sahu, Trinath

    2017-03-01

    We study the enhancement of electron mobility μ in barrier delta-doped GaAs/AlGaAs quantum-well-based modulation-doped field-effect transistor (MODFET) structures. We asymmetrically vary the doping concentrations N d1 and N d2 in the barriers on the substrate and surface sides, respectively, to obtain a nonlinear enhancement of μ as a function of the well width w through multi-subband effects. We show that an increase in doping concentration increases the surface electron density N s, which in turn enhances μ. Interchanging N d1 and N d2 leads to no change in N s but rather, an enhancement of μ as a function of w for N d2 > N d1 owing to asymmetric variation of subband wave functions, thereby implying a higher channel conductivity in a surface-doped structure than in an inverted doped structure. By keeping (N d1 + N d2) unchanged, the conductivity of a single-channel MODFET, N d1 (N d2) ≠ 0 and N d2 (N d1) = 0, can be enhanced by considering a MODFET based on an asymmetrically doped (N d1 ≠ N d2 ≠ 0) quantum well structure. We show that the highest N s and μ product for these structures occurs almost before the onset of the occupation of the second subband. Our analysis of the effect of asymmetric doping profiles on channel conductivity can be utilized for the performance improvement of MODFET-like devices.

  14. Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

    CERN Document Server

    Demenev, A A; Schneider, C; Brodbeck, S; Kamp, M; Höfling, S; Lobanov, S V; Weiss, T; Gippius, N A; Tikhodeev, S G

    2016-01-01

    We report the elliptically, close to circularly polarized lasing at $\\hbar\\omega = 1.473$ and 1.522 eV from an AlAs/AlGaAs Bragg microcavity with 12 GaAs quantum wells in the active region and chiral-etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.

  15. Trap modulated photoresponse of InGaN/Si isotype heterojunction at zero-bias

    Energy Technology Data Exchange (ETDEWEB)

    Chandan, Greeshma; Mukundan, Shruti; Mohan, Lokesh; Krupanidhi, S. B., E-mail: sbk@mrc.iisc.ernet.in [Materials Research Centre, Indian Institute of Science, Bangalore (India); Roul, Basanta [Materials Research Centre, Indian Institute of Science, Bangalore (India); Central Research Laboratory, Bharat Electronics, Bangalore (India)

    2015-07-14

    n-n isotype heterojunction of InGaN and bare Si (111) was formed by plasma assisted molecular beam epitaxy without nitridation steps or buffer layers. High resolution X-ray diffraction studies were carried out to confirm the formation of epilayers on Si (111). X-ray rocking curves revealed the presence of large number of edge threading dislocations at the interface. Room temperature photoluminescence studies were carried out to confirm the bandgap and the presence of defects. Temperature dependent I-V measurements of Al/InGaN/Si (111)/Al taken in dark confirm the rectifying nature of the device. I-V characteristics under UV illumination, showed modest rectification and was operated at zero bias making it a self-powered device. A band diagram of the heterojunction is proposed to understand the transport mechanism for self-powered functioning of the device.

  16. Incident angle dependence of GaAs/AlGaAs multiple quantum well spatial light modulators%GaAs/AlGaAs多量子阱空间光调制器入射角度特性研究

    Institute of Scientific and Technical Information of China (English)

    黄寓洋; 张耀辉; 刘惠春; Wasilewski Z R; Buchanan M; Laframboise S R; 杨晨; 崔国新; 边历峰; 杨辉

    2010-01-01

    研究了GaAs/AlGaAs多量子阱(MQW)空间光调制器(SLM)在不同入射角度下的调制特性.对腔模位置与入射角度的关系进行了理论计算和实验验证,两者具有较好的一致性.当入射角在0°~75°之间变化时,腔模从871 nm变化至845 nm,可调节范围达26 nm.当入射光从垂直入射变化为约45°入射时,SLM对比度从(CR)3.8提高到16.3,调制电压从9.5 V下降至6.5 V.理论分析和实验结果表明,入射角度调节能够有效提高GaAs/AlGaAs MQW SLM调制性能.

  17. A multilevel intermediate-band solar cell by InGaN/GaN quantum dots with a strain-modulated structure.

    Science.gov (United States)

    Sang, Liwen; Liao, Meiyong; Liang, Qifeng; Takeguchi, Masaki; Dierre, Benjamin; Shen, Bo; Sekiguchi, Takashi; Koide, Yasuo; Sumiya, Masatomo

    2014-03-05

    Multiple stacked InGaN/GaN quantum dots are embedded into an InGaN p-n junction to develop multilevel intermediateband (MIB) solar cells. An IB transition is evidenced from both experiment and theoretical calculations. The MIB solar cell shows a wide photovoltaic response from the UV to the near-IR region. This work opens up an interesting opportunity for high-efficiency IB solar cells in the photovoltaics field.

  18. Ultralow-energy electro-absorption modulator consisting of InGaAsP-embedded photonic-crystal waveguide

    Directory of Open Access Journals (Sweden)

    Kengo Nozaki

    2017-05-01

    Full Text Available Towards realizing highly integrable low-energy optical modulators, the small device capacitance (C as well as the low driving voltage (Vpp is demanded for suppressing the charging energy during the dynamic operation. Although an electro-absorption modulator (EAM has great potential in reducing them, the additional energy associated with the photocurrent flow will limit the lower-bound of the consumption energy. In this work, a broadband EAM based on an InGaAsP-embedded photonic crystal waveguide is demonstrated, revealing a high modulation bit rate of up to 56 Gbit/s. The air-bridge structure and a device length of 100 μm or less result in a small C ≤ 13 fF while operating with Vpp < 1 V. Particularly, the operation in low reverse voltage for a p-i-n junction, that is, −0.2 V as the minimum value in this study, works effective for the reduction of energy involving the photocurrent. This results in the total electrical energy consumption of <2 fJ/bit, which is lower than that of any waveguide EAMs.

  19. Characterization of efficiency-limiting resistance losses in monolithically integrated Cu(In,Ga)Se2 solar modules.

    Science.gov (United States)

    Yoon, Ju-Heon; Park, Jong-Keuk; Kim, Won Mok; Lee, JinWoo; Pak, Hisun; Jeong, Jeung-Hyun

    2015-01-09

    The cell-to-module efficiency gap in Cu(In,Ga)Se2 (CIGS) monolithically integrated solar modules is enhanced by contact resistance between the Al-doped ZnO (AZO) and Mo back contact layers, the P2 contact, which connects adjacent cells. The present work evaluated the P2 contact resistance, in addition to the TCO resistance, using an embedded transmission line structure in a commercial-grade module without using special sample fabrication methods. The AZO layers between cells were not scribed; instead, the CIGS/CdS/i-ZnO/AZO device was patterned in a long stripe to permit measurement of the Mo electrode pair resistance over current paths through two P2 contacts (Mo/AZO) and along the AZO layer. The intercept and slope of the resistance as a function of the electrode interval yielded the P2 contact resistance and the TCO resistance, respectively. Calibration of the parasitic resistances is discussed as a method of improving the measurement accuracy. The contribution of the P2 contact resistance to the series resistance was comparable to that of the TCO resistance, and its origin was attributed to remnant MoSe2 phases in the P2 region, as verified by transmission electron microscopy.

  20. 4 Gb/s two-level to 2 symbol/s four-level converter GaAs IC for semiconductor optical amplifier modulators

    DEFF Research Database (Denmark)

    Riishøj, J.; Nielsen, Torben Nørskov; Gliese, Ulrik Bo

    1993-01-01

    A design of a 50 Ω impedance matched two-to-four level converter GaAs IC for two-electrode semiconductor optical amplifier modulators is presented. Eye diagrams with good eye openings and 0.33 V spacing between adjacent logic levels are demonstrated for input bit rates up to 4 Gb/s. A novel...

  1. 1.55-μm InGaAsP/InP partially gain-coupled distributed feedback laser/electroabsorption modulator integrated device for trunkline communication

    Science.gov (United States)

    Luo, Yi; Wen, Guo-Peng; Sun, Changzheng; Li, TongNing; Yang, Xin-Min; Wang, Ren-Fan; Wang, Cai-Lin; Jin, Jin-Yan

    1998-08-01

    In this paper, a 1.55 micrometers InGaAsP/InP partially gain- coupled DFB laser monolithically integrated with electroabsorption modulator is fabricated for the first time. The threshold current and the extinction ratio are 40 mA and 11 dB respectively.

  2. GaAs-based superluminescent diodes with window-like facet structure for low spectral modulation at high output powers

    Science.gov (United States)

    Ghazal, O. M. S.; Childs, D. T.; Stevens, B. J.; Babazadeh, N.; Hogg, R. A.; Groom, K. M.

    2016-04-01

    We demonstrate a GaAs-based superluminescent diode (SLD) based on the incorporation of a window-like back facet into a self-aligned stripe structure in order to reduce the effective facet reflectivity. This allows the realisation of SLDs with low spectral modulation depth (SMD) at high power spectral density (PSD), without the application of anti-reflection coatings to either facet. This approach is therefore compatible with ultra-broadband gain active elements. We show that 30 mW output power can be attained in a narrow bandwidth, corresponding to 2.2 mW nm-1 PSD with only 5% SMD, centred about 990 nm. We discuss the design criteria for high power and low SMD and the deviation from a linear dependence of SMD on output power, resulting from Joule heating in the self-aligned stripe.

  3. GA SPEED AND DQ CURRNETS CONTROL OF PMSM WITH VECTOR CONTROL BASED SPACE VECTOR MODULATION USING MATLAB/SIMULINK

    Directory of Open Access Journals (Sweden)

    A. El Janati El Idrissi

    2011-08-01

    Full Text Available In recent years, permanent magnet synchronous motors (PMSM have gained variety industrial applications, because of simple structures, high efficiency and ease of maintenance. But these motors have a nonlinear mathematical model. To resolve this problem several studies have suggested the application of soft-computing technique. This paper presents vector control of PMSM fed by space vector modulation inverter using genetic algorithm (GA controllers to improve speed, currents and the electric torque by significantly reducing their ripples, which offer an extra advantage of this study. The proposed method effectiveness has been verified by computer simulations using Matlab/Simulink®. These results are compared with the ones obtained with a vector control using PI controllers for speed and current [1] and the second obtained with adaptive controller based speed estimation technique [2].

  4. Infrared to visible image up-conversion using optically addressed spatial light modulator utilizing liquid crystal and InGaAs photodiodes

    Energy Technology Data Exchange (ETDEWEB)

    Solodar, A., E-mail: asisolodar@gmail.com; Arun Kumar, T.; Sarusi, G.; Abdulhalim, I. [Department of Electro-Optics Engineering and The Ilse Katz Institute for Nanoscale Science and Technology, Ben Gurion University of the Negev, Beer Sheva 84105 (Israel)

    2016-01-11

    Combination of InGaAs/InP heterojunction photodetector with nematic liquid crystal (LC) as the electro-optic modulating material for optically addressed spatial light modulator for short wavelength infra-red (SWIR) to visible light image conversion was designed, fabricated, and tested. The photodetector layer is composed of 640 × 512 photodiodes array based on heterojunction InP/InGaAs having 15 μm pitch on InP substrate and with backside illumination architecture. The photodiodes exhibit extremely low, dark current at room temperature, with optimum photo-response in the SWIR region. The photocurrent generated in the heterojunction, due to the SWIR photons absorption, is drifted to the surface of the InP, thus modulating the electric field distribution which modifies the orientation of the LC molecules. This device can be attractive for SWIR to visible image upconversion, such as for uncooled night vision goggles under low ambient light conditions.

  5. 40 GHz AlGaInAs Multiple-Quantum-Well Integrated Electroabsorption Modulator/Distributed Feedback Laser Based on Identical Epitaxial Layer Scheme

    Science.gov (United States)

    Luo, Yi; Xiong, Bing; Wang, Jian; Cai, Pengfei; Sun, Changzheng

    2006-10-01

    An AlGaInAs multiple-quantum-well (MQW) distributed feedback (DFB) laser is monolithically integrated with a lumped-electrode electroabsorption (EA) modulator based on an identical epitaxial layer integration scheme. The device exhibits a threshold current of 12 mA and an extinction ratio of higher than 13 dB under a 3 V reverse bias. By adopting a dry-etched high-mesa ridge waveguide and planar electrode structures, the capacitance of the modulator is reduced to about 0.11 pF and a 3 dBe modulation bandwidth of over 40 GHz has been demonstrated. To our knowledge, this is the first report on a 40 GHz operation of AlGaInAs integrated light sources.

  6. Characterization of Cu(In,Ga)Se{sub 2} photovoltaic modules

    Energy Technology Data Exchange (ETDEWEB)

    Dyk, E.E. van [Physics Department, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 (South Africa)]. E-mail: ernest.vandyk@nmmu.ac.za; Radue, C. [Physics Department, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 (South Africa); Gxasheka, A.R. [Physics Department, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 (South Africa)

    2007-05-31

    In this study copper indium gallium diselenide photovoltaic (PV) modules were subjected to a thorough indoor assessment procedure. The assessment is to be used as a baseline for future evaluation of the modules deployed outdoors as part of an ongoing evaluation of device performance and degradation. The main focus of the study is the long term monitoring of the devices to determine service lifetime. In this paper we will present initial results of the baseline evaluation, namely I-V characteristics, thorough visual inspection and an analysis of performance parameters. The results obtained revealed that the performance of one of the modules was inferior to the others evaluated. In order to further investigate this, laser beam induced current (LBIC) measurements were conducted on regions that had a non-uniform appearance as observed visually.

  7. Influences of quantum noises on direct-modulated properties of 1.3-μm InGaAsP/InP laser diodes

    Institute of Scientific and Technical Information of China (English)

    Wang Jun; Ma Xiao-Yu; Bai Yi-Ming; Cao Li; Wu Da-Jin

    2006-01-01

    Due to the zero dispersion point at 1.3μm in optical fibres, 1.3-μm InGaAsP/InP laser diodes have become main light sources in fibre communication systems recently. Influences of quantum noises on direct-modulated properties of single-mode 1.3-μm InGaAsP/InP laser diodes are investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the direct-modulated single-mode laser system are calculated using the linear approximation method. We find that the stochastic resonance (SR) always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient between the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNRof direct-modulated InGaAsP/InP laser diodes and improve the quality of optical fibre communication systems.

  8. β-AgAl(1-x)Ga(x)O2 solid-solution photocatalysts: continuous modulation of electronic structure toward high-performance visible-light photoactivity.

    Science.gov (United States)

    Ouyang, Shuxin; Ye, Jinhua

    2011-05-25

    A series of β-AgAl(1-x)Ga(x)O(2) solid-solution materials were explored as novel visible-light-sensitive photocatalysts. These Ag-based solid solutions crystallize in a homogeneous crystal structure with orthorhombic symmetry but possess continuously modulated band gaps from 2.19 to 2.83 eV by decreasing the ratios of Ga/Al. Their photoactivities for iso-propanol degradation were found to be dependent on the variation of chemical compositions. Among them, the β-AgAl(0.6)Ga(0.4)O(2) sample showed the highest photocatalytic performance, which simultaneously exhibited 35 and 63 times higher activities than two terminus materials, β-AgAlO(2) and β-AgGaO(2), respectively. The apparent quantum efficiency of this sample for iso-propanol photodegradation achieved up to 37.3% at the wavelength of 425 ± 12 nm. The theoretical calculation based on density functional theory demonstrated that the levels of valence band maximum of β-AgAl(1-x)Ga(x)O(2) are similar, but the levels of conduction band minimum are gradually negatively shifted with the increase of the ratio of Ga/Al, thereby continuously narrowing the band gap. Nevertheless, the highest activity observed on β-AgAl(0.6)Ga(0.4)O(2) may be attributed to its optimized band structure, which adapts the balance between effective visible-light absorption and adequate redox potentials.

  9. Improved GaN Brown on Si(111 ) substrate using ammonia flow modulation on SiNx mask layer by MOCVD

    Institute of Scientific and Technical Information of China (English)

    YU NaiSen; WANG Yong; WANG Hui; NG KaiWei; LAU KeiMay

    2009-01-01

    In this paper, 1 μm n-GaN was grown by using varied and fixed ammonia flow (NH3) on SiNx mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three- to two-dimensional process has been prolonged by using varied ammonia flow on SiNx mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photolu-minescence, and compared with the sample grown by fixing ammonia flow, GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH3 flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiNx layer by enhancing vertical growth. Lateral growth was significantly favored by high NH3 flow in the subsequent step. As a result, the improved crystal and optical quality was achieved utilizing NH3 flow modulation for GaN buffer growth on Si(111) substrate.

  10. Improved GaN grown on Si(111) substrate using ammonia flow modulation on SiN_x mask layer by MOCVD

    Institute of Scientific and Technical Information of China (English)

    NG; KaiWei; LAU; KeiMay

    2009-01-01

    In this paper,1 μm n-GaN was grown by using varied and fixed ammonia flow (NH3) on SiNx mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVD). In-situ optical reflectivity traces of GaN growth show that the three-to two-dimensional process has been prolonged by using varied ammonia flow on SiNx mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photolu-minescence,and compared with the sample grown by fixing ammonia flow,GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH3 flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiNx layer by enhancing vertical growth. Lateral growth was significantly favored by high NH3 flow in the subsequent step. As a result,the improved crystal and optical quality was achieved utilizing NH3 flow modulation for GaN buffer growth on Si(111) substrate.

  11. Structure and microwave properties analysis of substrate removed GaAs/AIGaAs electro-optic modulator structure by finite element method

    Institute of Scientific and Technical Information of China (English)

    Kambiz ABEDI; Habib VAHIDI

    2013-01-01

    In this paper, structure and microwave properties of a substrate removed GaAs/A1GaAs traveling wave electro-optic modulator structure were analyzed and simulated by using the finite element numerical technique for lower loss, simultaneous matching of optical and microwave velocities and impedance matching with 50 Ω. The effects of core layer thickness, claddings thicknesses, and width of the modulator on the microwave effective index nm were investigated, the characteristic impedance Zc, the microwave losses a, and the half-wave voltage- length product VmL were calculated. The results of the simulation suggest that the electrical bandwidth of 22 GHz and the optical bandwidth of 48 GHz can be obtained for fully matched, lower loss structure, which correspond to a 13 V. cm drive voltage.

  12. Very Thin Flexible Coupled Inductors for PV Module Integrated GaN Converter

    DEFF Research Database (Denmark)

    Acanski, Milos; Ouyang, Ziwei; Popovic-Gerber, Jelena

    2012-01-01

    proposed with more granular power processing by means of distributed maximum power point tracking (DMPPT). This is achieved by adjoining a MPPT unit to each PV module in the PV array. This paper presents a step further in the distributed power tracking approach, with a concept of very low profile power......As the PV energy penetrates into the urban area, shortcomings of the conventional centralized PV system architectures become more pronounced under the influence of urban environment with shading, soiling and orientation mismatch issues. To overcome these limitations new PV system architectures were...

  13. Very Thin Flexible Coupled Inductors for PV Module Integrated GaN Converter

    DEFF Research Database (Denmark)

    Acanski, Milos; Ouyang, Ziwei; Popovic-Gerber, Jelena;

    2012-01-01

    As the PV energy penetrates into the urban area, shortcomings of the conventional centralized PV system architectures become more pronounced under the influence of urban environment with shading, soiling and orientation mismatch issues. To overcome these limitations new PV system architectures were...... proposed with more granular power processing by means of distributed maximum power point tracking (DMPPT). This is achieved by adjoining a MPPT unit to each PV module in the PV array. This paper presents a step further in the distributed power tracking approach, with a concept of very low profile power...

  14. Materials and process development for the monolithic interconnected module (MIM) InGaAs/InP TPV cells

    Energy Technology Data Exchange (ETDEWEB)

    Fatemi, N.S.; Jenkins, P.P.; Hoffman, R.W. Jr.; Weizer, V.G. [Essential Research, Inc., Cleveland, OH (United States); Wilt, D.M. [National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center; Murray, C.S.; Riley, D. [Westinghouse Electric Corp., West Mifflin, PA (United States)

    1997-06-01

    Four major components of a thermophotovoltaic (TPV) energy conversion system are a heat source, a graybody or a selective emitter, spectrum shaping elements such as filters, and photovoltaic (PV) cells. One approach to achieving a high voltage/low current configuration is to fabricate a device, where small area PV cells are monolithically series connected. The authors have termed this device a monolithic interconnected module (MIM). A MIM device has other advantages over conventional one-junction cells, such as simplified array interconnections and heat-sinking, and radiation recycling capability via a back surface reflector (BSR). The authors confine the contents of this article to the MIM materials, process development, and some optical results. The successful fabrication of InGaAs/InP MIM devices entails the development and optimization of several key components and processes. These include: isolation trench via geometry, selective chemical etching, contact and interconnect metallization, dielectric isolation barrier, back surface reflector (BSR), and anti-reflection (AR) coating. The selection, development, and testing of the materials and processes described above for MIM fabrication will be described.

  15. Effect of initial plastic strain on mechanical training of non-modulated Ni–Mn–Ga martensite structure

    Energy Technology Data Exchange (ETDEWEB)

    Szczerba, M.J., E-mail: m.szczerba@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Chulist, R. [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Kopacz, S.; Szczerba, M.S. [Department of Materials Science and Non-Ferrous Metals Engineering, AGH University of Science and Technology, 30 Mickiewicza Ave., 30-059 Kraków (Poland)

    2014-08-12

    The influence of plastic pre-straining on the mechanical training process of Ni–Mn–Ga single crystals with a non-modulated martensite structure was examined using uniaxial quasi static compression tests and electron backscatter diffraction technique. Firstly, the optimal pre-straining temperature, for which a large plastic strain can be imposed to as-grown crystals with low flow stress and low rate of strain hardening, was established. Then, the maximum value of plastic pre-straining which allows performing successful room temperature mechanical training was found to be of about 20% of total sample thickness reduction. Below this value, training process leads to single variant state, which is able to accommodate true plastic strain of about 0.14 in each step of further training. Above 20% of deformation a multiple martensite variant state of characteristic triangular arrangements is generated. The latter structure cannot practically afford any plastic accommodation during further training; thus the training process fails to operate.

  16. Electronic transport in n- and p-type modulation doped Ga{sub x}In{sub 1-x}N{sub y}As{sub 1-y}/ GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Y; Balkan, N [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ (United Kingdom); Aslan, M; Arikan, M C [Faculty of Science, Department of Physics, Istanbul University, 34134 Istanbul (Turkey); Lisesivdin, S B [Department of Physics, Faculty of Science and Arts, Gazi University, Teknikokullar, 06500 Ankara (Turkey); Carrere, H; Marie, X [Department of Physics, INSA, 135 avenue de Rangeil, 31077 Toulouse cedex 4 (France)], E-mail: balkan@essex.ac.uk

    2009-04-29

    We present a comprehensive study of longitudinal transport of two-dimensional (2D) carriers in n- and p-type modulation doped Ga{sub x}In{sub 1-x}N{sub y}As{sub 1-y} /GaAs quantum well structures. The Hall mobility and carrier density of electrons in the n-modulation doped quantum wells (QWs) decreases with increasing nitrogen composition. However, the mobility of the 2D holes in p-modulation doped wells is not influenced by nitrogen and it is significantly higher than that of 2D electrons in n-modulation doped material. The observed behaviour is explained in terms of increasing electron effective mass as well as enhanced N-related alloying scattering with increasing nitrogen content. In order to determine the conduction band (CB) and valence band (VB) structures as well as electron and hole effective masses, the band anticrossing model with an eight-band k.p approximation in the Luettinger-Kohn approach is used. The effects of strain, quantum confinement and the strong coupling between the localized nitrogen states and the CB extended states of GaInAs are considered in the calculations. The results indicate that the nitrogen induces a strong perturbation to the CB of the matrix semiconductor whilst the VB remains unaffected. The temperature dependent mobility of 2D electron gas is discussed using an analytical model that accounts for the most important scattering mechanisms. The results indicate that the interface roughness and N-related alloy scattering are the dominant mechanisms at low temperatures, while polar optical phonon and N-related alloy scattering limit mobility at high temperatures.

  17. A solid-state NMR and DFT study of compositional modulations in AlxGa1-xAs

    NARCIS (Netherlands)

    Knijn, Paulus J.; Bentum, P. Jan M. van; Eck, Ernst R.H. van; Fang, Changming; Grimminck, Dennis L.A.G.; Groot, Robert A. de; Havenith, Remco W.A.; Marsman, Martijn; Meerts, W. Leo; Wijs, Gilles A. de; Kentgens, Arno P.M.

    2010-01-01

    We have conducted 75As and 69Ga Nuclear Magnetic Resonance (NMR) experiments to investigate order/disorder in AlxGa1-xAs lift-off films with x ~ 0.297 and 0.489. We were able to identify all possible As(AlnGa4-n) sites with n = 0–4 coordinations in 75As NMR spectra using spin-echo experiments at 18.

  18. Magnetotransport measurements on modulation Si {delta}-doped pseudomorphic In{sub 0.2}Ga{sub 0.8}As/GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Babinski, A.; Li, G.; Jagadish, C. [The Australian National University, ACT (Australia). Institute of Advanced Studies, Research School of Physical Sciences and Engineering, Department of Electronic Materials Engineering

    1998-07-01

    The effect of doping concentration on electrical properties of Si {delta}-doped pseudomorphic In{sub 0} {sub .2}Ga{sub 0.} {sub 8}As/GaAs quantum wells (QWs) was examined in this work. Magnetotransport measurements were carried out in the magnetic fields up to 12 T in the dark at the temperature of T=1.7 K. The results were analysed using the fast Fourier transform (FFT). It was found that one electron subband was occupied in the QW with the doping concentrations of 2.3 x 10{sup 12} or 6.0 x 10{sup 12} cm{sup -2}. The parallel conduction was present in both samples, which increased with an increase of Si {delta}-doping concentration. The well-developed plateaus arising from the quantised Hall effect were observed in the Si {delta}-doped In{sub 0.} {sub 2}Ga{sub 0.} {sub 8}As/GaAs QW with reduced parallel conduction. The two subbands remain occupied within the V-shaped potential well formed at the Si doping plane when the Si {delta}-doping concentration was high. The results of measurements in tilted magnetic fields, confirming the attribution of FFT peaks to the particular 2DEG systems, are also presented.

  19. Effects of growth temperature modulated by HCl flow rate on the surface and crystal qualities of thick GaN by HVPE

    Energy Technology Data Exchange (ETDEWEB)

    Zhao Lubing [Research Center for Wide-gap Semiconductors, State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Wu Jiejun, E-mail: wujiejun@opt.elec.mie-u.ac.jp [Research Center for Wide-gap Semiconductors, State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China); Xu Ke; Yang Zhijian; Zhang Guoyi [Research Center for Wide-gap Semiconductors, State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871 (China)

    2009-06-30

    We studied the influence of the growth temperature and HCl flow rate on the morphological evolution of crack-free thick GaN films by using a home-made horizontal hydride vapor phase epitaxy on sapphire substrates. Optical difference microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cathodoluminescence (CL) were carried out to reveal the surface property of the GaN epilayer. It was found that the higher growth temperature is a key factor to obtain mirror, colorless and flat GaN surface. However, this key effect of temperature was modulated by HCl flow rate (HCl > 15 sccm). The surface RMS roughness was reduced from 206 to 2.51 nm for 10 {mu}m x 10 {mu}m scan area when GaN was grown at 1070 deg. C with HCl flow rate up to 30 sccm. These samples also reduced their (0 0 0 2) FWHM result from 1000 to 300 arcsec and showed a strong near-band-edge peak in CL spectra. Results indicated that growth temperature influence growth velocities on different crystalline planes, which will lead to the different morphologies obtained. High growth temperature can improve the lateral growth rate of vertical {l_brace}1 1 - 2 0{r_brace} facets and reduce the vertical growth rate of top {l_brace}0 0 0 1{r_brace} facet combined with higher HCl flow rate, which leads to completely coalescence of surface.

  20. Optical and electronic properties of single modulation doped GaAs/AlGaAs V-grooved quantum wire modified by ion implantation

    Institute of Scientific and Technical Information of China (English)

    HUANG Shaohua; CHEN Zhanghai; BAI Lihui; WANG Fangzhen; SHEN Xuechu

    2005-01-01

    Single GaAs/Al0.5Ga0.5As V-grooved quantum wire modified by selective ion-implantation and rapid thermally annealing was investigated by spatially-resolved microphotoluminescence and magneto-resistance measurement. Spatially-resolved photoluminescence results indicate that the ion-implantation induced quantum well intermixing raises significantly the electron subband energies of the side quantum wells and vertical quantum wells, and more efficient accumulation of electrons in the quantum wires is achieved. Furthermore, the polarization properties of the photoluminescence from the quantum wires show large linear polarization degree up to 63%. Magneto-transport investigation on the ion implanted quantum wire samples presents the quasi-one dimensional intrinsic motion of electrons, which is important for the design and optimization of one dimensional electronic devices.

  1. Comparative Transcriptome Analysis of Genes Involved in GA-GID1-DELLA Regulatory Module in Symbiotic and Asymbiotic Seed Germination of Anoectochilus roxburghii (Wall. Lindl. (Orchidaceae

    Directory of Open Access Journals (Sweden)

    Si-Si Liu

    2015-12-01

    Full Text Available Anoectochilus roxburghii (Wall. Lindl. (Orchidaceae is an endangered medicinal plant in China, also called “King Medicine”. Due to lacking of sufficient nutrients in dust-like seeds, orchid species depend on mycorrhizal fungi for seed germination in the wild. As part of a conservation plan for the species, research on seed germination is necessary. However, the molecular mechanism of seed germination and underlying orchid-fungus interactions during symbiotic germination are poorly understood. In this study, Illumina HiSeq 4000 transcriptome sequencing was performed to generate a substantial sequence dataset of germinating A. roxburghii seed. A mean of 44,214,845 clean reads were obtained from each sample. 173,781 unigenes with a mean length of 653 nt were obtained. A total of 51,514 (29.64% sequences were annotated, among these, 49 unigenes encoding proteins involved in GA-GID1-DELLA regulatory module, including 31 unigenes involved in GA metabolism pathway, 5 unigenes encoding GID1, 11 unigenes for DELLA and 2 unigenes for GID2. A total of 11,881 genes showed significant differential expression in the symbiotic germinating seed sample compared with the asymbiotic germinating seed sample, of which six were involved in the GA-GID1-DELLA regulatory module, and suggested that they might be induced or suppressed by fungi. These results will help us understand better the molecular mechanism of orchid seed germination and orchid-fungus symbiosis.

  2. Comparative Transcriptome Analysis of Genes Involved in GA-GID1-DELLA Regulatory Module in Symbiotic and Asymbiotic Seed Germination of Anoectochilus roxburghii (Wall.) Lindl. (Orchidaceae).

    Science.gov (United States)

    Liu, Si-Si; Chen, Juan; Li, Shu-Chao; Zeng, Xu; Meng, Zhi-Xia; Guo, Shun-Xing

    2015-12-18

    Anoectochilus roxburghii (Wall.) Lindl. (Orchidaceae) is an endangered medicinal plant in China, also called "King Medicine". Due to lacking of sufficient nutrients in dust-like seeds, orchid species depend on mycorrhizal fungi for seed germination in the wild. As part of a conservation plan for the species, research on seed germination is necessary. However, the molecular mechanism of seed germination and underlying orchid-fungus interactions during symbiotic germination are poorly understood. In this study, Illumina HiSeq 4000 transcriptome sequencing was performed to generate a substantial sequence dataset of germinating A. roxburghii seed. A mean of 44,214,845 clean reads were obtained from each sample. 173,781 unigenes with a mean length of 653 nt were obtained. A total of 51,514 (29.64%) sequences were annotated, among these, 49 unigenes encoding proteins involved in GA-GID1-DELLA regulatory module, including 31 unigenes involved in GA metabolism pathway, 5 unigenes encoding GID1, 11 unigenes for DELLA and 2 unigenes for GID2. A total of 11,881 genes showed significant differential expression in the symbiotic germinating seed sample compared with the asymbiotic germinating seed sample, of which six were involved in the GA-GID1-DELLA regulatory module, and suggested that they might be induced or suppressed by fungi. These results will help us understand better the molecular mechanism of orchid seed germination and orchid-fungus symbiosis.

  3. Thermal Effects and Small Signal Modulation of 1.3-μm InAs/GaAs Self-Assembled Quantum-Dot Lasers

    Directory of Open Access Journals (Sweden)

    Tong CZ

    2011-01-01

    Full Text Available Abstract We investigate the influence of thermal effects on the high-speed performance of 1.3-μm InAs/GaAs quantum-dot lasers in a wide temperature range (5–50°C. Ridge waveguide devices with 1.1 mm cavity length exhibit small signal modulation bandwidths of 7.51 GHz at 5°C and 3.98 GHz at 50°C. Temperature-dependent K-factor, differential gain, and gain compression factor are studied. While the intrinsic damping-limited modulation bandwidth is as high as 23 GHz, the actual modulation bandwidth is limited by carrier thermalization under continuous wave operation. Saturation of the resonance frequency was found to be the result of thermal reduction in the differential gain, which may originate from carrier thermalization.

  4. Environmental impact of thin-film GaInP/GaAs and multicrystalline silicon solar modules produced with solar electricity

    NARCIS (Netherlands)

    Mohr, N.; Meijer, A.; Huijbregts, M.A.J.; Reijnders, L.

    2009-01-01

    Background, aim, and scope: The environmental burden of photovoltaic (PV) solar modules is currently largely determined by the cumulative input of fossil energy used for module production. However, with an increased focus on limiting the emission of CO2 coming from fossil fuels, it is expected that

  5. Environmental impact of thin-film GaInP/GaAs and multicrystalline silicon solar modules produced with solar electricity

    NARCIS (Netherlands)

    Mohr, N.; Meijer, A.; Huijbregts, M.A.J.; Reijnders, L.

    2009-01-01

    Background, aim, and scope: The environmental burden of photovoltaic (PV) solar modules is currently largely determined by the cumulative input of fossil energy used for module production. However, with an increased focus on limiting the emission of CO2 coming from fossil fuels, it is expected that

  6. Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression.

    Science.gov (United States)

    Xie, Yanjie; Zhang, Chen; Lai, Diwen; Sun, Ya; Samma, Muhammad Kaleem; Zhang, Jing; Shen, Wenbiao

    2014-01-15

    Hydrogen sulfide (H2S) is considered as a cellular signaling intermediate in higher plants, but corresponding molecular mechanisms and signal transduction pathways in plant biology are still limited. In the present study, a combination of pharmacological and biochemical approaches was used to study the effect of H2S on the alleviation of GA-induced programmed cell death (PCD) in wheat aleurone cells. The results showed that in contrast with the responses of ABA, GA brought about a gradual decrease of l-cysteine desulfhydrase (LCD) activity and H2S production, and thereafter PCD occurred. Exogenous H2S donor sodium hydrosulfide (NaHS) not only effectively blocked the decrease of endogenous H2S release, but also alleviated GA-triggered PCD in wheat aleurone cells. These responses were sensitive to hypotaurine (HT), a H2S scavenger, suggesting that this effect of NaHS was in an H2S-dependent fashion. Further experiment confirmed that H2S, rather than other sodium- or sulphur-containing compounds derived from the decomposing of NaHS, was attributed to the rescuing response. Importantly, the reversing effect was associated with glutathione (GSH) because the NaHS triggered increases of endogenous GSH content and the ratio of GSH/oxidized GSH (GSSG) in GA-treated layers, and the NaHS-mediated alleviation of PCD was markedly eliminated by l-buthionine-sulfoximine (BSO, a selective inhibitor of GSH biosynthesis). The inducible effect of NaHS was also ascribed to the modulation of heme oxygenase-1 (HO-1), because the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPP) significantly suppressed the NaHS-related responses. By contrast, the above inhibitory effects were reversed partially when carbon monoxide (CO) aqueous solution or bilirubin (BR), two of the by-products of HO-1, was added, respectively. NaHS-triggered HO-1 gene expression in GA-treated layers was also confirmed. Together, the above results clearly suggested that the H2S-delayed PCD in GA-treated wheat

  7. InGaP HBT Lift-Off for High Efficiency L-band T/R Module Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This proposal addresses the need for the development of higher efficiency power amplifiers at L-band using GaAs HBT (heterojunction bipolar transistors) for pulsed...

  8. Rapid thermal annealing and modulation-doping effects on InAs/GaAs quantum dots photoluminescence dependence on excitation power

    Energy Technology Data Exchange (ETDEWEB)

    Chaâbani, W. [Laboratoire Matériaux-Molécules et Applications, Institut Préparatoire aux Etudes Scientifiques et Techniques, Université de Carthage, La Marsa 2070 (Tunisia); Melliti, A., E-mail: adnenmelliti@yahoo.fr [Laboratoire Matériaux-Molécules et Applications, Institut Préparatoire aux Etudes Scientifiques et Techniques, Université de Carthage, La Marsa 2070 (Tunisia); Maaref, M.A. [Laboratoire Matériaux-Molécules et Applications, Institut Préparatoire aux Etudes Scientifiques et Techniques, Université de Carthage, La Marsa 2070 (Tunisia); Testelin, C. [Institut des NanoSciences de Paris, UPMC Univ., Paris 06, UMR 7588, F-75005 Paris (France); CNRS, UMR 7588, INSP, F-75005 Paris (France); Lemaître, A. [Laboratoire de Photonique et Nanostructures (LPN), CNRS, Route de Nozay, F-91460 Marcoussis (France)

    2016-07-15

    The optical properties of p-doped and annealed InAs/GaAs quantum dots (QDs) was investigated by photoluminescence (PL) as a function of temperature and excitation power density (P{sub exc}). At low-T, PL spectra of rapid thermal annealing (RTA) and p-modulation doped QDs show an energy blueshift and redshift, respectively. A superlinear dependence of integrated PL intensity on P{sub exc} at high-T was found only for undoped QD. The superlinearity was suppressed by modulation-doping and RTA effects. A linear dependence of I{sub PL} at all temperatures and a decrease of the carrier-carrier Coulomb interaction at high-T was found after RTA.

  9. Field modulation in Na-incorporated Cu(In,Ga)Se2 (CIGS) polycrystalline films influenced by alloy-hardening and pair-annihilation probabilities.

    Science.gov (United States)

    Jeong, Yonkil; Kim, Chae-Woong; Park, Dong-Won; Jung, Seung Chul; Lee, Jongjin; Shim, Hee-Sang

    2011-11-07

    The influence of Na on Cu(In,Ga)Se2 (CIGS) solar cells was investigated. A gradient profile of the Na in the CIGS absorber layer can induce an electric field modulation and significantly strengthen the back surface field effect. This field modulation originates from a grain growth model introduced by a combination of alloy-hardening and pair-annihilation probabilities, wherein the Cu supply and Na diffusion together screen the driving force of the grain boundary motion (GBM) by alloy hardening, which indicates a specific GBM pinning by Cu and Na. The pair annihilation between the ubiquitously evolving GBMs has a coincident probability with the alloy-hardening event.PACS: 88. 40. H-, 81. 10. Aj, 81. 40. Cd.

  10. Effects of lithium iodide doping on devolatilization characteristics of brown coals; Yoka lithium no tenka ga kattan no kanetsu henka katei ni oyobosu eikyo

    Energy Technology Data Exchange (ETDEWEB)

    Muraoka, J.; Kumagai, H.; Hayashi, J.; Chiba, T. [Hokkaido University, Sapporo (Japan)

    1996-10-28

    In order to discuss effects of lithium iodide (LiI) doping on condensation structure of brown coals during heating, spectral changes were measured by using an in-situ FT-IR. It was found that the LiI doping accelerates weight reduction due to heating, and the doping effect is affected by coal structure. Both of Loy Yang (LY) coal and its LiI doped coal (DLY) had absorption intensity of the FT-IR spectra decreased with rising temperature, and the absorption center belonging to an OH group shows different shifts between the LY and DLY coals. This indicates that the LiI doping has affected the change in hydrogen bonding patterns associated with heating. Both of South Banko (SB) and LY coals had the absorption spectral intensity in the OH group decreased as the weight reduction (conversion) rate increased. Reduction in the OH groups associated with heating is caused by volatilization and condensation reaction in light-gravity fraction. However, in the case of equal conversion rate, the LiI doped coal shows higher spectral intensity than the original coal, with the LiI doping suppressing reduction in the OH groups. It appears that the doping suppresses the condensation reaction between the OH groups. 2 refs., 6 figs., 1 tab.

  11. Responsivity drop due to conductance modulation in GaN metal-semiconductor-metal Schottky based UV photodetectors on Si(111)

    Science.gov (United States)

    Ravikiran, L.; Radhakrishnan, K.; Dharmarasu, N.; Agrawal, M.; Wang, Zilong; Bruno, Annalisa; Soci, Cesare; Lihuang, Tng; Kian Siong, Ang

    2016-09-01

    GaN Schottky metal-semiconductor-metal (MSM) UV photodetectors were fabricated on a 600 nm thick GaN layer, grown on 100 mm Si (111) substrate using an ammonia-MBE growth technique. In this report, the effect of device dimensions, applied bias and input power on the linearity of the GaN Schottky-based MSM photodetectors on Si substrate were investigated. Devices with larger interdigitated spacing, ‘S’ of 9.0 μm between the fingers resulted in good linearity and flat responsivity characteristics as a function of input power with an external quantum efficiency (EQE) of ˜33% at an applied bias of 15 V and an input power of 0.8 W m-2. With the decrease of ‘S’ to 3.0 μm, the EQE was found to increase to ˜97%. However, devices showed non linearity and drop in responsivity from flatness at higher input power. Moreover, the position of dropping from flatter responsivity was found to shift to lower powers with increased bias. The drop in the responsivity was attributed to the modulation of conductance in the MSM due to the trapping of electrons at the dislocations, resulting in the formation of depletion regions around them. In devices with lower ‘S’, both the image force reduction and the enhanced collection efficiency increased the photocurrent as well as the charging of the dislocations. This resulted in the increased depletion regions around the dislocations leading to the modulation of conductance and non-linearity.

  12. Effect of Split Gate Size on the Electrostatic Potential and 0.7 Anomaly within Quantum Wires on a Modulation-Doped GaAs /AlGaAs Heterostructure

    Science.gov (United States)

    Smith, L. W.; Al-Taie, H.; Lesage, A. A. J.; Thomas, K. J.; Sfigakis, F.; See, P.; Griffiths, J. P.; Farrer, I.; Jones, G. A. C.; Ritchie, D. A.; Kelly, M. J.; Smith, C. G.

    2016-04-01

    We study 95 split gates of different size on a single chip using a multiplexing technique. Each split gate defines a one-dimensional channel on a modulation-doped GaAs /AlGaAs heterostructure, through which the conductance is quantized. The yield of devices showing good quantization decreases rapidly as the length of the split gates increases. However, for the subset of devices showing good quantization, there is no correlation between the electrostatic length of the one-dimensional channel (estimated using a saddle-point model) and the gate length. The variation in electrostatic length and the one-dimensional subband spacing for devices of the same gate length exceeds the variation in the average values between devices of different lengths. There is a clear correlation between the curvature of the potential barrier in the transport direction and the strength of the "0.7 anomaly": the conductance value of the 0.7 anomaly reduces as the barrier curvature becomes shallower. These results highlight the key role of the electrostatic environment in one-dimensional systems. Even in devices with clean conductance plateaus, random fluctuations in the background potential are crucial in determining the potential landscape in the active device area such that nominally identical gate structures have different characteristics.

  13. 4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication.

    Science.gov (United States)

    Lee, Changmin; Zhang, Chong; Cantore, Michael; Farrell, Robert M; Oh, Sang Ho; Margalith, Tal; Speck, James S; Nakamura, Shuji; Bowers, John E; DenBaars, Steven P

    2015-06-15

    We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.

  14. The modulation of multi-domain and harmonic wave in a GaN planar Gunn diode by recess layer

    Science.gov (United States)

    Wang, Ying; Yang, Lin'an; Wang, Zhizhe; Ao, Jinping; Hao, Yue

    2016-02-01

    In this paper, a novel structure of a gallium nitride (GaN) planar Gunn diode with isosceles trapezoidal recess layers in the aluminum gallium nitride (AlGaN) barrier layer is proposed to enhance the harmonic components of Gunn oscillation waveforms. Numerical simulations demonstrate that the oscillation frequency rises from 99.1 GHz up to 300.4 GHz with the recess number increasing from one to four, at which the maximum radio frequency (RF) output power and conversion efficiency are obtained. The output performance of the diode enhances at high harmonic frequencies and is mainly due to the multiple recess layer structure that can trigger the formation of multiple Gunn domains in the two-dimensional electron gas channel of the GaN planar Gunn diode. This indicates that the long channel GaN Gunn diode has the ability to output the available RF power associated with the device operating in a submillimeter-wave and terahertz (THz) regime.

  15. 4 Gbps direct modulation of 450 nm GaN laser for high-speed visible light communication

    KAUST Repository

    Lee, Changmin

    2015-06-10

    We demonstrate high-speed data transmission with a commercial high power GaN laser diode at 450 nm. 2.6 GHz bandwidth was achieved at an injection current of 500 mA using a high-speed visible light communication setup. Record high 4 Gbps free-space data transmission rate was achieved at room temperature.

  16. GaAs/AlxGa1-xAs表面单量子阱原位光调制反射光谱研究%IN-SITU PHOTO-MODULATED REFLECTANCE STUDY ON GaAs/AlxGa1-xAs SINGLE SURFACE QUANTUM WELLS

    Institute of Scientific and Technical Information of China (English)

    缪中林; 陈平平; 陆卫; 徐文兰; 李志锋; 蔡炜颖; 史国良; 沈学础

    2001-01-01

    We have studied the optical properties of surface quantum wells with different width of wells (5nm and 10nm) by means of In-situ photo-modulated reflectance(PR) spectroscopy on a molecular beam epitaxy system. The surface quantum well is confined on one side by the vacuum and on the other side by AlxGa1-xAs barrier. In experiments, we have observed clearly the transitions between the confined heavy and light hole states to the confined electron states. The transitions of the excited states in 10nm surface quantum well are observed at first. The effects of the surface on the confined states have been well studied by combination of the PR spectra and the effective mass approximation theory.%用分子束外延(MBE)方法生长了两种典型阱宽(5nm和10nm)的表面单量子阱,表面量子阱中的受限态被表面真空势垒和AlxGa1-xAs势垒束缚.以原位光调制光谱(PR)作为测量手段,明确观察到表面量子阱中空穴子带到电子子带的光跃迁以及真空势垒对于不同阱宽表面量子阱中的受限电子态的束缚作用,并且看到了10nm表面量子阱激发态的跃迁峰.采用有效质量近似理论对实验结果作了较好的解释.

  17. Controlled disordering of compressively strained InGaAsP multiple quantum wells under SiO:P encapsulant and application to laser-modulator integration

    Science.gov (United States)

    Hamoudi, A.; Rao, E. V. K.; Krauz, Ph.; Ramdane, A.; Ougazzaden, A.; Robein, D.; Thibierge, H.

    1995-11-01

    We investigated the potentiality of a phosphorus-doped silicon oxide (SiO:P) carrier-free disordering source for applications in photonic devices integration schemes. This is accomplished in three successive steps by employing an InGaAsP/InGaAsP structure with compressively strained wells and lattice-matched barriers designed for operation around ˜1.55 μm. First of all, we showed that the SiO:P encapsulant offers a good control over a wide range of disorder (blue shifts as high as ˜150 meV). Later on, the high optical quality of the disordered regions is demonstrated by detecting 300 K excitonic features in moderately blue-shifted (˜40 meV) samples. And, finally, a first attempt of its application in integration technology is made by realizing a monolithic composite of a distributed feedback laser and a quantum-confined stark effect electroabsorption modulator operating around 1.54 μm.

  18. Magnetooptical study of Zeeman effect in Mn modulation-doped InAs/InGaAs/InAlAs quantum well structures

    Energy Technology Data Exchange (ETDEWEB)

    Terent' ev, Ya. V. [Physics Department, University of Regensburg, 93040 Regensburg (Germany); Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Danilov, S. N.; Plank, H.; Loher, J.; Schuh, D.; Bougeard, D.; Weiss, D.; Ganichev, S. D. [Physics Department, University of Regensburg, 93040 Regensburg (Germany); Durnev, M. V.; Ivanov, S. V. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Tarasenko, S. A.; Rozhansky, I. V. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); St. Petersburg State Polytechnic University, 195251 St. Petersburg (Russian Federation); Yakovlev, D. R. [Ioffe Physical-Technical Institute, 194021 St. Petersburg (Russian Federation); Experimentelle Physik 2, Technische Universität Dortmund, 44227 Dortmund (Germany)

    2015-09-21

    We report on a magneto-photoluminescence (PL) study of Zeeman effect in Mn modulation-doped InAs/InGaAs/InAlAs quantum wells (QW). Two PL lines corresponding to the radiative recombination of photoelectrons with free and bound-on-Mn holes have been observed. In the presence of a magnetic field applied in the Faraday geometry, both lines split into two circularly polarized components. While temperature and magnetic field dependence of the splitting are well described by the Brillouin function, providing an evidence for exchange interaction with spin polarized manganese ions, the value of the splitting exceeds by two orders of magnitude the value of the giant Zeeman splitting estimated for the average Mn density in QW obtained by the secondary ion mass spectroscopy.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-06-15

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

  20. Electrical modulation of static and dynamic spectroscopic properties of coupled nanoscale GaSe quantum dot assemblies

    Science.gov (United States)

    Verma, Y. K.; Inman, R. H.; Ferri, C. G. L.; Mirafzal, H.; Ghosh, S. N.; Kelley, D. F.; Hirst, L. S.; Ghosh, S.; Chin, W. C.

    2010-10-01

    We demonstrate the formation and spatial modulation of strongly coupled gallium selenide quantum dot (QD) nanoassemblies suspended in a nematic liquid-crystal (NLC) matrix at room temperature. Using static and dynamic optical techniques we show that the coupled QDs aggregate with a well-defined directionality commensurate with the NLC director axis. This results in highly anisotropic spectral properties of the QD assembly. The spatial orientation of the aggregates is selectively controlled in situ by the application of in-plane electric fields. The strong interdot coupling further increases the excitonic recombination rate which is both direction and electric field dependent. This electrical modulation, a noninvasive process, could potentially be an important functionality for the design and creation of building blocks for novel optoelectronic devices.

  1. Photo-modulated thin film transistor based on dynamic charge transfer within quantum-dots-InGaZnO interface

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Xiang [Electronic Science and Engineering School, Southeast University, Nanjing (China); National Center for Nanoscience and Technology, Beijing (China); Yang, Xiaoxia; Liu, Mingju [National Center for Nanoscience and Technology, Beijing (China); Tao, Zhi; Wei, Lei, E-mail: lw@seu.edu.cn; Li, Chi, E-mail: lichi@seu.edu.cn; Zhang, Xiaobing; Wang, Baoping [Electronic Science and Engineering School, Southeast University, Nanjing (China); Dai, Qing, E-mail: daiq@nanoctr.cn [National Center for Nanoscience and Technology, Beijing (China); London Center for Nanotechnology, University College London, London WC1H 0AH (United Kingdom); Nathan, Arokia [Electronic Science and Engineering School, Southeast University, Nanjing (China); London Center for Nanotechnology, University College London, London WC1H 0AH (United Kingdom)

    2014-03-17

    The temporal development of next-generation photo-induced transistor across semiconductor quantum dots and Zn-related oxide thin film is reported in this paper. Through the dynamic charge transfer in the interface between these two key components, the responsibility of photocurrent can be amplified for scales of times (∼10{sup 4} A/W 450 nm) by the electron injection from excited quantum dots to InGaZnO thin film. And this photo-transistor has a broader waveband (from ultraviolet to visible light) optical sensitivity compared with other Zn-related oxide photoelectric device. Moreover, persistent photoconductivity effect can be diminished in visible waveband which lead to a significant improvement in the device's relaxation time from visible illuminated to dark state due to the ultrafast quenching of quantum dots. With other inherent properties such as integrated circuit compatible, low off-state current and high external quantum efficiency resolution, it has a great potential in the photoelectric device application, such as photodetector, phototransistor, and sensor array.

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

    Science.gov (United States)

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

    2013-04-08

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

  3. A Rutile Chevron Modulation in Delafossite-Like Ga3-xIn3TixO9+x/2

    Energy Technology Data Exchange (ETDEWEB)

    Rickert, Karl; Boullay, Philippe; Malo, Sylvie; Caignaert, Vincent; Poeppelmeier, Kenneth R. [NWU; (CNRS-UMR)

    2016-09-01

    The structure solution of the modulated, delafossite-related, orthorhombic Ga3–xIn3TixO9+x/2 for x = 1.5 is reported here in conjunction with a model describing the modulation as a function of x for the entire system. Previously reported structures in the related A3–xIn3TixO9+x/2 (A = Al, Cr, or Fe) systems use X-ray diffraction to determine that the anion lattice is the source of modulation. Neutron diffraction, with its enhanced sensitivity to light atoms, offers a route to solving the modulation and is used here, in combination with precession electron diffraction tomography (PEDT), to solve the structure of Ga1.5In3Ti1.5O9.75. We construct a model that describes the anion modulation through the formation of rutile chevrons as a function of x. This model accommodates the orthorhombic phase (1.5 ≤ x ≤ 2.1) in the Ga3-xIn3TixO9+x/2 system, which transitions to a biphasic mixture (2.2 ≤ x ≤ 2.3) with a monoclinic, delafossite-related phase (2.4 ≤ x ≤ 2.5). The optical band gaps of this system are determined, and are stable at ~3.4 eV before a ~0.4 eV decrease between x = 1.9 and 2.0. After this decrease, stability resumes at ~3.0 eV. Resistance to oxidation and reduction is also presented.

  4. Fabrication of an InP/GaInAsP based integrated gain-coupled DFB laser/M-Z phase modulator for 10Gb/sec fiber optic transmission

    Energy Technology Data Exchange (ETDEWEB)

    Puetz, N.; Adams, D.M.; Rolland, C.; Moore, R.; Mallard, R. [Bell-Northern Research, Ottawa, Ontario (Canada)

    1996-12-31

    The monolithic integration of lasers and modulators is an attractive approach for the manufacture of compact, low-chirp light sources with low packaging costs for high bit rate (10Gb/s) long haul fiber optic transmission systems. In this presentation the authors describe the fabrication of an InGaAsP/InP-based Mach/Zehnder phase modulator with a gain-coupled DFB laser which achieves 10Gb/s transmission at 1.55 {micro}m over 100km of non-dispersion shifted fiber. The use of an interferometric modulator provides greater freedom for the control of chirp when compared to modulation by electroabsorption. A strained layer multi quantum well gain-coupled DFB laser was employed for the cw-source because of its potential for very high yield of devices which laser in a single mode and for its greater immunity to external reflection. The integration of a phase modulator with a laser requires the deposition of InGaAsP-based quantum wells with different thicknesses over different, but adjacent areas of the InP substrate. Previous efforts of this kind employed Selective Area Epitaxy. Although SAE is an elegant method of locally varying thicknesses of epitaxial films it does not allow the independent growth of different numbers of quantum wells. Therefore, it reduces the designer`s flexibility in choosing the optimum parameters for wells and barriers as well as confinement layers (thickness, number, composition, doping) independently for both the laser and the modulator. For exactly that reason the authors have decided to pursue the butt-coupled approach and deposit the layer sequences for laser and modulator in 2 separate growth runs.

  5. Development and loss of ferromagnetism controlled by the interplay of Ge concentration and Mn vacancies in structurally modulated Y{sub 4}Mn{sub 1-x}Ga{sub 12-y}Ge{sub y}.

    Energy Technology Data Exchange (ETDEWEB)

    Francisco, M. C.; Malliakas, C. D.; Piccoli, P. M. B.; Gutmann, M. J.; Schultz, A. J.; Kanatzidis, M. G. (Intense Pulsed Neutron Source); ( MSD); (Northwestern Univ.); (Rutherford Appleton Lab.)

    2010-06-01

    The cubic intermetallic phase Y{sub 4}Mn{sub 1-x}Ga{sub 12-y}Ge{sub y} (x = 0-0.26, y = 0-4.0) has been isolated from a molten gallium flux reaction. It presents a rare example of a system where ferromagnetism can be induced by controlling the vacancies of the magnetic centers. The Y{sub 4}PdGa{sub 12} type crystal structure is made up of a corner-sharing octahedral network of Ga and Ge atoms with Mn atoms at the centers of half the octahedra and Y atoms in the voids. At the highest Ge concentration, y = 4.0, the Mn site is nearly fully occupied, x = 0.05, and the samples are paramagnetic. At a lower Ge concentration, y = 1.0, Mn deficiency develops with x = 0.10. Surprisingly, strong ferromagnetism is observed with T{sub c} = 223 K. When Ge is excluded, y = 0, Mn is substantially deficient at x = 0.26 and ferromagnetism is maintained with a T{sub c} of {approx}160 K. In addition, a 6-fold modulated superstructure appears owing to an ordered slab-like segregation of Mn atoms and vacancies. Corresponding bond distortions propagate throughout the octahedral Ga network. Structure-property relationships are examined with X-ray and neutron diffraction, magnetic susceptibility, and electrical resistivity measurements.

  6. Magnetotransport and charge transfer studies on delta-modulation-doped In sub x Ga sub 1 sub - sub x As/Al sub y Ga sub 1 sub - sub y As strained single quantum wells

    CERN Document Server

    Jung, M; Kim, T W; Yoo, K H; Kim, M D; Park, H S; Kim, D L

    1999-01-01

    Shubnikov-de Haas (S-dH) and Van der Pauw Hall-effect measurements on a In sub 0 sub . sub 1 sub 8 Ga sub 0 sub . sub 8 sub 2 As/Al sub 0 sub . sub 2 sub 5 Ga sub 0 sub . sub 7 sub 5 As strained single quantum well grown by molecular beam epitaxy have been performed to investigate the existence of the two-dimensional electron gas (2DEG) in the In sub 0 sub . sub 1 sub 8 Ga sub 0 sub . sub 8 sub 2 As single quantum well. The fast Fourier transform for the S-dH data and the observation of the quantum Hall effect clearly indicate 2DEG occupation of a subband in the In sub 0 sub . sub 1 sub 8 Ga sub 0 sub . sub 8 sub 2 As single quantum well. Electronic subband energy and the corresponding wavefunction in the In sub 0 sub . sub 1 sub 8 Ga sub 0 sub . sub 8 sub 2 As quantum well were calculated by a self-consistent method taking into account exchange-correlation effects together with strain and nonparabolicity effects.

  7. Efficient TE-Selective P-I-i-I-N GaAs/Al_( 0.35)Ga_(0.65)As Waveguide Phase Modulator at λ=1.55μm

    Institute of Scientific and Technical Information of China (English)

    Sun-Pil; Kim; Sang-Sun; Lee; Seok; Lee; Deok-Ha; Woo; Sun-Ho; Kim

    2003-01-01

    We fabricated a phase modulator with significant phase shift for TE mode but negligible for TM mode. The measured phase shift efficiency was 7.9°/V.mm for TE mode. No modulation was observed for TM mode.

  8. Efficient TE-Selective P-I-i-I-N GaAs/Al 0.35Ga0.65As Waveguide Phase Modulator at λ=1.55μm

    Institute of Scientific and Technical Information of China (English)

    Sun-Pil Kim; Sang-Sun Lee; Seok Lee; Deok-Ha Woo; Sun-Ho Kim

    2003-01-01

    We fabricated a phase modulator with significant phase shift for TE mode but negligible for TM mode. The measured phase shift efficiency was 7.9 /V mm for TE mode. No modulation was observed for TM mode.

  9. Monolithic integration of an InGaAsP InP strained DFB laser and an electroabsorption modulator by ultra-low-pressure selective-area-growth MOCVD

    Science.gov (United States)

    Zhao, Q.; Pan, J. Q.; Zhou, F.; Wang, B. J.; Wang, L. F.; Wang, W.

    2005-06-01

    The design and basic characteristics of a strained InGaAsP-InP multiple-quantum-well (MQW) DFB laser monolithically integrated with an electroabsorption modulator (EAM) by ultra-low-pressure (22 mbar) selective-area-growth (SAG) MOCVD are presented. A fundamental study of the controllability and the applicability of band-gap energy by using the SAG method is performed. A large band-gap photoluminescence wavelength shift of 88 nm was obtained with a small mask width variation (0-30 µm). The technique is then applied to fabricate a high performance strained MQW EAM integrated with a DFB laser. The threshold current of 26 mA at CW operation of the device with DFB laser length of 300 µm and EAM length of 150 µm has been realized at a modulator bias of 0 V. The devices also exhibit 15 dB on/off ratio at an applied bias voltage of 5 V.

  10. Three-dimensional numerical simulation of planar P+n heterojunction In0.53Ga0.47As photodiodes in dense arrays part II: modulation transfer function modeling

    Science.gov (United States)

    Wichman, Adam R.; DeWames, Roger E.; Bellotti, Enrico

    2014-06-01

    Processing improvements have facilitated manufacturing reduced pixel dimensions for lattice-matched InGaAs on InP short-wave infrared detectors. Due to its technological maturity, this material system continues to garner attention for low-light level imaging applications. With pixel dimensions smaller than minority carrier diffusion lengths, optimizing array performance by reducing crosstalk from lateral carrier diffusion remains an important design issue. Analytical models, however, have provided limited insight on underlying mechanisms limiting device performance in the conventional planar double heterointerface device. Quantitative modeling provides tools to investigate performance sensitivities and their underlying mechanisms. In this work we develop a three-dimensional numerical simulation for dense P+n In0.53Ga0.47As on InP photo detector focal plane arrays using a conventional planar, back-illuminated structure. We evaluate optical generation with finite-difference time-domain analysis, and model carrier transport in a drift diffusion analysis simultaneously solving the carrier continuity and Poisson equations. Using this model we investigate modulation transfer function variations with pixel pitch and diffused junction geometries for small dimension arrays. By accounting for carrier diffusion effects, these results should provide a benchmark against which to evaluate modulation transfer function contributions from other effects, such as crosstalk attributable to photon recycling.

  11. InGaAs/InAlAs Five Layer Asymmetric Coupled Quantum Well (FACQW) for Ultra-Wideband Ultrafast Optical Modulators

    Institute of Scientific and Technical Information of China (English)

    Taro Arakawa; Ryuji Iino; Tetsuya Ishie; Terumasa Kawabata; Kunio Tada

    2003-01-01

    An InGaAs/InAlAs five-layer asymmetric coupled quantum well (FACQW) is expected to show very large electrorefractive index change. n in a wideband transparency region. Band structures of the FACQW are analyzed with Luttinger-Kohn Hamiltonian. The electrorefractive characteristics of the FACQW are discussed.

  12. InGaAs/InAlAs Five Layer Asymmetric Coupled Quantum Well (FACQW) for Ultra-Wideband Ultrafast Optical Modulators

    Institute of Scientific and Technical Information of China (English)

    Taro; Arakawa; Ryuji; Iino; Tetsuya; Ishie; Terumasa; Kawabata; Kunio; Tada

    2003-01-01

    An InGaAs/InAlAs five-layer asymmetric coupled quantum well (FACQW) is expected to show very large electrorefractive index change . n in a wideband transparency region. Band structures of the FACQW are analyzed with Luttinger-Kohn Hamiltonian. The electrorefractive characteristics of the FACQW are discussed.

  13. STUDIES ON OPTICAL MODULATION OF III-V GaN AND InP BASED DDR IMPATT DIODE AT SUB-MILLIMETER WAVE FREQUENCY

    Directory of Open Access Journals (Sweden)

    Soumen Banerjee,

    2010-07-01

    Full Text Available The effect of optically illumination of III-V compound semiconductor Indium Phosphide (InP and Wurtzite phase of Gallium Nitride (Wz-GaN or -GaN based Double Drift Impatt diodes at 300 GHz (0.3 THz has been investigated. The composition of photocurrent is altered by shining light on the p+ side and n+ side of the device through optical windows; thereby giving rise to Top Mounted (TM and Flip Chip (FC structures. The current multiplication factors for lectrons (Mn and for holes (Mp are altered to study the effect of leakage current in controlling the dynamic properties of the device. The conversion efficiency and output power of -GaN Impatt at 0.3 THz are 15.47% and 6.23 W respectively at an optimum bias current density of 0.5 x 108 A/m2 while the same parameters for InP Impatt are 18.38% and 2.81 W respectively at an optimum bias current density of 8.0 x 108 A/m2. Under optical illumination of the device, the frequency shift is observed to be more upwards upon lowering of Mpthan lowering of Mn. The frequency chirping in InP and -GaN Impatt are found to be of the order of few GHz, thereby indicating their high photo-sensitiveness at Sub-millimeter or Terahertz domain.

  14. 6-12 GHz Double-Balanced Image-Reject Mixer MMIC in 0.25μm AlGaN/GaN Technology

    NARCIS (Netherlands)

    Heijningen, M. van; Hoogland, J.A.; Hek, A.P. de; Vliet, F.E. van

    2015-01-01

    The front-end circuitry of transceiver modules is slowly being updated from GaAs-based monolithic microwave integrated circuits (MMICs) to Gallium-Nitride (GaN). Especially GaN power amplifiers and T/R switches, but also low-noise amplifiers (LNAs), offer significant performance improvement over GaA

  15. Gigahertz optical modulation.

    Science.gov (United States)

    Riesz, R P; Biazzo, M R

    1969-07-01

    Light pulses from a mode-locked He-Ne laser have been modulated by a LiTaO(3) electrooptic crystal mounted on a thin film substrate. The crystal was driven by pulses from a GaAs Gunn effect diode. Amplitude modulation of 20% has been achieved at 2 GHz for a single pass through the modulator.

  16. Submicron-AlGaN/GaN MMICs for Space Applications

    NARCIS (Netherlands)

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

    2013-01-01

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

  17. Submicron-AlGaN/GaN MMICs for Space Applications

    NARCIS (Netherlands)

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

    2013-01-01

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

  18. Submicron-AlGaN/GaN MMICs for Space Applications

    NARCIS (Netherlands)

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

    2013-01-01

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

  19. Influence of shape change of impeller and scroll in the axial direction on performance and noise for multiblade blower; Tayoku sofuki no haneguruma oyobi scroll keijo no jiku hoko henka ga seino to soon ni oyobosu eikyo

    Energy Technology Data Exchange (ETDEWEB)

    Yanazaki, S.; Hashimoto, K.; Fukasaku, Y. [Hitachi, Ltd., Tokyo (Japan)

    1997-10-25

    In this paper, the influence of shape change of the impeller and scroll in the axial direction on performance and noise are investigated. It is shown that a 14% increase in the hub-side diameter of the impeller over that of the shroud side leads to a 4% increase in the efficiency {eta}t, and a 2dB reduction in the specific sound level SLs. It is also shown that an increase in the diffusion angle of the hub side of the scroll to that of the shroud side raises the efficiency by 2%. 8 refs., 10 figs.

  20. Formation of planetary systems is in sight now. ; On transformation on Initial solar system as seen from meteorites (On transformation of source celestial bodies). Wakuseikei no keisei ga mietekita. ; Inseki ni miru shoki taiyokei (Shigen botaiten no henka wo megutte)

    Energy Technology Data Exchange (ETDEWEB)

    Tomeoka, K. (The University of Tokyo, Tokyo (Japan). Faculty of Science)

    1992-02-01

    The meteoritic studies using high-resolution transmission electron microscopes are in a process of elucidating the problem as to whether the carbon-based chondrite meteorites regarded as initial chemically are the substance resulted from accumulation of solid particles which have had existed in the solar system nebulae, or whether they have had been subjected to any secondary modification after the accumulation. The initial state of the solar system was inferred through considering the latest research results on transforming actions given to these source celestial bodies. The intervention of the water quality transformation as a result of water actions at temperatures as low as associating no loss in volatile elements has been elucidated from the researches on micro-structures in a substance contained in the carbon-based chondrite. As to at what stage the water quality transformation has taken place, a view that its timing is after the formation of the base celestial bodies is predominant. A consideration was given on what the first celestial body integrated from a solar system nebula was like using a model presenting the transforming actions on the carbon-based chondrite celestial bodies. 11 refs., 4 figs.

  1. Correspondence between MOS and modulation-doped structures

    Science.gov (United States)

    Pierret, R. F.; Lundstrom, M. S.

    1984-03-01

    There is currently considerable interest in the development of modulation-doped field-effect transistors suitable for high-speed applications. A promising version of the modulation-doped FET consists of a Schottky-barrier contact atop a thin Al(x)Ga(1-x)As layer on a lightly doped GaAs underlayer. It is pointed out that for a n-AlGaAs/p-GaAs structure, the conduction band discontinuity at the AlGaAs-GaAs interface gives rise to an inversion layer at the GaAs surface. The present paper is concerned with the physical correspondence between n-AlGaAs/p-GaAs modulation-doped structures and MOS structures. It is shown that certain key modulation-doped relationships can be obtained directly from MOSFET relationships.

  2. 37 GHz Direct-Modulation Bandwidth of Multi-Section InGaAsP/InP DBR-Laser with weakly coupled active grating section

    DEFF Research Database (Denmark)

    Kaiser, W.; Bach, L.; Reithmaier, J. P.;

    2003-01-01

    37 GHz direct-modulation bandwidth could be obtained by a multi-section design with an integrated weakly coupled DBR grating. The laser shows side mode suppression ratios of 45 dB and output powers exceeding 20 mW.......37 GHz direct-modulation bandwidth could be obtained by a multi-section design with an integrated weakly coupled DBR grating. The laser shows side mode suppression ratios of 45 dB and output powers exceeding 20 mW....

  3. Performance characteristics of positive and negative delayed feedback on chaotic dynamics of directly modulated InGaAsP semiconductor lasers

    Indian Academy of Sciences (India)

    Bindu M Krishna; Manu P John; V M Nandakumaran

    2008-12-01

    The chaotic dynamics of directly modulated semiconductor lasers with delayed optoelectronic feedback is studied numerically. The effects of positive and negative delayed optoelectronic feedback in producing chaotic outputs from such lasers with nonlinear gain reduction in its optimum value range is investigated using bifurcation diagrams. The results are confirmed by calculating the Lyapunov exponents. A negative delayed optoelectronic feedback configuration is found to be more effective in inducing chaotic dynamics to such systems with nonlinear gain reduction factor in the practical value range.

  4. Lateral photovoltaic effect observed in doping-modulated GaAs/Alsub>0.3sub>Gasub>0.7sub>As.

    Science.gov (United States)

    Liu, Ji Hong; Qiao, Shuang; Liang, BaoLai; Wang, ShuFang; Fu, GuangSheng

    2017-02-20

    For photovoltaic effect (PE), both barrier height and carrier lifetime are all very important factors. However, how to distinguish their contributions to the PE is very difficult. In this paper, we prepared a series of GaAs/Alsub>0.3sub>Gasub>0.7sub>As two dimensional electron gas (2DEG) with typical Alsub>0.3sub>Gasub>0.7sub>As doping concentration of 0.6 × 1018/cm3, 1.2 × 1018/cm3, and 2.5 × 1018/cm3, respectively (sample number: #1, #2, #3), and studied their lateral photovoltaic effects (LPEs). It is found that their position sensitivities all increase with both laser wavelength and laser power. However, the position sensitivity exhibits a non-monotonic behavior with increasing doping concentration, which can be mainly ascribed to the doping concentration-dependent carrier lifetime, especially in the low power regime. With increasing laser power gradually, the position sensitivity difference between sample #1 and sample #2 is still large and increases a little, while the position sensitivity of sample #3 approaches to that of sample #2, suggesting that the doping concentration-dependent barrier height also starts to play an important role in the high power regime. Our results will provide important information for the design and development of novel and multifunctional PE devices.

  5. Phase-modulated spectroscopic ellipsometry and polarized transmission intensity studies of wide-gap biaxial CaGa{sub 2}S{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Shim, Yonggu; Mamedov, Nazim; Yamamoto, Nobuyuki

    2004-05-01

    Differently prepared natural (100)-oriented cleavage planes of the orthorhombic wide-gap (E{sub o}{approx}4.1 eV) single crystalline CaGa{sub 2}S{sub 4} were examined in two symmetric positions at room temperature over the photon energies 0.8-6.5 eV by spectroscopic ellipsometry. Complimentary, polarized transmission intensity technique was applied. The data obtained by both techniques were further treated within standard biaxial approach and the major refraction indices were restored for the practically important range below energy gap. The structure and polarization peculiarities of the obtained pseudo-dielectric function were related with apparently four critical points of interband electronic transitions in ZZ (E{sub 1}=4.49 eV, E{sub 3}=5.34 eV) and YY (E{sub 2}=5.00 eV, E{sub 4}=6.21 eV) configurations, respectively.

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

    Science.gov (United States)

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

    2016-09-06

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

  7. 6-12 GHz Double-Balanced Image-Reject Mixer MMIC in 0.25μm AlGaN/GaN Technology

    NARCIS (Netherlands)

    Heijningen, M. van; Hoogland, J.A.; Hek, A.P. de; Vliet, F.E. van

    2014-01-01

    The front-end circuitry of transceiver modules is slowly being updated from GaAs-based MMICs to Gallium-Nitride. Especially GaN power amplifiers and TR switches, but also low-noise amplifiers, offer significant performance improvement over GaAs components. Therefore it is interesting to also explore

  8. Investigation of 1.3 μm AlGaInAs multi-quantum wells for electro-absorption modulated laser

    Energy Technology Data Exchange (ETDEWEB)

    Binet, Guillaume [III-V Lab., Route de Nozay, 91461, Marcoussis (France); Institut Jean le Rond d' Alembert, Sorbonne Universites, UPMC Univ. Paris 06, CNRS, UMR 7190, 75005, Paris (France); Decobert, Jean; Lagay, Nadine; Chimot, Nicolas; Kazmierski, Christophe [III-V Lab., Route de Nozay, 91461, Marcoussis (France)

    2016-10-15

    Monolithic photonic integrated circuits (PIC) transmitters using the prefixed optical phase switching concept for BPSK modulation format have been shown promising at 1.55 μm band. These devices could also be crucial for short reach connections and access networks. With this aim, we are studying basic quantum well designs for a laser and an electro-absorption modulator switch to be integrated by selective area growth into PICs at 1.3 μm. Photocurrent measurements and band offset modeling have been performed to determine the MQW stack well-fitted for this application. Broad area laser measurements have also been checked on these structures to verify the material lasing properties. A 6 nm thick well with low barrier seems to be the best trade-off between absorption and shift for 1.3 μm EAM and it also gives good lasing properties. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. The -250G>A promoter variant in hepatic lipase associates with elevated fasting serum high-density lipoprotein cholesterol modulated by interaction with physical activity in a study of 16,156 Danish subjects

    DEFF Research Database (Denmark)

    Grarup, Niels; Andreasen, Camilla H; Andersen, Mette K;

    2008-01-01

    of variants in LIPC on metabolic traits and type 2 diabetes in a large sample of Danes. Because behavioral factors influence hepatic lipase activity, we furthermore examined possible gene-environment interactions in the population-based Inter99 study. DESIGN: The LIPC -250G>A (rs2070895) variant was genotyped...... Treatment in People with Screen Detected Diabetes in Primary Care study [0.038 mmol/liter per allele (95% CI 0.024-0.053); P = 2 x 10(-7)). The allelic effect on HDL-c was modulated by interaction with self-reported physical activity (P(interaction) = 0.002) because vigorous physically active homozygous A......-allele carriers had a 0.30 mmol/liter (95% CI 0.22-0.37) increase in HDL-c compared with homozygous G-allele carriers. CONCLUSIONS: We validate the association of LIPC promoter variation with fasting serum HDL-c and present data supporting an interaction with physical activity implying an increased effect on HDL...

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

    Science.gov (United States)

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

    2014-07-01

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

  11. Characterization of 2.3 μm GaInAsSb-based vertical-cavity surface-emitting laser structures using photo-modulated reflectance

    Energy Technology Data Exchange (ETDEWEB)

    Chai, G. M. T. [Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru 81310 (Malaysia); Hosea, T. J. C., E-mail: j.hosea@surrey.ac.uk [Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru 81310 (Malaysia); Advanced Technology Institute and Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); Fox, N. E.; Hild, K.; Ikyo, A. B.; Marko, I. P.; Sweeney, S. J. [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford GU2 7XH (United Kingdom); Bachmann, A.; Arafin, S.; Amann, M.-C. [Walter Schottky Institut, Technische Universität Munchen, Am Coulombwall 4, D-85748 Garching (Germany)

    2014-01-07

    We report angle dependent and temperature dependent (9 K–300 K) photo-modulated reflectance (PR) studies on vertical-cavity surface-emitting laser (VCSEL) structures, designed for 2.3 μm mid-infrared gas sensing applications. Changing the temperature allows us to tune the energies of the quantum well (QW) transitions relative to the VCSEL cavity mode (CM) energy. These studies show that this VCSEL structure has a QW-CM offset of 21 meV at room temperature. Consequently the QW ground-state transition comes into resonance with the CM at 220 ± 2 K. The results from these PR studies are closely compared with those obtained in a separate study of actual operating devices and show how the PR technique may be useful for device optimisation without the necessity of having first to process the wafers into working devices.

  12. WDM module research within the Canadian Solid State Optoelectronics Consortium

    Science.gov (United States)

    Fallahi, Mahmoud; Koteles, Emil S.; Delage, Andre; Chatenoud, F.; Templeton, Ian M.; Champion, Garth; He, Jian Jun; Wang, Weijian; Dion, Michael M.; Barber, Richard A.

    1995-02-01

    We report on the design, growth, fabrication, and characterization of monolithic wavelength division multiplexed (WDM) modules produced within the Canadian Solid State Optoelectronics Consortium. The transmitter module includes multiple, discrete wavelength, distributed Bragg reflector (DBR) laser diodes monolithically integrated with waveguide combiners fabricated using an InGaAs/GaAs heterostructure. The wavelength demultiplexer unit is based on a Rowland circle grating spectrometer monolithically integrated with a metal- semiconductor-metal (MSM) detector array fabricated on an InGaAs/AlGaAs/GaAs heterostructure. The epitaxial layer wafers for both transmitter and receiver modules were grown in single molecular beam epitaxy (MBE) runs.

  13. Electronic states of InSe/GaSe superlattice

    Science.gov (United States)

    Erkoç, Ş.; Allahverdi, K.; Ibrahim, Z.

    1994-06-01

    Analysis of recent publications revealed an increasing interest in epitaxial growth of InSe/GaSe superlattice. Within the effective mass theory we carried out self-consistent calculations of the confined and itinerant electronic states, potential profile and charge density distribution of InSe/GaSe superlattice, where the InSe layers are the well and the GaSe layers the barrier. Calculations were performed for three types of doping: uniform, modulated in the well, and modulated in the barrier. It has been found that the Coulomb interaction in the well and barrier forces the formation of localized states in the barrier region. The possibility of an insulator-metal transition in InSe/GaSe superlattice is predicted for modulation doping in the barrier and for a doping level n = 10 19cm-3. A decrease of the barrier height has been found for modulation doping in the well.

  14. 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.

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

    Science.gov (United States)

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

    2016-05-01

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

  16. 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).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-03-01

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

  18. Theoretical study on optimization of high efficiency GaInP/GaInAs/Ge tandem solar cells

    Science.gov (United States)

    Lin, Gui Jiang; Huang, Sheng Rong; Wu, Jyh Chiarng; Huang, Mei Chun

    2009-08-01

    This paper investigates which dopping concentration or layer thickness should be used to design practical GaInP/GaInAs/Ge triple-junction cells in order to optimize their performance. A rigorous model includes optical and electrical modules is developed to simulate the external quantumn efficiency, photocurrent and photovoltage of the GaInP/GaInAs/Ge tandem solar cells. It is found that cell efficiency strongly dependend on the top cell thickness and doping concentration at base and emitter layers. Proper structures of the tandem cell operating under AM0 ("air mass zero") illumination are suggested to obtain high efficiency.

  19. InGaN directional coupler made with a one-step etching technique

    Science.gov (United States)

    Gao, Xumin; Yuan, Jialei; Yang, Yongchao; Zhang, Shuai; Shi, Zheng; Li, Xin; Wang, Yongjin

    2017-06-01

    We propose, fabricate and characterize an on-chip integration of light source, InGaN waveguide, directional coupler and photodiode, in which AlGaN layers are used as top and bottom optical claddings to form an InGaN waveguide for guiding the in-plane emitted light from the InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED). The difference in etch rate caused by different exposure windows leads to an etching depth discrepancy using the one-step etching technique, which forms the InGaN directional coupler with the overlapped underlying slab. Light propagation results directly confirm effective light coupling in the InGaN directional coupler, which is achieved through high-order guided modes. The InGaN waveguide couples the modulated light from the InGaN/GaN MQW-LED and transfers part of light to the coupled waveguide via the InGaN directional coupler. The in-plane InGaN/GaN MQW-photodiode absorbs the guided light by the coupled InGaN waveguide and induces the photocurrent. The on-chip InGaN photonic integration experimentally demonstrates an in-plane light communication with a data transmission of 50 Mbps.

  20. High-performance electroabsorption modulator

    Science.gov (United States)

    Wei, Zhang; Jiaoqing, Pan; Hongliang, Zhu; Huan, Wang; Wei, Wang

    2009-09-01

    A 100-μm-long electroabsorption modulator monolithically integrated with passive waveguides at the input and output ports is fabricated through ion implantation induced quantum well intermixing, using only a two-step low-pressure metal-organic vapor phase epitaxial process. An InGaAsP/InGaAsP intra-step quantum well is introduced to the active region to improve the modulation properties. In the experiment high modulation speed and high extinction ratio are obtained simultaneously, the electrical-to-optical frequency response (E/O response) without any load termination reaches to 22 GHz, and extinction ration is as high as 16 dB.

  1. Magnetotransport measurements on AFM structured two-dimensional electron gases on cleaved edges of GaAs/AlGaAs; Magnetotransportmessungen an AFM-strukturierten zweidimensionalen Elektronengasen auf GaAs/AlGaAs-Spaltkanten

    Energy Technology Data Exchange (ETDEWEB)

    Reinwald, Elisabeth

    2009-06-25

    In this thesis a two dimensional electron gas (2DEG) on a (110) cleavage plane of a GaAs/AlGaAs(001) heterostructure was produced by means of cleaved edge overgrowth (CEO) and modulated in two dimensions. The 2DEG was modulated in one direction by a superlattice of the subjacent GaAs/AlGaAs(001) heterostructure. A second modulation, perpendicular to the first was realized by local anodic oxidation (LAO) with an atomic force microscope (AFM). For the process of LAO an electric voltage is applied between the tip of the AFM and the surface of the GaAs. The natural water film on the surface acts as electrolyte so that the GaAs surface is locally oxidized underneath the AFM tip. This oxide leads to a band bending so that the 2DEG underneath the oxide is locally depleted. On these systems magnetotransport measurements revealed that it is actually possible to modulate 2DEGs on a sufficient large area by local anodic oxidation. On the cleaved surfaces the influence of the two dimensional modulation on the electron gas has been demonstrated. (orig.)

  2. Electron mobility in modulation-doped heterostructures

    Science.gov (United States)

    Walukiewicz, W.; Ruda, H. E.; Lagowski, J.; Gatos, H. C.

    1984-01-01

    A model for electron mobility in a two-dimensional electron gas confined in a triangular well was developed. All major scattering processes (deformation potential and piezoelectric acoustic, polar optical, ionized impurity, and alloy disorder) were included, as well as intrasubband and intersubband scattering. The model is applied to two types of modulation-doped heterostructures, namely GaAs-GaAlAs and In(0.53)Ga(0.47)As-Al(0.52)In(0.48)As. In the former case, phonons and remote ionized impurities ultimately limit the mobility, whereas in the latter, alloy disorder is a predominant scattering process at low temperatures. The calculated mobilities are in very good agreement with recently reported experimental characteristics for both GaAs-Ga(1-x)Al(x)As and In(0.53)Ga(0.47)As-Al(0.52)In(0.48)As modulation-doped heterostructures.

  3. The -250G>A promoter variant in hepatic lipase associates with elevated fasting serum high-density lipoprotein cholesterol modulated by interaction with physical activity in a study of 16,156 Danish subjects.

    Science.gov (United States)

    Grarup, Niels; Andreasen, Camilla H; Andersen, Mette K; Albrechtsen, Anders; Sandbaek, Annelli; Lauritzen, Torsten; Borch-Johnsen, Knut; Jørgensen, Torben; Schmitz, Ole; Hansen, Torben; Pedersen, Oluf

    2008-06-01

    Hepatic lipase plays a pivotal role in the metabolism of high-density lipoprotein (HDL) and low-density lipoprotein by involvement in reverse cholesterol transport and the formation of atherogenic small dense low-density lipoprotein. The objective was to investigate the impact of variants in LIPC on metabolic traits and type 2 diabetes in a large sample of Danes. Because behavioral factors influence hepatic lipase activity, we furthermore examined possible gene-environment interactions in the population-based Inter99 study. The LIPC -250G>A (rs2070895) variant was genotyped in the Inter99 study (n = 6070), the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care Denmark screening cohort of individuals with risk factors for undiagnosed type 2 diabetes (n = 8662), and in additional type 2 diabetic patients (n = 1,064) and glucose-tolerant control subjects (n = 360). In the Inter99 study, the A allele of rs2070895 associated with a 0.057 mmol/liter [95% confidence interval (CI) 0.039-0.075] increase in fasting serum HDL-cholesterol (HDL-c) (P = 8 x 10(-10)) supported by association in the Anglo-Danish-Dutch Study of Intensive Treatment in People with Screen Detected Diabetes in Primary Care study [0.038 mmol/liter per allele (95% CI 0.024-0.053); P = 2 x 10(-7)). The allelic effect on HDL-c was modulated by interaction with self-reported physical activity (P(interaction) = 0.002) because vigorous physically active homozygous A-allele carriers had a 0.30 mmol/liter (95% CI 0.22-0.37) increase in HDL-c compared with homozygous G-allele carriers. We validate the association of LIPC promoter variation with fasting serum HDL-c and present data supporting an interaction with physical activity implying an increased effect on HDL-c in vigorous physically active subjects carrying the -250 A allele. This interaction may have potential implications for public health and disease prevention.

  4. Surface States in the AlxGa1-xN Barrier in AlxGa1-xN/GaN Heterosturctures

    Institute of Scientific and Technical Information of China (English)

    刘杰; 沈波; 王茂俊; 周玉刚; 陈敦军; 张荣; 施毅; 郑有炓

    2004-01-01

    Frequency-dependent capacitance-voltage (C-V) measurements have been performed on modulation-doped Al0.22Ga0.78N/GaN heterostructures to investigate the characteristics of the surface states in the Alx Ga1-xN barrier.Numerical fittings based on the experimental data indicate that there are surface states with high density locating on the AlxGa1-xN barrier. The density of the surface states is about 1012 cm-2 eV-1, and the time constant is about 1 μs. It is found that an insulating layer (Si3N4) between the metal contact and the surface of AlxGa1-xN can passivate the surface states effectively.

  5. Electric-field induced strain modulation of magnetization in Fe-Ga/Pb(Mg{sub 1/3}Nb{sub 2/3})-PbTiO{sub 3} magnetoelectric heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yue, E-mail: yuezhang@vt.edu; Wang, Zhiguang; Wang, Yaojin; Luo, Chengtao; Li, Jiefang; Viehland, Dwight [Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061 (United States)

    2014-02-28

    Magnetostrictive Fe-Ga thin layers were deposited on 〈110〉-oriented Pb(Mg{sub 1/3}Nb{sub 2/3})-30%PbTiO{sub 3} (PMN-30%PT) substrates by pulsed laser deposition. The as-prepared heterostructures showed columnar arrays aligned in the out-of-plane direction. Transmission electron microscopy revealed nanocrystalline regions within the columnar arrays of the Fe-Ga film. The heterostructure exhibited a strong converse magnetoelectric coupling effect of up to 4.55 × 10{sup −7} s m{sup −1}, as well as an electric field tunability of the in-plane magnetic anisotropy. Furthermore, the remanent magnetization states of the Fe-Ga films can be reversibly and irreversibly changed by external electric fields, suggesting a promising and robust application in magnetic random access memories and spintronics.

  6. The mobility of two-dimensional electron gas in AlGaN/GaN heterostructures with varied Al content

    Institute of Scientific and Technical Information of China (English)

    ZHANG JinFeng; HAO Yue; ZHANG JinCheng; NI JinYu

    2008-01-01

    The mobility of the two-dimensional electron gas (2DEG) in AlGaN/GaN hetero-structures changes significantly with AI content in the AlGaN barrier layer, while few mechanism analyses focus on it. Theoretical calculation and analysis of the 2DEG mobility in AlGaN/GaN heterostructures with varied Al content are carried out based on the recently reported experimental data. The 2DEG mobility is modeled analytically as the total effects of the scattering mechanisms including acoustic deformation-potential, piezoelectric, polar optic phonon, alloy disorder, interface roughness, dislocation and remote modulation doping scattering. We show that the increase of the 2DEG density, caused by the ascension of the Al content in the barrier layer, is a dominant factor that leads to the changes of the individual scat-tering processes. The change of the 2DEG mobility with Al content are mainly de-termined by the interface roughness scattering and the alloy disorder scattering at 77 K, and the polar optic phonon scattering and the interface roughness scattering at the room temperature. The calculated function of the interface roughness pa-rameters on the Al content shows that the stress caused AlGaN/GaN interface degradation at higher Al content is an important factor in the limitation of the in-terface roughness scattering on the 2DEG mobility in AlGaN/GaN heterostructures with high Al content.

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

    Directory of Open Access Journals (Sweden)

    P. Chen

    2016-03-01

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

  8. Degradation Mechanisms for GaN and GaAs High Speed Transistors

    Directory of Open Access Journals (Sweden)

    Fan Ren

    2012-11-01

    Full Text Available We present a review of reliability issues in AlGaN/GaN and AlGaAs/GaAs high electron mobility transistors (HEMTs as well as Heterojunction Bipolar Transistors (HBTs in the AlGaAs/GaAs materials systems. Because of the complex nature and multi-faceted operation modes of these devices, reliability studies must go beyond the typical Arrhenius accelerated life tests. We review the electric field driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plate, and the effect of device fabrication processes for both DC and RF stress conditions. We summarize the degradation mechanisms that limit the lifetime of these devices. A variety of contact and surface degradation mechanisms have been reported, but differ in the two device technologies: For HEMTs, the layers are thin and relatively lightly doped compared to HBT structures and there is a metal Schottky gate that is directly on the semiconductor. By contrast, the HBT relies on pn junctions for current modulation and has only Ohmic contacts. This leads to different degradation mechanisms for the two types of devices.

  9. DC Characteristics of AlGaN/GaN HEMTs Using a Dual-Gate Structure.

    Science.gov (United States)

    Hong, Sejun; Rana, Abu ul Hassan Sarwar; Heo, Jun-Woo; Kim, Hyun-Seok

    2015-10-01

    Multiple techniques such as fluoride-based plasma treatment, a p-GaN or p-AlGaN gate contact, and a recessed gate structure have been employed to modulate the threshold voltage of AlGaN/GaN-based high-electron-mobility transistors (HEMTs). In this study, we present dual-gate AlGaN/GaN HEMTs grown on a Si substrate, which effectively shift the threshold voltage in the positive direction. Experimental data show that the threshold voltage is shifted from -4.2 V in a conventional single-gate HEMT to -2.8 V in dual-gate HEMTs. It is evident that a second gate helps improve the threshold voltage by reducing the two-dimensional electron gas density in the channel. Furthermore, the maximum drain current, maximum transconductance, and breakdown voltage values of a single-gate device are not significantly different from those of a dual-gate device. For the fabricated single- and dual-gate devices, the values of the maximum drain current are 430 mA/mm and 428 mA/mm, respectively, whereas the values of the maximum transconductance are 83 mS/mm and 75 mS/mm, respectively.

  10. High-performance 980-nm emission wavelength InGaAs/AlGaAs/GaAs laser diodes

    Science.gov (United States)

    Suruceanu, Grigore I.; Caliman, Andrei N.; Vieru, Stanislav T.; Iakovlev, V. P.; Sarbu, A. V.; Mereuta, Alexandru Z.

    2000-02-01

    This paper present the fabrication and mirrors passivation process of InGaAs/AlGaAs/GaAs narrow stripe 980 nm emission wavelength laser diodes. After mesa-stripe definition and Au-contact deposition procedures, a procedure of in-vacuum cleaving and in-situ passivation with (lambda) /2-thick ZnSe layers was performed. 960 micrometers and 500 micrometers length laser diodes bars was fabricated as a result. Antireflection-high reflectivity coating were formed on the bars facets. Laser diodes were soldered p-junction-side down on copper submounts. The room temperature CW threshold current value of 20 mA and CW maximum output power of 440 mW at 760 mA pumping current were obtained. The far-field emission pattern of laser diodes is lateral single mode in large range of output powers. These laser diodes were used for laser diode module fabrication. In this module the laser diodes was coupled with tapered single mode 9 micrometers /125 micrometers optical fiber with a fused microlens at the end. CW output optical power of 40 mW from the fiber was obtained at 240 mA operating current of the laser diode module.

  11. Emission of terahertz radiation from GaN/AlGaN heterostructure under electron heating in lateral electric field

    Science.gov (United States)

    Shalygin, V. A.; Vorobjev, L. E.; Firsov, D. A.; Sofronov, A. N.; Melentyev, G. A.; Lundin, W. V.; Sakharov, A. V.; Tsatsulnikov, A. F.

    2013-12-01

    Spontaneous emission of terahertz radiation from modulation-doped AlGaN/GaN heterostructure under conditions of heating of a two-dimensional electron gas in the lateral electric field has been studied. The experimental data on the field dependence of the integral intensity of THz emission is compared with the theoretical simulation of blackbody-like emission from hot 2D electrons. Complementary transport measurements have been carried out to determine the dependence of effective electron temperature on electric field.

  12. Emission of terahertz radiation from GaN/AlGaN heterostructure under electron heating in lateral electric field

    Energy Technology Data Exchange (ETDEWEB)

    Shalygin, V. A.; Vorobjev, L. E.; Firsov, D. A.; Sofronov, A. N.; Melentyev, G. A. [St. Petersburg State Polytechnic University, 195251 St. Petersburg (Russian Federation); Lundin, W. V.; Sakharov, A. V.; Tsatsulnikov, A. F. [Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation)

    2013-12-04

    Spontaneous emission of terahertz radiation from modulation-doped AlGaN/GaN heterostructure under conditions of heating of a two-dimensional electron gas in the lateral electric field has been studied. The experimental data on the field dependence of the integral intensity of THz emission is compared with the theoretical simulation of blackbody-like emission from hot 2D electrons. Complementary transport measurements have been carried out to determine the dependence of effective electron temperature on electric field.

  13. 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...

  14. GaAs/GaSb nanowire heterostructures grown by MOVPE

    DEFF Research Database (Denmark)

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

    2008-01-01

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

  15. Selective epitaxial growth of monolithically integrated GaN-based light emitting diodes with AlGaN/GaN driving transistors

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-03-03

    In this Letter, we report selective epitaxial growth of monolithically integrated GaN-based light emitting diodes (LEDs) with AlGaN/GaN high-electron-mobility transistor (HEMT) drivers. A comparison of two integration schemes, selective epitaxial removal (SER), and selective epitaxial growth (SEG) was made. We found the SER resulted in serious degradation of the underlying LEDs in a HEMT-on-LED structure due to damage of the p-GaN surface. The problem was circumvented using the SEG that avoided plasma etching and minimized device degradation. The integrated HEMT-LEDs by SEG exhibited comparable characteristics as unintegrated devices and emitted modulated blue light by gate biasing.

  16. AlGaAs/GaAs/InGaAs pnp-type vertical-cavity surface-emitting transistor-lasers.

    Science.gov (United States)

    Xiang, Y; Reuterskiöld-Hedlund, C; Yu, X; Yang, C; Zabel, T; Hammar, M; Akram, M N

    2015-06-15

    We report on the design, fabrication and analysis of vertical-cavity surface-emitting transistor-lasers (T-VCSELs) based on the homogeneous integration of an InGaAs/GaAs VCSEL and an AlGaAs/GaAs pnp-heterojunction bipolar transistor (HBT). Epitaxial regrowth confinement, modulation doping, intracavity contacting and non-conducting mirrors are used to ensure a low-loss structure, and a variety of design variations are investigated for a proper internal biasing and current injection to ensure a wide operating range. Optimized devices show mW-range output power, mA-range base threshold current and high-temperature operation to at least 60°C with the transistor in its active mode of operation for base currents well beyond threshold. Current confinement schemes based on pnp-blocking layers or a buried tunnel junction are investigated as well as asymmetric current injection for reduced extrinsic resistances.

  17. Dynamic control of the optical emission from GaN/InGaN nanowire quantum dots by surface acoustic waves

    Energy Technology Data Exchange (ETDEWEB)

    Lazić, S., E-mail: lazic.snezana@uam.es; Chernysheva, E.; Meulen, H. P. van der; Calleja Pardo, J. M. [Departamento de Física de Materiales, Instituto “Nicolás Cabrera” and Instituto de Física de Materia Condensada (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid (Spain); Gačević, Ž.; Calleja, E. [ISOM-DIE, Universidad Politécnica de Madrid, 28040 Madrid (Spain)

    2015-09-15

    The optical emission of InGaN quantum dots embedded in GaN nanowires is dynamically controlled by a surface acoustic wave (SAW). The emission energy of both the exciton and biexciton lines is modulated over a 1.5 meV range at ∼330 MHz. A small but systematic difference in the exciton and biexciton spectral modulation reveals a linear change of the biexciton binding energy with the SAW amplitude. The present results are relevant for the dynamic control of individual single photon emitters based on nitride semiconductors.

  18. Dynamic control of the optical emission from GaN/InGaN nanowire quantum dots by surface acoustic waves

    Science.gov (United States)

    Lazić, S.; Chernysheva, E.; Gačević, Ž.; van der Meulen, H. P.; Calleja, E.; Calleja Pardo, J. M.

    2015-09-01

    The optical emission of InGaN quantum dots embedded in GaN nanowires is dynamically controlled by a surface acoustic wave (SAW). The emission energy of both the exciton and biexciton lines is modulated over a 1.5 meV range at ˜330 MHz. A small but systematic difference in the exciton and biexciton spectral modulation reveals a linear change of the biexciton binding energy with the SAW amplitude. The present results are relevant for the dynamic control of individual single photon emitters based on nitride semiconductors.

  19. Dynamic control of the optical emission from GaN/InGaN nanowire quantum dots by surface acoustic waves

    Directory of Open Access Journals (Sweden)

    S. Lazić

    2015-09-01

    Full Text Available The optical emission of InGaN quantum dots embedded in GaN nanowires is dynamically controlled by a surface acoustic wave (SAW. The emission energy of both the exciton and biexciton lines is modulated over a 1.5 meV range at ∼330 MHz. A small but systematic difference in the exciton and biexciton spectral modulation reveals a linear change of the biexciton binding energy with the SAW amplitude. The present results are relevant for the dynamic control of individual single photon emitters based on nitride semiconductors.

  20. Fluorescence x-ray standing wave study on (AlAs)(GaAs) superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Lessmann, A.; Brennan, S.; Munkholm, A. [Stanford Synchrotron Radiation Laboratory SSRL/SLAC, Menlo Park, CA (United States); Schuster, M.; Riechert, H. [Siemens AG, Corporate Technology, Munich (Germany); Materlik, G. [Hamburger Synchrotronstrahlungslabor HASYLAB/DESY, Hamburg (Germany)

    1999-05-21

    X-ray standing waves (XSW) were used to investigate the structure of molecular beam epitaxy (MBE) grown (AlAs){sub 3}(GaAs){sub 7} short-period superlattices (SPSL). The modulation of the Al K, As L, and Ga L x-ray fluorescence induced by XSW was measured at the zero-order superlattice (SL) satellite (AlAs)(GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the shape of the fluorescence yield modulations and the diffraction pattern, a model of the interfaces is derived by comparing the experimental data with dynamical calculations of the x-ray wave field distribution and reflectivity. A straightforward analysis of the fluorescence measurements at the SL satellite shows that in AlAs layers a high crystalline order is established, whereas in GaAs layers a fraction of the Ga and As atoms is not on ideal lattice sites, but is displaced towards the substrate. The data can be explained by a model in which, at each AlAs/GaAs interface of the GaAs layers, two Ga atom planes are displaced by 0.035 nm and 0.008 nm and one As atom plane by 0.023 nm. The displacements within the GaAs layers exhibit a mirror symmetry with respect to the centre of each layer. (author)

  1. GaN-based LEDs for light communication

    Science.gov (United States)

    Zhao, LiXia; Zhu, ShiChao; Wu, ChunHui; Yang, Chao; Yu, ZhiGuo; Yang, Hua; Liu, Lei

    2016-10-01

    Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current progresses of GaN-based LEDs for light communications. The modulation bandwidth of GaN-based LEDs has been first improved by optimizing the LED epilayer structures and the modulation bandwidth of 73 MHz was achieved at the driving current density of 40 A/cm2 by changing the multi-quantum well structures. After that, in order to increase the current density tolerance, different parallel flip-chip micro-LED arrays were fabricated. With a high injected current density of ˜7900 A/cm2, a maximum modulation bandwidth of ˜227 MHz was obtained with optical power greater than 30 mW. Besides the increase of carrier concentrations, the radiative recombination coefficient B was also enhanced by modifying the photon surrounding environment based on some novel nanostructures such as resonant cavity, surface plasmon, and photonic crystals. The optical 3 dB modulation bandwidth of GaN-based nanostructure LEDs with Ag nanoparticles was enhanced by 2 times compared with GaN-based nanostructure LEDs without Ag nanoparticles. Our results demonstrate that using the QW-SP coupling can effectively help to enhance the carrier spontaneous emission rate and also increase the modulation bandwidth for LEDs, especially for LEDs with high intrinsic IQE. In addition, we discuss the progress of the faster color conversion stimulated by GaN-based LEDs.

  2. GaN HEMTs

    Science.gov (United States)

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

    2012-03-01

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

  3. GaAs/AlGaAs photonic integrated circuits fabricated using impurity-free vacancy disordering

    Science.gov (United States)

    Marsh, John H.; Cusumano, P.; Bryce, A. Catrina; Ooi, Boon Siew; Ayling, Stephen G.

    1995-03-01

    Impurity free vacancy disordering (IFVD) using dielectric caps to induce intermixing in the GaAs/AlGaAs system is described. Silica is used to promote intermixing whilst strontium fluoride is used as a mask against intermixing. Selective bandgap-widening of GaAs/AlGaAs double quantum well laser material has been used to fabricate monolithic extended cavity strip- loaded waveguide lasers. With a differential shift of 21 nm in the wavelength of the photoluminescence peak, overall losses in the extended cavities were less than 6 cm-1 and a red-shift of the lasing spectrum with increasing passive section length is reported. Electroabsorption optical modulators integrated with passive waveguides have been fabricated using an epitaxial structure identical to that of the laser. At a wavelength of 861.6 nm, devices with a 400 micrometers long modulator section showed ON/OFF ratios greater than 35 dB for a reverse bias voltage of 3 V. A variation of the IFVD technique uses partial area coverage by a strontium fluoride mask under a silica cap to determine the amount of quantum well intermixing. The bandgap can then be varied at will across a wafer. Bandgap tuned lasers were fabricated using this technique. Five distinguishable lasing wavelengths were observed from five selected intermixed regions on a single chip. These lasers showed no significant change in transparency current, internal quantum efficiency or internal propagation loss, which indicates that the material quality was not degraded after intermixing.

  4. GaSbBi/GaSb quantum well laser diodes

    Science.gov (United States)

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

    2017-05-01

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

  5. Spin dependent transport properties of Mn-Ga/MgO/Mn-Ga magnetic tunnel junctions with metal(Mg, Co, Cr) insertion layer

    Energy Technology Data Exchange (ETDEWEB)

    Liang, S. H.; Tao, L. L.; Liu, D. P., E-mail: dpliu@iphy.ac.cn; Han, X. F., E-mail: xfhan@iphy.ac.cn [State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Lu, Y. [Institut Jean Lamour, UMR 7198, CNRS-Nancy Université, BP 239, 54506 Vandoeuvre (France)

    2014-04-07

    We report a first principles theoretical investigation of spin polarized quantum transport in Mn{sub 2}Ga/MgO/Mn{sub 2}Ga and Mn{sub 3}Ga/MgO/Mn{sub 3}Ga magnetic tunneling junctions (MTJs) with the consideration of metal(Mg, Co, Cr) insertion layer effect. By changing the concentration of Mn, our calculation shows a considerable disparity in transport properties: A tunneling magnetoresistance (TMR) ratio of 852% was obtained for Mn{sub 2}Ga-based MTJs, however, only a 5% TMR ratio for Mn{sub 3}Ga-based MTJs. In addition, the influence of insertion layer has been considered in our calculation. We found the Co insertion layer can increase the TMR of Mn{sub 2}Ga-based MTJ to 904%; however, the Cr insertion layer can decrease the TMR by 668%; A negative TMR ratio can be obtained with Mg insertion layer. Our work gives a comprehensive understanding of the influence of different insertion layer in Mn-Ga based MTJs. It is proved that, due to the transmission can be modulated by the interfacial electronic structure of insertion, the magnetoresistance ratio of Mn{sub 2}Ga/MgO/Mn{sub 2}Ga MTJ can be improved by inserting Co layer.

  6. Step-Flow Growth on Vicinal GaAs Surfaces by Migration-Enhanced Epitaxy

    Science.gov (United States)

    Yamaguchi, Hiroshi; Horikoshi, Yoshiji

    1989-08-01

    The mechanism of step-flow growth on vicinal GaAs substrates during migration-enhanced epitaxy are studied using the reflection high-energy electron diffraction technique. Results show that the low As pressure during migration-enhanced epitaxy growth accelerates step-flow growth. In addition, it is also shown that monolayer terraces composed of surface Ga atoms are formed from step edges during the Ga deposition process. A GaAs/AlAs tilted superlattice is established using this growth technique. X-ray diffraction measurement and transmission electron microscopy observations show that the fabricated structure has periodic composition modulation along the axis tilted from the substrate azimuth.

  7. Dislocation Mechanism of Twinning in Ni-Mn-Ga

    Science.gov (United States)

    Zárubová, N.; Ge, Y.; Gemperlová, J.; Gemperle, A.; Hannula, S.-P.

    2012-03-01

    Tensile tests were performed in situ in a transmission electron microscope to investigate the twinning mechanism in non-modulated Ni-Mn-Ga martensite. The reorientation of the twin variants occurs via twinning dislocations. Their generation and movement were followed; the glide plane and Burgers vector were verified. Individual twinning dislocations were visualized.

  8. Proposal to develop GaAs detectors for physics at the LHC

    CERN Document Server

    Beaumont, S P; Booth, C N; Buttar, C M; Carraresi, L; Colocci, M; Combley, F; D'Auria, S D; del Papa, C; Dogru, M; Edwards, M; Fiori, F; Francescato, A; Hou, Y; Lynch, J G; Lisowski, B; Matheson, J; Newett, S; Nuti, M; O'Shea, V; Pelfer, P G; Raine, P H; Sharp, P H; Skillicorn, Ian O; Smith, K M; Tartoni, N; ten Have, I; Turnbull, R M; Vanni, U; Vinattieri, A; Zichichi, Antonino; CERN. Geneva. Detector Research and Development Committee

    1990-01-01

    The present proposal first describes the results obtained using GaAs Schottky diode detectors which we have constructed, and the initial steps which we have taken towards the design of a GaAs preamplifier to match the detectors. We then propose a continuation of the programme of work towards a demonstration detector module for an LHC pre-shower tracker detector based on GaAs, within a time-scale of two years. The module will be compatible with the design of the proposed pre-shower tracker using silicon detectors (DRDC/P3), and should allow direct substitution for comparison purposes.

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

    CERN Document Server

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

    2004-01-01

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

  10. Cyclotron production of Ga-68 for human use from liquid targets: From theory to practice

    Science.gov (United States)

    Alves, F.; Alves, V. H.; Neves, A. C. B.; do Carmo, S. J. C.; Nactergal, B.; Hellas, V.; Kral, E.; Gonçalves-Gameiro, C.; Abrunhosa, A. J.

    2017-05-01

    A fully automated system for the production of 68Ga based on commercially available cyclotron liquid target and synthesis modules is described. A solution containing enriched 68Zn dissolved in a nitric solution is irradiated in a Cyclone 18/9 IBA cyclotron leading to the production of up to about 25 GBq of 68Ga. The irradiated solution is transferred to a Synthera synthesis module in which 68Ga is separated and purified with a yield superior to 85 % and where further labelling is achieved with yields no inferior to 70 %. The developed and implemented method presents an improved approach for the production of 68Ga-radiopharmaceuticals suitable for human use, in a process that takes less than 2 hours. This technique represents an economically viable alternative to 68Ge/68Ga generators with improved characteristics.

  11. Composition and doping control for metal-organic chemical vapor deposition of InP-based double heterojunction bipolar transistor with hybrid base structure consisting of GaAsSb contact and InGaAsSb graded layers

    Science.gov (United States)

    Hoshi, Takuya; Kashio, Norihide; Sugiyama, Hiroki; Yokoyama, Haruki; Kurishima, Kenji; Ida, Minoru; Matsuzaki, Hideaki

    2017-07-01

    We report on a method for composition and doping control for metalorganic chemical vapor deposition of a double heterojunction bipolar transistor (DHBT) with a hybrid base structure consisting of a compositionally graded InGaAsSb for boosting an average electron velocity and a heavily doped thin GaAsSb for lowering the base contact resistivity. The GaAsSb contact layer can be formed by simply turning off the supply of In precursor tetramethylindium (TMIn) after the growth of the composition and doping graded InGaAsSb base. Consequently, the solid composition and hole concentration of hybrid base can be properly controlled by just modulating the supply of only TMIn and carbon tetrabromide. Secondary ion mass spectroscopy for the DHBT wafer reveals that the contents of In, Ga, and C inside the base are actually modulated from the collector side to the emitter side as expected. Transmission-line-model measurements were performed for the compositionally graded-InGaAsSb/GaAsSb hybrid base. The contact resistivity is estimated to be 5.3 Ω µm2, which is lower than half the value of a compositionally graded InGaAsSb base without the GaAsSb contact layer. The results indicate that the compositionally-graded-InGaAsSb/GaAsSb-contact hybrid base structure grown by this simple method is very advantageous for obtaining DHBTs with a very high maximum oscillation frequency.

  12. Fluorescence x-ray standing wave study on (AlAs)(GaAs) superlattices

    CERN Document Server

    Lessmann, A; Munkholm, A; Schuster, M; Riechert, H; Materlik, G

    1999-01-01

    X-ray standing waves (XSW) were used to investigate the structure of molecular beam epitaxy (MBE) grown (AlAs) sub 3 (GaAs) sub 7 short-period superlattices (SPSL). The modulation of the Al K, As L, and Ga L x-ray fluorescence induced by XSW was measured at the zero-order superlattice (SL) satellite (AlAs)(GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the shape of the fluorescence yield modulations and the diffraction pattern, a model of the interfaces is derived by comparing the experimental data with dynamical calculations of the x-ray wave field distribution and reflectivity. A straightforward analysis of the fluorescence measurements at the SL satellite shows that in AlAs layers a high crystalline order is established, whereas in GaAs layers a fraction of the Ga and As atoms is not on ideal lattice sites, but is displaced towards the substrate. The data can be explained by a model in which, at each AlAs/GaAs interface of the GaAs layers, two Ga atom planes are displaced by 0.035 nm and 0...

  13. LD-pumped high repetition rate Q-switched Nd:YVO4 laser by using La3Ga5SiO14 single crystal electro-optic modulator

    Institute of Scientific and Technical Information of China (English)

    Chunyu Wang; Huaguo Zang; Xiaoli Li; Yutian Lu; Xiaolei Zhu

    2006-01-01

    A diode-end-pumped electro-optic (EO) Q-switched Nd:YVO4 laser operating at repetition rate of 10 kpps (pulses per second) was reported. A block of La3Ga5SiO14 (LGS) single crystal was used as a Q-switch and the driver was a metal oxide semiconductor field effect transistor (MOS-FET) pulser of high repetition rate and high voltage. At continuous wave (CW) operation, the slope efficiency of the laser was 46%, and maximum optical-to-optical efficiency was 38.5%. Using an output coupler with transmission of 70%, a 10-kpps Q-switched pulse train with 0.4-mJ monopulse energy and 8.2-ns pulse width was achieved, the optical conversion efficiency was around 15%, and the beam quality M2 factor was less than 1.2.

  14. Optical tuning of monolithic In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As/InP modulation-doped field-effect transistor oscillators at X and R band

    Science.gov (United States)

    Lai, R.; Bhattacharya, P. K.; Brock, T.

    1991-06-01

    In(0.53)Ga(0.47)As/In(0.52)Al(0.48)As MODFET devices were fabricated with a source-drain spacing of 2 microns and a 0.2 micron gate stripe. The optical control and optical tuning characteristics of these oscillators operating in the X and R bands were studied. For a 20 micro-W input light source, the maximum frequency shifts for the X- and R-band oscillator were 8.7 and 11.7 MHz, respectively. The amount of shift observed in the oscillators increased with decreasing drain bias, which is consistent with the observed dc photocurrent dependence with drain bias.

  15. 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...

  16. Cyclotron production of (68)Ga via the (68)Zn(p,n)(68)Ga reaction in aqueous solution.

    Science.gov (United States)

    Pandey, Mukesh K; Byrne, John F; Jiang, Huailei; Packard, Alan B; DeGrado, Timothy R

    2014-01-01

    The objective of the present work is to extend the applicability of the solution target approach to the production of (68)Ga using a low energy cyclotron. Since the developed method does not require solid target infrastructure, it offers a convenient alternative to (68)Ge/(68)Ga generators for the routine production of (68)Ga. A new solution target with enhanced heat exchange capacity was designed and utilized with dual foils of Al (0.20 mm) and Havar (0.038 mm) separated by helium cooling to degrade the proton energy to ~14 MeV. The water-cooled solution target insert was made of Ta and its solution holding capacity (1.6 mL) was reduced to enhance heat transfer. An isotopically enriched (99.23%) 1.7 M solution of (68)Zn nitrate in 0.2 N nitric acid was utilized in a closed target system. After a 30 min irradiation at 20 μA, the target solution was unloaded to a receiving vessel and the target was rinsed with 1.6 mL water, which was combined with the target solution. An automated module was used to pass the solution through a cation-exchange column (AG-50W-X8, 200-400 mesh, hydrogen form) which efficiently trapped zinc and gallium isotopes. (68)Zn was subsequently eluted with 30 mL of 0.5 N HBr formulated in 80% acetone without any measurable loss of (68)Ga. (68)Ga was eluted with 7 mL of 3 N HCl solution with 92-96% elution efficiency. The radionuclidic purity was determined using an HPGe detector. Additionally, ICP-MS was employed to analyze for non-radioactive metal contaminants. The product yield was 192.5 ± 11.0 MBq/μ·h decay-corrected to EOB with a total processing time of 60-80 min. The radionuclidic purity of (68)Ga was found to be >99.9%, with the predominant contaminant being 67Ga. The ICP-MS analysis showed small quantities of Ga, Fe, Cu, Ni and Zn in the final product, with (68)Ga specific activity of 5.20-6.27 GBq/μg. Depending upon the user requirements, (68)Ga production yield can be further enhanced by increasing the (68)Zn concentration in the

  17. Coulomb excitation of Ga-73

    NARCIS (Netherlands)

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

    2010-01-01

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

  18. A Study of Ga(.47)In(.53)As and Al(.48)In(.52)As for Very High Frequency Device Applications.

    Science.gov (United States)

    1985-01-01

    GaInAs/AlInAs modulation doped structures grown by molecular beam epitaxy (MBE) were studied. The parameters of the MBE growth were adjusted to give high room temperature mobilities (-12000 sq cm/v-sec) and high sheet electron concentrations 2 x 10 to the 12th power per sq cm. Because of higher electron velocities and high conductivities GaInAs modulation doped transistors should be significantly higher speed than those of GaAs. Originator-Supplied keywords include: Gallium indium arsenide, Aluminum indium arsenide, Indium phosphide, Modulation

  19. Analysis of energy states in modulation doped multiquantum well heterostructures

    Science.gov (United States)

    Ji, G.; Henderson, T.; Peng, C. K.; Huang, D.; Morkoc, H.

    1990-01-01

    A precise and effective numerical procedure to model the band diagram of modulation doped multiquantum well heterostructures is presented. This method is based on a self-consistent iterative solution of the Schroedinger equation and the Poisson equation. It can be used rather easily in any arbitrary modulation-doped structure. In addition to confined energy subbands, the unconfined states can be calculated as well. Examples on realistic device structures are given to demonstrate capabilities of this procedure. The numerical results are in good agreement with experiments. With the aid of this method the transitions involving both the confined and unconfined conduction subbands in a modulation doped AlGaAs/GaAs superlattice, and in a strained layer InGaAs/GaAs superlattice are identified. These results represent the first observation of unconfined transitions in modulation doped multiquantum well structures.

  20. SWIR InGaAs focal plane arrays in France

    Science.gov (United States)

    Rouvié, A.; Huet, O.; Hamard, S.; Truffer, J. P.; Pozzi, M.; Decobert, J.; Costard, E.; Zécri, M.; Maillart, P.; Reibel, Y.; Pécheur, A.

    2013-06-01

    SWIR detection band benefits from natural (sun, night glow, thermal radiation) or artificial (eye safe lasers) photons sources combined to low atmospheric absorption and specific contrast compared to visible wavelengths. It gives the opportunity to address a large spectrum of applications such as defense and security (night vision, active imaging), space (earth observation), transport (automotive safety) or industry (non destructive process control). InGaAs material appears as a good candidate to satisfy SWIR detection needs. The lattice matching with InP constitutes a double advantage to this material: attractive production capacity and uncooled operation thanks to low dark current level induced by high quality material. The study of InGaAs FPA has begun few years ago with III-VLab, gathering expertise in InGaAs material growth and imaging technology respectively from Alcatel-Lucent and Thales, its two mother companies. This work has led to put quickly on the market a 320x256 InGaAs module. The recent transfer of imagery activities from III-VLab to Sofradir allows developing new high performances products, satisfying customers' new requirements. Especially, a 640x512 InGaAs module with a pitch of 15µm is actually under development to fill the needs of low light level imaging.

  1. High mobility AlGaN/GaN devices for β--dosimetry

    Science.gov (United States)

    Schmid, Martin; Howgate, John; Ruehm, Werner; Thalhammer, Stefan

    2016-05-01

    There is a high demand in modern medical applications for dosimetry sensors with a small footprint allowing for unobtrusive or high spatial resolution detectors. To this end we characterize the sensoric response of radiation resistant high mobility AlGaN/GaN semiconductor devices when exposed to β--emitters. The samples were operated as a floating gate transistor, without a field effect gate electrode, thus excluding any spurious effects from β--particle interactions with a metallic surface covering. We demonstrate that the source-drain current is modulated in dependence on the kinetic energy of the incident β--particles. Here, the signal is shown to have a linear dependence on the absorbed energy calculated from Monte Carlo simulations. Additionally, a stable and reproducible sensor performance as a β--dose monitor is shown for individual radioisotopes. Our experimental findings and the characteristics of the AlGaN/GaN high mobility layered devices indicate their potential for future applications where small sensor size is necessary, like for instance brachytherapy.

  2. High mobility AlGaN/GaN devices for β{sup −}-dosimetry

    Energy Technology Data Exchange (ETDEWEB)

    Schmid, Martin; Howgate, John; Ruehm, Werner [Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg (Germany); Thalhammer, Stefan, E-mail: stefan.thalhammer@physik.uni-augsburg.de [Universität Augsburg, Universitätsstraße 1, 86159 Augsburg (Germany)

    2016-05-21

    There is a high demand in modern medical applications for dosimetry sensors with a small footprint allowing for unobtrusive or high spatial resolution detectors. To this end we characterize the sensoric response of radiation resistant high mobility AlGaN/GaN semiconductor devices when exposed to β{sup −}-emitters. The samples were operated as a floating gate transistor, without a field effect gate electrode, thus excluding any spurious effects from β{sup −}-particle interactions with a metallic surface covering. We demonstrate that the source–drain current is modulated in dependence on the kinetic energy of the incident β{sup −}-particles. Here, the signal is shown to have a linear dependence on the absorbed energy calculated from Monte Carlo simulations. Additionally, a stable and reproducible sensor performance as a β{sup −}-dose monitor is shown for individual radioisotopes. Our experimental findings and the characteristics of the AlGaN/GaN high mobility layered devices indicate their potential for future applications where small sensor size is necessary, like for instance brachytherapy.

  3. Cationic eluate pretreatment for automated synthesis of [⁶⁸Ga]CPCR4.2.

    Science.gov (United States)

    Martin, René; Jüttler, Steffen; Müller, Marco; Wester, Hans-Jürgen

    2014-01-01

    Fostered by the clinical success of sst-ligands, the development and evaluation of (68)Ga-labeled peptides have become a very active field in radiopharmaceutical chemistry. Consequently, various new peptide tracers have been developed, e.g. [(68)Ga]CPCR4.2 for in vivo imaging of solid and haematological tumors or [(68)Ga]TRAP(RGD)₃ for imaging of α(v)β₃ integrin expression. As a consequence of different matrices (TiO₂, SnO₂, polymers) exploited in commercial (68)Ge/(68)Ga-generators, HCl of different concentrations (0.05...1.0 M) is used to obtain (68)Ga as starting material for automated syntheses. We have developed a purification method which reduces the eluate volume and adjusts the HCl concentration. The method may potentially allow standardization of the eluate composition of different commercial generators prior to labeling. Recently, a cationic purification process has been reported which allows the pre-fixation of (68)Ga on a Varian SCX cation exchange cartridge and subsequent elution of (68)Ga with acidified NaCl solutions. As part of the development of ready-to-use cassettes for the automated production of (68)Ga-CPCR4.2 using a SCINTOMICS GRP module and an iThemba Labs generator that is eluted with 0.6...1.0 M HCl, we tested and compared the (68)Ga-trapping efficiency of various commercial available cation exchange cartridges, the efficiency of subsequent (68)Ga-elution from these cartridges by means of various protocols and the influence of these variations on the labeling efficiency of [(68)Ga]CPCR4.2, [(68)Ga]TRAP(RGD)₃ and [(68)Ga]DOTATATE/[(68)Ga]DOTANOC. Finally, we transferred the optimized method to the automated, cassette based synthesis of [(68)Ga]CPCR4.2 and the aforementioned peptides. From seven tested cation exchange cartridges, Chromafix PS-H(+) gave the best extraction results (>95%). Moreover, we observed that acidified solutions of 5 M NaCl or 2.5 M CaCl₂ can be used for efficient cartridge elution. Using a disposable c

  4. Characterization of GaSb-based heterostructures by spectroscopic investigations

    Energy Technology Data Exchange (ETDEWEB)

    Imhof, Sebastian; Bueckers, Christina; Metzger, Bjoern; Thraenhardt, Angela; Chatterjee, Sangam; Koch, Stephan W. [Fachbereich Physik, Wissenschaftliches Zentrum fuer Materialwissenschaften, Philipps Universitaet Marburg, Renthof 5, 35032 Marburg (Germany)

    2008-07-01

    The material system (AlGaIn)(AsSb) is suitable for laser emission at 2 {mu}m or longer wavelength, which is interesting for various applications, e.g. material processing, gas detection, medical diagnostic and laser surgery. A wide range of material combinations is being considered for application, but there are still uncertainties with regards to their structural properties, such as band alignment, strain and general bandstructure parameters. In order to gain information on these structural properties, we investigate GaSb-based heterostructures by modulation spectroscopy using e.g. photomodulated reflection. The experimental data are compared to simulations based on a microscopic theory.

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

    DEFF Research Database (Denmark)

    Gurpinar, Emre; Castellazzi, Alberto; Iannuzzo, Francesco;

    2016-01-01

    In this paper, an ultra-low inductance power cell design for a 3L-ANPC based on 650 V GaN HEMT devices is presented. The 3L-ANPC topology with GaN HEMT devices and the selected modulation scheme suitable for wide-bandgap (WBG) devices are presented. The commutation loops, which are the main contr...

  6. Quantized conductance in up to 20 μm long shallow etched GaAs/AlGaAs quantum wires

    Science.gov (United States)

    Worschech, L.; Beuscher, F.; Forchel, A.

    1999-07-01

    Conductance quantization is observed in up to 20 μm long and 135 nm wide quantum wires fabricated by wet chemical etching of modulation-doped GaAs/AlGaAs heterostructures. With increasing wire length, the higher plateaus in the conductance vanish, whereas a fundamental step persists up to a length comparable to the transport mean free path of the two-dimensional layers. Via magnetic depopulation of the one-dimensional (1D) subbands a lateral depletion length of wdep=15 nm is estimated for a gate voltage of 1.1 V. By temperature dependent measurements the energy spacings between the 1D subbands are investigated.

  7. A Terahertz Detector Based on AlGaN/GaN High Electron Mobility Transistor with Bowtie Antennas

    Science.gov (United States)

    Sun, J. D.; Sun, Y. F.; Zhou, Y.; Zhang, Z. P.; Lin, W. K.; Zen, C. H.; Wu, D. M.; Zhang, B. S.; Qin, H.; Li, L. L.; Xu, W.

    2011-12-01

    We report on the characterization of room temperature terahertz (THz) based on a GaN/AlGaN high electron mobility transistor(HEMT) including bowtie antennas. Under THz irradiation around 1 THz, strong photocurrent is observed when the electron channel is strongly modulated by the gate voltage. Both experimental and simulation data support the validity of self-mixing model. The equivalent noise power (NEP) and responsivity are estimated to be 1nW/√Hz and 42 mA/W at 300 K, respectively.

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

    Science.gov (United States)

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

    2011-03-01

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

  9. An X-band four-way combined GaN solid-state power amplifier

    Energy Technology Data Exchange (ETDEWEB)

    Chen Chi; Hao Yue; Feng Hui; Gu Wenping; Li Zhiming; Hu Shigang; Ma Teng, E-mail: ccachi@163.co [National Key Laboratory of Wide Band-Gap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China)

    2010-01-15

    An X-band four-way combined GaN solid-state power amplifier module is fabricated based on a self-developed AlGaN/GaN HEMT with 2.5-mm gate width technology on SiC substrate. The module consists of an AlGaN/GaN HEMT, Wilkinson power hybrids, a DC-bias circuit and microstrip matching circuits. For the stability of the amplifier module, special RC networks at the input and output, a resistor between the DC power supply and a transistor gate at the input and 3{lambda}/4 Wilkinson power hybrids are used for the cancellation of low frequency self-oscillation and crosstalk of each amplifier. Under V{sup ds} = 27 V, V{sup gs} = -4.0 V, CW operating conditions at 8 GHz, the amplifier module exhibits a line gain of 5 dB with a power added efficiency of 17.9%, and an output power of 42.93 dBm; the power gain compression is 2 dB. For a four-way combined solid-state amplifier, the power combining efficiency is 67.5%. It is concluded that the reduction in combining efficiency results from the non-identical GaN HMET, the loss of the hybrid coupler and the circuit fabricating errors of each one-way amplifier. (semiconductor integrated circuits)

  10. Direct current modulation of a photomixing signal

    Science.gov (United States)

    Constantin, Florin L.

    2016-04-01

    Direct modulation of the bias voltage of a LTG-GaAs photomixer is exploited to modulate the signal generated at the frequency of the optical beat between two diode lasers at 820 nm. The photomixing signal is calculated from an expansion in power series of the amplitude of the modulation voltage and displays amplitude modulation sidebands equidistantly spaced to the frequency of the optical beat by integer multiples of the modulation frequency. Modulation at harmonics of the modulation frequency is allowed by the electrical nonlinear response of the photomixer, driven at low voltage by the saturation of the electron drift velocity. Coupling of an alternative voltage to the photomixer operated at zero-bias leads to bifrequency operation. Modulation of the photomixing signal and bifrequency operation of the photomixer are observed experimentally with an optical beat in the microwave regime.

  11. Wavelength modulation spectroscopy of semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kohn, S.E.

    1977-10-01

    The use of modulation spectroscopy to study the electronic properties of solids has been very productive. The construction of a wide range Wavelength Modulation Spectrometer to study the optical properties of solids is described in detail. Extensions of the working range of the spectrometer into the vacuum ultraviolet are discussed. Measurements of the reflectivity and derivative reflectivity spectra of the lead chalcogenides, the chalcopyrite ZnGeP/sub 2/, the layer compounds GaSe and GaS and their alloys, the ferroelectric SbSI, layer compounds SnS/sub 2/ and SnSe/sub 2/, and HfS/sub 2/ were made. The results of these measurements are presented along with their interpretation in terms of band structure calculations.

  12. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-07-01

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

  14. Silicon optical modulators

    Directory of Open Access Journals (Sweden)

    Graham T. Reed

    2005-01-01

    Full Text Available Ever since the earliest research on optical circuits, dating back to the 1970s, there have been visions of an optical superchip (see for example1,2, containing a variety of integrated optical components to carry out light generation, modulation, manipulation, detection, and amplification (Fig. 1. The early work was associated with ferroelectric materials such as lithium niobate (LiNbO3, and III-V semiconductors such as gallium arsenide (GaAs and indium phosphide (InP based systems. LiNbO3 was interesting almost solely because of the fact that it possesses a large electro-optic coefficient3, enabling optical modulation via the Pockels effect. Alternatively, the III-V compounds were interesting because of the relative ease of laser fabrication and the prospect of optical and electronic integration.

  15. Change of photovoltaic module conversion efficiency with the environmental factors in different site. Comparison of the conversion efficiency in Tokyo with the one in Nagano; Kotonaru chiten ni okeru taiyo denchi module no shutsuryoku tokusei no henka. Tokyoto Shinjukuku to Naganoken Chinoshi tono hikaku

    Energy Technology Data Exchange (ETDEWEB)

    Higuchi, T.; Tani, T.; Hirata, Y.; Inasaka, T. [Science University of Tokyo, Tokyo (Japan)

    1997-11-25

    Assuming that photovoltaic power systems were installed at two points, Shinjuku Tokyo and Chino Nagano, a study was conducted of difference in generated output of the systems caused by the difference in environmental factors. In the study, it was assumed that two of the photovoltaic power system with rated capacity of 3kW were installed at the two points, and the annual generated output was calculated and compared by the conventional method considering only cell temperature and the output estimation method considering intensity of solar radiation, cell temperature, and spectral distribution of solar radiation. The result of the study was as follows: the difference in output ratio at the two points was 1.7% or lower under the influence of intensity of solar radiation and cell temperature. On the other hand, under the influence of the distribution of spectral solar radiation, the difference is larger than under other environmental factors, 2.4% in polycrystalline Si and 5.5% in amorphous Si. The generated output estimated by the conventional method and the spectral method produced a difference between 81 kWh in Tokyo and 258 kWh in Nagano in amorphous Si. This is because environmental factors such as intensity of solar radiation and distribution of spectral solar radiation are different between the two points. 1 ref., 2 figs., 3 tabs.

  16. Characteristics of cylindrical surrounding-gate GaAs x Sb1-x /In y Ga1-y As heterojunction tunneling field-effect transistors

    Science.gov (United States)

    Guan, Yun-He; Li, Zun-Chao; Luo, Dong-Xu; Meng, Qing-Zhi; Zhang, Ye-Fei

    2016-10-01

    A III-V heterojunction tunneling field-effect transistor (TFET) can enhance the on-state current effectively, and GaAs x Sb1-x /In y Ga1-y As heterojunction exhibits better performance with the adjustable band alignment by modulating the alloy composition. In this paper, the performance of the cylindrical surrounding-gate GaAs x Sb1-x /In y Ga1-y As heterojunction TFET with gate-drain underlap is investigated by numerical simulation. We validate that reducing drain doping concentration and increasing gate-drain underlap could be effective ways to reduce the off-state current and subthreshold swing (SS), while increasing source doping concentration and adjusting the composition of GaAs x Sb1-x /In y Ga1-y As can improve the on-state current. In addition, the resonant TFET based on GaAs x Sb1-x /In y Ga1-y As is also studied, and the result shows that the minimum and average of SS reach 11 mV/decade and 20 mV/decade for five decades of drain current, respectively, and is much superior to the conventional TFET. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176038 and 61474093), the Science and Technology Planning Project of Guangdong Province, China (Grant No. 2015A010103002), and the Technology Development Program of Shaanxi Province, China (Grant No. 2016GY-075).

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

    Science.gov (United States)

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

    1995-10-01

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

  18. An apparatus comprising a waveguide-modulator and laser-diode and a method of manufacture thereof

    KAUST Repository

    Ooi, Boon S.

    2017-04-13

    Example apparatuses are provided for simultaneous generation of high intensity light and modulated light signals at low modulation bias operating characteristics. An example apparatus includes a semipolar or nonpolar GaN-based substrate, a reverse- biased waveguide modulator section, and a forward-biased gain section based on InGaN/GaN quantum-well active regions, wherein the forward-biased gain section is grown on the semipolar or nonpolar GaN-based substrate. Methods of manufacturing the apparatuses described herein are also contemplated and described herein.

  19. Quantum well saturable absorber mirror with electrical control of modulation depth

    DEFF Research Database (Denmark)

    Liu, Xiaomin; Rafailov, E.U.; Livshits, D.

    2010-01-01

    A saturable absorber mirror comprizing InGaAs/GaAs quantum wells incorporated into a p-i-n structure is demonstrated. Its modulation depth can be reduced from 4.25 % to 1.63 % by applying reverse bias voltage in the range 0–1 V.......A saturable absorber mirror comprizing InGaAs/GaAs quantum wells incorporated into a p-i-n structure is demonstrated. Its modulation depth can be reduced from 4.25 % to 1.63 % by applying reverse bias voltage in the range 0–1 V....

  20. Si上GaN研究

    Institute of Scientific and Technical Information of China (English)

    陈裕权

    2004-01-01

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

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

    Science.gov (United States)

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

    2014-01-01

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

  2. Robust Manipulation of Magnetism in Dilute Magnetic Semiconductor (Ga,Mn)As by Organic Molecules.

    Science.gov (United States)

    Wang, Xiaolei; Wang, Hailong; Pan, Dong; Keiper, Timothy; Li, Lixia; Yu, Xuezhe; Lu, Jun; Lochner, Eric; von Molnár, Stephan; Xiong, Peng; Zhao, Jianhua

    2015-12-22

    Surface adsorption of organic molecules provides a new method for the robust manipulation of ferromagnetism in (Ga,Mn)As. Electron acceptor and donor molecules yield significant enhancement and suppression, respectively, of ferromagnetism with modulation of the Curie temperature spanning 36 K. Dip-pen nanolithography is employed to directly pattern monolayers on (Ga,Mn)As, which is presented as a novel pathway toward producing magnetic nanostructures.

  3. Robust AlGaN/GaN MMIC Receiver Components

    NARCIS (Netherlands)

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

    2009-01-01

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

  4. 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.

  5. Comprehensive Quality Control of the ITG 68Ge/68Ga Generator and Synthesis of 68Ga-DOTATOC and 68Ga-PSMA-HBED-CC for Clinical Imaging.

    Science.gov (United States)

    Amor-Coarasa, Alejandro; Schoendorf, Megan; Meckel, Marian; Vallabhajosula, Shankar; Babich, John W

    2016-09-01

    A good-manufacturing-practices (GMP) (68)Ge/(68)Ga generator that uses modified dodecyl-3,4,5-trihydroxybenzoate hydrophobically bound to a octadecyl silica resin (C-18) as an adsorbent has been developed that allows for dilute HCl (0.05N) to efficiently elute metal-impurity-free (68)Ga(3+) ready for peptide labeling. We characterized the performance of this generator system over a year in conjunction with the production of (68)Ga-labeled DOTATOC and Glu-NH-CO-NH-Lys(Ahx)-HBED-CC (PSMA-HBED-CC) intended for clinical studies and established protocols for batch release. A 2,040-MBq self-shielded (68)Ge/(68)Ga generator provided metal-free (68)GaCl3 ready for peptide labeling in the fluidic labeling module after elution with 4 mL of 0.05N HCl. The compact system was readily housed in a laminar flow cabinet allowing an ISO class-5 environment. (68)Ga labeling of peptides using GMP kits was performed in 15-20 min, and the total production time was 45-50 min. Batch release quality control specifications were established to meet investigational new drug submission and institutional review board approval standards. Over a period of 12 mo, (68)Ga elution yields from the generator averaged 80% (range, 72.0%-95.1%), and (68)Ge breakthrough was less than 0.006%, initially decreasing with time to 0.001% (expressed as percentage of (68)Ge activity present in the generator at the time of elution), a unique characteristic of this generator. The radiochemical purity of both (68)Ga-DOTATOC and (68)Ga-PSMA-HBED-CC determined by high-performance liquid chromatography analysis was greater than 98%, with a minimum specific activity of 12.6 and 42 GBq/μmol, respectively. The radionuclidic ((68)Ge) impurity was 0.00001% or less (under the detection limit). Final sterile, pyrogen-free formulation was provided in physiologic saline with 5%-7% ethanol. The GMP-certified (68)Ge/(68)Ga generator system was studied for a year. The generator system is contained within the fluidic labeling

  6. DLTS measurements on GaSb/GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-07-01

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

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

    Science.gov (United States)

    2013-08-01

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

  8. -Regular Modules

    Directory of Open Access Journals (Sweden)

    Areej M. Abduldaim

    2013-01-01

    Full Text Available We introduced and studied -regular modules as a generalization of -regular rings to modules as well as regular modules (in the sense of Fieldhouse. An -module is called -regular if for each and , there exist and a positive integer such that . The notion of -pure submodules was introduced to generalize pure submodules and proved that an -module is -regular if and only if every submodule of is -pure iff   is a -regular -module for each maximal ideal of . Many characterizations and properties of -regular modules were given. An -module is -regular iff is a -regular ring for each iff is a -regular ring for finitely generated module . If is a -regular module, then .

  9. 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.

  10. The influence of AlN interlayers on the microstructural and electrical properties of p-type AlGaN/GaN superlattices grown on GaN/sapphire templates

    Energy Technology Data Exchange (ETDEWEB)

    Li, Lei; Liu, Lei; Wang, Lei; Li, Ding; Song, Jie; Liu, Ningyang; Chen, Weihua; Wang, Yuzhou; Yang, Zhijian; Hu, Xiaodong [Peking University, State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Beijing (China)

    2012-09-15

    AlN with different thicknesses were grown as interlayers (ILs) between GaN and p-type Al{sub 0.15}Ga{sub 0.85}N/GaN superlattices (SLs) by metal organic vapor phase epitaxy (MOVPE). It was found that the edge-type threading dislocation density (TDD) increased gradually from the minimum of 2.5 x 10{sup 9} cm{sup -2} without AlN IL to the maximum of 1 x 10{sup 10} cm{sup -2} at an AlN thickness of 20 nm, while the screw-type TDD remained almost unchanged due to the interface-related TD suppression and regeneration mechanism. We obtained that the edge-type dislocations acted as acceptors in p-type Al{sub x} Ga{sub 1-x} N/GaN SLs, through the comparison of the edge-type TDD and hole concentration with different thicknesses of AlN IL. The Mg activation energy was significantly decreased from 153 to 70 meV with a 10-nm AlN IL, which was attributed to the strain modulation between AlGaN barrier and GaN well. The large activation efficiency, together with the TDs, led to the enhanced hole concentration. The variation trend of Hall mobility was also observed, which originated from the scattering at TDs. (orig.)

  11. Modeling of parasitic elements in high voltage multiplier modules

    NARCIS (Netherlands)

    Wang, J.

    2014-01-01

    It is an inevitable trend that the power conversion module will have higher switching frequency and smaller volume in the future. Bandgap devices, such as SiC and GaN devices, accelerate the process. With this process, the parasitic elements in the module will probably have stronger influence on cir

  12. Prostatic uptake of Ga-67

    Energy Technology Data Exchange (ETDEWEB)

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

    1984-08-01

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

  13. Characterization of a room temperature terahertz detector based on a GaN/AlGaN HEMT*

    Institute of Scientific and Technical Information of China (English)

    ZhouYu; Wu Dongmin; Lou Shitao; Qin Hua; Zhang Baoshun; Sun Jiandong; Sun Yunfei; Zhang Zhipeng; Lin Wenkui; Liu Hongxin; Zeng Chunhong; Lu Min; Cai Yong

    2011-01-01

    We report on the characterization of a room temperature terahertz detector based on a GaN/AlGaN high electron mobility transistor integrated with three patch antennas. Experimental results prove that both horizontal and perpendicular electric fields are induced in the electron channel. A photocurrent is generated when the electron channel is strongly modulated by the gate voltage. Despite the large channel length and gate-source/drain distance,significant horizontal and perpendicular fields are achieved. The device is well described by the self-mixing ofterahertz fields in the electron channel. The noise-equivalent power and responsivity are estimated to be 100 nW/(√Hz) and 3 mA/W at 292 K, respectively. No decrease in responsivity is observed up to a modulation frequency of 5 kHz.The detector performance can be further improved by engineering the source-gate-drain geometry to enhance the nonlinearity.

  14. Characterization of a room temperature terahertz detector based on a GaN/AlGaN HEMT

    Energy Technology Data Exchange (ETDEWEB)

    Zhou Yu; Sun Jiandong; Sun Yunfei; Zhang Zhipeng; Lin Wenkui; Liu Hongxin; Zeng Chunhong; Lu Min; Cai Yong; Wu Dongmin; Lou Shitao; Qin Hua; Zhang Baoshun, E-mail: hqin2007@sinano.ac.cn [Key Laboratory of Nanodevices, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China)

    2011-06-15

    We report on the characterization of a room temperature terahertz detector based on a GaN/AlGaN high electron mobility transistor integrated with three patch antennas. Experimental results prove that both horizontal and perpendicular electric fields are induced in the electron channel. A photocurrent is generated when the electron channel is strongly modulated by the gate voltage. Despite the large channel length and gate-source/drain distance, significant horizontal and perpendicular fields are achieved. The device is well described by the self-mixing of terahertz fields in the electron channel. The noise-equivalent power and responsivity are estimated to be 100 nW/{radical}Hz and 3 mA=W at 292 K, respectively. No decrease in responsivity is observed up to a modulation frequency of 5 kHz. The detector performance can be further improved by engineering the source-gate-drain geometry to enhance the nonlinearity. (semiconductor devices)

  15. Characterization of a room temperature terahertz detector based on a GaN/AlGaN HEMT

    Science.gov (United States)

    Yu, Zhou; Jiandong, Sun; Yunfei, Sun; Zhipeng, Zhang; Wenkui, Lin; Hongxin, Liu; Chunhong, Zeng; Min, Lu; Yong, Cai; Dongmin, Wu; Shitao, Lou; Hua, Qin; Baoshun, Zhang

    2011-06-01

    We report on the characterization of a room temperature terahertz detector based on a GaN/AlGaN high electron mobility transistor integrated with three patch antennas. Experimental results prove that both horizontal and perpendicular electric fields are induced in the electron channel. A photocurrent is generated when the electron channel is strongly modulated by the gate voltage. Despite the large channel length and gate-source/drain distance, significant horizontal and perpendicular fields are achieved. The device is well described by the self-mixing of terahertz fields in the electron channel. The noise-equivalent power and responsivity are estimated to be and 3 mA=W at 292 K, respectively. No decrease in responsivity is observed up to a modulation frequency of 5 kHz. The detector performance can be further improved by engineering the source-gate-drain geometry to enhance the nonlinearity.

  16. Insulated gate and surface passivation structures for GaN-based power transistors

    Science.gov (United States)

    Yatabe, Zenji; Asubar, Joel T.; Hashizume, Tamotsu

    2016-10-01

    Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Si- and GaAs-based devices counterparts. Metal-insulator-semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator materials have been applied to GaN-based transistors, the properties of insulator/III-N interfaces are still not fully understood. This is mainly due to the difficulty of characterizing insulator/AlGaN interfaces in a MIS HEMT because of the two resulting interfaces: insulator/AlGaN and AlGaN/GaN, making the potential modulation rather complicated. Although there have been many reports of low interface-trap densities in HEMT MIS capacitors, several papers have incorrectly evaluated their capacitance-voltage (C-V) characteristics. A HEMT MIS structure typically shows a 2-step C-V behavior. However, several groups reported C-V curves without the characteristic step at the forward bias regime, which is likely to the high-density states at the insulator/AlGaN interface impeding the potential control of the AlGaN surface by the gate bias. In this review paper, first we describe critical issues and problems including leakage current, current collapse and threshold voltage instability in AlGaN/GaN HEMTs. Then we present interface properties, focusing on interface states, of GaN MIS systems using oxides, nitrides and high-κ dielectrics. Next, the properties of a variety of AlGaN/GaN MIS

  17. AlGaInN laser diode technology and systems for defence and security applications

    Science.gov (United States)

    Najda, Stephen P.; Perlin, Piotr; Suski, Tadek; Marona, Lujca; Boćkowski, Mike; Leszczyński, Mike; Wisniewski, Przemek; Czernecki, Robert; Kucharski, Robert; Targowski, Grzegorz; Watson, Scott; Kelly, Antony E.

    2015-10-01

    AlGaInN laser diodes is an emerging technology for defence and security applications such as underwater communications and sensing, atomic clocks and quantum information. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Thus AlGaInN laser diode technology is a key enabler for the development of new disruptive system level applications in displays, telecom, defence and other industries. Ridge waveguide laser diodes are fabricated to achieve single mode operation with optical powers up to 100mW with the 400-440nm wavelength range with high reliability. Visible free-space and underwater communication at frequencies up to 2.5GHz is reported using a directly modulated 422nm GaN laser diode. Low defectivity and highly uniform GaN substrates allow arrays and bars to be fabricated. High power operation operation of AlGaInN laser bars with up to 20 emitters have been demonstrated at optical powers up to 4W in a CS package with common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space or optical fibre system integration with a very small form-factor.

  18. Simultaneous light emission and detection of InGaN/GaN multiple quantum well diodes for in-plane visible light communication

    Science.gov (United States)

    Wang, Yongjin; Xu, Yin; Yang, Yongchao; Gao, Xumin; Zhu, Bingcheng; Cai, Wei; Yuan, Jialei; Zhang, Rong; Zhu, Hongbo

    2017-03-01

    This paper presents the design, fabrication, and experimental characterization of monolithically integrated p-n junction InGaN/GaN multiple quantum well diodes (MQWDs) and suspended waveguides. Suspended MQWDs can be used as transmitters and receivers simultaneously, and suspended waveguides are used for light coupling to create an in-plane visible light communication system. Compared to the waveguide with separation trench, the calculated total light efficiency is increased from 18% to 22% for the continuous waveguide. The MQWDs are characterized by their typical current-voltage performance, and the pulse excitation measurements confirm that the InGaN/GaN MQWDs can achieve the light emission and photodetection at the same time. The photocurrent measurements indicate that the photocurrent is modulated by a bias voltage and that the photons are being supplied from another transmitter. An experimental demonstration is presented showing that the proposed device works well for in-plane full-duplex communication using visible light.

  19. Simultaneous light emission and detection of InGaN/GaN multiple quantum well diodes for in-plane visible light communication on a chip

    CERN Document Server

    Wang, Yongjin; Yang, Yongchao; Gao, Xumin; Zhu, Bingcheng; Cai, Wei; Yuan, Jialei; Zhang, Rong; Zhu, Hongbo

    2016-01-01

    This paper presents the design, fabrication, and experimental characterization of monolithically integrated p-n junction InGaN/GaN multiple quantum well diodes (MQWDs) and suspended waveguides. Suspended MQWDs can be used as transmitters and receivers simultaneously, and suspended waveguides are used for light coupling to create an in-plane visible light communication system. Compared to the waveguide with separation trench, the calculated total light efficiency is increased from 18% to 22% for the continuous waveguide. The MQWDs are characterized by their typical current-voltage performance, and the pulse excitation measurements confirm that the InGaN/GaN MQWDs can achieve the light emission and photodetection at the same time. The photocurrent measurements indicate that the photocurrent is modulated by a bias voltage and that the photons are being supplied from another transmitter. An experimental demonstration is presented showing that the proposed device works well for in-plane full-duplex communication u...

  20. Electrically sign-reversible transverse g -factors of holes in droplet epitaxial GaAs/AlGaAs quantum dots under uniaxial stress

    Science.gov (United States)

    Wu, Yu-Nien; Wu, Ming-Fan; Ou, Ya-Wen; Chou, Ying-Lin; Cheng, Shun-Jen

    2017-08-01

    We present a theoretical investigation of anisotropic g -factor tensors of single holes confined in droplet epitaxial GaAs/AlGaAs quantum dots under electrical and mechanical controls using the gauge-invariant discretization method within the framework of four-band Luttinger-Kohn k ⃗.p ⃗ theory. We reveal an intrinsic obstacle to realize the electrical sign reversal of the hole g -factors, being a key condition required for a full spin control in the scheme of g -tensor modulation, for the quantum dots solely with electrical bias control. Constructively, our studies show that, besides electrical gating, slightly stressing an inherently unstrained droplet epitaxial GaAs/AlGaAs quantum dot can offset the transverse hole g -factor to be nearly zero and make the electrical sign reversal of the hole g -factors feasible.

  1. Monolithic integration of enhancement-mode vertical driving transistorson a standard InGaN/GaN light emitting diode structure

    Science.gov (United States)

    Lu, Xing; Liu, Chao; Jiang, Huaxing; Zou, Xinbo; Zhang, Anping; Lau, Kei May

    2016-08-01

    In this letter, monolithic integration of InGaN/GaN light emitting diodes (LEDs) with vertical metal-oxide-semiconductor field effect transistor (VMOSFET) drivers have been proposed and demonstrated. The VMOSFET was achieved by simply regrowing a p- and n-GaN bilayer on top of a standard LED structure. After fabrication, the VMOSFET is connected with the LED through the conductive n-GaN layer, with no need of extra metal interconnections. The junction-based VMOSFET is inherently an enhancement-mode (E-mode) device with a threshold voltage of 1.6 V. By controlling the gate bias of the VMOSFET, the light intensity emitted from the integrated VMOSFET-LED device could be well modulated, which shows great potential for various applications, including solid-state lighting, micro-displays, and visible light communications.

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

    Directory of Open Access Journals (Sweden)

    Campesato Roberta

    2017-01-01

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

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

    Science.gov (United States)

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

    2002-12-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2006-01-01

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

  5. GaInNAs laser gain

    Energy Technology Data Exchange (ETDEWEB)

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

    2000-05-23

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

  6. Hydrogenation of GaSb/GaAs quantum rings

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-08-25

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

  7. Quantum well saturable absorber mirror with electrical control of modulation depth

    DEFF Research Database (Denmark)

    Liu, Xiaomin; Rafailov, Edik U.; Livshits, Daniil

    2010-01-01

    We demonstrate a quantum well QW semiconductor saturable absorber mirror SESAM comprising low-temperature grown InGaAs/GaAs QWs incorporated into a p-i-n structure. By applying the reverse bias voltage in the range 0–2 V to the p-i-n structure, we were able to change the SESAM modulation depth...

  8. AlGaInN laser diode technology for defence, security and sensing applications

    Science.gov (United States)

    Najda, Stephen P.; Perlin, Piotr; Suski, Tadek; Marona, Lucja; Boćkowski, Mike; Leszczyński, Mike; Wisniewski, Przemek; Czernecki, Robert; Kucharski, Robert; Targowski, Grzegorz; Watson, Scott; Kelly, Antony E.

    2014-10-01

    The latest developments in AlGaInN laser diode technology are reviewed for defence, security and sensing applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Advantages of using Plasma assisted MBE (PAMBE) compared to more conventional MOCVD epitaxy to grow AlGaInN laser structures are highlighted. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Gallium-nitride (GaN) blue laser diode is reported. High power operation of AlGaInN laser diodes is demonstrated with a single chip, AlGaInN laser diode `mini-array' with a common p-contact configuration at powers up to 2.5W cw at 410nm. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. GaN laser bars of up to 5mm with 20 emitters, mounted in a CS mount package, give optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.or.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-08-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-11-01

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

  11. Turn-key Near-Infrared Photon-Counting Detector Module for LIDAR Applications Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose to design and deliver a turn-key photon counting detector module for near-infrared wavelengths, based on large-area InGaAs/InP avalanche photodiodes...

  12. Outdoor Performance of a Thin-Film Gallium-Arsenide Photovoltaic Module

    Energy Technology Data Exchange (ETDEWEB)

    Silverman, T. J.; Deceglie, M. G.; Marion, B.; Cowley, S.; Kayes, B.; Kurtz, S.

    2013-06-01

    We deployed a 855 cm2 thin-film, single-junction gallium arsenide (GaAs) photovoltaic (PV) module outdoors. Due to its fundamentally different cell technology compared to silicon (Si), the module responds differently to outdoor conditions. On average during the test, the GaAs module produced more power when its temperature was higher. We show that its maximum-power temperature coefficient, while actually negative, is several times smaller in magnitude than that of a Si module used for comparison. The positive correlation of power with temperature in GaAs is due to temperature-correlated changes in the incident spectrum. We show that a simple correction based on precipitable water vapor (PWV) brings the photocurrent temperature coefficient into agreement with that measured by other methods and predicted by theory. The low operating temperature and small temperature coefficient of GaAs give it an energy production advantage in warm weather.

  13. ITER Central Solenoid Module Fabrication

    Energy Technology Data Exchange (ETDEWEB)

    Smith, John [General Atomics, San Diego, CA (United States)

    2016-09-23

    The fabrication of the modules for the ITER Central Solenoid (CS) has started in a dedicated production facility located in Poway, California, USA. The necessary tools have been designed, built, installed, and tested in the facility to enable the start of production. The current schedule has first module fabrication completed in 2017, followed by testing and subsequent shipment to ITER. The Central Solenoid is a key component of the ITER tokamak providing the inductive voltage to initiate and sustain the plasma current and to position and shape the plasma. The design of the CS has been a collaborative effort between the US ITER Project Office (US ITER), the international ITER Organization (IO) and General Atomics (GA). GA’s responsibility includes: completing the fabrication design, developing and qualifying the fabrication processes and tools, and then completing the fabrication of the seven 110 tonne CS modules. The modules will be shipped separately to the ITER site, and then stacked and aligned in the Assembly Hall prior to insertion in the core of the ITER tokamak. A dedicated facility in Poway, California, USA has been established by GA to complete the fabrication of the seven modules. Infrastructure improvements included thick reinforced concrete floors, a diesel generator for backup power, along with, cranes for moving the tooling within the facility. The fabrication process for a single module requires approximately 22 months followed by five months of testing, which includes preliminary electrical testing followed by high current (48.5 kA) tests at 4.7K. The production of the seven modules is completed in a parallel fashion through ten process stations. The process stations have been designed and built with most stations having completed testing and qualification for carrying out the required fabrication processes. The final qualification step for each process station is achieved by the successful production of a prototype coil. Fabrication of the first

  14. Investigation of Cu(In,Ga)Se{sub 2} using Monte Carlo and the cluster expansion technique

    Energy Technology Data Exchange (ETDEWEB)

    Ludwig, Christian D.R.; Gruhn, Thomas; Felser, Claudia [Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg-University, Mainz (Germany); Windeln, Johannes [IBM Germany, Mgr. Technology Center ISC EMEA, Mainz (Germany)

    2010-07-01

    CIGS based solar cells are among the most promising thin-film techniques for cheap, yet efficient modules. They have been investigated for many years, but the full potential of CIGS cells has not yet been exhausted and many effects are not understood. For instance, the band gap of the absorber material Cu(In,Ga)Se{sub 2} varies with Ga content. The question why solar cells with high Ga content have low efficiencies, despite the fact that the band gap should have the optimum value, is still unanswered. We are using Monte Carlo simulations in combination with a cluster expansion to investigate the homogeneity of the In-Ga distribution as a possible cause of the low efficiency of cells with high Ga content. The cluster expansion is created by a fit to ab initio electronic structure energies. The results we found are crucial for the processing of solar cells, shed light on structural properties and give hints on how to significantly improve solar cell performance. Above the transition temperature from the separated to the mixed phase, we observe different sizes of the In and Ga domains for a given temperature. The In domains in the Ga-rich compound are smaller and less abundant than the Ga domains in the In-rich compound. This translates into the Ga-rich material being less homogeneous.

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

    Science.gov (United States)

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

    2015-01-01

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

  16. Development of GaAs Detectors for Physics at the LHC

    CERN Multimedia

    Chu, Zhonghua; Krais, R; Rente, C; Syben, O; Tenbusch, F; Toporowsky, M; Xiao, Wenjiang; Cavallini, A; Fiori, F; Edwards, M; Geppert, R; Goppert, R; Haberla, C; Hornung, M F; Irsigler, R; Rogalla, M; Beaumont, S; Raine, C; Skillicorn, I; Margelevicius, J; Meshkinis, S; Smetana, S; Jones, B; Santana, J; Sloan, T; Zdansky, K; Alexiev, D; Donnelly, I J; Canali, C; Chiossi, C; Nava, F; Pavan, P; Kubasta, J; Tomiak, Z; Tchmil, V; Tchountonov, A; Tsioupa, I; Dogru, M; Gray, R; Hou, Yuqian; Manolopoulos, S; Walsh, S; Aizenshtadt, G; Budnitsky, D L; Gossen, A; Khludkov, S; Koretskaya, O B; Okaevitch, L; Potapov, A; Stepanov, V E; Tolbanov, O; Tyagev, A; Matulionis, A; Pozela, J; Kavaliauskiene, G; Kazukauskas, V; Kiliulis, R; Rinkevicius, V; Slenys, S; Storasta, J V

    2002-01-01

    % RD-8 Development of GaAs Detectors for Physics at the LHC \\\\ \\\\The aims of the collaboration are to investigate the available material options, performance and limitations of simple pad, pixel and microstrip GaAs detectors for minimum ionising particles with radiation hardness and speed which are competitive with silicon detectors. This new technology was originally developed within our university laboratories but now benefits from increasing industrial interest and collaboration in detector fabrication. Initial steps have also been taken towards the fabrication of GaAs preamplifiers to match the detectors in radiation hardness. The programme of work aims to construct a demonstration detector module for an LHC forward tracker based on GaAs.

  17. Suppression of low-frequency charge noise in gates-defined GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    You, Jie; Li, Hai-Ou, E-mail: haiouli@ustc.edu.cn, E-mail: gpguo@ustc.edu.cn; Wang, Ke; Cao, Gang; Song, Xiang-Xiang; Xiao, Ming; Guo, Guo-Ping, E-mail: haiouli@ustc.edu.cn, E-mail: gpguo@ustc.edu.cn [Key Laboratory of Quantum Information, Chinese Academy of Sciences, University of Science and Technology of China, Hefei, Anhui 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2015-12-07

    To reduce the charge noise of a modulation-doped GaAs/AlGaAs quantum dot, we have fabricated shallow-etched GaAs/AlGaAs quantum dots using the wet-etching method to study the effects of two-dimensional electron gas (2DEG) underneath the metallic gates. The low-frequency 1/f noise in the Coulomb blockade region of the shallow-etched quantum dot is compared with a non-etched quantum dot on the same wafer. The average values of the gate noise are approximately 0.5 μeV in the shallow-etched quantum dot and 3 μeV in the regular quantum dot. Our results show the quantum dot low-frequency charge noise can be suppressed by the removal of the 2DEG underneath the metallic gates, which provides an architecture for noise reduction.

  18. Epitaxial thin film GaAs solar cells using OM-CVD techniques. [Organometallics

    Science.gov (United States)

    Stirn, R. J.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    A new approach has been initiated at JPL to fabricate thin-film, high efficiency GaAs solar cells on low-cost, single-crystal Si substrates having a thin CVD interlayer of Ge to minimize the lattice and thermal expansion mismatch. For initial experiments, n(+)/p GaAs cells were grown by OM-CVD on single-crystal GaAs and Ge wafers. Details of the growths and performance results will be presented. Subsequently, a combined epitaxial structure of OM-CVD GaAs on a strongly adherent Ge interlayer on (100) Si was grown. This is the first report of the successful growth of this composite structure. Low module costs projected by JPL SAMICS methodology calculations and the potential for 400-600W/kg space solar arrays will be discussed.

  19. A low cost, green method to synthesize GaN nanowires

    Science.gov (United States)

    Zhao, Jun-Wei; Zhang, Yue-Fei; Li, Yong-He; Su, Chao-Hua; Song, Xue-Mei; Yan, Hui; Wang, Ru-Zhi

    2015-12-01

    The synthesis of gallium nitride nanowires (GaN NWs) by plasma enhanced chemical vapor deposition (PECVD) are successfully demonstrated in this work. The simple and green synthesis route is to introduce gallium oxide (Ga2O3) and nitrogen (N2) for the growth of nanowires. The prepared GaN nanowires have a single crystalline wurtzite structure, which the length of some nanowires is up to 20 μm, with a maximum diameter about 140 nm. The morphology and quantity of the nanowires can be modulated by the growth substrate and process parameters. In addition, the photoluminescence and field emission properties of the prepared GaN nanowires have been investigated, which were found to be largely affected by their structures. This work renders an environmentally benign strategy and a facile approach for controllable structures on nanodevice.

  20. GaAs-MnAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-07-15

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

  1. An x-ray absorption spectroscopy study of Ni-Mn-Ga shape memory alloys.

    Science.gov (United States)

    Sathe, V G; Dubey, Aditi; Banik, Soma; Barman, S R; Olivi, L

    2013-01-30

    The austenite to martensite phase transition in Ni-Mn-Ga ferromagnetic shape memory alloys was studied by extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy. The spectra at all the three elements', namely, Mn, Ga and Ni, K-edges in several Ni-Mn-Ga samples (with both Ni and Mn excess) were analyzed at room temperature and low temperatures. The EXAFS analysis suggested a displacement of Mn and Ga atoms in opposite direction with respect to the Ni atoms when the compound transforms from the austenite phase to the martensite phase. The first coordination distances around the Mn and Ga atoms remained undisturbed on transition, while the second and subsequent shells showed dramatic changes indicating the presence of a modulated structure. The Mn rich compounds showed the presence of antisite disorder of Mn and Ga. The XANES results showed remarkable changes in the unoccupied partial density of states corresponding to Mn and Ni, while the electronic structure of Ga remained unperturbed across the martensite transition. The post-edge features in the Mn K-edge XANES spectra changed from a double peak like structure to a flat peak like structure upon phase transition. The study establishes strong correlation between the crystal structure and the unoccupied electronic structure in these shape memory alloys.

  2. Fabrication and characteristics of high speed InGaAs/GaAs quantum-wells superluminescent diode emitting at 1053 nm

    Science.gov (United States)

    Duan, L. H.; Fang, L.; Zhang, J.; Zhou, Y.; Guo, H.; Luo, Q. C.; Zhang, S. F.

    2014-05-01

    A high speed 1053 nm superluminescent diode (SLD) with a ridge-waveguide structure has been fabricated for the first time to the best of our knowledge. InGaAs/GaAs quantum well epitaxial structure, the etched depth of the insulation channel and the area of p-side electrode were optimized to enhance the modulation bandwidth of the SLD. Bend-waveguide unpumped absorbing region structure and facet coating methods have been adopted to suppress the lasing oscillation. As a result, a -3 dB cutoff frequency of 1.7 GHz is obtained at a dc bias current of 100 mA and 25 °C heat-sink temperature, corresponding to 2.5 mW output power from single-mode fiber with spectral modulation of less than 0.15 dB and spectral width of 24 nm. The SLD module shows a good reliability.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1991-01-01

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

  4. Effect of the band structure of InGaN/GaN quantum well on the surface plasmon enhanced light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-07-07

    The spontaneous emission (SE) of InGaN/GaN quantum well (QW) structure with silver(Ag) coated on the n-GaN layer has been investigated by using six-by-six K-P method taking into account the electron-hole band structures, the photon density of states of surface plasmon polariton (SPP), and the evanescent fields of SPP. The SE into SPP mode can be remarkably enhanced due to the increase of electron-hole pairs near the Ag by modulating the InGaN/GaN QW structure or increasing the carrier injection. However, the ratio between the total SE rates into SPP mode and free space will approach to saturation or slightly decrease for the optimized structures with various distances between Ag film and QW layer at a high injection carrier density. Furthermore, the Ga-face QW structure has a higher SE rate than the N-face QW structure due to the overlap region of electron-hole pairs nearer to the Ag film.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-12-15

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

  6. Fabrication of novel III-N and III-V modulator structures by ECR plasma etching

    Energy Technology Data Exchange (ETDEWEB)

    Pearton, S.J.; Abernathy, C.R.; MacKenzie, J.D. [Univ. of Florida, Gainesville, FL (United States)] [and others

    1995-12-01

    Quantum well microdisk laser structures have been fabricated in the GaN/InGaN, GaAs/AlGaAs and GaAs/InGaP systems using a combination of ECR dry etching (Cl{sub 2}/CH{sub 4}/H{sub 2}/Ar, BCl{sub 3}/Ar or CH{sub 4}/H{sub 2}/Ar plasma chemistries respectively) and subsequent wet chemical etching of a buffer layer underlying the quantum wells. While wet etchants such as HF/H{sub 2}O and HCl/HNO{sub 3}/H{sub 2} O are employed for AlGaAs and InGaP, respectively, a new KOH based solution has been developed for AlN which is completely selective over both GaN and InGaN. Typical mask materials include PR or SiN{sub x}, while the high surface recombination velocity of exposed AlGaAs ({approximately} 10{sup 5} cm{center_dot}sec {sup {minus}1}) requires encapsulation with ECR-CVD SiN{sup x} to stabilize the optical properties of the modulators.

  7. Making quantum devices with electrical properties that are robust to thermal cycling using AlGaAs/GaAs HIGFET structures

    Science.gov (United States)

    Micolich, Adam; See, Andrew; Klochan, Oleh; Burke, Adam; Hamilton, Alex; Pilgrim, Ian; Scannell, Billy; Montgomery, Rick; Taylor, Richard; Aagesen, Martin; Lindelof, Poul; Farrer, Ian; Ritchie, David

    2013-03-01

    The transport properties of quantum devices on modulation-doped AlGaAs/GaAs heterostructures change after thermal cycling above ~130 K due to charge redistribution in the modulation doping layer. This is particularly evident in a quantum dot's magnetoconductance fluctuations (MCF) which provide a sensitive fingerprint of electron trajectories through the dot. We show that the MCF become reproducible with high-fidelity after thermal cycling to 300 K in quantum dots made using AlGaAs/GaAs heterostructures without modulation doping. This is achieved by populating the dot electrostatically using a Heterostructure Insulated Gate Field Effect Transistor (HIGFET) architecture. Our result demonstrates ionized impurity scattering has a measurable effect on transport in quantum dots, even in the ballistic transport regime. It highlights the potential for HIGFET-based architectures to provide devices with significantly reduced small-angle scattering at equivalent transport mobility, and more thermally robust electrical properties. More broadly, we suggest a quantum dot's MCF may be a useful tool for studying the temporal/thermal stability of disorder in other semiconductor materials.

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

    Science.gov (United States)

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

    2017-01-01

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

  9. Improved on-state performance of AlGaN/GaN Fin-HEMTs by reducing the length of the nanochannel

    Science.gov (United States)

    Zhang, Meng; Ma, Xiao-Hua; Mi, Min-Han; He, Yun-Long; Hou, Bin; Zheng, Jia-Xin; Zhu, Qing; Chen, Li-Xiang; Zhang, Peng; Yang, Ling

    2017-05-01

    In this letter, AlGaN/GaN Fin-HEMTs with different nanochannel geometric parameters were fabricated and characterized. The drain current density, transconductance, and on-resistance were improved by reducing the length of the nanochannel, which was attributed to the modulation of access resistance by changing the length of the nanochannel. The threshold voltage shifted to the positive direction with the decrease in the width of the nanochannel and showed the independence on the length of the nanochannel. With the reduction in the length of the nanochannel, the gate swing was increased by suppressing the increase of source resistance, improving the linearity of transconductance.

  10. High-quality MOVPE butt-joint integration of InP/AlGaInAs/InGaAsP-based all-active optical components

    DEFF Research Database (Denmark)

    Kulkova, Irina; Kadkhodazadeh, Shima; Kuznetsova, Nadezda

    2014-01-01

    In this paper, we demonstrate the applicability of MOVPE butt-joint regrowth for integration of all-active InP/AlGaAs/InGaAsP optical components and the realization of high-functionality compact photonic devices. Planar high-quality integration of semiconductor optical amplifiers of various epi......-structures with a multi-quantum well electro-absorption modulator has been successfully performed and their optical and crystalline quality was experimentally investigated. The regrown multi-quantum well material exhibits a slight bandgap blue-shift of less than 20 meV, when moving away from the regrowth interface...

  11. Blackbody-like emission of terahertz radiation from AlGaN/GaN heterostructure under electron heating in lateral electric field

    Science.gov (United States)

    Shalygin, V. A.; Vorobjev, L. E.; Firsov, D. A.; Sofronov, A. N.; Melentyev, G. A.; Lundin, W. V.; Nikolaev, A. E.; Sakharov, A. V.; Tsatsulnikov, A. F.

    2011-04-01

    The authors report on the observation and study of terahertz radiation emission from modulation-doped AlGaN/GaN heterostructure under conditions of heating of a two-dimensional electron gas in the lateral electric field. The experimental results are compared with the theoretical model of blackbody-like emission from hot two-dimensional electrons. Complementary transport measurements and a theoretical simulation were carried out to determine the dependence of effective electron temperature on electric field. The role of nonequilibrium optical phonon accumulation is discussed.

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

    Institute of Scientific and Technical Information of China (English)

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

    2016-01-01

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

  13. Fundamental and dynamic properties of intermixed InGaAs-InGaAsP quantum-well lasers

    KAUST Repository

    Chen, Cheng

    2010-09-01

    The fundamental and dynamic properties of InGaAs-InGaAsP lasers, where emission wavelengths were blue-shifted by quantum-well intermixing through ion implantation and annealing, were investigated to assess possible degradation by intermixing. It was found that the fundamental properties such as threshold current and slope efficiency were largely unchanged even after as much as 120 nm of wavelength shift. Meanwhile, the dynamic properties such as modulation efficiency and K factor were degraded after just a moderate degree of intermixing, but the degradation was not worsened by further intermixing. Provided the finite degradation of dynamic properties is tolerable, the present intermixing technique will be very useful for the fabrication of photonic integrated circuits. © 2006 IEEE.

  14. Micromechanical sensors based on GaAs/AlGaAs

    OpenAIRE

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

    1994-01-01

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

  15. The electron-phonon interaction in GaAs/(AlGa)As quantum wells

    CERN Document Server

    Cross, A J

    2001-01-01

    detected phonon emission energy spectra. This thesis presents a study of the electron-phonon interaction in two dimensional electron gases (2DEGs), by measuring of the acoustic phonon emission from a sequence of n-type doped GaAs/(AIGa)As quantum wells. Previous studies of emission from 2DEGs confined in GaAs heterojunctions (Chin et al., 1984) have shown a surprising absence of longitudinal acoustic (LA) mode phonon emission, in contrast with theoretical studies (Vass, 1987) which predict that deformation potential coupled LA mode emission should dominate the energy relaxation processes. This may be attributed to the finite width of the quasi-2D sheet, which imposes a restriction on the maximum emitted phonon wavevector component perpendicular to the 2DEG, leading to a suppression of the emission (the '1/a sub 0 cutoff') at smaller phonon wavevectors than predicted by the earlier theory. By using the quantum well width w as a means of modulating the thickness of the 2DEG, the dependence of the 1/a sub 0 cuto...

  16. Kink effect in AlGaN/GaN high electron mobility transistors by electrical stress

    Institute of Scientific and Technical Information of China (English)

    Ma Xiao-Hua; Ma Ji-Gang; Yang Li-Yuan; He Qiang; Jiao Ying; Ma Ping; Hao Yue

    2011-01-01

    The kink effect is studied in an AlGaN/GaN high electron mobility transistor by measuring DC performance during fresh, short-term stress and recovery cycle with negligible degradation. Vdg plays an assistant role in detrapping electrons and short-term stress results in no creation of new category traps but an increase in number of active traps.A possible mechanism is proposed that electrical stress supplies traps with the electric field for activation and when device is under test field-assisted hot-electrons result in electrons detrapping from traps, thus deteriorating the kink effect. In addition, experiments show that the impact ionization is at a relatively low level, which is not the dominant mechanism compared with trapping effect. We analyse the complicated link between the kink effect and stress bias through groups of electrical stress states: Vds = 0-state, off-state, on-state (on-state with low voltage, high-power state,high field state). Finlly, a conclusion is drawn that electric field brings about more severe kink effect than hot electrons.With the assistance of electric field, hot electrons tend to be possible to modulate the charges in deep-level trap.

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

    Institute of Scientific and Technical Information of China (English)

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

    2007-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-03-02

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

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

    Directory of Open Access Journals (Sweden)

    Wang Zhiming

    2010-01-01

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

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

    Science.gov (United States)

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

    2011-03-02

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

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

    Institute of Scientific and Technical Information of China (English)

    罗子江; 周勋; 杨再荣; 贺业全; 何浩; 邓朝勇; 丁召

    2011-01-01

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

  2. Thermal Stability of Strained AlGaN/GaN Heterostructures

    Institute of Scientific and Technical Information of China (English)

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

    2006-01-01

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

  3. Development of GaN/AlGaN Terahertz Quantum Cascade Laser

    Science.gov (United States)

    2008-11-19

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

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

    OpenAIRE

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

    2001-01-01

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

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

    OpenAIRE

    Krishnamoorthy, Sriram; Akyol, Fatih; Rajan, Siddharth

    2014-01-01

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

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

    Directory of Open Access Journals (Sweden)

    P. C. Chang

    2014-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-28

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-19

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

  10. Effects of ternary mixed crystal and size on intersubband optical absorption in wurtzite InGaN/GaN core-shell nanowires

    Science.gov (United States)

    Liu, W. H.; Yang, S.; Feng, H. M.; Yang, L.; Qu, Y.; Ban, S. L.

    2015-07-01

    Based on the density matrix approach, the effects of ternary mixed crystal and size on intersubband optical absorption coefficients in InxGa1-xN/GaN core-shell nanowires (CSNWs) are investigated. The results show that the optical absorption can be modulated by In component x and the size of CSNWs, since the variation of electron states in these systems. It is found that photonic frequencies of resonant absorption and the absorption coefficient increase obviously when x increases or the radius of InGaN core reduces, while the half-width of the coefficient decreases as its peak becomes higher and sharper. A saturation phenomenon of optical absorption is also found when the incident light intensity exceeds a certain value. The theoretical results are expected to be helpful to develop CSNW optic devices.

  11. Mid-infrared electro-luminescence and absorption from AlGaN/GaN-based multi-quantum well inter-subband structures

    Science.gov (United States)

    Hofstetter, Daniel; Bour, David P.; Kirste, Lutz

    2014-06-01

    We present electro-modulated absorption and electro-luminescence measurements on chirped AlGaN/GaN-based multi-quantum well inter-subband structures grown by metal-organic vapour phase epitaxy. The absorption signal is a TM-polarized, 70 meV wide feature centred at 230 meV. At medium injection current, a 58 meV wide luminescence peak corresponding to an inter-subband transition at 1450 cm-1 (180 meV) is observed. Under high injection current, we measured a 4 meV wide structure peaking at 92.5 meV in the luminescence spectrum. The energy location of this peak is exactly at the longitudinal optical phonon of GaN.

  12. Mid-infrared electro-luminescence and absorption from AlGaN/GaN-based multi-quantum well inter-subband structures

    Energy Technology Data Exchange (ETDEWEB)

    Hofstetter, Daniel, E-mail: Daniel.Hofstetter@unine.ch [University of Neuchâtel, Institute of Physics, 51 Avenue de Bellevaux, Neuchâtel, CH–2009 (Switzerland); Bour, David P. [Avogy, Inc., 677 River Oaks Parkway, San Jose, California 95134 (United States); Kirste, Lutz [Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, D-79108 Freiburg i. Brsg. (Germany)

    2014-06-16

    We present electro-modulated absorption and electro-luminescence measurements on chirped AlGaN/GaN-based multi-quantum well inter-subband structures grown by metal-organic vapour phase epitaxy. The absorption signal is a TM-polarized, 70 meV wide feature centred at 230 meV. At medium injection current, a 58 meV wide luminescence peak corresponding to an inter-subband transition at 1450 cm{sup −1} (180 meV) is observed. Under high injection current, we measured a 4 meV wide structure peaking at 92.5 meV in the luminescence spectrum. The energy location of this peak is exactly at the longitudinal optical phonon of GaN.

  13. 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.

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

    Institute of Scientific and Technical Information of China (English)

    Li Wei; Chen Xiaoyang; Li Hui; Guo Hai

    2003-01-01

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

  15. Valence band hybridization in N-rich GaN1-xAsx alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wu, J.; Walukiewicz, W.; Yu, K.M.; Denlinger, J.D.; Shan, W.; Ager III, J.W.; Kimura, A.; Tang, H.F.; Kuech, T.F.

    2004-05-04

    We have used photo-modulated transmission and optical absorption spectroscopies to measure the composition dependence of interband optical transitions in N-rich GaN{sub 1-x}As{sub x} alloys with x up to 0.06. The direct bandgap gradually decreases as x increases. In the dilute x limit, the observed band gap approaches 2.8 eV; this limiting value is attributed to a transition between the As localized level, which has been previously observed in As-doped GaN at 0.6 eV above the valence band maximum in As-doped GaN, and the conduction band minimum. The structure of the valence band of GaN{sub 1-x}As{sub x} is explained by the hybridization of the localized As states with the extended valence band states of GaN matrix. The hybridization is directly confirmed by soft x-ray emission experiments. To describe the electronic structure of the GaN{sub 1-x}As{sub x} alloys in the entire composition range a linear interpolation is used to combine the effects of valence band hybridization in N-rich alloys with conduction band anticrossing in As-rich alloys.

  16. Intensity modulated short circuit current spectroscopy for solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Kavasoglu, Nese; Sertap Kavasoglu, A.; Birgi, Ozcan; Oktik, Sener [Mugla University, Faculty of Arts and Sciences, Physics Department, TR-48000 Mugla (Turkey); Mugla University Clean Energy Research and Development Centre, TR-48000 Mugla (Turkey)

    2011-02-15

    Understanding charge separation and transport is momentously important for the rectification of solar cell performance. To probe photo-generated carrier dynamics, we implemented intensity modulated short circuit current spectroscopy (IMSCCS) on porous Si and Cu(In{sub x},Ga{sub 1-x})Se{sub 2} solar cells. In this experiment, the solar cells were lightened with sinusoidally modulated monochromatic light. The photocurrent response of the solar cell as a function of modulation frequency is measured as the optoelectronic transfer function of the system. The optoelectronic transfer function introduces the connection between the modulated light intensity and measured AC current of the solar cell. In this study, interaction of free carriers with the density of states of the porous Si and Cu(In{sub x}, Ga{sub 1-x})Se{sub 2} solar cells was studied on the basis of charge transport time by IMSCCS data. (author)

  17. Effect of Trivalent Additions and Processing on Structural and Magnetic Transitions in Ni-Mn-Ga Ferromagnetic Shape Memory Alloys

    OpenAIRE

    R. P. Mathur; Singh, R. K.; Ray, S.; P. Ghosal; Chandrasekaran, V.

    2012-01-01

    Ferromagnetic shape memory Ni50Mn30Ga15Al5-xBx (x = 0, 1, and 4) alloys were prepared by vacuum arc melting and subsequent heat-treatment as well as by melt spinning to investigate the effect of trivalent element additions in ternary Ni-Mn-Ga alloys. The heat-treated alloys containing Al were reported to possess a modulated martensite structure, however alloy containing both Al and B showed a loss of modulated structure in martensite formed. The rapidly solidified alloys on the other hand sho...

  18. GaInN LEDs: straight way for solid state lighting

    Science.gov (United States)

    Zehnder, U.; Hahn, B.; Baur, J.; Peter, M.; Bader, S.; Lugauer, H. J.; Weimar, A.

    2007-09-01

    With the new Generation of InGaN-based thinfilm Chips efficacies of 110/lm/W and output power of 32 mW at 20 mA (5 mm Radial lamp, 438nm, chip-size 255μm x 460μm) are reached. Due to the scalability of the ThinGaN concept chip brightness and efficiency are scalable to larger chip sizes: the brightness achieved for a 1 mm2 ThinGaN Power chip at 350 mA were 495mW (445nm) and 202mW or 100 lm (527nm). White LEDs with phosphorus achieved 102 lm at 350mA, mounted in an OSTAR module with six LED chips 1200 lm were demonstrated at 1000 mA driving current. White emitting automotive headlamp modules with 620lm (5x 1mm2 chip at 700mA) and 41 MCd/m2 as well as green emitting projection modules with 57 MCd/m2 at 2A/mm2 drive current and 12mm2 chip area are realized. These technological improvements demonstrate the straight way of GaInN-LEDs for Solid State lighting.

  19. 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).

  20. Simulation of polarization effects in AlGaN/GaN heterojunction

    Institute of Scientific and Technical Information of China (English)

    LI; Na; ZHAO; Degang; YANG; Hui

    2004-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Palash Das

    2011-01-01

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

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

    Science.gov (United States)

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

    2016-02-01

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

  3. Irreducible Specht modules are signed Young modules

    OpenAIRE

    Hemmer, David J.

    2005-01-01

    Recently Donkin defined signed Young modules as a simultaneous generalization of Young and twisted Young modules for the symmetric group. We show that in odd characteristic, if a Specht module $S^\\lambda$ is irreducible, then $S^\\lambda$ is a signed Young module. Thus the set of irreducible Specht modules coincides with the set of irreducible signed Young modules. This provides evidence for our conjecture that the signed Young modules are precisely the class of indecomposable self-dual module...

  4. Dislocation blocking by AlGaN hot electron injecting layer in the epitaxial growth of GaN terahertz Gunn diode

    Science.gov (United States)

    Li, Liang; Yang, Lin'an; Zhang, Jincheng; Hao, Yue

    2013-09-01

    This paper reports an efficient method to improve the crystal quality of GaN Gunn diode with AlGaN hot electron injecting layer (HEI). An evident reduction of screw dislocation and edge dislocation densities is achieved by the strain management and the enhanced lateral growth in high temperature grown AlGaN HEI layer. Compared with the top hot electron injecting layer (THEI) structure, the bottom hot electron injecting layer (BHEI) structure enhances the crystal quality of transit region due to the growth sequence modulation of HEI layer. A high Hall mobility of 2934 cm2/Vs at 77 K, a nearly flat downtrend of Hall mobility at the temperature ranging from 300 to 573 K, a low intensity of ratio of yellow luminescence band to band edge emission, a narrow band edge emission line-width, and a smooth surface morphology are observed for the BHEI structural epitaxy of Gunn diode, which indicates that AlGaN BHEI structure is a promising candidate for fabrication of GaN Gunn diodes in terahertz regime.

  5. Influence of delta doping on intersubband transition and absorption in AlGaN/GaN step quantum wells for terahertz applications

    Science.gov (United States)

    Tang, Chenjie; Shi, Junxia

    2015-05-01

    Effects of delta doping location and density on intersubband transitions in AlGaN/GaN step quantum wells for terahertz (THz) applications have been investigated by solving Schrödinger and Poisson equations self-consistently. It shows that delta doping near the GaN well/AlGaN step well interface causes a blue-shift, while delta doping in the barrier or near barrier/GaN well and barrier/step well interfaces cause a red-shift first and then a blue-shift with increasing doping density. The shifts are attributed to the combination of many body effect and internal field modulation effect, and can be more than 200% or 70% of the e1-e2 transition energy, as for blue-shift or red-shift, respectively. In addition, the influences of delta-doping location and density on the absorption coefficient are also investigated in detail. Delta doping at the middle of a layer is found much more desirable over uniform-doping in order to improve the absorption coefficient, especially in the step well.

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

    Science.gov (United States)

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

    2011-02-01

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

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

    Science.gov (United States)

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

    2016-11-01

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

  8. Relaxation time and impurity effects on linear and nonlinear refractive index changes in (In,Ga)N-GaN spherical QD

    Science.gov (United States)

    El Ghazi, Haddou; Jorio, Anouar

    2014-10-01

    By means of a combination of Quantum Genetic Algorithm and Hartree-Fock-Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N-GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.

  9. Relaxation time and impurity effects on linear and nonlinear refractive index changes in (In,Ga)N–GaN spherical QD

    Energy Technology Data Exchange (ETDEWEB)

    El Ghazi, Haddou, E-mail: hadghazi@gmail.com [LPS, Faculty of Science, Dhar El Mehrez, BP 1796 Fes-Atlas (Morocco); Special Mathematics, CPGE My Youssef, Rabat (Morocco); Jorio, Anouar [LPS, Faculty of Science, Dhar El Mehrez, BP 1796 Fes-Atlas (Morocco)

    2014-10-01

    By means of a combination of Quantum Genetic Algorithm and Hartree–Fock–Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N–GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity's position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.

  10. Ultraviolet Phototransistors on AlGaN/GaN Heterostructures

    Institute of Scientific and Technical Information of China (English)

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

    2007-01-01

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

  11. 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.

  12. Integrated L-Band T/R Module Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The goal of this Phase II project is to deliver an integrated L-band transmit/receive (T/R) module which will be fabricated from a GaAs-based combined HBT/PHEMT...

  13. Visible light communication using InGaN optical sources with AlInGaP nanomembrane down-converters.

    Science.gov (United States)

    Santos, J M M; Rajbhandari, S; Tsonev, D; Chun, H; Guilhabert, B; Krysa, A B; Kelly, A E; Haas, H; O'Brien, D C; Laurand, N; Dawson, M D

    2016-05-02

    We report free space visible light communication using InGaN sources, namely micro-LEDs and a laser diode, down-converted by a red-emitting AlInGaP multi-quantum-well nanomembrane. In the case of micro-LEDs, the AlInGaP nanomembrane is capillary-bonded between the sapphire window of a micro-LED array and a hemispherical sapphire lens to provide an integrated optical source. The sapphire lens improves the extraction efficiency of the color-converted light. For the case of the down-converted laser diode, one side of the nanomembrane is bonded to a sapphire lens and the other side optionally onto a dielectric mirror; this nanomembrane-lens structure is remotely excited by the laser diode. Data transmission up to 870 Mb/s using pulse amplitude modulation (PAM) with fractionally spaced decision feedback equalizer is demonstrated for the micro-LED-integrated nanomembrane. A data rate of 1.2 Gb/s is achieved using orthogonal frequency division multiplexing (ODFM) with the laser diode pumped sample.

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

    Science.gov (United States)

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

    1982-01-01

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

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

    Science.gov (United States)

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

    2010-04-01

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

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

    OpenAIRE

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

    2013-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-10-05

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

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

    Science.gov (United States)

    2015-02-01

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

  19. Plasmonic modulator based on gain-assisted metal-semiconductor-metal waveguide

    DEFF Research Database (Denmark)

    Babicheva, Viktoriia E.; Kulkova, Irina V.; Malureanu, Radu;

    2012-01-01

    We investigate plasmonic modulators with a gain material to be implemented as ultra-compact and ultra-fast active nanodevices in photonic integrated circuits. We analyze metal-semiconductor-metal (MSM) waveguides with InGaAsP-based active material layers as ultra-compact plasmonic modulators. The...

  20. Heterodyne technique for measuring the amplitude and phase transfer functions of an optical modulator

    DEFF Research Database (Denmark)

    Romstad, Francis Pascal; Birkedal, Dan; Mørk, Jesper

    2002-01-01

    In this letter, we propose a technique based on heterodyne detection for accurately and simultaneously measuring the amplitude and phase transfer functions of an optical modulator. The technique is used to characterize an InGaAsp multiple quantum-well electroabsorption modulator. From...

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

    Science.gov (United States)

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

    2016-09-01

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

  2. *-Modules, co-*-modules and cotilting modules over Noetherian rings

    Institute of Scientific and Technical Information of China (English)

    汪明义; 许永华

    1996-01-01

    Let R be a Noetherian ring. The projectivity and injectivity of modules over R are discussed. The concept of modules is introduced and the descriptions for co-*-modules over R are given. At last, cotilting modules over R are characterized by means of co-*-modules.

  3. Active mode locking at 50 GHz repetition frequency by half-frequency modulation of monolithic semiconductor lasers integrated with electroabsorption modulators

    Science.gov (United States)

    Sato, Kenji; Kotaka, Isamu; Kondo, Yasuhiro; Yamamoto, Mitsuo

    1996-10-01

    Active mode locking achieved at a 50 GHz repetition frequency by modulation at half (25 GHz) the cavity resonance frequency using a monolithic mode-locked InGaAsP laser integrated with an electroabsorption modulator is described. A pulse width of around 3 ps and a high suppression ratio of more than 33 dB of the intensity modulation at the driving frequency are obtained.

  4. Crosstalk study of near infrared InGaAs detectors

    Science.gov (United States)

    Li, Xue; Tang, Hengjing; Li, Tao; Fan, Cui; Shao, Xiumei; Li, Jianwei; Wei, Jun; Gong, Haimei

    2016-05-01

    Crosstalk characteristics of high density FPA detectors attract widespread attention in the application of electro-optical systems. Crosstalk characteristics of near-infrared (NIR) InGaAs photodiodes and focal plane arrays (FPAs) were studied in this paper. The mesa type detector was investigated by using laser beam induced current technique (LBIC) to measure the absorption outside the designed photosensitive area, and the results show that the excess absorption enlarges the crosstalk of the adjacent pixels. The structure optimization using the effective absorption layer between the pixels can effectively reduce the crosstalk to 2.5%. The major crosstalk components of the optimization photodiode come from the electronic signal caused by carrier lateral diffusion. For the planar type detectors, test structures were used to compare the crosstalk of different structures, and the guard ring structure shows good suppression of the crosstalk. Then the back-illuminated 32x32 InGaAs photodiodes with 30μm pitch were designed, and LBIC was used to measure its lateral diffusion of the effective carriers and fill factor of photosensitive area. The results indicate that the fill factor of detectors can reach up to 98% when the diffusion region is optimized, and the minimum response exists between two neighborhood pixels. Based on these crosstalk measurement results and optimizing structure designs, the linear InGaAs photodiodes were designed and thus the InGaAs FPA assembly was fabricated. The assembly shows higher electro-optical performance and good improvement on crosstalk. The assembly was applied in infrared imaging system and modulation transfer function (MTF) of FPA assembly was calculated to be above 0.50. The clear image based on FPA assembly was obtained.

  5. Thruster Module

    Science.gov (United States)

    Andersson, G.

    2015-09-01

    The thruster module described in this paper provides a low but controlled acceleration in a mission which would normally be labelled “microgravity”. The first mission was Cryofenix, where tanks containing liquid hydrogen were used in the experiment. The experiment utilizing the low acceleration is using liquids and requires a precise acceleration profile throughout the mission. Acceleration obtained by payload rotation is not feasible due to that the transversal forces required to change the acceleration will cause undesired liquid turbulence. In order to satisfy the experiment requirements a thruster module was developed by SSC for the Cryofenix mission funded by CNES. The Cryofenix mission had a payload weight of 380 kg and an apogee of about 260 km. The module produces a controlled thrust in flight direction by means of a cold gas system.

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

    OpenAIRE

    Wang Yongjin; Hu Fangren; Hane Kazuhiro

    2011-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-21

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

  8. MQW electroabsorption modulator-integrated DFB laser modules for high-speed transmission

    Science.gov (United States)

    Zhao, Q.; Pan, J. Q.; Zhang, J.; Li, B. X.; Zhou, F.; Wang, B. J.; Wang, L. F.; Zhao, L. J.; Zhou, G. T.; Wang, W.

    2006-06-01

    Details of the design, fabrication and testing of a strained InGaAsP/InGaAsP multiple quantum well (MQW) electroabsorption modulator (EAM) monolithically integrated with a DFB laser by ultra-low-pressure selective area growth (SAG) are presented. The method greatly simplifies the integration process. A study of the controllability of band-gap energy by SAG has been performed. After being completely packaged in a seven-pin butterfly compact module, the device successfully performs 10 Gb s-1 nonreturn to zero (NRZ) operation on uncompensated transmission span >53 km in a standard fibre with a 8.7 dB dynamic extinction ratio. A receiver sensitivity of -18.9 dBm at a bit error rate (BER) of 10-10 is confirmed. 10 GHz short pulse trains with 15.3 ps pulsewidth have also been generated.

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

    Institute of Scientific and Technical Information of China (English)

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

    2009-01-01

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

  10. Monolithic integration on InP of a Wannier Stark modulator with a strained MQW DFB 1.55-micron laser

    Science.gov (United States)

    Allovon, Michel; Fouchet, Sylvie; Harmand, Jean-Christophe; Ougazzaden, Abdallah; Rose, Benoit; Gloukhian, Andre; Devaux, Fabrice

    1995-02-01

    We present the technical approach and the preliminary device results on the first integration of a Wannier Stark (WS) electroabsorption (EA) modulator with a DFB laser on InP. The WS modulator active layer consists of a lattice matched InGaAs-InAlAs superlattice (SL) grown by solid source MBE (Molecular Beam Epitaxy). It is butt-coupled to a laser grown by AP-MOVPE whose active layer includes a strained InGaAsP-InGaAsP MQW stack. Device results cover static performances of integrated lasers and modulators, and measurements of high frequency characteristics (small signal bandwidth and 10 Gb/s eye diagram).

  11. Signed Young Modules and Simple Specht Modules

    OpenAIRE

    Danz, Susanne; Lim, Kay Jin

    2015-01-01

    By a result of Hemmer, every simple Specht module of a finite symmetric group over a field of odd characteristic is a signed Young module. While Specht modules are parametrized by partitions, indecomposable signed Young modules are parametrized by certain pairs of partitions. The main result of this article establishes the signed Young module labels of simple Specht modules. Along the way we prove a number of results concerning indecomposable signed Young modules that are of independent inter...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-11-15

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2013-01-01

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

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

    Science.gov (United States)

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

    2016-07-01

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

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

    Data.gov (United States)

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

  16. Memory Modulation

    NARCIS (Netherlands)

    Roozendaal, Benno; McGaugh, James L.

    2011-01-01

    Our memories are not all created equally strong: Some experiences are well remembered while others are remembered poorly, if at all. Research on memory modulation investigates the neurobiological processes and systems that contribute to such differences in the strength of our memories. Extensive evi

  17. Development of Cu(In,Ga)Se2 Test Coupons for Potential Induced Degradation Studies

    Energy Technology Data Exchange (ETDEWEB)

    Contreras, Miguel A.; Hacke, Peter; Repins, Ingrid

    2016-11-21

    We report on the design, fabrication and accelerated testing of fully encapsulated small area coupons (approximately 7.5cm x 7.5 cm) for the purpose of researching potential induced degradation in Cu(In, Ga)Se2 based PV modules. The fabrication of these coupons enables the study of the solar cells and the materials used in PV module manufacturing such as top and bottom glass covers of different composition (soda-lime glass, high temperature glass, alkaline-free glass, etc), plastic-based top covers, ethylene vinyl acetate and edge seal encapsulation materials. The coupons can also be used to emulate framed and frameless modules that utilize either monolithically interconnected modules or singular cell type of modules. The design of the coupons, their fabrication, the materials used and their testing for 1000 hours under 85 degrees C and 85% RH conditions are presented.

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2002-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-28

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

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

    Science.gov (United States)

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

    2017-04-01

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

  2. 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....

  3. Molecular beam epitaxy engineered III-V semiconductor structures for low-power optically addressed spatial light modulators

    Science.gov (United States)

    Larsson, Anders G.; Maserjian, Joseph

    1992-01-01

    Device approaches are investigated for optically addressed SLMs based on molecular-beam epitaxy (MBE) engineered III-V materials and structures. Strong photooptic effects can be achieved in periodically delta-doped multiple-quantum-well structures, but are still insufficient for high-contrast modulation with only single- or double-pass absorption through active layers of practical thickness. The asymmetric Fabry-Perot cavity approach is employed to permit extinction of light due to interference of light reflected from the front and back surfaces of the cavity. This approach is realized with an all-MBE-grown structure consisting of GaAs/AlAs quarter-wave stack reflector grown over the GaAs substrate as the high reflectance mirror and the GaAs surface as the low reflectance mirror. High-contrast modulation is achieved using a low-power InGaAs/GaAs quantum well laser for the control signal.

  4. Analysis of small-signal intensity modulation of semiconductor lasers taking account of gain suppression

    Indian Academy of Sciences (India)

    Moustafa Ahmed; Ali El-Lafi

    2008-07-01

    This paper demonstrates theoretical characterization of intensity modulation of semiconductor lasers (SL’s). The study is based on a small-signal model to solve the laser rate equations taking into account suppression of optical gain. Analytical forms of the small-signal modulation response and modulation bandwidth are derived. Influences of the bias current, modulation index and modulation frequency as well as gain suppression on modulation characteristics are examined. Computer simulation of the model is applied to 1.55-m InGaAsP lasers. The results show that when the SL is biased far-above threshold, the increase of gain suppression increases both the modulation response and its peak frequency. The modulation bandwidth also increases but the laser damping rate decreases. Quantitative description of the relationships of both modulation bandwidth vs. relaxation frequency and maximum modulation bandwidth vs. nonlinear gain coefficient are presented.

  5. Multiple Applications of GaAs semiconductors

    Science.gov (United States)

    Martel, Jenrené; Wonka, Willy

    2003-03-01

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

  6. On SA, CA, and GA numbers

    CERN Document Server

    Caveney, Geoffrey; Sondow, Jonathan

    2011-01-01

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

  7. Tetrabromidobis(dicyclohexylphosphane-κPdigallium(Ga—Ga

    Directory of Open Access Journals (Sweden)

    Dennis H. Mayo

    2012-10-01

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

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

    Science.gov (United States)

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

    2015-08-01

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

  9. 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...

  10. 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.

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

    Science.gov (United States)

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

    2017-05-01

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

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

    Science.gov (United States)

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

    2014-09-01

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

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

    Science.gov (United States)

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

    2016-04-01

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

  14. Dynamics of longitudinal and transverse modes along the junction plane in GaAlAs stripe lasers

    DEFF Research Database (Denmark)

    Mengel, F; Ostoich, V

    1977-01-01

    Observations of the transient excitation of higher order transverse modes along the junction plane in DH GaAlAs stripe lasers during subnanosecond pulse modulation is reported. These modes are strongly excited at the onset of the light pulse, they decay during 200 ps, and reappear after 400-600 ps...

  15. Martensitic transformation and magnetic properties of Heusler alloy Ni-Fe-Ga ribbon

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Z.H. [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (China)]. E-mail: zhliu@aphy.iphy.ac.cn; Liu, H. [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (China); Zhang, X.X. [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (China); Zhang, M. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Dai, X.F. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Hu, H.N. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Chen, J.L. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Wu, G.H. [State Key Laboratory for Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)]. E-mail: userm201@aphy.iphy.ac.cn

    2004-08-23

    The martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Ni{sub 50+x}Fe{sub 25-x}Ga{sub 25} (x=-1, 0, 1, 2, 3, 4) ribbons have been systematically studied. It has been found that with the increase of Ni concentration, the martensitic transformation temperature increases, but the Curie temperature decreases. Both the two-step thermally induced structural transformation and the one-step transition have been observed in NiFeGa alloys with different compositions. It is found that the two-step transition became the one-step transition after the ribbon being heat treated at 873 K or higher. X-ray diffraction patterns show that only L21->B2 transition occurs in the samples treated at 873 K, while the {gamma} phase will form in the samples treated at higher temperature. Transmission electron microscopy (TEM) studies show that the alloys with martensitic transformation temperature above the room temperature are non-modulated martensite with the large domain size, being different from the stoichiometric Ni{sub 2}FeGa alloy that is a modulated martensite with small domain size. The influences of Fe substitution for Ni in Ni{sub 2}FeGa on the saturation magnetization and exchange interaction are also discussed.

  16. Step buffer layer of Al0.25Ga0.75N/Al0.08Ga0.92N on P-InAlN gate normally-off high electron mobility transistors

    Science.gov (United States)

    Shrestha, Niraj M.; Li, Yiming; Chang, E. Y.

    2016-07-01

    Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable devices for power electronics as they can greatly simplify circuit designs in a cost-effective way. In this work, the electrical characteristics of p-type InAlN gate normally-off AlGaN/GaN HEMTs with a step buffer layer of Al0.25Ga0.75N/Al0.1Ga0.9N is studied numerically. Our device simulation shows that a p-InAlN gate with a step buffer layer allows the transistor to possess normally-off behavior with high drain current and high breakdown voltage simultaneously. The gate modulation by the p-InAlN gate and the induced holes appearing beneath the gate at the GaN/Al0.25Ga0.75N interface is because a hole appearing in the p-InAlN layer can effectively vary the threshold voltage positively. The estimated threshold voltage of the normally-off HEMTs explored is 2.5 V at a drain bias of 25 V, which is 220% higher than the conventional p-AlGaN normally-off AlGaN/GaN gate injection transistor (GIT). Concurrently, the maximum current density of the explored HEMT at a drain bias of 10 V slightly decreases by about 7% (from 240 to 223 mA mm-1). At a drain bias of 15 V, the current density reached 263 mA mm-1. The explored structure is promising owing to tunable positive threshold voltage and the maintenance of similar current density; notably, its breakdown voltage significantly increases by 36% (from 800 V, GIT, to 1086 V). The engineering findings of this study indicate that novel p-InAlN for both the gate and the step buffer layer can feature a high threshold voltage, large current density and high operating voltage for advanced AlGaN/GaN HEMT devices.

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

    Science.gov (United States)

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

    2016-08-12

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

  18. Module Evaluation

    Science.gov (United States)

    2006-02-01

    MODULES IN LIFE TEST CHAMBER (LEFT SIDE) 68 MODULE TRANSMIT TEMP CA1 54.8°C CB1 65.3°C CC1 70.5°C CD1 75.2°C CE1 68.5°C CA2 72.1°C CB2 ...NO. PA (Contractor) PA (MELTS) DRV (Contractor) DRV (MELTS) CA1 058 +11.0 VOLTS +10.3 VOLTS + 7.5 VOLTS + 3.64 VOLTS CB1 085 +11.0 VOLTS +10.13...CE1 032 +11.0 VOLTS + 7.02 VOLTS + 7.5 VOLTS + 4.23 VOLTS CA2 065 +11.0 VOLTS +11.03 VOLTS + 7.5 VOLTS + 7.53 VOLTS CB2 057 +11.0 VOLTS + 9.49

  19. Controllable Schottky barrier in GaSe/graphene heterostructure: the role of interface dipole

    Science.gov (United States)

    Si, Chen; Lin, Zuzhang; Zhou, Jian; Sun, Zhimei

    2017-03-01

    The discoveries of graphene and other related two-dimensional crystals have recently led to a new technology: van der Waals (vdW) heterostructures based on these atomically thin materials. Such a paradigm has been proved promising for a wide range of applications from nanoelectronics to optoelectronics and spintronics. Here, using first-principles calculations, we investigate the electronic structure and interface characteristics of a newly synthesized GaSe/graphene (GaSe/g) vdW heterostructure. We show that the intrinsic electronic properties of GaSe and graphene are both well preserved in the heterostructure, with a Schottky barrier formed at the GaSe/g interface. More interestingly, the band alignment between graphene and GaSe can be effectively modulated by tuning the interfacial distance or applying an external electric filed. This makes the Schottky barrier height (SBH) controllable, which is highly desirable in the electronic and optoelectronic devices based on vdW heterostructures. In particular, the tunability of the interface dipole and potential step is further uncovered to be the underlying mechanism that ensures this controllable tuning of SBH.

  20. High Performance Ultrathin GaAs Solar Cells Enabled with Heterogeneously Integrated Dielectric Periodic Nanostructures.

    Science.gov (United States)

    Lee, Sung-Min; Kwong, Anthony; Jung, Daehwan; Faucher, Joseph; Biswas, Roshni; Shen, Lang; Kang, Dongseok; Lee, Minjoo Larry; Yoon, Jongseung

    2015-10-27

    Due to their favorable materials properties including direct bandgap and high electron mobilities, epitaxially grown III-V compound semiconductors such as gallium arsenide (GaAs) provide unmatched performance over silicon in solar energy harvesting. Nonetheless, their large-scale deployment in terrestrial photovoltaics remains challenging mainly due to the high cost of growing device quality epitaxial materials. In this regard, reducing the thickness of constituent active materials under appropriate light management schemes is a conceptually viable option to lower the cost of GaAs solar cells. Here, we present a type of high efficiency, ultrathin GaAs solar cell that incorporates bifacial photon management enabled by techniques of transfer printing to maximize the absorption and photovoltaic performance without compromising the optimized electronic configuration of planar devices. Nanoimprint lithography and dry etching of titanium dioxide (TiO2) deposited directly on the window layer of GaAs solar cells formed hexagonal arrays of nanoscale posts that serve as lossless photonic nanostructures for antireflection, diffraction, and light trapping in conjunction with a co-integrated rear-surface reflector. Systematic studies on optical and electrical properties and photovoltaic performance in experiments, as well as numerical modeling, quantitatively describe the optimal design rules for ultrathin, nanostructured GaAs solar cells and their integrated modules.

  1. Monolithically integrated enhancement/depletion-mode AlGaN/GaN HEMTs SRAM unit and voltage level shifter using fluorine plasma treatment

    Science.gov (United States)

    Yonghe, Chen; Xuefeng, Zheng; Jincheng, Zhang; Xiaohua, Ma; Yue, Hao

    2016-05-01

    A GaN-based E/D mode direct-couple logic 6 transistors SRAM unit and a voltage level shifter were designed and fabricated. E-mode and D-mode AlGaN/GaN HEMTs were integrated in one wafer using fluorine plasma treatment and using a moderate AlGaN barrier layer heterojunction structure. The 6 transistors SRAM unit consists of two symmetrical E/D mode inverters and two E-mode switch HEMTs. The output low and high voltage of the SRAM unit are 0.95 and 0.07 V at a voltage supply of 1 V. The voltage level shifter lowers the supply voltage using four Ni-AlGaN Schottky diodes in a series at a positive supply voltage of 6 V and a negative supply voltage of -6 V. By controlling the states of inverter modules of the level shifter in turn, the level shifter offers two channel voltage outputs of -0.5 and -5 V. The flip voltage of the level shifter is 0.76 V. Both the SRAM unit and voltage shifter operate correctly, demonstrating the promising potential for GaN-based E/D mode digital and analog integrated circuits. Several considerations are proposed to avoid the influence of threshold voltage degradation of D-mode and E-mode HEMT on the operation of the circuit. Project supported by the National Natural Science Foundation of China (No. 61334002), the Opening Project of Science and Technology on Reliability Physics and Application Technology of Electronic Component Laboratory (No. ZHD201206), and the Program for New Century Excellent Talents in University (No. NCET-12-0915).

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-02-07

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

  3. Module descriptor

    DEFF Research Database (Denmark)

    Vincenti, Gordon; Klausen, Bodil; Kjær Jensen, Jesper

    2016-01-01

    The Module Descriptor including a Teacher’s Guide explains and describes how to work innovatively and co-creatively with wicked problems and young people. The descriptor shows how interested educators and lecturers in Europe can copy the lessons of the Erasmus+ project HIP when teaching their own...... students how to include marginalized young people and practitioners in the education of future social workers and social educators....

  4. Module descriptor

    DEFF Research Database (Denmark)

    Vincenti, Gordon; Klausen, Bodil; Kjær Jensen, Jesper

    2016-01-01

    The Module Descriptor including a Teacher’s Guide explains and describes how to work innovatively and co-creatively with wicked problems and young people. The descriptor shows how interested educators and lecturers in Europe can copy the lessons of the Erasmus+ project HIP when teaching their own...... students how to include marginalized young people and practitioners in the education of future social workers and social educators....

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

    Institute of Scientific and Technical Information of China (English)

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

    2006-01-01

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

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

    Science.gov (United States)

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

    2016-10-01

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

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

    OpenAIRE

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

    2001-01-01

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

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

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

    Science.gov (United States)

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

    2015-08-01

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

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

    Science.gov (United States)

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

    2004-09-01

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

  11. COMPOSITION TRIANGLE DIAGRAMS OF Ni-Mn-Ga MAGNETIC SHAPE MEMORY ALLOYS

    Institute of Scientific and Technical Information of China (English)

    Y.F. Wang; J.M. Wang; C.B. Jiang; H.B. Xu

    2006-01-01

    A statistical work has been done to collect the composition ranges of Ni-Mn-Ga alloys exhibiting different structures and martensite start temperature (Ms), large magnetostrain or the co-existence of magnetic and structural transitions. The alloys with five-layered ( 5M), seven-layered(7M) modulated and non-modulated (T) martensitic structures were mapped in the graph. An empirical formula has been presented to reflect the effect of elements nickel (Ni), manganese (Mn)and gallium (Ga), on the martensite start temperature (Ms). The martensitic structure is sensitive to the composition and the martensitic transformation temperature is most drastically affected by the Ni content. The alloys with large magnetostrain or co-existence effect of the magnetic and structural transitions were also listed in a limited area.

  12. Studies of Ga NMR and NQR in SrGa4

    Science.gov (United States)

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

    2015-04-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-04-15

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

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

    Science.gov (United States)

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

    2016-11-01

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

  15. Automation synthesis modules review.

    Science.gov (United States)

    Boschi, S; Lodi, F; Malizia, C; Cicoria, G; Marengo, M

    2013-06-01

    The introduction of (68)Ga labelled tracers has changed the diagnostic approach to neuroendocrine tumours and the availability of a reliable, long-lived (68)Ge/(68)Ga generator has been at the bases of the development of (68)Ga radiopharmacy. The huge increase in clinical demand, the impact of regulatory issues and a careful radioprotection of the operators have boosted for extensive automation of the production process. The development of automated systems for (68)Ga radiochemistry, different engineering and software strategies and post-processing of the eluate were discussed along with impact of automation with regulations. Copyright © 2012 Elsevier Ltd. All rights reserved.

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

    Science.gov (United States)

    2010-05-17

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

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

    Science.gov (United States)

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

    2016-08-01

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

  18. Bulk ammonothermal GaN

    Science.gov (United States)

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

    2009-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-12-15

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

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

    Directory of Open Access Journals (Sweden)

    G. Naresh-Kumar

    2014-12-01

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

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

    Science.gov (United States)

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

    2017-02-02

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

  2. Anelasticity of GaN Epitaxial Layer in GaN LED

    Science.gov (United States)

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

    2016-10-01

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

  3. Micro-modulated luminescence tomography

    CERN Document Server

    Cong, Wenxiang; Wang, Chao; Wang, Ge

    2013-01-01

    Imaging depth of optical microscopy has been fundamentally limited to millimeter or sub-millimeter due to light scattering. X-ray microscopy can resolve spatial details of few microns deeply inside a sample but the contrast resolution is still inadequate to depict heterogeneous features at cellular or sub-cellular levels. To enhance and enrich biological contrast at large imaging depth, various nanoparticles are introduced and become essential to basic research and molecular medicine. Nanoparticles can be functionalized as imaging probes, similar to fluorescent and bioluminescent proteins. LiGa5O8:Cr3+ nanoparticles were recently synthesized to facilitate luminescence energy storage with x-ray pre-excitation and the subsequently stimulated luminescence emission by visible/near-infrared (NIR) light. In this paper, we suggest a micro-modulated luminescence tomography (MLT) approach to quantify a nanophosphor distribution in a thick biological sample with high resolution. Our numerical simulation studies demonst...

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

    Institute of Scientific and Technical Information of China (English)

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

    2005-01-01

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

  5. Electronic- and band-structure evolution in low-doped (Ga,Mn)As

    OpenAIRE

    Yastrubchak, O.; J. Sadowski; Krzyzanowska, H.; Gluba, L.; Zuk, J.; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    2013-01-01

    Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap transition energy with increasing Mn content in very low-doped ...

  6. Photovoltaic module and module arrays

    Science.gov (United States)

    Botkin, Jonathan; Graves, Simon; Lenox, Carl J. S.; Culligan, Matthew; Danning, Matt

    2012-07-17

    A photovoltaic (PV) module including a PV device and a frame. The PV device has a PV laminate defining a perimeter and a major plane. The frame is assembled to and encases the laminate perimeter, and includes leading, trailing, and side frame members, and an arm that forms a support face opposite the laminate. The support face is adapted for placement against a horizontal installation surface, to support and orient the laminate in a non-parallel or tilted arrangement. Upon final assembly, the laminate and the frame combine to define a unitary structure. The frame can orient the laminate at an angle in the range of 3.degree.-7.degree. from horizontal, and can be entirely formed of a polymeric material. Optionally, the arm incorporates integral feature(s) that facilitate interconnection with corresponding features of a second, identically formed PV module.

  7. Orbital pseudotumor imaged with Ga-67 citrate

    Energy Technology Data Exchange (ETDEWEB)

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

    1989-11-01

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

  8. 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.

  9. Optical Properties of GaSb Nanofibers

    Directory of Open Access Journals (Sweden)

    Perez-Bergquist Alejandro

    2011-01-01

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

  10. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-05-04

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

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

    Science.gov (United States)

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

    2014-01-24

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-02-15

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

  14. AlGaN/GaN HEMT技术与其专利申请分析研究

    Institute of Scientific and Technical Information of China (English)

    2016-01-01

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

  15. Bandgap engineering of GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-05-15

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

  16. Gallium incorporation kinetics during GSMBE of GaN

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-11-01

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

  17. Efficient Exciton Transfer from In0.35Ga0.65As Template into InAs Quantum Dots Grown on GaAs (311)B Substrates

    Institute of Scientific and Technical Information of China (English)

    WANG Fang-Zhen; CHEN Zhang-Hai; GONG Qian; R. N(o)tzel; BAI Li-Hui; SHEN Xue-Chu

    2006-01-01

    @@ Atomic force microscopy (AFM) and power-dependent micro-photoluminescence (μ-PL) spectroscopy are used to study the structure and exciton energy states in InAs quantum dots (QDs) grown on an In0.35 Ga0.65As template on GaAs (311)B. The In0.35Ga0.65As template, consisting of a two-dimensionally modulated layer of closely packed connected cells, has a remarkable effect on the optical properties of the InAs QDs. By comparing the emission spectra of the samples without and with InAs QDs and the work carried out by Gong et al. [J. Cryst.Growth 251 (2003) 150; Appl. Phys. Lett. 81 (2002) 3254] we conclude that the existence of the In0.35Ga0.65As template enhances the photo-absorption and therefore the exciton emission from the QDs due to efficient exciton transfer from the template into the QDs. Furthermore, the PL emission from the QDs clearly reveals four discrete energy levels, S, P, D, and F with increasing excitation power.

  18. Reverse blocking characteristics and mechanisms in Schottky-drain AlGaN/GaN HEMT with a drain field plate and floating field plates

    Science.gov (United States)

    Wei, Mao; Wei-Bo, She; Cui, Yang; Jin-Feng, Zhang; Xue-Feng, Zheng; Chong, Wang; Yue, Hao

    2016-01-01

    In this paper, a novel AlGaN/GaN HEMT with a Schottky drain and a compound field plate (SD-CFP HEMT) is presented for the purpose of better reverse blocking capability. The compound field plate (CFP) consists of a drain field plate (DFP) and several floating field plates (FFPs). The physical mechanisms of the CFP to improve the reverse breakdown voltage and to modulate the distributions of channel electric field and potential are investigated by two-dimensional numerical simulations with Silvaco-ATLAS. Compared with the HEMT with a Schottky drain (SD HEMT) and the HEMT with a Schottky drain and a DFP (SD-FP HEMT), the superiorities of SD-CFP HEMT lie in the continuous improvement of the reverse breakdown voltage by increasing the number of FFPs and in the same fabrication procedure as the SD-FP HEMT. Two useful optimization laws for the SD-CFP HEMTs are found and extracted from simulation results. The relationship between the number of the FFPs and the reverse breakdown voltage as well as the FP efficiency in SD-CFP HEMTs are discussed. The results in this paper demonstrate a great potential of CFP for enhancing the reverse blocking ability in AlGaN/GaN HEMT and may be of great value and significance in the design and actual manufacture of SD-CFP HEMTs. Project supported by the National Natural Science Foundation of China (Grant Nos. 61204085, 61334002, 61306017, 61474091, 61574112, and 61574110).

  19. Tuning carrier lifetime in InGaN/GaN LEDs via strain compensation for high-speed visible light communication

    Science.gov (United States)

    Du, Chunhua; Huang, Xin; Jiang, Chunyan; Pu, Xiong; Zhao, Zhenfu; Jing, Liang; Hu, Weiguo; Wang, Zhong Lin

    2016-11-01

    In recent years, visible light communication (VLC) technology has attracted intensive attention due to its huge potential in superior processing ability and fast data transmission. The transmission rate relies on the modulation bandwidth, which is predominantly determined by the minority-carrier lifetime in III-group nitride semiconductors. In this paper, the carrier dynamic process under a stress field was studied for the first time, and the carrier recombination lifetime was calculated within the framework of quantum perturbation theory. Owing to the intrinsic strain due to the lattice mismatch between InGaN and GaN, the wave functions for the holes and electrons are misaligned in an InGaN/GaN device. By applying an external strain that “cancels” the internal strain, the overlap between the wave functions can be maximized so that the lifetime of the carrier is greatly reduced. As a result, the maximum speed of a single chip was increased from 54 MHz up to 117 MHz in a blue LED chip under 0.14% compressive strain. Finally, a bandwidth contour plot depending on the stress and operating wavelength was calculated to guide VLC chip design and stress optimization.

  20. Effects of threading dislocations on drain current dispersion and slow transients in unpassivated AlGaN/GaN/Si heterostructure field-effect transistors

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Saptarsi, E-mail: saptarsi123@gmail.com; Dinara, Syed Mukulika; Mukhopadhyay, Partha; Jana, Sanjay K.; Bag, Ankush; Kabi, Sanjib [Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Chakraborty, Apurba [Department of E and E C E, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Chang, Edward Yi [Department of Material Science and Engineering, National Chiao Tung University, Hsinchu 30050, Taiwan (China); Biswas, Dhrubes [Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Department of E and E C E, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India)

    2014-08-18

    Current transient analysis combined with response to pulsed bias drives have been used to explore the possibilities of threading dislocations affecting the current dispersion characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs). A growth strategy is developed to modulate the dislocation density among the heterostructures grown on silicon by plasma-assisted molecular-beam epitaxy. Slow pulsed I-V measurements show severe compressions and appear to be significantly dependent on the threading dislocation density. By analyzing the corresponding slow detrapping process, a deep-level trap with emission time constant in the order of seconds was identified as the cause. Among the specimens, both in the epilayers and at the surface, the number of dislocations was found to have a notable influence on the spatial distribution of deep-level trap density. The observations confirm that the commonly observed degraded frequency performance among AlGaN/GaN HFETs in the form of DC-radio frequency dispersions can at least partly be correlated with threading dislocation density.

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

    CERN Document Server

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

    2002-01-01

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

  2. The QTL GNP1 Encodes GA20ox1, Which Increases Grain Number and Yield by Increasing Cytokinin Activity in Rice Panicle Meristems

    Science.gov (United States)

    Mi, Xue-Fei; Shan, Jun-Xiang; Xu, Jian-Long

    2016-01-01

    Cytokinins and gibberellins (GAs) play antagonistic roles in regulating reproductive meristem activity. Cytokinins have positive effects on meristem activity and maintenance. During inflorescence meristem development, cytokinin biosynthesis is activated via a KNOX-mediated pathway. Increased cytokinin activity leads to higher grain number, whereas GAs negatively affect meristem activity. The GA biosynthesis genes GA20oxs are negatively regulated by KNOX proteins. KNOX proteins function as modulators, balancing cytokinin and GA activity in the meristem. However, little is known about the crosstalk among cytokinin and GA regulators together with KNOX proteins and how KNOX-mediated dynamic balancing of hormonal activity functions. Through map-based cloning of QTLs, we cloned a GA biosynthesis gene, Grain Number per Panicle1 (GNP1), which encodes rice GA20ox1. The grain number and yield of NIL-GNP1TQ were significantly higher than those of isogenic control (Lemont). Sequence variations in its promoter region increased the levels of GNP1 transcripts, which were enriched in the apical regions of inflorescence meristems in NIL-GNP1TQ. We propose that cytokinin activity increased due to a KNOX-mediated transcriptional feedback loop resulting from the higher GNP1 transcript levels, in turn leading to increased expression of the GA catabolism genes GA2oxs and reduced GA1 and GA3 accumulation. This rebalancing process increased cytokinin activity, thereby increasing grain number and grain yield in rice. These findings uncover important, novel roles of GAs in rice florescence meristem development and provide new insights into the crosstalk between cytokinin and GA underlying development process. PMID:27764111

  3. The QTL GNP1 Encodes GA20ox1, Which Increases Grain Number and Yield by Increasing Cytokinin Activity in Rice Panicle Meristems.

    Science.gov (United States)

    Wu, Yuan; Wang, Yun; Mi, Xue-Fei; Shan, Jun-Xiang; Li, Xin-Min; Xu, Jian-Long; Lin, Hong-Xuan

    2016-10-01

    Cytokinins and gibberellins (GAs) play antagonistic roles in regulating reproductive meristem activity. Cytokinins have positive effects on meristem activity and maintenance. During inflorescence meristem development, cytokinin biosynthesis is activated via a KNOX-mediated pathway. Increased cytokinin activity leads to higher grain number, whereas GAs negatively affect meristem activity. The GA biosynthesis genes GA20oxs are negatively regulated by KNOX proteins. KNOX proteins function as modulators, balancing cytokinin and GA activity in the meristem. However, little is known about the crosstalk among cytokinin and GA regulators together with KNOX proteins and how KNOX-mediated dynamic balancing of hormonal activity functions. Through map-based cloning of QTLs, we cloned a GA biosynthesis gene, Grain Number per Panicle1 (GNP1), which encodes rice GA20ox1. The grain number and yield of NIL-GNP1TQ were significantly higher than those of isogenic control (Lemont). Sequence variations in its promoter region increased the levels of GNP1 transcripts, which were enriched in the apical regions of inflorescence meristems in NIL-GNP1TQ. We propose that cytokinin activity increased due to a KNOX-mediated transcriptional feedback loop resulting from the higher GNP1 transcript levels, in turn leading to increased expression of the GA catabolism genes GA2oxs and reduced GA1 and GA3 accumulation. This rebalancing process increased cytokinin activity, thereby increasing grain number and grain yield in rice. These findings uncover important, novel roles of GAs in rice florescence meristem development and provide new insights into the crosstalk between cytokinin and GA underlying development process.

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

    Institute of Scientific and Technical Information of China (English)

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

    2012-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-03-01

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

  6. InGaAs/GaAs, strained-layer superlattice (SLS), junction photodetectors, LED's, injection LASER's and FET's for optelectronic IC applications

    Energy Technology Data Exchange (ETDEWEB)

    Zipperian, T.E.; Dawson, L.R.; Barnes, C.E.; Wiczer, J.J.; Osbourn, G.C.

    1984-01-01

    A set of optoelectronic devices including p/sup -/n junction photodetectors, emitters (both an LED and a stripe-geometry, injection LASER), and a gain device have been fabricated from In/sub 0/./sub 2/Ga/sub 0/./sub 8/As/GaAs strained-layer superlattice (SLS) material. The photodetectors have demonstrated a peak external quantum efficiency at zero volts reverse bias uncorrected for surface reflection) of 50% at 770nm and an optical absorption edge at 1050nm. Both the LED and injection LASER have peak, room temperature, emission wavelengths near 1020nm. The LASER exhibited cw, 77k operation at 976nm with a threshold current of 95mA, the first reported cw operation of an InGaAs/GaAs SLS LASER. Previously reported studies of prototype, double-gate, modulation-doped FETs (channel length = 2.5um) have demonstrated peak intrinsic transconductances of 120mS/mm at room temperature and 190mS/mm at 77K. These encouraging photodetector, LED, LASER, and FET results demonstrate that useful optical and electronic devices can be fabricated from mismatched materials and that the InGaAs/GaAs SLS system in an attractive candidate for integrated optoelectronic applications.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-09-15

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

  8. Dilute GaAsN and GaInAsN grown by liquid phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-04-01

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

  9. Dilute GaAsN and GaInAsN grown by liquid phase epitaxy

    Science.gov (United States)

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

    2010-04-01

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

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

    Science.gov (United States)

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

    1997-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-12-01

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

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

    Science.gov (United States)

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

    2017-01-01

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

  13. High speed gain coupled DFB laser diode integrated with MQW electroabsorption modulator

    CERN Document Server

    Kim, M G; Park, S S; Oh, D K; Lee, H T; Kim, H M; Pyun, K E

    1998-01-01

    We have demonstrated stable modulation characteristics of the gain coupled distributed feedback(GC-DFB) laser diode integrated with butt-coupled InGaAsP/InGaAsP strain compensated MQW(multiple-Quantum-well) modulator for high speed optical transmission. For this purpose, we have adopted the InGaAsP/InGaAsP strain compensated MQW structure for the EA modulator and n-doped InGaAs absorptive grating for DFB laser. The typical threshold current and slope efficiency were about 15 mA and 0.1 mW/mA, respectively. The extinction ratio of fabricated integrated device was about 15 dB at -2 V, and the small signal bandwidth was shown to be around 17GHz. We also found that the alpha parameter becomes negative at below a -0.6 V bias voltage. We transmitted 10 Gbps NRZ electrical signal over 90 km of standard single mode optical fiber (SMF). A clearly opened eye diagram was observed in the modulated output.

  14. Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn)As epitaxial layers

    Science.gov (United States)

    Yastrubchak, O.; Wosinski, T.; Gluba, L.; Andrearczyk, T.; Domagala, J. Z.; Żuk, J.; Sadowski, J.

    2014-01-01

    The effect of outdiffusion of Mn interstitials from (Ga,Mn)As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn)As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn)As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn)As, in agreement with the Zener model for ferromagnetic semiconductors.

  15. High Quality GaAs Epilayers Grown on Si Substrate Using 100 nm Ge Buffer Layer

    Directory of Open Access Journals (Sweden)

    Wei-Cheng Kuo

    2016-01-01

    Full Text Available We present high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers. The thin Ge buffer layers were modulated by hydrogen flow rate from 60 to 90 sccm to improve crystal quality by electron cyclotron resonance chemical vapor deposition (ECR-CVD at low growth temperature (180°C. The GaAs and Ge epilayers quality was verified by X-ray diffraction (XRD and spectroscopy ellipsometry (SE. The full width at half maximum (FWHM of the Ge and GaAs epilayers in XRD is 406 arcsec and 220 arcsec, respectively. In addition, the GaAs/Ge/Si interface is observed by transmission electron microscopy (TEM to demonstrate the epitaxial growth. The defects at GaAs/Ge interface are localized within a few nanometers. It is clearly showed that the dislocation is well suppressed. The quality of the Ge buffer layer is the key of III–V/Si tandem cell. Therefore, the high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers is suitable to develop the low cost and high efficiency III–V/Si tandem solar cells.

  16. Free-space and underwater GHz data transmission using AlGaInN laser diode technology

    Science.gov (United States)

    Najda, S. P.; Perlin, P.; Suski, T.; Marona, L.; Boćkowski, M.; Leszczyński, M.; Wisniewski, P.; Czernecki, R.; Kucharski, R.; Targowski, G.; Watson, S.; Kelly, A. E.

    2016-05-01

    Laser diodes fabricated from the AlGaInN material system is an emerging technology for defence and security applications; in particular for free space laser communication. Conventional underwater communication is done acoustically with very slow data rates, short reach, and vulnurable for interception. AlGaInN blue-green laser diode technology allows the possibility of both airbourne links and underwater telecom that operate at very fast data rates (GHz), long reach (100's of metres underwater) and can also be quantum encrypted. The latest developments in AlGaInN laser diode technology are reviewed for defence and security applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Galliumnitride (GaN) blue laser diode is reported in free-space and underwater.

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

    Institute of Scientific and Technical Information of China (English)

    郑丽萍; 严北平; 孙海锋; 刘新宇; 和致经; 吴德馨

    2003-01-01

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

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

    Directory of Open Access Journals (Sweden)

    María Luisa Soto-Montenegro

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-02-01

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

  20. MEnDiGa: A Minimal Engine for Digital Games

    Directory of Open Access Journals (Sweden)

    Filipe M. B. Boaventura

    2017-01-01

    Full Text Available Game engines generate high dependence of developed games on provided implementation resources. Feature modeling is a technique that captures commonalities and variabilities results of domain analysis to provide a basis for automated configuration of concrete products. This paper presents the Minimal Engine for Digital Games (MEnDiGa, a simplified collection of game assets based on game features capable of building small and casual games regardless of their implementation resources. It presents minimal features in a representative hierarchy of spatial and game elements along with basic behaviors and event support related to game logic features. It also presents modules of code to represent, interpret, and adapt game features to provide the execution of configured games in multiple game platforms. As a proof of concept, a clone of the Doodle Jump game was developed using MEnDiGa assets and compared with original game version. As a result, a new G-factor based approach for game construction is provided, which is able to separate the core of game elements from the implementation itself in an independent, reusable, and large-scale way.

  1. Low Cost Fiber Optic Module Development Program.

    Science.gov (United States)

    1979-12-01

    159.04 G&A @28% 24.89 28.63 SUBTOTAL 163.19 187.67 PROFIT @12% 19.58 22.52 TOTAL $ 182.77 $ 210.19 2 manufacturing aids should be performed with the...Characteristics Parameter Test Condition Min.lTypical Max. Unit High-level input voltage, VIH --- 2.0 2.4 --- V Low-level input voltage, VIL --- 0.4 0.8 V...retaining plate, and ceramic substrate temperatures were measured with the module under different operating modes at 250C and 950C ambient temperature. A

  2. Characteristics of GaN-based light emitting diodes with different thicknesses of buffer layer grown by HVPE and MOCVD

    Science.gov (United States)

    Tian, Pengfei; Edwards, Paul R.; Wallace, Michael J.; Martin, Robert W.; McKendry, Jonathan J. D.; Gu, Erdan; Dawson, Martin D.; Qiu, Zhi-Jun; Jia, Chuanyu; Chen, Zhizhong; Zhang, Guoyi; Zheng, Lirong; Liu, Ran

    2017-02-01

    GaN-based light emitting diodes (LEDs) have been fabricated on sapphire substrates with different thicknesses of GaN buffer layer grown by a combination of hydride vapor phase epitaxy and metalorganic chemical vapor deposition. We analyzed the LED efficiency and modulation characteristics with buffer thicknesses of 12 μm and 30 μm. With the buffer thickness increase, cathodoluminescence hyperspectral imaging shows that the dislocation density in the buffer layer decreases from  ∼1.3  ×  108 cm‑2 to  ∼1.0  ×  108 cm‑2, and Raman spectra suggest that the compressive stress in the quantum wells is partly relaxed, which leads to a large blue shift in the peak emission wavelength of the photoluminescence and electroluminescent spectra. The combined effects of the low dislocation density and stress relaxation lead to improvements in the efficiency of LEDs with the 30 μm GaN buffer, but the electrical-to-optical modulation bandwidth is higher for the LEDs with the 12 μm GaN buffer. A rate equation analysis suggests that defect-related nonradiative recombination can help increase the modulation bandwidth but reduce the LED efficiency at low currents, suggesting that a compromise should be made in the choice of defect density.

  3. Biological modulation of tectonics

    Science.gov (United States)

    Sleep, N. H.; Bird, D. K.

    2008-12-01

    Photosynthesis has had geologic consequences over the Earth's history. In addition to modifying Earth's atmosphere and ocean chemistry, it has also modulated tectonic processes through enhanced weathering and modification of the nature and composition of sedimentary rocks within fold mountain belts and convergent margins. Molecular biological studies indicate that bacterial photosynthesis evolved just once and that most bacterial clades descend from this photosynthetic common ancestor. Iron-based photosynthesis (ideally 4FeO + CO2 + H2O = 2Fe2O3 + CH2O) was the most bountiful anoxygenic niche on land. The back reaction provided energy to heterotrophic microbes and returned FeO to the photosynthetic microbes. Bacterial land colonists evolved into ecosystems that effectively weathered FeO-bearing minerals and volcanic glass. Clays, sands, and dissolved cations from the weathering process entered the ocean and formed our familiar classes sedimentary rocks: shales, sandstones, and carbonates. Marine photosynthesis caused organic carbon to accumulate in black shales. In contrast, non-photosynthetic ecosystems do not cause organic carbon to accumulate in shale. These evolutionary events occurred before 3.8 Ga as black shales are among the oldest rock types (Rosing and Frei, Earth Planet. Sci. Lett. 217, 237-244, 2004). Thick sedimentary sequences deformed into fold mountain belts. They remelted at depth to form granitic rocks (Rosing et al., Palaeoclimatol. Palaeoecol. 232, 99-11, 2006). Regions of outcropping low-FeO rocks including granites, quartzites, and some shales were a direct result. This dearth of FeO favored the evolution of oxic photosynthesis of cyanobacteria from photosynthetic soil bacteria. Black shales have an additional modulation effect on tectonics as they concentrate radioactive elements, particularly uranium (e.g. so that the surface heat flow varies by a factor of ca. 2). Thick sequences of black shales at continental rises of passive margins are

  4. MEMORY MODULATION

    Science.gov (United States)

    Roozendaal, Benno; McGaugh, James L.

    2011-01-01

    Our memories are not all created equally strong: Some experiences are well remembered while others are remembered poorly, if at all. Research on memory modulation investigates the neurobiological processes and systems that contribute to such differences in the strength of our memories. Extensive evidence from both animal and human research indicates that emotionally significant experiences activate hormonal and brain systems that regulate the consolidation of newly acquired memories. These effects are integrated through noradrenergic activation of the basolateral amygdala which regulates memory consolidation via interactions with many other brain regions involved in consolidating memories of recent experiences. Modulatory systems not only influence neurobiological processes underlying the consolidation of new information, but also affect other mnemonic processes, including memory extinction, memory recall and working memory. In contrast to their enhancing effects on consolidation, adrenal stress hormones impair memory retrieval and working memory. Such effects, as with memory consolidation, require noradrenergic activation of the basolateral amygdala and interactions with other brain regions. PMID:22122145

  5. X-ray standing-wave study of (AlAs){sub m}(GaAs){sub n} short-period superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Lessmann, A.; Brennan, S.; Munkholm, A. [Stanford Synchrotron Radiation Laboratory SSRL/SLAC, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Schuster, M.; Riechert, H. [Siemens AG, Corporate Technology, Otto-Hahn-Ring 6, D-81739 Munich (Germany); Materlik, G. [Hamburger Synchrotronstrahlungslabor HASYLAB am Deutschen Elektronen-Synchrotron DESY, Notkestrasse 85, D-22603 Hamburg (Germany)

    1999-04-01

    X-ray standing-waves (XSW) are used for an investigation of the structure of (AlAs){sub m}(GaAs){sub n} short-period superlattices (SL{close_quote}s). The XSW induced modulation of x-ray fluorescence from the Al, As, and Ga atoms and the total photoelectron yield are monitored around the 0th order SL satellite (AlAs)(GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the specific shape of these modulations and the sample reflectivity, an atomic model about the interfaces is derived. This is accomplished by comparing the experimental data with dynamical calculations of x-ray wavefield distribution and reflectivity, which are based on the Takagi-Taupin equation. The fluorescence measurements at the 0th order SL satellite reveal a high crystalline order in the AlAs layers of the short-period SL, whereas in the GaAs layers, a fraction of the Ga and As atoms is not on the ideal lattice positions. From the analysis, a model of the atomic distribution along the [001] direction can be determined. This reveals that at each internal interface in the GaAs layers, two Ga atom planes are shifted by up to 0.035 nm and one As atom plane by 0.023 nm. At each interface, the shifts are directed towards the substrate. In addition, the XSW field at the GaAs(004) substrate reflection results in a moir{acute e} or beating effect in the SL structure, which can be used to determine the information depth {Lambda}{sub e} of total electron-yield measurements in a more detailed approach. {copyright} {ital 1999} {ital The American Physical Society}

  6. Radiation-induced resistance oscillation and instability in GaAS/A1GaAS heterostructure under transverse magnetic fields

    Institute of Scientific and Technical Information of China (English)

    Yang Gui; Tu Bi-Hong; Li Guo-Hui; Zhao Hong-Wei; Zhou Shi-Ping

    2008-01-01

    This paper studies dynamics of a modulation-doped GaAs/AlGaAs heterostructure under transverse magnetic fields and microwave radiations. It finds that negative differential conductivity, due to the real-space electron transfer and delayed dielectric relaxation of the interface potential barrier, can lead to complex behaviours when a relatively small magnetic field is applied. Quasiperiodicity, frequency-locking and the routes from period-doubling to chaos are found. Under a large magnetic field, however, two time-independent homogeneous steady states exist; and the longitudinal resistance of the system shows an interesting oscillation with period tuned by the ratio of microwave radiation frequency ω to the cyclotron frequency we and local minima at ω/ωc= integer + 1/4.

  7. Accelerated aging of GaAs concentrator solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Gregory, P.E.

    1982-04-01

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

  8. Ultrafast Coercivity Dynamics in GaMnAs

    Science.gov (United States)

    Hall, Kimberley; Zahn, Jeremy; March, Samuel; Liu, Xinyu; Furdyna, Jacek

    2008-03-01

    The hole-mediated ferromagnetism in III-Mn-V diluted magnetic semiconductors opens up a whole host of possibilities for future multifunctional devices. Control over the ferromagnetic properties in these materials through hole density modulation has been demonstrated using electrical gates [1] and CW optical excitation [2], and more recently using femtosecond optical excitation [3,4]. Using time-resolved magneto-optical Kerr Effect spectroscopy, we have measured the magnetization and coercivity dynamics in GaMnAs. Our experiments reveal a subpicosecond ferromagnetic to paramagnetic phase transition followed by coercivity enhancement on longer time scales. Our findings are promising for possible applications in ultrafast, nonthermal magneto-optical recording using diluted magnetic semiconductors. [1] H. Ohno et al., Nature 408, 944 (2000). [2] S. Koshihara et al., Phys. Rev. Lett. 78, 4617 (1997). [3] J. Wang et al., Phys. Rev. Lett. 95, 167401 (2005). [4] J. Wang et al., Phys. Rev. Lett. 98, 217401 (2007).

  9. Ultra-low inductance design for a GaN HEMT based 3L-ANPC inverter

    OpenAIRE

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

    2016-01-01

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

  10. Enhancement of the Modulation Bandwidth for surface Plasmon coupled LEDs for Visible Light Communication

    DEFF Research Database (Denmark)

    Li, Jiehui; Fadil, Ahmed; Ou, Haiyan

    2016-01-01

    The modulation bandwidth of surface plasmon coupled GaN-based LEDs is increased by ~1.2 times to 434.5 MHz compared with normal LED by applying Ag nanoparticles. These findings will help for the industrialization of VLC system.......The modulation bandwidth of surface plasmon coupled GaN-based LEDs is increased by ~1.2 times to 434.5 MHz compared with normal LED by applying Ag nanoparticles. These findings will help for the industrialization of VLC system....

  11. Effect of tunneling injection on the modulation response of quantum dot lasers

    Directory of Open Access Journals (Sweden)

    Y. Yekta kiya

    2014-03-01

    Full Text Available In this paper, modulation bandwidth characteristics of InGaAs/GaAs quantum dot (QD laser were theoretically investigated. Simulation was done by using the fourth order Runge-Kutta method. Effect of carrier relaxation life time, temperature and current density on characteristics of tunneling injection QD laser (TIL and conventional QD laser (CL were analyzed. Results showed that tunneling injection in QD laser increases the modulation bandwidth indicating that it is very useful for using in the fiber optic communication systems.

  12. 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.

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

  14. 60Co gamma radiation effect on AlGaN/AlN/GaN HEMT devices

    Institute of Scientific and Technical Information of China (English)

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

    2013-01-01

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

  15. 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.

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

    Science.gov (United States)

    Biswas, Dipankar; Panda, Siddhartha

    2013-07-01

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

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

    Science.gov (United States)

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

    2017-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-02-15

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

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

    Science.gov (United States)

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

    2013-02-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-01-21

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

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

    Science.gov (United States)

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

    2008-12-01

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

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

    Science.gov (United States)

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

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

  3. 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%.

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

    Science.gov (United States)

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

    2016-05-01

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

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

    Science.gov (United States)

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

    1998-01-01

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

  6. 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.

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

    Directory of Open Access Journals (Sweden)

    M. D. Yang

    2009-01-01

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

  8. 68Ga-triacetylfusarinine C and 68Ga-ferrioxamine E for Aspergillus infection imaging: uptake specificity in various microorganisms

    NARCIS (Netherlands)

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

    2014-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-12-15

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

  10. 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...

  11. 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.

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

    Science.gov (United States)

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

    2010-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-24

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

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

    Science.gov (United States)

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

    2008-09-18

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

  15. Epitaxial growth of aligned GaN nanowires and nanobridges

    OpenAIRE

    2007-01-01

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

  16. High-efficiency, thin-film- and concentrator solar cells from GaAs. Final report; High-efficiency, Duennschicht- und Konzentrator-Solarzellen aus Galliumarsenid. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Wettling, W. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Bett, A.W. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Pilkuhn, M. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Scholz, F. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Baldus, A. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Blieske, U. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Blug, A. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Duong, T. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Schetter, C. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Stollwerck, G. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Sulima, O. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Wegener, A. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Doernen, A. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Frankowsky, G. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Haase, D. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Hahn, G. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Hangleiter, A. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Stauss, P. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Tsai, C.Y. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Zieger, K. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4

    1996-10-01

    Main topic of the project was the manufacturing of highly efficient GaAs-solar cells and the fabrication of concentrator cells. During this process significant progress was made with the material preparation, the solar cell technology and the material and process characterisation. This succeeded in the following efficiencies: - GaAs solar cell made by MOVPE technology: 22.9% on 4 cm{sup 2} (AM1.5g) - GaAs solar cell made by LPE-ER process: 22.8% on 4 cm{sup 2} (AM1.5g) - GaAs concentrator solar cell made by LPE-ER process: 24.9% at C=100xAM1.5d - GaAs concentrator module with fresnel lenses: Module efficiency 20.1% (under irradiation of 793 W/m{sup 2}). Another main focus was the epitaxy of GaAs on Si substrate. Two different approaches were investigated. Together with the cooperation partner ASE, Heilbronn a selective growth technology was developed that led to a decreased crack formation. By a simultanous optimization of the other epitaxy and process parameters, the efficiency was increased up to 16.6% AM0 on 1 cm{sup 2} solar cells. Furthermore a hybrid epitaxy was investigated. A GaAs layer was deposited onto a Si substrate using MOVPE. The solar cell structure was grown with a low temperature LPE. Unexpected difficulties appeared with this process, so that fundamental experiments needed to be done with the LPE technology. So far, no solar cells could be manufactured with this method. In addition, work was performed on GaInP solar cells on GaAs substrate. An efficiency of 15.7% (AM0) was acchieved. (orig.) [Deutsch] Gegenstand des Projekts war die Herstellung hocheffizienter GaAs-Solarzellen und die Fertigung von Konzentratorsolarzellen. Dazu wurden wesentliche Fortschritte bei der Materialpraeparation, der Solarzellentechnologie und der Material- and Prozesscharakterisierung erzielt. Diese Erfolge druecken sich in den erzielten Wirkungsgraden aus: - GaAs-Solarzelle hergestellt mit MOVPE-Technologie: 22.9% auf 4 cm{sup 2} (AM1.5g) - GaAs-Solarzelle hergestellt

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

    Science.gov (United States)

    2010-03-04

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

  18. Fast and ultrafast processes in AlGaN/GaN channels

    Energy Technology Data Exchange (ETDEWEB)

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

    2002-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-08-07

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

  20. Energy characteristics of excitons in InGaN/GaN heterostructures

    Science.gov (United States)

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

    2008-04-01

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

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

    Science.gov (United States)

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

    2016-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-02

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

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

    CERN Document Server

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

    2011-01-01

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

  4. 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....

  5. High-modulation-efficiency, integrated waveguide modulator-laser diode at 448 nm

    KAUST Repository

    Shen, Chao

    2016-01-25

    To date, solid-state lighting (SSL), visible light communication (VLC) and optical clock generation functionalities in the blue-green color regime have been demonstrated based on discrete devices, including light-emitting diodes, laser diodes, and transverse-transmission modulators. This work presents the first integrated waveguide modulator-laser diode (IWM-LD) at 448 nm, offering the advantages of small-footprint, high-speed, and low power-consumption. A high modulation efficiency of 2.68 dB/V, deriving from a large extinction ratio of 9.4 dB and a low operating voltage range of 3.5 V, was measured. The electroabsorption characteristics revealed that the modulation effect, as observed from the red-shifting of the absorption edge, was resulted from the external-field-induced quantum-confined-Stark-effect (QCSE). A comparative analysis of the photocurrent versus wavelength spectra in semipolar- and polar-plane InGaN/GaN quantum wells (QWs) confirmed that the IWM-LD based on semipolar (20¯2 ¯1) QWs was able to operate in a manner similar to other III-V materials typically used in optical telecommunications, due to the reduced piezoelectric field. Utilizing the integrated modulator, a -3dB bandwidth of ~1 GHz was measured, and a data rate of 1 Gbit/s was demonstrated using on-off keying (OOK) modulation. Our experimental investigation highlighted the advantage of implementing the IWM-LD on the same semipolar QW epitaxy in enabling a high-efficiency platform for SSL-VLC dual-functionalities.

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

    Institute of Scientific and Technical Information of China (English)

    唐龙娟; 郑新和; 张东炎; 董建荣; 王辉; 杨辉

    2011-01-01

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

  7. 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.

  8. 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.

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

    Science.gov (United States)

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

    2017-09-01

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

  10. Graphene-GaN Schottky Photodiodes Project

    Data.gov (United States)

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

  11. EXAFS characterization of amorphous GaAs

    Energy Technology Data Exchange (ETDEWEB)

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

    1998-12-31

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

  12. Optical anisotropy in GaSe

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-09-01

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

  13. Hydrogen molecules in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Lavrov, E.V.; Weber, J

    2003-12-31

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

  14. 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.

  15. GaN three dimensional nanostructures

    Energy Technology Data Exchange (ETDEWEB)

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

    1996-11-01

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

  16. 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.

  17. Data processing system of GA and PPPL

    Energy Technology Data Exchange (ETDEWEB)

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

    2001-11-01

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

  18. 2015 Cook & Tift County (GA) Lidar

    Data.gov (United States)

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

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

    Science.gov (United States)

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

    2012-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-10-01

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

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

    OpenAIRE

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

    2016-01-01

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

  2. Photoluminescence of Ga(AsBi)

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-07-01

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

  3. Imaging of InGaN inhomogeneities using visible aperturelessnear-field scanning optical microscope

    Energy Technology Data Exchange (ETDEWEB)

    Stebounova, Larissa V.; Romanyuk, Yaroslav E.; Chen, Dongxue; Leone, Stephen R.

    2007-06-14

    The optical properties of epitaxially grown islands of InGaN are investigated with nanometer-scale spatial resolution using visible apertureless near-field scanning optical microscopy. Scattered light from the tip-sample system is modulated by cantilever oscillations and detected at the third harmonic of the oscillation frequency to distinguish the near-field signal from unwanted scattered background light. Scattered near-field measurements indicate that the as-grown InGaN islanded film may exhibit both inhomogeneous In composition and strain-induced changes that affect the optical signal at 633 nm and 532 nm. Changes are observed in the optical contrast for large 3D InGaN islands (100's of nm) of the same height. Near-field optical mapping of small grains on a finer scale reveals InGaN composition or strain-induced irregularities in features with heights of only 2 nm, which exhibit different near-field signals at 633 nm and 532 nm incident wavelengths. Optical signal contrast from topographic features as small as 30 nm is detected.

  4. 0.52eV Quaternary InGaAsSb Thermophotovoltaic Diode Technology

    Energy Technology Data Exchange (ETDEWEB)

    MW Dashiell; JF Beausang; G Nichols; DM Depoy; LR Danielson; H Ehsani; KD Rahner; J Azarkevich; P Talamo; E Brown; S Burger; P Fourspring; W Topper; PF Baldasaro; CA Wang; R Huang; M Connors; G Turner; Z Shellenbarger; G Taylor; Jizhong Li; R Marinelli; D Donetski; S Anikeev; G Belenky; S Luryi; DR Taylor; J Hazel

    2004-06-09

    Thermophotovoltaic (TPV) diodes fabricated from 0.52eV lattice-matched InGaAsSb alloys are grown by Metal Organic Vapor Phase Epitaxy (MOVPE) on GaSb substrates. 4cm{sup 2} multi-chip diode modules with front-surface spectral filters were tested in a vacuum cavity and attained measured efficiency and power density of 19% and 0.58 W/cm{sup 2} respectively at operating at temperatures of T{sub radiator} = 950 C and T{sub diode} = 27 C. Device modeling and minority carrier lifetime measurements of double heterostructure lifetime specimens indicate that diode conversion efficiency is limited predominantly by interface recombination and photon energy loss to the GaSb substrate and back ohmic contact. Recent improvements to the diode include lattice-matched p-type AlGaAsSb passivating layers with interface recombination velocities less than 100 cm/s and new processing techniques enabling thinned substrates and back surface reflectors. Modeling predictions of these improvements to the diode architecture indicate that conversion efficiencies from 27-30% and {approx}0.85 W/cm{sup 2} could be attained under the above operating temperatures.

  5. Analog Module Placement Design Using Genetic Algorithm

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    This paper presents a novel genetic algorithm for analog module placement based on ageneralization of the two-dimensional bin packing problem. The genetic encoding and operators assure that allproblem constraints are always satisfied. Thus the potential problems of adding penalty terms to the costfunction are eliminated so that the search configuration space is drastically decreased. The dedicated costfunction is based on the special requirements of analog integrated circuits. A fractional factorial experimentwas conducted using an orthogonal array to study the algorithm parameters. A meta GA was applied todetermine the optimal parameter values. The algorithm was tested with several local benchmark circuits. Theexperimental results show that the algorithm has better performance than the simulated annealing approachwith satisfactory results comparable to manual placement. This study demonstrates the effectiveness of thegenetic algorithm in the analog module placement problem. The algorithm has been successfully used in alayout synthesis tool.

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

    Science.gov (United States)

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

    2016-08-01

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

  7. The Y-Ag-Ga system

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-01-11

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

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

    Science.gov (United States)

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

    2015-11-01

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

  9. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-04

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-12-01

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

  13. Sun batteries module based on А3В5 compounds with concentrators of sun energy and system of heatsink

    Directory of Open Access Journals (Sweden)

    Vakiv M.

    2010-03-01

    Full Text Available Characteristics of technology of manufacturing epitaxial structures GaAs(AlGaAs/InGaP with two active p–n-junctions for photocells which are able to work at concentrated solar radiation are considered. New suitable for industry technology of manufacturing and structure of solar batteries module based on epitaxial structures GaAs with Fresnel lens as concentrators of solar energy and a heat sink on the base of a heat pipe, equipped with a radiator sheet are developed. In conditions of 500-fold concentration of natural solar illumination at AM1,5 and 27,8% COE of a photocell, the electric power that is generated by the module reaches 78 Vt.

  14. 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.)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-03-15

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

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

    Science.gov (United States)

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

    2013-01-01

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

  17. Module theory, extending modules and generalizations

    CERN Document Server

    Tercan, Adnan

    2016-01-01

    The main focus of this monograph is to offer a comprehensive presentation of known and new results on various generalizations of CS-modules and CS-rings. Extending (or CS) modules are generalizations of injective (and also semisimple or uniform) modules. While the theory of CS-modules is well documented in monographs and textbooks, results on generalized forms of the CS property as well as dual notions are far less present in the literature. With their work the authors provide a solid background to module theory, accessible to anyone familiar with basic abstract algebra. The focus of the book is on direct sums of CS-modules and classes of modules related to CS-modules, such as relative (injective) ejective modules, (quasi) continuous modules, and lifting modules. In particular, matrix CS-rings are studied and clear proofs of fundamental decomposition results on CS-modules over commutative domains are given, thus complementing existing monographs in this area. Open problems round out the work and establish the...

  18. Electron beam source molecular beam epitaxial growth of analog graded Al(x)Ga(1-x)As ballistic transistors

    Science.gov (United States)

    Malik, Roger J.; Levi, Anthony F. J.

    1988-01-01

    A new method has been developed for the growth of graded band-gap Al(x)Ga(1-x)As alloys by molecular beam epitaxy which is based upon electron beam evaporation of the group III elements. The metal fluxes are measured and feedback controlled using a modulated ion gauge sensor. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables growth of variable band-gap III-V alloys with arbitrary composition profiles. This new technique is demonstrated by synthesis of analog graded Al(x)Ga(1-x)As unipolar ballistic electron transistors.

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

    Directory of Open Access Journals (Sweden)

    Jenshan Lin

    2009-06-01

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

  20. Magnetocaloric Effect of Ni56Mn18.8Ga24.5Gd0.7 Alloy

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    With the addition of Gd, the Ni56Mn18.8Ga24.5Gd0.7 alloy exhibits non-modulated martensite phase at room temperature. From the illustration of Gd microstructure, it can be found that Gd exists along the subgrain boundaries. Hence,he crystalline size decreases and the mechanical properties improve. Ac-susceptibility results show that Ni56Mn18.8Ga24.5Gd0.7 alloy still undergoes simultaneous structural and magnetic transitions and transforms from ferromagnetic martensitic phase to paramagnetic austenitic phase with increasing temperature. The maximum magnetic entropy change is 13.4 J· (kg· K) - 1 under 1.9 T field at 338 K. The giant magnetocaloric effect found in Ni56Mn18.8Ga24.5Gd0.7 alloy is attributed to the concurrently occurring first-order structural- and magnetic-phase transitions.