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Sample records for semi-insulating gaas doped

  1. Effect of the V{sub As}V{sub Ga} complex defect doping on properties of the semi-insulating GaAs

    SciTech Connect

    Ma, Deming Qiao, Hongbo; Shi, Wei; Li, Enling

    2014-04-21

    The different position V{sub As}V{sub Ga} cluster defect doping in semi-insulating (SI) GaAs has been studied by first-principles calculation based on hybrid density functional theory. Our calculated results show that EL6 level is formed due to the V{sub As}V{sub Ga} complex defect, which is very close to the experimental result. It provides the explanation of the absorption of laser with the wavelength beyond in semi-insulating GaAs. The formation energy of V{sub As}V{sub Ga} complex defect is found to decrease from surface to interior gradually. The conduction band minima and valence band maxima of GaAs (001) surface with the V{sub As}V{sub Ga} complex defect are all located at Γ point, and some defect levels are produced in the forbidden band. In contrast, the conduction band minima and valence band maxima of GaAs with the interior V{sub As}V{sub Ga} complex defect are not located at the same k-point, so it might involve the change of momentum in the electron transition process. The research will help strengthen the understanding of photoelectronic properties and effectively guide the preparation of the SI-GaAs materials.

  2. Characterisation of semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Walukiewicz, W.; Pawlowicz, L.; Lagowski, J.; Gatos, H. C.

    1982-01-01

    Hole and electron mobilities as functions of temperature and ionised impurity concentration are calculated for GaAs. It is shown that these calculations, when used to analyse electrical properties of semi-insulating GaAs, enable an assessment of the Fermi energy position and ionised impurity concentration to be made. In contrast to previous work, the analysis does not require any phenomenological assumptions.

  3. Microscopic modelling of semi-insulating GaAs detectors

    NASA Astrophysics Data System (ADS)

    Cola, A.; Vasanelli, L.; Reggiani, L.; Cavallini, A.; Nava, F.

    1997-08-01

    We present a drift-diffusion model of semi-insulating n-GaAs detectors, taking into account the presence of hot-carrier dynamics, conduction band features and the kinetics of trapping and detrapping from deep and shallow centres. We provide unambiguous evidence of a field-enhanced capture cross section for EL2 and EL3 centres as conjectured by McGregor [1] for the case of EL2. This result is shown to be strictly correlated with the active thickness of the detector varying almost linearly with the applied voltage, in excellent agreement with recent experimental measurements performed with the Optical Beam-Induced Currents (OBIC) technique. Evidence of Poole-Frenkel effects at the highest applied voltages is provided by the current-voltage characteristics.

  4. Deep levels in semi-insulating LEC GaAs before and after silicon implantation

    SciTech Connect

    Dindo, S.; Abdel-Motaleb, I.; Lowe, K.; Tang, W.; Young, L.

    1985-11-01

    The deep trapping levels present before ion implantation of silicon into the semi-insulating LEC GaAs starting material were investigated using optical transient current spectroscopy (OTCS). MESFET channel current deep level transient spectroscopy (DLTS) was used for the implanted material. With a silicon nitride layer used t encapsulate the GaAs for postimplantation annealing and with implantation directly into the GaAs, it was found tha of seven or more deep levels seen in the semi-insulating substrate prior to silicon implantation only the level believed to be EL12 remained. On implanting through a thin Si/sub 3/N/sub 4/ encapsulating layer and annealing under Si/sub 3/N/sub 4/, only EL2 was found. With a silicon dioxide layer as an encapsulant, two traps remained and two apparently unreported levels appeared.

  5. 20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas.

    PubMed

    Hale, P J; Madeo, J; Chin, C; Dhillon, S S; Mangeney, J; Tignon, J; Dani, K M

    2014-10-20

    We demonstrate broadband (20 THz), high electric field, terahertz generation using large area interdigitated antennas fabricated on semi-insulating GaAs. The bandwidth is characterized as a function of incident pulse duration (15-35 fs) and pump energy (2-30 nJ). Broadband spectroscopy of PTFE is shown. Numerical Drude-Lorentz simulations of the generated THz pulses are performed as a function of the excitation pulse duration, showing good agreement with the experimental data. PMID:25401668

  6. EPR evidence for As interstitial-related defects in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Christoffel, E.; Benchiguer, T.; Goltzené, A.; Schwab, C.; Guangyu, Wang; Ju, Wu

    1990-08-01

    We report the analysis of the residual paramagnetic structure appearing in semi-insulating GaAs after microwave saturation of the AsGa-related spectrum and most intense after preliminary plastic deformation of the material. It is separable into two similar and correlated central hyperfine partially resolved spectra of trigonal symmetry, both attributed to As interstitial-related defects. Some possibilities of suitable complexes, especially in the recent context of the EL2 identification with an As+Ga-Asi pair, are discussed.

  7. Influence of electron irradiation on properties of semi-insulating GaAs detectors

    NASA Astrophysics Data System (ADS)

    Šagátová, Andrea; Zaťko, Bohumír; Sedlačková, Katarína; Pavlovič, Márius; Nečas, Vladimír

    2015-03-01

    The effects of electron beam irradiation on electrical and spectrometric properties of semi-insulating (SI) GaAs detectors were studied. The electric properties were monitored by reverse and forward current-voltage characteristics. In general, a breakdown voltage decrease with the dose was observed. However, some samples showed a local increase in the breakdown voltage at doses between 5 and 10 kGy. The detector spectrometric properties (the charge collection efficiency (CCE), the energy resolution and the detection efficiency) were evaluated from measured spectra of the 241Am radionuclide gamma source before and after electron irradiation. The CCE and energy resolution showed minor changes after irradiation. The detection efficiency noticed an initial increase (up to a dose of 5 kGy) followed by a permanent decrease. At 30 kGy, the overall degradation of detector functionality was observed with all samples.

  8. Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Walukiewicz, W.; Wang, L.; Pawlowicz, L. M.; Lagowski, J.; Gatos, H. C.

    1986-01-01

    It is shown that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 sq cm/V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.

  9. Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

    NASA Astrophysics Data System (ADS)

    Xiangrong, Ma; Wei, Shi; Weili, Ji; Hong, Xue

    2011-12-01

    A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch.

  10. Conduction mechanisms on annealed semi-insulating GaAs samples

    NASA Astrophysics Data System (ADS)

    Peres, M. L.; Chaves, A. S.; Rubinger, R. M.; Chitta, V. A.; Ribeiro, G. M.; de Oliveira, A. G.

    2011-12-01

    We have measured electrical resistivity in the range of 100-500 K on six semi-insulating low-temperature grown molecular-beam epitaxy GaAs samples that were exposed to annealing treatment. Samples 2, 3, 4, 5 and 6 were annealed with temperatures of 350 °C, 400 °C, 450 °C, 500 °C and 550 °C, while sample 1 was not exposed to the annealing process. We used the differential activation energy method to precisely identify the temperature region where the different conduction regimes dominate, i.e. band conduction, nearest neighbor hopping and variable range hopping. We will also show that the change on the density of states in the impurity band caused by annealing significantly alters the conduction mechanisms present in those samples.

  11. Gettering of donor impurities by V in GaAs and the growth of semi-insulating crystals

    NASA Technical Reports Server (NTRS)

    Ko, K. Y.; Lagowski, J.; Gatos, H. C.

    1989-01-01

    Vanadium added to the GaAs melt getters shallow donor impurities (Si and S) and decreases their concentration in the grown crystals. This gettering is driven by chemical reactions in the melt rather than in the solid. Employing V gettering, reproducibly semi-insulating GaAs were grown by horizontal Bridgman and liquid-encapsulated Czochralski techniques, although V did not introduce any midgap energy levels. The compensation mechanism in these crystals was controlled by the balance between the native midgap donor EL2 and residual shallow acceptors. Vanadium gettering contributed to the reduction of the concentration of shallow donors below the concentration of acceptors. The present findings clarify the long-standing controversy on the role of V in achieving semi-insulating GaAs.

  12. Controlling chaos with magnetic field in semi-insulating GaAs

    SciTech Connect

    Oliveira, A. G. de; Ribeiro, G. M.; Moreira, M. V. B.; Gonzalez, J. C.; Silva, R. L. da; Rubinger, R. M.

    2007-10-15

    Chaos control has stimulated a large amount of work. We have studied the effect of an external parallel magnetic field on the low-frequency current oscillations observed on a molecular beam epitaxy GaAs sample grown at 265 deg. C, and we have shown that it can be efficiently used for chaos control. The study of the magnetoresistance indicates that the effect of the magnetic field on the charges of the hopping conduction mechanism induces changes in the low-frequency oscillations. Due to this, we have used the magnetic field to control chaos assessed through direct observation low-frequency oscillations, their attractors, and bifurcation diagrams. We also found that the magnetic field interferes indirectly with the Coulombian interaction between the free charges in the conduction band and the hopping carriers, as well as with the recombination mechanism of field enhanced trapping. Controlling the low-frequency oscillations in semi-insulating GaAs by means of an external magnetic field permits probing the interaction of the slow hopping carriers and the fast free carriers in the electric-field domains.

  13. Carbon irradiated semi insulating GaAs for photoconductive terahertz pulse detection.

    PubMed

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S S; Mathimalar, S; Nanal, Vandana; Pillay, R G; Döhler, G H

    2015-03-01

    We report here a photoconductive material for THz detection with sub-picosecond carrier lifetime made by C(12) (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C(12)) ions. With an increase of the irradiation dose from ~10(12) /cm(2) to ~10(15) /cm(2) the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, whereas that of usual non-irradiated SI-GaAs is ~70 picosecond. This decreased carrier lifetime has resulted in a strong improvement in THz pulse detection compared with normal SI-GaAs. Improvement in signal to noise ratio as well as in detection bandwidth is observed. Carbon irradiated SI-GaAs appears to be an economical alternative to low temperature grown GaAs for fabrication of THz devices.

  14. Effect of the Si-doped In0.49Ga0.51P barrier layer on the device performance of In0.4Ga0.6As MOSFETs grown on semi-insulating GaAs substrates

    NASA Astrophysics Data System (ADS)

    Chang, Hu-Dong; Sun, Bing; Xue, Bai-Qing; Liu, Gui-Ming; Zhao, Wei; Wang, Sheng-Kai; Liu, Hong-Gang

    2013-07-01

    In0.4Ga0.6As channel metal—oxide—semiconductor field-effect transistors (MOSFETs) with and without an Si-doped In0.49Ga0.51P barrier layer grown on semi-insulating GaAs substrates have been investigated for the first time. Compared with the In0.4Ga0.6As MOSFETs without an In0.49Ga0.51P barrier layer, In0.4Ga0.6As MOSFETs with an In0.49Ga0.51P barrier layer show higher drive current, higher transconductance, lower gate leakage current, lower subthreshold swing, and higher effective channel mobility. These In0.4Ga0.6As MOSFETs (gate length 2 μm) with an In0.49Ga0.51P barrier layer exhibit a high drive current of 117 mA/mm, a high transconductance of 71.9 mS/mm, and a maximum effective channel mobility of 1266 cm2/(V·s).

  15. On the optical evaluation of the EL2 deep level concentration in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

    A practical procedure for the evaluation of the Fermi energy in semi-insulating (SI)GaAs from electrical measurements is presented. This procedure makes it possible to reliably extend the determination of the major deep level (EL2) concentration, by near-infrared absorption measurements, to SIGaAs. Employing this procedure, it is shown that the EL2 concentration in Czochralski-grown GaAs increases monotonically with increasing As/Ga ratio (throughout the conversion from SI n type to semiconducting p-type crystals) rather than abruptly as previously proposed.

  16. Continuous wave terahertz radiation from antennas fabricated on C¹²-irradiated semi-insulating GaAs.

    PubMed

    Deshmukh, Prathmesh; Mendez-Aller, M; Singh, Abhishek; Pal, Sanjoy; Prabhu, S S; Nanal, Vandana; Pillay, R G; Döhler, G H; Preu, S

    2015-10-01

    We demonstrate continuous wave (CW) terahertz generation from antennas fabricated on C12-irradiated semi-insulating (SI) GaAs substrates. The dark current drawn by the antennas fabricated on irradiated substrates is ∼3 to 4 orders of magnitude lower compared to antennas fabricated on un-irradiated substrates, while the photocurrents decrease by only ∼1.5 orders of magnitude. This can be attributed to the strong reduction of the carrier lifetime that is 2.5 orders of magnitude, with values around τ(rec)=0.2  ps. Reduced thermal heating allows for higher bias voltages to the irradiated antenna devices resulting in higher CW terahertz power, just slightly lower than that of low-temperature grown GaAs (LT GaAs)at similar excitation conditions.

  17. Continuous wave terahertz radiation from antennas fabricated on C¹²-irradiated semi-insulating GaAs.

    PubMed

    Deshmukh, Prathmesh; Mendez-Aller, M; Singh, Abhishek; Pal, Sanjoy; Prabhu, S S; Nanal, Vandana; Pillay, R G; Döhler, G H; Preu, S

    2015-10-01

    We demonstrate continuous wave (CW) terahertz generation from antennas fabricated on C12-irradiated semi-insulating (SI) GaAs substrates. The dark current drawn by the antennas fabricated on irradiated substrates is ∼3 to 4 orders of magnitude lower compared to antennas fabricated on un-irradiated substrates, while the photocurrents decrease by only ∼1.5 orders of magnitude. This can be attributed to the strong reduction of the carrier lifetime that is 2.5 orders of magnitude, with values around τ(rec)=0.2  ps. Reduced thermal heating allows for higher bias voltages to the irradiated antenna devices resulting in higher CW terahertz power, just slightly lower than that of low-temperature grown GaAs (LT GaAs)at similar excitation conditions. PMID:26421576

  18. Study on the high-power semi-insulating GaAs PCSS with quantum well structure

    NASA Astrophysics Data System (ADS)

    Luan, Chongbiao; Wang, Bo; Huang, Yupeng; Li, Xiqin; Li, Hongtao; Xiao, Jinshui

    2016-05-01

    A high-power semi-insulating GaAs photoconductive semiconductor switch (PCSS) with quantum well structure was fabricated. The AlGaAs layer was deposited on the surface of the GaAs material, and the reflecting film and the antireflection film have been made on the surface of the GaAs and AlGaAs, respectively. When the prepared PCSS worked at a bias voltage of 9.8 kV and triggered by a laser pulse with an incident optical energy of 5.4 mJ, a wavelength of 1064 nm and an optical pulse width of 25 ns, the on-state resistance of the AlGaAs/GaAs PCSS was only 0.45 Ω, and the longevity of the AlGaAs/GaAs PCSS was larger than 106 shots. The results show that this structure reduces the on-state resistance and extends the longevity of the GaAs PCSS.

  19. Photocurrent spectra of semi-insulating GaAs M-S-M diodes: Role of the contacts

    NASA Astrophysics Data System (ADS)

    Dubecký, František; Oswald, Jiří; Kindl, Dobroslav; Hubík, Pavel; Dubecký, Matúš; Gombia, Enos; Šagátová, Andrea; Boháček, Pavol; Sekáčová, Mária; Nečas, Vladimír

    2016-04-01

    Current-voltage (I-V) characteristics and photocurrent (PC) spectra (600-1000 nm) of the metal-semiconductor-metal (M-S-M) structures based on high-quality undoped semi-insulating (SI) GaAs with AuGeNi backside contact and different semitransparent top contacts (AuGeNi, Pt, Gd and Nd) are reported, and analysed with the help of a simple physical model. It is shown that the dominant peak in the PC spectra and the change of photocurrent sign can be explained by a presence of two Schottky-like barriers at the top and bottom surfaces. In addition, I-V and PC results show dependence on the bias and its polarity, and on the contact metal used. The possible origins of these effects are discussed.

  20. Emission characteristics of photoconductive antennas based on low-temperature-grown GaAs and semi-insulating GaAs.

    PubMed

    Tani, M; Matsuura, S; Sakai, K; Nakashima, S

    1997-10-20

    Terahertz radiation was generated with several designs of photoconductive antennas (three dipoles, a bow tie, and a coplanar strip line) fabricated on low-temperature-grown (LT) GaAs and semi-insulating (SI) GaAs, and the emission properties of the photoconductive antennas were compared with each other. The radiation spectrum of each antenna was characterized with the photoconductive sampling technique. The total radiation power was also measured by a bolometer for comparison of the relative radiation power. The radiation spectra of the LT-GaAs-based and SI-GaAs-based photoconductive antennas of the same design showed no significant difference. The pump-power dependencies of the radiation power showed saturation for higher pump intensities, which was more serious in SI-GaAs-based antennas than in LT-GaAs-based antennas. We attributed the origin of the saturation to the field screening of the photocarriers. PMID:18264312

  1. Field effect on positron diffusion in semi-insulating GaAs

    SciTech Connect

    Shan, Y.Y.; Asoka-Kumar, P.; Lynn, K.G.; Fung, S.; Beling, C.D.

    1996-07-01

    An energy-tunable monoenergetic positron beam was used to study positron diffusion in the space-charge region of an Au/GaAs(SI) (semi-insulating) Schottky contact, where the electric field reaches {approximately}10{sup 5} Vcm{sup {minus}1} by reverse biasing the diode. An analytical solution of the time-dependent positron drift-diffusion model under an electric field was obtained for the case of a semi-infinite body with a capturing boundary, and explains the experimental results well. A positron diffusion coefficient of 1.8{plus_minus}0.2 cm{sup 2}s{sup {minus}1}, and a positron mobility of 70{plus_minus}10 cm{sup 2}V{sup {minus}1}s{sup {minus}1} in GaAs(SI) at 300 K, were obtained independently. This result is consistent with the Einstein relation. The dependence of the positron current density at the Au/GaAs interface on the electric field shows that GaAs(SI) is a possible candidate for the fabrication of the field-assisted positron moderator. {copyright} {ital 1996 The American Physical Society.}

  2. Electric-field distribution in Au-semi-insulating GaAs contact investigated by positron-lifetime technique

    NASA Astrophysics Data System (ADS)

    Ling, C. C.; Shek, Y. F.; Huang, A. P.; Fung, S.; Beling, C. D.

    1999-02-01

    Positron-lifetime spectroscopy has been used to investigate the electric-field distribution occurring at the Au-semi-insulating GaAs interface. Positrons implanted from a 22Na source and drifted back to the interface are detected through their characteristic lifetime at interface traps. The relative intensity of this fraction of interface-trapped positrons reveals that the field strength in the depletion region saturates at applied biases above 50 V, an observation that cannot be reconciled with a simple depletion approximation model. The data, are, however, shown to be fully consistent with recent direct electric-field measurements and the theoretical model proposed by McGregor et al. [J. Appl. Phys. 75, 7910 (1994)] of an enhanced EL2+ electron-capture cross section above a critical electric field that causes a dramatic reduction of the depletion region's net charge density. Two theoretically derived electric field profiles, together with an experimentally based profile, are used to estimate a positron mobility of ~95+/-35 cm2 V-1 s-1 under the saturation field. This value is higher than previous experiments would suggest, and reasons for this effect are discussed.

  3. Backgating effect in GaAs FETs with a channel—semi-insulating substrate boundary

    NASA Astrophysics Data System (ADS)

    Chaouki Megherbi, Ahmed; Benramache, Said; Guettaf, Abderrazak

    2014-03-01

    This study focuses on modeling the effects of deep hole traps, mainly the effect of the substrate (backgating effect) in a GaAs transistor MESFT. This effect is explained by the existence, at the interface, of a space charge zone. Any modulation in this area leads to response levels trapping the holes therein to the operating temperature. We subsequently developed a model treating the channel substrate interface as an N—P junction, allowing us to deduce the time dependence of the component parameters of the total resistance Rds, the pinch-off voltage VP, channel resistance, fully open Rco and the parasitic series resistance RS to bind the effect trap holes H1 and H0. When compared with the experimental results, the values of the RDS (tS) model for both traps show that there is an agreement between theory and experiment; it has inferred parameter traps, namely the density and the time constant of the trap. This means that a space charge region exists at the channel—substrate interface and that the properties can be approximated to an N—P junction.

  4. AlGaAs/GaAs p-i-n photodiode/preamplifier monolithic photoreceiver integrated on a semi-insulating GaAs substrate

    NASA Astrophysics Data System (ADS)

    Wada, O.; Hamaguchi, H.; Miura, S.; Makiuchi, M.; Nakai, K.; Horimatsu, H.; Sakurai, T.

    1985-05-01

    A fully monolithic photoreceiver circuit incorporating an AlGaAs/GaAs p-i-n photodiode and a GaAs field-effect transistor based transimpedance amplifier has been fabricated in the form of a horizontally integrated structure on a semi-insulating GaAs substrate. Parasitic capacitances of the circuit elements have been minimized in the present monolithic circuit, and a short rise and fall time of 1.0 ns, corresponding to an approximate -3 dB frequency of 300 MHz, has been demonstrated at the internal feedback resistance of 1.3 kΩ. Preliminary measurement of the noise characteristics of the present circuit has exhibited an encouraging value of the equivalent input noise current of 13 pA Hz-1/2 at 300 MHz.

  5. Frequency and intensity dependence of the sub-band-gap features observed in the surface photovoltage spectrum of semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Sharma, T. K.; Kumar, Shailendra; Rustagi, K. C.

    2002-11-01

    Surface photovoltage spectroscopy studies on thick semi-insulating GaAs wafers are reported in the range 850-950 nm using the chopped light geometry. We observed some interesting sharp features in the sub-band-gap of SI-GaAs, which were reported recently [Appl. Phys. Lett. 79, 1715(2001); Rev. Sci. Instrum. 73, 1835 (2002)]. In this article, we present the dependence of these features on the chopping frequency and the source intensity. The intensity variation in the above-band-gap region and for the A peak (898 nm) in the sub-band-gap region could be fitted with single component while it is necessary to consider more than one component to fit the data for the Q peak (887 nm) in the sub-band-gap region. A model consistent with the observed features is also proposed.

  6. The reverse mode of the photo activated charge domain in high field biased semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Qu, Guanghui; Shi, Wei

    2013-02-01

    The nonlinear accumulation of the photogenerated electrons in high field biased SI-GaAs has been defined as photo activated charge domain (PACD). The transient transport dynamics of the PACD is investigated. The result shows that the PACD, working as a reverse gun dipole domain when biased electric field much higher than 4 kV/cm, and the reverse mode of the PACD could dominate the electric field shielding by its main electric field ultrafast and exponential rising against the bias field. Such mechanisms could play an important role in GaAs THz antenna, GaAs photoconductive semiconductor switch, and the other ultrafast GaAs devices.

  7. EBIC spectroscopy - A new approach to microscale characterization of deep levels in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Li, C.-J.; Sun, Q.; Lagowski, J.; Gatos, H. C.

    1985-01-01

    The microscale characterization of electronic defects in (SI) GaAs has been a challenging issue in connection with materials problems encountered in GaAs IC technology. The main obstacle which limits the applicability of high resolution electron beam methods such as Electron Beam-Induced Current (EBIC) and cathodoluminescence (CL) is the low concentration of free carriers in semiinsulating (SI) GaAs. The present paper provides a new photo-EBIC characterization approach which combines the spectroscopic advantages of optical methods with the high spatial resolution and scanning capability of EBIC. A scanning electron microscope modified for electronic characterization studies is shown schematically. The instrument can operate in the standard SEM mode, in the EBIC modes (including photo-EBIC and thermally stimulated EBIC /TS-EBIC/), and in the cathodo-luminescence (CL) and scanning modes. Attention is given to the use of CL, Photo-EBIC, and TS-EBIC techniques.

  8. Semi-insulating GaAs detectors with HDPE layer for detection of fast neutrons from D-T nuclear reaction

    NASA Astrophysics Data System (ADS)

    Sagatova, Andrea; Zatko, Bohumir; Sedlackova, Katarina; Pavlovic, Marius; Necas, Vladimir; Fulop, Marko; Solar, Michael; Granja, Carlos

    2016-09-01

    Bulk semi-insulating (SI) GaAs detectors optimized for fast-neutron detection were examined using mono-energetic neutrons. The detectors have an active area of 7.36 mm2 defined by a multi-pixel structure of a AuZn Schottky contact allowing a relatively high breakdown voltage (300 V) sufficient for full depletion of the detector structure. The Schottky contact is covered by a HDPE (high density polyethylene) conversion layer, where neutrons transfer their kinetic energy to hydrogen atoms through elastic nuclear collisions. The detectors were exposed to mono-energetic neutrons generated by a deuterium (D)-tritium (T) nuclear reaction at a Van de Graaff accelerator. Neutrons reached a kinetic energy of 16.8 MeV when deuterons were accelerated by 1 MV potential. The influence of the HDPE layer thickness on the detection efficiency of the fast neutrons was studied. The thickness of the conversion layer varied from 50 μm to 1300 μm. The increase of the HDPE layer thickness led to a higher detection efficiency due to higher conversion efficiency of the HDPE layer. The effect of the active detector thickness modified by the detector reverse bias voltage on the detection efficiency was also evaluated. By increasing the detector reverse voltage, the detector active volume expands to the depth and also to the sides, slightly increasing the neutron detection efficiency.

  9. Charge transfer in semi-insulating Fe-doped GaN

    NASA Astrophysics Data System (ADS)

    Dashdorj, J.; Zvanut, M. E.; Harrison, J. G.; Udwary, K.; Paskova, T.

    2012-07-01

    Charge transfer kinetics is studied in free-standing Fe-doped GaN using photo-induced electron paramagnetic resonance (EPR). Samples with Fe concentrations of 1017 cm-3 reveal an increase in Fe3+ during exposure with photon energy greater than 0.8 eV, while samples with higher Fe concentrations exhibit a decrease in the Fe3+ under the same conditions. Steady-state photo-EPR measurements of the most lightly doped sample imply the existence of an Fe2+/3+ defect level within 0.8 eV of the conduction band edge consistent with earlier work, but time-dependent measurements of more heavily doped crystals indicate a multi-step charge transfer process. Analysis of time-dependent photo-EPR data reveals that charge exchange may be separated into two processes, one that is temperature independent and one that depends monotonically on temperature. While a physical model for the charge transfer is not apparent, likely scenarios involve charge trapping at extended defects and phonon interactions.

  10. Semi-insulating GaAs and Au Schottky barrier photodetectors for near-infrared detection (1280 nm)

    NASA Astrophysics Data System (ADS)

    Nusir, A. I.; Makableh, Y. F.; Manasreh, O.

    2015-08-01

    Schottky barriers formed between metal (Au) and semiconductor (GaAs) can be used to detect photons with energy lower than the bandgap of the semiconductor. In this study, photodetectors based on Schottky barriers were fabricated and characterized for the detection of light at wavelength of 1280 nm. The device structure consists of three gold fingers with 1.75 mm long and separated by 0.95 mm, creating an E shape while the middle finger is disconnected from the outer frame. When the device is biased, electric field is stretched between the middle finger and the two outermost electrodes. The device was characterized by measuring the current-voltage (I-V) curve at room temperature. This showed low dark current on the order of 10-10 A, while the photocurrent was higher than the dark current by four orders of magnitude. The detectivity of the device at room temperature was extracted from the I-V curve and estimated to be on the order of 5.3x1010 cm.Hz0.5/W at 5 V. The step response of the device was measured from time-resolved photocurrent curve at 5 V bias with multiple on/off cycles. From which the average recovery time was estimated to be 0.63 second when the photocurrent decreases by four orders of magnitude, and the average rise time was measured to be 0.897 second. Furthermore, the spectral response spectrum of the device exhibits a strong peak close to the optical communication wavelength (~1.3 μm), which is attributed to the internal photoemission of electrons above the Schottky barrier formed between Au and GaAs.

  11. High-Resistivity Semi-insulating AlSb on GaAs Substrates Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Vaughan, E. I.; Addamane, S.; Shima, D. M.; Balakrishnan, G.; Hecht, A. A.

    2016-04-01

    Thin-film structures containing AlSb were grown using solid-source molecular beam epitaxy and characterized for material quality, carrier transport optimization, and room-temperature radiation detection response. Few surface defects were observed, including screw dislocations resulting from shear strain between lattice-mismatched layers. Strain was also indicated by broadening of the AlSb peak in x-ray diffraction measurements. Threading dislocations and interfacial misfit dislocations were seen with transmission electron microscopy imaging. Doping of the AlSb layer was introduced during growth using GaTe and Be to determine the effect on Hall transport properties. Hall mobility and resistivity were largest for undoped AlSb samples, at 3000 cm2/V s and 106 Ω cm, respectively, and increased doping levels progressively degraded these values. To test for radiation response, p-type/intrinsic/ n-type (PIN) diode structures were grown using undoped AlSb on n-GaAs substrates, with p-GaSb cap layers to protect the AlSb from oxidation. Alpha-particle radiation detection was achieved and spectra were produced for 241Am, 252Cf, and 239Pu sources. Reducing the detector surface area increased the pulse height observed, as expected based on voltage-capacitance relationships for diodes.

  12. Measured and computed performance of a microstrip filter composed of semi-insulating GaAs on a fused quartz substrate

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Dengler, Robert J.; Oswald, John E.; Sheen, David M.; Ali, Sami M.

    1991-01-01

    The performance of a microstrip hammerhead filter that has been fabricated on an electrically thin layer of semiinsulating GaAs backed by a fused quartz substrate was measured and compared to results of a three-dimensional finite-difference time-domain (FD-TD) program used to calculate the response of the filter both with and without the GaAs layer. The program, presented by Sheen et al. (1990), discretizes the entire structure and then simulates the propagation of a Gaussian pulse through the filter. The microstrip filter is intended for applications involving ultrathin lifted-off or etched-back GaAs containing both active devices and passive microstrip circuitry backed by a much thicker mechanically rigid low-loss, low-dielectric-constant substrate. The low-pass characteristics of the hammerhead filter with the intermediate GaAs layer are compared with those of the same filter on quartz alone. Both the measured and computed data show a significant shift in cutoff frequency (about 10 percent at the 3 dB points) for a GaAs layer that is 0.007 wavelengths thick at 4 GHz.

  13. High-resolution transmission electron microscopy study on the growth modes of GaSb islands grown on a semi-insulating GaAs (001) substrate

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Lee, J. Y.; Noh, Y. G.; Kim, M. D.; Oh, J. E.

    2007-06-01

    The initial growth behaviors of GaSb on a GaAs substrate were studied using a high-resolution electron microscope (HRTEM). Four types of GaSb islands were observed by HRTEM. HRTEM micrographs showed that strain relaxation mechanisms were different in the four types of islands. Although 90° misfit dislocations relieve misfit strain in the islands, additional mechanisms are required to relax the remaining strain. The existence of elastic deformation near the surface related to dislocations and intermediate layers between GaSb and GaAs were demonstrated in island growths. Finally, the generation of planar defects to relieve strain was observed in a specific GaSb growth.

  14. Characterization of semi-insulating gallium arsenide

    NASA Astrophysics Data System (ADS)

    Blakemore, John S.

    1993-11-01

    The project was established 18 Nov. 1992 to continue for 12 months. Its purpose has been electrical and optical characterization of samples from semi-insulating (SI) melt-grown crystals of gallium arsenide (GaAs). As a further definition of the project's purpose, the primary goal has been to assist NRL in assessing the properties of SI GaAs crystals grown at NRL by the vertical zone melt (VZM) method. A second aspect of this characterization work has involved samples from SI GaAs crystals grown by various commercial vendors including samples of pre-synthesized GaAs evaluated for its suitability as starting 'feedstock' for VZM growth. Measurements made at Western Washington University (WWU) under the terms of this project accord with a Statement of Work provided at the outset. These have included the following: (1) low-field dc electrical transport data for SI GaAs samples, as functions of temperature; (2) near-infrared (NIR) transmittance/absorption spectra of polished slabs, with data concerning the well-known EL2 defect determined from NIR absorption strength and spectral form; and (3) mid-IR data on absorption caused by carbon acceptors in SI GaAs.

  15. Current oscillations in semi-insulating GaAs associated with field-enhanced capture of electrons by the major deep donor EL2

    NASA Technical Reports Server (NTRS)

    Kaminska, M.; Parsey, J. M.; Lagowski, J.; Gatos, H. C.

    1982-01-01

    Current oscillations thermally activated by the release of electrons from deep levels in undoped semiinsulating GaAs were observed for the first time. They were attributed to electric field-enhanced capture of electrons by the dominant deep donor EL2 (antisite AsGa defect). This enhanced capture is due to the configurational energy barrier of EL2, which is readily penetrated by hot electrons.

  16. Optical characterization of semi-insulating GaAs - Determination of the Fermi energy, the concentraion of the midgap EL2 level and its occupancy

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Bugajski, M.; Matsui, M.; Gatos, H. C.

    1987-01-01

    The key electronic characteristics of semiinsulating GaAs, i.e., the Fermi energy, concentration, and occupancy of the midgap donor EL2, and the net concentration of ionized acceptors can all be determined from high-resolution measurements of the EL2 intracenter absorption. The procedure is based on the measurement of zero-phonon line intensity before and after the complete transfer of EL2 to its metastable state followed by thermal recovery. The procedure is quantitative, involves no fitting parameters, and unlike existing methods, is applicable even when a significant part of the EL2 is ionized.

  17. Photoluminescence of Mn+ doped GaAs

    NASA Astrophysics Data System (ADS)

    Zhou, Huiying; Qu, Shengchun; Liao, Shuzhi; Zhang, Fasheng; Liu, Junpeng; Wang, Zhanguo

    2010-10-01

    Photoluminescence is one of the most useful techniques to obtain information about optoelectronic properties and defect structures of materials. In this work, the room-temperature and low temperature photoluminescence of Mn-doped GaAs were investigated, respectively. Mn-doped GaAs structure materials were prepared by Mn+ ion implantation at room temperature into GaAs. The implanted samples were subsequently annealed at various temperatures under N2 atmosphere to recrystallize the samples and remove implant damage. A strong peak was found for the sample annealed at 950 °C for 5 s. Transitions near 0.989 eV (1254 nm), 1.155 eV (1074 nm) and 1.329 eV (933 nm) were identified and formation of these emissions was analyzed for all prepared samples. This structure material could have myriad applications, including information storage, magnet-optical properties and energy level engineering.

  18. Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation

    SciTech Connect

    Biswas, Pranab; Banerji, P.; Halder, Nripendra N.; Kundu, Souvik; Shripathi, T.; Gupta, M.

    2014-05-15

    The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-à-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 ºC and 700 ºC showed p-type conductivity with a hole concentration of 1.1 × 10{sup 18} cm{sup −3} and 2.8 × 10{sup 19} cm{sup −3} respectively, whereas those annealed at 800 ºC showed n-type conductivity with a carrier concentration of 6.5 × 10{sup 16} cm{sup −3}. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (As{sub Zn}–2V{sub Zn}), by substituting Zn atoms (As{sub Zn}) and thereby creating two zinc vacancies (V{sub Zn}). Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 ºC, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, Ga{sub Zn}. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.

  19. Differential etching behavior between semi-insulating and n-doped 4H-SiC in high-density SF{sub 6}/O{sub 2} inductively coupled plasma

    SciTech Connect

    Okamoto, Naoya

    2009-05-15

    The author investigated the etching characteristics of semi-insulating (SI) and n-doped (n-) 4H-SiC substrates at a high etch rate of about 2 {mu}m/min using high-density SF{sub 6}/O{sub 2} inductively coupled plasma. The etch rate of SI-SiC was found to be lower than that of n-SiC, and the etching profile of SI-SiC showed retrograde features with a larger sidewall angle and a rounder etched bottom compared to n-SiC. These characteristics are attributed to the difference in wafer heating and negative charging of the sidewall during plasma etching between both substrates. The temperature of n-SiC increases by radiative heating from the high-density plasma during etching because of the higher free-carrier absorption compared to SI-SiC. Furthermore, the negative charge buildup at the sidewall of SI-SiC becomes stronger because of the lower electrical conductivity compared to n-SiC.

  20. The semi-insulating GaAs-based particle detector at IEE SAS: first imaging results

    NASA Astrophysics Data System (ADS)

    Darmo, J.; Dubecký, F.; Zat'ko, B.; Boháček, P.; Sekáčová, M.; Kvitkovič, J.; Nečas, V.; Pelfer, P. G.

    2001-02-01

    A particle detector made of semi-insulating GaAs is used for preliminary study of X-ray imaging. A standard technology developed in our laboratory is applied to prepare this detector. The detector works at room temperature in the photon counting mode. Results show that the quality of images taken at chosen exposure range is limited only by the photonic noise from used X-ray source 241Am.

  1. Advanced BCD technology with vertical DMOS based on a semi-insulation structure

    NASA Astrophysics Data System (ADS)

    Kui, Ma; Xinghua, Fu; Jiexin, Lin; Fashun, Yang

    2016-07-01

    A new semi-insulation structure in which one isolated island is connected to the substrate was proposed. Based on this semi-insulation structure, an advanced BCD technology which can integrate a vertical device without extra internal interconnection structure was presented. The manufacturing of the new semi-insulation structure employed multi-epitaxy and selectively multi-doping. Isolated islands are insulated with the substrate by reverse-biased PN junctions. Adjacent isolated islands are insulated by isolation wall or deep dielectric trenches. The proposed semi-insulation structure and devices fixed in it were simulated through two-dimensional numerical computer simulators. Based on the new BCD technology, a smart power integrated circuit was designed and fabricated. The simulated and tested results of Vertical DMOS, MOSFETs, BJTs, resistors and diodes indicated that the proposed semi-insulation structure is reasonable and the advanced BCD technology is validated. Project supported by the National Natural Science Foundation of China (No. 61464002), the Science and Technology Fund of Guizhou Province (No. Qian Ke He J Zi [2014]2066), and the Dr. Fund of Guizhou University (No. Gui Da Ren Ji He Zi (2013)20Hao).

  2. Studies of Nonradiative Recombination Centers in GaAs and InP*

    NASA Astrophysics Data System (ADS)

    Tuzemen, S.; Liang, Difei; Ucer, K. B.; Williams, R. T.

    2001-03-01

    The "reverse contrast" recombination center in semi-insulating GaAs, so named because of its anti-correlation with EL2 defects in spatial mapping, has been attributed to As-vacancy centers.^1 Several details of the nature of its optical transitions and of its spatial distribution are among questions open to experimental investigation. We report experiments on spectroscopy and spatial mapping of defects in semi-insulating GaAs and Fe-doped InP. *ST acknowledges the CIES for support as a Fulbright Scholar at WFU. The research at WFU is supported by NSF grant DMR-9732023. Confocal microscopy in cooperation with K. Grant and the MicroMed Facility of WFU. 1. C. Le Berre, C. Corbel, R. Mih, M. R. Brozel, S. Tüzemen, S. Kuisma, K. Saarinen, P. Hautojarvi, and R. Fornari, Appl. Phys. Lett. 66, 2354 (1995).

  3. Extrinsic doped n- and p-type CdTe layers grown by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Taskar, N. R.; Natarajan, V.; Bhat, I. B.; Grandhi, S. K.

    1988-01-01

    In this paper we report on the extrinsic n- and p-doping of CdTe layers, grown by organometallic vapor phase epitaxy. Triethylindium and arsine gas were used as n- and p-type dopants respectively, with doping levels of around 1017 cm-3 in both cases. Layers were grown on both semi-insulating CdTe and GaAs substrates. Layers grown on semi-insulating GaAs had an intervening 1-2 μm undoped CdTe layer to relieve the strain caused by the large (14.6%) lattice mismatch of the CdTe-GaAs combination. Van der Pauw measurements were made to evaluate the quality of these layers, and mobility values as high as 3600 cm2/V h- s obtained at 40 K for lightly doped n-type samples. Grown junctions, made using extrinsic doped layers, have resulted in diodes with excellent electrical characteristics.

  4. Extrinsic doped n- and p-type CdTe layers grown by organometallic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Taskar, N. R.; Natarajan, V.; Bhat, I. B.; Grandhi, S. K.

    1990-01-01

    In this paper we report on the extrinsic n- and p-doping of CdTe layers, grown by organometallic vapor phase epitaxy. Triethylindium and arsine gas were used as n- and p-type dopants respectively, with doping levels of around 10 17 cm -3 in both cases. Layers were grown on both semi-insulating CdTe and GaAs substrates. Layers grown on semi-insulating GaAs had an intervening 1-2 μm undoped CdTe layer to relieve the strain caused by the large (14.6%) lattice mismatch of the CdTe-GaAs combination. Van der Pauw measurements were made to evaluate the quality of these layers, and mobility values as high as 3600 cm 2/V h- s obtained at 40 K for lightly doped n-type samples. Grown junctions, made using extrinsic doped layers, have resulted in diodes with excellent electrical characteristics.

  5. Doping incorporation paths in catalyst-free Be-doped GaAs nanowires

    SciTech Connect

    Casadei, Alberto; Heiss, Martin; Colombo, Carlo; Ruelle, Thibaud; Fontcuberta i Morral, Anna; Krogstrup, Peter; Roehr, Jason A.; Upadhyay, Shivendra; Sorensen, Claus B.; Nygard, Jesper

    2013-01-07

    The incorporation paths of Be in GaAs nanowires grown by the Ga-assisted method in molecular beam epitaxy have been investigated by electrical measurements of nanowires with different doping profiles. We find that Be atoms incorporate preferentially via the nanowire side facets, while the incorporation path through the Ga droplet is negligible. We also show that Be can diffuse into the volume of the nanowire giving an alternative incorporation path. This work is an important step towards controlled doping of nanowires and will serve as a help for designing future devices based on nanowires.

  6. Crystal growth of completely dislocation-free and striation-free GaAs

    NASA Astrophysics Data System (ADS)

    Kohda, H.; Yamada, K.; Nakanishi, H.; Kobayashi, T.; Osaka, J.

    1985-06-01

    Completely dislocation-free and striation-free, semi-insulating GaAs crystals with 50 mm diameter were grown by means of the newly developed Czochralski process. These crytals were obtained by combining the following techniques: (1) A dislocation-free seed crystal is used to eliminate grown-in dislocations; (2) the fully encapsulated Czochralski (FEC) method is applied in combination with indium doping to suppress stress-induced dislocations; and (3) a vertical magnetic-field is applied to homogenize the distribution of doped indium.

  7. n-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires

    NASA Astrophysics Data System (ADS)

    Gutsche, Christoph; Lysov, Andrey; Regolin, Ingo; Blekker, Kai; Prost, Werner; Tegude, Franz-Josef

    2011-12-01

    In this letter, n-type doping of GaAs nanowires grown by metal-organic vapor phase epitaxy in the vapor-liquid-solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations N D of GaAs nanowires are found to vary from 7 × 1017 cm-3 to 2 × 1018 cm-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices.

  8. n-Type Doping of Vapor-Liquid-Solid Grown GaAs Nanowires.

    PubMed

    Gutsche, Christoph; Lysov, Andrey; Regolin, Ingo; Blekker, Kai; Prost, Werner; Tegude, Franz-Josef

    2011-12-01

    In this letter, n-type doping of GaAs nanowires grown by metal-organic vapor phase epitaxy in the vapor-liquid-solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 10(17) cm(-3) to 2 × 10(18) cm(-3). The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal-insulator-semiconductor field-effect transistor devices.

  9. Ohmic contacts to GaAs for high-temperature device applications

    NASA Technical Reports Server (NTRS)

    Anderson, W. T., Jr.; Christou, A.; Giuliani, J. F.; Dietrich, H. B.

    1981-01-01

    Ohmic contacts to n-type GaAs were developed for high temperature device applications up to 300 C. Refractory metallizations were used with epitaxial Ge layers to form the contacts: TiW/Ge/GaAs, Ta/Ge/GaAs, Mo/Ge/GaAs, and Ni/Ge/GaAs. Contacts with high dose Si or Se ion implantation of the Ge/GaAs interface were also investigated. The contacts were fabricated on epitaxial GaAs layer grown on N+ or semi-insulating GaAs substrates. Ohmic contact was formed by both thermal annealing (at temperatures up to 700 C) and laser annealing (pulsed Ruby). Examination of the Ge/GaAs interface revealed Ge migration into GaAs to form an N+ doping layer. The specific contact resistances of specimens annealed by both methods are given.

  10. Recombination dynamics in aerotaxy-grown Zn-doped GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Yang, Fangfang; Messing, Maria E.; Mergenthaler, Kilian; Pistol, Mats-Erik; Deppert, Knut; Samuelson, Lars; Magnusson, Martin H.; Yartsev, Arkady

    2016-11-01

    In this paper we have investigated the dynamics of photo-generated charge carriers in a series of aerotaxy-grown GaAs nanowires (NWs) with different levels of Zn doping. Time-resolved photo-induced luminescence and transient absorption have been employed to investigate radiative (band edge transition) and non-radiative charge recombination processes, respectively. We find that the photo-luminescence (PL) lifetime of intrinsic GaAs NWs is significantly increased after growing an AlGaAs shell over them, indicating that an AlGaAs shell can effectively passivate the surface of aerotaxy-grown GaAs NWs. We observe that PL decay time as well as PL intensity decrease with increasing Zn doping, which can be attributed to thermally activated electron trapping with the trap density increased due to the Zn doping level.

  11. Infrared absorption properties of the EL2 and the isolated As/sub Ga/ defects in neutron-transmutation-doped GaAs: Generation of an EL2-like defect

    SciTech Connect

    Manasreh, M.O.; Fischer, D.W.

    1989-02-15

    The EL2 and the isolated As/sub Ga/ antisite defects in neutron-transmutation-doped (NTD) GaAs were studied by using the infrared (ir) absorption technique concurrent with thermal annealing. The results show that irradiation with low thermal-neutron doses partially decomposes the EL2 complex in semi-insulating (si) GaAs grown by the liquid-encapsulated Czochralski (LEC) growth technique. On the other hand, a small amount of EL2 is generated in as-grown Ga-rich undoped p-type LEC GaAs. The EL2 defect in low-dose thermal-neutron-irradiated samples (both si and p-type) was found to be stable up to 850 /sup 0/C. High neutron-irradiation doses, however, completely annihilate EL2 but generate a different EL2-like defect (DL2). The DL2 defect is observed after annealing the high-dose NTD samples for 6 min at 600 /sup 0/C. The DL2 concentration is observed to be larger than that of EL2 in as-grown LEC si GaAs by a factor of 2.3 or higher. The photoquenching and thermal recovery properties of DL2 and EL2 defects are identical. However, the DL2 defect does not exhibit the same thermal stability or the zero-phonon line of the EL2 defect. Thermal annealing kinetics shows that DL2 is composed of three point defects. The residual absorption (unquenchable component) after photoquenching the EL2 (DL2) defect is interpreted as the photoionization of the isolated As/sub Ga/ antisite.

  12. Dielectric properties of semi-insulating silicon at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Krupka, Jerzy; Kamiński, Paweł; Kozłowski, Roman; Surma, Barbara; Dierlamm, Alexander; Kwestarz, Michał

    2015-08-01

    The permittivity and dielectric loss tangent of high-purity silicon with semi-insulating properties achieved by the irradiation with 23-MeV protons have been measured at frequencies from 1 GHz to 15 GHz. The dielectric losses were separated from the conductor losses on the basis of the total loss tangent measurements versus frequency. The resistivity measurements of the material performed at radio frequencies (RF) by means of the capacitance spectroscopy method have shown the non-uniform resistivity distribution in the direction perpendicular to the surface of the semi-insulating wafer. The excellent agreement between the resistivity measurements results at RF and those obtained by using microwave methods have been achieved. It has been confirmed that high-purity, semi-insulating silicon is practically non-dispersive and possesses extremely low dielectric losses that are constant to within experimental errors in the frequency range from 1 GHz to 350 GHz. In this frequency range, the dielectric loss tangent of semi-insulating silicon is equal to 1.2 ×10-5 .

  13. Te-doping of self-catalyzed GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Suomalainen, S.; Hakkarainen, T. V.; Salminen, T.; Koskinen, R.; Honkanen, M.; Luna, E.; Guina, Mircea

    2015-07-01

    Tellurium (Te)-doping of self-catalyzed GaAs nanowires (NWs) grown by molecular beam epitaxy is reported. The effect of Te-doping on the morphological and crystal structure of the NWs is investigated by scanning electron microscopy and high-resolution transmission electron microscopy. The study reveals that the lateral growth rate increases and axial growth rate decreases with increasing Te doping level. The changes in the NW morphology can be reverted to some extent by changing the growth temperature. At high doping levels, formation of twinning superlattice is observed alongside with the {111}-facetted sidewalls. Finally, the incorporation of Te is confirmed by Raman spectroscopy.

  14. Te-doping of self-catalyzed GaAs nanowires

    SciTech Connect

    Suomalainen, S. Hakkarainen, T. V.; Salminen, T.; Koskinen, R.; Guina, Mircea; Honkanen, M.; Luna, E.

    2015-07-06

    Tellurium (Te)-doping of self-catalyzed GaAs nanowires (NWs) grown by molecular beam epitaxy is reported. The effect of Te-doping on the morphological and crystal structure of the NWs is investigated by scanning electron microscopy and high-resolution transmission electron microscopy. The study reveals that the lateral growth rate increases and axial growth rate decreases with increasing Te doping level. The changes in the NW morphology can be reverted to some extent by changing the growth temperature. At high doping levels, formation of twinning superlattice is observed alongside with the (111)-facetted sidewalls. Finally, the incorporation of Te is confirmed by Raman spectroscopy.

  15. Inversion of spin dependent photocurrent at Fe3O4/modulation doped GaAs heterointerfaces

    NASA Astrophysics Data System (ADS)

    Shirahata, Y.; Wada, E.; Itoh, M.; Taniyama, T.

    2011-04-01

    We demonstrate inversion of the spin dependent photocurrent across an Fe3O4/modulation doped GaAs interface under optical spin orientation condition. The spin dependent photocurrent for fully epitaxial Fe3O4/GaAs and Fe/GaAs interfaces clearly show the opposite magnetic field dependence, where the spin filtering efficiency for the Fe3O4/GaAs decreases with increasing magnetic field. The results clearly indicate that the spin polarization of the Fe3O4 layer has the opposite sign to that of Fe at the Fermi energy, consistent with theoretical predictions, and the result is a consequence of the atomically flat Fe3O4/GaAs interface we obtained.

  16. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Nam Hai, Pham; Maruo, Daiki; Tanaka, Masaaki

    2014-03-01

    We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4A2(4F) → 4T1(4G) and 4T1(4G) → 6A1(6S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs.

  17. Passively Q-switched and mode-locked Nd:GGG laser with a Bi-doped GaAs saturable absorber.

    PubMed

    Cong, Wen; Li, Dechun; Zhao, Shengzhi; Yang, Kejian; Li, Xiangyang; Qiao, Hui; Liu, Ji

    2014-06-16

    A simultaneously passively Q-switched and mode-locked (QML) Nd:GGG laser using a Bi-doped GaAs wafer as saturable absorber is accomplished for the first time. The Bi-doped GaAs wafer is fabricated by ion implantation and subsequent annealing. In comparison to the passively QML laser with GaAs, the QML laser with Bi-doped GaAs can generate more stable pulses with 99% modulation depth. The experiment results indicate that the Bi-doped GaAs could be an excellent saturable absorber for diode-pumped QML lasers.

  18. Passively Q-switched and mode-locked Nd:GGG laser with a Bi-doped GaAs saturable absorber.

    PubMed

    Cong, Wen; Li, Dechun; Zhao, Shengzhi; Yang, Kejian; Li, Xiangyang; Qiao, Hui; Liu, Ji

    2014-06-16

    A simultaneously passively Q-switched and mode-locked (QML) Nd:GGG laser using a Bi-doped GaAs wafer as saturable absorber is accomplished for the first time. The Bi-doped GaAs wafer is fabricated by ion implantation and subsequent annealing. In comparison to the passively QML laser with GaAs, the QML laser with Bi-doped GaAs can generate more stable pulses with 99% modulation depth. The experiment results indicate that the Bi-doped GaAs could be an excellent saturable absorber for diode-pumped QML lasers. PMID:24977576

  19. Diode-pumped passively Q-switched Nd:GGG laser with a Bi-doped GaAs semiconductor saturable absorber

    NASA Astrophysics Data System (ADS)

    Cong, Wen; Li, Dechun; Zhao, Shengzhi; Yang, Kejian; Li, Xiangyang; Qiao, Hui; Liu, Ji

    2014-12-01

    Passive Q-switching of a diode-pumped Nd:GGG laser is demonstrated using Bi-doped GaAs as saturable absorber. The Bi-doped GaAs wafer is fabricated by ion implantation and subsequent annealing. Compared with the Q-switched laser by undoped GaAs semiconductor saturable absorber, the laser with Bi-doped GaAs as saturable absorber can produce higher output power, shorter pulses, higher single pulse energies and higher peak powers. These results suggest that Bi-doped GaAs can be a promising new candidate of semiconductor saturable absorber in Q-switched laser.

  20. Increased Photoconductivity Lifetime in GaAs Nanowires by Controlled n-Type and p-Type Doping.

    PubMed

    Boland, Jessica L; Casadei, Alberto; Tütüncüoglu, Gözde; Matteini, Federico; Davies, Christopher L; Jabeen, Fauzia; Joyce, Hannah J; Herz, Laura M; Fontcuberta I Morral, Anna; Johnston, Michael B

    2016-04-26

    Controlled doping of GaAs nanowires is crucial for the development of nanowire-based electronic and optoelectronic devices. Here, we present a noncontact method based on time-resolved terahertz photoconductivity for assessing n- and p-type doping efficiency in nanowires. Using this technique, we measure extrinsic electron and hole concentrations in excess of 10(18) cm(-3) for GaAs nanowires with n-type and p-type doped shells. Furthermore, we show that controlled doping can significantly increase the photoconductivity lifetime of GaAs nanowires by over an order of magnitude: from 0.13 ns in undoped nanowires to 3.8 and 2.5 ns in n-doped and p-doped nanowires, respectively. Thus, controlled doping can be used to reduce the effects of parasitic surface recombination in optoelectronic nanowire devices, which is promising for nanowire devices, such as solar cells and nanowire lasers.

  1. Determination of Fe{sup 2+} and Fe{sup 3+} concentrations of semi- insulating InP:Fe

    SciTech Connect

    Zach, F.X.; Bourret, E.D.; Bliss, D.; Weber, E.R.; Haller, E.E.

    1992-01-01

    Semi-insulating InP is most commonly obtained by doping with the deep acceptor iron to compensate the shallow donors which otherwise render the material n-type conducting. As the Fermi level in semi-insulating InP is closed to the iron acceptor level, both charge states - Fe{sup 2+} as well as Fe{sup 3+} corresponding to the acceptor level occupied unoccupied by an electron - are present. Mayor et al.(1) presented a method based on absorption measurements in the nearbandgap region of InP to determine the concentration of both charge states separately. In this paper we compare iron concentrations obtained by this method with the results from intracenter absorption, DLTS, EPR, Hall effect measurements and glow discharge mass spectroscopy. We present a new calibration for the optical absorption cross sections.

  2. Determination of Fe sup 2+ and Fe sup 3+ concentrations of semi- insulating InP:Fe

    SciTech Connect

    Zach, F.X.; Bourret, E.D. ); Bliss, D. ); Weber, E.R.; Haller, E.E. . Dept. of Materials Science and Mineral Engineering)

    1992-01-01

    Semi-insulating InP is most commonly obtained by doping with the deep acceptor iron to compensate the shallow donors which otherwise render the material n-type conducting. As the Fermi level in semi-insulating InP is closed to the iron acceptor level, both charge states - Fe{sup 2+} as well as Fe{sup 3+} corresponding to the acceptor level occupied unoccupied by an electron - are present. Mayor et al.(1) presented a method based on absorption measurements in the nearbandgap region of InP to determine the concentration of both charge states separately. In this paper we compare iron concentrations obtained by this method with the results from intracenter absorption, DLTS, EPR, Hall effect measurements and glow discharge mass spectroscopy. We present a new calibration for the optical absorption cross sections.

  3. On magnetism and the insulator-to-metal transition in p-doped GaAs

    NASA Astrophysics Data System (ADS)

    Chapler, Brian; Myers, R. C.; Mack, S.; Frenzel, A.; Pursley, B. C.; Burch, K. S.; Singley, E. J.; Dattelbaum, A. M.; Samarth, N.; Awschalom, D. D.; Basov, D. N.

    2011-03-01

    Although Ga 1-x Mn x As is often described as the prototypical ferromagnetic semiconductor, many aspects of the electronic structure and nature of mediating carriers remain open. A central question in this regard is whether the insulator-to-metal transition (IMT) in p -doped GaAs is significantly modified when dopants are magnetic. We address this through an infrared spectroscopic study of GaAs doped with either non-magnetic Be or magnetic Mn acceptors. Through our comparison, we are able to isolate effects of magnetic dopants in GaAs from those associated with disorder and proximity to the IMT. Here we show Mn-doped samples exhibit an unusual electronic transport regime, combining elements of both metallic and insulating behavior, at doping concentrations far beyond the onset of the IMT. Be-doped films however, reveal genuine metallicity just above the IMT boundary. These results underscore the pivotal role of magnetism in transport and optical phenomena of Ga 1-x Mn x As.

  4. Thermal annealing and zinc doping effects on the lattice constant of organometallic vapor phase grown GaAs epilayers on heavily In-doped substrates

    NASA Astrophysics Data System (ADS)

    Imai, Tetsuji; Fuke, Shunro; Mori, Katsumi; Kuwahara, Kazuhiro

    1989-02-01

    Undoped and Zn-doped (˜3×1020/cm3) GaAs epilayers are grown on In-doped (order of 1020/cm3) GaAs substrates by the organometallic vapor phase epitaxy method. By thermal annealing of the undoped epilayer, changes in the perpendicular lattice constant a⊥, together with the apparent changes in surface morphology such as the appearance of a cross-hatched structure or a narrowing of the cross-hatched line spacing, are observed. It is also found that Zn doping is very effective to obtain thick, coherently grown epilayers on In-doped GaAs substrates. No appreciable changes in a⊥ and no generation of misfit dislocations are found because of the hardening of the crystalline lattice, similar to the case of In doping to GaAs bulk crystals.

  5. Supralinear photoconductivity of copper doped semi-insulating gallium arsenide

    SciTech Connect

    Schoenbach, K.H.; Joshi, R.P.; Peterkin, F.; Druce, R.L.

    1995-05-15

    We report on the intensity dependent supralinear photoconductivity in GaAs:Si:Cu material. The results of our measurements show that the effective carrier lifetime can change over two orders of magnitude with variations in the intensity of the optical excitation. A threshold intensity level has been observed and can be related to the occupancy of the deep copper level. Numerical simulations have also been carried out to analyze the trapping dynamics. The intensity dependent lifetimes obtained from the simulations match the experimental data very well. Finally, based on the nonlinear intensity dependence of the effective lifetimes, a possible low-energy phototransistor application for the GaAs:Cu material system is presented. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  6. Doping concentration dependence of the photoluminescence spectra of n-type GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Arab, Shermin; Yao, Maoqing; Zhou, Chongwu; Daniel Dapkus, P.; Cronin, Stephen B.

    2016-05-01

    In this letter, the photoluminescence spectra of n-type doped GaAs nanowires, grown by the metal organic chemical vapor deposition method, are measured at 4 K and 77 K. Our measurements indicate that an increase in carrier concentration leads to an increase in the complexity of the doping mechanism, which we attribute to the formation of different recombination centers. At high carrier concentrations, we observe a blueshift of the effective band gap energies by up to 25 meV due to the Burstein-Moss shift. Based on the full width at half maximum (FWHM) of the photoluminescence peaks, we estimate the carrier concentrations for these nanowires, which varies from 6 × 1017 cm-3 (lightly doped), to 1.5 × 1018 cm-3 (moderately doped), to 3.5 × 1018 cm-3 (heavily doped) as the partial pressure of the disilane is varied from 0.01 sccm to 1 sccm during the growth process. We find that the growth temperature variation does not affect the radiative recombination mechanism; however, it does lead to a slight enhancement in the optical emission intensities. For GaAs nanowire arrays measured at room temperature, we observe the same general dependence of band gap, FWHM, and carrier concentration on doping.

  7. Local electronic structure and magnetic properties of 3d transition metal doped GaAs

    NASA Astrophysics Data System (ADS)

    Lin, He; Duan, Haiming

    2008-05-01

    The local electronic structure and magnetic properties of GaAs doped with 3d transition metal (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) were studied by using discrete variational method (DVM) based on density functional theory. The calculated result indicated that the magnetic moment of transition metal increases first and then decreases, and reaches the maximum value when Mn is doped into GaAs. In the case of Mn concentration of 1.4%, the magnetic moment of Mn is in good agreement with the experimental result. The coupling between impure atoms in the system with two impure atoms was found to have obvious variation. For different transition metal, the coupling between the impure atom and the nearest neighbor As also has different variation.

  8. Optical and Surface Characteristics of Mg-Doped GaAs Nanocrystalline Thin Film Deposited by Thermionic Vacuum Arc Technique

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Magnesium (Mg) is the most promising p-type dopant for gallium arsenide (GaAs) semiconductor technology. Mg-doped GaAs nanocrystalline thin film has been deposited at room temperature by the thermionic vacuum arc technique, a rapid deposition method for production of doped GaAs material. The microstructure and surface and optical properties of the deposited sample were investigated by x-ray diffraction analysis, scanning electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, ultraviolet-visible spectrophotometry, and interferometry. The crystalline direction of the deposited sample was determined to be (220) plane and (331) plane at 44.53° and 72.30°, respectively. The Mg-doped GaAs nanocrystalline sample showed high transmittance.

  9. Determination of doping profiles on bevelled GaAs structures by Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Srnanek, R.; Kinder, R.; Sciana, B.; Radziewicz, D.; McPhail, D. S.; Littlewood, S. D.; Novotny, I.

    2001-06-01

    A method for determination of doping concentration profiles of GaAs multilayer structures on a bevelled surface by Raman spectroscopy is presented. By scanning the laser beam along the bevel we obtained micro-Raman spectra in different depth positions in the structure. Calculated ITO/ ILO intensities determine the doping concentration in these points for values above 3×10 16 cm -3. The results are compared with electrochemical capacitance-voltage technique and secondary ion mass spectrometry. Some specific problems are discussed.

  10. Carbon doping in molecular beam epitaxy of GaAs from a heated graphite filament

    NASA Technical Reports Server (NTRS)

    Malik, R. J.; Nottenberg, R. N.; Schubert, E. F.; Walker, J. F.; Ryan, R. W.

    1988-01-01

    Carbon doping of GaAs grown by molecular beam epitaxy has been obtained for the first time by use of a heated graphite filament. Controlled carbon acceptor concentrations over the range of 10 to the 17th-10 to the 20th/cu cm were achieved by resistively heating a graphite filament with a direct current power supply. Capacitance-voltage, p/n junction and secondary-ion mass spectrometry measurements indicate that there is negligible diffusion of carbon during growth and with postgrowth rapid thermal annealing. Carbon was used for p-type doping in the base of Npn AlGaAs/GaAs heterojunction bipolar transistors. Current gains greater than 100 and near-ideal emitter heterojunctions were obtained in transistors with a carbon base doping of 1 x 10 to the 19th/cu cm. These preliminary results indicate that carbon doping from a solid graphite source may be an attractive substitute for beryllium, which is known to have a relatively high diffusion coefficient in GaAs.

  11. Doped Contacts for High-Longevity Optically Activated, High Gain GaAs Photoconductive Semiconductor Switches

    SciTech Connect

    MAR,ALAN; LOUBRIEL,GUILLERMO M.; ZUTAVERN,FRED J.; O'MALLEY,MARTIN W.; HELGESON,WESLEY D.; BROWN,DARWIN JAMES; HJALMARSON,HAROLD P.; BACA,ALBERT G.; THORNTON,R.L.; DONALDSON,R.D.

    1999-12-17

    The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 100 million pulses. This was achieved by improving the ohmic contacts through the incorporation of a doped layer that is very effective in the suppression of filament formation, alleviating current crowding. Damage-free operation is now possible with virtually infinite expected lifetime at much higher current levels than before. The inherent damage-free current capacity of the bulk GaAs itself depends on the thickness of the doped layers and is at least 100A for a dopant diffusion depth of 4pm. The contact metal has a different damage mechanism and the threshold for damage ({approx}40A) is not further improved beyond a dopant diffusion depth of about 2{micro}m. In a diffusion-doped contact switch, the switching performance is not degraded when contact metal erosion occurs, unlike a switch with conventional contacts. This paper will compare thermal diffusion and epitaxial growth as approaches to doping the contacts. These techniques will be contrasted in terms of the fabrication issues and device characteristics.

  12. Passive Q-switching with GaAs or Bi-doped GaAs saturable absorber in Tm:LuAG laser operating at 2μm wavelength.

    PubMed

    Wu, Lin; Li, Dechun; Zhao, Shengzhi; Yang, Kejian; Li, Xiangyang; Wang, Reng; Liu, Ji

    2015-06-15

    We report the first demonstration of a diode pumped passively Q-switched Tm:LuAG laser near 2μm wavelength with Bi-doped or undoped GaAs wafer as saturable absorber. For Bi-doped GaAs saturable absorber, stable Q-switched pulses with duration of 63.3ns under a repetition rate of 132.7 kHz and pulse energy of 5.51μJ are generated. In comparison to the passively Q-switched laser with undoped GaAs saturable absorber, the laser with Bi-doped GaAs can produce shorter pulses and higher peak power at almost the same incident pump power. The results suggest that Bi-doped GaAs can be an attractive candidate of saturable absorber for Q-switched laser near 2μm wavelength.

  13. Effects of gold diffusion on n-type doping of GaAs nanowires.

    PubMed

    Tambe, Michael J; Ren, Shenqiang; Gradecak, Silvija

    2010-11-10

    The deposition of n-GaAs shells is explored as a method of n-type doping in GaAs nanowires grown by the Au-mediated metal-organic chemical vapor deposition. Core-shell GaAs/n-GaAs nanowires exhibit an unintended rectifying behavior that is attributed to the Au diffusion during the shell deposition based on studies using energy dispersive X-ray spectroscopy, current-voltage, capacitance-voltage, and Kelvin probe force measurements. Removing the gold prior to n-type shell deposition results in the realization of n-type GaAs nanowires without rectification. We directly correlate the presence of gold impurities to nanowire electrical properties and provide an insight into the role of seed particles on the properties of nanowires and nanowire heterostructures.

  14. Elimination of DX centerlike behavior of donors in heavily doped GaAs

    NASA Astrophysics Data System (ADS)

    Suski, T.; Wisniewski, P.; Skierbiszewski, C.; Dmowski, L. H.; van der Wel, P. J.; Singleton, J.; Giling, L. J.; Harris, J. J.

    1991-03-01

    The pressure dependencies of the electrical conductivity, Hall coefficient, and Shubnikov-de-Haas effect have been studied for n-GaAs heavily doped with Sn and Te. The results demonstrate that the energy level related to the DX centers formed by these donors is resonant and degenerate with the conduction band of GaAs. The energy separation of the GaAs conduction-band minimum and the DX center (EDX) for the Sn donor has been found to be similar to those of the Si- and S-related DX centers (around 0.3 eV at T≊100 K), whereas EDX(Te) is much greater, at around 0.55 eV. An analysis of the sample recovery after pressure-induced freezeout of electrons onto the DX centers has enabled the energy barrier for electron emission from the Sn-related DX center to the conduction band and the barrier for electron capture by the DX center, the inverse process, to be determined. Both energy barriers are very small compared to those associated with Si- and S-donor-induced DX centers. The values for EDX (for Sn and Te) and the barrier sizes (for Sn) measured in this work for donors in GaAs are found to be rather different than the equivalent energies in (Ga,Al)As, and this difference is interpreted as evidence that the local vicinity of the DX center (Ga only or Al/Ga) strongly influences its properties. Finally, these results have led to the proposal of Te as the most effective dopant from the point of view of elimination of the DX centerlike properties of donors in heavily doped GaAs.

  15. Wavelength dependent negative and positive persistent photoconductivity in Sn δ-doped GaAs structures

    NASA Astrophysics Data System (ADS)

    Kulbachinskii, V. A.; Kytin, V. G.; Golikov, A. V.; Lunin, R. A.; van Schaijk, R. T. F.; de Visser, A.; Senichkin, A. P.; Bugaev, A. S.

    2000-09-01

    The photoconductivity of GaAs structures δ-doped by Sn has been investigated for wavelengths λ = 650-1200 nm in the temperature interval T = 4.2-300 K. The electron densities and mobilities, before and after illumination, have been determined by magnetoresistance, Shubnikov-de Haas effect and Hall effect measurements, in high magnetic fields. For the heavily doped structures (Hall density nH>2×1013 cm-2) we observe under illumination by light with wavelengths larger than the bandgap wavelength of the host material (λ = 815 nm at T = 4.2 K) first positive (PPPC) and then negative (NPPC) persistent photoconductivity. The NPPC is attributed to the ionization of DX centres and PPPC is explained by the excitation of electrons from Cr impurity states in the substrate. For λ<815 nm, in addition, the excitation of electrons over the bandgap of GaAs contributes to the PPPC. For the lightly doped structures (nH≤2×1013 cm-2) the photoconductivity effect is always positive.

  16. Indium-doped GaAs: Investigation of deep traps

    NASA Astrophysics Data System (ADS)

    Laurenti, J. P.; Wolter, K.; Roentgen, P.; Seibert, K.; Kurz, H.; Camassel, J.

    1989-03-01

    The effect of indium incorporation on the concentration of deep traps in a series of GaAs epitaxial layers has been investigated by performing quantitative photoluminescence (PL) and capacitance [deep-level transient spectroscopy (DLTS)] spectroscopic studies. All samples were epitaxial layers of n-type GaAs:In, grown by organometallic vapor-phase epitaxy (OMVPE) on liquid-encapsulated Czochralski (LEC) -grown GaAs:Cr substrates. The calibrated indium concentration ranged between 0 and 6.5×1019 atoms cm-3, which is about 0.3% in alloy composition. We have investigated (i) the bands associated with chromium in both the epitaxial layers and the original substrates; (ii) a large recombination band, associated with an unidentified (D-VGa) complex, at about 1.2 eV; and (iii) the DLTS signal associated with the well-known deep trap EL2. We find the following. First, there is a one-to-one correspondence between the PL intensity associated with Cr2+, at 0.84 eV, and the D-VGa signal at 1.2 eV. This is true for both the epitaxial layers and the original substrates and suggests identification of the unknown donor participating in the D-VGa complex as Cr4+. Second, we find all PL intensities to decrease with increasing indium concentration, while the concentration and depth profile of EL2 are not affected. In contrast to the near-band-edge PL intensity, which increased with increasing indium content, there is a drop by about 1 order of magnitude for all chromium-related features when going from indium-free to about 0.3% indium-rich sample. Moreover, there is a one-to-one correspondence between the increase in the near-band-edge PL intensity and the decrease in the chromium-related signals. This establishes, on a fully experimental basis, the relative roles played by indium and chromium in our epitaxial samples: both compete to incorporate on gallium sites in the strain field of neighboring vacancies but, because of a higher incorporation rate, increasing the indium

  17. Controlled axial and radial Te-doping of GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Salehzadeh, O.; Kavanagh, K. L.; Watkins, S. P.

    2012-09-01

    Tellurium (Te)-doping of Au-catalyzed GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy (MOVPE) via the vapor-liquid-solid (VLS) mechanism is presented. Electrical measurements were performed inside a scanning electron microscope by contacting a tungsten nanoprobe to the Au end of individual NWs grown on a heavily n-type GaAs substrate. Rectifying current-voltage (I-V) characteristics are observed due to the formation of a junction at the Au nanoparticle (NP)/NW interface. The electron concentration ne and contact barrier heights, φ0b, were determined from the analyses of these characteristics. As expected, φ0b increased (from 0.63 ± 0.03 eV to 0.71 ± 0.02 eV) with decreasing Te-precursor flow rate, corresponding to a decrease in ne from (9 ± 1) × 1017 cm-3 to (1.5 ± 0.5) × 1017 cm-3. Meanwhile, undoped NWs had space-charge-limited characteristics. There was a large influence of the residual gallium (Ga) in the NP, on barrier properties, controlled by the group V precursor flow (on or off) during the cooling of the NW sample at the end of the growth process. With the group V flow off during cooling, a decrease in φ0b from 0.79 ± 0.04 eV to 0.63 ± 0.03 eV is observed consistent with a higher Ga alloy concentration in the NP, confirmed by energy dispersive spectroscopy measurements. We also demonstrate the fabrication of core/shell, undoped/Te-doped, GaAs NWs with very high Te doping (˜1019 cm-3).

  18. Doped Contacts for High-Longevity Optically Activated, High Gain GaAs Photoconductive Semiconductor Switches

    SciTech Connect

    Baca, A.G.; Brown, D.J.; Donaldson, R.D.; Helgeson, W.D.; Hjalmarson, H.P.; Loubriel, G.M.; Mar, A.; O'Malley, M.W.; Thornton, R.L.; Zutavern, F.J.

    1999-08-05

    The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 50 million pulses. This was achieved by improving the ohmic contacts through the incorporation of a doped layer beneath the PCSS contacts which is very effective in the suppression of filament formation and alleviating current crowding to improve the longevity of PCSS. Virtually indefinite, damage-free operation is now possible at much higher current levels than before. The inherent damage-free current capacity of the switch depends on the thickness of the doped layers and is at least 100A for a dopant diffusion depth of 4pm. The contact metal has a different damage mechanism and the threshold for damage ({approximately}40A) is not further improved beyond a dopant diffusion depth of about 2{micro}m. In a diffusion-doped contact switch, the switching performance is not degraded when contact metal erosion occurs. This paper will compare thermal diffusion and epitaxial growth as approaches to doping the contacts. These techniques will be contrasted in terms of the fabrication issues and device characteristics.

  19. Large anomalous Hall resistance of pair {delta}-doped GaAs structures grown by molecular-beam epitaxy

    SciTech Connect

    Jung, D. W.; Noh, J. P.; Touhidul Islam, A. Z. M.; Otsuka, N.

    2008-02-15

    Beryllium/silicon pair {delta}-doped GaAs structures grown by molecular-beam epitaxy exhibit a Hall resistance which has a nonlinear dependence on the applied magnetic field and which is strongly correlated to the negative magnetoresistance observed under the applied magnetic field parallel to the {delta}-doped layers. Dependence of the occurrence of the nonlinear Hall resistance on the growth condition is investigated. A significantly large increase in both the magnitude and the nonlinearity of the Hall resistance is observed from samples whose GaAs buffer layers are grown under the condition of a low As/Ga flux ratio. Reflection high energy electron diffraction and electron microscope observations show that a faceted surface develops with the growth and postgrowth annealing of a GaAs buffer layer under the condition of a low As flux. From samples which have only Si {delta}-doped layers and exhibit the n-type conduction, such nonlinear Hall resistance is not observed. The nonlinearity of the Hall resistance of Be/Si pair {delta}-doped structures depends on the single parameter B/T, where B and T are the applied magnetic field and the temperature, respectively. Based on these results, it is suggested that the nonlinear Hall resistance of Be/Si pair {delta}-doped structures is the anomalous Hall effect caused by localized spins in {delta}-doped layers.

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

    SciTech Connect

    Shim, Seong Hoon; Kim, Hyung-jun; Koo, Hyun Cheol; Lee, Yun-Hi; Chang, Joonyeon

    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.

  1. Pressure-dependent studies of the DX centre in Si- and Sn-doped n +GaAs

    NASA Astrophysics Data System (ADS)

    Portal, J. C.; Maude, D. K.; Foster, T. J.; Eaves, L.; Dmowski, L.; Nathan, M.; Heiblum, M.; Harris, J. J.; Beall, R. B.; Simmonds, P. E.

    Shubnikov-de Haas and persistent photoconductivity measurements are used to study the effect of hydrostatic pressure on the free electron concentration, mobility, and the occupancy of the DX centre in MBE grown n +GaAs heavily doped with either Si or Sn. The results show that the DX centre produces a resonant donor level between the Γ- and L- conduction band minima at a concentration comparable with the doping level. The position and occupancy of the DX centre are calculated using Fermi-Dirac statistics. For the Si-doped samples comparison with local vibrational mode measurements indicate that the DX level can be identified with Si Ga.

  2. Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Burgess, Tim; Saxena, Dhruv; Mokkapati, Sudha; Li, Zhe; Hall, Christopher R.; Davis, Jeffrey A.; Wang, Yuda; Smith, Leigh M.; Fu, Lan; Caroff, Philippe; Tan, Hark Hoe; Jagadish, Chennupati

    2016-06-01

    Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications.

  3. Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires

    PubMed Central

    Burgess, Tim; Saxena, Dhruv; Mokkapati, Sudha; Li, Zhe; Hall, Christopher R.; Davis, Jeffrey A.; Wang, Yuda; Smith, Leigh M.; Fu, Lan; Caroff, Philippe; Tan, Hark Hoe; Jagadish, Chennupati

    2016-01-01

    Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications. PMID:27311597

  4. Doping-enhanced radiative efficiency enables lasing in unpassivated GaAs nanowires.

    PubMed

    Burgess, Tim; Saxena, Dhruv; Mokkapati, Sudha; Li, Zhe; Hall, Christopher R; Davis, Jeffrey A; Wang, Yuda; Smith, Leigh M; Fu, Lan; Caroff, Philippe; Tan, Hark Hoe; Jagadish, Chennupati

    2016-01-01

    Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications. PMID:27311597

  5. Electro-optic imagery of high-voltage GaAs photoconductive switches

    SciTech Connect

    Falk, R.A.; Adams, J.C.; Capps, C.D.; Ferrier, S.G.; Krinsky, J.A. )

    1995-01-01

    The authors present electro-optic images of GaAs high-voltage photoconductive switches utilizing the electro-optic effect of the semi-insulating GaAs substrate. Experimental methodology for obtaining the images is described along with a self-calibrating data reduction algorithm. Use of the technique for observing fabrication defects is shown.

  6. Optical and surface properties of the in doped GaAs layer deposition using thermionic vacuum arc method.

    PubMed

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

    2016-07-01

    A broadband optical transparent InGaAs semiconductor layer production of micron thicknesses was produced in only 75 s by thermionic vacuum arc (TVA) method at the first time. The optical and surface properties of the produced layers have been investigated. InGaAs structure is using in electronics and optoelectronics devices. The main advantage of TVA method is its fast deposition rate, without any loss in the quality of the films. Doping is a very simple and fast according to common production methods. InGaAs is an alloy of indium arsenide (InAs) and gallium arsenide (GaAs). InAs with (220) crystallographic direction and GaAs with (024)/(022) crystallographic directions were detected using by XRD analysis. GaAs and InAs are in the cubic and zinc blende crystal system, respectively. According to the transmittance spectra, sample has a broadband transparency in the range of 1000-3300 nm. According to results, defined TVA method for In doping to GaAs is proper fast and friendly method. SCANNING 38:297-302, 2016. © 2015 Wiley Periodicals, Inc.

  7. Mesoscopic homogenization of semi-insulating GaAs by two-step post growth annealing

    SciTech Connect

    Hoffmann, B.; Jurisch, M.; Koehler, A.; Reinhold, T.; Weinert, B.; Kissinger, G.

    1996-12-31

    Mesoscopic homogenization of the electrical properties of s.i. LEC-GaAs is commonly realized by thermal treatment of the crystals including the steps of dissolution of arsenic precipitates, homogenization of excess As and re-precipitation by creating a controlled supersaturation. Caused by the inhomogeneous distribution of dislocations and the corresponding cellular structure along and across LEC-grown crystals a proper choice of the time-temperature program is necessary to minimize fluctuations of mesoscopic homogeneity. A modified two-step ingot annealing process is demonstrated to ensure the homogeneous distribution of mesoscopic homogeneity.

  8. Diffusive electronic transport in superconductor-semiconductor-superconductor junctions of Al or Nb on δ-doped GaAs

    NASA Astrophysics Data System (ADS)

    Kutchinsky, J.; Taboryski, R. J.; Clausen, T.; Sørensen, C. B.; Lindelof, P. E.; Hansen, J. Bindslev; Jacobsen, C. Schelde; Skov, J. L.

    1996-02-01

    We report measurements on planar superconductor-semiconductor-superconductor (S-Sm-S) junctions consisting of a n++ modulation doped conduction layer in MBE grown GaAs with superconducting contacts of Al or Nb. At distances between the two superconducting banks below ≈3.5μm we observe a coupling between the two superconductors, due to multiple Andreev reflections at the S-Sm interfaces.

  9. Specific features of the photoconductivity of semi-insulating cadmium telluride

    SciTech Connect

    Golubyatnikov, V. A.; Grigor’ev, F. I.; Lysenko, A. P. Strogankova, N. I.; Shadov, M. B.; Belov, A. G.

    2014-12-15

    The effect of local illumination providing a high level of free-carrier injection on the conductivity of a sample of semi-insulating cadmium telluride and on the properties of ohmic contacts to the sample is studied. It is found that, irrespective of the illumination region, the contact resistance of ohmic contacts decreases and the concentration of majority carriers in the sample grows in proportion to the illumination intensity. It is shown that inherent heterogeneities in crystals of semi-insulating semiconductors can be studied by scanning with a light probe.

  10. Observations of exciton and carrier spin relaxation in Be doped p-type GaAs

    SciTech Connect

    Asaka, Naohiro; Harasawa, Ryo; Tackeuchi, Atsushi; Lu, Shulong; Dai, Pan

    2014-03-17

    We have investigated the exciton and carrier spin relaxation in Be-doped p-type GaAs. Time-resolved spin-dependent photoluminescence (PL) measurements revealed spin relaxation behaviors between 10 and 100 K. Two PL peaks were observed at 1.511 eV (peak 1) and 1.497 eV (peak 2) at 10 K, and are attributed to the recombination of excitons bound to neutral Be acceptors (peak 1) and the band-to-acceptor transition (peak 2). The spin relaxation times of both PL peaks were measured to be 1.3–3.1 ns at 10–100 K, and found to originate from common electron spin relaxation. The observed existence of a carrier density dependence of the spin relaxation time at 10–77 K indicates that the Bir-Aronov-Pikus process is the dominant spin relaxation mechanism.

  11. Surface passivation of tellurium-doped GaAs nanowires by GaP: Effect on electrical conduction

    SciTech Connect

    Darbandi, A.; Salehzadeh, O.; Watkins, S. P.; Kuyanov, P.; LaPierre, R. R.

    2014-06-21

    We report on the surface passivation of Au-assisted Te-doped GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy. The electrical properties of individual free standing NWs were assessed using a tungsten nano-probe inside a scanning electron microscope. The diameter independent apparent resistivity of both strained and relaxed passivated NWs suggests the unpinning of the Fermi level and reduction of sidewalls surface states density. Similar current-voltage properties were observed for partially axially relaxed GaAs/GaP NWs. This indicates a negligible contribution of misfit dislocations in the charge transport properties of the NWs. Low temperature micro-photoluminescence (μ-PL) measurements were also carried out for both uncapped and passivated GaAs NWs. The improvement of the integrated (μ-PL) intensity for GaAs/GaP NWs further confirms the effect of passivation.

  12. The influence of a doping profile on the characteristics of an ion-implanted GaAs field-effect transistor with a Schottky barrier

    SciTech Connect

    Shestakov, A. K. Zhuravlev, K. S.

    2011-12-15

    A GaAs field-effect ion-implanted transistor with a Schottky barrier is simulated. The doping profile obtained when doping through an insulator mask is determined and the dependences of the static transistor characteristics on the parameters of the doping profile are calculated and analyzed. The physical processes controlling the transistor characteristics in the case of a variation in the parameters of its doping profile and the coefficient of compensation of the substrate are studied. Based on calculations, the optimal doping-profile parameters ensuring the best characteristics for transistors are predicted.

  13. High pressure and DX centers in heavily doped bulk GaAs

    NASA Astrophysics Data System (ADS)

    Suski, T.; Piotrzkowski, R.; Wiśniewski, P.; Litwin-Staszewska, E.; Dmowski, L.

    1989-08-01

    Measurements of the pressure dependence of electron concentration and mobility have been analyzed for heavily doped, bulk GaAs:(Si,Sn,S,Te). It is demonstrated that the samples with n>2×1018 cm-3 exhibit the effect of carrier freeze-out for pressures below 20 kbar. GaAs:Te represents the exception to this behavior (n versus pressure is constant up to 25 kbar). Two models of the localized state of the donor are considered. Neutral, DX0, or negatively charged, DX-, states might appear after trapping one or two electrons, respectively, by the positively charged donor center. The results obtained show that the energetic level related to the DX center, EDX, is located much higher in the conduction band than could be deduced from results extrapolated from Al1-xGaxAs (EDX situated about 170 meV above the bottom of the Γ conduction band, versus EDX>250 meV obtained in this work). The results show that the localized and metastable DX center is not related to any single conduction-band minimum; its energy position and pressure coefficient exhibit significant temperature dependence. For a Si donor in GaAs, weakening of the electron-lattice coupling strength as a result of applying pressure is anticipated. Increase of electron mobility with decreasing carrier concentration has been observed here. Though it is suggestive to use this result for eliminating the concept of the DX- center, some objections to this conclusion, due to possible correlations in dopant distribution, are presented in the paper.

  14. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; KĘbŁOwski, , A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Gaflux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  15. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; Kębłowski, A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  16. The effect of oscillation amplitudes on the noise of IMPATT-diode oscillators with uniformly doped GaAs

    NASA Astrophysics Data System (ADS)

    Kornilov, S. A.; Pavlov, V. M.

    Experimental results are presented concerning the effect of load conditions on the spectral densities of fluctuations of the oscillation amplitude and frequency of uniformly doped GaAs Schottky-barrier IMPATT diode oscillators. It is shown that at frequencies of the order of hundreds of Hz to several MHz (where avalanche noise occurs) the character of the dependence of noise levels on oscillation amplitude is determined by the ratio of operating current to nominal current. This dependence becomes very sharp when the operator current approaches the nominal current.

  17. GaAs surface cleaning by thermal oxidation and sublimation in molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Saito, Junji; Nanbu, Kazuo; Ishikawa, Tomonori; Kondo, Kazuo

    1988-01-01

    GaAs surface cleaning by thermal oxidation and sublimation prior to molecular-beam-epitaxial growth has been investigated as a means of reducing the carrier depletion at the substrate and epitaxial layer interface. The carrier depletion between the substrate and epitaxial films, measured by a C-V carrier profiling technique, was shown to decrease significantly with an increase in the thickness of the thermal oxidation. The concentration of carbon contamination near the substrate-epitaxial interface was measured using secondary ion mass spectroscopy. The carbon concentration correlated very well with the carrier depletion. Therefore, the main origin of the carrier depletion is believed to be the carbon concentration of the initial growth surface. Based on these results, the thermal oxidation and sublimation of a semi-insulating GaAs substrate was successfully applied to improve the mobility and sheet concentration of the two-dimensional electron gas in selectively doped GaAs/N-Al0.3Ga0.7As heterostructures with very thin GaAs buffer layers.

  18. Growth of silver nanowires on GaAs wafers.

    PubMed

    Sun, Yugang

    2011-05-01

    Silver (Ag) nanowires with chemically clean surfaces have been directly grown on semi-insulating gallium arsenide (GaAs) wafers through a simple solution/solid interfacial reaction (SSIR) between the GaAs wafers themselves and aqueous solutions of silver nitrate (AgNO(3)) at room temperature. The success in synthesis of Ag nanowires mainly benefits from the low concentration of surface electrons in the semi-insulating GaAs wafers that can lead to the formation of a low-density of nuclei that facilitate their anisotropic growth into nanowires. The resulting Ag nanowires exhibit rough surfaces and reasonably good electric conductivity. These characteristics are beneficial to sensing applications based on single-nanowire surface-enhanced Raman scattering (SERS) and possible surface-adsorption-induced conductivity variation.

  19. Photoluminescence study on heavily donor and acceptor impurity doped GaAs layers grown by molecular-beam epitaxy

    SciTech Connect

    Islam, A. Z. M. Touhidul; Jung, D. W.; Noh, J. P.; Otsuka, N.

    2009-05-01

    Gallium arsenide layers doped with high concentrations of Be and Si by molecular-beam epitaxy are studied by photoluminescence (PL) spectroscopy. PL peaks from doped layers are observed at energies significantly lower than the band-gap of GaAs. The growth and doping conditions suggest that the origin of these peaks is different from that of low energy PL peaks, which were observed in earlier studies and attributed to impurity-vacancy complexes. The dependence of the peak energy on the temperature and the annealing is found to differ from that of the peaks attributed to impurity-vacancy complexes. On the basis of these observations, it is suggested that the low energy peaks are attributed to short range ordered arrangements of impurity ions. This possibility is examined by calculations of the PL spectra with models of pairs of acceptor and donor delta-doped layers and PL experiments of a superlattice of pairs of Be and Si delta-doped layers.

  20. Longevity improvement of optically activated, high gain GaAs photoconductive semiconductor switches

    SciTech Connect

    MAR,ALAN; LOUBRIEL,GUILLERMO M.; ZUTAVERN,FRED J.; O'MALLEY,MARTIN W.; HELGESON,WESLEY D.; BROWN,DARWIN JAMES; HJALMARSON,HAROLD P.; BACA,ALBERT G.

    2000-03-02

    The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 100 million pulses at 23A, and over 100 pulses at 1kA. This is achieved by improving the ohmic contacts by doping the semi-insulating GaAs underneath the metal, and by achieving a more uniform distribution of contact wear across the entire switch by distributing the trigger light to form multiple filaments. This paper will compare various approaches to doping the contacts, including ion implantation, thermal diffusion, and epitaxial growth. The device characterization also includes examination of the filament behavior using open-shutter, infra-red imaging during high gain switching. These techniques provide information on the filament carrier densities as well as the influence that the different contact structures and trigger light distributions have on the distribution of the current in the devices. This information is guiding the continuing refinement of contact structures and geometries for further improvements in switch longevity.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Observation of the DX center in Pb-doped GaAs

    NASA Astrophysics Data System (ADS)

    Willke, U.; Maude, D. K.; Sallese, J. M.; Fille, M. L.; el Jani, B.; Gibart, P.; Portal, J. C.

    1993-06-01

    Pb in GaAs introduces a DX center-like (metastable) defect level that is (229±16) meV above the Γ-conduction-band edge, in a similar energetic position to the Si and Sn related DX centers in GaAs. The persistent photoconductivity effect quenches at approximately 50 K, indicating that the barrier to capture for the Pb and Sn dopants are similar. Despite the quite different atomic parameters of the Pb atom compared with the Sn atom, no significant chemical shifts have been found.

  3. Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

    DOE PAGESBeta

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-09-01

    We report the use of a simple close-spaced vapor transport technique for the growth of high-quality epitaxial GaAs films using potentially inexpensive GaAs powders as precursors. The free carrier type and density (1016 to 1019 cm–3) of the films were adjusted by addition of Te or Zn powder to the GaAs source powder. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs films reached ~3 μm and ~8 μm, respectively. Hall mobilities approach those achieved for GaAs grown by metal–organic chemical vapor deposition, 1000–4200 cm2 V–1 s–1 for n-GaAsmore » and 50–240 cm V–1 s–1 for p-GaAs depending on doping level. We conclude that the electronic quality of GaAs grown by close-spaced vapor transport is similar to that of GaAs made using conventional techniques and is thus sufficient for high-performance photovoltaic applications.« less

  4. Doping and electronic properties of GaAs grown by close-spaced vapor transport from powder sources for scalable III–V photovoltaics

    SciTech Connect

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-09-01

    We report the use of a simple close-spaced vapor transport technique for the growth of high-quality epitaxial GaAs films using potentially inexpensive GaAs powders as precursors. The free carrier type and density (1016 to 1019 cm–3) of the films were adjusted by addition of Te or Zn powder to the GaAs source powder. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs films reached ~3 μm and ~8 μm, respectively. Hall mobilities approach those achieved for GaAs grown by metal–organic chemical vapor deposition, 1000–4200 cm2 V–1 s–1 for n-GaAs and 50–240 cm V–1 s–1 for p-GaAs depending on doping level. We conclude that the electronic quality of GaAs grown by close-spaced vapor transport is similar to that of GaAs made using conventional techniques and is thus sufficient for high-performance photovoltaic applications.

  5. Design Issues of GaAs and AlGaAs Delta-Doped p-i-n Quantum-Well APD's

    NASA Technical Reports Server (NTRS)

    Wang, Yang

    1994-01-01

    We examine the basic design issues in the optimization of GaAs delta-doped and AlGAs delta-doped quantum-well avalanche photodiode (APD) structures using a theoretical analysis based on an ensemble Monte Carlo simulation. The devices are variations of the p-i-n doped quantum-well structure previously described in the literature. They have the same low-noise, high-gain and high-bandwidth features as the p-i-n doped quantum-well device. However, the use of delta doping provides far greater control or the doping concentrations within each stage possibly enhancing the extent to which the device can be depleted. As a result, it is expected that the proposed devices will operate at higher gain levels (at very low noise) than devices previously developed.

  6. High-field electroluminescence in semiconductor tunnel junctions with a Mn-doped GaAs layer

    SciTech Connect

    Hai, Pham Nam; Yatsui, Takashi; Ohtsu, Motoichi; Tanaka, Masaaki

    2014-09-21

    We investigated high-field electroluminescence (EL) in semiconductor tunnel junctions with a Mn-doped GaAs layer (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show visible light emissions with two peaks at 1.94 eV and 2.19 eV, which are caused by d-d transitions of the Mn atoms excited by hot electrons. The threshold voltages for band-gap and visible light EL in the tunnel junctions with a GaAs:Mn electrode are 1.3 V higher than those of GaAs:Mn excited by hot holes in reserve biased p⁺-n junctions, which is consistent with the hot carrier transport in the band profiles of these structures. Our EL results at room temperature show that the electron temperature in GaAs:Mn can be as high as ~700 K for a low input electrical power density of 0.4 W/cm², while the lattice temperature of the GaAs:Mn layer can be kept at 340 K.

  7. Comparison of OARE Accelerometer Data with Dopant Distribution in Se-Doped GaAs Crystals Grown During USML-1

    NASA Technical Reports Server (NTRS)

    Moskowitz, Milton E.; Bly, Jennifer M.; Matthiesen, David H.

    1997-01-01

    Experiments were conducted in the crystal growth furnace (CGF) during the first United States Microgravity Laboratory (USML-1), the STS-50 flight of the Space Shuttle Columbia, to determine the segregation behavior of selenium in bulk GaAs in a microgravity environment. After the flight, the selenium-doped GaAs crystals were sectioned, polished, and analyzed to determine the free carrier concentration as a function of position, One of the two crystals initially exhibited an axial concentration profile indicative of diffusion controlled growth, but this profile then changed to that predicted for a complete mixing type growth. An analytical model, proposed by Naumann [R.J. Naumann, J. Crystal Growth 142 (1994) 253], was utilized to predict the maximum allowable microgravity disturbances transverse to the growth direction during the two different translation rates used for each of the experiments. The predicted allowable acceleration levels were 4.86 microgram for the 2.5 micrometers/s furnace translation rate and 38.9 microgram for the 5.0 micrometers/s rate. These predicted values were compared to the Orbital Acceleration Research Experiment (OARE) accelerometer data recorded during the crystal growth periods for these experiments. Based on the analysis of the OARE acceleration data and utilizing the predictions from the analytical model, it is concluded that the change in segregation behavior was not caused by any acceleration events in the microgravity environment.

  8. First Principles Electronic Structure of Mn doped GaAs, GaP, and GaN Semiconductors

    SciTech Connect

    Schulthess, Thomas C; Temmerman, Walter M; Szotek, Zdzislawa; Svane, Axel; Petit, Leon

    2007-01-01

    We present first-principles electronic structure calculations of Mn doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn-d levels in GaAs. We find good agreement between computed values and estimates from photoemisison experiments.

  9. Perpendicular-to-Parallel Spin Reorientation in a Mn-Doped GaAs Quantum Canting or Phase Separation

    SciTech Connect

    Fishman, Randy Scott; Reboredo, Fernando A; Brandt, Alex B; Moreno, Juana

    2007-01-01

    It is well known that the magnetic anisotropy in a compressively-strained Mn-doped GaAs film changes from perpendicular to parallel with increasing hole concentration p. We study this reorientation transition at T = 0 for a quantum well with Mn impurities confined to the z = 0 plane. With increasing p, the angle 0 that minimizes the energy E increases continuously from 0 (perpendicular anisotropy) to /2 (parallel anisotropy) within some range of p. The shape of Emin(p) suggests that the quantum well becomes phase separated with regions containing low hole concentrations and perpendicular moments interspersed with other regions containing high hole concentrations and parallel moments. However, consideration of the Coulomb energy costs associated with phase separation suggests that the true magnetic state in the transition region is canted with 0 < < /2.

  10. Intense laser field effects on p-d exchange interaction in single manganese doped GaAs

    SciTech Connect

    Vieira Moura, Fabio; Qu Fanyao; Gargano, Ricardo

    2011-11-01

    We have developed a comprehensive theory about optical control of p - d exchange interaction between spins of hole and Mn{sup 2+} in single-manganese doped GaAs material irradiated by a monochromatic, linearly polarized, intense pulsed laser field (PLF) under nonresonant conditions. The p - d exchange interaction leads to formation of magnetic polaron. While the PLF induces a dressed acceptor Coulomb potential, which transforms single center problem into the one with two virtual positively charged centers, resembling hydrogen molecule ion (H{sub 2}{sup +}). The dichotomy of hole wave functions, determined by the laser-intensity, affects strongly the p - d exchange interaction as well as binding energy of magnetic polaron. Increasing the laser intensity reduces the magnetic polaron binding energy. At larger excitation intensity, the magnetic polaron can be completely dissolved.

  11. Evaluation of modulating field of photoreflectance of surface-intrinsic-n+ type doped GaAs by using photoinduced voltage

    NASA Astrophysics Data System (ADS)

    Lee, W. Y.; Chien, J. Y.; Wang, D. P.; Huang, K. F.; Huang, T. C.

    2002-04-01

    Photoreflectance (PR) of surface-intrinsic-n+ type doped GaAs has been measured for various power densities of pump laser. The spectra exhibited many Franz-Keldysh oscillations, whereby the strength of electric field F in the undoped layer can be determined. The thus obtained Fs are subject to photovoltaic effect and are less than built-in field Fbi. In the previous work we have obtained the relation F≈Fbi-δF/2 when δF≪Fbi by using electroreflectance to simulate PR, where δF is the modulating field of the pump beam. In this work a method was devised to evaluate δF by using photoinduced voltages Vs and, hence, the relation can be verified by PR itself. The δFs obtained by Vs are also consistent with those of using imaginary part of fast Fourier transform of PR spectra.

  12. Raman study of As outgassing and damage induced by ion implantation in Zn-doped GaAs

    SciTech Connect

    Barba, D.; Aimez, V.; Beauvais, J.; Beerens, J.; Drouin, D.; Chicoine, M.; Schiettekatte, F.

    2004-11-01

    Room temperature micro-Raman investigations of LO phonon and LO phonon-plasmon coupling is used to study the As outgassing mechanism and the disordering effects induced by ion implantation in Zn-doped GaAs with nominal doping level p=7x10{sup 18} cm{sup -3}. The relative intensity of these two peaks is measured right after rapid vacuum thermal annealings (RVTA) between 200 and 450 deg. C, or after ion implantations carried out at energies of 40 keV with P{sup +}, and at 90 and 170 keV with As{sup +}. These intensities provide information regarding the Schottky barrier formation near the sample surface. Namely, the Raman signature of the depletion layer formation resulting from As desorption is clearly observed in samples submitted to RVTA above 300 deg. C, and the depletion layer depths measured in ion implanted GaAs:Zn are consistent with the damage profiles obtained through Monte Carlo simulations. Ion channeling effects, maximized for a tilt angle set to 45 deg. during implantation, are also investigated. These results show that the Raman spectroscopy is a versatile tool to study the defects induced by postgrowth processes in multilayered heterostructures, with probing range of about 100 nm in GaAs-based materials.

  13. Structural and magnetic characteristics of MnAs nanoclusters embedded in Be-doped GaAs

    NASA Astrophysics Data System (ADS)

    Rench, D. W.; Schiffer, P.; Samarth, N.

    2011-09-01

    We describe a systematic study of the synthesis, microstructure, and magnetization of hybrid ferromagnet-semiconductor nanomaterials comprised of MnAs nanoclusters embedded in a p-doped GaAs matrix. These samples are created during the in situ annealing of Be-doped (Ga,Mn)As heterostructures grown by molecular beam epitaxy. Transmission electron microscopy and magnetometry studies reveal two distinct classes of nanoclustered samples whose structural and magnetic properties depend on the Mn content of the initial (Ga,Mn)As layer. For Mn content in the range 5-7.5%, annealing creates a superparamagnetic material with a uniform distribution of small clusters (diameter ˜6 nm) and with a low blocking temperature (TB˜10 K). While transmission electron microscopy cannot definitively identify the composition and crystalline phase of these small clusters, our experimental data suggest that they may be comprised of either zinc-blende MnAs or Mn-rich regions of (Ga,Mn)As. At higher Mn content (≳8%), we find that annealing results in an inhomogeneous distribution of both small clusters as well as much larger NiAs-phase MnAs clusters (diameter ˜25 nm). These samples also exhibit supermagnetism, albeit with substantially larger magnetic moments and coercive fields, and blocking temperatures well above room temperature.

  14. Selfsimilar and fractal analysis of n-type delta-doped quasiregular GaAs quantum wells

    SciTech Connect

    García-Cervantes, H.; Rodríguez-Vargas, I.

    2014-05-15

    We study the electronic structure of n-type delta-doped quantum wells in GaAs in which the multiple well system is built according to the Fibonacci sequence. The building blocks A and B correspond to delta-doped wells with impurities densities n{sub 2DA} and n{sub 2DB}, and the same well width. The Thomas-Fermi approximation, the semi-empirical sp{sub 3}s* tight-binding model including spin, the Surface Green Function Matching method and the Transfer Matrix approach were implemented to obtain the confining potential, the electronic structure and the selfsimilarity of the spectrum. The fragmentation of the electronic spectra is observed whenever the building blocks A and B interact and it increases as the difference of impurities density between A and B increases as well. The wave function of the first sate of the fragmented bands presents critical characteristics, this is, it is not a localized state nor a extended one as well as it has selfsimilar features. So, the quasiregular characteristics are preserved irrespective of the complexity of the system and can affect the performance of devices based on these structures.

  15. The influence of Sb doping on the growth and electronic properties of GaAs(100) and AlGaAs(100)

    NASA Technical Reports Server (NTRS)

    Jamison, K. D.; Chen, H. C.; Bensaoula, A.; Lim, W.; Trombetta, L.

    1989-01-01

    Isoelectronic doping using antimony has been shown to reduce traps and improve material properties during epitaxial growth of Si doped GaAs(100) and AlGaAs(100). In this study, the effect of the antimony dopant on the optimal growth temperature is examined with the aim of producing high-quality heterostructures at lower temperatues. High-quality films of GaAs and AlGaAs have been grown by molecular-beam epitaxy at the normal growth temperatures of 610 and 700 C, respectively, and 50-100 C below this temperature using varying small amounts of Sb as a dopant. Electrical properties of the films were then examined using Hall mobility measurements and deep-level transient spectroscopy.

  16. Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

    NASA Technical Reports Server (NTRS)

    Bhattacharya, P. K.; Dhar, S.; Berger, P.; Juang, F.-Y.

    1986-01-01

    A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).

  17. GaAs nanowires grown on Al-doped ZnO buffer layer

    NASA Astrophysics Data System (ADS)

    Haggren, Tuomas; Perros, Alexander; Dhaka, Veer; Huhtio, Teppo; Jussila, Henri; Jiang, Hua; Ruoho, Mikko; Kakko, Joona-Pekko; Kauppinen, Esko; Lipsanen, Harri

    2013-08-01

    We report a pathway to grow GaAs nanowires on a variety of substrates using a combination of atomic layer deposition and metallo-organic vapor phase epitaxy (MOVPE). GaAs nanowires were grown via MOVPE at 430-540 °C on an atomic-layer-deposited Al:ZnO buffer layer. The resulting nanowires were affected only by the properties of the buffer layer, allowing nanowire growth on a number of substrates that withstand ˜400 °C. The growth occurred in two phases: initial in-plane growth and subsequent out-plane growth. The nanowires grown exhibited a strong photoluminescence signal both at room temperature and at 12 K. The 12 K photoluminescence peak was at 1.47 eV, which was attributed to Zn autodoping from the buffer layer. The crystal structure was zincblende plagued with either twin planes or diagonal defect planes, which were related to perturbations in the seed particle during the growth. The used method combines substrates with variable properties to nanowire growth on a transparent and conductive Al:ZnO buffer layer.

  18. Resonant photodiffractive four-wave mixing in semi-insulating GaAs/AlGaAs quantum wells.

    PubMed

    Glass, A M; Nolte, D D; Olson, D H; Doran, G E; Chemla, D S; Knox, W H

    1990-03-01

    We have performed photodiffractive four-wave mixing in semi-insulating multiple GaAs/AlGaAs quantum wells at a wavelength of 0.83 microm. The quantum wells were made semi-insulating by proton implantation, which introduces defects that are available to trap and store charge during holographic recording. The experiments demonstrate how photodiffractive behavior using the large resonant nonlinearities of quantum-confined excitons yields highly sensitive material for optical image processing. When pump powers of 1 mW/cm(2) are used, the measured sensitivity is 2 orders of magnitude greater than that of bulk, nonresonant photorefractive semiconductors.

  19. A comparative study of micropipe decoration and counting in conductive and semi-insulating silicon carbide wafers

    NASA Astrophysics Data System (ADS)

    Wan, Jianwei; Park, Seung-Ho; Chung, Gilyong; Loboda, Mark

    2005-10-01

    Micropipes are considered to be one of the most serious defects in silicon carbide (SiC) wafers affecting device yield. Developing a method to count and map micropipes accurately has been a challenging task. In this study, the different etching behavior of conductive and semi-insulating wafers in molten potassium oxide (KOH) is compared. Micropipes and closed-core screw dislocations exhibit different morphology after etching and can be easily distinguished with a polishing process. Based on a new sample preparation procedure and a digital imaging technique, a novel method of efficiently and reliably mapping and counting micropipes in both conductive and semi-insulating SiC wafers is developed.

  20. Optical and electrical characterization of surface passivated GaAs nanostructures

    NASA Astrophysics Data System (ADS)

    Arab, Shermin; Chi, Chun Yung; Yao, Maoqing; Chang, Chia-Chi; Dapkus, P. Daniel; Cronin, Stephen B.

    2014-02-01

    GaAs nanostructures are used in different optoelectronic applications including solar cells, LEDs and fast electronics. Although GaAs shows outstanding optical properties, it suffers from surface states and consequently high surface recombination velocity. The surface depletion effects lead to semi-insulating behaviors in GaAs devices. Passivation of GaAs nanostructures (AlGaAs or ionic liquid) lead to surface stability and improvement in optoelectronic properties. We provide a systematic study to compare the optical and electrical improvement after passivation (AlGaAs or ionic liquid) of GaAs nanostructure including nanowires and nanosheets. Both room temperature and low temperature photoluminescent (PL) spectra indicate increase in optical activity of GaAs nanostructures after passivation. Electron beam induced current (EBIC) measurements reveal the diffusion length of carries in different GaAs nanostructures.

  1. Mechanisms of the passage of dark currents through Cd(Zn)Te semi-insulating crystals

    NASA Astrophysics Data System (ADS)

    Sklyarchuk, V.; Fochuk, P.; Rarenko, I.; Zakharuk, Z.; Sklyarchuk, O.; Nykoniuk, Ye.; Rybka, A.; Kutny, V.; Bolotnikov, A. E.; James, R. B.

    2014-09-01

    We investigated the passage of dark currents through semi-insulating crystals of Cd(Zn)Te with weak n-type conductivity that are used widely as detectors of ionizing radiation. The crystals were grown from a tellurium solution melt at 800 оС by the zone-melting method, in which a polycrystalline rod in a quartz ampoule was moved through a zone heater at a rate of 2 mm per day. The synthesis of the rod was carried out at ~1150 оС. We determined the important electro-physical parameters of this semiconductor, using techniques based on a parallel study of the temperature dependence of current-voltage characteristics in both the ohmic and the space-charge-limited current regions. We established in these crystals the relationship between the energy levels and the concentrations of deep-level impurity states, responsible for dark conductivity and their usefulness as detectors.

  2. High effective terahertz radiation from semi-insulating-GaAs photoconductive antennas with ohmic contact electrodes

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Hou, Lei; Wang, Xinmei

    2011-07-01

    Terahertz (THz) radiation efficiency of a photoconductive antenna with Schottky contact electrodes is low because the electrical field is limited to a narrow region close to the anode. However, the electrical field in the gap of an antenna with ohmic contact electrodes is more uniform, which contributes to improving THz generation efficiency. In this paper, the semi-insulating (SI)-GaAs antennas with ohmic contact electrodes and SI-GaAs antennas with Schottky contact electrodes were fabricated by using AuGeNi alloy electrodes and Ti/Au electrodes, respectively. The voltage-ampere characteristic and the distribution of electrical field of the two kinds of antennas were tested. At the same condition, the THz intensity from the antenna with ohmic contact electrodes was 3-8 times higher than that from the antenna with Schottky contact electrodes, and the larger gap antennas with ohmic contact electrodes have higher optical and electrical energy to THz intensity conversion efficiency.

  3. Simulation of Electric Field in Semi Insulating Au/CdTe/Au Detector under Flux

    SciTech Connect

    Franc, J.; James, R.; Grill, R.; Kubat, J.; Belas, E.; Hoschl, P.; Moravec, P.; Praus, P.

    2009-08-02

    We report our simulations on the profile of the electric field in semi insulating CdTe and CdZnTe with Au contacts under radiation flux. The type of the space charge and electric field distribution in the Au/CdTe/Au structure is at high fluxes result of a combined influence of charge formed due to band bending at the electrodes and from photo generated carriers, which are trapped at deep levels. Simultaneous solution of drift-diffusion and Poisson equations is used for the calculation. We show, that the space charge originating from trapped photo-carriers starts to dominate at fluxes 10{sup 15}-10{sup 16}cm{sup -2}s{sup -1}, when the influence of contacts starts to be negligible.

  4. Microscopic determination of stress distribution in GaAs grown at low temperature on GaAs (100)

    NASA Astrophysics Data System (ADS)

    Liliental-Weber, Z.; Tanaka, M.; Ishikawa, A.; Teriauchi, M.

    1991-01-01

    A microscopic strain distribution across commensurate interfaces between GaAs layers grown on semi-insulating GaAs substrates was observed by means of convergent beam electron diffraction (CBED) and large angle convergent beam methods (LACBED). Strain relaxation at a specific distance from the interface was observed in these layers without formation of misfit dislocations. It was proposed that specific point defects distributed close to the interface can explain the asymmetric broadening of high-order Laue zone (HOLZ) lines in the CBED patterns.

  5. Indium-doped GaAs: A very dilute alloy system

    NASA Astrophysics Data System (ADS)

    Laurenti, J. P.; Roentgen, P.; Wolter, K.; Seibert, K.; Kurz, H.; Camassel, J.

    1988-03-01

    The influence of indium incorporation in GaAs organometallic-vapor-phase-epitaxy (OMVPE) layers has been investigated in great detail. The results obtained concern the change in band-gap energy, the concentration of residual impurities, and the low-temperature (2-K) photoluminescence (PL) efficiency. For In concentrations ranging between 0 and 6.5×1019 cm-3, both A0X and D0X bound-exciton lines could be resolved. Together with the near-band-gap transitions involving shallow impurities (DA- and eA-related recombination lines), they shift toward lower energies versus indium content. This indicates the formation of a ternary compound Ga1-xInxAs, even at these extremely dilute indium concentrations. After a quantitative calibration of the indium content, linear relations have been found which connect the PL emission line energies and the indium concentration. They make low-temperature PL measurements the most quantitative, and nondestructive, tool for precise composition studies. In this case, care should be taken that the slope parameters are line dependent. For instance, we find a slight, but finite, discrepancy between the slope parameters corresponding to substitutional acceptors on Ga and As sites, respectively. This is discussed in terms of the two different sublattices by using a simple cluster model of 17 atoms. Lastly, we find the absolute PL intensities to increase versus indium concentration: This indicates an improvement in the optical quality of our samples. Since, on a relative scale, the PL signals involving ZnGa and/or MgGa residual acceptors are not significantly affected by the amount of indium incorporated, but depend mainly on the growth sequence, we feel that indium in GaAs acts primarily by closing nonradiative-recombination paths which are not necessarily associated with gallium vacancies.

  6. Semi-insulating behaviour of self-assembled tin(IV)corrole nanospheres.

    PubMed

    Sinha, Woormileela; Kumar, Mohit; Garai, Antara; Purohit, Chandra Shekhar; Som, Tapobrata; Kar, Sanjib

    2014-09-01

    Three novel tin(iv)corrole complexes have been prepared and characterized by various spectroscopic techniques including single crystal X-ray structural analysis. Packing diagrams of the tin(iv)corroles revealed that corrolato-tin(iv)-chloride molecules are interconnected by intermolecular C-HCl hydrogen bonding interactions. HCl distances are 2.848 Å, 3.051 Å, and 2.915 Å, respectively, for the complexes. In addition, the C-HCl angles are 119.72°, 144.70°, and 147.08°, respectively, for the complexes. It was also observed that in one of the three synthesized complexes dimers were formed, while in the other two cases 1D infinite polymer chains were formed. Well-defined and nicely organized three-dimensional hollow nanospheres (SEM images on silicon wafers) with diameters of ca. 676 nm and 661 nm are obtained in the complexes, forming 1D polymer chains. By applying a thin layer of tin(iv)corrole nanospheres to an ITO surface (AFM height images of ITO films; ∼200 nm in height), a device was fabricated with the following composition: Ag/ITO-coated glass/tin(iv)corrole nanospheres/ITO-coated glass/Ag. The resistivity (ρ) of the nanostructured film was calculated to be ∼2.4 × 10(8) Ω cm, which falls in the range of semi-insulating semiconductors. CAFM current maps at 10 V bias show bright spots with a 10-20 pA intensity and indicate that the nanospheres (∼250 nm in diameter) are the electron-conducting pathway in the device. The semi-insulating behavior arises from the non-facile electron transfer in the HOMOs of the tin(iv)corrole nanospheres.

  7. Deep traps and temperature effects on the capacitance of p-type Si-doped GaAs Schottky diodes on (2 1 1) and (3 1 1) oriented GaAs substrates

    NASA Astrophysics Data System (ADS)

    Boumaraf, R.; Sengouga, N.; Mari, R. H.; Meftah, Af.; Aziz, M.; Jameel, Dler; Al Saqri, Noor; Taylor, D.; Henini, M.

    2014-01-01

    The SILVACO-TCAD numerical simulator is used to explain the effect of different types of deep levels on the temperature dependence of the capacitance of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates, namely (3 1 1)A and (2 1 1)A oriented GaAs substrates. For the (3 1 1)A diodes, the measured capacitance-temperature characteristics at different reverse biases show a large peak while the (2 1 1)A devices display a much smaller one. This peak is related to the presence of different types of deep levels in the two structures. These deep levels are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (3 1 1)A structure only majority deep levels (hole deep levels) were observed while both majority and minority deep levels were present in the (2 1 1)A diodes. The simulation software, which calculates the capacitance-voltage and the capacitance-temperature characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behavior of the capacitance-temperature properties. A further evidence to confirm that deep levels are responsible for the observed phenomenon is provided by a simulation of the capacitance-temperature characteristics as a function of the ac-signal frequency.

  8. Passive Q-switching of diode-pumped Yb:YAG microchip laser with ion-implanted GaAs

    NASA Astrophysics Data System (ADS)

    Wang, Yonggang; Ma, Xiaoyu; Zhong, Bin; Wang, Desong; Zhang, Qiulin; Feng, Baohua

    2004-01-01

    We reported a passive Q-switched diode laser pumped Yb:YAG microchip laser with an ion-implanted semi-insulating GaAs wafer. The wafer was implanted with 400-keV As^(+) in the concentration of 10^(16) ions/cm^(2). To decrease the non-saturable loss, we annealed the ion-implanted GaAs at 500 oC for 5 minutes and coated both sides of the ion-implanted GaAs with antireflection (AR) and highreflection (HR) films, respectively. Using GaAs wafer as an absorber and an output coupler, we obtained 52-ns pulse duration of single pulse.

  9. Heat load of a P-doped GaAs photocathode in SRF electron gun

    SciTech Connect

    Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

    2010-05-23

    Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

  10. Growth studies of erbium-doped GaAs deposited by metalorganic vapor phase epitaxy using noval cyclopentadienyl-based erbium sources

    NASA Technical Reports Server (NTRS)

    Redwing, J. M.; Kuech, T. F.; Gordon, D. C.; Vaartstra, B. A.; Lau, S. S.

    1994-01-01

    Erbium-doped GaAS layers were grown by metalorganic vapor phase epitaxy using two new sources, bis(i-propylcyclopentadienyl)cyclopentadienyl erbium and tris(t-butylcyclopentadienyl) erbium. Controlled Er doping in the range of 10(exp 17) - 10(exp 18)/cu cm was achieved using a relatively low source temperature of 90 C. The doping exhibits a second-order dependence on inlet source partial pressure, similar to behavior obtained with cyclopentadienyl Mg dopant sources. Equivalent amounts of oxygen and Er are present in 'as-grown' films indicating that the majority of Er dopants probably exist as Er-O complexes in the material. Er(+3) luminescence at 1.54 micrometers was measured from the as-grown films, but ion implantation of additional oxygen decreases the emission intensity. Electrical compensation of n-type GaAs layers codoped with Er and Si is directly correlated to the Er concentration is proposed to arise from the deep centers associated with Er which are responsible for a broad emission band near 0.90 micrometers present in the photoluminescence spectra of GaAs:Si, Er films.

  11. Magnesium doping of efficient GaAs and Ga(0.75)In(0.25)As solar cells grown by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Lewis, C. R.; Ford, C. W.; Werthen, J. G.

    1984-01-01

    Magnesium has been substituted for zinc in GaAs and Ga(0.75)In(0.25)As solar cells grown by metalorganic chemical vapor deposition (MOCVD). Bis(cyclopentadienyl)magnesium (Cp2Mg) is used as the MOCVD transport agent for Mg. Full retention of excellent material quality and efficient cell performance results. The substitution of Mg for Zn would enhance the abruptness and reproducibility of doping profiles, and facilitate high temperature processing and operation, due to the much lower diffusion coefficient of Mg, relative to Zn, in these materials.

  12. Investigation of the optical properties of GaAs with δ-Si doping grown by molecular-beam epitaxy at low temperatures

    SciTech Connect

    Lavrukhin, D. V. Yachmenev, A. E.; Bugaev, A. S.; Galiev, G. B.; Klimov, E. A.; Khabibullin, R. A.; Ponomarev, D. S.; Maltsev, P. P.

    2015-07-15

    Molecular-beam epitaxy is used for the preparation of structures based on “low-temperature” grown GaAs with introduced d-Si doping. Specific features in the photon-energy range of 1.28–1.48 eV are observed in the photoluminescence spectrum after structures annealing at temperatures of 520 and 580°C; these features are related to the formation of point defects and their complexes. The “pump–probe” light transmission measurements reveal that the characteristic lifetimes of nonequilibrium carriers in the fabricated structures amount to T{sup c} ≈ 1.2–1.5 ps.

  13. Electrical and structural properties of semi-insulating polycrystalline silicon thin films

    NASA Astrophysics Data System (ADS)

    Lombardo, S.; Campisano, S. U.; Baroetto, F.

    1993-05-01

    Semi-insulating polycrystalline silicon layers with oxygen concentrations ranging from 2 up to 30 at. % O have been prepared by low-pressure chemical vapor deposition. After deposition, the samples were annealed at 920 °C for 30 min. Grain-size distributions, high- and low-frequency dielectric constants were measured, respectively, by transmission-electron microscopy, capacitance, and optical measurements as a function of the oxygen content. The average grain radius decreases with the oxygen content from 15 up to 2.5 nm. The current-voltage characteristics have been measured as a function of temperature in the range 80-450 K and under applied transverse electric fields up to ~=106 V/cm. In weak-transverse-field conditions, the current density as a function of temperature shows two thermally activated regions at low and high temperatures, with activation energies of ~=0.14 and ~=0.54 eV, respectively. The application of transverse electric fields of the order of ~=106 V/cm produces a current enhancement depending upon field intensity, temperature, and oxygen content. The results have been modeled by assuming thermionic emission, tunneling, and Frenkel generation in a long series of Schottky barriers formed at the boundary of the adjacent grains. The best-fit values of the model parameters indicate that for 30 at. % O a continuous SiO2 shell, two monolayers thick, surrounds each grain. For lower oxygen contents this shell is discontinuous and the carrier transport parameters change considerably.

  14. Direct determination of impact-parameter-dependent stopping powers for million-electron-volt He ions penetrating Er-doped GaAs

    SciTech Connect

    Yamamoto, Y.; Kaczanowski, J.; Kido, Y.; Nakata, J.; Yamaguchi, H.; Takahei, K.

    1996-03-01

    We have directly determined the impact-parameter-dependent stopping powers for 2.0- and 2.5-MeV He ions passing through GaAs single crystals. The points reside in the preparation of the single-crystal sample with a dopant of a heavy element located in some definite interstitial site at definite depth and in synthesis of a Monte Carlo program to simulate accurately the ion trajectories. Er-doped homoepitaxial GaAs layers grown by molecular-beam epitaxy and by metal-organic chemical-vapor deposition were used for this purpose. As previously reported, fine single-crystal clusters of ErAs are formed in the GaAs host and Er takes the position exactly equivalent to the tetrahedral interstitial site. The present Monte Carlo simulation has revealed the fact that some definite impact-parameter region dominates the backscattering Er peak position and this region shifts continuously by tilting the incident beam axis slightly from a major crystal axis. The results obtained are compared with the Oen-Robinson [Nucl. Instrum. Methods {bold 132}, 647 (1976)] model and other theoretical predictions and clearly show that inner-shell excitations and ionizations contribute significantly to the stopping power even for large impact parameters. {copyright} {ital 1996 The American Physical Society.}

  15. Schottky junctions on semi-insulating LEC gallium arsenide for X- and {gamma}-ray spectrometers operated at and below room temperature

    SciTech Connect

    Bertuccio, G.; Pullia, A. |; Canali, C. |; Nava, F. |; Lanzieri

    1997-04-01

    This work deals with the study of a Schottky junction used as an X- and {gamma}-ray detector in a spectrometer operated in the temperature range from {minus}30 C to +22 C. The device, fabricated on liquid encapsulated Czochralski (LEC) semi-insulating Gallium Arsenide, is designed with a noninjecting ohmic contact which allows biasing voltages up to 550 V. At room temperature (22 C) the energy resolution is found to be relatively poor (15.5-keV full-width at half-maximum (FWHM) at 59.5 keV) due to the large junction reverse current, whose density is within the typical values for Schottky junctions on SI LEC GaAs. By cooling of the detector to {minus}30 C, the noise of the reverse current is drastically lowered, thus achieving electronic noise levels around 160--180 rms electrons. At 500-V bias, the {sup 241}Am spectrum has been resolved down to an energy of 4 keV with charge collection efficiency of cce = 97% and a resolution of about 2-keV FWHM for the Np L lines and 2.4-keV FWHM for the 59.5-keV {gamma} photons. The linearity of the detector has been measured to be better than {+-}0.6% within the explored energy range (14--59 keV). From the experimental spectra, it has been analyzed how either the electronic noise or the trapping of the signal charge contribute to the energy resolution of the spectrometer. The result is that despite the high measured cce, the trapping gives a contribution higher than 1.5 keV FWHM for the 59.5-keV spectral line. A comparison between the experimental results and Monte Carlo simulations, based on the Hecht model of charge trapping in detectors, is shown to give a satisfactory justification of the observed phenomena.

  16. Selective-area growth of heavily n-doped GaAs nanostubs on Si(001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Chang, Yoon Jung; Simmonds, Paul J.; Beekley, Brett; Goorsky, Mark S.; Woo, Jason C. S.

    2016-04-01

    Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO2 mask act as a template for GaAs-on-Si selective-area growth (SAG) of nanostubs 120 nm tall and ≤100 nm in diameter. We investigate the influence of growth parameters including substrate temperature and growth rate on SAG. Optimizing these parameters results in complete selectivity with GaAs growth only on the exposed Si(001). Due to the confined-geometry, strain and defects in the GaAs nanostubs are restricted in lateral dimensions, and surface energy is further minimized. We assess the electrical properties of the selectively grown GaAs nanostubs by fabricating heterogeneous p+-Si/n+-GaAs p-n diodes.

  17. Plasma Deposited SiO2 for Planar Self-Aligned Gate Metal-Insulator-Semiconductor Field Effect Transistors on Semi-Insulating InP

    NASA Technical Reports Server (NTRS)

    Tabory, Charles N.; Young, Paul G.; Smith, Edwyn D.; Alterovitz, Samuel A.

    1994-01-01

    Metal-insulator-semiconductor (MIS) field effect transistors were fabricated on InP substrates using a planar self-aligned gate process. A 700-1000 A gate insulator of Si02 doped with phosphorus was deposited by a direct plasma enhanced chemical vapor deposition at 400 mTorr, 275 C, 5 W, and power density of 8.5 MW/sq cm. High frequency capacitance-voltage measurements were taken on MIS capacitors which have been subjected to a 700 C anneal and an interface state density of lxl0(exp 11)/eV/cq cm was found. Current-voltage measurements of the capacitors show a breakdown voltage of 107 V/cm and a insulator resistivity of 10(exp 14) omega cm. Transistors were fabricated on semi-insulating InP using a standard planar self-aligned gate process in which the gate insulator was subjected to an ion implantation activation anneal of 700 C. MIS field effect transistors gave a maximum extrinsic transconductance of 23 mS/mm for a gate length of 3 microns. The drain current drift saturated at 87.5% of the initial current, while reaching to within 1% of the saturated value after only 1x10(exp 3). This is the first reported viable planar InP self-aligned gate transistor process reported to date.

  18. Approximation of HRPITS results for SI GaAs by large scale support vector machine algorithms

    NASA Astrophysics Data System (ADS)

    Jankowski, Stanisław; Wojdan, Konrad; Szymański, Zbigniew; Kozłowski, Roman

    2006-10-01

    For the first time large-scale support vector machine algorithms are used to extraction defect parameters in semi-insulating (SI) GaAs from high resolution photoinduced transient spectroscopy experiment. By smart decomposition of the data set the SVNTorch algorithm enabled to obtain good approximation of analyzed correlation surface by a parsimonious model (with small number of support vector). The extracted parameters of deep level defect centers from SVM approximation are of good quality as compared to the reference data.

  19. GaAs detectors irradiated by low doses of electrons

    NASA Astrophysics Data System (ADS)

    Šagátová, A.; Zat'ko, B.; Pavlovič, M.; Sedlačková, K.; Hybler, P.; Dubecký, F.; Nečas, V.

    2014-04-01

    Semi-insulating (SI) GaAs detectors were irradiated by 5 MeV electrons up to a dose of 69 kGy, in order to test their radiation hardness. The electric and spectrometric stability of detectors was examined as a function of the absorbed dose. Investigated detectors showed a very good detector radiation resistance within a dose up to 40 kGy followed by deterioration of some spectrometric and electric properties. However, the reverse current and the detector charge collection efficiency showed minimum changes with the overall applied doses. The obtained results will be used as a preliminary study for further radiation-hardness investigations of GaAs detectors against high energy electrons. This will complete our previous studies of GaAs detector radiation hardness against fast neutrons and γ-rays.

  20. Oxygen in GaAs - Direct and indirect effects

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Skowronski, M.; Pawlowicz, L.; Lagowski, J.

    1984-01-01

    Oxygen has profound effects on the key electronic properties and point defects of GaAs crystals. Thus, when added in the growth system, it decreases the free electron concentration and enhances the concentration of deep donors in the resulting crystals. Both of these effects are highly beneficial for achieving semi-insulating material and have been utilized for that purpose. They have been attributed to the tendency of oxygen to getter silicon impurities during crystal growth. Only recently, it has been found that oxygen in GaAs introduces also a midgap level, ELO, with essentially the same activation energy as EL2 but with four times greater electron capture cross section. The present report reassesses the electrical and optical properties of the midgap levels in GaAs crystals grown by the horizontal Bridgman (HB) and the Czochralski-LEC techniques. Emphasis is placed on the identification of the specific effects of ELO.

  1. Electric field perturbation due to impurities in GaAs through single electron transistor

    NASA Astrophysics Data System (ADS)

    Abdalla, S.

    2009-11-01

    The present work shows the presence of inevitable impurities in the semi-insulating GaAs domains when one is developing a single electron transistor (SET) and alters the quantization mechanism of single electron tunneling through the island. It is also indicated that these impurities decrease the amount of energy required to change the number of electrons on the island, which leads to a drastic reduction of SET quality. A theoretical model has been presented for elucidating the I- V characteristics of GaAs nano-crystals. It is found that this proposed model fits well the experimental data.

  2. Effects of Si doping on the strain relaxation of metamorphic (Al)GaInP buffers grown on GaAs substrates

    NASA Astrophysics Data System (ADS)

    Li, K. L.; Dong, J. R.; Sun, Y. R.; Zeng, X. L.; Zhao, Y. M.; Yu, S. Z.; Zhao, C. Y.; Yang, H.

    2014-01-01

    We investigate the effects of Si doping on the strain relaxation of the compositionally step-graded (Al)GaInP buffers grown by metal-organic chemical vapor deposition on (0 0 1) GaAs substrates with different miscuts toward (1 1 1)A. It is found that in the 2° samples, high Si doping can reduce both the α and β dislocation densities by delaying and suppressing the formation of phase separation in the buffer. In contrast, in the 7° samples, Si dopants deteriorate the buffer quality through increasing the dislocation density accompanying with the tilt reduction along the [1 1 0] direction, and a striking feature, bunches of β dislocations away from the interfaces, is observed in the [1 1 0] cross-sectional transmission electron microscopy images. A cross-slip mechanism closely associated with the pinning effect of Si on α dislocation motion is proposed to explain the multiplication of β dislocations. These results indicate that selecting a moderate Si doping density and substrate miscut are critical for the design and fabrication of metamorphic optoelectronic devices.

  3. A new technique to study transient conductivity under pulsed monochromatic light in Cr-doped GaAs using acoustoelectric voltage measurement

    NASA Technical Reports Server (NTRS)

    Tabib-Azar, Massood

    1991-01-01

    The transient conductivity of high-resistivity Bridgman-grown Cr-doped GaAs under pulsed monochromatic light is monitored using transverse acoustoelectric voltage (TAV) at 83 K. Keeping the photon flux constant, the height and transient time constant at the TAV are used to calculate the energy dependence of the trap density and its cross section, respectively. Two prominent trap profiles with peak trap densities of approximately 10 to the 17th/cu cm eV near the valence and the conduction bands are detected. These traps have very small capture cross sections in the range of 10 to the -23 to 10 to the -21st cm sq. A phenomenon similar to the persistent photoconductivity with transient time constants in excess of a few seconds in high-resistivity GaAs at T = 83 K is also detected using this technique. These long relaxation times are readily explained by the spatial separation of the photo-excited electron-hole pairs and the small capture cross section and large density of trap distribution near the conduction band.

  4. 808-nm diode-pumped dual-wavelength passively Q-switched Nd:LuLiF4 laser with Bi-doped GaAs

    NASA Astrophysics Data System (ADS)

    Li, S. X.; Li, T.; Li, D. C.; Zhao, S. Z.; Li, G. Q.; Hang, Y.; Zhang, P. X.; Li, X. Y.; Qiao, H.

    2015-09-01

    Diode-pumped CW and passively Q-switched Nd:LuLiF4 lasers with stable, synchronous dual-wavelength operations near 1047 and 1053 nm were demonstrated for the first time. The maximal CW output power of 821 mW was obtained at an incident pump power of 6.52 W. Employing high quality Bi-doped GaAs as saturable absorber, stable dual-wavelength Q-switched operation was realized. Under 6.52 W incident pump power, the minimal pulse duration of 1.5 ns, the largest single pulse energy of 11.32 μJ, and the highest peak power of 7.25 kW were achieved.

  5. The remote electron beam-induced current analysis of grain boundaries in semiconducting and semi-insulating materials.

    PubMed

    Holt, D B

    2000-01-01

    When no charge collecting p-n junction or Schottky barrier is present in the specimen, but two contacts are applied, conductive mode scanning electron microscope (SEM) observations known as remote electron beam-induced current (REBIC) can be made. It was described as "remote" EBIC because the contacts to the specimen can lie at macroscopic distances from the beam impact point. In recent years, REBIC has been found to be useful not only for studies of grain boundaries in semiconducting silicon and germanium, but also in semi-insulating materials such as the wider bandgap II-VI compounds and electroceramic materials like varistor ZnO and positive temperature coefficient resistor (PTCR) BaTiO3. The principles of this method are outlined. Accounts are given of the five forms of charge collection and resistive contrast that appear at grain boundaries (GBs) in REBIC micrographs. These are (1) terraced contrast due to high resistivity boundary layers, (2) peak and trough (PAT) contrast due to charge on the boundary, (3) reversible contrast seen only under external voltage bias due to the beta-conductive effect in a low conductivity boundary layer, (4) dark contrast due to enhanced recombination, and (5) bright contrast apparently due to reduced recombination. For comparison, the results of the extensive EBIC studies of GBs in Si and Ge are first outlined and then the results of recent REBIC grain boundary studies in both semiconducting and semi-insulating materials are reviewed.

  6. Towards semi-insulating InGaAsP/InP layers by post-growth processing using Fe ion implantation and rapid thermal annealing

    NASA Astrophysics Data System (ADS)

    Fekecs, André; Chicoine, Martin; Ilahi, Bouraoui; Schiettekatte, François; Charette, Paul G.; Arès, Richard

    2013-04-01

    In this paper, we report on an effective post-growth processing technique for developing semi-insulating (SI) photonic thin films absorbing in 1.3 µm. For that purpose, we examined a 1 µm thick unintentionally n-doped In0.72Ga0.28As0.61P0.39 epilayer (0.95 eV bandgap) modified by multiple-energy MeV Fe ion implantation. Fe was chosen as a deep-level impurity. The ion beam processing was performed at room temperature, followed by rapid thermal annealing (RTA) at 800 °C for 15 s. We investigated the impact of ion fluence on electrical properties by Hall effect measurements. Channelling Rutherford backscattering spectrometry, x-ray diffraction and photoluminescence measurements were carried out to evaluate crystal quality after each fabrication step. Beyond the onset of amorphization, when the total Fe fluence was more than 4.8 × 1013 cm-2, the implanted InGaAsP layer showed evidence of a poor recrystallization after RTA, and its isolation was impaired. Maximum resistivity values were achieved below the onset of amorphization where annealing reduced ion de-channelling and recovered damage-induced strain. With a total Fe fluence of 1.6 × 1013 cm-2, the electrical resistivity and Hall mobility reached values of 1.4 × 104 Ω cm and 4 × 102 cm2 V-1 s-1. These results add important insights on the optimization of this process for the development of InP-based SI photoconductive films.

  7. Diagnostics of Si multi-δ-doped GaAs layers by Raman spectroscopy on bevelled structures

    NASA Astrophysics Data System (ADS)

    Srnanek, R.; Gurnik, P.; Harmatha, L.; Gregora, I.

    2001-11-01

    A new procedure for determination of the doping spikes location and the spatial extent of dopants in Si single and multi-δ-doped layers by micro-Raman spectroscopy is presented. The procedure is based on the evaluation of ITO/ ILO intensities along the bevelled structure. The obtained values of Si extent from 4.0 to 4.5 nm are in good coincidence with values presented in the literature. After calibration, the procedure will be suitable for direct estimation of dopant profiles in δ-doped layers in semiconductor materials, where a bevel through the structures can be prepared.

  8. Photodetectors based on carbon nanotubes deposited by using a spray technique on semi-insulating gallium arsenide.

    PubMed

    Melisi, Domenico; Nitti, Maria Angela; Valentini, Marco; Valentini, Antonio; Ligonzo, Teresa; De Pascali, Giuseppe; Ambrico, Marianna

    2014-01-01

    In this paper, a spray technique is used to perform low temperature deposition of multi-wall carbon nanotubes on semi-insulating gallium arsenide in order to obtain photodectors. A dispersion of nanotube powder in non-polar 1,2-dichloroethane is used as starting material. The morphological properties of the deposited films has been analysed by means of electron microscopy, in scanning and transmission mode. Detectors with different layouts have been prepared and current-voltage characteristics have been recorded in the dark and under irradiation with light in the range from ultraviolet to near infrared. The device spectral efficiency obtained from the electrical characterization is finally reported and an improvement of the photodetector behavior due to the nanotubes is presented and discussed.

  9. Optical absorption and photocurrent enhancement in semi-insulating gallium arsenide by femtosecond laser pulse surface microstructuring.

    PubMed

    Zhao, Zhen-Yu; Song, Zhi-Qiang; Shi, Wang-Zhou; Zhao, Quan-Zhong

    2014-05-19

    We observe an enhancement of optical absorption and photocurrent from semi-insulating gallium arsenide (SI-GaAs) irradiated by femtosecond laser pulses. The SI-GaAs wafer is treated by a regeneratively amplified Ti: Sapphire laser of 120 fs laser pulse at 800 nm wavelength. The laser ablation induced 0.74 μm periodic ripples, and its optical absorption-edge is shifted to a longer wavelength. Meanwhile, the steady photocurrent of irradiated SI-GaAs is found to enhance 50%. The electrical properties of samples are calibrated by van der Pauw method. It is found that femtosecond laser ablation causes a microscale anti-reflection coating surface which enhances the absorption and photoconductivity.

  10. Characterization of the semi-insulating properties of AlHfO3.5 for power devices

    NASA Astrophysics Data System (ADS)

    Alandia, B. S.; Huanca, D. R.; Christiano, V.; dos Santos Filho, S. G.

    2015-03-01

    Physical and electrical characterization of hafnium aluminates gate dielectrics was carried out to investigate their semi-insulating characteristics as passivating layer for power devices. The deposited films were annealed in pure nitrogen to simulate the thermal budget during a conventional CMOS processing. C-V measurements were performed having as a result a high-frequency behavior of the flat band voltage (VFB) and values greater than or equal to zero. On the other hand, the leakage phenomenon was modeled with a simplified electrical model using a leakage admittance YC whose influence was predominant at the accumulation region. Using X-ray reflectometry (XRR), the average thickness obtained was 15.5nm and a leakage process was inferred to occur for AlHfO3.5 due to the observed phase separation and crystallization that occurs after annealing in pure N2.

  11. Optical and electrical properties of heavily carbon-doped GaAs fabricated by high-energy ion-implantation

    SciTech Connect

    Shima, Takayuki |; Makita, Yunosuke; Kimura, Shinji

    1996-12-31

    High-energy (400 keV) implantation of carbon (C) ions was made into LEC-GaAs substrates with C concentration ([C]) of 10{sup 19}--10{sup 22} cm{sup {minus}3}. 2 K photoluminescence (PL) and Hall effect measurements indicated that activation rate of C in LEC GaAs is both optically and electrically extremely low even after furnace-annealing at 850 C for 20 min. For [C] = 1 {times} 10{sup 22} cm{sup {minus}3}, two novel strong emissions were obtained and PL measurements as a function of excitation power and sample temperature suggested that the two emissions one at 1.485 eV and the other at 1.305 eV should reflect the formation of a new alloy between GaAs and C. Dual implantation of C{sup +} and Ga{sup +} ions was carried out to improve the activation or substitution rate. The authors found that nearly 90% activation rate can be achieved for C dose of 2.2 {times} 10{sup 13} cm{sup {minus}2}.

  12. The effects of the magnitude of the modulation field on electroreflectance spectroscopy of undoped-n+ type doped GaAs

    NASA Astrophysics Data System (ADS)

    Wang, D. P.; Huang, K. M.; Shen, T. L.; Huang, K. F.; Huang, T. C.

    1998-01-01

    The electroreflectance (ER) spectra of an undoped-n+ type doped GaAs has been measured at various amplitudes of modulating fields (δF). Many Franz-Keldysh oscillations were observed above the band gap energy, thus enabling the electric field (F) in the undoped layer to be determined. The F is obtained by applying fast Fourier transformation to the ER spectra. When δF is small, the power spectrum can be clearly resolved into two peaks, which corresponds to heavy- and light-hole transitions. When δF is less than ˜1/8 of the built-in field (Fbi˜77 420 V/cm), the F deduced from the ER is almost independent of δF. However, when larger than this, F is increased with δF. Also, when δF is increased to larger than ˜1/8 of Fbi, a shoulder appears on the right side of the heavy-hole peak of the power spectrum. The separation between the main peak and the shoulder of the heavy-hole peak becomes wider as δF becomes larger.

  13. Photoluminescence fatigue and inhomogeneous line broadening in semi-insulating Tl6SeI4 single crystals

    NASA Astrophysics Data System (ADS)

    Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.

    2016-06-01

    Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10–265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.

  14. Photoluminescence fatigue and inhomogeneous line broadening in semi-insulating Tl6SeI4 single crystals

    NASA Astrophysics Data System (ADS)

    Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.

    2016-06-01

    Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10-265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.

  15. A thermal ionization model for the sustaining phase of lock-on in GaAs

    SciTech Connect

    Hjalmarson, H.P.; Zutavern, F.J.; Loubriel, G.M.; Buttram, M.T.; Baca, A.G.; Romero, L.A.

    1992-01-01

    Thermal ionization of electrons and holes is proposed as an explanation for the sustained phase of lock-on in semi-insulating GaAs. In this mechanism, thermal ionization leads to a current instability which drives the formation of current filaments. The model predicts bistable states: either a highly conductive on-state or weakly conductive off-state. The model predicts that a transition from the off-state to a filamentary-current on-state can be triggered by illumination in agreement with experiments using photoexcitation.

  16. Coherent dynamics of Landau-Levels in modulation doped GaAs quantum wells at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Liu, Cunming; Paul, Jagannath; Reno, John; McGill, Stephen; Hilton, David; Karaiskaj, Denis

    By using two-dimensional Fourier transform spectroscopy, we investigate the dynamics of Landau-Levels formed in modulation doped GaAs/AlGaAs quantum wells of 18 nm thickness at high magnetic fields and low temperature. The measurements show interesting dephasing dynamics and linewidth dependency as a function of the magnetic field. The work at USF and UAB was supported by the National Science Foundation under grant number DMR-1409473. The work at NHMFL, FSU was supported by the National Science Foundation under grant numbers DMR-1157490 and DMR-1229217. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.

  17. Band-gap narrowing in Mn-doped GaAs probed by room-temperature photoluminescence

    NASA Astrophysics Data System (ADS)

    Prucnal, S.; Gao, K.; Skorupa, I.; Rebohle, L.; Vines, L.; Schmidt, H.; Khalid, M.; Wang, Y.; Weschke, E.; Skorupa, W.; Grenzer, J.; Hübner, R.; Helm, M.; Zhou, S.

    2015-12-01

    The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here, we present room-temperature photoluminescence and ellipsometry measurements of G a100 %-xM nxAs alloy. The upshift of the valence band is proven by the redshift of the room temperature near band-gap emission from the G a100 %-xM nxAs alloy with increasing Mn content. It is shown that even a doping by 0.02% of Mn affects the valence-band edge, and it merges with the impurity band for a Mn concentration as low as 0.6%. Both x-ray diffraction pattern and high-resolution cross-sectional transmission electron microscopy images confirmed full recrystallization of the implanted layer and GaMnAs alloy formation.

  18. Index grating lifetime in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Partovi, Afshin

    1988-01-01

    The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measure was about 8 s under a read beam intensity of 0.7 mW/sq cm with the grating periodicity being 0.63 microns. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to about 10 mW/sq cm and 4 microns, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements, for optical computing. In addition, the results suggest that the lifetime is sensitive to residual imperfections in the crystal.

  19. An AFM-based surface oxidation process for heavily carbon-doped p-type GaAs with a hole concentration of 1.5×1021 cm-3

    NASA Astrophysics Data System (ADS)

    Shirakashi, J.-I.; Matsumoto, K.; Konagai, M.

    Under appropriate bias conditions in ambient humidity, AFM can be used to selectively oxidize the surface of electronic materials such as metals and semiconductors. Therefore, an AFM-based surface modification technique would be a powerful tool for fabricating nanometer-sized metal (M)/insulator (I) or semiconductor (S)/insulator (I) junction structures. Heavily carbon-doped p-type GaAs with a hole concentration of 1.5×1021 cm-3 is also of great interest for application to novel device structures, because the carrier concentration is comparable to that of normal metals. Selective surface oxidation of carbon-doped p-type GaAs was achieved using a negatively biased conductive tip. The oxidation shown here was carried out under 20-25% ambient humidity. By changing the applied bias voltage and the scanning speed of the cantilever, the size of the modified structure wires was precisely controlled, with a feature size of 10 nm. These results suggest that GaAs-based devices with ultra-small SIS junction systems could be realized using the AFM-based surface oxidation process.

  20. Growth of highly doped p-type ZnTe films by pulsed laser ablation in molecular nitrogen

    SciTech Connect

    Lowndes, D.H.; Rouleau, C.M.; Budai, J.D.; Poker, D.B.; Geohegan, D.B.; Zhu, Shen; McCamy, J.W.; Puretzky, A.

    1995-04-01

    Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N{sub 2} ambient without the use of any assisting (DC or AC) plasma source. Free hole concentrations in the mid-10{sup 19} cm{sup {minus}3} to > 10{sup 20} cm{sup {minus}3} range were obtained for a range of nitrogen pressures The maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. The highest hole mobilities were attained for nitrogen pressures of 50--100 mTorr ({approximately}6.5-13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N{sub 2} do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be the first time that any wide band gap (Eg > 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSe{sub l-x}S{sub x} films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy.

  1. A comparative study of heavily irradiated silicon and non irradiated SI LEC GaAs detectors

    SciTech Connect

    Biggeri, U.; Borchi, E.; Bruzzi, M.

    1998-06-01

    Silicon p{sup +}n junctions irradiated with neutron and proton fluences in the range 5 {times} 10{sup 11}--4 {times} 10{sup 15} cm{sup {minus}2} and non-irradiated Semi Insulating (SI) LEC GaAs Schottky barriers have been analyzed. In silicon the concentration N{sub t} of the main radiation-induced deep traps (Et {approx} 0.44--0.54 eV) is found to increase as N{sub t} {alpha} f achieving values up to 5 {times} 10{sup 15} cm{sup {minus}3} and a mobility saturation at 100 cm{sup 2}/Vs has been observed at the highest fluences. A quantitative comparison between heavily irradiated silicon and non-irradiated GaAs evidenced similar charge collection efficiencies, a quasi-intrinsic bulk and similar concentrations of deep defects. On this basis, a unique model, correlating the lattice disorder and the detector performance, is suggested.

  2. InAs growth and development of defect microstructure on GaAs

    NASA Astrophysics Data System (ADS)

    Khandekar, A. A.; Suryanarayanan, G.; Babcock, S. E.; Kuech, T. F.

    2005-02-01

    Epitaxially deposited thin films of InAs on semi-insulating GaAs substrates are commonly used for high-speed electronic devices. Large (7%) lattice mismatch between InAs and GaAs leads to Stranski-Krastanov growth mode with formation of 3D islands. The effect of growth temperature in MOVPE deposition, on InAs crystal microstructure was studied. The origin of multiple tilting of the InAs crystal lattice observed for the high temperature growths was investigated in detail. The microstructure of uncoalesced InAs islands was determined using X-ray diffraction rocking curve scans and backscattered electron Kikuchi pattern crystal orientation imaging. Misoriented grains are formed within uncoalesced InAs islands at an early stage during the growth.

  3. Transient radiation effects in GaAs devices: Bulk conduction and channel modulation phenomena in D-MESFET, E-JFET, AND n/sup +/-SI-n/sup +/ structures

    SciTech Connect

    Flesner, L.D.

    1984-12-01

    Transient radiation effects in GaAs devices have been studied using localized electron-beam pulses. Distinct response mechanisms are described and compared for different device structures of similar dimension, fabricated by ion-implantation into undoped semi-insulating GaAs substrates. An n-channel transient conduction increase with non-exponential recovery and millisecond time scale is quantitatively analyzed using a phenomenological model which incorporates the photovoltaic effect and charge separation at the channel-substrate junction. Good agreement is found using reasonable values for junction capacitance and recombination current. Slow emission of trapped positive charge from deep levels is not required to explain the observed recovery dynamics.

  4. LEC GaAs for integrated circuit applications

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

    1984-01-01

    Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

  5. Pressure-induced shallow-to-deep donor-state transition in 119doped GaAs observed by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Gibart, P.; Williamson, D. L.; Moser, J.; Basmaji, P.

    1990-08-01

    The Sn DX center in GaAs, a deep donor state of Sn, has been observed by Mössbauer measurements at high pressure. The size of the pressure-induced Sn DX Mössbauer resonance compared to the net conduction-electron concentration at zero pressure provides evidence that the Sn DX center localizes two or three electrons in the ground state.

  6. Analysis of high field effects on the steady-state current-voltage response of semi-insulating 4H-SiC for photoconductive switch applications

    SciTech Connect

    Tiskumara, R.; Joshi, R. P. Mauch, D.; Dickens, J. C.; Neuber, A. A.

    2015-09-07

    A model-based analysis of the steady-state, current-voltage response of semi-insulating 4H-SiC is carried out to probe the internal mechanisms, focusing on electric field driven effects. Relevant physical processes, such as multiple defects, repulsive potential barriers to electron trapping, band-to-trap impact ionization, and field-dependent detrapping, are comprehensively included. Results of our model match the available experimental data fairly well over orders of magnitude variation in the current density. A number of important parameters are also extracted in the process through comparisons with available data. Finally, based on our analysis, the possible presence of holes in the samples can be discounted up to applied fields as high as ∼275 kV/cm.

  7. Measured Attenuation of Coplanar Waveguide on 6H, p-type SiC and High Purity Semi-Insulating 4H SiC through 800 K

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Schwartz, Zachary D.; Alterovitz, Samuel A.; Downey, Alan N.

    2004-01-01

    Wireless sensors for high temperature applications such as oil drilling and mining, automobiles, and jet engine performance monitoring require circuits built on wide bandgap semiconductors. In this paper, the characteristics of microwave transmission lines on 4H-High Purity Semi-Insulating SiC and 6H, p-type SiC is presented as a function of temperature and frequency. It is shown that the attenuation of 6H, p-type substrates is too high for microwave circuits, large leakage current will flow through the substrate, and that unusual attenuation characteristics are due to trapping in the SiC. The 4H-HPSI SiC is shown to have low attenuation and leakage currents over the entire temperature range.

  8. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    SciTech Connect

    Iwamoto, Naoya Azarov, Alexander; Svensson, Bengt G.; Ohshima, Takeshi; Moe, Anne Marie M.

    2015-07-28

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 10{sup 15 }cm{sup −3} range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ∼10{sup 14 }cm{sup −3}). Schottky barrier diodes fabricated on substrates annealed at 1400–1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  9. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    NASA Astrophysics Data System (ADS)

    Iwamoto, Naoya; Azarov, Alexander; Ohshima, Takeshi; Moe, Anne Marie M.; Svensson, Bengt G.

    2015-07-01

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 1015 cm-3 range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ˜1014 cm-3). Schottky barrier diodes fabricated on substrates annealed at 1400-1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  10. Studies and comparisons of a N+-InGaP/δ(P+)-InGaP/n- GaAs hetero-planar-doped structure to high-linearity microwave field-effect transistors

    NASA Astrophysics Data System (ADS)

    Lour, W. S.; Tsai, M. K.; Lai, K. Y.; Chen, B. L.; Yang, Y. J.

    2001-04-01

    We report a promising N+-InGaP/δ(P+)-InGaP/n-GaAs hetero-planar-doped barrier, which is used to fabricate both high-breakdown and self-aligned T-gate (SAT-gate) field-effect transistors (FETs). The characteristics of the devices and comparisons with previous reports are discussed. The enhanced conduction- and valence-band offsets associated with the new hetero-planar doped barrier show high-breakdown behaviour. In addition, high selective etching between InGaP and GaAs layers together with an ohmic gate allows the fabrication of a SAT-gate with a reduced gate-length of 0.8 µm. In the case of a high-breakdown FET, the drain-source breakdown voltage is as high as 32 V. In addition to competitive direct-current (dc) performances, a reduced knee voltage and improved frequency performances are obtained in SAT-gate FETs. The available unity-current-gain and unity-power-gain frequencies are, respectively, 19.5 and 30 GHz achieved as a 0.6 µm gate is obtained by forming a 1 µm metal gate. Furthermore, all the measured SAT-gate FETs exhibit high-linearity and high-uniformity dc and alternating-current performances.

  11. EL2 and related defects in GaAs - Challenges and pitfalls. [microdefect introducing a deep donor level

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is necessary, therefore, to rely on indirect methods and phenomenological models and deal with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of most recent results.

  12. The electrical properties of 60 keV zinc ions implanted into semi-insulating gallium arsenide

    NASA Technical Reports Server (NTRS)

    Littlejohn, M. A.; Anikara, R.

    1972-01-01

    The electrical behavior of zinc ions implanted into chromium-doped semiinsulating gallium arsenide was investigated by measurements of the sheet resistivity and Hall effect. Room temperature implantations were performed using fluence values from 10 to the 12th to 10 to the 15th power/sq cm at 60 keV. The samples were annealed for 30 minutes in a nitrogen atmosphere up to 800 C in steps of 200 C and the effect of this annealing on the Hall effect and sheet resistivity was studied at room temperature using the Van der Pauw technique. The temperature dependence of sheet resistivity and mobility was measured from liquid nitrogen temperature to room temperature. Finally, a measurement of the implanted profile was obtained using a layer removal technique combined with the Hall effect and sheet resistivity measurements.

  13. Field dependent emission rates in radiation damaged GaAs

    SciTech Connect

    Fleming, R. M.; Myers, S. M.; Wampler, W. R.; Lang, D. V.; Seager, C. H.; Campbell, J. M.

    2014-07-07

    We have measured the temperature and field dependence of emission rates from five traps in electron damaged GaAs. Four of the traps have previously been identified as radiation defects. One of the traps, seen in higher doped diodes, has not been previously identified. We have fit the data to a multiphonon emission theory that allows recombination in GaAs to be characterized over a broad range of temperature and electric field. These results demonstrate an efficient method to calculate field-dependent emission rates in GaAs.

  14. A numerical model of GaAs MESFET's including energy balance for microwave applications

    NASA Astrophysics Data System (ADS)

    Yoganathan, S.; Banerjee, S.; Itoh, T.; Shichijo, H.; El-Ghazaly, S.

    1991-07-01

    A novel decoupled solver has been developed that allows larger time steps than conventional decoupled Gummel algorithms and is less central processing unit (CPU) memory and time intensive than coupled Newton solvers. The order in which the quasi-hydrodynamic equations are solved exploits the large difference between the energy relaxation time, (typically 0.5 ps), and the dielectric relaxation time, tau(d) (10 fs). The new decoupled scheme is numerically stable for time steps as large as 20 x tau(d). This makes it possible to reduce Cray Y-MP CPU times by 5-7 times compared to those required by conventional Gummel algorithms. This algorithm allows efficient analysis of GaAs MESFETs to study phenomena such as carrier heating near the drain, Gunn domain formation, and carrier injection into the semi-insulating substrate.

  15. Study of defects in GaAs by differential thermal analysis

    SciTech Connect

    Lim, H.; von Bardeleben, H.J.; Bourgoin, J.C.

    1987-10-01

    Differential thermal analysis is applied to the measurement of defect total energies in GaAs. First, the technique is used to determine the energy liberated in the recombination of an As vacancy-interstitial pair; the result, in agreement with the theoretical estimate of the energy stored in such defect, allows the demonstration of the validity of the technique as well as its limitations. Then, the technique is used to evaluate the introduction rate of such defects by electron irradiation in a semi-insulating material in which electrical techniques cannot be applied. Finally, a characterization of native defects is attempted; it shows that recombination of native vacancies, with interstitials liberated when the movement of ..cap alpha.. dislocations takes place, occurs around 450 /sup 0/C.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Photoluminescence properties of modulation-doped In{sub x}Al{sub 1–x}As/In{sub y}Ga{sub 1–y}As/In{sub x}Al{sub 1–x}As structures with strained inas and gaas nanoinserts in the quantum well

    SciTech Connect

    Galiev, G. B.; Vasil’evskii, I. S.; Klimov, E. A.; Klochkov, A. N.; Lavruhin, D. V.; Pushkarev, S. S.; Maltsev, P. P.

    2015-09-15

    The photoluminescence spectra of modulation-doped InAlAs/InGaAs/InAlAs heterostructures with quantum wells containing thin strained InAs and GaAs inserts are investigated. It is established that the insertion of pair InAs layers and/ or a GaAs transition barriers with a thickness of 1 nm into a quantum well leads to a change in the form and energy position of the photoluminescence spectra as compared with a uniform In{sub 0.53}Ga{sub 0.47}As quantum well. Simulation of the band structure shows that this change is caused by a variation in the energy and wave functions of holes. It is demonstrated that the use of InAs inserts leads to the localization of heavy holes near the InAs layers and reduces the energy of optical transitions, while the use of GaAs transition barriers can lead to inversion of the positions of the light- and heavy-hole subbands in the quantum well. A technique for separately controlling the light- and heavy-hole states by varying the thickness and position of the GaAs and InAs inserts in the quantum well is suggested.

  18. Modelling of semiconductor diodes made of high defect concentration, irradiated, high resistivity and semi-insulating material: The capacitance voltage characteristics

    NASA Astrophysics Data System (ADS)

    Saadoune, A.; Dehimi, L.; Sengouga, N.; McPherson, M.; Jones, B. K.

    2006-07-01

    Full modelling is reported of the capacitance of a long PIN semiconductor diode with a high concentration of generation-recombination (g-r) centres and different concentrations of deep traps. There are considerable differences from the textbook results given for normal lifetime diodes which have low concentrations of g-r centres. For a low density of g-r centres, the capacitance is the usual value. That is it decreases as V-1/2 with increasing reverse bias while it increases rapidly with increasing forward bias. For high density of g-r centres and in reverse bias a departure from this voltage dependence is observed, while in forward bias a negative capacitance appears. This agrees with experiment. From these results we present a physical understanding of the processes involved. There are specific applications of these results to radiation damaged devices, lifetime killed diodes and devices made from high resistance and semi-insulating materials, especially in the interpretation of the C- V curves to evaluate the fixed space charge density.

  19. Isoelectronic co-doping

    DOEpatents

    Mascarenhas, Angelo

    2004-11-09

    Isoelectronic co-doping of semiconductor compounds and alloys with deep acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, N and Bi, to customize solar cells, thermal voltaic cells, light emitting diodes, photodetectors, and lasers on GaP, InP, GaAs, Ge, and Si substrates. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  20. Origin and reduction of impurities at GaAs epitaxial layer-substrate interfaces

    NASA Astrophysics Data System (ADS)

    Kanber, H.; Yang, H. T.; Zielinski, T.; Whelan, J. M.

    1988-09-01

    Surface cleaning techniques used for semi-insulating GaAs substrates prior to epitaxial growth can have an important and sometimes detrimental effect on the quality and characteristics of epitaxial layers that are grown on them. We observe that a HF rinse followed by a 5:1:1 H 2SO 4:H 2O 2:H 2O etch and H 2O rinse drastically reduced the maximum concentrations and total amount of both SIMS detected S and Si for MOCVD grown GaAs undoped epitaxial layers. Subsequent final HCl and H 2O reduced the S interfacial residues to the SIMS detection limit. Total amounts of residual Si are estimated to be equivalent to 10 -2 to 10 -3 monolayers. Residual S is less. Alternately the S residue can be comparable reduced by a HF rinse followed by a NH 4OH:H 2O 2:H 2O etch and H 2O rinse. Hot aqueous HCl removes S but not Si residues. The Si residue is not electrically active and most likely exists as islands of SiO 2. The relative significance of the impurity residues is most pronounced for halide VPE, smaller for MBE and least for MOCVD grown GaAs epitaxial layers.

  1. Identification of As-vacancy complexes in Zn-diffused GaAs

    SciTech Connect

    Elsayed, M.; Krause-Rehberg, R.; Korff, B.; Richter, S.; Leipner, H. S.

    2013-03-07

    We have used positron annihilation spectroscopy to study the introduction of point defects in Zn-diffused semi-insulating GaAs. The diffusion was performed by annealing the samples for 2 h at 950 Degree-Sign C. The samples were etched in steps of 7 {mu}m. Both Doppler broadening using slow positron beam and lifetime spectroscopy studies were performed after each etching step. Both techniques showed the existence of vacancy-type defects in a layer of about 45 {mu}m. Secondary ion mass spectroscopy measurements illustrated the presence of Zn at high level in the sample almost up to the same depth. Vacancy-like defects as well as shallow positron traps were observed by lifetime measurements. We distinguish two kinds of defects: As vacancy belongs to defect complex, bound to most likely one Zn atom incorporated on Ga sublattice, and negative-ion-type positron traps. Zn acceptors explained the observation of shallow traps. The effect of Zn was evidenced by probing GaAs samples annealed under similar conditions but without Zn treatment. A defect-free bulk lifetime value is detected in this sample. Moreover, our positron annihilation spectroscopy measurements demonstrate that Zn diffusion in GaAs system is governed by kick-out mechanism.

  2. X-ray imaging using a 320 x 240 hybrid GaAs pixel detector

    SciTech Connect

    Irsigler, R.; Andersson, J.; Alverbro, J.

    1999-06-01

    The authors present room temperature measurements on 200 {micro}m thick GaAs pixel detectors, which were hybridized to silicon readout circuits. The whole detector array contains 320 x 240 square shaped pixel with a pitch of 38 {micro}m and is based on semi-insulating liquid-encapsulated Czochralski (LEC) GaAs material. After fabricating and dicing, the detector chips were indium bump flip chip bonded to CMOS readout circuits based on charge integration and finally evaluated. This readout chip was originally designed for the readout of flip chip bonded infrared detectors, but appears to be suitable for X-ray applications as well. A bias voltage between 50 V and 100 V was sufficient to operate the detector at room temperature. The detector array did respond to x-ray radiation by an increase in current due to production of electron hole pairs by the ionization processes. Images of various objects and slit patterns were acquired by using a standard X-ray source for dental imaging. The new X-ray hybrid detector was analyzed with respect to its imaging properties. Due to the high absorption coefficient for X-rays in GaAs and the small pixel size, the sensor shows a high modulation transfer function up to the Nyquist frequency.

  3. Comparison of semi-insulating InAlAs and InP:Fe for InP-based buried-heterostructure QCLs

    NASA Astrophysics Data System (ADS)

    Flores, Y. V.; Aleksandrova, A.; Elagin, M.; Kischkat, J.; Kurlov, S. S.; Monastyrskyi, G.; Hellemann, J.; Golovynskyi, S. L.; Dacenko, O. I.; Kondratenko, S. V.; Tarasov, G. G.; Semtsiv, M. P.; Masselink, W. T.

    2015-09-01

    In a previous work [Flores et al., J. Cryst. Growth 398 (2014) 40] [3] we demonstrated the advantages of using a thin InAlAs spacer layer in the fabrication of buried-heterostructure quantum-cascade lasers (QCLs), as it improves the morphology of the interface between the laser core and the InP:Fe lateral cladding. In this paper we investigate aspects of InAlAs, which are relevant for its role as insulating lateral cladding of the laser sidewalls: carrier traps, electrical resistivity, and functionality as a sole lateral cladding. We find that a thin InAlAs spacer layer not only improves the regrowth interface morphology, but also eliminates interface-related shallow electronic states, thus improving the electrical resistivity of the interface. We further find that bulk InAlAs grown by gas-source molecular-beam epitaxy as well as InP:Fe are semi-insulating at room temperature, with specific resistivities of 3 ×107 Ω cm and 2 ×108 Ω cm, respectively. Both materials have also a high thermal activation energy for electrical conductivity (0.79 eV and 0.68 eV, respectively). In order to compare the performance of InP:Fe and InAlAs as a lateral cladding, lasers were fabricated from the same QCL wafer with differing stripe insulation materials. The resulting lasers differ mainly by the lateral insulation material: SiO2, InP:Fe (with InAlAs spacer), and pure InAlAs. All devices show a similar performance and similar temperature dependence, indicating insulating properties of InAlAs adequate for application in lateral regrowth of buried-heterostructure QCLs.

  4. Enzyme-Based Lactic Acid Detection Using Algaas/gaas High Electron Mobility Transistor with Sb-Doped Zno Nanowires Grown on the Gate Region

    NASA Astrophysics Data System (ADS)

    Ma, Siwei; Huang, Yunhua; Liu, Hanshuo; Zhang, Xiaohui; Liao, Qingliang

    2012-08-01

    Sb-doped ZnO nanowires were synthesized via chemical vapor deposition method. Scanning electron microscopic, transmission electron microscopic, X-ray diffraction and energy dispersive spectrometer have been used to characterize the morphology and structure of the nanowires. The AlGaAs/GaAs HEMT drain-source current exhibited a fast response of about 1s when different concentrations of lactic acid solutions were added to the surface of lactate oxidase immobilized on the ZnO nanowires. The HEMT could detect a range of lactic acid concentrations from 3 pM to 30 μM. The biosensor exhibited good performance along with fast response, high sensitivity, and long-term stability. Our results demonstrate the possibility of using AlGaAs/GaAs HEMTs for lactic acid measurements and provide new further fundamental insights into the study of nanoscience and nanodevices.

  5. Characterization of Semi-Insulating Polycrystalline Silicon: the Influence of the Structural Properties of Sipos Films on the Electrical Properties of Their Interfaces with Crystalline Silicon.

    NASA Astrophysics Data System (ADS)

    Brunson, Kevin Michael

    Available from UMI in association with The British Library. Semi-Insulating POlycrystalline Silicon SIPOS layers containing a wide range of oxygen concentrations have been deposited using a low pressure chemical vapour deposition reactor. Physical analysis techniques such as Rutherford backscattering, X-ray photoemission spectroscopy, and transmission electron microscopy have been brought to bear on the question of the structure of these films. A conceptual model based on percolation theory is presented to explain the observations. The 51 at. % oxygen SIPOS-silicon heterojunction has been characterized using admittance measurements in both the voltage and frequency domain. The form of the equivalent parallel conductance of the interface states, for both as-deposited and 900^circ C annealed SIPOS-silicon junctions, is found to be described adequately by Nicollian's statistical model (Bell. Syst. Tech. J. Vol 46(6), p 1055; 1967). Preier's competing tunnelling model (Appl. Phys. Lett. Vol 10(12), p 361; 1967) is shown to be conceptually in error when describing interface state response, but possible modifications to the model are discussed at length. For the as-deposited material the calculated density of localised states at the SIPOS-silicon interface exhibits a U-shaped continuum with densities of ~eq6 times 10^{10} cm^{-2} eV^ {-1} near mid-gap rising to ~eq 6 times 10^ {11} cm^{-2} eV^{-1} at the band edges. In addition to the interface state contributions in the equivalent parallel conductance a second resonance is detected which has been identified as being due to trapping states in the p-silicon depletion region. A quantitative estimate of the density of these bulk states is presented. After annealing the junction at 900^circ C the interface state density not only increased by approximately one order of magnitude, but also a discrete interface state peak appeared on the background continuum at an energy of ~eq0.1 eV below the conduction band edge. The barrier

  6. First principles study of bismuth alloying effects in GaAs saturable absorber.

    PubMed

    Li, Dechun; Yang, Ming; Zhao, Shengzhi; Cai, Yongqing; Feng, Yuanping

    2012-05-01

    First principles hybrid functional calculations have been carried out to study electronic properties of GaAs with Bi alloying effects. It is found that the doping of Bi into GaAs reduces the bandgap due to the intraband level repulsions between Bi induced states and host states, and the Bi-related impurity states originate from the hybridization of Bi-6p and its nearest As-4p orbitals. With the increase of Bi concentration in GaAs, the bandgap decreases monotonously. The calculated optical properties of the undoped and Bi-doped GaAs are similar except the shift toward lower energy of absorption edge and main absorption peaks with Bi doping. These results suggest a promising application of GaBi(x)As(1-x) alloy as semiconductor saturable absorber in Q-switched or mode-locked laser.

  7. Continuous visible-light emission at room temperature in Mn-doped GaAs and Si light-emitting diodes (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Tanaka, Masaaki; Hai, Pham Nam; Anh, Le Duc

    2015-09-01

    We demonstrate visible-light electroluminescence due to d-d transitions in GaAs:Mn based light emitting diodes (LEDs) [1][2]. We prepared p+n junctions with a p+GaAs:Mn layer. At a reverse bias voltage (-3 to -6V), holes are injected from the n-type layer to the depletion layer and accelerated by the intense electric field, and excite the d electrons of Mn in the p+GaAs:Mn layer by impact excitations. We observe visible-light emission E1 = 1.89eV and E2 = 2.16eV, which are exactly the same as the 4T1 -> 6A1 and 4A2 -> 4 T1 transition energy of Mn. Furthermore, by utilizing optical transitions between the p-d hybridized orbitals of Mn atoms doped in Si, we demonstrate Si-based LEDs that continuously emit reddish-yellow visible light at room temperature. The Mn p-d hybrid states are excited by hot holes that are accelerated in the depletion layers of reverse biased Si pn junctions. Above a threshold reverse bias voltage of about -4V, our LEDs show strong visible light emission with two peaks at E1 = 1.75eV and E2 = 2.30eV, corresponding to optical transitions from the t-a (spin-down anti-bonding) states to the e- (spin-down non-bonding) states, and from the e- to the t+a (spin-up anti-bonding) states. The internal quantum efficiency of the E1 and E2 transitions is 3-4 orders of magnitude higher than that of the indirect band-gap transition [3]. [1] P. N. Hai, et al., APL 104, 122409 (2014). [2] P. N. Hai, et al., JAP 116, 113905 (2014). [3] P. N. Hai, et al., submitted.

  8. Polarization doping of graphene on silicon carbide

    NASA Astrophysics Data System (ADS)

    Mammadov, Samir; Ristein, Jürgen; Koch, Roland J.; Ostler, Markus; Raidel, Christian; Wanke, Martina; Vasiliauskas, Remigijus; Yakimova, Rositza; Seyller, Thomas

    2014-12-01

    The doping of quasi-freestanding graphene (QFG) on H-terminated, Si-face 6H-, 4H-, and 3C-SiC is studied by angle-resolved photoelectron spectroscopy close to the Dirac point. Using semi-insulating as well as n-type doped substrates we shed light on the contributions to the charge carrier density in QFG caused by (i) the spontaneous polarization of the substrate, and (ii) the band alignment between the substrate and the graphene layer. In this way we provide quantitative support for the previously suggested model of polarization doping of graphene on SiC (Ristein et al 2012 Phys. Rev. Lett. 108 246104).

  9. Origin and enhancement of the 1.3 μm luminescence from GaAs treated by ion-implantation and flash lamp annealing

    NASA Astrophysics Data System (ADS)

    Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

    2013-09-01

    GaAs and GaAs based materials have outstanding optoelectronic properties and are widely used as light emitting media in devices. Many approaches have been applied to GaAs to generate luminescence at 0.88, 1.30, and 1.55 μm which are transmission windows of optical fibers. In this paper, we present the photoluminescence at 1.30 μm from deep level defects in GaAs treated by ion-implantation and flash lamp annealing (FLA). Such emission, which exhibits superior temperature stability, can be obtained from FLA treated virgin GaAs as well as doped GaAs. Indium-doping in GaAs can greatly enhance the luminescence. By photoluminescence, Raman measurements, and positron annihilation spectroscopy, we conclude that the origin of the 1.30 μm emission is from transitions between the VAs-donor and X-acceptor pairs.

  10. EL2 and related defects in GaAs - Challenges and pitfalls

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry, and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is therefore necessary to rely on indirect methods and phenomenological models and be confronted with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of the most recent results.

  11. Magnetron Sputtered Gold Contacts on N-gaas

    NASA Technical Reports Server (NTRS)

    Buonaquisti, A. D.; Matson, R. J.; Russell, P. E.; Holloway, P. H.

    1984-01-01

    Direct current planar magnetron sputtering was used to deposit gold Schottky barrier electrical contacts on n-type GaAs of varying doping densities. The electrical character of the contact was determined from current voltage and electron beam induced voltage data. Without reducing the surface concentration of carbon and oxide, the contacts were found to be rectifying. There is evidence that energetic neutral particles reflected from the magnetron target strike the GaAs and cause interfacial damage similar to that observed for ion sputtering. Particle irradiation of the surface during contact deposition is discussed.

  12. Interface demarcation in GaAs by current pulsing

    NASA Technical Reports Server (NTRS)

    Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

    1990-01-01

    GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

  13. Ferromagnetic GaAs structures with single Mn delta-layer fabricated using laser deposition.

    PubMed

    Danilov, Yuri A; Vikhrova, Olga V; Kudrin, Alexey V; Zvonkov, Boris N

    2012-06-01

    The new technique combining metal-organic chemical vapor epitaxy with laser ablation of solid targets was used for fabrication of ferromagnetic GaAs structures with single Mn delta-doped layer. The structures demonstrated anomalous Hall effect, planar Hall effect, negative and anisotropic magnetoresistance in temperature range of 10-35 K. In GaAs structures with only single Mn delta-layer (without additional 2D hole gas channel or quantum well) ferromagnetism was observed for the first time.

  14. Selective-area epitaxial growth of GaAs in deep dielectric windows using molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Loke, W. K.; Yoon, S. F.; Zheng, H. Q.

    2001-01-01

    An improved selective-area epitaxial growth process for GaAs in deep dielectric windows (DDWs) is reported. The growth was carried out on (100)-oriented semi-insulating (SI) GaAs substrate at ˜520°C by solid source molecular beam epitaxy (SSMBE) using a valved arsenic cracker source. Dielectric stacks with 10 periods of alternating silicon nitride (2000 Å) and silicon dioxide (1000 Å) layers were deposited using plasma-enhanced chemical vapor deposition (PECVD) for the formation of deep (3 μm) dielectric windows. The alternating dielectric layer stack has been shown to be of greater stability than a single dielectric layer for the purpose of forming the DDW. A process of fabricating the DDW structures, which eliminates the possible contamination at the growth area during photoresist patterning and removing, and subsequent etching of the DDW, has resulted in improved epitaxial layer quality. Micro-Raman spectroscopy measurements showed a significant increase in the longitudinal-optic (LO) to transverse-optic (TO) signal intensity ratio ( ILO/TO) from ˜4.0 to ˜16.0 of the first-order Raman line of GaAs. Supporting evidence from low-temperature (4 K) photoluminescence (PL) showed a reduction in intensity of the conduction band to neutral carbon acceptor (e-C°) emission by a factor of 4.5. This suggests lower levels of carbon contamination originating from the improved fabrication process of the DDW. Scanning electron microscopy (SEM) images showed smoother surface morphology of the GaAs inside the DDW area. These results have important implications on the process of MBE regrowth for optoelectronics integration.

  15. Epitaxial Fe on free-standing GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Yang, Mingze; Darbandi, Ali; Majumder, Sarmita; Watkins, Simon; Kavanagh, Karen

    2016-07-01

    Epitaxial Fe contacts have been fabricated onto the top half of free-standing, Te-doped GaAs nanowires (NWs) via electrodeposition. Electrical isolation from the substrate via a polymeric layer enabled the measurement of electrical transport through individual wires. Using a fixed probe within a scanning electron microscope, an average metal-semiconductor diode barrier height of 0.69 ± 0.03 eV (ideality factor 1.48 ± 0.02) was found.

  16. Localized corrosion of GaAs surfaces and formation of porous GaAs

    SciTech Connect

    Schmuki, P.; Vitus, C.M.; Isaacs, H.S.; Fraser, J.; Graham, M.J.

    1995-12-01

    The present work deals with pitting corrosion of p- and n-type GaAs (100). Pit growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-type material, localized corrosion is only observed if a passivating film is present on the surface, otherwise -- e.g. in acidic solutions -- the material suffers from a uniform attack (electropolishing) which is independent of the anion present. In contrast, pitting corrosion of n-type material can be triggered independent of the presence of an oxide film. This is explained in terms of the different current limiting factor for the differently doped materials (oxide film in the case of the p- and a space charge layer in the case of the n-GaAs). The porous structure was characterized by SEM, EDX and AES, and consists mainly of GaAs. From scratch experiments it is clear that the pit initiation process is strongly influenced by surface defects. For n-type material, AFM investigations show that light induced roughening of the order of several hundred nm occurs under non-passivating conditions. This nm- scale roughening however does not affect the pitting process.

  17. Small signal model parameters analysis of GaN and GaAs based HEMTs over temperature for microwave applications

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    Thermal and small-signal model parameters analysis have been carried out on 0.5 μm × (2 × 100 μm) AlGaAs/GaAs HEMT grown on semi-insulating GaAs substrate and 0.25 μm × (2 × 100 μm) AlGaN/GaN HEMT grown on SiC substrate. Two different technologies are investigated in order to establish a detailed understanding of their capabilities in terms of frequency and temperature using on-wafer S-parameter measurement over the temperature range from -40 to 150 °C up to 50 GHz. The equivalent circuit parameters as well as their temperature-dependent behavior of the two technologies were analyzed and discussed for the first time. The principle elevation or degradation of transistor parameters with temperature demonstrates the great potential of GaN device for high frequency and high temperature applications. The result provides some valuable insights for future design optimizations of advanced GaN and a comparison of this with the GaAs technology.

  18. Schottky barrier measurements on individual GaAs nanowires by X-ray photoemission microscopy

    NASA Astrophysics Data System (ADS)

    di Mario, Lorenzo; Turchini, Stefano; Zamborlini, Giovanni; Feyer, Vitaly; Tian, Lin; Schneider, Claus M.; Rubini, Silvia; Martelli, Faustino

    2016-11-01

    We present measurements of the Schottky barrier height on individual GaAs nanowires by means of x-ray photoelectron emission microscopy (XPEEM). Values of 0.73 and 0.51 eV, averaged over the entire wires, were measured on Cu-covered n-doped and p-doped GaAs nanowires, respectively, in agreement with results obtained on bulk material. Our measurements show that XPEEM can become a feasible and reliable investigation tool of interface formation at the nanoscale and pave the way towards the study of size-dependent effects on semiconductor-based structures.

  19. GaAs detectors irradiated by electrons at different dose rates

    NASA Astrophysics Data System (ADS)

    Sagatova, A.; Zatko, B.; Sedlackova, K.; Pavlovic, M.; Fulop, M.; Bohacek, P.; Necas, V.

    2014-12-01

    The radiation hardness of Semi-Insulating (SI) GaAs detectors against high-energy electrons was investigated. The detectors were irradiated by 5 MeV electrons. The influence of two irradiation parameters, the total absorbed dose (up to 24 kGy) and the applied dose rate (20, 40 and 80 kGy/h), on their spectrometric properties was studied. An 241Am gamma-ray source was used to evaluate the spectrometric properties. The applied dose has negatively affected the detector CCE (Charge Collection Efficiency) and has influenced also the energy resolution. Nevertheless, a global increase of detection efficiency with the dose was observed. Three different dose rates used during irradiation did not affect the CCE, but in the range of doses from 4 to 16 kGy an influence of the applied dose rate upon two other parameters was observed. With higher dose rates, a steeper increase in the detection efficiency and significant worsening of energy resolution were achieved.

  20. Breakover mechanism of GaAs photoconductive switch triggering spark gap for high power applications

    NASA Astrophysics Data System (ADS)

    Tian, Liqiang; Shi, Wei; Feng, Qingqing

    2011-11-01

    A spark gap (SG) triggered by a semi-insulating GaAs photoconductive semiconductor switch (PCSS) is presented. Currents as high as 5.6 kA have been generated using the combined switch, which is excited by a laser pulse with energy of 1.8 mJ and under a bias of 4 kV. Based on the transferred-electron effect and gas streamer theory, the breakover characteristics of the combined switch are analyzed. The photoexcited carrier density in the PCSS is calculated. The calculation and analysis indicate that the PCSS breakover is caused by nucleation of the photoactivated avalanching charge domain. It is shown that the high output current is generated by the discharge of a high-energy gas streamer induced by the strong local electric field distortion or by overvoltage of the SG resulting from quenching of the avalanching domain, and periodic oscillation of the current is caused by interaction between the gas streamer and the charge domain. The cycle of the current oscillation is determined by the rise time of the triggering electric pulse generated by the PCSS, the pulse transmission time between the PCSS and the SG, and the streamer transit time in the SG.

  1. Performance analysis of undoped cylindrical gate all around (GAA) MOSFET at subthreshold regime

    NASA Astrophysics Data System (ADS)

    Jena, B.; Pradhan, K. P.; Dash, S.; Mishra, G. P.; Sahu, P. K.; Mohapatra, S. K.

    2015-09-01

    In this work the sensitivity of process parameters like channel length (L), channel thickness (tSi), and gate work function (φM) on various performance metrics of an undoped cylindrical gate all around (GAA) metal-oxide-semiconductor field effect transistor (MOSFET) are systematically analyzed. Undoped GAA MOSFET is a radical invention as it introduces a new direction for transistor scaling. In conventional MOSFET, generally the channel doping concentration is very high to provide high on-state current, but in contrary it causes random dopant fluctuation and threshold voltage variation. So, the undoped nature of GAA MOSFET solves the above complications. Hence, we have analyzed the electrical characteristics as well as the analog/RF performances of undoped GAA MOSFET through Sentaurus device simulator.

  2. Processing and characterization of epitaxial GaAs radiation detectors

    NASA Astrophysics Data System (ADS)

    Wu, X.; Peltola, T.; Arsenovich, T.; Gädda, A.; Härkönen, J.; Junkes, A.; Karadzhinova, A.; Kostamo, P.; Lipsanen, H.; Luukka, P.; Mattila, M.; Nenonen, S.; Riekkinen, T.; Tuominen, E.; Winkler, A.

    2015-10-01

    GaAs devices have relatively high atomic numbers (Z=31, 33) and thus extend the X-ray absorption edge beyond that of Si (Z=14) devices. In this study, radiation detectors were processed on GaAs substrates with 110 - 130 μm thick epitaxial absorption volume. Thick undoped and heavily doped p+ epitaxial layers were grown using a custom-made horizontal Chloride Vapor Phase Epitaxy (CVPE) reactor, the growth rate of which was about 10 μm / h. The GaAs p+/i/n+ detectors were characterized by Capacitance Voltage (CV), Current Voltage (IV), Transient Current Technique (TCT) and Deep Level Transient Spectroscopy (DLTS) measurements. The full depletion voltage (Vfd) of the detectors with 110 μm epi-layer thickness is in the range of 8-15 V and the leakage current density is about 10 nA/cm2. The signal transit time determined by TCT is about 5 ns when the bias voltage is well above the value that produces the peak saturation drift velocity of electrons in GaAs at a given thickness. Numerical simulations with an appropriate defect model agree with the experimental results.

  3. Sn-seeded GaAs nanowires grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Sun, Rong; Vainorius, Neimantas; Jacobsson, Daniel; Pistol, Mats-Erik; Lehmann, Sebastian; Dick, Kimberly A.

    2016-05-01

    It has previously been reported that in situ formed Sn nanoparticles can successfully initiate GaAs nanowire growth with a self-assembled radial p-n junction composed of a Sn-doped n-type core and a C-doped p-type shell. In this paper, we investigate the effect of fundamental growth parameters on the morphology and crystal structure of Sn-seeded GaAs nanowires. We show that growth can be achieved in a broad temperature window by changing the TMGa precursor flow simultaneously with decreasing temperature to prevent nanowire kinking at low temperatures. We find that changes in the supply of both AsH3 and TMGa can lead to nanowire kinking and that the formation of twin planes is closely related to a low V/III ratio. From PL results, we observe an increase of the average luminescence energy induced by heavy doping which shifts the Fermi level into the conduction band. Furthermore, the doping level of Sn and C is dependent on both the temperature and the V/III ratio. These results indicate that using Sn as the seed particle for nanowire growth is quite different from traditionally used Au in for example growth conditions and resulting nanowire properties. Thus, it is very interesting to explore alternative metal seed particles with controllable introduction of other impurities.

  4. Sn-seeded GaAs nanowires grown by MOVPE.

    PubMed

    Sun, Rong; Vainorius, Neimantas; Jacobsson, Daniel; Pistol, Mats-Erik; Lehmann, Sebastian; Dick, Kimberly A

    2016-05-27

    It has previously been reported that in situ formed Sn nanoparticles can successfully initiate GaAs nanowire growth with a self-assembled radial p-n junction composed of a Sn-doped n-type core and a C-doped p-type shell. In this paper, we investigate the effect of fundamental growth parameters on the morphology and crystal structure of Sn-seeded GaAs nanowires. We show that growth can be achieved in a broad temperature window by changing the TMGa precursor flow simultaneously with decreasing temperature to prevent nanowire kinking at low temperatures. We find that changes in the supply of both AsH3 and TMGa can lead to nanowire kinking and that the formation of twin planes is closely related to a low V/III ratio. From PL results, we observe an increase of the average luminescence energy induced by heavy doping which shifts the Fermi level into the conduction band. Furthermore, the doping level of Sn and C is dependent on both the temperature and the V/III ratio. These results indicate that using Sn as the seed particle for nanowire growth is quite different from traditionally used Au in for example growth conditions and resulting nanowire properties. Thus, it is very interesting to explore alternative metal seed particles with controllable introduction of other impurities. PMID:27087548

  5. Sn-seeded GaAs nanowires grown by MOVPE.

    PubMed

    Sun, Rong; Vainorius, Neimantas; Jacobsson, Daniel; Pistol, Mats-Erik; Lehmann, Sebastian; Dick, Kimberly A

    2016-05-27

    It has previously been reported that in situ formed Sn nanoparticles can successfully initiate GaAs nanowire growth with a self-assembled radial p-n junction composed of a Sn-doped n-type core and a C-doped p-type shell. In this paper, we investigate the effect of fundamental growth parameters on the morphology and crystal structure of Sn-seeded GaAs nanowires. We show that growth can be achieved in a broad temperature window by changing the TMGa precursor flow simultaneously with decreasing temperature to prevent nanowire kinking at low temperatures. We find that changes in the supply of both AsH3 and TMGa can lead to nanowire kinking and that the formation of twin planes is closely related to a low V/III ratio. From PL results, we observe an increase of the average luminescence energy induced by heavy doping which shifts the Fermi level into the conduction band. Furthermore, the doping level of Sn and C is dependent on both the temperature and the V/III ratio. These results indicate that using Sn as the seed particle for nanowire growth is quite different from traditionally used Au in for example growth conditions and resulting nanowire properties. Thus, it is very interesting to explore alternative metal seed particles with controllable introduction of other impurities.

  6. Basic properties of GaAs oxide generated by scanning probe microscope tip-induced nano-oxidation process

    NASA Astrophysics Data System (ADS)

    Okada, Yoshitaka; Iuchi, Yoshimasa; Kawabe, Mitsuo; Harris, James S.

    2000-07-01

    The basic properties of GaAs oxide generated by atomic force microscope (AFM) tip-induced nano-oxidation process have been investigated. The chemical analysis of the AFM tip-generated GaAs oxide was performed by using scanning microprobe x-ray photoelectron spectroscopy, and the main constituents of GaAs anodic oxide were determined to be Ga2O3 and As2O3. The electrical characterization showed that the electron transport across a GaAs oxide nanodot of ˜5.7 nm thickness, from a doped n+-Si tip into the n+-GaAs substrate follows the Fowler-Nordheim tunneling mechanism over a range of applied bias. Further, the tip-generated GaAs oxide nanodots were found to withstand moderate thermal treatments, but some volume reduction was observed.

  7. Thermal conductivity of bulk GaN—Effects of oxygen, magnesium doping, and strain field compensation

    SciTech Connect

    Simon, Roland B.; Anaya, Julian; Kuball, Martin

    2014-11-17

    The effect of oxygen doping (n-type) and oxygen (O)-magnesium (Mg) co-doping (semi-insulating) on the thermal conductivity of ammonothermal bulk GaN was studied via 3-omega measurements and a modified Callaway model. Oxygen doping was shown to significantly reduce thermal conductivity, whereas O-Mg co-doped GaN exhibited a thermal conductivity close to that of undoped GaN. The latter was attributed to a decreased phonon scattering rate due the compensation of impurity-generated strain fields as a result of dopant-complex formation. The results have great implications for GaN electronic and optoelectronic device applications on bulk GaN substrates.

  8. Growth of single GaAs nanowhiskers on the tip of a tungsten needle and their electrical properties

    SciTech Connect

    Golubok, A. O.; Samsonenko, Yu. B.; Mukhin, I. S. Buravlev, A. D.; Cirlin, G. E.

    2011-08-15

    A method for the formation of single GaAs semiconductor nanowhiskers and their assemblies on the tip of a chemically etched tungsten needle by molecular-beam epitaxy is proposed. The focused-ionbeam technique was used to separate a single nanowhisker. Electronic properties of single nanowhiskers were studied by elastic tunneling spectroscopy in ultrahigh vacuum. The band gap and the doping level of GaAs whiskers were determined using the current-voltage characteristics obtained from these measurements.

  9. Formation and properties of porous GaAs

    SciTech Connect

    Schmuki, P.; Lockwood, D.J.; Fraser, J.W.; Graham, M.J.; Isaacs, H.S.

    1996-06-01

    Porous structures on n-type GaAs (100) can be grown electrochemically in chloride-containing solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existanece of a critical onset potential for por formation (PFP). PFP is strongly dependent on the doping level of the sample and presence of surface defects. Good agreement between PFP and breakdown voltage of the space charge layer is found. Surface analysis by EDX, AES, and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only observed after attackhas been initiated. Photoluminescence measurements reveal (under certain conditions) visible light emission from the porous structure.

  10. GaAs Blocked-Impurity-Band Detectors for Far-Infrared Astronomy

    SciTech Connect

    Cardozo, Benjamin Lewin

    2004-01-01

    High-purity and doped GaAs films have been grown by Liquid-phase epitaxy (LPE) for development of a blocked impurity band (BIB) detector for far-infrared radiation. The film growth process developed has resulted in the capability to grow GaAs with a net active impurity concentration below 1 x 1013 cm-3, ideal for the blocking layer of the BIB detector. The growth of n-type LPE GaAs films with donor concentrations below the metal-insulator transition, as required for the absorbing layer of a BIB detector, has been achieved. The control of the donor concentration, however, was found to be insufficient for detector production. The growth by LPE of a high-purity film onto a commercially grown vapor-phase epitaxial (VPE) n-type GaAs doped absorbing layer resulted in a BIB device that showed a significant reduction in the low-temperature dark current compared to the absorbing layer only. Extended optical response was not detected, most likely due to the high compensation of the commercially grown GaAs absorbing layer, which restricts the depletion width of the device.

  11. Investigation of the optical and electrical properties of p-type porous GaAs structure

    NASA Astrophysics Data System (ADS)

    Saghrouni, H.; Missaoui, A.; Hannachi, R.; Beji, L.

    2013-12-01

    Porous GaAs layers have been formed by electrochemical anodic etching of (1 0 0) heavily doped p-type GaAs substrate in a HF:C2H5OH solution. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). Nano-structural nature of the porous layer has been demonstrated by X-ray diffraction analysis (XRD) and confirmed by AFM. An estimation of the main size of the GaAs crystallites obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results. The porous p-GaAs samples are characterised by spectroscopic ellipsometry and modulation spectroscopy techniques. The objective of this study is to determine the porosity, refractive index, and thickness. The porosity of GaAs determined by atomic force microscopy confirmed by the value obtained from the spectroscopic ellipsometry. In fact the current-voltage I(V) characteristics of metal-semiconductor Au/p-GaAs are investigated and compared with Au/p-porous GaAs structures. From the forward bias I(V) characteristics of these devices, the main electrical parameters such as ideality factor, barrier height, and series resistance have been determined.

  12. Epitaxial two-dimensional nitrogen atomic sheet in GaAs

    SciTech Connect

    Harada, Yukihiro Yamamoto, Masuki; Baba, Takeshi; Kita, Takashi

    2014-01-27

    We have grown an epitaxial two-dimensional nitrogen (N) atomic sheet in GaAs by using the site-controlled N δ-doping technique. We observed a change of the electronic states in N δ-doped GaAs from the isolated impurity centers to the delocalized impurity band at 1.49 eV with increasing N-doping density. According to the excitation-power- and temperature-dependent photoluminescence (PL) spectra, the emission related to localized levels below the impurity band edge was dominant at low excitation power and temperature, whereas the effects of the localized levels can be neglected by increasing the excitation power and temperature. Furthermore, a clear Landau shift of the PL-peak energy was observed at several Tesla in the Faraday configuration, in contrast to the case in the impurity limit.

  13. Biexciton emission from single isoelectronic traps formed by nitrogen-nitrogen pairs in GaAs

    SciTech Connect

    Takamiya, Kengo; Fukushima, Toshiyuki; Yagi, Shuhei; Hijikata, Yasuto; Yaguchi, Hiroyuki; Mochizuki, Toshimitsu; Yoshita, Masahiro; Akiyama, Hidefumi; Kuboya, Shigeyuki; Onabe, Kentaro; Katayama, Ryuji

    2013-12-04

    We have studied photoluminescence (PL) from individual isoelectronic traps formed by nitrogen-nitrogen (NN) pairs in GaAs. Sharp emission lines due to exciton and biexciton were observed from individual isoelectronic traps in nitrogen atomic-layer doped (ALD) GaAs. The binding energy of biexciton bound to individual isoelectronic traps was approximately 8 meV. Both the exciton and biexciton luminescence lines show completely random polarization and no fine-structure splitting. These results are desirable to the application to the quantum cryptography used in the field of quantum information technology.

  14. Strain effect of multilayer FeN structure on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaowei; Ji, Nian; Lauter, Valeria; Ambaye, Hailemariam; Wang, Jian-Ping

    2013-05-01

    Overly doped FeN multilayer structure on GaAs substrate was fabricated. After the post-annealing process, FeN martensite in each Fe/FeN layer formed partially chemically ordered Fe16N2, which was observed by X-ray diffraction. To detect the saturation magnetization (Ms) depth profile, polarized neutron reflectivity was conducted. Fe/FeN layer showed a significant improvement of Ms for each layer compared to Ms of Fe. More importantly, different FeN layers showed different Ms according to the physical distance to the substrate GaAs. The most enhanced Ms (exceeding the limit of Fe65Co35 Ms) observed at the bottom part of the film, consistent with previous reports, should be attributed to the lattice strain by GaAs substrate. In order to detect the lattice constant, In-plane X-ray Diffraction was done and a large in-plane lattice constant was determined.

  15. A modified horizontal Bridgman technique without arsenic zone for growth of GaAs crystals

    NASA Astrophysics Data System (ADS)

    Chen, T. P.; Guo, Y. D.; Huang, T. S.

    1989-03-01

    A modified two temperature zone horizontal Bridgman system without arsenic zone has been developed for the growth of GaAs single crystal. In this process, a short quartz ampoule, which was just long enough for sealing off the boat, was used. With a short quartz ampoule and a large charge of polycrystalline GaAs, the arsenic loss due to the dissociation of the melt was very small. The sticking between the boat and the crystal was eliminated; therefore, the crystal yield was greatly enhanced. The possible reasons for the elimination of the boat sticking and the stoichiometry control in this process are discussed. High quality Si-doped GaAs crystals with 2 inches in diameter and 30 cm in length have been routinely grown. The optoelectronic devices fabricated with these wafers showed better performance than commercial products.

  16. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Dutta, P.; Rathi, M.; Zheng, N.; Gao, Y.; Yao, Y.; Martinez, J.; Ahrenkiel, P.; Selvamanickam, V.

    2014-09-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ˜107 cm-2. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm2/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  17. Properties and use of cycled grown OMVPE GaAs:Zn, GaAs:Se, and GaAs:Si layers for high-conductance GaAs tunnel junctions

    SciTech Connect

    Venkatasubramanian, R.; Timmons, M.L.; Colpitts, T.S. ); Asher, S. )

    1992-09-01

    Heavily doped GaAs layers for high conductance GaAs tunnel junctions have been grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE) using Zn as the dopant for the p[sup +] regions and either Se or Si as the dopant for the n[sup +] regions. At a growth temperature of 700[degrees]C using a [open quotes]cycled[close quotes] growth technique for the Zn-doped p[sup ++]-GaAs layer, both the conductance and the peak current density of the tunnel diode has been increased by a factor of [approximately]65 compared to a tunnel junction with a continuously grown Zn-doped p[sup +]-GaAs. The conductance of the tunnel junction, which is maximized at a growth temperature of 650[degrees]C using cycled growth, is comparable to the best reported values for tunnel junctions grown by molecular beam epitaxy. Cycled growths for n[sup +] Se-doped regions are found to reduce the conductance of a tunnel junction by more than two orders of magnitude. However, cycled growth for the n[sup +]-GaAs regions with Si doping show no conductance degradation. A model based on incorporation sites of these dopants during OMVPE growth of GaAs is presented to account for the experimental observations. 14 refs., 7 figs., 4 tabs.

  18. Determination of carrier concentration and compensation microprofiles in GaAs

    NASA Technical Reports Server (NTRS)

    Jastrzebski, L.; Lagowski, J.; Walukiewicz, W.; Gatos, H. C.

    1980-01-01

    Simultaneous microprofiling of semiconductor free carrier, donor, and acceptor concentrations was achieved for the first time from the absolute value of the free carrier absorption coefficient and its wavelength dependence determined by IR absorption in a scanning mode. Employing Ge- and Si-doped melt-grown GaAs, striking differences were found between the variations of electron concentration and those of ionized impurity concentrations. These results showed clearly that the electronic characteristics of this material are controlled by amphoteric doping and deviations from stoichiometry rather than by impurity segregation.

  19. Identification of oxygen-related midgap level in GaAs

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Lin, D. G.; Gatos, H. C.; Aoyama, T.

    1984-01-01

    An oxygen-related deep level ELO was identified in GaAs employing Bridgman-grown crystals with controlled oxygen doping. The activation energy of ELO is almost the same as that of the dominant midgap level: EL2. This fact impedes the identification of ELO by standard deep level transient spectroscopy. However, it was found that the electron capture cross section of ELO is about four times greater than that of EL2. This characteristic served as the basis for the separation and quantitative investigation of ELO employing detailed capacitance transient measurements in conjunction with reference measurements on crystals grown without oxygen doping and containing only EL2.

  20. Resonant Transport in Nb/gaas/algaas/gaas Microstructures

    NASA Astrophysics Data System (ADS)

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

    2003-03-01

    Resonant transport in a hybrid semiconductor-superconductor microstructure grown by MBE on GaAs in presented. This structure experimentally realizes the prototype system originally proposed by de Gennes and Saint-James in 1963 in 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.

  1. Effect of Bi isovalent dopants on the formation of homogeneous coherently strained InAs quantum dots in GaAs matrices

    SciTech Connect

    Peleshchak, R. M.; Guba, S. K.; Kuzyk, O. V.; Kurilo, I. V.; Dankiv, O. O.

    2013-03-15

    The distribution of hydrostatic strains in Bi{sup 3+}-doped InAs quantum dots embedded in a GaAs matrix are calculated in the context of the deformation-potential model. The dependences of strains in the material of spherical InAs quantum dots with substitutional (Bi {yields} As) and interstitial (Bi) impurities on the quantum-dot size are derived. The qualitative correlation of the model with the experiment is discussed. The data on the effect of doping on the morphology of self-assembled InAs:Bi quantum dots in a GaAs matrix are obtained.

  2. GaAs solar cell development

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    The motivation for developing GaAs solar cells is based on their superior efficiency when compared to silicon cells, their lower degradation with increasing temperature, and the expectation for better resistance to space radiation damage. The AMO efficiency of GaAs solar cells was calculated. A key consideration in the HRL technology is the production of GaAs cells of large area (greater than 4 sg cm) at a reasonable cost without sacrificing efficiency. An essential requirement for the successful fabrication of such cells is the ability to grow epitaxially a uniform layer of high quality GaAs (buffer layer) on state-of-the-art GaAs substrates, and to grow on this buffer layer the required than layer of (AlGa)As. A modified infinite melt liquid phase epitaxy (LPE) growth technique is detailed.

  3. Spin Hall Effect in Doped Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Das Sarma, Sankar

    2006-03-01

    We present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump (SJ) and skew-scattering (SS) contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show their effects scale as σxy^SJ/σxy^SS ˜(/τ)/ɛF, where τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n-doped and p-doped 3D and 2D GaAs structures, obtaining analytical formulas for the SJ and SS contributions. Moreover, the ratio of the spin Hall conductivity to longitudinal conductivity is found as σs/σc˜10-3-10-4, in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

  4. Growth and characterization of Czochralski-grown n and p-type GaAs for space solar cell substrates

    NASA Technical Reports Server (NTRS)

    Chen, R. T.

    1983-01-01

    Progress in LEC (liquid encapsulated Czochralski) crystal growth techniques for producing high-quality, 3-inch-diameter, n- and p-type GaAs crystals suitable for solar cell applications is described. The LEC crystals with low dislocation densities and background impurities, high electrical mobilities, good dopant uniformity, and long diffusion lengths were reproducibly grown through control of the material synthesis, growth and doping conditions. The capability for producing these large-area, high-quality substrates should positively impact the manufacturability of highly efficiency, low cost, radiation-hard GaAs solar cells.

  5. Correspondence between MOS and modulation-doped structures

    NASA Astrophysics Data System (ADS)

    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.

  6. GaAs photocathodes for low light level imaging

    NASA Astrophysics Data System (ADS)

    André, J. P.; Guittard, P.; Hallais, J.; Piaget, C.

    1981-10-01

    The use of high efficiency GaAs transmission mode photocathodes in image tubes is an achievement which has been made possible thanks to the improvement of material technology and vacuum technology. As background into the description of the material technology, the device characteristics are used for the definition of the material criteria. Possible epitaxial structures and growth methods which have been studied for the preparation of the material are reviewed with emphasis on the GaAs/(Al,Ga)As/ transparent window type of structure. Recent progress in MOVPE shows that this technique is now capable of growing high quality GaAs(Al,Ga)As double heterostructures suitable for photocathode fabrication. The assessment of p-type GaAs active layers shows electron diffusion lengths of 5 to 7 μm for a doping level of 1 × 10 19cm-3 with neglectible interface recombination. Reproduvibility of the results and further development of MOVPE for large scale growth of photocathode materials is discussed.

  7. Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

    SciTech Connect

    Hendra, P. I. B. Rahayu, F. Darma, Y.

    2014-03-24

    Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

  8. High-Performance GaAs Nanowire Solar Cells for Flexible and Transparent Photovoltaics.

    PubMed

    Han, Ning; Yang, Zai-xing; Wang, Fengyun; Dong, Guofa; Yip, SenPo; Liang, Xiaoguang; Hung, Tak Fu; Chen, Yunfa; Ho, Johnny C

    2015-09-16

    Among many available photovoltaic technologies at present, gallium arsenide (GaAs) is one of the recognized leaders for performance and reliability; however, it is still a great challenge to achieve cost-effective GaAs solar cells for smart systems such as transparent and flexible photovoltaics. In this study, highly crystalline long GaAs nanowires (NWs) with minimal crystal defects are synthesized economically by chemical vapor deposition and configured into novel Schottky photovoltaic structures by simply using asymmetric Au-Al contacts. Without any doping profiles such as p-n junction and complicated coaxial junction structures, the single NW Schottky device shows a record high apparent energy conversion efficiency of 16% under air mass 1.5 global illumination by normalizing to the projection area of the NW. The corresponding photovoltaic output can be further enhanced by connecting individual cells in series and in parallel as well as by fabricating NW array solar cells via contact printing showing an overall efficiency of 1.6%. Importantly, these Schottky cells can be easily integrated on the glass and plastic substrates for transparent and flexible photovoltaics, which explicitly demonstrate the outstanding versatility and promising perspective of these GaAs NW Schottky photovoltaics for next-generation smart solar energy harvesting devices.

  9. Formation of oxides and their role in the growth of Ag nanoplates on GaAs substrates.

    SciTech Connect

    Sun, Y.; Gosztola, D.; Lei, C.; Haasch, R.; Center for Nanoscale Materials; Univ. of Illinois

    2008-10-21

    Simple galvanic reactions between highly doped n-type GaAs wafers and a pure aqueous solution of AgNO3 at room temperature provide an easy and efficient protocol to directly deposit uniform Ag nanoplates with tunable dimensions on the GaAs substrates. The anisotropic growth of the Ag nanoplates in the absence of surfactant molecules might be partially ascribed to the codeposition of oxides of gallium and arsenic, which are revealed by extensive data from electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, during the growth of the Ag nanoplates. The electron microscopic characterization shows that each Ag nanoplate has a 'necked' geometry, that is, it pins on the GaAs lattices through only a tiny neck (with sizes of <10 nm). In addition, the as-grown Ag nanoplates exhibit strong enhancement toward Raman scattering of materials on (or around) their surfaces.

  10. Characterization of GaAs solar cells made by ion implantation and rapid thermal annealing using selective photoetching

    SciTech Connect

    van Sark, W.G.J.H.M.; Weyher, J.L.; Giling, L.J. ); de Potter, M.; van Rossum, M. )

    1990-05-01

    Shallow {ital n}-{ital p} GaAs solar cells have been made by implantation of Si into Zn-doped ({ital p}-type) GaAs substrates followed by rapid thermal annealing. The structure of the GaAs crystal has been determined by the DSL photoetching method (Diluted Sirtl-like etchants used with Light). It was found that implantation-induced-damage (revealed by DSL as microroughness and craters) was not removed after annealing for energies exceeding 60 keV. This leads to substrates that contain many precipitates, which appears to be disastrous for the fabrication of good solar cells. In addition, good cell performance is hampered by compensation effects in the {ital n}-{ital p} transition region and in the {ital n}-type layer itself.

  11. Carbon doping of III-V compound semiconductors

    SciTech Connect

    Moll, A.J.

    1994-09-01

    Focus of the study is C acceptor doping of GaAs, since C diffusion coefficient is at least one order of magnitude lower than that of other common p-type dopants in GaAs. C ion implantation results in a concentration of free holes in the valence band < 10% of that of the implanted C atoms for doses > 10{sup 14}/cm{sup 2}. Rutherford backscattering, electrical measurements, Raman spectroscopy, and Fourier transform infrared spectroscopy were amonth the techniques used. Ga co-implantation increased the C activation in two steps: first, the additional radiation damage creates vacant As sites that the implanted C can occupy, and second, it maintains the stoichiometry of the implanted layer, reducing the number of compensating native defects. In InP, the behavior of C was different from that in GaAs. C acts as n-type dopant in the In site; however, its incorporation by implantation was difficult to control; experiments using P co-implants were inconsistent. The lattice position of inactive C in GaAs in implanted and epitaxial layers is discussed; evidence for formation of C precipitates in GaAs and InP was found. Correlation of the results with literature on C doping in III-V semiconductors led to a phenomenological description of C in III-V compounds (particularly GaAs): The behavior of C is controlled by the chemical nature of C and the instrinsic Fermi level stabilization energy of the material.

  12. Electron-beam activated GaAs-switches

    SciTech Connect

    Kirkman, G.; Hur, J.; Jiang, B.; Reinhardt, N.; Allen, R.J.; Schoenbach, K.H.

    1994-12-31

    Electron-beam excitation allows the authors to modulate the conductance of wide-gap semi-insulating semiconductors over a wide range and to use them as variable resistors and as high power switches. The penetration depth of electrons, the electron range, was computed by means of a Monte-Carlo code. For electron energies of 30 keV, it is approximately 2 micrometers. In order to activate the switch material over a larger depth, the switch material, semi-insulating GaAs, was doped over a thickness corresponding to the electron range with zinc, which form shallow acceptors in GaAs. The Zn layers serves as an efficient source of cathodoluminescence, transforming the electron energy into photon energy and therefore converting the electron-beam activated switch into a photoconductive one. Experiments with 2 mm semi-insulating GaAs-switches with p-doped cathode layer have been performed where the electron beam was injected through one of the metal contacts which were placed on either face of the GaAs wafer. The 500 ns electron beam has electron energies of up to 30 keV and current densities of several A/cm{sup 2}. The results show that electron-beam controlled GaAs switches can be safely operated at switch voltages of several kV`s and current densities of 50 A/cm{sup 2} with low energy electron-beams as control elements.

  13. High-efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.

    1979-01-01

    GaAs chemical vapor deposition (CVD) growth on single-crystal GaAs substrates was investigated over a temperature range of 600 to 750 C, As/GA mole-ratio range of 3 to 11, and gas molefraction range 5 x 10 to the minus 9th power to 7x 10 to the minus 7th power for H2S doping. GasAs CVD growth on recrystallized Ge films was investigated for a temperature range of 550 to 700 C, an As/GA mole ratio of 5, and for various H2S mole fraction. The highest efficiency cell observed on these films with 2 mm dots was 4.8% (8% when AR-coated). Improvements in fill factor and opencircuit voltage by about 40% each are required in order to obtain efficiencies of 15% or greater.

  14. Investigation of the origin of deep levels in CdTe doped with Bi

    SciTech Connect

    Saucedo, E.; Franc, J.; Elhadidy, H.; Horodysky, P.; Ruiz, C. M.; Bermudez, V.; Sochinskii, N. V.

    2008-05-01

    Combining optical (low temperature photoluminescence), electrical (thermoelectric effect spectroscopy), and structural (synchrotron X-ray powder diffraction) methods, the defect structure of CdTe doped with Bi was studied in crystals with dopant concentration in the range of 10{sup 17}-10{sup 19} at./cm{sup 3}. The semi-insulating state observed in crystals with low Bi concentration is assigned to the formation of a shallow donor level and a deep donor recombination center. Studying the evolution of lattice parameter with temperature, we postulate that the deep center is formed by a Te-Te dimer and their formation is explained by a tetrahedral to octahedral distortion, due to the introduction of Bi in the CdTe lattice. We also shows that this model agrees with the electrical, optical, and transport charge properties of the samples.

  15. Spin Hall effect in doped semiconductor structures.

    PubMed

    Tse, Wang-Kong; Das Sarma, S

    2006-02-10

    In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as sigma(xy)SJ/sigma(xy)SS approximately (h/tau)/epsilonF, with tau being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining sigma(s)/sigma(c) approximately 10(-3)-10(-4), where sigma(s(c)) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

  16. Spin Hall Effect in Doped Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Das Sarma, S.

    2006-02-01

    In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as σxySJ/σxySS˜(ℏ/τ)/ɛF, with τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining σs/σc˜10-3-10-4, where σs(c) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)]SCIEAS0036-807510.1126/science.1105514 in n-doped 3D GaAs system.

  17. Analysis of Hyperabrupt and Uniform Junctions in GaAs for the Application of Varactor Diode.

    PubMed

    Heo, Jun-Woo; Hong, Sejun; Choi, Seok-Gyu; Kim, Hyun-Seok

    2015-10-01

    In this study, we present a GaAs varactor diode with a hyperabrupt junction for the enhancement of breakdown voltage and capacitance variation in a reverse bias state. The hyperabrupt doping profile in the n-type active layer is prepared in a controlled nonlinear manner, with the density of the dopants increasing towards the Schottky junction. The hyperabrupt GaAs varactor diode is fabricated and characterized for breakdown voltage and capacitance over the electric field, induced by an applied reverse bias voltage. A reduced value of the electric field is observed owing to the nonlinear behavior of the electric field at the hyperabrupt junction, although the device has a larger doping density at the Schottky junction. Furthermore, the capacitance ratio of the hyperabrupt junction diode is also improved. Variation in the device capacitance is affected by variation in the depletion region across the junction. Technology CAD is used to understand the experimental phenomena by considering the magnitude of charge density as a function of the doping profile. A higher breakdown voltage and greater capacitance modulation are shown in the hyperabrupt junction diode compared to the uniform junction diode.

  18. Ultra-Thin-Film GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    Process based on organo-metallic chemical vapor deposition (OM/CVD) of trimethyl gallium with arsine forms economical ultrathin GaAs epitaxial films. Process has higher potential for low manufacturing cost and large-scale production compared with more-conventional halide CVD and liquid-phase epitaxy processes. By reducing thickness of GaAs and substituting low-cost substrate for single-crystal GaAs wafer, process would make GaAs solar cells commercially more attractive.

  19. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1979-01-01

    The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

  20. GaAs Solar Cell Radiation Handbook

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1996-01-01

    The handbook discusses the history of GaAs solar cell development, presents equations useful for working with GaAs solar cells, describes commonly used instrumentation techniques for assessing radiation effects in solar cells and fundamental processes occurring in solar cells exposed to ionizing radiation, and explains why radiation decreases the electrical performance of solar cells. Three basic elements required to perform solar array degradation calculations: degradation data for GaAs solar cells after irradiation with 1 MeV electrons at normal incidence; relative damage coefficients for omnidirectional electron and proton exposure; and the definition of the space radiation environment for the orbit of interest, are developed and used to perform a solar array degradation calculation.

  1. Ultrafast properties of femtosecond-laser-ablated GaAs and its application to terahertz optoelectronics.

    PubMed

    Madéo, Julien; Margiolakis, Athanasios; Zhao, Zhen-Yu; Hale, Peter J; Man, Michael K L; Zhao, Quan-Zhong; Peng, Wei; Shi, Wang-Zhou; Dani, Keshav M

    2015-07-15

    We report on the first terahertz (THz) emitter based on femtosecond-laser-ablated gallium arsenide (GaAs), demonstrating a 65% enhancement in THz emission at high optical power compared to the nonablated device. Counter-intuitively, the ablated device shows significantly lower photocurrent and carrier mobility. We understand this behavior in terms of n-doping, shorter carrier lifetime, and enhanced photoabsorption arising from the ablation process. Our results show that laser ablation allows for efficient and cost-effective optoelectronic THz devices via the manipulation of fundamental properties of materials.

  2. Single-hole transistor in p-type GaAs /AlGaAs heterostructures

    NASA Astrophysics Data System (ADS)

    Grbić, Boris; Leturcq, Renaud; Ensslin, Klaus; Reuter, Dirk; Wieck, Andreas D.

    2005-12-01

    A single-hole transistor is patterned in a p-type, C-doped GaAs /AlGaAs heterostructure by scanning probe oxidation lithography. Clear Coulomb blockade resonances have been observed at Thole=300mK. A charging energy of ˜1.5meV is extracted from Coulomb diamond measurements, in agreement with the lithographic dimensions of the dot. The absence of excited states in Coulomb diamond measurements, as well as the temperature dependence of Coulomb peak heights indicate that the dot is in the multilevel transport regime. Fluctuations in peak spacings larger than the estimated mean single-particle level spacing are observed.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. A 4-W 56-dB gain microstrip amplifier at 15 GHz utilizing GaAs FET's and IMPATT diodes

    NASA Technical Reports Server (NTRS)

    Sokolov, V.; Namordi, M. R.; Doerbeck, F. H.

    1979-01-01

    Performance results and design considerations are presented for an all solid-state Ku-band power amplifier which is feasible for use in PM communication systems for airborne or spacecraft transmitter applications. A six-stage GaAs FET preamplifier and a driver and balanced power amplifier utilizing GaAs IMPATT diodes operating in the injection locked oscillator mode are discussed. For high power and efficiency Schottky-Read IMPATT's with low-high-low doping profiles are employed. For improved reliability the IMPATT's incorporate a TiW barrier metallization to retard degradation of the IMPATT's. Results of accelerated life testing of the IMPATT devices are also presented.

  5. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

    1998-01-01

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

  6. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

    1998-09-08

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

  7. Electrical and optical properties of Fe doped AlGaN grown by molecular beam epitaxy

    SciTech Connect

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Kozhukhova, E. A.; Dabiran, A. M.; Chow, P. P.; Wowchak, A. M.; Pearton, S. J.

    2010-01-15

    Electrical and optical properties of AlGaN grown by molecular beam epitaxy were studied in the Al composition range 15%-45%. Undoped films were semi-insulating, with the Fermi level pinned near E{sub c}-0.6-0.7 eV. Si doping to (5-7)x10{sup 17} cm{sup -3} rendered the 15% Al films conducting n-type, but a large portion of the donors were relatively deep (activation energy 95 meV), with a 0.15 eV barrier for capture of electrons giving rise to strong persistent photoconductivity (PPC) effects. The optical threshold of this effect was {approx}1 eV. Doping with Fe to a concentration of {approx}10{sup 17} cm{sup -3} led to decrease in concentration of uncompensated donors, suggesting compensation by Fe acceptors. Addition of Fe strongly suppressed the formation of PPC-active centers in favor of ordinary shallow donors. For higher Al compositions, Si doping of (5-7)x10{sup 17} cm{sup -3} did not lead to n-type conductivity. Fe doping shifted the bandedge luminescence by 25-50 meV depending on Al composition. The dominant defect band in microcathodoluminescence spectra was the blue band near 3 eV, with the energy weakly dependent on composition.

  8. Defect studies in low-temperature-grown GaAs

    SciTech Connect

    Bliss, D.E.

    1992-11-01

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

  9. Defect studies in low-temperature-grown GaAs

    SciTech Connect

    Bliss, D.E.

    1992-11-01

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

  10. GaAs Substrates for High-Power Diode Lasers

    NASA Astrophysics Data System (ADS)

    Mueller, Georg; Berwian, Patrick; Buhrig, Eberhard; Weinert, Berndt

    GaAs substrate crystals with low dislocation density (Etch-Pit Density (EPD) < 500,^-2) and Si-doping ( ~10^18,^-3) are required for the epitaxial production of high-power diode-lasers. Large-size wafers (= 3 mathrm{in} -> >=3,) are needed for reducing the manufacturing costs. These requirements can be fulfilled by the Vertical Bridgman (VB) and Vertical Gradient Freeze (VGF) techniques. For that purpose we have developed proper VB/VGF furnaces and optimized the thermal as well as the physico-chemical process conditions. This was strongly supported by extensive numerical process simulation. The modeling of the VGF furnaces and processes was made by using a new computer code called CrysVUN++, which was recently developed in the Crystal Growth Laboratory in Erlangen.GaAs crystals with diameters of 2 and 3in were grown in pyrolytic Boron Nitride (pBN) crucibles having a small-diameter seed section and a conical part. Boric oxide was used to fully encapsulate the crystal and the melt. An initial silicon content in the GaAs melt of c (melt) = 3 x10^19,^-3 has to be used in order to achieve a carrier concentration of n = (0.8- 2) x10^18,^-3, which is the substrate specification of the device manufacturer of the diode-laser. The EPD could be reduced to values between 500,^-2 and 50,^-2 with a Si-doping level of 8 x10^17 to 1 x10^18,^-3. Even the 3in wafers have rather large dislocation-free areas. The lowest EPDs ( <100,^-2) are achieved for long seed wells of the crucible.

  11. P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

    NASA Astrophysics Data System (ADS)

    Jin, Y. J.; Chia, C. K.; Liu, H. F.; Wong, L. M.; Chai, J. W.; Chi, D. Z.; Wang, S. J.

    2016-07-01

    In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures.

  12. P-doping mechanisms in catalyst-free gallium arsenide nanowires.

    PubMed

    Dufouleur, Joseph; Colombo, Carlo; Garma, Tonko; Ketterer, Bernt; Uccelli, Emanuele; Nicotra, Marco; Fontcuberta i Morral, Anna

    2010-05-12

    Doped catalyst-free GaAs nanowires have been grown by molecular beam epitaxy with the gallium-assisted method. The spatial dependence of the dopant concentration and resistivity have been measured by Raman spectroscopy and four point electrical measurements. Along with theoretical considerations, the doping mechanisms have been revealed. Two competing mechanisms have been revealed: dopant incorporation from the side facets and from the gallium droplet. In the latter incorporation path, doping compensation seems to play an important role in the effective dopant concentration. Hole concentrations of at least 2.4 x 10(18) cm(-3) have been achieved, which to our knowledge is the largest p doping range obtained up to date. This work opens the avenue for the use of doped GaAs nanowires in advanced applications and in mesoscopic physics experiments.

  13. Au impact on GaAs epitaxial growth on GaAs (111)B substrates in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liao, Zhi-Ming; Chen, Zhi-Gang; Lu, Zhen-Yu; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-01

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {111}B substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {113}B faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  14. GaAs Solar Cell Radiation Handbook

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1996-01-01

    History of GaAs solar cell development is provided. Photovoltaic equations are described along with instrumentation techniques for measuring solar cells. Radiation effects in solar cells, electrical performance, and spacecraft flight data for solar cells are discussed. The space radiation environment and solar array degradation calculations are addressed.

  15. GaAs optoelectronic neuron arrays.

    PubMed

    Lin, S; Grot, A; Luo, J; Psaltis, D

    1993-03-10

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10(4) cm(-2) are discussed.

  16. GaAs optoelectronic neuron arrays

    NASA Technical Reports Server (NTRS)

    Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

    1993-01-01

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

  17. Homojunction GaAs solar cells grown by close space vapor transport

    SciTech Connect

    Boucher, Jason W.; Ritenour, Andrew J.; Greenaway, Ann L.; Aloni, Shaul; Boettcher, Shannon W.

    2014-06-08

    We report on the first pn junction solar cells grown by homoepitaxy of GaAs using close space vapor transport (CSVT). Cells were grown both on commercial wafer substrates and on a CSVT absorber film, and had efficiencies reaching 8.1%, open circuit voltages reaching 909 mV, and internal quantum efficiency of 90%. The performance of these cells is partly limited by the electron diffusion lengths in the wafer substrates, as evidenced by the improved peak internal quantum efficiency in devices fabricated on a CSVT absorber film. Unoptimized highly-doped n-type emitters also limit the photocurrent, indicating that thinner emitters with reduced doping, and ultimately wider band gap window or surface passivation layers, are required to increase the efficiency.

  18. N + doping of gallium arsenide by rapid thermal oxidation of a silicon cap

    NASA Astrophysics Data System (ADS)

    Sadana, D. K.; de Souza, J. P.; Cardone, F.

    1990-10-01

    Shallow (<200 nm) Si profiles with doping levels in excess of 2×1018 cm-3 were reproducively obtained in GaAs by rapid thermal oxidation (RTO) of Si caps (50 or 160 nm) in 0.1% O2/Ar ambient at 850-1050 °C. The doping level as well as distribution of the diffused Si can be controlled by the thickness of the Si cap, RTO temperature, RTO time, and oxygen level in the annealing ambient. It appears that the generation of Si interstitials at the oxidizing surface of the Si cap during RTO is responsible for the Si diffusion into the underlying GaAs substrate.

  19. Planar doped barrier subharmonic mixers

    NASA Technical Reports Server (NTRS)

    Lee, T. H.; East, J. R.; Haddad, G. I.

    1992-01-01

    The Planar Doped Barrier (PDB) diode is a device consisting of a p(+) doping spike between two intrinsic layers and n(+) ohmic contacts. This device has the advantages of controllable barrier height, diode capacitance and forward to reverse current ratio. A symmetrically designed PDB has an anti-symmetric current vs. voltage characteristic and is ideal for use as millimeter wave subharmonic mixers. We have fabricated such devices with barrier heights of 0.3, 0.5 and 0.7 volts from GaAs and InGaAs using a multijunction honeycomb structure with junction diameters between one and ten microns. Initial RF measurements are encouraging. The 0.7 volt barrier height 4 micron GaAs devices were tested as subharmonic mixers at 202 GHz with an IF frequency of 1 GHz and had 18 dB of conversion loss. The estimated mismatch loss was 7 dB and was due to higher diode capacitance. The LO frequency was 100.5 GHz and the pump power was 8 mW.

  20. Variation of spectral response curves of GaAs photocathodes in activation chamber

    NASA Astrophysics Data System (ADS)

    Zou, Jijun; Chang, Benkang; Yang, Zhi; Wang, Hui; Gao, Pin

    2006-09-01

    The spectral response curves of reflection-mode GaAs (100) photocathodes are measured in activation chamber by multi-information measurement system at RT, and by applying quantum efficiency formula, the variation of spectral response curves have been studied. Reflection-mode GaAs photocathodes materials are grown over GaAs wafer (100) by MBE with p-type beryllium doping, doping concentration is 1×10 19 cm -3 and the active layer thickness is 1.6μm. During the high-temperature activation process, the spectral response curves varied with activation time are measured. After the low-temperature activation, the photocathode is illuminated by a white light source, and the spectral response curves varied with illumination time are measured every other hour. Experimental results of both high-temperature and low-temperature activations show that the spectral response curve shape of photocathodes is a function of time. We use traditional quantum efficiency formulas of photocathodes, in which only the Γ photoemission is considered, to fit experimental spectral response curves, and find the theoretical curves are not in agreement with the experimental curves, the reason is other valley and hot-electron yields are necessary to be included in yields of reflection-mode photocathodes. Based on the two-minima diffusion model and the fit of escape probability, we modified the quantum efficiency formula of reflection-mode photocathodes, the modified formula can be used to explain the variation of yield curves of reflection-mode photocathodes very well.

  1. Sn-Seeded GaAs Nanowires as Self-Assembled Radial p–n Junctions

    PubMed Central

    2015-01-01

    The widespread use of Au as a seed particle in the fabrication of semiconductor nanowires presents a fundamental limitation to the potential incorporation of such nanostructures into electronic devices. Although several other growth techniques have been demonstrated, the use of alternative seed particle metals remains an underexplored but potentially very promising way to influence the properties of the resulting nanowires while simultaneously avoiding gold. In this Letter, we demonstrate the use of Sn as a seed particle metal for GaAs nanowires grown by metal–organic vapor phase epitaxy. We show that vertically aligned and stacking defect-free GaAs nanowires can be grown with very high yield. The resulting nanowires exhibit Esaki diode behavior, attributed to very high n-doping of the nanowire core with Sn, and simultaneous C-doping of the radial overgrowth. These results demonstrate that the use of alternative seed particle metals is a potentially important area to explore for developing nanowire materials with controlled material properties. PMID:25989532

  2. Acoustic Wave Chemical Microsensors in GaAs

    SciTech Connect

    Albert G. Baca; Edwin J. Heller; Gregory C. Frye-Mason; John L. Reno; Richard Kottenstette; Stephen A. Casalnuovo; Susan L. Hietala; Vincent M. Hietala

    1998-09-20

    High sensitivity acoustic wave chemical microsensors are being developed on GaAs substrates. These devices take advantage of the piezoelectric properties of GaAs as well as its mature microelectronics fabrication technology and nascent micromachining technology. The design, fabrication, and response of GaAs SAW chemical microsensors are reported. Functional integrated GaAs SAW oscillators, suitable for chemical sensing, have been produced. The integrated oscillator requires 20 mA at 3 VK, operates at frequencies up to 500 MHz, and occupies approximately 2 mmz. Discrete GaAs sensor components, including IC amplifiers, SAW delay lines, and IC phase comparators have been fabricated and tested. A temperature compensation scheme has been developed that overcomes the large temperature dependence of GaAs acoustic wave devices. Packaging issues related to bonding miniature flow channels directly to the GaAs substrates have been resolved. Micromachining techniques for fabricating FPW and TSM microsensors on thin GaAs membranes are presented and GaAs FPW delay line performance is described. These devices have potentially higher sensitivity than existing GaAs and quartz SAW sensors.

  3. GaInP /GaAs double heterojunction bipolar transistor with GaAs /Al0.11Ga0.89As/GaInP composite collector

    NASA Astrophysics Data System (ADS)

    Poh, Z. S.; Yow, H. K.; Houston, P. A.; Krysa, A. B.; Ong, D. S.

    2006-07-01

    GaInP /GaAs/GaInP double heterojunction bipolar transistor (DHBT) with an Al0.11Ga0.89As layer within lowly doped GaAs-GaInP composite collector was characterized. In comparison to an abrupt GaInP /GaAs/GaInP DHBT with saturation voltages in excess of 20V, current gains of 25 at high biases, and breakdown voltages in the range of 22V, the DHBT incorporating GaAs -Al0.11Ga0.89As-GaInP composite collector has demonstrated lower saturation voltages of less than 6V and high current gains of 50 without compromising the breakdown voltages of the GaInP collector. Al0.11Ga0.89As layer can thus provide an alternative design to effectively minimize the potential spike effects at the GaAs /GaInP heterojunction.

  4. Carbon Doping of Compound Semiconductor Epitaxial Layers Grown by Metalorganic Chemical Vapor Deposition Using Carbon Tetrachloride.

    NASA Astrophysics Data System (ADS)

    Cunningham, Brian Thomas

    1990-01-01

    A dilute mixture of CCl_4 in high purity H_2 has been used as a carbon dopant source for rm Al_ {x}Ga_{1-x}As grown by low pressure metalorganic chemical vapor deposition (MOCVD). To understand the mechanism for carbon incorporation from CCl_4 doping and to provide experimental parameters for the growth of carbon doped device structures, the effects of various crystal growth parameters on CCl _4 doping have been studied, including growth temperature, growth rate, V/III ratio, Al composition, and CCl_4 flow rate. Although CCl _4 is an effective p-type dopant for MOCVD rm Al_{x}Ga_ {1-x}As, injection of CCl_4 into the reactor during growth of InP resulted in no change in the carrier concentration or carbon concentration. Abrupt, heavy carbon doping spikes in GaAs have been obtained using CCl_4 without a dopant memory effect. By annealing samples with carbon doping spikes grown within undoped, n-type, and p-type GaAs, the carbon diffusion coefficient in GaAs at 825 ^circC has been estimated and has been found to depend strongly on the GaAs background doping. Heavily carbon doped rm Al_{x}Ga _{1-x}As/GaAs superlattices have been found to be more stable against impurity induced layer disordering (IILD) than Mg or Zn doped superlattices, indicating that the low carbon diffusion coefficient limits the IILD process. Carbon doping has been used in the base region on an Npn AlGaAs/GaAs heterojunction bipolar transistor (HBT). Transistors with 3 x 10 μm self-aligned emitter fingers have been fabricated which exhibit a current gain cutoff frequency of f_ {rm t} = 26 GHz.

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

    NASA Astrophysics Data System (ADS)

    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).

  6. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    SciTech Connect

    Dutta, P. Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V.; Zheng, N.; Ahrenkiel, P.; Martinez, J.

    2014-09-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10{sup 7 }cm{sup −2}. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm{sup 2}/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  7. GaAs shallow-homojunction solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1981-01-01

    The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

  8. High Growth Rate Metal-Organic Molecular Beam Epitaxy for the Fabrication of GaAs Space Solar Cells

    NASA Technical Reports Server (NTRS)

    Freundlich, A.; Newman, F.; Monier, C.; Street, S.; Dargan, P.; Levy, M.

    2005-01-01

    In this work it is shown that high quality GaAs photovoltaic devices can be produced by Molecular Beam Epitaxy (MBE) with growth rates comparable to metal-organic chemical vapor deposition (MOCVD) through the subsitution of group III solid sources by metal-organic compounds. The influence the III/V flux-ratio and growth temperatures in maintaining a two dimensional layer by layer growth mode and achieving high growth rates with low residual background impurities is investigated. Finally subsequent to the study of the optimization of n- and p doping of such high growth rate epilayers, results from a preliminary attempt in the fabrication of GaAs photovoltaic devices such as tunnel diodes and solar cells using the proposed high growth rate approach are reported.

  9. Eight-Bit-Slice GaAs General Processor Circuit

    NASA Technical Reports Server (NTRS)

    Weissman, John; Gauthier, Robert V.

    1989-01-01

    Novel GaAs 8-bit slice enables quick and efficient implementation of variety of fast GaAs digital systems ranging from central processing units of computers to special-purpose processors for communications and signal-processing applications. With GaAs 8-bit slice, designers quickly configure and test hearts of many digital systems that demand fast complex arithmetic, fast and sufficient register storage, efficient multiplexing and routing of data words, and ease of control.

  10. Development of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Mcnally, P. J.

    1972-01-01

    This is the second quarterly technical report on a program, the goal of which is to achieve high efficiency GaAs solar cells. Analysis was concerned with providing design information for use in experimentally determining optimum solar cell process parameters. The first quarterly report contained the results of those design calculations. Using those results as a guide, experimental work was initiated to determine optimum cell process parameters. The initial results on this phase of the program are reported.

  11. Piezoelectric field in strained GaAs.

    SciTech Connect

    Chow, Weng Wah; Wieczorek, Sebastian Maciej

    2005-11-01

    This report describes an investigation of the piezoelectric field in strained bulk GaAs. The bound charge distribution is calculated and suitable electrode configurations are proposed for (1) uniaxial and (2) biaxial strain. The screening of the piezoelectric field is studied for different impurity concentrations and sample lengths. Electric current due to the piezoelectric field is calculated for the cases of (1) fixed strain and (2) strain varying in time at a constant rate.

  12. Surface-modified GaAs terahertz plasmon emitter

    NASA Astrophysics Data System (ADS)

    Darmo, J.; Strasser, G.; Muller, T.; Bratschitsch, R.; Unterrainer, K.

    2002-07-01

    We studied the THz emission from n-GaAs plasmon emitters modified by low-temperature-grown (LT) GaAs surface layers. The THz emission is increased since the LT GaAs pins the Fermi level at a midgap position, increasing the surface depletion field. For a THz emitter with a 70-nm-thick LT GaAs layer we observe without external fields a THz emission intensity of 140 nW. In addition, the long-term performance of the modified emitters is improved by the LT GaAs surface layer.

  13. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The crystal growth, device processing and device related properties and phenomena of GaAs are investigated. Our GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor materials (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; (3) investigation of electronic properties and phenomena controlling device applications and device performance. The ground based program is developed which would insure successful experimentation with and eventually processing of GaAs in a near zero gravity environment.

  14. High efficiency, low cost thin GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1982-01-01

    The feasibility of fabricating space-resistant, high efficiency, light-weight, low-cost GaAs shallow-homojunction solar cells for space application is demonstrated. This program addressed the optimal preparation of ultrathin GaAs single-crystal layers by AsCl3-GaAs-H2 and OMCVD process. Considerable progress has been made in both areas. Detailed studies on the AsCl3 process showed high-quality GaAs thin layers can be routinely grown. Later overgrowth of GaAs by OMCVD has been also observed and thin FaAs films were obtained from this process.

  15. Effect of variations in the doping profiles on the properties of doped multiple quantum well avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Menkara, H. M.; Wagner, B. K.; Summers, C. J.

    1996-01-01

    The purpose of this study is to use both theoretical and experimental evidence to determine the impact of doping imbalance and symmetry on the physical and electrical characteristics of doped multiple quantum well avalanche photodiodes (APD). Theoretical models have been developed to calculate the electric field valence and conduction bands, capacitance-voltage (CV), and carrier concentration versus depletion depth profiles. The models showed a strong correlation between the p- and n-doping balance inside the GaAs wells and the number of depleted stages and breakdown voltage of the APD. A periodic doping imbalance in the wells has been shown to result in a gradual increase (or decrease) in the electric field profile throughout the device which gave rise to partially depleted devices at low bias. The MQW APD structures that we modeled consisted of a 1 micron top p(+)-doped (3 x 10(exp 18) cm(exp -3)) GaAs layer followed by a 1 micron region of alternating layers of GaAs (500 A) and Al(0.42)Ga(0.58)As (500 A), and a 1 micron n(+) back layer (3 x 10(exp 18) cm(exp -3)). The GaAs wells were doped with p-i-n layers placed at the center of each well. The simulation results showed that in an APD with nine doped wells, and where the 50 A p-doped layer is off by 10% (p = 1.65 x 10(exp 18) cm(exp -3), n = 1.5 x 10(exp 18) cm(exp -3)), almost half of the MQW stages were shown to be undepleted at low bias which was a result of a reduction in the electric field near the p(+) cap layer by over 50% from its value in the balanced structure. Experimental CV and IV data on similar MBE grown MQW structures have shown very similar depletion and breakdown characteristics. The models have enabled us to better interpret our experimental data and to determine both the extent of the doping imbalances in the devices as well as the overall p- or n-type doping characteristics of the structures.

  16. DX centers in Sn-doped Ga0.7Al0.3As

    NASA Astrophysics Data System (ADS)

    Hayes, T. M.; Williamson, D. L.; Outzourhit, A.; Small, P.; Gibart, P.; Rudra, A.

    1989-03-01

    We have measured and analyzed the extended fine structure on the Sn K-shell x-ray absorption spectra of GaAs and Ga0.7Al0.3As doped with ˜5 x 1018 cm-3 Sn. Our results and their implications for the atomic structure of DX centers are discussed.

  17. Panel fabrication utilizing GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Mardesich, N.

    1984-01-01

    The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

  18. Electron density dependence of the spin Hall effect in GaAs probed by scanning Kerr rotation microscopy

    NASA Astrophysics Data System (ADS)

    Matsuzaka, S.; Ohno, Y.; Ohno, H.

    2009-12-01

    We studied electron density (n) dependence of the extrinsic spin Hall effect in n -doped GaAs with n raging from 1.8×1016 to 3.3×1017cm-3 . By scanning Kerr microscopy measurements, we observed spin accumulation near the channel edges in all the samples due to the extrinsic spin Hall effect. The spin Hall conductivity σSH is obtained for each sample by comparing the Kerr rotation induced by optically injected spins. σSH is found to increase with n , and it is shown that a theoretical model reported earlier agrees well with the experimental n dependence of σSH .

  19. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    SciTech Connect

    Li, X.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Janzén, E.; Forsberg, U.; Bergsten, J.; Rorsman, N.

    2015-12-28

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  20. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    NASA Astrophysics Data System (ADS)

    Li, X.; Bergsten, J.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Rorsman, N.; Janzén, E.; Forsberg, U.

    2015-12-01

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 1018 cm-3) epitaxial layer closest to the substrate and a lower doped layer (3 × 1016 cm-3) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 1018 cm-3) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  1. Peeled film GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    Wilt, D. M.; Thomas, R. D.; Bailey, S. G.; Brinker, D. J.; Deangelo, F. L.

    1990-01-01

    Thin-film, single-crystal gallium arsenide (GaAs) solar cells could exhibit a specific power approaching 700 W/kg including coverglass. A simple process has been described whereby epitaxial GaAs layers are peeled from a reusable substrate. This process takes advantage of the extreme selectivity of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofluoric acid. The feasibility of using the peeled film technique to fabricate high-efficiency, low-mass GaAs solar cells is presently demonstrated. A peeled film GaAs solar cell was successfully produced. The device, although fractured and missing the aluminum gallium arsenide window and antireflective coating, had a Voc of 874 mV and a fill factor of 68 percent under AM0 illumination.

  2. Ion implanted GaAs microwave FET's

    NASA Astrophysics Data System (ADS)

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

    1988-06-01

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

  3. Growth and characterization of Czochralski-grown n and p-type GaAs for space solar cell substrates. Final Report, 29 May 1981-28 May 1982

    SciTech Connect

    Chen, R.T.

    1983-06-01

    Progress in LEC (liquid encapsulated Czochralski) crystal growth techniques for producing high-quality, 3-inch-diameter, n- and p-type GaAs crystals suitable for solar cell applications is described. The LEC crystals with low dislocation densities and background impurities, high electrical mobilities, good dopant uniformity, and long diffusion lengths were reproducibly grown through control of the material synthesis, growth and doping conditions. The capability for producing these large-area, high-quality substrates should positively impact the manufacturability of highly efficiency, low cost, radiation-hard GaAs solar cells.

  4. Airplane dopes and doping

    NASA Technical Reports Server (NTRS)

    Smith, W H

    1919-01-01

    Cellulose acetate and cellulose nitrate are the important constituents of airplane dopes in use at the present time, but planes were treated with other materials in the experimental stages of flying. The above compounds belong to the class of colloids and are of value because they produce a shrinking action on the fabric when drying out of solution, rendering it drum tight. Other colloids possessing the same property have been proposed and tried. In the first stages of the development of dope, however, shrinkage was not considered. The fabric was treated merely to render it waterproof. The first airplanes constructed were covered with cotton fabric stretched as tightly as possible over the winds, fuselage, etc., and flying was possible only in fine weather. The necessity of an airplane which would fly under all weather conditions at once became apparent. Then followed experiments with rubberized fabrics, fabrics treated with glue rendered insoluble by formaldehyde or bichromate, fabrics treated with drying and nondrying oils, shellac, casein, etc. It was found that fabrics treated as above lost their tension in damp weather, and the oil from the motor penetrated the proofing material and weakened the fabric. For the most part the film of material lacked durability. Cellulose nitrate lacquers, however were found to be more satisfactory under varying weather conditions, added less weight to the planes, and were easily applied. On the other hand, they were highly inflammable, and oil from the motor penetrated the film of cellulose nitrate, causing the tension of the fabric to be relaxed.

  5. Polarization and charge limit studies of strained GaAs photocathodes

    SciTech Connect

    Saez, P.J.

    1997-03-01

    This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of {approximately} 2.5 A/cm{sup 2} at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don`t have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes.

  6. Theory of Spin Hall Effect in GaAs

    NASA Astrophysics Data System (ADS)

    Engel, Hans-Andreas

    2006-03-01

    In the spin Hall effect, an electric current in a system with spin-orbit coupling induces a transverse spin current which leads to non-equilibrium spin accumulation near sample boundaries. Generating and manipulating non-equilibrium spin magnetization by electric fields is one of the most desirable goals of semiconductor spintronics, because electric fields have potentialities for accessing individual spins at nanometer scales. In this talk, I review the different spin-orbit coupling mechanisms in direct gap semiconductors and the implications of these mechanisms for the spin Hall effect. In particular, we recently developed a theory that accounts for spin-orbit coupling at charged impurities. This coupling leads to extrinsic spin currents that contain skew scattering and side jump contribution [1]. Applying our theory to bulk n-GaAs, without any free parameters, we find spin currents that are in reasonable agreement with recent experiments by Kato et al. [2]. Also, such contributions are important for p-doped GaAs. Furthermore, we analyzed the effect of intrinsic spin-orbit coupling in the presence of anisotropic impurity scattering, and found that, somewhat surprisingly, an electrical field can lead to a bulk magnetization component perpendicular to both the spin-orbit field and an external magnetic field. These works have been done in collaboration with B.I. Halperin, E.I. Rashba, and A.A. Burkov. [1] H.-A. Engel, B.I. Halperin, and E.I. Rashba, Phys. Rev.Lett. 95, 166605 (2005). [2] Y.K. Kato, R.C. Myers, A.C. Gossard, and D.D. Awschalom, Science 306, 1910 (2004).

  7. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  8. Spin Current Amplification in Presence of Nonuniform Doping

    NASA Astrophysics Data System (ADS)

    Mirzaee, Sh.; Soleimani, H. Rahimpour

    In this paper, for the first time in our knowledge, the influence of nonuniform and continuous doping in semiconductor on amplification of spin polarization current especially in n-type GaAs semiconductor have been studied. Numerical calculations based on a selfconsistent solution of the continuity equation, the Poisson equation and rate-equation are used to explain the amplification of spin polarization density. The influences of the diffusion coefficient (Dn) and relaxation time (τsf) on the spin polarization density are also studied. The amplifying effect of nonuniform doping on spin polarization density is important because it might have many applications in spintronic devices.

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

    SciTech Connect

    Kalentyeva, I. L. Zvonkov, B. N.; Vikhrova, O. V.; Danilov, Yu. A.; Demina, P. B.; Dorokhin, M. V.; Zdoroveyshchev, A. V.

    2015-11-15

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

  10. X-point Shallow Donors in GaAs under pressure

    NASA Astrophysics Data System (ADS)

    Hsu, L.; Haller, E. E.

    1996-03-01

    Transitions from the ground to bound excited states associated with shallow donors in GaAs under large hydrostatic pressure are studied with IR absorption spectroscopy. A modified Merrill-Basset diamond anvil cell was used to apply hydrostatic pressures of several GPa to lightly doped ( 10^15 cm-3) n-type GaAs samples. At such pressures, the energy of the conduction band at the X point falls below that at the Γ point and the wavefunctions of donor impurities take on X-band character. The deep DX centers which exist at these pressures were converted to shallow donors by illumination at low temperature with a red LED. The X-band absorption spectra for Sn and Si show one line each at 50 and 61 meV, respectively. The spectrum for S shows a broad absorption starting at 90 meV, which shifts to lower energies with increasing pressure. The presence of only one line in the Si and Sn spectra can be explained by the non-parabolicity of the X-point conduction band minimum. The binding energies of these donors are estimated to be 74, 85, and 117 meV for Sn, Si, and S respectively. This work supported by USNSF DMR-94 17763.

  11. The role of d levels of substitutional magnetic impurities at the (110) GaAs surface

    NASA Astrophysics Data System (ADS)

    Mahani, M. R.; Pertsova, Anna; Islam, Fhokrul; Canali, C. M.

    2013-03-01

    The study of the spin of individual transition-metal dopants in a semiconductor host is an emergent field known as magnetic solotronics, bearing exciting prospects for novel spintronics devices at the atomic scale. Advances in different STM based techniques allowed experimentalists to investigate substitutional dopants at a semiconductor surface with unprecedented accuracy and degree of details. Theoretical studies based both on microscopic tight-binding (TB) models and DFT techniques have contributed in elucidating the experimental findings. In particular, for the case of Mn dopants on the (110) GaAs surface, TB models have provided a quantitative description of the properties of the associated acceptor states. Most of these TB calculations ignore dealing explicitly with the Mn d-levels and treat the associated magnetic moment as a classical vector. However recent STM experiments involving other TM impurities, such as Fe, reveal topographic features that might be related to electronic transitions within the d-level shell of the dopant. In this work we have included explicitly the d levels in the Hamiltonian. The parameters of the model have been extracted from DFT calculations. We have investigated the role that d levels play on the properties of the acceptor states of the doped GaAs(110) surface, and analyzed their implications for STM spectroscopy.

  12. Plasma-induced-damage of GaAs during etching of refractory metal contacts

    SciTech Connect

    Shul, R.J.; Lovejoy, M.L.; Baca, A.G.; Zolper, J.C.; Rieger, D.J.; Hafich, M.J.; Corless, R.F.; Vartuli, C.R.

    1994-10-01

    The effect of plasma-induced-damage on the majority carrier transport properties of GaAs has been studied by monitoring changes in sheet resistance (R{sub s}) of thin conducting layers under various plasma conditions including etch conditions for refractory metal contacts. R{sub s} determined from transmission line measurements are used to evaluate plasma-induced-damage for electron cyclotron resonance (ECR) and reactive ion etch (RIE) conditions by varying the thickness of doped epitaxial layers. The authors speculate that plasma-induced-damage in the near surface region plays a major role in explaining the damage mechanism observed in this study. Very consistent trends have been observed where R{sub s} increases with increasing ECR and RIE dc-bias, increasing microwave power, and decreasing pressure, thus showing R{sub s} increases as either the ion energy or ion flux increases. The authors have also observed that R{sub s} is lower for samples exposed to the RIE than the ECR, possibly due to higher ion and electron densities generated in the ECR and higher pressures in the RIE. It has also been observed R{sub s} dependence on ECR plasma chemistry where, R{sub s} is lower in SF{sub 6}/Ar plasmas than Ar and N{sub 2} plasmas possibly related to interactions of F or S atoms with the GaAs surface. Moderate anneal temperatures (200 to 500{degrees}C) have shown significant R{sub s} recovery.

  13. Dyakonov-Perel Effect on Spin Dephasing in n-Type GaAs

    NASA Technical Reports Server (NTRS)

    Ning, C. Z.; Wu, M. W.

    2003-01-01

    A paper presents a study of the contribution of the Dyakonov-Perel (DP) effect to spin dephasing in electron-donor-doped bulk GaAs in the presence of an applied steady, moderate magnetic field perpendicular to the growth axis of the GaAs crystal. (The DP effect is an electron-wave-vector-dependent spin-state splitting of the conduction band, caused by a spin/orbit interaction in a crystal without an inversion center.) The applicable Bloch equations of kinetics were constructed to include terms accounting for longitudinal optical and acoustic phonon scattering as well as impurity scattering. The contributions of the aforementioned scattering mechanisms to spin-dephasing time in the presence of DP effect were examined by solving the equations numerically. Spin-dephasing time was obtained from the temporal evolution of the incoherently summed spin coherence. Effects of temperature, impurity level, magnetic field, and electron density on spin-dephasing time were investigated. Spin-dephasing time was found to increase with increasing magnetic field. Contrary to predictions of previous simplified treatments of the DP effect, spin-dephasing time was found to increase with temperature in the presence of impurity scattering. These results were found to agree qualitatively with results of recent experiments.

  14. Analytical model of threshold voltage degradation due to localized charges in gate material engineered Schottky barrier cylindrical GAA MOSFETs

    NASA Astrophysics Data System (ADS)

    Kumar, Manoj; Haldar, Subhasis; Gupta, Mridula; Gupta, R. S.

    2016-10-01

    The threshold voltage degradation due to the hot carrier induced localized charges (LC) is a major reliability concern for nanoscale Schottky barrier (SB) cylindrical gate all around (GAA) metal-oxide-semiconductor field-effect transistors (MOSFETs). The degradation physics of gate material engineered (GME)-SB-GAA MOSFETs due to LC is still unexplored. An explicit threshold voltage degradation model for GME-SB-GAA-MOSFETs with the incorporation of localized charges (N it) is developed. To accurately model the threshold voltage the minimum channel carrier density has been taken into account. The model renders how +/- LC affects the device subthreshold performance. One-dimensional (1D) Poisson’s and 2D Laplace equations have been solved for two different regions (fresh and damaged) with two different gate metal work-functions. LCs are considered at the drain side with low gate metal work-function as N it is more vulnerable towards the drain. For the reduction of carrier mobility degradation, a lightly doped channel has been considered. The proposed model also includes the effect of barrier height lowering at the metal-semiconductor interface. The developed model results have been verified using numerical simulation data obtained by the ATLAS-3D device simulator and excellent agreement is observed between analytical and simulation results.

  15. Individual iso-electronic N and Bi centers in GaAs studied by Scanning Tunneling Microscopy

    NASA Astrophysics Data System (ADS)

    Koenraad, Paul; Krammel, Christian; Plantenga, Rianne; Kortan, Victoria; Flatté, Michael; Tilley, Freddy; Roy, Mervin; Maksym, Peter; Kita, Takashi

    Nitrogen and bismuth iso-electronic doping centers in GaAs have received considerable interest in the last few years due to their peculiar behaviour in dilute nitrides and bismides. In these materials effects such as a strong band bowing and the formation of resonant states in respectively the conduction and valence band have been reported. In this contribution we will report our exploration of individual nitrogen and bismuth atoms in the outermost layers of a freshly cleaved (110) GaAs surface by STM. Depending on the tunnel conditions we are able to either visualise the lattice distortion or image the charge distribution of the resonant state. We clearly observe that nitrogen pulls its neighbouring atoms inwards whereas bismuth pushes its neighbouring atoms away. A straightforward geometrical model based on the covalent radii of the dopants and substrate atoms is used to interpret the observed crystal deformation seen in our STM images of nitrogen and bismuth under the appropriate tunnel conditions. At small positive voltages we could observe the charge distribution of the resonant state induced by iso-electronic nitrogen atoms in GaAs. Tight Binding Modelling (TBM) was used to explain the observed strongly anisotropic charge distribution.

  16. GaAs VLSI for aerospace electronics

    NASA Technical Reports Server (NTRS)

    Larue, G.; Chan, P.

    1990-01-01

    Advanced aerospace electronics systems require high-speed, low-power, radiation-hard, digital components for signal processing, control, and communication applications. GaAs VLSI devices provide a number of advantages over silicon devices including higher carrier velocities, ability to integrate with high performance optical devices, and high-resistivity substrates that provide very short gate delays, good isolation, and tolerance to many forms of radiation. However, III-V technologies also have disadvantages, such as lower yield compared to silicon MOS technology. Achieving very large scale integration (VLSI) is particularly important for fast complex systems. At very short gate delays (less than 100 ps), chip-to-chip interconnects severely degrade circuit clock rates. Complex systems, therefore, benefit greatly when as many gates as possible are placed on a single chip. To fully exploit the advantages of GaAs circuits, attention must be focused on achieving high integration levels by reducing power dissipation, reducing the number of devices per logic function, and providing circuit designs that are more tolerant to process and environmental variations. In addition, adequate noise margin must be maintained to ensure a practical yield.

  17. Implantation of carbon in GaAs

    SciTech Connect

    Moll, A.J.

    1992-03-01

    Carbon implanted into GaAs and thermally annealed typically exhibits very low (<3%) electrical activity. It has been demonstrated that the electrical activity of C can be significantly enhanced by co-implantation with Ga. Improved activation may result from either additional damage of the crystal lattice or from stoichiometric changes, forcing the C atoms onto As sites. To determine the relative importance of each of these effects, I have undertaken a systematic study of carbon activation in GaAs. A range of co-implants have been used: group III (B, Ga), group V (N, P, As) and noble gases (Ar, Kr). The damage introduced to the substrate will depend on the mass of the ion implanted. The group III and group V co-implants will affect the crystal stoichiometry. The results indicate that both lattice damage and crystal stoichiometry are important for high electrical activity of C. Increasing the damage will increase the activation due to the increased number of As vacancies but maximum activation can be obtained only by a co-implant which not only damages the lattice but also forces the C to occupy an As site.

  18. Spectroscopy of defects induced by ohmic contact preparation in LEC GaAs particle detectors

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Canali, C.; Nava, F.

    1996-12-01

    Semi-insulating LEC gallium arsenide particle detectors were realized with differently manufactured ohmic contacts to improve their performances and possibly avoid injection effects often experienced when the detectors work in full depletion conditions. I-V and C-V measurements on Schottky structures were carried out. Photo-induced current transient spectroscopy and also photo-deep level transient spectroscopy investigations, performed on both planar and Schottky structures, identified electron and hole traps. Detector performances were correlated to defects action.

  19. The development of integrated chemical microsensors in GaAs

    SciTech Connect

    CASALNUOVO,STEPHEN A.; ASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; BACA,ALBERT G.; HIETALA,S.L.

    1999-11-01

    Monolithic, integrated acoustic wave chemical microsensors are being developed on gallium arsenide (GaAs) substrates. With this approach, arrays of microsensors and the high frequency electronic components needed to operate them reside on a single substrate, increasing the range of detectable analytes, reducing overall system size, minimizing systematic errors, and simplifying assembly and packaging. GaAs is employed because it is both piezoelectric, a property required to produce the acoustic wave devices, and a semiconductor with a mature microelectronics fabrication technology. Many aspects of integrated GaAs chemical sensors have been investigated, including: surface acoustic wave (SAW) sensors; monolithic SAW delay line oscillators; GaAs application specific integrated circuits (ASIC) for sensor operation; a hybrid sensor array utilizing these ASICS; and the fully monolithic, integrated SAW array. Details of the design, fabrication, and performance of these devices are discussed. In addition, the ability to produce heteroepitaxial layers of GaAs and aluminum gallium arsenide (AlGaAs) makes possible micromachined membrane sensors with improved sensitivity compared to conventional SAW sensors. Micromachining techniques for fabricating flexural plate wave (FPW) and thickness shear mode (TSM) microsensors on thin GaAs membranes are presented and GaAs FPW delay line and TSM resonator performance is described.

  20. Growth And Characterization Of GaAs, GaInAs, and GaInAsP for microwave applications

    NASA Astrophysics Data System (ADS)

    Jolly, S. T.; Narayan, S. Y.; Paczkowski, J. P.; Capewell, D.

    1982-09-01

    Vapor-phase epitaxy (VPE) systems for the growth of 1) GaAs on Cr-doped GaAs substrates, and 2) lattice matched GaInAs and GaInAsP on Fe-doped InP substrates are briefly described. Layer composition of the ternary and quaternary compounds were measured by electron probe microanalysis, lattice mismatch by X-ray diffractometry, average carrier concentration and mobility determined using the Van der Pauw technique. Carrier profiles were investigated using an electro-chemical profiler. Several hundred n-type Ga0.47In0.53As/InP structures have been grown and characterized. Unintentionally-doped layers with a carrier concentration of 2x1015cm-3 and μ(300) and μ(77) of 11x103 and 38x103cm2V-ls-1, respectively, were realized. These represent the highest mobility values reported for VPE Ga0.47In0.53As at this doping level. Se-doped n-layers ranging in thickness from 0.2 to several μm and with carrier density from 1x1016 cm to 3x1018cm-3 + were grown. n-n structures with sharp n+-n transitions were grown for device fabrication studies. The doping profile of a 2 cm x 1 cm ternary layer grown using a rotating substrate holder was found to be fairly uniform; this n+-n wafer had an n+-layer doping of 1.6+/-0.1x1018cm-3, n+-layer thickness of 0.31+/-0.01 μm, n-layer doping of 9.5+/-0.5x101bcm-3, and n-layer thickness of 0.3+/-0.03 μm. The mobility profile of submicrometer n-layers was measured using the differential Van der Pauw technique. The high mobility was found to be maintained down to the ternary-substrate interface.

  1. Photocurrent Spectroscopy of Single Wurtzite GaAs Nanowires

    SciTech Connect

    Kim, D. C.; Ahtapodov, L.; Boe, A. B.; Moses, A. F.; Dheeraj, D. L.; Fimland, B. O.; Weman, H.; Choi, J. W.; Ji, H.; Kim, G. T.

    2011-12-23

    Photocurrent of single wurtzite GaAs nanowires grown by Au-assisted molecular beam epitaxy is measured at room and low temperature (10 K). At room temperature a high photo-response with more than two orders of magnitude increase of current is observed. The wavelength dependence of the photocurrent shows a sharp change near the zinc blende GaAs band gap. The absence of the free exciton peak in the low temperature photocurrent spectrum, and problems related to determining the exact position of the energy bandgap of wurtzite GaAs from the observed data are discussed.

  2. Towards low-cost high-efficiency GaAs photovoltaics and photoelectrodes grown via vapor transport from a solid source

    SciTech Connect

    Boucher, Jason; Ritenour, Andrew; Boettcher, Shannon W.

    2013-04-29

    Towards low-cost high-efficiency GaAs photovoltaics and photoelectrodes grown via vapor transport from a solid source GaAs is an attractive material for thin-film photovoltaic applications, but is not widely used for terrestrial power generation due to the high cost of metal-organic chemical vapor deposition (MOCVD) techniques typically used for growth. Close space vapor transport is an alternative that allows for rapid growth rates of III-V materials, and does not rely on the toxic and pyrophoric precursors used in MOCVD. We characterize CSVT films of GaAs using photoelectrochemical current-voltage and quantum efficiency measurements. Hole diffusion lengths which exceed 1.5 um are extracted from internal quantum efficiency measurements using the Gartner model. Device physics simulations suggest that solar cells based on these films could reach efficiencies exceeding 24 %. To reach this goal, a more complete understanding of the electrical properties and characterization of defects will be necessary, including measurements on complete solid-state devices. Doping of films is achieved by using source material containing the desired impurity (e.g., Te or Zn). We discuss strategies for growing III-V materials on inexpensive substrates that are not lattice-matched to GaAs.

  3. Measuring the magnetic-field-dependent chemical potential of a low-density three-dimensional electron gas in n -GaAs and extracting its magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Roy Choudhury, Aditya N.; Venkataraman, V.

    2016-01-01

    We report the magnetic-field-dependent shift of the electron chemical potential in bulk, n -type GaAs at room temperature. A transient voltage of ˜100 μ V was measured across a Au-Al2O3 -GaAs metal-oxide-semiconductor capacitor in a pulsed magnetic field of ˜6 T . Several spurious voltages larger than the signal that had plagued earlier researchers performing similar experiments were carefully eliminated. The itinerant magnetic susceptibility of GaAs is extracted from the experimentally measured data for four different doping densities, including one as low as 5 ×1015cm-3 . Though the susceptibility in GaAs is dominated by Landau-Peierls diamagnetism, the experimental technique demonstrated can be a powerful tool for extracting the total free carrier magnetization of any electron system. The method is also virtually independent of the carrier concentration and is expected to work better in the nondegenerate limit. Such experiments had been successfully performed in two-dimensional electron gases at cryogenic temperatures. However, an unambiguous report on having observed this effect in any three-dimensional electron gas has been lacking. We highlight the 50 year old literature of various trials and discuss the key details of our experiment that were essential for its success. The technique can be used to unambiguously yield only the itinerant part of the magnetic susceptibility of complex materials such as magnetic semiconductors and hexaborides, and thus shed light on the origin of ferromagnetism in such systems.

  4. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    NASA Technical Reports Server (NTRS)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  5. Temperature-Programmed Scattering (TPS) Study on Reactivity Difference of GaAs and GaAs Oxide Surfaces

    NASA Astrophysics Data System (ADS)

    Sasaki, Masahiro; Yoshida, Seikoh; Yamada, Chikashi

    1993-10-01

    The reactivity of GaAs and GaAs oxide surfaces to trimethylgallium (TMG) was studied by temperature-programmed scattering (TPS) through the energy accommodation coefficient (EAC). The substrate temperature was increased at a constant rate while the scattered TMG was being measured under a constant flux of TMG supplied to the substrate by a cryo-shrouded quadrupole mass spectrometer. Since the detection efficiency of the spectrometer is inversely proportional to the translational velocity of scattered TMG, the observed intensity variation represents the change in translational velocity of reflected TMG during the temperature increase. The variation of the signal intensities was least-squares analyzed to yield the EAC, which is a measure of the surface reactivity. The thus-obtained reactivity of photo-oxidized GaAs to TMG is smaller than that of dark-oxidized GaAs, which is even smaller than that of a bare GaAs surface. This difference in the reactivity is discussed in relation to the mechanism of selective area growth of GaAs using GaAs oxide as a mask.

  6. GaAs VLSI technology and circuit elements for DSP

    NASA Astrophysics Data System (ADS)

    Mikkelson, James M.

    1990-10-01

    Recent progress in digital GaAs circuit performance and complexity is presented to demonstrate the current capabilities of GaAs components. High density GaAs process technology and circuit design techniques are described and critical issues for achieving favorable complexity speed power and cost tradeoffs are reviewed. Some DSP building blocks are described to provide examples of what types of DSP systems could be implemented with present GaAs technology. DIGITAL GaAs CIRCUIT CAPABILITIES In the past few years the capabilities of digital GaAs circuits have dramatically increased to the VLSI level. Major gains in circuit complexity and power-delay products have been achieved by the use of silicon-like process technologies and simple circuit topologies. The very high speed and low power consumption of digital GaAs VLSI circuits have made GaAs a desirable alternative to high performance silicon in hardware intensive high speed system applications. An example of the performance and integration complexity available with GaAs VLSI circuits is the 64x64 crosspoint switch shown in figure 1. This switch which is the most complex GaAs circuit currently available is designed on a 30 gate GaAs gate array. It operates at 200 MHz and dissipates only 8 watts of power. The reasons for increasing the level of integration of GaAs circuits are similar to the reasons for the continued increase of silicon circuit complexity. The market factors driving GaAs VLSI are system design methodology system cost power and reliability. System designers are hesitant or unwilling to go backwards to previous design techniques and lower levels of integration. A more highly integrated system in a lower performance technology can often approach the performance of a system in a higher performance technology at a lower level of integration. Higher levels of integration also lower the system component count which reduces the system cost size and power consumption while improving the system reliability

  7. Rapid thermal anneal in InP, GaAs and GaAs/GaAlAs

    NASA Astrophysics Data System (ADS)

    Descouts, B.; Duhamel, N.; Godefroy, S.; Krauz, P.

    Ion implantation in semiconductors provides a doping technique with several advantages over more conventional doping methods and is now extensively used for device applications, e.g. field effect transistors (MESFET GaAs, MIS (InP), GaAs/GaAlAs heterojunction bipolar transistors (HBT). Because of the lattice disorder produced by the implantation, the dopant must be made electrically active by a postimplant anneal. As the device performances are very dependent on its electrical characteristics, the anneal is a very important stage of the process. Rapid anneal is known to provide less exodiffusion and less induffusion of impurities compared to conventional furnace anneal, so this technique has been used in this work to activate an n-type dopant (Si) in InP and a p-type dopant (Mg) in GaAs and GaAs/GaAIAs. These two ions have been chosen to realize implanted MIS InP and the base contacts for GaAs/GaAlAs HBTs. The experimental conditions to obtain the maximum electrical activity in these two cases will be detailed. For example, although we have not been able to obtain a flat profile in Mg + implanted GaAs/GaAlAs heterostructure by conventional thermal anneal, rapid thermal anneal gives a flat hole profile over a depth of 0.5 μm with a concentration of 1 x 10 19 cm -3.

  8. Nitrogen-concentration control in GaNAs/AlGaAs quantum wells using nitrogen δ-doping technique

    SciTech Connect

    Mano, Takaaki; Jo, Masafumi; Kuroda, Takashi; Noda, Takeshi; Sugimoto, Yoshimasa; Sakuma, Yoshiki; Elborg, Martin; Sakoda, Kazuaki

    2014-05-15

    GaNAs/Al{sub 0.35}Ga{sub 0.65}As multiple quantum wells (MQWs) with nitrogen δ-doping were fabricated on GaAs (100) substrates by plasma-assisted molecular beam epitaxy. High controllability of nitrogen-concentrations in the MQWs was achieved by tuning nitrogen δ-doping time. The maximum nitrogen concentration in the MQWs was 2.8%. The MQWs exhibit intense, narrow photoluminescence emission.

  9. Slot plasmonic waveguide based on doped-GaAs for terahertz deep-subwavelength applications.

    PubMed

    Amarloo, Hadi; Safavi-Naeini, Safieddin

    2015-11-01

    A new plasmonic waveguide for deep-subwavelength field localization at the terahertz (THz) range of frequency is proposed. GaAs with optimum doping level is used as the plasmonic material. The waveguide structure is a narrow slot in a thin GaAs film on top of the quartz substrate. The waveguide characteristics are analyzed, and its dimensions are optimized to minimize the losses. It is shown that the mode size of the proposed waveguide is less than λ/16 by λ/16. The proposed plasmonic waveguide can be a platform for numerous THz plasmonic-based integrated devices, such as integrated sensors and imagers.

  10. GaAs Films Prepared by RF-Magnetron Sputtering

    SciTech Connect

    L.H. Ouyang; D.L. Rode; T. Zulkifli; B. Abraham-Shrauner; N. Lewis; M.R. Freeman

    2001-08-01

    The authors reported on the optical absorption, adhesion, and microstructure of RF-magnetron sputtered films of hydrogenated amorphous and microcrystalline GaAs films for the 1 to 25 {micro}m infrared wavelength rate. Sputtering parameters which were varied include sputtering power, temperature and pressure, and hydrogen sputtering-gas concentration. TEM results show a sharp transition from purely amorphous GaAs to a mixture of microcrystalline GaAs in an amorphous matrix at 34 {+-} 2 C. By optimizing the sputtering parameters, the optical absorption coefficient can be decreased below 100 cm{sup -1} for wavelengths greater than about 1.25 {micro}m. These results represent the lowest reported values of optical absorption for sputtered films of GaAs directly measured by spectrophotometry for the near-infrared wavelength region.

  11. GaAs monolithic RF modules for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Cauley, Michael A.

    1991-01-01

    Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

  12. Interfacial Ga-As suboxide: Structural and electronic properties

    SciTech Connect

    Colleoni, Davide Pasquarello, Alfredo

    2015-07-20

    The structural and electronic properties of Ga-As suboxide representative of the transition region at the GaAs/oxide interface are studied through density functional calculations. Two amorphous models generated by quenches from the melt are taken under consideration. The absence of As–O bonds indicates that the structure is a mixture of GaAs and Ga-oxide, in accordance with photoemission experiments. The band edges of the models are found to be closely aligned to those of GaAs. The simulation of charging and discharging processes leads to the identification of an As-related defect with an energy level at ∼0.7 eV above the GaAs valence band maximum, in good agreement with the experimental density of interface states.

  13. Crystal Growth of Device Quality Gaas in Space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.

    1985-01-01

    The GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and (3) investigation of electronic properties and phenomena controlling device applications and device performance. This effort is aimed at the essential ground-based program which would insure successful experimentation with and eventually processing of GaAs in near zero gravity environment. It is believed that this program addresses in a unique way materials engineering aspects which bear directly on the future exploitation of the potential of GaAs and related materials in device and systems applications.

  14. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1983-01-01

    GaAs device technology has recently reached a new phase of rapid advancement, made possible by the improvement of the quality of GaAs bulk crystals. At the same time, the transition to the next generation of GaAs integrated circuits and optoelectronic systems for commercial and government applications hinges on new quantum steps in three interrelated areas: crystal growth, device processing and device-related properties and phenomena. Special emphasis is placed on the establishment of quantitative relationships among crystal growth parameters-material properties-electronic properties and device applications. The overall program combines studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and investigation of electronic properties and phenomena controlling device applications and device performance.

  15. Characteristics of GaAs with inverted thermal conversion

    NASA Technical Reports Server (NTRS)

    Kang, C. H.; Lagowski, J.; Gatos, H. C.

    1987-01-01

    GaAs crystals exhibiting inverted thermal conversion (ITC) of resistivity were investigated in conjunction with standard semiinsulating (SI) GaAs regarding characteristics important in device processing. It was established that dislocation density and Si implant activation are unaffected by transformation to the ITC state. However, in ITC GaAs the controlled increase of the EL2 (native midgap donor) concentration during annealing makes it possible to attain resistivities one order of magnitude greater (e.g., about 10 to the 9th ohm cm of 300 K) than those attained in standard SI GaAs (e.g., 10 to the 7th-10 to the 8th ohm cm).

  16. Ultrafast spectroscopy of GaAs under magnetic field

    SciTech Connect

    Mycek, M.A.; Siegner, U.; Glutsch, S.

    1995-03-01

    Surprising and novel results are obtained for both the linear and the nonlinear optical response of GaAs under magnetic field. Using a variety of spectroscopic techniques, we measure field dependent effects due to Coulomb correlation.

  17. GaAs solar cells for space applications

    NASA Technical Reports Server (NTRS)

    Conway, E. J.; Walker, G. H.; Heinbockel, J. H.

    1980-01-01

    GaAs solar cells offer substantial advantages for space photovoltaic power over Si solar cells in the areas of efficiency, elevated temperature operation, and radiation damage stability. A mission cost comparison is made for GaAs and Si solar cells. For Si cell arrays, the total mission cost is found to be a minimum for a solar concentration of 2.9. For GaAs, modes of operation and construction are investigated. Modes having lower mission costs than the minimum Si mission cost are defined. These include higher concentrations, lightweight cells, and simultaneous power generation and annealing. The technological progress necessary for GaAs to operate in these modes is identified.

  18. Interfacial Ga-As suboxide: Structural and electronic properties

    NASA Astrophysics Data System (ADS)

    Colleoni, Davide; Pasquarello, Alfredo

    2015-07-01

    The structural and electronic properties of Ga-As suboxide representative of the transition region at the GaAs/oxide interface are studied through density functional calculations. Two amorphous models generated by quenches from the melt are taken under consideration. The absence of As-O bonds indicates that the structure is a mixture of GaAs and Ga-oxide, in accordance with photoemission experiments. The band edges of the models are found to be closely aligned to those of GaAs. The simulation of charging and discharging processes leads to the identification of an As-related defect with an energy level at ˜0.7 eV above the GaAs valence band maximum, in good agreement with the experimental density of interface states.

  19. GaAs Hall devices produced by local ion implantation

    NASA Astrophysics Data System (ADS)

    Pettenpaul, E.; Huber, J.; Weidlich, H.; Flossmann, W.; von Borcke, U.

    1981-08-01

    GaAs Hall devices were produced by complete planar technology using two selective silicon ion implantation steps. The fundamental characteristics of these devices with respect to reproducible implantation dose and geometry of cross-shaped elements are obtained both by experiment and calculation. The prominent properties of the GaAs Hall elements presented are high sensitivity and linearity, small temperature dependence of sensitivity and resistance, and low residual voltage.

  20. Novel GAA mutations in patients with Pompe disease.

    PubMed

    Turaça, Lauro Thiago; de Faria, Douglas Oliveira Soares; Kyosen, Sandra Obikawa; Teixeira, Valber Dias; Motta, Fabiana Louise; Pessoa, Juliana Gilbert; Rodrigues E Silva, Marina; de Almeida, Sandro Soares; D'Almeida, Vânia; Munoz Rojas, Maria Verônica; Martins, Ana Maria; Pesquero, João Bosco

    2015-04-25

    Pompe disease is an autosomal recessive disorder linked to GAA gene that leads to a multi-system intralysosomal accumulation of glycogen. Mutation identification in the GAA gene can be very important for early diagnosis, correlation between genotype-phenotype and therapeutic intervention. For this purpose, peripheral blood from 57 individuals susceptible to Pompe disease was collected and all exons of GAA gene were amplified; the sequences and the mutations were analyzed in silico to predict possible impact on the structure and function of the human protein. In this study, 46 individuals presented 33 alterations in the GAA gene sequence, among which five (c.547-67C>G, c.547-39T>G, p.R437H, p.L641V and p.L705P) have not been previously described in the literature. The alterations in the coding region included 15 missense mutations, three nonsense mutations and one deletion. One insertion and other 13 single base changes were found in the non-coding region. The mutation p.G611D was found in homozygosis in a one-year-old child, who presented low levels of GAA activity, hypotonia and hypertrophic cardiomyopathy. Two patients presented the new mutation p.L705P in association with c.-32-13T>G. They had low levels of GAA activity and developed late onset Pompe disease. In our study, we observed alterations in the GAA gene originating from Asians, African-Americans and Caucasians, highlighting the high heterogeneity of the Brazilian population. Considering that Pompe disease studies are not very common in Brazil, this study will help to better understand the potential pathogenic role of each change in the GAA gene. Furthermore, a precise and early molecular analysis improves genetic counseling besides allowing for a more efficient treatment in potential candidates.

  1. An analytical study of current-voltage characteristics and breakdown performance of GaInP /GaAs composite collector double heterojunction bipolar transistor

    NASA Astrophysics Data System (ADS)

    Goh, Y. L.; Ong, D. S.; Yow, H. K.

    2004-10-01

    An analytical model taking into account the nonlocal dead-space effects is developed to study the dc characteristics and avalanche multiplication of GaInP /GaAs double heterojunction bipolar transistor (DHBT) incorporating composite collector designs. The dependence of the turn-on characteristics and the multiplication onset of the HBT on the device composite layer thickness and doping densities are investigated. In this paper, optimum combinations of composite parameters are presented to obtain zero spike effect in the base-collector heterojunction conduction band and to improve output breakdown voltages. The model is then applied to the GaInP /GaAs DHBT with AlGaAs in the composite collector, which is found to have good I-V characteristics and high operating voltage range before the onset of avalanche multiplication.

  2. AlGaN/GaN high electron mobility transistors with intentionally doped GaN buffer using propane as carbon precursor

    NASA Astrophysics Data System (ADS)

    Bergsten, Johan; Li, Xun; Nilsson, Daniel; Danielsson, Örjan; Pedersen, Henrik; Janzén, Erik; Forsberg, Urban; Rorsman, Niklas

    2016-05-01

    AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on a heterostructure grown by metalorganic chemical vapor deposition using an alternative method of carbon (C) doping the buffer are characterized. C-doping is achieved by using propane as precursor, as compared to tuning the growth process parameters to control C-incorporation from the gallium precursor. This approach allows for optimization of the GaN growth conditions without compromising material quality to achieve semi-insulating properties. The HEMTs are evaluated in terms of isolation and dispersion. Good isolation with OFF-state currents of 2 × 10-6 A/mm, breakdown fields of 70 V/µm, and low drain induced barrier lowering of 0.13 mV/V are found. Dispersive effects are examined using pulsed current-voltage measurements. Current collapse and knee walkout effects limit the maximum output power to 1.3 W/mm. With further optimization of the C-doping profile and GaN material quality this method should offer a versatile approach to decrease dispersive effects in GaN HEMTs.

  3. Spectroscopy of GaAs quantum wells

    SciTech Connect

    West, L.C.

    1985-07-01

    A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.

  4. Quantitative determination of local potential values in inhomogeneously doped semiconductors by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Weidlich, P. H.; Dunin-Borkowski, R. E.; Ebert, Ph.

    2011-08-01

    Local potential changes arising from nanoscale three-dimensional spatial fluctuations in the dopant distribution in Zn-doped GaAs were investigated quantitatively by scanning tunneling microscopy and spectroscopy at (110) cleavage surfaces. Tunneling spectra measured in areas with different local doping concentration show apparent shifts of the valence band edge and apparent changes of the band gap. A quantitative analysis, combined with band bending and tunnel current simulations, demonstrates that these effects arise from tip-induced band bending that modulates the real potential changes. It is illustrated how exact potential changes between locally high and low doped areas can be determined. It is found that the local potential fluctuations in three-dimensionally doped semiconductors are approximately one order of magnitude smaller that those observed in two-dimensionally doped semiconductors.

  5. Effect of doping on room temperature carrier escape mechanisms in InAs/GaAs quantum dot p-i-n junction photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Sellers, D. G.; Chen, E. Y.; Polly, S. J.; Hubbard, S. M.; Doty, M. F.

    2016-05-01

    We investigate the effect of doping on the mechanisms of carrier escape from intermediate states in delta-doped InAs/GaAs intermediate band solar cells. The intermediate states arise from InAs quantum dots embedded in a GaAs p-i-n junction cell. We find that doping the sample increases the number of excited-state carriers participating in a cycle of trapping and carrier escape via thermal, optical, and tunneling mechanisms. However, we find that the efficiency of the optically-driven carrier escape mechanism is independent of doping and remains small.

  6. Terahertz pulse detection by the GaAs Schottky diodes

    NASA Astrophysics Data System (ADS)

    Laperashvili, Tina; Kvitsiani, Orest; Imerlishvili, Ilia; Laperashvili, David

    2010-06-01

    We present the results of experimental studies of physical properties of the detection process of GaAs Schottky diodes for terahertz frequency radiation. The development of technology in the THz frequency band has a rapid progress recently. Considered as an extension of the microwave and millimeter wave bands, the THz frequency offers greater communication bandwidth than is available at microwave frequencies. The Schottky barrier contact has an important role in the operation of many GaAs devices. GaAs Schottky diodes have been the primary nonlinear device used in millimeter and sub millimeter wave detectors and receivers. GaAs Schottky diodes are especially interesting due to their high mobility transport characteristics, which allows for a large reduction of the resistance-capacitance (RC) time constant and thermal noise. In This work are investigated the electrical and photoelectric properties of GaAs Schottky diodes. Samples were obtained by deposition of different metals (Au, Ni, Pt, Pd, Fe, In, Ga, Al) on semiconductor. For fabrication metal-semiconductor (MS) structures is used original method of metal electrodepositing. In this method electrochemical etching of semiconductor surface occurs just before deposition of metal from the solution, which contains etching material and metal ions together. For that, semiconductor surface cleaning processes and metal deposition carries out in the same technological process. In the experiments as the electrolyte was used aqueous solution of chlorides. Metal deposition was carried out at room temperature.

  7. Nondestructive tribochemistry-assisted nanofabrication on GaAs surface

    PubMed Central

    Song, Chenfei; Li, Xiaoying; Dong, Hanshan; Yu, Bingjun; Wang, Zhiming; Qian, Linmao

    2015-01-01

    A tribochemistry-assisted method has been developed for nondestructive surface nanofabrication on GaAs. Without any applied electric field and post etching, hollow nanostructures can be directly fabricated on GaAs surfaces by sliding a SiO2 microsphere under an ultralow contact pressure in humid air. TEM observation on the cross-section of the fabricated area shows that there is no appreciable plastic deformation under a 4 nm groove, confirming that GaAs can be removed without destruction. Further analysis suggests that the fabrication relies on the tribochemistry with the participation of vapor in humid air. It is proposed that the formation and breakage of GaAs-O-Si bonding bridges are responsible for the removal of GaAs material during the sliding process. As a nondestructive and conductivity-independent method, it will open up new opportunities to fabricate defect-free and well-ordered nucleation positions for quantum dots on GaAs surfaces. PMID:25761910

  8. Semiconducting properties of zinc-doped cubic boron nitride thin films

    SciTech Connect

    Nose, K.; Yoshida, T.

    2007-09-15

    We have examined the electronic properties of zinc-doped cubic boron nitride (cBN) thin films prepared by sputter deposition. The electric conductivity of films deposited in pure Ar increased as the concentration of zinc dopant increased, and hole conduction was identified by the measurement of thermoelectric currents. It was also found that the conductivity increment in such films was accompanied by a linear increase in the B/(B+N) ratio. At the same time, no modification of the composition and the conductivity by incorporated zinc was observed when film growth took place in presence of nitrogen gas. The effect of the excess boron on the conductivity emerged only when films show semi-insulating behavior. These results suggest that Zn substitution for nitrogen causes high electric conductivity of cBN. The electric contact between Ti electrode and semiconducting cBN was examined by the transfer length method, and Ohmic conduction was observed in the Ti/cBN contact. The specific contact resistance was affected by the specific resistance of cBN films, and it was reduced from 10{sup 5} to 100 {omega} cm{sup 2} by increasing the concentration of incorporated Zn.

  9. Gene doping.

    PubMed

    Harridge, Stephen D R; Velloso, Cristiana P

    2008-01-01

    Gene doping is the misuse of gene therapy to enhance athletic performance. It has recently been recognised as a potential threat and subsequently been prohibited by the World Anti-Doping Agency. Despite concerns with safety and efficacy of gene therapy, the technology is progressing steadily. Many of the genes/proteins which are involved in determining key components of athletic performance have been identified. Naturally occurring mutations in humans as well as gene-transfer experiments in adult animals have shown that altered expression of these genes does indeed affect physical performance. For athletes, however, the gains in performance must be weighed against the health risks associated with the gene-transfer process, whereas the detection of such practices will provide new challenges for the anti-doping authorities.

  10. Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

    DOEpatents

    Mascarenhas, Angelo

    2015-07-07

    Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  11. Giant magnetoresistance in a two-dimensional electron gas modulated by magnetic barriers and the δ-doping

    NASA Astrophysics Data System (ADS)

    Zhang, Lan-Lan; Lu, Mao-Wang; Yang, Shi-Peng; Tang, Qiang

    2016-10-01

    We theoretically investigate the modulation of the δ-doping to a semiconductor-based giant magnetoresistance (GMR) device, which can be realized experimentally by depositing two parallel ferromagnetic (FM) stripes on top and bottom of a GaAs /AlxGa1-xAs heterostructure. It is shown that a considerable GMR effect still exists in this device with the δ-doping. It is also shown that the magnetoresistance ratio (MR) depends on not only the weight but also the position of the δ-doping. These interesting results will be useful in understanding and designing structurally-controllable GMR devices for magnetic information storage.

  12. Characterization of production GaAs solar cells for space

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1988-01-01

    The electrical performance of GaAs solar cells was characterized as a function of irradiation with protons and electrons with the underlying goal of producing solar cells suitable for use in space. Proton energies used varied between 50 keV and 10 MeV, and damage coefficients were derived for liquid phase epitaxy GaAs solar cells. Electron energies varied between 0.7 and 2.4 MeV. Cells from recent production runs were characterized as a function of electron and proton irradiation. These same cells were also characterized as a function of solar intensity and operating temperature, both before and after the electron irradiations. The long term stability of GaAs cells during photon exposure was examined. Some cells were found to degrade with photon exposure and some did not. Calibration standards were made for GaAs/Ge solar cells by flight on a high altitude balloon.

  13. Atomic hydrogen cleaning of GaAS Photocathodes

    SciTech Connect

    M. Poelker; J. Price; C. Sinclair

    1997-01-01

    It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs.

  14. Humidity effects on tribochemical removal of GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Bingjun; Gao, Jian; Jin, Chenning; Xiao, Chen; Wu, Jiang; Liu, Huiyun; Jiang, Shulan; Chen, Lei; Qian, Linmao

    2016-06-01

    Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1-90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

  15. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

  16. A GaAs phononic crystal with shallow noncylindrical holes.

    PubMed

    Petrus, Joseph A; Mathew, Reuble; Stotz, James A H

    2014-02-01

    A square lattice of shallow, noncylindrical holes in GaAs is shown to act as a phononic crystal (PnC) reflector. The holes are produced by wet-etching a GaAs substrate using a citric acid:H2O2 etching procedure and a photolithographed array pattern. Although nonuniform and asymmetric etch rates limit the depth and shape of the phononic crystal holes, the matrix acts as a PnC, as demonstrated by insertion loss measurements together with interferometric imaging of surface acoustic waves propagating on the GaAs surface. The measured vertical displacement induced by surface phonons compares favorably with finite-difference time-domain simulations of a PnC with rounded-square holes.

  17. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Zwerdling, S.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

  18. Microwave GaAs Integrated Circuits On Quartz Substrates

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

    1994-01-01

    Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

  19. Impact of the modulation doping layer on the ν = 5/2 anisotropy

    DOE PAGESBeta

    Shi, X.; Pan, W.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.

    2015-03-30

    We have carried out a systematic study of the tilted magnetic field induced anisotropy at the Landau level filling factor ν = 5/2 in a series of high quality GaAs quantum wells, where the setback distance (d) between the modulation doping layer and the GaAs quantum well is varied from 33 to 164 nm. We have observed that in the sample of the smallest d, electronic transport is anisotropic when the in-plane magnetic field (Bip) is parallel to the [1–10] crystallographic direction, but remains more or less isotropic when Bip // [110]. In contrast, in the sample of largest d,more » electronic transport is anisotropic in both crystallographic directions. Lastly, our results clearly show that the modulation doping layer plays an important role in the tilted field induced ν = 5/2 anisotropy.« less

  20. Impact of the modulation doping layer on the ν = 5/2 anisotropy

    SciTech Connect

    Shi, X.; Pan, W.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.

    2015-03-30

    We have carried out a systematic study of the tilted magnetic field induced anisotropy at the Landau level filling factor ν = 5/2 in a series of high quality GaAs quantum wells, where the setback distance (d) between the modulation doping layer and the GaAs quantum well is varied from 33 to 164 nm. We have observed that in the sample of the smallest d, electronic transport is anisotropic when the in-plane magnetic field (Bip) is parallel to the [1–10] crystallographic direction, but remains more or less isotropic when Bip // [110]. In contrast, in the sample of largest d, electronic transport is anisotropic in both crystallographic directions. Lastly, our results clearly show that the modulation doping layer plays an important role in the tilted field induced ν = 5/2 anisotropy.

  1. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.

    1977-01-01

    Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

  2. MBE Growth of GaAs Whiskers on Si Nanowires

    SciTech Connect

    Maxwell Andrews, Aaron

    2010-01-04

    We present the growth of GaAs nanowhiskers by molecular beam epitaxy on Si (111) nanowires grown by low-pressure chemical vapor deposition. The whiskers grow in the wurtzite phase, along the [0001] direction, on the {l_brace}112{r_brace} facets of the Si nanowire, forming a star-like six-fold radial symmetry. The photoluminescence shows a 30 meV blue shift with respect to bulk GaAs, additionally a GaAs/AlAs core-shell heterostructure shows increased luminescence.

  3. Ga nanoparticle-enhanced photoluminescence of GaAs

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Jeon, S.; Wu, J. H.; Lee, J.-E.; Saucer, T. W.; Zhao, L.; Sih, V.; Katzenstein, A. L.; Sofferman, D. L.; Goldman, R. S.

    2013-09-02

    We have examined the influence of surface Ga nanoparticles (NPs) on the enhancement of GaAs photoluminescence (PL) efficiency. We have utilized off-normal focused-ion-beam irradiation of GaAs surfaces to fabricate close-packed Ga NP arrays. The enhancement in PL efficiency is inversely proportional to the Ga NP diameter. The maximum PL enhancement occurs for the Ga NP diameter predicted to maximize the incident electromagnetic (EM) field enhancement. The PL enhancement is driven by the surface plasmon resonance (SPR)-induced enhancement of the incident EM field which overwhelms the SPR-induced suppression of the light emission.

  4. Simple intrinsic defects in GaAs : numerical supplement.

    SciTech Connect

    Schultz, Peter Andrew

    2012-04-01

    This Report presents numerical tables summarizing properties of intrinsic defects in gallium arsenide, GaAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz and O.A. von Lilienfeld, 'Simple intrinsic defects in GaAs', Modelling Simul. Mater. Sci Eng., Vol. 17, 084007 (2009), and intended for use as reference tables for a defect physics package in device models. The numerical results for density functional theory calculations of properties of simple intrinsic defects in gallium arsenide are presented.

  5. ICP etching of GaAs via hole contacts

    SciTech Connect

    Shul, R.J.; Baca, A.G.; Briggs, R.D.; McClellan, G.B.; Pearton, S.J.; Constantine, C.

    1996-09-01

    Deep etching of GaAs is a critical process step required for many device applications including fabrication of through-substrate via holes for monolithic microwave integrated circuits (MMICs). Use of high-density plasmas, including inductively coupled plasmas (ICP), offers an alternative approach to etching vias as compared to more conventional parallel plate reactive ion etch systems. This paper reports ICP etching of GaAs vias at etch rates of about 5.3 {mu}m/min with via profiles ranging from highly anistropic to conical.

  6. Defect interactions in GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

  7. Nuclear spin warm up in bulk n -GaAs

    NASA Astrophysics Data System (ADS)

    Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

    2016-08-01

    We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

  8. Crystal growth of GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Pawlowicz, L. M.; Dabkowski, F.; Li, C. J.

    1984-01-01

    It is shown that stoichiometry variations in the GaAs melt during growth constitute the most critical parameter regarding defect formations and their interactions; this defect structure determines all relevant characteristics of GaAs. Convection in the melt leads to stoichiometric variations. Growth in axial magnetic fields reduces convection and permits the study of defect structure. In order to control stoichiometry in space and to accommodate expansion during solidification, a partially confined configuration was developed. A triangular prism is employed to contain the growth melt. This configuration permits the presence of the desired vapor phase in contact with the melt for controlling the melt stoichiometry.

  9. Electronic contribution to friction on GaAs

    SciTech Connect

    Applied Science and Technology Graduate Group, UC Berkeley; Dept. of Materials Sciences and Engineering, UC Berkeley; Salmeron, Miquel; Qi, Yabing; Park, J.Y.; Hendriksen, B.L.M.; Ogletree, D.F.; Salmeron, Miquel

    2008-04-15

    The electronic contribution to friction at semiconductor surfaces was investigated by using a Pt-coated tip with 50nm radius in an atomic force microscope sliding against an n-type GaAs(100) substrate. The GaAs surface was covered by an approximately 1 nm thick oxide layer. Charge accumulation or depletion was induced by the application of forward or reverse bias voltages. We observed a substantial increase in friction force in accumulation (forward bias) with respect to depletion (reverse bias). We propose a model based on the force exerted by the trapped charges that quantitatively explains the experimental observations of excess friction.

  10. Epitaxial EuO thin films on GaAs

    SciTech Connect

    Swartz, A. G.; Ciraldo, J.; Wong, J. J. I.; Li Yan; Han Wei; Lin Tao; Shi, J.; Kawakami, R. K.; Mack, S.; Awschalom, D. D.

    2010-09-13

    We demonstrate the epitaxial growth of EuO on GaAs by reactive molecular beam epitaxy. Thin films are grown in an adsorption-controlled regime with the aid of an MgO diffusion barrier. Despite the large lattice mismatch, it is shown that EuO grows well on MgO(001) with excellent magnetic properties. Epitaxy on GaAs is cube-on-cube and longitudinal magneto-optic Kerr effect measurements demonstrate a large Kerr rotation of 0.57 deg., a significant remanent magnetization, and a Curie temperature of 69 K.

  11. Peeled film GaAs solar cells for space power

    NASA Technical Reports Server (NTRS)

    Wilt, D. M.; Deangelo, F. L.; Thomas, R. D.; Bailey, S. G.; Landis, G. A.; Brinker, D. J.; Fatemi, N. S.

    1990-01-01

    Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg.

  12. High gain single GaAs nanowire photodetector

    NASA Astrophysics Data System (ADS)

    Wang, Hao

    2013-08-01

    An undoped single GaAs nanowire (NW) photodetector based on a metal-semiconductor-metal Schottky diode structure is fabricated by a focused ion beam method. The photoconductive gain of the device reaches 20 000 at low laser excitation. Bias-dependence of gain proves that the surface contributes more to the gain at higher bias because of an increased surface charge region. The spectral response demonstrates not only the band-edge absorption profile of the single GaAs NW, but also the existence of leaky-mode resonance.

  13. Surface structure of GaAs with adsorbed Te

    NASA Astrophysics Data System (ADS)

    Feldman, R. D.; Austin, R. F.

    1986-10-01

    The surface structures that result from the adsorption of Te on (100) GaAs have been shown to affect the orientation of CdTe films on GaAs. Two structures are described here. A low-temperature (6×1) surface leads to (100) film growth. At 580 °C, a new surface results which is characterized by ordering along directions 60° from [011¯] and [01¯1], and leads to (111) growth of CdTe. Both surface structure and the interaction of the group II element with the surface are believed to be important in determining the orientation of the film.

  14. Local Structures and Interface Morphology of InGaAsN Thin Films Grown on GaAs

    SciTech Connect

    Allerman, A.A.; Chen, J.G.; Geisz, J.F.; Huang, S.; Hulbert, S.L.; Jones, E.D.; Kao, Y.H.; Kurtz, S.; Kurtz, S.R.; Olson, J.M.; Soo, Y.L.

    1999-02-23

    The compound semiconductor system InGaAsN exhibits many intriguing properties which are particularly useful for the development of innovative high efficiency thin film solar cells and long wavelength lasers. The bandgap in these semiconductors can be varied by controlling the content of N and In and the thin films can yet be lattice-matched to GaAs. In the present work, x-ray absorption fine structure (XAFS) and grazing incidence x-ray scattering (GIXS) techniques have been employed to probe the local environment surrounding both N and In atoms as well as the interface morphology of InGaAsN thin films epitaxially grown on GaAs. The soft x-ray XAFS results around nitrogen K-edge reveal that N is in the sp{sup 3} hybridized bonding configuration in InGaAsN and GaAsN, suggesting that N impurities most likely substitute for As sites in these two compounds. The results of In K-edge XAFS suggest a possible trend of a slightly larger coordination number of As nearest neighbors around In atoms in InGaAsN samples with a narrower bandgap whereas the In-As interatomic distance remains practically the same as in InAs within the experimental uncertainties. These results combined suggest that N-substitution of the As sites plays an important role of bandgap-narrowing while in the meantime counteracting the compressive strain caused by In-doping. Grazing incidence x-ray scattering (GIXS) experiments verify that InGaAsN thin films can indeed form very smooth interfaces with GaAs yielding an average interfacial roughness of 5-20{angstrom}.

  15. Raman scattering study of (GaAs)1-x(Si2)x alloys epitaxially grown on GaAs

    NASA Astrophysics Data System (ADS)

    Rodríguez, A. G.; Navarro-Contreras, H.; Vidal, M. A.

    2001-11-01

    (GaAs)1-x(Si2)x metastable alloys grown on (001), (110), (112), and (111) GaAs substrates, with Si fractions in the range 0⩽x⩽0.43, were studied by Raman scattering. Two modes near the LO and TO modes of GaAs, besides two local modes associated either with Si-As or Si-Ga and Si-Si bonds, are observed in the Raman spectra. The ratio of integrated intensities of TO-like and LO-like modes (ITO/ILO) is used to evaluate the short range order. It is observed that the zinc blende to diamond transition reported in the literature for these alloys does not influence the Si fraction dependence of the short range order.

  16. Inversion-mode GaAs wave-shaped field-effect transistor on GaAs (100) substrate

    SciTech Connect

    Zhang, Jingyun; Si, Mengwei; Wu, Heng; Ye, Peide D.; Lou, Xiabing; Gordon, Roy G.; Shao, Jiayi; Manfra, Michael J.

    2015-02-16

    Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La{sub 2}O{sub 3} as gate dielectric on (111)A nano-facets formed on a GaAs (100) substrate. The wave-shaped nano-facets, which are desirable for the device on-state and off-state performance, are realized by lithographic patterning and anisotropic wet etching with optimized geometry. A well-behaved 1 μm gate length GaAs WaveFET shows a maximum drain current of 64 mA/mm, a subthreshold swing of 135 mV/dec, and an I{sub ON}/I{sub OFF} ratio of greater than 10{sup 7}.

  17. Structure of high-index GaAs surfaces - the discovery of the stable GaAs(2511) surface

    NASA Astrophysics Data System (ADS)

    Jacobi, K.; Geelhaar, L.; Márquez, J.

    We present a brief overview of surface structures of high-index GaAs surfaces, putting emphasis on recent progress in our own laboratory. By adapting a commercial scanning tunneling microscope (STM) to our molecular beam epitaxy and ultra high vacuum analysis chamber system, we have been able to atomically resolve the GaAs( {1} {1} {3})B(8 ×1), (114)Aα2(2×1), (137), (3715), and (2511) surface structures. In cooperation with P. Kratzer and M. Scheffler from the Theory Department of the Fritz-Haber Institute we determined the structure of some of these surfaces by comparing total-energy calculations and STM image simulations with the atomically resolved STM images. We present the results for the {112}, {113}, and {114} surfaces. Then we describe what led us to proceed into the inner parts of the stereographic triangle and to discover the hitherto unknown stable GaAs(2511) surface.

  18. GaAs on Si as a substrate for microwave and millimeter-wave monolithic integration

    NASA Astrophysics Data System (ADS)

    Aksun, M. I.; Morkoc, H.

    1988-01-01

    The effective dielectric constant, characteristic impedance, and dielectric loss of a shielded microstrip line manufactured on namely GaAs, Si, and GaAs/Si are calculated. Dielectric loss versus frequency for the GaAs and Si substrates are shown. The same parameters for GaAs/Si substrate were plotted for two different resistivities of the GaAs overlay material, and for each of three different GaAs overlayer thicknesses. The measurements covered the 10-100-GHz frequency range. Depending on the thickness, results show that high-resistivity GaAs epitaxial layers on Si substrates having moderate resistivities reduce the dielectric loss.

  19. Influence of fast neutrons on the recombination and electrical properties of neutron transmutation doped gallium arsenide

    SciTech Connect

    Bykovsky, V.A.; Karas, V.I.; Shoh, V.F.; Strzelecka, S.; Hruban, A.; Gladysz, M.

    1996-12-31

    The electrical properties, photoluminescence and DLTS spectra of LEC gallium arsenide crystals after neutron transmutation doping (NTD) has been investigated as function of starting material properties, irradiation dose and thermal to fast neutron fluences-ratio. The residual carbon acceptors interact with radiation induced defects (RD) in neutron irradiated GaAs crystals and formed nonradiative recombination centers, which are stable up to 700 C temperature.

  20. Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy.

    PubMed

    Joyce, Hannah J; Docherty, Callum J; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Lloyd-Hughes, James; Herz, Laura M; Johnston, Michael B

    2013-05-31

    We have performed a comparative study of ultrafast charge carrier dynamics in a range of III-V nanowires using optical pump-terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm² V⁻¹ s⁻¹, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s⁻¹. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10⁵  cm s⁻¹. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices.

  1. Electronic and magnetic properties of N-N split substitution in GaAs: A hybrid density functional study

    SciTech Connect

    Huang, Ruiqi; Wang, Qingxia; Cai, Xiaolin; Li, Chong; Jia, Yu; Wang, Fei; Wang, Sanjun

    2015-07-15

    Employing the first-principles combined with hybrid functional calculations, the electronic and magnetic properties of GaAs doped with a N{sub 2} molecule are investigated in this work. We find that in Ga{sub 32}As{sub 31}(N{sub 2}){sub As} the N-N split is able to saturate the dangling bond of Ga atom ,form sp{sup 3}-like hybridization, and simultaneously supply an extra localized electron, leading to a magnetic ground state with a magnetic moment of ∼1μ{sub B}. This magnetic ground state is different from previously nonmagnetic results predicted by PBE functional, which results from the self-interaction error inherent in semi-local density functional theory. Moreover, the band gap of magnetic ground state of Ga{sub 32}As{sub 31}(N{sub 2}){sub As} alloy decreases, which is relative to GaAs . Finally we discuss and explain why the magnetism is not discovered in previous experiments and theories.

  2. Gallium arsenide (GaAs) island growth under SiO(2) nanodisks patterned on GaAs substrates.

    PubMed

    Tjahjana, Liliana; Wang, Benzhong; Tanoto, Hendrix; Chua, Soo-Jin; Yoon, Soon Fatt

    2010-05-14

    We report a growth phenomenon where uniform gallium arsenide (GaAs) islands were found to grow underneath an ordered array of SiO(2) nanodisks on a GaAs(100) substrate. Each island eventually grows into a pyramidal shape resulting in the toppling of the supported SiO(2) nanodisk. This phenomenon occurred consistently for each nanodisk across a large patterned area of approximately 50 x 50 microm(2) (with nanodisks of 210 nm diameter and 280 nm spacing). The growth mechanism is attributed to a combination of 'catalytic' growth and facet formation.

  3. Discrimination between energy transfer and back transfer processes for GaAs host and Er luminescent dopants using electric response analysis

    SciTech Connect

    Ishii, Masashi; Koizumi, Atsushi; Fujiwara, Yasufumi; Takeda, Yoshikazu

    2014-04-07

    The energy transfer and back transfer processes of GaAs co-doped with Er and O (GaAs:Er,O) were experimentally distinguished by using a frequency response analysis of the AC photocurrent. The results were achieved by using the difference in the frequency dispersion between (1) the dispersion of the energy transfer, which is triggered by the trapping of free charges in the GaAs host and is represented with the Debye relaxation response and (2) the dispersion of the energy back transfer, which is induced by non-radiative transition of 4f bound electrons in the Er dopants and is described with a Lorentzian. The Debye relaxation response found in GaAs:Er,O provided a charge trapping time that was dependent on temperature, which was well correlated with the thermal quenching property of intense intra-4f-shell luminescence. The spectral shape of the Lorentzian dependence on the temperature was explained with the thermal excitation of Er 4f electrons and release of trapped charges in GaAs. The thermal excitation and release of charges consistently explained the characteristics of weak 4f luminescence in low- and high-temperature regions, respectively.

  4. Present status of GaAs. [including space processing and solid state applications

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Jastrzebski, L.

    1979-01-01

    An extensive literature survey on GaAs was carried out for the period December 31, 1970, to December 31, 1977. The increasing interest in GaAs device structures increased steadily during that period. The leading research and development centers and the specific areas of interest were identified. A workshop on GaAs was held in November 1977 to assess the present status of melt-grown GaAs and the existing needs for reliable chemical, structural, and electronic characterization methods. It was concluded that the present available bulk GaAs crystals are of poor quality and that GaAs technology is lagging demonstrated or potentially feasible GaAs devices and systems.

  5. Hopping Magnetotransport in the δ-DOPING Layer

    NASA Astrophysics Data System (ADS)

    Koch, F.

    We review the observations on hopping transport in planar arrays of Si donor atoms in GaAs epitaxial layers grown by molecular beam epitaxy. It is shown that properly designed δ-doping layers permit one to unambigously identify interference effects that result from the coherent superposition of the tunneling amplitudes along alternative paths in the plane. Magnetic flux through the area generated by the paths destroys the interference and leads to negative magnetoresistance. We discuss the observed non-monotonic variation of the resistance.

  6. GaAs Photovoltaics on Polycrystalline Ge Substrates

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

    2007-01-01

    High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

  7. Advances in GaAs bistable optical devices

    NASA Astrophysics Data System (ADS)

    Jewell, J. L.; Tarng, S. S.; Gibbs, H. M.; Tai, K.; Weinberger, D. A.; Gossard, A. C.; McCall, S. L.; Passner, A.; Venkatesan, T. N. C.; Weigmann, W.

    1984-01-01

    Bistable optical devices (BOD's) using GaAs as the nonlinear medium are viable candidators for the achievement of fast ( ns), room temperature, low-power (mw), externally controllable optical switches which are easily fabricated and operated. Advances were made in all of these areas and efforts are in progress to improve performances in ways that are simultaneously compatible.

  8. The 20 GHz power GaAs FET development

    NASA Technical Reports Server (NTRS)

    Crandell, M.

    1986-01-01

    The development of power Field Effect Transistors (FET) operating in the 20 GHz frequency band is described. The major efforts include GaAs FET device development (both 1 W and 2 W devices), and the development of an amplifier module using these devices.

  9. ZnSe Films in GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Kachare, Ram H.

    1987-01-01

    ZnSe increases efficiency and conserves material. Two proposed uses of zinc selenide films promise to boost performance and reduce cost of gallium arsenide solar cells. Accordingly ZnSe serves as surface-passivation layer and as sacrificial layer enabling repeated use of costly GaAs substrate in fabrication.

  10. High purity, low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  11. Measuring Carrier Lifetime in GaAs by Luminescence

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1986-01-01

    Luminescence proposed as nondestructive technique for measuring Shockley-Read-Hall (SRH) recombination lifetime GaAs. Sample irradiated, and luminescence escapes through surface. Measurement requires no mechanical or electrical contact with sample. No ohmic contacts or p/n junctions needed. Sample not scrapped after tested.

  12. Fermi energy tuning with light to control doping profiles during epitaxy

    SciTech Connect

    Sanders, C. E.; Beaton, D. A.; Reedy, R. C.; Alberi, K.

    2015-05-04

    The influence of light stimulation and photogenerated carriers on the process of dopant surface segregation during growth is studied in molecular beam epitaxially grown Si-doped GaAs structures. The magnitude of surface segregation decreases under illumination by above-bandgap photons, wherein splitting of the quasi Fermi levels reduces the band bending at the growth surface and raises the formation energy of compensating defects that can enhance atomic diffusion. We further show that light-stimulated epitaxy can be used as a practical approach to diminish dopant carry-forward in device structures and improve the performance of inverted modulation-doped quantum wells.

  13. Visualization of carrier dynamics in p(n)-type GaAs by scanning ultrafast electron microscopy

    PubMed Central

    Cho, Jongweon; Hwang, Taek Yong; Zewail, Ahmed H.

    2014-01-01

    Four-dimensional scanning ultrafast electron microscopy is used to investigate doping- and carrier-concentration-dependent ultrafast carrier dynamics of the in situ cleaved single-crystalline GaAs(110) substrates. We observed marked changes in the measured time-resolved secondary electrons depending on the induced alterations in the electronic structure. The enhancement of secondary electrons at positive times, when the electron pulse follows the optical pulse, is primarily due to an energy gain involving the photoexcited charge carriers that are transiently populated in the conduction band and further promoted by the electron pulse, consistent with a band structure that is dependent on chemical doping and carrier concentration. When electrons undergo sufficient energy loss on their journey to the surface, dark contrast becomes dominant in the image. At negative times, however, when the electron pulse precedes the optical pulse (electron impact), the dynamical behavior of carriers manifests itself in a dark contrast which indicates the suppression of secondary electrons upon the arrival of the optical pulse. In this case, the loss of energy of material’s electrons is by collisions with the excited carriers. These results for carrier dynamics in GaAs(110) suggest strong carrier–carrier scatterings which are mirrored in the energy of material’s secondary electrons during their migration to the surface. The approach presented here provides a fundamental understanding of materials probed by four-dimensional scanning ultrafast electron microscopy, and offers possibilities for use of this imaging technique in the study of ultrafast charge carrier dynamics in heterogeneously patterned micro- and nanostructured material surfaces and interfaces. PMID:24469803

  14. LPE growth of GaAs1-xSbx

    NASA Astrophysics Data System (ADS)

    Lendvay, E.; Görög, T.; Tóth, A. L.

    1981-06-01

    Single and multilayer ternary GaAs1±xSb x and quaternary AlyGa 1±yAs 1±xSb x systems were grown by LPE onto (100)GaAs substrates, investigating the As-rich side of the phase diagram. The composition of solid phase was investigated by microprobe analysis. Two major observations have been made; (a) GaAs1± xSb x epitaxial layers grown by the usual LPE techniques in the solid composition range of x ≤ 0.1 and above 750°C show mirror like surfaces and practically homogeneous composition. (b) GaAs1±xSb x layers produced by LPE, cooling the system down below this temperature show the presence at least two regions; one rich in As, the other in Sb. Owing to the dislocation network originating as a consequence of the misfit, the surfaces of these layers consists of <110> aligned ridges and elements with cubic symmetry. The formation of Sb-rich (generally GaSb) layer is independent of the melt composition. Its presence was proved by microprobe analysis as well as by optical measurements. Similar observations were made on AlyGa 1± yAs 1± xSb x layers. For the quaternary the critical temperature, in agreement with previously published value, was found to be 715°C. Undoped GaAs1±xSb x layers showed p-type conduction with ϱ 10 -2 Ω cm, p = 5× 10 17-2×10 18 cm -3 and room temperature hole mobility of 260-280 cm 2 V -1 s -1.

  15. Raman spectroscopy of InGaAs/GaAs nanoheterostructures δ-doped with Mn

    SciTech Connect

    Plankina, S. M.; Vikhrova, O. V.; Danilov, Yu. A.; Zvonkov, B. N.; Kalentyeva, I. L.; Nezhdanov, A. V.; Chunin, I. I.; Yunin, P. A.

    2015-01-15

    The results of complex studies of InGaAs/GaAs nanoheterostructures δ-doped with Mn are reported. The structures are grown by metal-organic vapor-phase epitaxy in combination with laser deposition. By confocal Raman spectroscopy, it is shown that the low-temperature δ-doped GaAs cap layers are of higher crystal quality compared to uniformly doped layers. Scattering of light in the coupled phonon-plasmon mode is observed. The appearance of this mode is conditioned by the diffusion of manganese from the δ-layer. The thickness of the cap layer is found to be d{sub c} ≈ 9–20 nm, optimal for attainment of the highest photoluminescence intensity of the quantum well and the highest layer concentration of holes by doping with manganese.

  16. Dependence of the electrical parameters of MBE-grown Cd{sub x}Hg{sub 1} {sub -} {sub x}Te films on the level of doping with indium

    SciTech Connect

    Varavin, V. S. Dvoretskii, S. A.; Ikusov, D. G.; Mikhailov, N. N.; Sidorov, Yu. G.; Sidorov, G. Yu.; Yakushev, M. V.

    2008-06-15

    Dependences of the minority-carrier lifetime and electron mobility in Cd{sub x}Hg{sub 1-x}Te films on their indium-doping level are studied. Films with x {approx} 0.22 grown by molecular-beam epitaxy on GaAs substrates were in situ doped with indium across their entire thickness. The temperature dependences of the lifetime were studied in the temperature range 77-300 K. The decrease in the lifetime, observed as the doping level increases, is governed by the mechanism of Auger recombination. As the doping level becomes higher, the mobility decreases in qualitative agreement with theoretical calculations.

  17. Ka-Band GaAs FET Monolithic Power Amplifier Development

    NASA Technical Reports Server (NTRS)

    Saunier, Paul; Tserng, Hua Quen

    1997-01-01

    Over the course of this program, very extensive progress was made in Ka-band GaAs technology. At the beginning of the program, odd-shaped VPE MESFET wafers were used. A breakthrough in power and efficiency was achieved with highly doped (8 x 10(exp 17) cm(exp -3) MBE grown MESFET material. We obtained power of 112 mW with 16 dB gain and 21.6% efficiency at 34 GHz with a monolithic 50-100-250 micron amplifier. The next breakthrough came with the use of heterostructures grown by MBE (AlGaAs/InGaAs where the InGaAs is highly doped). This allowed us to achieve high power density with high efficiency. A benchmark 40% efficiency was achieved with a single-stage 100 micron MMIC at 32.5 GHz. The corresponding three-stage 50-100-250 micron amplifier achieved 180 mW with 23 dB gain and 30.3% efficiency. The next breakthrough came with 3-inch MBE grown PHEMT wafers incorporating an etch-stop layer for the gate recess (using RIE). Again, state-of-the-art performances were achieved: 40% efficiency with 235 mW output power and 20.7 dB gain. The single-stage 2 x 600 micron chip demonstrated 794 mW output power with 5 dB gain and 38.2% power-added efficiency (PAE). The Ka-band technology developed under this program has promise for extensive use: JPL demonstrated 32 GHz phased arrays with a three-stage amplifier developed under this contract. A variation of the three-stage amplifier was used successfully in a 4 x 4 phased array transmitter developed under another NASA contract.

  18. alloy lattice-matched to GaAs: a first-principles study

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

    2014-10-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1- x- y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1- x- y N x Bi y alloy with y/ x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1- x- y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1- x- y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1- x- y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1- x- y N x Bi y quaternary alloys in optoelectronic devices.

  19. Fermi energy control of vacancy coalescence and dislocation density in melt-grown GaAs

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Lin, D. G.; Aoyama, T.

    1984-01-01

    A striking effect of the Fermi energy on the dislocation density in melt-grown GaAs has been discovered. Thus, a shift of the Fermi energy from 0.1 eV above to 0.2 eV below its intrinsic value (at high temperature, i.e., near 1100 K) increases the dislocation density by as much as five orders of magnitude. The Fermi energy shift was brought about by n-type and p-type doping at a level of about 10 to the 17th per cu cm (under conditions of optimum partial pressure of As, i.e., under optimum melt stoichiometry). This effect must be associated with the fact that the Fermi energy controls the charge state of vacancies (i.e., the occupancy of the associated electronic states) which in turn must control their tendency to coalesce and thus the dislocation density. It appears most likely that gallium vacancies are the critical species.

  20. Large-area, high-speed PIN detectors in GaAs

    NASA Astrophysics Data System (ADS)

    Jackson, D. J.; Persechini, D. L.

    1986-02-01

    Large-area PIN detectors have been manufactured with bandwidths exceeding 8 GHz. The devices were fabricated in concert with design rules for the manufacture of ICs and incorporate an interdigitated format which permits the large detector area with low device capacitance. The PIN detectors were deposited on GaAs substrates. First, an SiO2 layer was deposited, then etched. Next, a 50 nm layer of Zn and then a 50 nm layer of Au were sputter deposited and the interdigitated pattern was defined by photoresist techniques. The electrodes were plated to a 1 micron thickness, the photoresist was removed, and the Zn:Au film was etched away before doping the substrate with Zn and Ge. The device was then sintered at 430 C. A response level of 5 dB/div was obtained over the range 2-8 GHz, with the roll-off point at 8 GHz being 3 dB. The performance levels were achieved without packaging optimization.

  1. Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

    NASA Technical Reports Server (NTRS)

    Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

    1988-01-01

    GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

  2. Optical detectors for GaAs MMIC integration: Technology assessment

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.

    1989-01-01

    Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

  3. Oxygen-enhanced wet thermal oxidation of GaAs

    NASA Astrophysics Data System (ADS)

    Bauters, J. F.; Fenlon, R. E.; Seibert, C. S.; Yuan, W.; Plunkett, J. S. B.; Li, J.; Hall, D. C.

    2011-10-01

    An oxygen-enhanced wet thermal oxidation process is used to grow smooth, uniform, insulating native oxides of GaAs. At 420 °C, a maximum linear growth rate of 4.8 nm/min is observed for oxidation in water vapor with 2000 ppm O2 added relative to the N2 carrier gas, with growth ceasing by 7000 ppm. Films as thick as 800 nm with surface roughness as low as 0.2 nm are demonstrated. In fabricated metal-oxide-semiconductor capacitors, a 412 nm thick native oxide film exhibits a factor of ˜2700 reduction in leakage current density at 1 V relative to a direct metal (Au:Ti) to GaAs contact.

  4. Thick sodium overlayers on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Heinemann, Martina; Scheffler, Matthias

    1994-02-01

    We report density-functional theory calculations of the electronic structure, total energy, and forces for the Na adsorption on GaAs(110) using the local-density approximation of the exchange-correlation functional and ab initio pseudopotentials. Results are presented for coverages ranging from one adatom per substrate surface cell up to the thick overlayer limit. The atomic and electronic structure of the substrate is locally changed by the sodium adsorption on GaAs(110), depending on the coverage. In particular, we analyze the wave-function character of the states at the Fermi level, how it changes with sodium coverage, and we identify the formation of metal induced gap states (MIGS) at the interface. These MIGS are found to have mostly Ga dangling-bond character for all coverages. The calculated values of the p-type Schottky barrier and of the variation of photothreshold as a function of coverage are in good agreement with experimental data.

  5. Time domain optical susceptibility of intrinsic GaAs

    NASA Astrophysics Data System (ADS)

    Thomas, M. E.; Miragliotta, J. A.; Joseph, R. I.

    2002-06-01

    Intrinsic GaAs optical constant values are well known as functions of frequency (10 000-65 000 cm-1 or 1.24-8.06 eV) and temperature (22-754 K). Room-temperature far-infrared optical constant data also exist as a function of frequency, and are representable by a classical oscillator model. In this article, the frequency-domain, temperature-dependent intrinsic dielectric function of GaAs has been Fourier transformed to obtain an analytical, closed-form representation of the time-domain susceptibility. Results from these expressions are consistent with the temporal characteristics of electronic transitions impeded by elastic scattering, which are in the femtosecond regime. The closed form nature of these expressions makes them well suited for finite difference time domain simulations of waveguides, optoelectronic devices, and microwave devices.

  6. Cryogenic measurements of aerojet GaAs n-JFETs

    NASA Technical Reports Server (NTRS)

    Goebel, John H.; Weber, Theodore T.

    1993-01-01

    The spectral noise characteristics of Aerojet gallium arsenide (GaAs) junction field effect transistors (JFET's) have been investigated down to liquid-helium temperatures. Noise characterization was performed with the field effect transistor (FET) in the floating-gate mode, in the grounded-gate mode to determine the lowest noise readings possible, and with an extrinsic silicon photodetector at various detector bias voltages to determine optimum operating conditions. The measurements indicate that the Aerojet GaAs JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to silicon (Si) metal oxide semiconductor field effect transistor (MOSFET's) operating at liquid helium temperatures, and is equal to the best Si n channel junction field effect transistor (n-JFET's) operating at 300 K.

  7. Testing a GaAs cathode in SRF gun

    SciTech Connect

    Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2011-03-28

    RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high

  8. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1986-01-01

    It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

  9. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C.; Lagowski, Jacek

    1989-01-01

    The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

  10. Single Material Band Gap Engineering in GaAs Nanowires

    SciTech Connect

    Spirkoska, D.; Abstreiter, G.; Efros, A.; Conesa-Boj, S.; Morante, J. R.; Arbiol, J.; Fontcuberta i Morral, A.

    2011-12-23

    The structural and optical properties of GaAs nanowire with mixed zinc-blende/wurtzite structure are presented. High resolution transmission electron microscopy indicates the presence of a variety of shorter and longer segments of zinc-blende or wurtzite crystal phases. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV. The downward shift of the emission peaks can be understood by carrier confinement at the wurtzite/zinc-blende heterojunction, in quantum wells and in random short period superlattices existent in these nanowires, assuming the theoretical staggered band-offset between wurtzite and zinc-blende GaAs.

  11. GaAs solar cells for laser power beaming

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.; Dunham, Glen; Huber, Daniel A.; Addis, F. William; Anheier, Norman; Coomes, E. P.

    1991-01-01

    Efforts to develop GaAs solar cells for coupling to laser beams in the wavelength range of 800 to 840 nm are described. This work was motivated primarily by interests in space-tp-space power beaming applications. In particular, the Battelle Pacific Northwest Laboratories is conducting studies of the utilization of power beaming for several future space missions. Modeling calculations of GaAs cell performance were carried out using PC-1D to determine an appropriate design for a p/n cell structure. Epitaxial wafers were grown by MOCVD and cells fabricated at WSU Tri-Cities. Under simulated conditions, an efficiency of 53 percent was achieved for a cell coupled to 806 nm light at 400 mW/sq cm.

  12. Experimental examination of gaas dissolution in in-p melt

    NASA Astrophysics Data System (ADS)

    Bolkhovityanov, Yu. B.; Bolkhovityanova, R. I.; Chikichev, S. I.

    1983-05-01

    The “solubility” of GaAs crystals in quaternary In-Ga-As-P liquids (X{Ga/I} = X{As/I}) has been studied experi-mentally at 770°C using seed-dissolution technique. The location of the true liquidus isotherm has been established independently by means of the direct vi-sual observation technique. Comparison between the two data sets indicates that the first method can be successfully used only for those In-Ga-As-P melt compositions which have the corresponding solid InxGa1-xAsyP1-y alloys nearly lattice-matched to the GaAs substrate. In other cases the results obtained by this method are totally misleading although in-teresting as they are. The phenomenon of “catastro-phic” substrate erosion is investigated. The results of the present study are interpreted within the conceptual framework developed previously.

  13. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Lagowski, J.

    1981-01-01

    Experimental and theoretical efforts in the development of crystal growth approaches, effective techniques for electronic characterization on a macro and microscale, and in the discovery of phenomena and processes relevant to GaAs device applications are reported. The growth of electron trap-free bulk GaAS with extremely low density of dislocations is described. In electroepitaxy, growth configuration which eliminates the substrate back-contact was developed. This configuration can be extended to the simultaneous growth on many substrates with a thin solution layer sandwiched between any two of them. The significant reduction of Joule heating effects in the configuration made it possible to realize the in situ measurement of the layer thickness and the growth velocity. Utilizing the advantages of electroepitaxy in achieving abrupt acceleration (or deceleration) of the growth it was shown that recombination centers are formed as a result of growth acceleration.

  14. The GaAs solar cell research and development programs of the Air Force

    NASA Technical Reports Server (NTRS)

    Masloski, K. T.

    1980-01-01

    The compound GaAs is of interest for space application photovoltaics due to its inherent advantages over silicon. Higher efficiencies, superior radiation hardness, and a greater temperature resistance are the major advantages of GaAs over Si. Air Force programs look for ways of maximizing these advantages while minimizing disadvantages such as higher costs and weights. Four programs in GaAs photovoltaics are described and each program is discussed in terms of its objective, approach and status.

  15. Solar heating of GaAs nanowire solar cells.

    PubMed

    Wu, Shao-Hua; Povinelli, Michelle L

    2015-11-30

    We use a coupled thermal-optical approach to model the operating temperature rise in GaAs nanowire solar cells. We find that despite more highly concentrated light absorption and lower thermal conductivity, the overall temperature rise in a nanowire structure is no higher than in a planar structure. Moreover, coating the nanowires with a transparent polymer can increase the radiative cooling power by 2.2 times, lowering the operating temperature by nearly 7 K. PMID:26698787

  16. GaAs Optoelectronic Integrated-Circuit Neurons

    NASA Technical Reports Server (NTRS)

    Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

    1992-01-01

    Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

  17. Gallium arsenide (GaAs) solar cell modeling studies

    NASA Technical Reports Server (NTRS)

    Heinbockel, J. H.

    1980-01-01

    Various models were constructed which will allow for the variation of system components. Computer studies were then performed using the models constructed in order to study the effects of various system changes. In particular, GaAs and Si flat plate solar power arrays were studied and compared. Series and shunt resistance models were constructed. Models for the chemical kinetics of the annealing process were prepared. For all models constructed, various parametric studies were performed.

  18. On the dissolution properties of GaAs in Ga

    NASA Technical Reports Server (NTRS)

    Davidson, M. C.; Moynahan, A. H.

    1977-01-01

    The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

  19. Incommensurate phase of Te adsorbed on (001) GaAs

    NASA Astrophysics Data System (ADS)

    Cibert, J.; Saminadayar, K.; Tatarenko, S.; Gobil, Y.

    1989-06-01

    Occurrence of commensurate and incommensurate phases is reported for adsorption of Te on Ga-rich (001) GaAs surfaces. The Te coverage is measured directly through x-ray photoelectron spectroscopy, and the incommensurate phase is studied in detail as a function of Te coverage; two regimes are demonstrated, one at low coverage where Te is mainly bound to Ga, and another one at high coverage where Te mainly bound to As is also present.

  20. A high-speed GaAs MESFET optical controller

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.; Richard, M.; Bendett, M.; Gustafson, G.

    1989-01-01

    Optical interconnects are being considered for control signal distribution in phased array antennas. A packaged hybrid GaAs optical controller with a 1:16 demultiplexed output that is suitable for this application is described. The controller, which was fabricated using enhancement/depletion mode MESFET technology, operates at demultiplexer-limited input data rates up to 305 Mb/s and requires less than 200 microW optical input power.

  1. Ab initio study of hot electrons in GaAs.

    PubMed

    Bernardi, Marco; Vigil-Fowler, Derek; Ong, Chin Shen; Neaton, Jeffrey B; Louie, Steven G

    2015-04-28

    Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation theory. Our computed electron-phonon relaxation times at the onset of the Γ, L, and X valleys are in excellent agreement with ultrafast optical experiments and show that the ultrafast (tens of femtoseconds) hot electron decay times observed experimentally arise from electron-phonon scattering. This result is an important advance to resolve a controversy on hot electron cooling in GaAs. We further find that, contrary to common notions, all optical and acoustic modes contribute substantially to electron-phonon scattering, with a dominant contribution from transverse acoustic modes. This work provides definitive microscopic insight into hot electrons in GaAs and enables accurate ab initio computation of hot carriers in advanced materials.

  2. Sb-Stabilized GaAs(100) Surfaces

    NASA Astrophysics Data System (ADS)

    Shanabrook, B. V.; Whitman, L. J.; Bennett, B. R.

    1997-03-01

    Recently, there has been considerable speculation about the structure of Sb-terminated GaAs(100) surfaces.(Esser et al., Phys. Rev. Lett. 77, 4402 (1996)) (Moriarty et al., Phys. Rev. B53, R16148 (1996)) In addition to the previously studied (2x4) reconstruction, we also investigate the more Sb-rich (2x8) reconstruction with in situ RHEED and STM. The (2x8) Sb-terminated surface was prepared by exposing a well-ordered MBE-grown As-terminated (2x4) GaAs (100) surface to Sb. The Sb-terminated (2x4) reconstruction can be formed by heating the (2x8) reconstruction in the absence of Sb flux. The STM images of the (2x8) reconstruction exhibit a complex multilayer structure with a significant dependence on bias. In contrast, the (2x4) reconstruction appears somewhat simpler and suggests that the two As-dimers on the GaAs surface have been replaced by either 1 or 2 Sb dimers. Possible models for each of these novel reconstructions will be presented.

  3. Improved performance of GaAs radiation detectors

    SciTech Connect

    Nava, F.; Vanni, P.; Bertuccio, G.

    1996-12-31

    Gallium arsenide (GaAs) offers an attractive choice for room temperature X- and {gamma}-ray detectors. However performance of SI LEC bulk GaAs detectors is at present limited by the short carrier lifetime and by the diode breakdown occurring as soon as the electric field reaches the back ohmic contact. We have shown that ohmic contacts based on ion implantation allowed us to go far beyond the bias voltage necessary to achieve a fully active detector. However the conventional thermal treatments (850 {degrees}C, 30 s) required to anneal the damage induced by ion implantation strongly reduces the electron lifetime in the detector. Alenia has developed two improved processes (RA and RB) which avoid high temperature annealing and the consequent electron lifetime reduction. With the new detectors, in pixel (200x200 {mu}m{sup 2}) configuration, a charge collection efficiency (cce) of 90 % for 59.5 keV X-rays and a FWHM of 3.35 keV has been achieved at room temperature. These features, thickness, applied voltage, cce and FWRM are suitable for application of GaAs pixel detectors in medical imaging. Results obtained with of particles and X-rays at different temperatures and in a wide range of applied bias in detectors made with standard, implantated and improved processes are presented, compared and discussed.

  4. Preparation and characterization of pulse electrodeposited GaAs films

    NASA Astrophysics Data System (ADS)

    Murali, K. R.; Trivedi, D. C.

    2006-04-01

    GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV, making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared by plating an aqueous solution containing GaCl3 and As2O3 at a pH of 2 and at room temperature. The current density was kept at 50 mA cm-2 and the duty cycle was varied in the range 10-50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single-phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Atomic force microscope measurements indicated uniform coverage with large crystallites for the films deposited at higher duty cycles. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm-2 illumination, an open-circuit voltage of 0.5 V and a short-circuit current density of 5.0 mA cm-2 were observed for the films deposited at a duty cycle of 50%.

  5. Ab initio study of hot electrons in GaAs

    PubMed Central

    Bernardi, Marco; Vigil-Fowler, Derek; Ong, Chin Shen; Neaton, Jeffrey B.; Louie, Steven G.

    2015-01-01

    Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation theory. Our computed electron–phonon relaxation times at the onset of the Γ, L, and X valleys are in excellent agreement with ultrafast optical experiments and show that the ultrafast (tens of femtoseconds) hot electron decay times observed experimentally arise from electron–phonon scattering. This result is an important advance to resolve a controversy on hot electron cooling in GaAs. We further find that, contrary to common notions, all optical and acoustic modes contribute substantially to electron–phonon scattering, with a dominant contribution from transverse acoustic modes. This work provides definitive microscopic insight into hot electrons in GaAs and enables accurate ab initio computation of hot carriers in advanced materials. PMID:25870287

  6. GAA triplet-repeats cause nucleosome depletion in the human genome.

    PubMed

    Zhao, Hongyu; Xing, Yongqiang; Liu, Guoqing; Chen, Ping; Zhao, Xiujuan; Li, Guohong; Cai, Lu

    2015-08-01

    Although there have been many investigations into how trinucleotide repeats affect nucleosome formation and local chromatin structure, the nucleosome positioning of GAA triplet-repeats in the human genome has remained elusive. In this work, the nucleosome occupancy around GAA triplet-repeats across the human genome was computed statistically. The results showed a nucleosome-depleted region in the vicinity of GAA triplet-repeats in activated and resting CD4(+) T cells. Furthermore, the A-tract was frequently adjacent to the upstream region of GAA triplet-repeats and could enhance the depletion surrounding GAA triplet-repeats. In vitro chromatin reconstitution assays with GAA-containing plasmids also demonstrated that the inserted GAA triplet-repeats destabilized the ability of recombinant plasmids to assemble nucleosomes. Our results suggested that GAA triplet-repeats have lower affinity to histones and can change local nucleosome positioning. These findings may be helpful for understanding the mechanism of Friedreich's ataxia, which is associated with GAA triplet-repeats at the chromatin level.

  7. Recovery of gallium and arsenic from GaAs wafer manufacturing slurries

    SciTech Connect

    Jadvar, R.; McCoy, B.J. ); Ford, B.; Galt, J. )

    1991-11-01

    Lapping and polishing slurries from the gallium arsenide (GaAs) wafer manufacturing process were used to develop simple and inexpensive methods for separation and recovery of valuable gallium and toxic arsenic. The lapping slurry, containing GaAs, glycerol, alumina, iron oxide, and water, is treated by a process involving water addition, dissolution of GaAs, mixing, sedimentation, decantation, and evaporation. The polishing slurry, containing GaAs, silica, sodium bicarbonate, sodium hypochlorite and water, is treated simply by a repetitive cycle of adding water, mixing, settling, decanting, and evaporating. After treatment, the slurries contain less than 5 ppm of dissolved arsenic and are considered non-hazardous.

  8. GaAs thin films and methods of making and using the same

    DOEpatents

    Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

    2016-06-14

    Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

  9. Inverted thermal conversion - GaAs, a new alternative material for integrated circuits

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Kang, C. H.; Skowronski, M.; Ko, K. Y.

    1986-01-01

    A new type of GaAs is developed which exhibits inverted thermal conversion (ITC); i.e., it converts from conducting to semiinsulating upon annealing at about 850 C. In device fabrication, its low resistivity prior to high-temperature processing differentiates ITC GaAs from the standard semiinsulating GaAs. The ITC characteristics are obtained through control of the concentration of the midgap donor EL2 based on heat treatment and crystal-growth modification. Thus EL2 does not exist in the conducting state of ITC GaAs. Conversion to the semiinsulating state during 850 C annealing is caused by the formation of EL2.

  10. Ti/Pd/Ag Contacts to n-Type GaAs for High Current Density Devices

    NASA Astrophysics Data System (ADS)

    Huo, Pengyun; Rey-Stolle, Ignacio

    2016-06-01

    The metallization stack Ti/Pd/Ag on n-type Si has been readily used in solar cells due to its low metal/semiconductor specific contact resistance, very high sheet conductance, bondability, long-term durability, and cost-effectiveness. In this study, the use of Ti/Pd/Ag metallization on n-type GaAs is examined, targeting electronic devices that need to handle high current densities and with grid-like contacts with limited surface coverage (i.e., solar cells, lasers, or light emitting diodes). Ti/Pd/Ag (50 nm/50 nm/1000 nm) metal layers were deposited on n-type GaAs by electron beam evaporation and the contact quality was assessed for different doping levels (from 1.3 × 1018 cm-3 to 1.6 × 1019 cm-3) and annealing temperatures (from 300°C to 750°C). The metal/semiconductor specific contact resistance, metal resistivity, and the morphology of the contacts were studied. The results show that samples doped in the range of 1018 cm-3 had Schottky-like I- V characteristics and only samples doped 1.6 × 1019 cm-3 exhibited ohmic behavior even before annealing. For the ohmic contacts, increasing annealing temperature causes a decrease in the specific contact resistance ( ρ c,Ti/Pd/Ag ~ 5 × 10-4 Ω cm2). In regard to the metal resistivity, Ti/Pd/Ag metallization presents a very good metal conductivity for samples treated below 500°C ( ρ M,Ti/Pd/Ag ~ 2.3 × 10-6 Ω cm); however, for samples treated at 750°C, metal resistivity is strongly degraded due to morphological degradation and contamination in the silver overlayer. As compared to the classic AuGe/Ni/Au metal system, the Ti/Pd/Ag system shows higher metal/semiconductor specific contact resistance and one order of magnitude lower metal resistivity.

  11. Modulation doping of GaAs/AlGaAs core-shell nanowires with effective defect passivation and high electron mobility.

    PubMed

    Boland, Jessica L; Conesa-Boj, Sonia; Parkinson, Patrick; Tütüncüoglu, Gözde; Matteini, Federico; Rüffer, Daniel; Casadei, Alberto; Amaduzzi, Francesca; Jabeen, Fauzia; Davies, Christopher L; Joyce, Hannah J; Herz, Laura M; Fontcuberta i Morral, Anna; Johnston, Michael B

    2015-02-11

    Reliable doping is required to realize many devices based on semiconductor nanowires. Group III-V nanowires show great promise as elements of high-speed optoelectronic devices, but for such applications it is important that the electron mobility is not compromised by the inclusion of dopants. Here we show that GaAs nanowires can be n-type doped with negligible loss of electron mobility. Molecular beam epitaxy was used to fabricate modulation-doped GaAs nanowires with Al0.33Ga0.67As shells that contained a layer of Si dopants. We identify the presence of the doped layer from a high-angle annular dark field scanning electron microscopy cross-section image. The doping density, carrier mobility, and charge carrier lifetimes of these n-type nanowires and nominally undoped reference samples were determined using the noncontact method of optical pump terahertz probe spectroscopy. An n-type extrinsic carrier concentration of 1.10 ± 0.06 × 10(16) cm(-3) was extracted, demonstrating the effectiveness of modulation doping in GaAs nanowires. The room-temperature electron mobility was also found to be high at 2200 ± 300 cm(2) V(-1) s(-1) and importantly minimal degradation was observed compared with undoped reference nanowires at similar electron densities. In addition, modulation doping significantly enhanced the room-temperature photoconductivity and photoluminescence lifetimes to 3.9 ± 0.3 and 2.4 ± 0.1 ns respectively, revealing that modulation doping can passivate interfacial trap states.

  12. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Maruo, Daiki; Hai, Pham Nam; Tanaka, Masaaki

    2015-03-01

    We demonstrate visible-light electroluminescence (EL) due to d- d transitions in GaAs:Mn based LEDs. We design p+-n junctions with a p+ GaAs:Mn layer, in which at a reverse bias voltage (-3 to -6 V), an intense electric field builds up in the depletion layers of the p+-n junctions. Holes are injected to the depletion layer by Zener tunneling from the conduction band or by diffusion of minority holes from the valence band of the n-type layer. These holes are accelerated by the intense electric field in the depletion layer, and excite the d electrons of Mn in the p+ GaAs:Mn layer by impact excitations. We observe visible-light emission at E1 = 1.89 eV and E2 = 2.16 eV, which are exactly the same as the 4T1-->6A1 and 4A2-->4T1 transition energy of Mn. The threshold voltage for observation of visible-light EL is -4 V, corresponding to -(E1 +E2) / e. This indicates that the impact excitation is most effective for the one step excitation from the ground state 6A1 to the highest excited state 4A2 .

  13. Diffused P+-N solar cells in bulk GaAs

    NASA Technical Reports Server (NTRS)

    Borrego, J. M.; Ghandhi, S. K.

    1982-01-01

    Recently melt grown GaAs, made by liquid encapsulation techniques, has become available. This material is of sufficiently good quality to allow the fabrication of solar cells by direct diffusion. Results obtained with p(+)/n junction solar cells made by zinc diffusion are described. The quality of bulk GaAs for this application is evaluated.

  14. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports...

  15. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports...

  16. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports...

  17. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports...

  18. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports...

  19. Electrical and Optical Properties of ZnO Films Grown on GaAs Substrates

    NASA Astrophysics Data System (ADS)

    Yuldashev, Shavkat U.; Panin, Gennady N.; Choi, Sung Woo; Yalishev, Vadim Sh.; Nosova, Ludmila A.; Ryu, Min Ki; Lee, Sanghern; Jang, Min Su; Chung, Kwan Soo; Kang, Tae Won

    2003-06-01

    Undoped ZnO films were deposited on GaAs substrates by conventional rf magnetron sputtering technique. After thermal annealing at temperatures of 500°C and higher for 20 min, the Hall coefficient of ZnO films on GaAs substrate becomes positive. The long-time annealing of 550 min at a temperature of 400°C also converts the sign of the Hall coefficient to positive. X-ray microanalysis shows that the diffusion of Zn atoms into the GaAs substrate and Ga atoms from the GaAs substrate into the ZnO film during thermal annealing occurs. The results of Hall measurements were analyzed by using the two-layer model of conductivity. It was shown that the positive sign of the Hall coefficient for the annealed ZnO film on the GaAs substrate is due to p-type conductivity of the GaAs substrate as a result of the diffusion of the Zn atoms from ZnO film into the GaAs substrate. With increasing annealing temperature or annealing time the ZnO films become more n-type due to the diffusion of Ga atoms from the GaAs substrate into the ZnO film.

  20. Electrical performance of conducting polymer (SPAN) grown on GaAs with different substrate orientations

    NASA Astrophysics Data System (ADS)

    Jameel, D. A.; Aziz, M.; Felix, J. F.; Al Saqri, N.; Taylor, D.; Albalawi, H.; Alghamdi, H.; Al Mashary, F.; Henini, M.

    2016-11-01

    This article reports the effect of n-type GaAs substrate orientation, namely (100), (311)A and (311)B, on the electrical properties of sulfonated polyaniline (SPAN)/GaAs heterojunction devices. In addition, the inhomogeneity of the interface between various GaAs substrates and SPAN is investigated in terms of barrier height and ideality factor by performing I-V measurements at different temperatures (20-420 K). The I-V results indicate that the value of the rectification ratio (IF/IR) at 0.5 V is higher for SPAN/(311)B GaAs samples than for SPAN/(100) GaAs and SPAN/(311)A GaAs samples. Moreover, the barrier height decreases and the ideality factor increases with decreasing temperature for all three heterostructure devices. The high value of mean barrier Φbarb of SPAN/(311)B (calculated from the plots of Φb 0 as a function of 1/2kT) confirms that the GaAs substrate orientation results in an increase of barrier homogeneities. Furthermore, the C-V characteristics were obtained at room temperature. The C-V measurements showed that the carrier distributions at the interface and away from the interface in high index (311) GaAs orientations are more uniform and have better barrier homogeneity than those grown on the conventional (100) GaAs substrates.

  1. Implementation and Performance of GaAs Digital Signal Processing ASICs

    NASA Technical Reports Server (NTRS)

    Whitaker, William D.; Buchanan, Jeffrey R.; Burke, Gary R.; Chow, Terrance W.; Graham, J. Scott; Kowalski, James E.; Lam, Barbara; Siavoshi, Fardad; Thompson, Matthew S.; Johnson, Robert A.

    1993-01-01

    The feasibility of performing high speed digital signal processing in GaAs gate array technology has been demonstrated with the successful implementation of a VLSI communications chip set for NASA's Deep Space Network. This paper describes the techniques developed to solve some of the technology and implementation problems associated with large scale integration of GaAs gate arrays.

  2. Rare Earth Doped Semiconductors and Materials Research Society Symposium Proceedings, Volume 301

    NASA Astrophysics Data System (ADS)

    Ballance, John

    1994-02-01

    The properties of rare earth ions in solids were studied in detail for decades, but until recently this work was restricted to dominantly ionic hosts such as fluorides and oxides, and to a lesser extent to more covalently bonded hosts, such as tetrahedral 2-6 semiconductors. The idea of rare earth elements incorporated into covalent semiconductors such as GaAs and Si may be traced to a short communication in 1963 by R.L. Bell (J. Appl. Phys. 34, 1563 (1963)) proposing a dc-pumped rare earth laser. At about the same time, three unpublished technical reports appeared as a result of U.S. Department of Defense sponsored research in rare earth doped Si, GaAs, and InP to fabricate LED's. Attempts by other researchers to identify sharp 4f specific emissions in these hosts essentially failed.

  3. Simultaneous dual-wavelength operation around 1.06 μm of a LD-end-pumped, passively Q-switched Nd:GGG laser with GaAs as saturable absorber

    NASA Astrophysics Data System (ADS)

    Chu, Hongwei; Zhao, Shengzhi; Li, Yufei; Yang, Kejian; Li, Guiqiu; Li, Dechun; Zhao, Jia; Qiao, Wenchao; Feng, Chuansheng

    2013-08-01

    By using neodymium-doped gadolinium gallium garnet (Nd:GGG) as the laser medium, a passively Q-switched simultaneous dual-wavelength Nd:GGG laser with a GaAs saturable absorber has been realized. The Nd:GGG laser operates at a stable dual-wavelength peaked at 1060.8 and 1062.7 nm without any wavelength selective elements in the cavity. Stable Q-switched pulses with a shortest duration of 6 ns have been obtained, corresponding to a single pulse energy of 2.1 μJ and a peak power of 335 W.

  4. Empirical-Statistics Analysis for Zero-Failure GaAs MMICs Life Testing Data

    NASA Astrophysics Data System (ADS)

    Huang, Zheng-Liang; Yu, Fa-Xin; Zhang, Shu-Ting; Luo, Hao; Wang, Ping-Hui; Zheng, Yao

    GaAs MMICs (Monolithic Microwave Integrated Circuits) reliability is a critical part of the overall reliability of the thermal solution in semiconductor devices. With MMICs reliability improved, GaAs MMICs failure rates will reach levels which are impractical to measure with conventional methods in the near future. This letter proposes a methodology to predict the GaAs MMICs reliability by combining empirical and statistical methods based on zero-failure GaAs MMICs life testing data. Besides, we investigate the effect of accelerated factors on MMICs degradation and make a comparison between the Weibull and lognormal distributions. The method has been used in the reliability evaluation of GaAs MMICs successfully.

  5. Stalled DNA Replication Forks at the Endogenous GAA Repeats Drive Repeat Expansion in Friedreich's Ataxia Cells.

    PubMed

    Gerhardt, Jeannine; Bhalla, Angela D; Butler, Jill Sergesketter; Puckett, James W; Dervan, Peter B; Rosenwaks, Zev; Napierala, Marek

    2016-08-01

    Friedreich's ataxia (FRDA) is caused by the expansion of GAA repeats located in the Frataxin (FXN) gene. The GAA repeats continue to expand in FRDA patients, aggravating symptoms and contributing to disease progression. The mechanism leading to repeat expansion and decreased FXN transcription remains unclear. Using single-molecule analysis of replicated DNA, we detected that expanded GAA repeats present a substantial obstacle for the replication machinery at the FXN locus in FRDA cells. Furthermore, aberrant origin activation and lack of a proper stress response to rescue the stalled forks in FRDA cells cause an increase in 3'-5' progressing forks, which could enhance repeat expansion and hinder FXN transcription by head-on collision with RNA polymerases. Treatment of FRDA cells with GAA-specific polyamides rescues DNA replication fork stalling and alleviates expansion of the GAA repeats, implicating DNA triplexes as a replication impediment and suggesting that fork stalling might be a therapeutic target for FRDA.

  6. A study of binding biotinylated nano-beads to the surface of (001) GaAs

    NASA Astrophysics Data System (ADS)

    Ding, Ximing; Moumanis, Khalid; Dubowski, Jan J.; Frost, Eric H.

    2006-02-01

    We have investigated the deposition of biotinylated nano-beads on the surface of GaAs. The deposition procedure involved either direct coating of (001) GaAs with nano-beads, or binding the nano-beads with avidin immobilized on the surface of (001) GaAs through the interface of biotin and the NH II terminal group of 11-amino-1-undecanethiol (HS(CH II) 11NH II). The efficiency of binding was tested by washing the samples in a solution of a commercial detergent and by subjecting them to a deionized water ultrasonic bath. The results indicate that nano-beads deposited directly on the surface of (001) GaAs withstand the detergent washing test but they are easily removed by ultrasonic washing. In contrast, the nano-beads attached to (001) GaAs through the avidin-biotin-thiol interface survive the ultrasonic washing tests.

  7. Improvement of interface electronic properties of GaF 3/GaAs MIS structures

    NASA Astrophysics Data System (ADS)

    Ricard, H.; Aizawa, K.; Ishiwara, H.

    The interface electronic properties of GaF 3/GaAs structures are investigated for three different deposition procedures, the GaF 3 films have been deposited on n-type GaAs epitaxial layers without breaking the vacuum, or after being exposed to air, or after being treated in (NH 4) 2S 1 solution. It has been found from low-temperature C-V measurements in MIS diodes that a real modulation of the Fermi level in the forbidden band gap of GaAs occurs only when the GaAs epitaxial layer is treated in the sulfur solution and annealed at an optimum temperature prior to deposition of GaF 3. The unpinning mechanism is also discussed in conjunction with the simplified model for sulfur-treated GaAs surfaces.

  8. Stalled DNA Replication Forks at the Endogenous GAA Repeats Drive Repeat Expansion in Friedreich's Ataxia Cells.

    PubMed

    Gerhardt, Jeannine; Bhalla, Angela D; Butler, Jill Sergesketter; Puckett, James W; Dervan, Peter B; Rosenwaks, Zev; Napierala, Marek

    2016-08-01

    Friedreich's ataxia (FRDA) is caused by the expansion of GAA repeats located in the Frataxin (FXN) gene. The GAA repeats continue to expand in FRDA patients, aggravating symptoms and contributing to disease progression. The mechanism leading to repeat expansion and decreased FXN transcription remains unclear. Using single-molecule analysis of replicated DNA, we detected that expanded GAA repeats present a substantial obstacle for the replication machinery at the FXN locus in FRDA cells. Furthermore, aberrant origin activation and lack of a proper stress response to rescue the stalled forks in FRDA cells cause an increase in 3'-5' progressing forks, which could enhance repeat expansion and hinder FXN transcription by head-on collision with RNA polymerases. Treatment of FRDA cells with GAA-specific polyamides rescues DNA replication fork stalling and alleviates expansion of the GAA repeats, implicating DNA triplexes as a replication impediment and suggesting that fork stalling might be a therapeutic target for FRDA. PMID:27425605

  9. High pressure and time resolved studies of optical properties of n-type doped GaN/AlN multi-quantum wells: Experimental and theoretical analysis

    NASA Astrophysics Data System (ADS)

    Kaminska, A.; Jankowski, D.; Strak, P.; Korona, K. P.; Beeler, M.; Sakowski, K.; Grzanka, E.; Borysiuk, J.; Sobczak, K.; Monroy, E.; Krukowski, S.

    2016-09-01

    High-pressure and time-resolved studies of the optical emission from n-type doped GaN/AlN multi-quantum-wells (MQWs) with various well thicknesses are analysed in comparison with ab initio calculations of the electronic (band structure, density of states) and optical (emission energies and their pressure derivatives, oscillator strength) properties. The optical properties of GaN/AlN MQWs are strongly affected by quantum confinement and polarization-induced electric fields. Thus, the photoluminescence (PL) peak energy decreases by over 1 eV with quantum well (QW) thicknesses increasing from 1 to 6 nm. Furthermore, the respective PL decay times increased from about 1 ns up to 10 μs, due to the strong built-in electric field. It was also shown that the band gap pressure coefficients are significantly reduced in MQWs as compared to bulk AlN and GaN crystals. Such coefficients are strongly dependent on the geometric factors such as the thickness of the wells and barriers. The transition energies, their oscillator strength, and pressure dependence are modeled for tetragonally strained structures of the same geometry using a full tensorial representation of the strain in the MQWs under external pressure. These MQWs were simulated directly using density functional theory calculations, taking into account two different systems: the semi-insulating QWs and the n-doped QWs with the same charge density as in the experimental samples. Such an approach allowed an assessment of the impact of n-type doping on optical properties of GaN/AlN MQWs. We find a good agreement between these two approaches and between theory and experimental results. We can therefore confirm that the nonlinear effects induced by the tetragonal strain related to the lattice mismatch between the substrates and the polar MQWs are responsible for the drastic decrease of the pressure coefficients observed experimentally.

  10. Microwave characteristics of an optically controlled GaAs MESFET

    NASA Astrophysics Data System (ADS)

    Mizuno, H.

    1983-07-01

    This paper presents the results of an experimental investigation of microwave characteristics of a GaAs MESFET under optically direct-controlled conditions. The gain, drain current, and S-parameters were measured under various optical conditions in the frequency region from 3.0 GHz to 8.0 GHz., and it was found that they can be controlled by varying the incident light intensity in the same manner as when varying the gate bias voltage. As applications of this phenomenon, optical/microwave transformers and an optically switched amplifiers were investigated.

  11. High speed GaAs static RAM technology and design

    NASA Astrophysics Data System (ADS)

    Lundgren, R. E.; Waldner, M.

    A design and analysis study of potential high-speed GaAs MESFET memory circuits was performed. The results show that a 1-kbit static RAM having a 1-ns access time is feasible using low-power enhancement-mode MESFETs to realize static flip-flop memory cells; power dissipation would be 5 microwatts per cell. To achieve maximum memory speed, the control and drive circuitry incorporates depletion-mode devices throughout; total power dissipation would be about 1 W. Details of the memory design and analysis are presented.

  12. Quantum effects in electron beam pumped GaAs

    SciTech Connect

    Yahia, M. E.; Azzouz, I. M.; Moslem, W. M.

    2013-08-19

    Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.

  13. Hydrogen Effects on GaAs Device Reliability

    NASA Technical Reports Server (NTRS)

    Kayali, Sammy A.

    1996-01-01

    GaAs and InP devices in hermetically sealed packages have been observed to exhibit unacceptable degradation in both RF and DC characteristics. This degradation has been observed to occur at temperatures as low as 125oC. The source of the degradation has been linked to hydrogen gas that has been absorbed in the package's metals (Kovar, plating, etc.) and converted into atomic hydrogen within the Pt or Pd metallization of the gate structure. Subsequently, atomic hydrogen diffuses into the channel region of the FET structure and neutralizes the Si donors, resulting in a degradation of the device characteristics.

  14. Activation modeling of Si implanted GaAs

    NASA Astrophysics Data System (ADS)

    Apiwatwaja, R.; Gwilliam, R.; Wilson, R.; Sealy, B. J.

    1997-02-01

    The total concentration of ionized impurities in silicon implanted GaAs was estimated from carrier concentration and mobility values obtained by Hall effect measurements together with published compensations. We have demonstrated that the calculated profiles (ND++NA-) are in good agreement with that of the silicon atomic distributions obtained by secondary-ion-mass spectroscopy. We have observed that a large concentration of gallium vacancies are injected into the sample during a 900 °C anneal for 1000 s using a Si3N4 cap.

  15. Molecular dynamics simulations of displacement cascades in GaAs.

    SciTech Connect

    Foiles, Stephen Martin

    2010-04-01

    The quantification of the production of primary defects via displacement cascades is an important ingredient in the prediction of the influence of radiation on the performance of electronic components in radiation environments. Molecular dynamics simulations of displacement cascades are performed for GaAs The interatomic interactions are described using a recently proposed Bond Order Potential, and a simple model of electronic stopping is incorporated. The production of point defects is quantified as a function of recoil energy and recoil species. Correlations in the point defects are examined. There are a large number of anti-site defects nearest-neighbor pairs as well as di-vacancies and larger order vacancy clusters. Radiation damage and ion implantation in materials have been studied via molecular dynamics for many years. A significant challenge in these simulations is the detailed identification and quantification of the primary defect production. For the present case of a compound semiconductor, GaAs, there are a larger number of possible point defects compared to elemental materials; two types of vacancies, two types of interstitials and antisite defects. This is further complicated by the fact that, in addition to the formation of point defects, amorphous zones may also be created. The goal of the current work is to quantify the production of primary defects in GaAs due to radiation exposures. This information will be used as part of an effort to predict the influence of radiation environments on the performance of electronic components and circuits. The data provide the initial state for continuum-level analysis of the temporal evolution of defect populations. For this initial state, it is important to know both the number of the various point defects that may be produced as well as the initial spatial correlations between the primary defects. The molecular dynamics simulations employ a recently developed Bond Order Potential (BOP) for GaAs. The analysis

  16. Experimental demonstration of strained Si nanowire GAA n-TFETs and inverter operation with complementary TFET logic at low supply voltages

    NASA Astrophysics Data System (ADS)

    Luong, G. V.; Strangio, S.; Tiedemannn, A.; Lenk, S.; Trellenkamp, S.; Bourdelle, K. K.; Zhao, Q. T.; Mantl, S.

    2016-01-01

    In this work, strained Si (sSi) nanowire array of n-TFETs with gates all around (GAA) yielding ON-currents of 5 μA/μm at a supply voltage Vdd = 0.5 V are presented. Tilted ion implantation with BF2+ into NiSi2 dopant has been used to form a highly doped pocket for the source to channel tunneling junction. These devices indicate sub-threshold slopes (SS) below 60 mV/dec for Id < 10-4 μA/μm at Vds = 0.1 V at room temperature. Common analog device characteristics have been determined at Vdd = 0.5 V resulting in a transconductance gm = 24 μS/μm, transconductance efficiency gm/Id = 23 V-1 and the conductance gd = 0.8 μS/μm normalized to the gate width. Based on the good saturation behavior in the output characteristic, an intrinsic gain of 188 is observed. In addition, we present operation of the first experimental sSi GAA NW C-TFET inverter. In spite of ambipolar behavior, the voltage transfer curves (VTC) indicate wide and constant noise margin levels with steep transitions offering a voltage gain of 25 at Vdd = 1 V.

  17. High-efficiency GaAs solar cells

    SciTech Connect

    Knechtli, R.C.; Loo, R.Y.

    1984-05-01

    An updated review of the state of the art in the development of GaAs solar cells is provided, with emphasis on AlGaAs-GaAs cells suitable for space applications. A set of theoretically derived characteristics is given for this type of solar cell. Comparison of measured performance with theory shows excellent agreement. Data on the effects of radiation damage (high-energy electrons, protons, and neutrons) is also integrated into a form useful for evaluation purposes. Techniques for fabricating (AlGa)As-GaAs solar cells in quantities large enough for practical applications are discussed and are shown to have been demonstrated. The possibility of extending these techniques to the fabrication of very thin low-weight cells for space applications is also considered. Finally, the results obtained to date in the development of GaAs solar cells for applications requiring concentrated sunlight are reviewed, for terrestrial as well as for space applications. As a milestone toward the practical application of AlGaAs-GaAs solar cells in space systems, a brief account is provided on the development status of small experimental AlGaAs-GaAs solar-cell panels for specific space flights.

  18. Sol-gel derived ? thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Arscott, S.; Smith, N.; Kurchania, R.; Milne, S. J.; Miles, R. E.

    1998-02-01

    Sol-gel derived thin films of lead zirconate titanate (PZT) have been fabricated on a platinized GaAs substrate using a propane-1,3-diol based sol-gel route. PZT can be used as the piezoelectric component in bulk acoustic wave devices for monolithic microwave integrated circuit applications. A 100 nm silicon nitride buffer layer was deposited onto the GaAs by plasma-enhanced chemical vapour deposition in order to prevent gallium and arsenic outdiffusion during film fabrication. Rapid thermal processing (RTP) techniques were employed to decompose thermally the sol-gel layer to PZT in a further effort to minimize problems of gallium and arsenic outdiffusion. Adhesion between the bottom electrode and substrate was found to improve when an intermediate titanium layer deposited between the platinum and silicon nitride was oxidized prior to deposition of the platinum electrode. A crystalline PZT film was produced on the 0268-1242/13/2/016/img9 substrate configuration by firing the sol-gel coating at 0268-1242/13/2/016/img10C for 10 s using RTP. A single deposition of sol resulted in a film having a thickness of 0268-1242/13/2/016/img11. Ferroelectric hysteresis measurements yielded average values of remanant polarization and coercive field of 0268-1242/13/2/016/img12 and 0268-1242/13/2/016/img13 respectively.

  19. Image processing using Gallium Arsenide (GaAs) technology

    NASA Technical Reports Server (NTRS)

    Miller, Warner H.

    1989-01-01

    The need to increase the information return from space-borne imaging systems has increased in the past decade. The use of multi-spectral data has resulted in the need for finer spatial resolution and greater spectral coverage. Onboard signal processing will be necessary in order to utilize the available Tracking and Data Relay Satellite System (TDRSS) communication channel at high efficiency. A generally recognized approach to the increased efficiency of channel usage is through data compression techniques. The compression technique implemented is a differential pulse code modulation (DPCM) scheme with a non-uniform quantizer. The need to advance the state-of-the-art of onboard processing was recognized and a GaAs integrated circuit technology was chosen. An Adaptive Programmable Processor (APP) chip set was developed which is based on an 8-bit slice general processor. The reason for choosing the compression technique for the Multi-spectral Linear Array (MLA) instrument is described. Also a description is given of the GaAs integrated circuit chip set which will demonstrate that data compression can be performed onboard in real time at data rate in the order of 500 Mb/s.

  20. Subnanosecond, high voltage photoconductive switching in GaAs

    SciTech Connect

    Druce, R.L.; Pocha, M.D.; Griffin, K.L. ); O'Bannon, B.J. )

    1990-01-01

    We are conducting research on the switching properties of photoconductive materials to explore their potential for generating high-power microwaves (HPM) and for high rep-rate switching. We have investigated the performance of Gallium Arsenide (GaAs) in linear mode (the conductivity of the device follows the optical pulse) as well as an avalanche-like mode (the optical pulse only controls switch closing). Operating in the linear mode, we have observed switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps at several kV/cm fields using neutron irradiated GaAs. In avalanche and lock-on modes, high fields are switched with lower laser pulse energies, resulting in higher efficiencies; but with measurable switching delay and jitter. We are currently investigating both large area (1 cm{sup 2}) and small area (<1 mm{sup 2}) switches illuminated by AlGaAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 {mu}m.

  1. High-efficiency nanostructured window GaAs solar cells.

    PubMed

    Liang, Dong; Kang, Yangsen; Huo, Yijie; Chen, Yusi; Cui, Yi; Harris, James S

    2013-10-01

    Nanostructures have been widely used in solar cells due to their extraordinary optical properties. In most nanostructured cells, high short circuit current has been obtained due to enhanced light absorption. However, most of them suffer from lowered open circuit voltage and fill factor. One of the main challenges is formation of good junction and electrical contact. In particular, nanostructures in GaAs only have shown unsatisfactory performances (below 5% in energy conversion efficiency) which cannot match their ideal material properties and the record photovoltaic performances in industry. Here we demonstrate a completely new design for nanostructured solar cells that combines nanostructured window layer, metal mesa bar contact with small area, high quality planar junction. In this way, we not only keep the advanced optical properties of nanostructures such as broadband and wide angle antireflection, but also minimize its negative impact on electrical properties. High light absorption, efficient carrier collection, leakage elimination, and good lateral conductance can be simultaneously obtained. A nanostructured window cell using GaAs junction and AlGaAs nanocone window demonstrates 17% energy conversion efficiency and 0.982 V high open circuit voltage.

  2. Thermal stress cycling of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Janousek, B. K.; Francis, R. W.; Wendt, J. P.

    1985-01-01

    A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

  3. 28 percent efficient GaAs concentrator solar cells

    NASA Technical Reports Server (NTRS)

    Macmillan, H. F.; Hamaker, H. C.; Kaminar, N. R.; Kuryla, M. S.; Ladle Ristow, M.

    1988-01-01

    AlGaAs/GaAs heteroface solar concentrator cells which exhibit efficiencies in excess of 27 percent at high solar concentrations (over 400 suns, AM1.5D, 100 mW/sq cm) have been fabricated with both n/p and p/n configurations. The best n/p cell achieved an efficiency of 28.1 percent around 400 suns, and the best p/n cell achieved an efficiency of 27.5 percent around 1000 suns. The high performance of these GaAs concentrator cells compared to earlier high-efficiency cells was due to improved control of the metal-organic chemical vapor deposition growth conditions and improved cell fabrication procedures (gridline definition and edge passivation). The design parameters of the solar cell structures and optimized grid pattern were determined with a realistic computer modeling program. An evaluation of the device characteristics and a discussion of future GaAs concentrator cell development are presented.

  4. GaAs clean up studied with synchrotron radiation photoemission

    NASA Astrophysics Data System (ADS)

    Tallarida, Massimo; Adelmann, Christoph; Delabie, Annelies; van Elshocht, Sven; Caymax, Matty; Schmeisser, Dieter

    2012-12-01

    In this contribution we describe the chemical changes at the surface of GaAs upon adsorption of tri-methyl-aluminum (TMA). TMA is used to grow Al2O3 with atomic layer deposition (ALD) usually using H2O as oxygen source. Recently, it was pointed out that the adsorption of TMA on various III-V surfaces reduces the native oxide, allowing the growth of an abrupt III-V/High-K interface with reduced density of defects. Synchrotron radiation photoemission spectroscopy (SR-PES) is a powerful method to characterize surfaces and interfaces of many materials, as it is capable to determine their chemical composition as well as the electronic properties. We performed in-situ SR-PES measurements after exposing a GaAs surface to TMA pulses at about 250°C. Upon using the possibility of tuning the incident photon energy we compared the Ga3d spectra at 41 eV, 71 eV, 91 eV and 121 eV, as well as the As3d at 71 eV and 91 eV. Finally, we show that using SR-PES allows a further understanding of the surface composition, which is usually not accessible with other techniques.

  5. Step-step interactions on GaAs (110) nanopatterns

    SciTech Connect

    Galiana, B.; Benedicto, M.; Tejedor, P.

    2013-01-14

    The step-step interactions on vicinal GaAs (110) surface patterns have been extracted from the quantitative analysis of the terrace width distribution (TWD). We have specifically studied the interactions in near-equilibrium faceting and kinetics-driven step bunching and meandering formed by spontaneous self-organization or through the modification of GaAs growth kinetics by atomic hydrogen. We show that the experimental TWDs determined from atomic force microscopy measurements can be accurately described by a weighed sum of a generalized Wigner distribution and several Gaussians. The results of our calculations indicate that straight facets are formed during high temperature homoepitaxy due to attractive interactions between [110] steps. At low temperatures, steady state attractive interactions in [110] step bunches are preceded by a transition regime dominated by entropic and energetic repulsions between meandering [11n]-type steps (n {>=} 2), whose population density exceeds that of the [110] bunched steps. In addition, it has been found that atomic H reduces the attractive interactions between [110] bunched steps and enhances entropic and dipole-induced energetic repulsions between H-terminated [11n] steps through the inhibition of As-As bond formation at step edges. Our analysis has evidenced a correlation between the value of the adjustable parameter that accounts in our model for the specific weight of the secondary peaks in the TWD ({beta}) and the extent of transverse meandering on the vicinal surface.

  6. Preparation of pulse plated GaAs films

    NASA Astrophysics Data System (ADS)

    Murali, K. R.; Trivedi, D. C.

    2006-07-01

    Thin GaAs films were prepared by pulse plating from an aqueous solution containing 0.20 M GaCl3 and 0.15 M As2O3 at a pH of 2 and at room temperature. The current density was kept as 50 mA cm-2 the duty cycle was varied in the range 10 50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm-2 illumination, an open circuit voltage of 0.5 V and a short circuit current density of 5.0 mA cm-2 were observed for the films deposited at a duty cycle of 50%.

  7. Phase Transformation in Radially Merged Wurtzite GaAs Nanowires

    PubMed Central

    2015-01-01

    III–V Nanowires (NWs) grown with metal–organic chemical vapor deposition commonly show a polytypic crystal structure, allowing growth of structures not found in the bulk counterpart. In this paper we studied the radial overgrowth of pure wurtzite (WZ) GaAs nanowires and characterized the samples with high resolution X-ray diffraction (XRD) to reveal the crystal structure of the grown material. In particular, we investigated what happens when adjacent WZ NWs radially merge with each other by analyzing the evolution of XRD peaks for different amounts of radial overgrowth and merging. By preparing cross-sectional lamella samples we also analyzed the local crystal structure of partly merged NWs by transmission electron microscopy. Once individual NWs start to merge, the crystal structure of the merged segments is transformed progressively from initial pure WZ to a mixed WZ/ZB structure. The merging process is then modeled using a simple combinatorial approach, which predicts that merging of two or more WZ NWs will result in a mixed crystal structure containing WZ, ZB, and 4H. The existence large and relaxed segments of 4H structure within the merged NWs was confirmed by XRD, allowing us to accurately determine the lattice parameters of GaAs 4H. We compare the measured WZ and 4H unit cells with an ideal tetrahedron and find that both the polytypes are elongated in the c-axis and compressed in the a-axis compared to the geometrically converted cubic ZB unit cell. PMID:26494983

  8. Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

    1985-01-01

    The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

  9. Electrical transport and resistance switching characteristics of BiFeO3/Nb:SrTiO3/GaAs heterostructure fabricated by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Huang, W.; Yang, J. J.; Gao, G. Y.; Lei, Y.; Zhu, J.; Zeng, H. Z.; Zheng, F. G.; Hao, J. H.

    2014-08-01

    BiFeO3 thin films were epitaxially grown on (001) GaAs substrate by pulsed laser deposition with Nb doped SrTiO3 as a buffer layer. Piezoresponse force microscopy images exhibit effective ferroelectric switching of the heterostructure. The temperature-dependent current-voltage characteristics of the heterostructure reveal a resistance switching phenomenon and diode-like behavior with a rectifying ratio of 2 × 102 at the applied voltage of ±13.4 V. The electrical transport mechanism in the heterostructure has been illustrated by constructing the energy band structure. In addition, the resistance switching behavior in the heterostructure could be explained by the polarization modulation of the depletion region at the interface of the semiconductor and the ferroelectric layers.

  10. Enhanced spin-polarization lifetimes in a two-dimensional electron gas in a gate-controlled GaAs quantum well

    NASA Astrophysics Data System (ADS)

    Anghel, Sergiu; Singh, Akshay; Passmann, Felix; Iwata, Hikaru; Moore, John N.; Yusa, Go; Li, Xiaoqin; Betz, Markus

    2016-07-01

    Exciton, trion, and electron spin dynamics in a 20-nm-wide modulation-doped GaAs single quantum well are investigated using resonant ultrafast two-color Kerr rotation spectroscopy. Excitons and trions are selectively detected by resonant probe pulses while their relative spectral weight is controlled by adjusting the gate voltage which tunes the carrier density. Tuning the carrier density markedly influences the spin decay time of the two-dimensional electron gas. The spin decay time can be enhanced by a factor of 3 at an intermediate carrier concentration in the quantum well where excitons and trions coexist in the system. In addition, we explore the capability to tune the g factor of the electron gas via the carrier density.

  11. Extremely deep profiling analysis of the atomic composition of thick (>100 μm) GaAs layers within power PIN diodes by secondary ion mass spectrometry

    NASA Astrophysics Data System (ADS)

    Drozdov, M. N.; Drozdov, Yu. N.; Yunin, P. A.; Folomin, P. I.; Gritsenko, A. B.; Kryukov, V. L.; Kryukov, E. V.

    2016-08-01

    A new opportunity to analyze the atomic composition of thick (>100 μm) epitaxial GaAs layers by SIMS with lateral imaging of the cross section of a structure is demonstrated. The standard geometry of ldepth analysis turns out to be less informative owing to material redeposition from the walls of a crater to its floor occurring when the crater depth reaches several micrometers. The profiles of concentration of doping impurities Te and Zn and concentrations of Al and major impurities in PIN diode layers are determined down to a depth of 130 μm. The element sensitivity is at the level of 1016 at/cm3 (typical for depth analysis at a TOF.SIMS-5 setup), and the resolution is twice the diameter of the probing beam of Bi ions. The possibility of enhancing the depth resolution and the element sensitivity of the proposed analysis method is discussed.

  12. Raman-scattering and optical studies of argon-etched GaAs surfaces

    SciTech Connect

    Feng, G.F.; Zallen, R. ); Epp, J.M.; Dillard, J.G. )

    1991-04-15

    We have studied the structual damage in low-energy argon-ion-bombarded (ion-etched) GaAs using Raman scattering and ultraviolet reflectivity. When combined with post-bombardment sequential chemical etching, the Raman results reveal a graded depth profile of the damage layer, with a nearly linear damage dropoff with depth. The total damage-layer thickness is about 600 A for high-fluence bombardment with 3.89-keV Ar{sup +} ions. The spectral effects produced by argon etching are very different from those produced by high-energy ion implantation. The longitudinal-optic Raman line seen for argon-etched GaAs is not shifted and broadened as in ion-implanted GaAs. More striking are the results of the reflectivity measurements. For argon-etched GaAs, the electronic interband peaks are both broadened and strongly red shifted relative to the crystal peaks; for ion-implanted GaAs, only the broadening occurs. Distinct nanocrystals, which account for the effects seen in ion-implanted GaAs, are evidently absent in argon-etched GaAs. Instead, the damage layer caused by argon etching appears to be characterized by a very high density of point defects, which previous work suggests may be arsenic vacancies.

  13. Computational study of the Effect of Sulfur Passivation on GaAs Heterojunction Solar Cells

    NASA Astrophysics Data System (ADS)

    Yu, Ted; Laghuvamarapu, Ramesh; Yan, Liang; You, Wei; Huffaker, Diana; Ratsch, Christian

    2013-03-01

    We report DFT calculations that study the effect of sulfur passivation ((NH4)2 S and octanethiol) on GaAs surfaces. Sulfur passivation of GaAs solar cells is an area of interest, as it improves the I-V characteristics of heterojunctions by decreasing the density of surface states. We elucidate the fundamental mechanism of sulfur passivation on GaAs by showing how the sulfur species react with different reconstructed GaAs (100) and (111B) surfaces. Using state of the art hybrid functionals to calculate band structures and density of states, we find that a reconstructed GaAs surface does not have mid-gap surface states. Therefore, we show that sulfur passivation does not reduce surface states on reconstructed surfaces. We also study arsenic vacancies and adatoms on these surfaces to determine the energies of creating these imperfections. They lead to mid-gap surface states that are shown to be energetically plausible in certain GaAs surface reconstruction. We study the most energetically favorable surface reconstructions with As vacancies and show how sulfur passivation plays a role in removing surface states. These results will guide in the selection of passivating agents for GaAs solar cells and lead to a better understanding of such systems. We appreciate the support of the NSF, Grant Number: DMR-1125931

  14. Ribbon growth of single crystal GaAs for solar cell application

    NASA Astrophysics Data System (ADS)

    Gould, T. A.; Seidensticker, R. G.; Mazelsky, R.

    1981-11-01

    This report describes the results of a 3-year effort to develop GaAs dendritic web for high-efficiency solar cells. A unique GaAs ribbon growth system was developed by applying dentritic-web growth techniques to a liquid-encapsulated GaAs system. Computerized thermal modelling and experimental modification produced a thermal geometry from which 48 GaAs webs were grown. These crystals had a multidendrite and/or faceted morphology rather than typical web morphology. Crystal quality improved as thermal geometry, growth techniques, dendrite seeds, and melt chemistry were optimized during the course of the program; however, conventional web morphology was not achieved. Analyses of chemical modification, crystal-growth characteristics, and orientation relationships suggest that inherent materials properties of GaAs produce a typical web morphology under conventional web-growth conditions. Consequently, a simple transfer of Si web growth technology to our GaAs system was inadequate for the growth of high quality GaAs web.

  15. DX centers in Sn-doped AlxGa1-xAs grown by metalorganic vapor phase epitaxy at T≥850 °C

    NASA Astrophysics Data System (ADS)

    Mooney, P. M.; Parker, B. D.; Cardone, F.; Gibart, P.; Portal, J. C.

    1992-01-01

    It was recently inferred from low-temperature transport measurements that DX centers are not formed in Sn-doped AlGaAs grown by metalorganic vapor phase epitaxy at T≥850 °C. Deep level transient spectroscopy measurements reported here show that DX centers are present in this material. The high conductivity measured at low temperature comes from parallel conduction in the underlying GaAs due to Sn diffusion during growth at high temperature.

  16. The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

    SciTech Connect

    Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.; Zhurbina, I. A.; Domashevskaya, E. P.; Arsent'ev, I. N. Shishkov, M. V.

    2009-08-15

    In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

  17. Relationship between planar GaAs nanowire growth direction and substrate orientation

    NASA Astrophysics Data System (ADS)

    Dowdy, Ryan S.; Walko, Donald A.; Li, Xiuling

    2013-01-01

    Planar GaAs nanowires are epitaxially grown on GaAs substrates of various orientations, via the Au-catalyzed vapor-liquid-solid mechanism using metal organic chemical vapor deposition. The nanowire geometry and growth direction are examined using scanning electron microscopy and x-ray microdiffraction. A hypothesis relating the planar nanowire growth direction to the surface projections of <111> B crystal directions is proposed. GaAs planar nanowire growth on vicinal substrates is performed to test this hypothesis. Good agreement between the experimental results and the projection model is found.

  18. Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

    NASA Technical Reports Server (NTRS)

    Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

    1987-01-01

    Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

  19. Sulfur-mediated palladium catalyst immobilized on a GaAs surface

    SciTech Connect

    Shimoda, M.; Konishi, T.; Nishiwaki, N.; Yamashita, Y.; Yoshikawa, H.

    2012-06-15

    We present a hard x-ray photoelectron spectroscopy study on the preparation process of palladium catalyst immobilized on an S-terminated GaAs(100) surface. It is revealed that Pd(II) species are reduced on the GaAs surface and yield Pd nanoparticles during the process of Pd immobilization and the subsequent heat treatment. A comparison with the results on GaAs without S-termination suggests that the reduction of Pd is promoted by hydroxy groups during the Pd immobilization and by S during the heat treatment.

  20. Surface and coordination chemistry related to GaAs

    NASA Astrophysics Data System (ADS)

    Keys, Andrea

    The vapor phase structures of Al(tBU)3 and Ga(tBU)3 have been investigated by gas phase electron diffraction and consist of planar three-coordinate monomers. Salient structural parameters (ra) include: Al-C = 2.005(3) A, Ga-C = 2.034(2) A. The geometries are controlled by inter-ligand interactions. The electron diffraction structures are compared to those determined by ab initio calculations for M(tBU)3 (M = Al, Ga, In). To understand the most suitable linkages for the surface of GaAs, model compounds were synthesized by reacting Ga(tBU)3 and [tBu2Ga(mu-Cl]2 with one molar equivalent of varying ligands. The synthesized compounds include chlorides, benzenethiolate, dithiocarbamates, carboxylates, amides, benzohydroxamate, and phenylphosphonate. The Ga ⋯ Ga and Ga-ligand interatomic distances for these compounds, as well as Group 15 and 16 donor bridging ligands, are compared to the values for the surface of GaAs and cubic-GaS in order to determine their suitability as linkage groups for self-assembled monolayers. The most suitable linkages were determined to be benzenethiol and phenylphophonic acid, and these were used to grow self-assembled monolayers on {100} GaAs. Carboxylic acid was also used, to determine the success of the organometallic model compounds in predicting the suitability of ligands for surface reaction. Self-assembled monolayers were also grown on Al2O3, using carboxylic acids and phenylphosphonic acids as the surface linkages. Metallo-organic chemical vapor deposition was performed using single-source precursors ( tBU)2Ga(S2CNR2). The tert -butyl gallium bis-dialkyl-dithiocarbamate compounds, (tBu)Ga(S2CNR2)2, are formed as minor products via ligand disproportionation reactions. Gallium sulfide (GaS) thin films have been grown at 375-425°C by atmospheric pressure metal-organic chemical vapor deposition using compounds (tBu) 2Ga(S2CNMe2) and (tBu)2Ga(S 2CNEt2) as single source precursors. Polycrystalline samples of the chalcogenides InSe, In2Se3

  1. The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study

    PubMed Central

    2014-01-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices. PMID:25337061

  2. The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study.

    PubMed

    Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

    2014-01-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.

  3. Electron spin relaxation dynamics in GaN: influence of temperature, doping density, and crystal orientation

    NASA Astrophysics Data System (ADS)

    Buß, J. H.; Rudolph, J.; Starosielec, S.; Schaefer, A.; Semond, F.; Hägele, D.

    2013-03-01

    We present a systematic study of electron spin relaxation in wurtzite GaN. Fast relaxation is caused by a Rashba effective magnetic field that linearly depends on the electron momentum k. The field prevents spin lifetimes to exceed 50 ps at room temperature and is the origin of an anisotropic spin relaxation tensor that we evidence by magnetic field dependent magneto-optical pump-probe measurements. In addition, the spin lifetime depends - as compared to GaAs - weaker on temperature and doping density. We give a fully analytical description of both effects based on D'yakonov-Perel' theory that describes our results quantitatively without any fitting parameter.

  4. The Anti-Doping Movement.

    PubMed

    Willick, Stuart E; Miller, Geoffrey D; Eichner, Daniel

    2016-03-01

    Historical reports of doping in sports date as far back as the ancient Greek Olympic Games. The anti-doping community considers doping in sports to be cheating and a violation of the spirit of sport. During the past century, there has been an increasing awareness of the extent of doping in sports and the health risks of doping. In response, the anti-doping movement has endeavored to educate athletes and others about the health risks of doping and promote a level playing field. Doping control is now undertaken in most countries around the world and at most elite sports competitions. As athletes have found new ways to dope, however, the anti-doping community has endeavored to strengthen its educational and deterrence efforts. It is incumbent upon sports medicine professionals to understand the health risks of doping and all doping control processes. PMID:26972261

  5. The Anti-Doping Movement.

    PubMed

    Willick, Stuart E; Miller, Geoffrey D; Eichner, Daniel

    2016-03-01

    Historical reports of doping in sports date as far back as the ancient Greek Olympic Games. The anti-doping community considers doping in sports to be cheating and a violation of the spirit of sport. During the past century, there has been an increasing awareness of the extent of doping in sports and the health risks of doping. In response, the anti-doping movement has endeavored to educate athletes and others about the health risks of doping and promote a level playing field. Doping control is now undertaken in most countries around the world and at most elite sports competitions. As athletes have found new ways to dope, however, the anti-doping community has endeavored to strengthen its educational and deterrence efforts. It is incumbent upon sports medicine professionals to understand the health risks of doping and all doping control processes.

  6. Ohmic Contacts to n-type GaSb and n-type GaInAsSb

    SciTech Connect

    R.K. Huang; C.A. Wang; C.T. Harris; M.K. Connors; D.A. Shiau

    2003-06-16

    An investigation with the objective of improving n-type ohmic contacts to GaSb-based devices is described. This study involves a series of n-GaInAsSb and n-GaSb samples with varying doping, grown on both n-GaSb and semi-insulating GaAs substrates. These samples were fabricated into mesa-etched TLM structures, and the specific contact resistivity and sheet resistance of these layers as a function of majority electron concentration were measured. Extremely low specific contact resistivities of about 2 x 10{sup -6} {Omega}-cm{sup 2} and sheet resistances of about 4 {Omega}/{open_square} are found for n-type GaInAsSb doped at about 3 x 10{sup 18} cm{sup -3}.

  7. Antireflection coatings for GaAs solar cell applications

    NASA Astrophysics Data System (ADS)

    Alexieva, Z. I.; Nenova, Z. S.; Bakardjieva, V. S.; Milanova, M. M.; Dikov, Hr M.

    2010-04-01

    A double-layer structure of Al2O3 over ZrO2 film is studied. Minimization of the average weighted reflectance is carried out to optimize the thickness of the two layers in the antireflection coating. An optimal value of 2.17% for the weighted average reflection is estimated. The optimal thicknesses of the layers are 49 nm for the bottom and 45 nm for the top layer. Low temperature spin coating technique is used to deposit ZrO2 and Al2O3 films from sol gel solutions on polished silicon wafers, GaAs multilayer heterostructures and AlGaAs/GaAs solar cells. The density of the short-circuit photocurrent increases from 25 mA.cm-2 for solar cells without an antireflection coating to 36 mA.cm-2 for those with a double layer coating.

  8. The binding energies of a bulged GaAs nanowire

    NASA Astrophysics Data System (ADS)

    Zamani, A.; Estabar, Th.; Safarpour, Gh.; Moradi, M.

    2014-12-01

    As it is well-known the electronic structure of the semiconductor nanostructures are so sensitive to alteration of confinement while the nanostructure morphology often determines the confinement. Accordingly existence of a bulge on the wire surface will affect the features of the nanowire. In the present work we consider an on-center hydrogenic donor impurity in a GaAs nanowire with bulge. The ground and first excited states energy levels as well as their binding energies are calculated as functions of bulge and nanowire radius. It is found that both the energy levels and binding energies are strongly influenced by the bulge size for ultrafine nanowires. For large wire radii the effects of bulge existence is trivial and the electronic properties of the system approach to those of the simple nanowire.

  9. Thermal annealing of GaAs concentrator solar cells

    NASA Technical Reports Server (NTRS)

    Curtis, H. B.; Brinker, David J.

    1991-01-01

    Isochronal and isothermal annealing tests were performed on GaAs concentrator cells which were irradiated with electrons of various energies to fluences up to 1 x 10(exp 16) e/sq cm. The results include: (1) For cells irradiated with electrons from 0.7 to 2.3 MeV, recovery decreases with increasing electron energy. (2) As determined by the un-annealed fractions, isothermal and isochronal annealing produce the same recovery. Also, cells irradiated to 3 x 10(exp 15) or 1 x 10(exp 16) e/sq cm recover to similar un-annealed fractions. (3) Some significant annealing is being seen at 150 C although very long times are required.

  10. Morphology of thermal oxide layers on GaAs

    NASA Astrophysics Data System (ADS)

    Beserman, R.; Schwarz, S. A.; Hwang, D. M.; Chen, C. Y.

    1991-08-01

    The oxidation process of pure GaAs has been studied with use of several complementary experimental techniques: Raman scattering, electrical conductivity, transmission electron microscopy, and secondary-ion mass spectrometry. The morphology of the oxide layer and the oxide-GaAs interface evolve as a function of oxidation time. A high density of well-oriented As microcrystallites penetrates into the substrate, forming a conductive interfacial layer in the early stages of the oxidation process. After longer oxidation times, when the Raman As intensity and the interfacial conductivity are reduced, As is distributed into the oxide layer, forming crystallites that are no longer well oriented. Simultaneously, the crystalline gallium oxide breaks up to into microcrystallites that could provide channels for the outdiffusion of As. From the experimental evidence, we deduce that the interfacial density of crystalline As is reduced for long oxidation times.

  11. High gain GaAs photoconductive semiconductor switches: Switch longevity

    SciTech Connect

    Loubriel, G.M.; Zutavern, F.J.; Mar, A.

    1998-07-01

    Optically activated, high gain GaAs switches are being tested for many different pulsed power applications that require long lifetime (longevity). The switches have p and n contact metallization (with intentional or unintentional dopants) configured in such a way as to produce p-i-n or n-i-n switches. The longevity of the switches is determined by circuit parameters and by the ability of the contacts to resist erosion. This paper will describe how the switches performed in test-beds designed to measure switch longevity. The best longevity was achieved with switches made with diffused contacts, achieving over 50 million pulses at 10 A and over 2 million pulses at 80 A.

  12. Effect of illumination uniformity on GaAs photoconductive switches

    SciTech Connect

    Donaldson, W.R.; Mu, L. . Lab. for Laser Energetics)

    1994-12-01

    The dynamic behavior of a GaAs photoconductive switch was studied with an electro-optic imaging system during the first 2 ns after optical illumination. The switch behavior changed as a function of the spatial distribution of the optical illumination. Symmetric and asymmetric illumination schemes were investigated experimentally with their electro-optic imaging system. The electric fields were significantly enhanced in the regions of low photo-carrier density. Approximately 1 ns after illumination the simple longitudinal variation of the electric field gave way to nonuniform transverse structure. The experimental results were modeled by treating the switch as an integral part of a transmission line consisting of discrete elements. The experimental results matched the predictions of the transmission-line model in terms of the electric-field enhancements and efficiency.

  13. Adsorption of Te on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Gobil, Y.; Cibert, J.; Saminadayar, K.; Tatarenko, S.

    1989-04-01

    We present a diagram of the GaAs-Te surface, precursor of the molecular beam epitaxy of CdTe on GaAs(100), as a function of As/Ga stoichiometry and Te coverage. In particular, three new GaAs-Te superstructures are reported: (2 × 1), "Te-poor" (6 × 1) and a (∗ × 3) incommensurate phase. Conditions of formation of the different surfaces are detailed and these surfaces are characterized using reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). On these surfaces, tellurium can be adsorbed on different sites: the Te3d {5}/{2} XPS line reveals three components located at 573.0, 572.6 and 572.1 eV which we attribute to Te mainly bound to As, to Ga and to adsorbed Te respectively, the relative population of these states depending on the precursor surface.

  14. Polarization induced doped transistor

    DOEpatents

    Xing, Huili; Jena, Debdeep; Nomoto, Kazuki; Song, Bo; Zhu, Mingda; Hu, Zongyang

    2016-06-07

    A nitride-based field effect transistor (FET) comprises a compositionally graded and polarization induced doped p-layer underlying at least one gate contact and a compositionally graded and doped n-channel underlying a source contact. The n-channel is converted from the p-layer to the n-channel by ion implantation, a buffer underlies the doped p-layer and the n-channel, and a drain underlies the buffer.

  15. XPS and AFM Study of GaAs Surface Treatment

    SciTech Connect

    Contreras-Guerrero, R.; Wallace, R. M.; Aguirre-Francisco, S.; Herrera-Gomez, A.; Lopez-Lopez, M.

    2008-11-13

    Obtaining smooth and atomically clean surfaces is an important step in the preparation of a surface for device manufacturing. In this work different processes are evaluated for cleaning a GaAs surface. A good surface cleaning treatment is that which provides a high level of uniformity and controllability of the surface. Different techniques are useful as cleaning treatments depending on the growth process to be used. The goal is to remove the oxygen and carbon contaminants and then form a thin oxide film to protect the surface, which is easy to remove later with thermal desorption mechanism like molecular beam epitaxy (MBE) with minimal impact to the surface. In this study, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the structure of the surface, the composition, as well as detect oxygen and carbon contaminant on the GaAs surface. This study consists in two parts. The first part the surface was subjected to different chemical treatments. The chemical solutions were: (a)H{sub 2}SO{sub 4}:H{sub 2}O{sub 2}:H{sub 2}O(4:1:100), (b) HCl: H{sub 2}O(1:3), (c)NH{sub 4}OH 29%. The treatments (a) and (b) reduced the oxygen on the surface. Treatment (c) reduces carbon contamination. In the second part we made MOS devices on the surfaces treated. They were characterized by CV and IV electrical measurements. They show frequency dispersion.

  16. Vacancy and Doping States in Monolayer and bulk Black Phosphorus.

    PubMed

    Guo, Yuzheng; Robertson, John

    2015-09-18

    The atomic geometries and transition levels of point defects and substitutional dopants in few-layer and bulk black phosphorus are calculated. The vacancy is found to reconstruct in monolayer P to leave a single dangling bond, giving a negative U defect with a +/- transition level at 0.24 eV above the valence band edge. The V(-) state forms an unusual 4-fold coordinated site. In few-layer and bulk black P, the defect becomes a positive U site. The divacancy is much more stable than the monovacancy, and it reconstructs to give no deep gap states. Substitutional dopants such as C, Si, O or S do not give rise to shallow donor or acceptor states but instead reconstruct to form non-doping sites analogous to DX or AX centers in GaAs. Impurities on black P adopt the 8-N rule of bonding, as in amorphous semiconductors, rather than simple substitutional geometries seen in tetrahedral semiconductors.

  17. Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride.

    PubMed

    Lin, Shisheng; Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhang, Shengjiao; Zhong, Huikai; Wu, Zhiqian; Xu, Wenli; Chen, Hongsheng

    2015-01-01

    MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells. PMID:26458358

  18. Quantitative description of photoexcited scanning tunneling spectroscopy and its application to the GaAs(110) surface

    NASA Astrophysics Data System (ADS)

    Schnedler, M.; Portz, V.; Weidlich, P. H.; Dunin-Borkowski, R. E.; Ebert, Ph.

    2015-06-01

    A quantitative description of photoexcited scanning tunneling spectra is developed and applied to photoexcited spectra measured on p -doped nonpolar GaAs(110) surfaces. Under illumination, the experimental spectra exhibit an increase of the tunnel current at negative sample voltages only. In order to analyze the experimental data quantitatively, the potential and charge-carrier distributions of the photoexcited tip-vacuum-semiconductor system are calculated by solving the Poisson as well as the hole and electron continuity equations by a finite-difference algorithm. On this basis, the different contributions to the tunnel current are calculated using an extension of the model of Feenstra and Stroscio to include the light-excited carrier concentrations. The best fit of the calculated tunnel currents to the experimental data is obtained for a tip-induced band bending, which is limited by the partial occupation of the C3 surface state by light-excited electrons. The tunnel current at negative voltages is then composed of a valence band contribution and a photoinduced tunnel current of excited electrons in the conduction band. The quantitative description of the tunnel current developed here is generally applicable and provides a solid foundation for the quantitative interpretation of photoexcited scanning tunneling spectroscopy.

  19. Interface designed MoS2/GaAs heterostructure solar cell with sandwich stacked hexagonal boron nitride

    PubMed Central

    Lin, Shisheng; Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhang, Shengjiao; Zhong, Huikai; Wu, Zhiqian; Xu, Wenli; Chen, Hongsheng

    2015-01-01

    MoS2 is a layered two-dimensional semiconductor with a direct band gap of 1.8 eV. The MoS2/bulk semiconductor system offers a new platform for solar cell device design. Different from the conventional bulk p-n junctions, in the MoS2/bulk semiconductor heterostructure, static charge transfer shifts the Fermi level of MoS2 toward that of bulk semiconductor, lowering the barrier height of the formed junction. Herein, we introduce hexagonal boron nitride (h-BN) into MoS2/GaAs heterostructure to suppress the static charge transfer, and the obtained MoS2/h-BN/GaAs solar cell exhibits an improved power conversion efficiency of 5.42%. More importantly, the sandwiched h-BN makes the Fermi level tuning of MoS2 more effective. By employing chemical doping and electrical gating into the solar cell device, PCE of 9.03% is achieved, which is the highest among all the reported monolayer transition metal dichalcogenide based solar cells. PMID:26458358

  20. Deep Levels in p-Type InGaAsN Lattice Matched to GaAs

    SciTech Connect

    Allerman, A.A.; Jones, E.D.; Kaplar, R.J.; Kurtz, S.R.; Kwon, D.; Ringel, S.A.

    1999-03-02

    Deep level transient spectroscopy (DLTS) measurements were utilized to investigate deep level defects in metal-organic chemical deposition (MOCVD)-grown unintentionally doped p-type InGaAsN films lattice matched to GaAs. The as-grown material displayed a high concentration of deep levels distributed within the bandgap, with a dominant hole trap at E{sub v} + 0.10 eV. Post-growth annealing simplified the deep level spectra, enabling the identification of three distinct hole traps at 0.10 eV, 0.23 eV, and 0.48 eV above the valence band edge, with concentrations of 3.5 x 10{sup 14} cm{sup {minus}3}, 3.8 x 10{sup 14} cm{sup {minus}3}, and 8.2 x 10{sup 14} cm{sup {minus}3}, respectively. A direct comparison between the as-grown and annealed spectra revealed the presence of an additional midgap hole trap, with a concentration of 4 x 10{sup 14} cm{sup {minus}3} in the as-grown material. The concentration of this trap is sharply reduced by annealing, which correlates with improved material quality and minority carrier properties after annealing. Of the four hole traps detected, only the 0.48 eV level is not influenced by annealing, suggesting this level may be important for processed InGaAsN devices in the future.

  1. Carrier effects on the excitonic absorption in GaAs quantum-well structures: Phase-space filling

    SciTech Connect

    Huang, D.; Chyi, J.; Morkoc, H. )

    1990-09-15

    The carrier effects on the excitonic absorption in GaAs quantum-well structures have been investigated both theoretically and experimentally. A two-dimensional model was used to calculate the oscillator strength and binding energy of excitons associated with filled subbands, with phase-space filling being taken into account. The calculation gives explicitly the oscillator strength of excitons as a function of two-dimensional carrier density. The results are compared with measured absorption data from a series of {ital p}-type modulation-doped GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As multiple-quantum-well structures, and quantitative agreement is obtained. The calculation shows that the effect of phase-space filling on the binding energy of a bound state can be described by an effective dielectric constant as a function of carrier density. It predicts the decrease of exciton binding energy with carrier density due to phase-space filling, which has been experimentally observed.

  2. High-power question - Will diamonds be the next GaAs?

    NASA Astrophysics Data System (ADS)

    Manz, Barry

    1988-05-01

    It is shown that, due to the outstanding properties of diamond material, diamond technology offers much promise for microwave power generation. For example, diamond exhibits high dielectric breakdown voltage (10 to the 7th V, 50 times that of conventional semiconductors such as GaAs), high thermal conductivity (20 W/cm per C, which is about four times that of Cu), a low dielectric constant (5.5, half that of GaAs), and high saturated carrier velocity (2.7 times that of GaAs, Si, or InP). Moreover, unlike GaAs, Si, or InP, the saturated carrier velocity of diamond maintains its high rate in electric fields of increasing intensity. However, the process of growing pure thin-film material is still at experimental stages. The approaches used in growing diamond by the laboratories in the U.S, USSR, and Japan are discussed.

  3. Fracture strength of GaAs solar cells as a function of manufacturing process steps

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1985-01-01

    Fracture of single crystal GaAs substrate during the solar cell processing is an important factor in solar cell yield and cost. Fracture mechanics technique was utilized to evaluate cell cracking characteristics and changes in fracture strength of GaAs solar cells in a present state-of-the-art of manufacturing process for GaAs solar cells from wafer to complete cell of a typical production line. Considerable change in the fracture strength of GaAs solar cells as a function of cell processing was found. The strength data were described by Weibull statistical analysis and can be interpreted with the change of flaw distribution of each of the manufacturing process steps.

  4. Consideration of velocity saturation in the design of GaAs varactor diodes

    NASA Technical Reports Server (NTRS)

    Crowe, Thomas W.; Peatman, William C. B.; Zimmermann, Ruediger; Zimmermann, Ralph

    1993-01-01

    The design of GaAs Schottky barrier varactor diodes is reconsidered in light of the recent discovery of velocity saturation effects in these devices. Experimental data is presented which confirms that improved multiplier performance can be achieved.

  5. GaAs monolithic R.F. modules for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Cauley, Michael A.

    1991-01-01

    Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

  6. Direct Observation of the E_ Resonant State in GaAs1-xBix

    SciTech Connect

    Alberi, Kirstin; Beaton, Daniel A.; Mascarenhas, Angelo

    2015-12-15

    Bismuth-derived resonant states with T2 symmetry are detected in the valence band of GaAs1-xBix using electromodulated reflectance. A doublet is located 42 meV below the valence band edge of GaAs that is split by local strain around isolated Bi impurity atoms. A transition associated with a singlet is also observed just above the GaAs spin orbit split-off band. These states move deeper into the valence band with increasing Bi concentration but at a much slower rate than the well-known giant upward movement of the valence band edge in GaAs1-xBix. Our results provide key new insights for clarifying the mechanisms by which isovalent impurities alter the bandstructure of the host semiconductor.

  7. Free-standing GaAs nanowires growth on ITO glass by MOCVD

    NASA Astrophysics Data System (ADS)

    Wu, D.; Tang, X. H.; Olivier, A.; Li, X. Q.

    2015-04-01

    GaAs nanowires (NWs) are directly grown on indium tin oxide (ITO) glass substrate by metalorganic chemical vapour deposition (MOCVD), using Au nanoparticles (NPs) as catalyst. By functionalization of the ITO glass and optimization of the Au NPs deposition time, the Au NPs area density deposited on the ITO glass reaches 92 NP μm-2. Uniform and free-standing GaAs NWs without kinking or worm-shape defects have been grown at 430 °C. More than 96% of the NWs have tilt angles larger than 45° with respect of the substrate. The effects of the growth temperature and the Au NPs size on the GaAs NWs growth rate, the NW diameter, and tapering effect are investigated. These results of GaAs NWs growth are the essential step for understanding III-V NWs integration on transparent conductive oxide coated low cost substrate and developing high efficiencyhybrid solar cells.

  8. Accelerated life testing and temperature dependence of device characteristics in GaAs CHFET devices

    NASA Technical Reports Server (NTRS)

    Gallegos, M.; Leon, R.; Vu, D. T.; Okuno, J.; Johnson, A. S.

    2002-01-01

    Accelerated life testing of GaAs complementary heterojunction field effect transistors (CHFET) was carried out. Temperature dependence of single and synchronous rectifier CHFET device characteristics were also obtained.

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  11. Neuropathology in respiratory-related motoneurons in young Pompe (Gaa(-/-)) mice.

    PubMed

    Turner, Sara M F; Hoyt, Aaron K; ElMallah, Mai K; Falk, Darin J; Byrne, Barry J; Fuller, David D

    2016-06-15

    Respiratory and/or lingual dysfunction are among the first motor symptoms in Pompe disease, a disorder resulting from absence or dysfunction of the lysosomal enzyme acid α-glucosidase (GAA). Here, we histologically evaluated the medulla, cervical and thoracic spinal cords in 6 weeks old asymptomatic Pompe (Gaa(-/-)) mice to determine if neuropathology in respiratory motor regions has an early onset. Periodic acid-Schiff (PAS) staining indicated glycogen accumulation was exclusively occurring in Gaa(-/-) hypoglossal, mid-cervical and upper thoracic motoneurons. Markers of DNA damage (Tunel) and ongoing apoptosis (Cleaved Caspase 3) did not co-localize with PAS staining, but were prominent in a medullary region which included the nucleus tractus solitarius, and also in the thoracic spinal dorsal horn. We conclude that respiratory-related motoneurons are particularly susceptible to GAA deficiency and that neuronal glycogen accumulation and neurodegeneration may occur independently in early stage disease. The data support early therapeutic intervention in Pompe disease. PMID:26921786

  12. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells were manufactured with both GaAs and InP, and the improved optical absorption was demonstrated. Preferred parameters for various applications are listed and discussed.

  13. New dynamic FET logic and serial memory circuits for VLSI GaAs technology

    NASA Technical Reports Server (NTRS)

    Eldin, A. G.

    1991-01-01

    The complexity of GaAs field effect transistor (FET) very large scale integration (VLSI) circuits is limited by the maximum power dissipation while the uniformity of the device parameters determines the functional yield. In this work, digital GaAs FET circuits are presented that eliminate the DC power dissipation and reduce the area to 50% of that of the conventional static circuits. Its larger tolerance to device parameter variations results in higher functional yield.

  14. Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

    NASA Technical Reports Server (NTRS)

    Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

    1988-01-01

    The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

  15. Basic mechanisms study for MIS solar cell structures on GaAs

    NASA Technical Reports Server (NTRS)

    Fonash, S. J.

    1978-01-01

    The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

  16. Possibility of incongruous interface behavior of In on GaAs(110)

    NASA Astrophysics Data System (ADS)

    Chin, K. K.; Lindau, I.

    1985-11-01

    Photoemission spectroscopy has been used to study the Schottky-barrier formation of In on n- and p-type GaAs(110) interfaces. Our result is different from that reported by R. R. Daniels et al. [J. Vac. Sci. Technol. A 2(2), 831 (1984)]. It is suggested that this incongruous behavior of In on GaAs(110) is due to the kinetics of interface defect formation. Various experimental details which may affect the kinetics are also discussed.

  17. Electron transfer and capture dynamics in ZnSe quantum wells grown on GaAs

    SciTech Connect

    Dongol, A.; Wagner, H. P.

    2013-12-04

    We investigate the transfer and capture dynamics of electrons in phase coherent photorefractive ZnSe quantum wells grown on GaAs using degenerate three-beam four-wave-mixing. The measurements reveal electron capture times by the quantum well in the order of several tens of picoseconds and a transit time of approximately 5 picoseconds from the GaAs substrate through the ZnMgSe barrier.

  18. High quality superconducting NbN thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Marsili, Francesco; Gaggero, Alessandro; Li, Lianhe H.; Surrente, Alessandro; Leoni, Roberto; Lévy, Francis; Fiore, Andrea

    2009-09-01

    A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature TS = 400 °C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar+N2 plasma. 5.5 nm thick NbN films on GaAs exhibit TC = 10.7 K, ΔTC = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

  19. Enhanced light absorption in GaAs solar cells with internal Bragg reflectors

    NASA Astrophysics Data System (ADS)

    Tobin, S. P.; Vernon, S. M.; Sanfacon, M. M.; Mastrovito, A.

    The use of epitaxial multilayer dielectric mirrors (Bragg reflectors) as back-surface reflectors in thin-film GaAs solar cells on GaAs and silicon substrates is investigated. Al0.3Ga0.9As/Al0.85Ga0.15As Bragg reflectors were grown by low-pressure MOCVD on GaAs substrates and shown to exhibit near-ideal optical reflectance and structural perfection. Thin GaAs solar cells grown on Bragg reflectors showed increases in short-circuit current (0.5 to 1.0 mA/sq cm) and efficiency (0.7 percentage points) relative to cells without back reflectors. Efficiencies of 24.7 percent at one sun AM1.5 were measured for GaAs cells only 2 microns thick on Bragg reflectors. In addition to the optical enhancements, Bragg reflectors also appear to improve the defect structure of GaAs-on-Si solar cells. This approach should lead to improved efficiency for GaAs-on-Si solar cells and improved radiation resistance on GaAs cells.

  20. Antireflective disordered subwavelength structure on GaAs using spin-coated Ag ink mask.

    PubMed

    Yeo, Chan Il; Kwon, Ji Hye; Jang, Sung Jun; Lee, Yong Tak

    2012-08-13

    We present a simple, cost-effective, large scale fabrication technique for antireflective disordered subwavelength structures (d-SWSs) on GaAs substrate by Ag etch masks formed using spin-coated Ag ink and subsequent inductively coupled plasma (ICP) etching process. The antireflection characteristics of GaAs d-SWSs rely on their geometric profiles, which were controlled by adjusting the distribution of Ag etch masks via changing the concentration of Ag atoms and the sintering temperature of Ag ink as well as the ICP etching conditions. The fabricated GaAs d-SWSs drastically reduced the reflection loss compared to that of bulk GaAs (>30%) in the wavelength range of 300-870 nm. The most desirable GaAs d-SWSs for practical solar cell applications exhibited a solar-weighted reflectance (SWR) of 2.12%, which is much lower than that of bulk GaAs (38.6%), and its incident angle-dependent SWR was also investigated.