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Sample records for semi-insulating gaas doped

  1. Depth uniformity of electrical properties and doping limitation in neutron-transmutation-doped semi-insulating GaAs

    SciTech Connect

    Satoh, M.; Kuriyama, K. ); Kawakubo, T. )

    1990-04-01

    Depth uniformity of electrical properties has been evaluated for neutron-transmutation-doped (NTD), semi-insulating GaAs irradiated with thermal neutrons of 1.5{times}10{sup 18} cm{sup {minus}2} by the van der Pauw method combined with iterative etching of the surface. In NTD-GaAs wafers (thickness {similar to}410 {mu}m) annealed for 30 min at 700 {degree}C, the depth profiles of the resistivity, the carrier concentration, and the Hall mobility show constant values of 1{times}10{sup {minus}2} {Omega} cm, 2.0{times}10{sup 17} cm{sup {minus}3}, and 3100 cm{sup 2}/V s, respectively, within an experimental error of 5%. In an annealing process, the redistribution and/or the segregation of NTD impurities is not observed. We also discuss the limitations of low-level NTD in semi-insulating GaAs. It is suggested that the activation of the NTD-impurities below {similar to}1{times}10{sup 16} cm{sup {minus}3} is mainly restricted by the presence of the midgap electron trap (EL2).

  2. 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.

  3. 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.

  4. Slow domains in semi-insulating GaAs

    SciTech Connect

    Neumann, A.

    2001-07-01

    Semi-insulating GaAs shows current oscillations if a high dc voltage is applied to a sample. These oscillations are caused by traveling high-electric-field domains that are formed as a result of electric-field-enhanced electron trapping. This article describes the various types of experiments that have been carried out with this system, including recent ones that use the electro-optic Pockels effect in order to measure the local electric fields in the sample in a highly accurate manner. An historical overview of the theoretical developments is given and shows that no satisfying theory is currently available. A list of all the required ingredients for a successful theory is provided and the experimental data are explained in a qualitative manner. Furthermore, the main electron trap in semi-insulating GaAs is the native defect EL2, the main properties of which are described. {copyright} 2001 American Institute of Physics.

  5. Undoped semi-insulating LEC GaAs - A model and a mechanism. [Liquid Encapsulated Czochralski

    NASA Technical Reports Server (NTRS)

    Oliver, J. R.; Fairman, R. D.; Chen, R. T.; Yu, P. W.

    1981-01-01

    Undoped semi-insulating GaAs grown by the high-pressure liquid encapsulated Czochralski (LEC) method has been produced for use in direct ion implantation in several laboratories. A clear understanding of the factors controlling impurity transport and compensation in these materials has been lacking to date. In this work, detailed characterization has been performed on undoped semi-insulating crystals grown from both SiO2 and PBN crucibles followed by a proposed impurity model and compensation mechanism.

  6. 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.

  7. 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.

  8. Role of electrode metallization in performance of semi-insulating GaAs radiation detectors

    NASA Astrophysics Data System (ADS)

    Dubecký, František; Boháček, Pavol; Sekáčová, Mária; Zaťko, Bohumír; Lalinský, Tibor; Linhart, Vladimír; Šagátová-Perd'ochová, Andrea; Mudroň, Ján; Pospíšil, Stanislav

    2007-06-01

    In the present work, a comparative study of semi-insulating (SI) GaAs radiation detectors with different blocking (Schottky) and ohmic contact metallization is presented. The detectors fabricated from "detector-grade" bulk SI GaAs are characterized by current-voltage measurements and their detection performance is evaluated from pulse-height spectra of 241Am and 57Co γ-sources. Observed results are evaluated and discussed. Importance of the optimized electrodes technology of SI GaAs detector with good performance is demonstrated.

  9. 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.

  10. Native and irradiation-induced monovacancies in n -type and semi-insulating GaAs

    SciTech Connect

    Corbel, C.; Pierre, F. ); Hautojaervi, P.; Saarinen, K. ); Moser, P. )

    1990-05-15

    Defects induced by electron irradiation in semi-insulating and {ital n}-type GaAs crystals have been characterized by positron-lifetime measurements. We conclude that electron irradiation with energies of 1.5--3 MeV produces negative monovacancies and negative ions at low and room temperature. The results also show that the native monovacancy defects in lightly {ital n}-type GaAs change their properties under irradiation. We relate this change to the existence of an ionization level {minus}{r arrow}0 or 0{r arrow}+ of the native monovacancy defects in the upper half of the band gap. We propose that irradiation produces negative Ga{sub As} antisites and negative {ital V}{sub Ga} vacancies. In {ital n}-type GaAs the behavior of the native defects under irradiation is in agreement with their earlier assignment to {ital V}{sub As}.

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

    NASA Astrophysics Data System (ADS)

    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 generation and detection with sub-picosecond carrier lifetime made by C12 (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 (C12) ions. With an increase of the irradiation dose from ~1012 /cm2 to ~1015 /cm2 the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, resulting in strongly improved THz pulse detection compared with normal SI-GaAs.

  12. Photoquenching phenomenon enhanced by proton irradiation in semi-insulating GaAs

    SciTech Connect

    Kuriyama, K.; Takahashi, H.; Kawahara, H. ); Hayashi, N.; Watanabe, H.; Sakamoto, I. ); Kohno, I. )

    1990-12-15

    In undoped semi-insulating GaAs, we have found that the quenching phenomena of photoconductance and infrared absorption are enhanced by proton irradiation above 10{sup 13} /cm{sup 2}, accompanied by an increase in near-band-edge infrared absorption. These phenomena disappear with the annihilation of the proton-induced near-band absorption by annealing at 350 {degree}C. It is suggested that the enhanced photoquenching phenomena arise from the increase in the quenchable component due to the transition from the ionized midgap electron trap (EL2{sup +}) to the neutral EL2{sup 0}.

  13. ``EL2'' revisited: Observation of metastable and stable energy levels of EL2 in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Kabiraj, D.; Ghosh, Subhasis

    2005-12-01

    By using a combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in light of the recently proposed models for EL2 in GaAs.

  14. Complete set of deep traps in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Pavlović, M.; Desnica, U. V.; Gladić, J.

    2000-10-01

    Reevaluation and recalculation of thermally stimulated current (TSC) data from semi-insulating (SI) GaAs, published by many different authors over a period of three decades were done by means of the new analytical method, simultaneous multiple peak analysis (SIMPA). The SIMPA procedure clearly resolved contributions from various overlapping TSC peaks and enabled the precise determination of signatures (activation energy, Ea and capture cross section, σ) of all observed deep traps. The analyzed TSC spectra refer to SI GaAs samples that have been grown/treated in quite different ways (various growth techniques, growth under As or Ga rich conditions, different annealing procedures, irradiation with neutrons, γ rays, etc.). Although the SIMPA procedure was applied to apparently quite different TSC spectra, in all cases excellent fits were achieved, with the unique set (or subset from it) of eleven different deep traps, the only difference being in relative and absolute concentrations of traps. Despite a broad variety of samples analyzed in this article, the set of deep traps obtained is the same as the one being previously seen in the narrow range of SI GaAs samples. This finding suggests that this set of traps is a finite and complete set of all defects with deep levels in SI GaAs. It was also concluded that these defects are primarily complexes containing simple native defects.

  15. 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.

  16. Low frequency oscillations in semi-insulating GaAs: a nonlinear analysis.

    PubMed

    Rubinger, R M; da Silva, R L; de Oliveira, A G; Ribeiro, G M; Albuquerque, H A; Rodrigues, W N; Moreira, M V B

    2003-06-01

    We have observed low frequency current oscillations in a semi-insulating GaAs sample grown by low temperature molecular beam epitaxy. For this, an experimental setup proper to measure high impedance samples with small external noise was developed. Spontaneous oscillations in the current were observed for some bias conditions. Although measurements were carried out from room temperature down to liquid helium, the dynamical analysis was carried out around 200 K where the signal to noise ratio was fairly favorable. To increase the data quality we have also used a noise reduction algorithm suitably developed for nonlinear systems. We observed attractors having low embedding dimension, limit cycle bifurcations, and chaotic behavior characteristic of nonlinear dynamical processes in route to chaos. Attractor reconstruction, Poincare sections, Lyapunov exponents, and correlation dimension were also analyzed.

  17. Detection of fast neutrons using detectors based on semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Zat'ko, B.; Sedlačková, K.; Dubecký, F.; Boháček, P.; Sekáčová, M.; Nečas, V.

    2011-12-01

    Detectors with AuZn square Schottky contact of the area of 2.5 × 2.5 mm2 were fabricated. On the back side, the whole area AuGeNi eutectic ohmic contact was evaporated. The thickness of the base material (semi-insulating GaAs) was 220 μm. The connection of 4 detectors in parallel was tested to get the detection area of 25 mm2. The 239Pu-Be fast neutron source with energies between 0.5 and 12 MeV was used in experimental measurements. We have investigated the optimal thickness of HDPE (high-density polyethylene) conversion layer for fast neutron detection. The spectra of the neutrons were measured by detectors covered by HDPE converter of different thicknesses. The fast neutron detection efficiency proved experimentally was compared with results from simulations performed by MCNPX (Monte Carlo N-Particle eXtended) code.

  18. 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.

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

    SciTech Connect

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

    1986-05-01

    We show 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 cm/sup 2//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.

  20. Characterization of semi-insulating GaAs by photoreflectance and photoluminescence

    SciTech Connect

    Durbin, C.M.

    1992-12-31

    Semi-insulating (SI) GaAs was characterized using photoreflectance, a modulation spectroscopy technique. Anomalous splitting was observed in the photoreflectance (PR) response of SI:GaAs in the vicinity of the exciton at 78 K. Recent photoluminescence (PL) measurements suggest the splitting is correlated with the EL2 content of the samples. Separation between the two peaks in PR measurements range from about 2 to 4 meV. A striking effect is that each peak is maximized by a different phase setting of the lock-in. The splitting is sample dependent and is also affected by several other factors including surface conditions, temperature, pump beam intensity and modulation frequency.

  1. Evidence for field enhanced electron capture by EL2 centers in semi-insulating GaAs and the effect on GaAs radiation detectors

    SciTech Connect

    McGregor, D.S.; Rojeski, R.A.; Knoll, G.F. ); Terry, F.L. Jr.; East, J. ); Eisen, Y. )

    1994-06-15

    The performance of Schottky contact semiconductor radiation detectors fabricated from semi-insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi-insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi-insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.

  2. 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.

  3. Introduction of metastable vacancy defects in electron-irradiated semi-insulating GaAs

    SciTech Connect

    Saarinen, K.; Kuisma, S.; Maekinen, J.; Hautojaervi, P.; Toernqvist, M.; Corbel, C.

    1995-05-15

    Positron-lifetime experiments have been performed to investigate the metastability of the point defects produced in the electron irradiation of semi-insulating GaAs. The measurements in darkness indicate the presence of Ga vacancies and Ga antisite defects in a negative charge state. Illumination at 25 K reveals another type of a defect, which has a vacancy in its metastable state. The metastable vacancies can be observed most effectively after illumination with 1.1-eV photons and they are persistent up to the annealing temperature of 80--100 K. The introduction rate of the metastable defects is about 0.3 cm{sup {minus}1}, which is close to the values reported earlier for the As antisite. The metastable properties of the defects resemble those of the well-known {ital EL}2 center in as-grown GaAs. We associate these defects to As antisites, which exhibit the metastability predicted by the theory: in the metastable configuration the As antisite atom relaxes away from the lattice position, leaving a Ga site vacant.

  4. 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.

  5. 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

    2015-03-09

    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.

  6. Electrical properties of unintentionally doped semi-insulating and conducting 6H-SiC

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Mitchell, W. D.; Fang, Z. Q.; Look, D. C.; Smith, S. R.; Smith, H. E.; Khlebnikov, Igor; Khlebnikov, Y. I.; Basceri, C.; Balkas, C.

    2006-08-01

    Temperature dependent Hall effect (TDH), low temperature photoluminescence (LTPL), secondary ion mass spectrometry (SIMS), optical admittance spectroscopy (OAS), and thermally stimulated current (TSC) measurements have been made on 6H-SiC grown by the physical vapor transport technique without intentional doping. n- and p-type as well semi-insulating samples were studied to explore the compensation mechanism in semi-insulating high purity SiC. Nitrogen and boron were found from TDH and SIMS measurements to be the dominant impurities that must be compensated to produce semi-insulating properties. The electrical activation energy of the semi-insulating sample determined from the dependence of the resistivity was 1.0eV. LTPL lines near 1.00 and 1.34eV, identified with the defects designated as UD-1 and UD-3, were observed in all three samples but the intensity of the UD-1 line was almost a factor of 10 more in the n-type sample than in the the p-type sample with that in the semi-insulating sample being intermediate between those two. OAS and TSC experiments confirmed the high purity of this material. The results suggest that the relative concentrations of a dominant deep level and nitrogen and boron impurities can explain the electrical properties in this material.

  7. Investigation of the compensation mechanism in semi-insulating GaAs from alpha-spectra studies at low temperature

    SciTech Connect

    Chen, J.W.; Ebling, D.G.; Geppert, R.; Irsigler, R.; Schmid, T.; Rogalla, M.; Ludwig, J.; Runge, K.

    1997-05-01

    We present the results of charge collection measurements on liquid encapsulated Czochralski grown semi-insulating GaAs devices for alpha particles. Experimental evidence is given which demonstrates a drastic enhancement of charge collection efficiency after prolonged illumination with 1.086 {mu}m below-gap light. The recovery of EL2 from metastable state to normal state can also be achieved by electric field at high bias voltage. The experimental result shows that the EL2 defect is practically the dominant trap for free charge carriers and together with other shallow defects responsible for the electric compensation in semi-insulating GaAs. The metastable transition of the EL2 defect is always simultaneously accompanied by the neutralization of a shallow acceptor. No change in the type of conductivity was found. {copyright} {ital 1997 American Institute of Physics.}

  8. Photoinduced absorption of THz radiation in semi-insulating GaAs crystal

    NASA Astrophysics Data System (ADS)

    Kurdyubov, A. S.; Trifonov, A. V.; Gerlovin, I. Ya.; Ignatiev, I. V.; Kavokin, A. V.

    2017-07-01

    The influence of optical illumination on transmission of THz radiation through a bulk crystal of semi-insulating GaAs is experimentally studied. It is established that, without additional illumination, absorption of electromagnetic waves with a frequency of about 1 THz in the studied crystal is almost absent. Optical illumination in the spectral range of fundamental absorption of the crystal does not affect the transmission of THz waves. At the same time, if the illumination photon energy is a little below the edge of fundamental absorption, i.e., actually in the transparency region, the transmission of THz radiation drops sharply. At liquid helium temperature, the maximum effect is achieved for the energy of optical photons lower by approximately 30 meV than the crystal band gap. Further shift of the illumination toward lower photon energies is accompanied by almost complete recovery of the transmission. With increasing sample temperature, the spectral range of efficient action of the illumination shifts together with the edge of fundamental absorption toward lower photon energies.

  9. Role of deep level trapping on surface photovoltage of semi-insulating GaAs

    SciTech Connect

    Liu, Q.; Ruda, H.E.; Koutzarov, I.P.; Jedral, L.; Chen, G.; Prasad, M.

    1996-12-31

    Dual beam (bias and probe) transient Surface Photovoltage (SPV) measurements were made on undoped Semi-Insulating (SI) GaAs over an extended temperature range. Above 270 K, SPV recovery transients following a bias pulse were shown to reflect near surface conductivity changes; these are in turn controlled by surface/interface state thermal emission. Owing to the absence of a strong surface electric field in this material, the emitted carriers are not immediately removed from the near surface region. The recapturing of the emitted carriers is shown to be responsible for non-exponential conductivity and reciprocal-SPV transients. This behavior is considered to be characteristic of relaxation-type semiconductors with near-surface ungated structures. Below 150 K, the photoinduced transition of EL2 from its ground to metastable state El2* was shown to change the effective electron and hole mobilities and augment the SPV signals immediately following the bias pulse. Thermally induced EL2* recovery above 120 K decreases the SPV signal from its maximum. This decay transient was analyzed and the decay rate fitted to a single exponential. An activation energy of 0.32 eV and a pre-exponential constant of 1.9 {times} 10{sup 12} s{sup {minus}1} were obtained, and attributed to the thermal recovery rate for EL2*.

  10. 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.

  11. 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.

  12. Fe-doping in hydride vapor-phase epitaxy for semi-insulating gallium nitride

    NASA Astrophysics Data System (ADS)

    Richter, E.; Gridneva, E.; Weyers, M.; Tränkle, G.

    2016-12-01

    Fe-doping of GaN layers of 3 in. in diameter and a thickness of 1 mm in a vertical AIX-HVPE reactor is studied. Ferrocen was used as Fe source. It is shown that a sufficient uniformity of growth conditions, a high purity of undoped GaN layers, and a moderate Fe incorporation of 2×1018 cm-3 allow for growth of semi-insulating GaN layers with a sufficiently high specific resistivity even at elevated temperature. This makes the material suitable as substrate for electronic power devices at high power or in harsh ambient.

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

    SciTech Connect

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

    2016-05-15

    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 10{sup 6} shots. The results show that this structure reduces the on-state resistance and extends the longevity of the GaAs PCSS.

  14. Photoresistances of semi-insulating GaAs photoconductive switch illuminated by 1.064 μm laser pulse

    NASA Astrophysics Data System (ADS)

    Wu, Minghe; Zheng, Xiaoming; Ruan, Chengli; Yang, Hongchun; Sun, Yunqing; Wang, Shan; Zhang, Kedi; Liu, Hong

    2009-07-01

    The Shockley-Read-Hall model (SRHM) and its simplified model (SSRHM) were used to describe the characteristics of a photoconductive semiconductor switch (PCSS) made from a semi-insulating (SI) gallium arsenide (GaAs) chip, biased at low voltage, and illuminated by a 1.064 μm laser pulse. These characteristics include the free carrier densities, dynamic photoresistance, and time evolution of output pulses of the PCSS. The deep donor EL2 centers in SI GaAs play a dominant role in both the SRHM and SSRHM as electrons at EL2 unionized centers are strongly excited by the subband-gap photons at the wavelength of 1.064 μm. Theoretical modeling on the evolution of the experimental measured output pulses led to a two-step micromechanism of electron excitation process within the GaAs chip. The minimum photoresistances predicted by the SSRHM are in good agreement with experimental measurements, which confirms the dominant role of EL2 in the generation of electric pulses from a SI GaAs photoconductivity switch on which the 1064 nm laser pulse is illuminated.

  15. Precise determination of deep trap signatures and their relative and absolute concentrations in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Pavlović, M.; Desnica, U. V.

    1998-08-01

    The new analytical method, simultaneous multiple peak analysis (SIMPA) which comprises simultaneous fitting of whole measured thermally stimulated current (TSC) spectra is presented. The procedure clearly resolves contributions from various overlapping TSC peaks, which results in precise determination of trap parameters (signature) for each trap. In combination with photocurrent temperature dependent measurements, IPC(T), which reflects free carrier lifetime temperature dependence, the estimates of relative and absolute trap concentrations were made as well. The advantage of the SIMPA method in comparison with the single peak approach was demonstrated and analyzed. The SIMPA method was applied to different semi-insulating (SI) GaAs samples, particularly to samples having very high and others having very low deep trap concentrations; and for both extremes excellent fits were achieved. The method also seems very promising for characterization of deep levels and other similar SI materials, like SI InP or SI CdTe.

  16. Distributions of residual stress, dislocations, and EL2 in Czochralski-grown semi-insulating GaAs

    SciTech Connect

    Dobrilla, P.; Blakemore, J.S.

    1986-07-01

    Distributions of stress, dislocations, and the EL2 midgap defect have been optically mapped in semi-insulating GaAs wafers, from (100)-grown crystals created by the liquid-encapsulated Czochralski method. The evolution of EL2 along the growth axis indicates that assessment of this property through the majority of the crystal volume is often poorly represented by wafers from near the two end regions. A comparison of maps for stress, dislocation and EL2 patterns as all measured with a given wafer does not support hypotheses that EL2 is a direct consequence either of stress or of dislocations. Other mechanisms, such as segregation and melt dynamics, thus appear more likely to control the formation and distribution of EL2.

  17. Influence of EL2 deep level on photoconduction of semi-insulating GaAs under ultrashort pulse photoinjection

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Xie, Guangyong

    2016-02-01

    To investigate the influence of EL2 deep level on photoconduction of in semi-insulating GaAs (SI-GaAs), a 3 mm-electrode-gap lateral SI-GaAs photoconductive chip was manufactured and tested by using ultrashort pulse laser with 1064 nm wavelength, 10 ns pulsewidth, 3.0 mm light spot diameter and single pulse energy mean of 3.0 mJ. Based on the experimental results and the theory of trapping effect, the photon absorption process of EL2 defects in SI-GaAs is analyzed. For the influence of EL2 deep level, the lifetime of the electron gets shorter and the persistent photoconductivity (PPC) is significant. With increasing of voltage, the decay time constant of photoconduction is reduced and the decay index gets bigger for the ultrashort pulse photoinjection.

  18. Defects induced by protons and {gamma}-rays in semi-insulating GaAs detectors

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Del Papa, C. |; Fuochi, G.; Alietti, M.; Canali, C.; Nava, F. |; Paccagnella, A.; Lanzieri, C.

    1995-09-01

    Semi-insulating gallium arsenide has been irradiated by protons and by gamma-rays with different doses. The irradiation-induced deep level defects have been investigated by current transient spectroscopy to find their energy, capture cross sections and generation rate. Two electron traps at E{sub c}{minus}0.14V(E13) and E{sub c}{minus}0.70eV(E4) and a hole trap at E{sub v}+0.41eV(H2) in addition to the levels existing before the irradiation have been detected in the irradiated samples. These findings have been related to the performance of gallium arsenide charge particle detectors.

  19. Growth of double doped semi-insulating indium phosphide single crystals

    NASA Astrophysics Data System (ADS)

    Toudic, Y.; Coquillé, R.; Gauneau, M.; Grandpierre, G.; Le Maréchal, L.; Lambert, B.

    1987-05-01

    Semi-insulating (SI) InP, co-doped with a shallow acceptor (Hg or Cd) and a deep donor (Ti or Cr) has been grown by the gradient freeze method or by the liquid encapsulated Czochralski (LEC) technique. Three dopant couples have been studied: Hg+Ti, Hg+Cr and Cd+Cr. The crystals have been characterized by spark source mass spectrometry (SSMS), secondary ion mass spectrometry (SIMS) and thermally dependent Hall (TDH) effect using the Van der Pauw technique. Deduced from the activation energy measurements, the donor deep levels of titanium and chromium have been found to be at Ec-0.53 eV and Ev+0.56 eV, respectively. SIMS profiles on SI substrates annealed at 975°C show that SI InP (Ti, Hg) is more thermally stable than SI InP(Fe) and SI InP(Cr, Hg or Cd).

  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.

  1. EL2 deep level defects and above-band gap two-photon absorption in high gain lateral semi-insulating GaAs photoconductive switch

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Wang, Wei; Niu, Hongjian; Zhang, Xianbin; Ji, Weili

    2005-01-01

    Experiments of a lateral semi-insulating GaAs photoconductive switch, both linear and nonlinear mode of the switch were observed when the switch was triggered by 1064 nm laser pulses, with energy of 1.9 mJ and the pulse width of 60 ns, and operated at biased electric field of 4.37 kV/cm. It"s wavelength is longer than 876nm, but the experiments indicate that the semi-insulating GaAs photoconductive switches can absorb 1064 nm laser obviously, which is out of the absorption range of the GaAs material. It is not possible to explain this behavior by using intrinsic absorption mechanism. We think that there are two mostly kinds of absorption mechanisms play a key part in absorption process, they are the two-steps-single-photon absorption that based on the EL2 energy level and two-photon absorption.

  2. Semi-insulating GaAs based detector of fast neutrons produced by D-T nuclear reaction

    NASA Astrophysics Data System (ADS)

    Šagátová, A.; Kubanda, D.; Zat'ko, B.; Sedlačková, K.; Nečas, V.; Solar, M.; Granja, C.

    2016-12-01

    We have examined semi-insulating (SI) GaAs detectors with high density polyethylene (HDPE) conversion layer by a mono-energetic neutrons with kinetic energy of 16.755 MeV generated by a deuterium—tritium nuclear reaction. First, the influence of HDPE layer thickness on the relative detection efficiency of fast neutrons was studied. The MCNPX (Monte Carlo N-particle eXtended) code has been used to support the analysis of the experiment. The theoretical optimum thickness of the conversion layer was determined to 1.9 mm using the MCNPX code. The HDPE conversion layers of various thicknesses, in the range from 50 μ m to 3200 μ m, were glued on the top Schottky contact of SI GaAs detector in the experiment. The neutron detection efficiency was evaluated from measured spectra and compared to results from simulations. The experimental data showed very good agreement with simulation results. Then the effect of active detector thickness modified by detector reverse bias on neutron detection efficiency was studied. Finally, the effect of the angle of irradiation on neutron detection efficiency was evaluated exhibiting decreasing tendency with increasing deviation from perpendicular direction of impinging neutrons.

  3. Photoluminescence of PbS Quantum Dots on Semi-Insulating GaAs (Postprint)

    DTIC Science & Technology

    2010-07-01

    ns ity (a rb .u ni ts ) Energy (eV) 5 K 100 K 200 K 300 K InGaAs...detector. 0 20 40 60 80 100 120 140 0.20 0.40 0.60 0.80 1.00 PL in te ns ity (a rb .u ni ts ) Energy (eV) 5 K 20 K 50 K 100 K 150 K 200 K 250 K 300 K InSb...3.0 0 10 20 30 40 50 0.2 0.4 0.6 0.8 1.0 PL in te ns ity (a rb .u ni ts ) Energy (eV) SI GaAs PbS/SI GaAs5 K FIG. 4. Color online Comparison of the

  4. Gallium vacancies and gallium antisites as acceptors in electron-irradiated semi-insulating GaAs

    SciTech Connect

    Corbel, C.; Pierre, F. ); Saarinen, K.; Hautojaervi, P. ); Moser, P. )

    1992-02-15

    Positron-lifetime measurements show that acceptors are produced in semi-insulating GaAs by 1.5-MeV electron irradiation at 20 K. Two types of acceptors can be separated. The first ones are negative vacancy-type defects which anneal out over a very broad range of temperature between 77 and 500 K. The second ones are negative ion-type defects which are stable still at 450 K. The data show that these two types of defects are independent and do not form close pairs. We attribute both to gallium-related defects. We identify the ion-type acceptors as isolated gallium antisites. The vacancy-type acceptors are identified as gallium vacancies which are isolated or involved in negatively charged complexes. The introduction rate of the gallium antisite is estimated to be 1.8{plus minus}0.3 cm{sup {minus}1} in the fluence range 10{sup 17}--10{sup 18} cm{sup {minus}2} for 1.5-MeV electron irradiation at 20 K.

  5. 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.

  6. Simulating and modeling the breakdown voltage in a semi-insulating GaAs P+N junction diode

    NASA Astrophysics Data System (ADS)

    Resfa, A.; Menezla, Brahimi. R.; Benchhima, M.

    2014-08-01

    This work aims to determine the characteristic I (breakdown voltage) of the inverse current in a GaAs PN junction diode, subject to a reverse polarization, while specifying the parameters that influence the breakdown voltage of the diode. In this work, we simulated the behavior of the ionization phenomenon by impact breakdown by avalanche of the PN junctions, subject to an inverse polarization. We will take into account both the trapping model in a stationary regime in the P+N structure using like material of basis the III-V compounds and mainly the GaAs semi-insulating in which the deep centers have in important densities. We are talking about the model of trapping in the space charge region (SCR) and that is the trap density donor and acceptor states. The carrier crossing the space charge region (SCR) of W thickness creates N electron—hole pairs: for every created pair, the electron and the hole are swept quickly by the electric field, each in an opposite direction, which comes back, according to an already accepted reasoning, to the crossing of the space charge region (SCR) by an electron or a hole. So the even N pair created by the initial particle provoke N2 ionizations and so forth. The study of the physical and electrical behaviour of semiconductors is based on the influence of the presence of deep centers on the characteristic I(V) current-tension, which requires the calculation of the electrostatic potential, the electric field, the integral of ionization, the density of the states traps, the diffusion current of minority in the regions (1) and (3), the current thermal generation in the region (2), the leakage current in the surface, and the breakdown voltage.

  7. Improved thermally stimulated current analysis in semi-insulating GaAs: New conclusions

    SciTech Connect

    Fang, Z.Q.; Look, D.C.

    1996-12-01

    Measurements of EL2{degrees} and EL2{sup +} concentrations by IR absorption and temperature-dependent photocurrent (1.13 eV) and dark current at 80K < T < 300K in semiinsulating GaAs, allow a more accurate analysis of the thermally stimulated current spectrum. We conclude that trap T{sub 2}, at 220K, is related to ASG. and controlled by both EL2{degrees} and EL2{sup +}, and T{sub 3}, at 200K is most likely a V{sub As}-related defect complex.

  8. 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.

  9. Growth of Ru doped semi-insulating InP by low pressure metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Dadgar, A.; Stenzel, O.; Köhne, L.; Näser, A.; Straßburg, M.; Stolz, W.; Bimberg, D.; Schumann, H.

    1998-12-01

    Ruthenium doping has been successfully applied for the growth of semi-insulating (s.i.) InP. In contrast to the 3d-transition metal (TM) Fe, the isovalent 4d-TM Ru exhibits a four orders of magnitude lower diffusion coefficient and shows no interdiffusion with p-type dopants. Most important, Ru compensates electrons as well as holes, a prerequisite for complete compensation under double injection conditions. The growth of Ru doped InP layers has been investigated using bis( η5-2,4-dimethylpentadienyl)ruthenium(II) for Ru doping, different P-precursors (PH 3, TBP, DTBP) and H 2 or N 2 carrier gas.

  10. Modifications of EL2 related stable and metastable defects in semi-insulating GaAs by high energy light ion irradiation

    NASA Astrophysics Data System (ADS)

    Kabiraj, D.; Ghosh, S.

    2005-10-01

    We report the effect of high energy light ion irradiation on the defect energy levels related to the stable and metastable states of EL2 in undoped semi-insulating GaAs. GaAs samples have been irradiated at different fluences with 50 MeV Li ions. The energy of the irradiated ions is chosen in such a way that the range of the ions is more than the sample thickness. So the implantation of the irradiated ions and the formation of the extended defects at the end of the range could be avoided. The modification of the existing native point defects and the formation of new point defects under irradiation have been studied by photocurrent and thermally stimulated current spectroscopic measurements under the photoexcitation of both sub-band gap and above band gap lights.

  11. Optical evaluation of the ionized EL2 fraction in proton (24 GeV) irradiated semi-insulating GaAs

    SciTech Connect

    Ferrini, R.; Galli, M.; Guizzetti, G.; Patrini, M.; Nava, F.

    1997-11-01

    Semi-insulating SI GaAs samples from a zone refined crystal were irradiated with high energy protons (24 GeV/c, fluences up to 1.64{times}10{sup 14}p/cm{sup 2}). Optical spectra in transmittance and reflectance were accurately measured in the energy range of 0.6{endash}1.4 eV to determine, through the absorption coefficient, the concentrations of both neutral and ionized EL2 defects as a function of the proton fluence. Both these concentrations have been shown to increase linearly with the proton fluence; this behavior well explains the remarkable decrease of the charge collection efficiency observed in proton irradiated GaAs detectors at doses associated with high luminosity beams at a new particle collider accelerator (e.g., the LHC at the CERN laboratory). {copyright} {ital 1997 American Institute of Physics.}

  12. Interaction of deep levels and potential fluctuations in scattering and recombination phenomena in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Kažukauskas, V.; Storasta, J.; Vaitkus, J.-V.

    1996-08-01

    The complex influence of recombination centers and potential fluctuations of the band gap on the scattering and recombination phenomena in n-type semiinsulating liquid- encapsulated-Czochralski-grown GaAs were investigated by using the transient photoconductivity and photo-Hall effects. The inhomogeneities cause a hyperbolic decrease of nonequilibrium carrier concentration and the saturation of Hall mobility, while the exponential parts of the decay appear due to the recharge of deep levels. The mean recombination barrier heights of potential fluctuations were evaluated. We propose a complex ``island'' model of scattering and recombination centers, consisting of defect clusters and their associations around dislocations, surrounded by potential barriers. At low light intensities and at the temperatures below 330 K they are insulating for majority charge carriers, thus reducing an effective crystal volume and causing percolation transport effects. At the temperature higher than 330-360 K the main barrier of the island can be recharged or screened by nonequilibrium carriers and its fine barrier structure appears as an effective scatterer, causing a sharp decrease of the nonequilibrium Hall mobility. It was demonstrated that although doping with Sb reduce dislocation density, it can intensify the effect of smaller defects on transport phenomena.

  13. Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tang, H.; Fang, Z. Q.; Rolfe, S.; Bardwell, J. A.; Raymond, S.

    2010-05-01

    Growth of unintentionally doped (UID) semi-insulating GaN on SiC and highly resistive GaN on sapphire using the ammonia molecular-beam epitaxy technique is reported. The semi-insulating UID GaN on SiC shows room temperature (RT) resistivity of 1011 Ω cm and well defined activation energy of 1.0 eV. The balance of compensation of unintentional donors and acceptors is such that the Fermi level is lowered to midgap, and controlled by a 1.0 eV deep level defect, which is thought to be related to the nitrogen antisite NGa, similar to the "EL2" center (arsenic antisite) in unintentionally doped semi-insulating GaAs. The highly resistive GaN on sapphire shows RT resistivity in range of 106-109 Ω cm and activation energy varying from 0.25 to 0.9 eV. In this case, the compensation of shallow donors is incomplete, and the Fermi level is controlled by levels shallower than the 1.0 eV deep centers. The growth mechanisms for the resistive UID GaN materials were investigated by experimental studies of the surface kinetics during growth. The required growth regime involves a moderate growth temperature range of 740-780 °C, and a high ammonia flux (beam equivalent pressure of 1×10-4 Torr), which ensures supersaturated coverage of surface adsorption sites with NHx radicals. Such highly nitrogen rich growth conditions lead to two-dimensional layer by layer growth and reduced oxygen incorporation.

  14. Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

    SciTech Connect

    Tang, H.; Rolfe, S.; Bardwell, J. A.; Raymond, S.; Fang, Z. Q.

    2010-05-15

    Growth of unintentionally doped (UID) semi-insulating GaN on SiC and highly resistive GaN on sapphire using the ammonia molecular-beam epitaxy technique is reported. The semi-insulating UID GaN on SiC shows room temperature (RT) resistivity of 10{sup 11} {Omega} cm and well defined activation energy of 1.0 eV. The balance of compensation of unintentional donors and acceptors is such that the Fermi level is lowered to midgap, and controlled by a 1.0 eV deep level defect, which is thought to be related to the nitrogen antisite N{sub Ga}, similar to the ''EL2'' center (arsenic antisite) in unintentionally doped semi-insulating GaAs. The highly resistive GaN on sapphire shows RT resistivity in range of 10{sup 6}-10{sup 9} {Omega} cm and activation energy varying from 0.25 to 0.9 eV. In this case, the compensation of shallow donors is incomplete, and the Fermi level is controlled by levels shallower than the 1.0 eV deep centers. The growth mechanisms for the resistive UID GaN materials were investigated by experimental studies of the surface kinetics during growth. The required growth regime involves a moderate growth temperature range of 740-780 deg. C, and a high ammonia flux (beam equivalent pressure of 1x10{sup -4} Torr), which ensures supersaturated coverage of surface adsorption sites with NH{sub x} radicals. Such highly nitrogen rich growth conditions lead to two-dimensional layer by layer growth and reduced oxygen incorporation.

  15. High Resolution Parameter-Space from a Two-Level Model on Semi-Insulating GaAs

    NASA Astrophysics Data System (ADS)

    da Silva, S. L.; Viana, E. R.; de Oliveira, A. G.; Ribeiro, G. M.; da Silva, R. L.

    Semi-insulating Gallium Arsenide (SI-GaAs) samples experimentally show, under high electric fields and even at room temperature, negative differential conductivity in N-shaped form (NNDC). Since the most consolidated model for n-GaAs, namely, "the model", proposed by E. Schöll was not capable to generate the NNDC curve for SI-GaAs, in this work we have proposed an alternative model. The model proposed, "the two-valley model" is based on the minimal set of generation-recombination equations for two valleys inside of the conduction band, and an equation for the drift velocity as a function of the applied electric field, that covers the physical properties of the nonlinear electrical conduction of the SI-GaAs system. The "two-valley model" was capable to generate theoretically the NNDC region for the first time, and with that, we were able to build a high resolution parameter-space of the periodicity (PSP) using a Periodicity-Detection (PD) routine. In the parameter-space were observed self-organized periodic structures immersed in chaotic regions. The complex regions are presented in a "shrimp" shape rotated around a focal point, which forms in large-scale a "snail shell" shape, with intricate connections between different "shrimps". The knowledge of detailed information on parameter spaces is crucial to localize wide regions of smooth and continuous chaos.

  16. 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.

  17. High energy oxygen irradiation-induced defects in Fe-doped semi-insulating indium phosphide by positron annihilation technique

    NASA Astrophysics Data System (ADS)

    Pan, S.; Mandal, A.; Sohel, Md. A.; Saha, A. K.; Das, D.; Sen Gupta, A.

    2017-02-01

    Positron annihilation technique is applied to study the recovery of radiation-induced defects in 140 MeV oxygen (O6+) irradiated Fe-doped semi-insulating indium phosphide during annealing over a temperature region of 25∘C-650∘C. Lifetime spectra of the irradiated sample are fitted with three lifetime components. Trapping model analysis is used to characterize defect states corresponding to the de-convoluted lifetime values. After irradiation, the observed average lifetime of positron τavg = 263 ps at room temperature is higher than the bulk lifetime by 21 ps which reveals the presence of radiation-induced defects in the material. A decrease in τavg occurs during room temperature 25∘C to 200∘C indicating the dissociation of higher order defects, might be due to positron trapping in acceptor-type of defects (VIn). A reverse annealing stage is found at temperature range of 250∘C-425∘C for S-parameter probably due to the migration of vacancies and the formation of vacancy clusters. Increase in R-parameter from 325∘C to 425∘C indicates the change in the nature of predominant positron trapping sites. Beyond 425∘C, τavg, S-parameter and R-parameter starts decreasing and around 650∘C, τavg and S-parameter approached almost the bulk value showing the annealing out of radiation-induced defects.

  18. 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.

  19. Fe-doped semi-insulating GaN with solid Fe source grown on (110) Si substrates by NH3 molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Noh, Young Kyun; Lee, Sang Tae; Kim, Moon Deock; Oh, Jae Eung

    2017-02-01

    Iron doped GaN layers were grown on (110) Si substrates by ammonia molecular beam epitaxy (MBE) using solid elemental iron as a source. Specular films with concentrations up to 1×1020 cm-3, as determined by secondary ion mass spectroscopy, were grown, unlike a limited incorporation of Fe into GaN by metal-rich rf plasma MBE. The Fe concentration in the film showed an exponential dependence on the inverse of source temperature with an activation energy of 3.4 eV, which agrees well to the reported value for the sublimation of Fe. A 1.5 μm thick GaN film with a sheet resistance of 1 GΩ/sq. was obtained by compensating unintentional residual donors with a small Fe concentration of 1×1017 cm-3. X-ray diffraction rocking curves indicated high crystalline quality, very similar to an undoped film, showing that the Fe incorporation required to obtain the semi-insulating film properties did not affect the structural properties of the film. The low-temperature PL spectra of highly resistive and semi-insulating Fe:GaN in the range of 1017 1018 cm-3 show dominant exciton emissions and enhanced donor-acceptor-pair (DAP) emissions, implying that Fe ions contribute to the DAP transition between donor levels and Fe-related acceptor levels, possibly compensating the residual donors to achieve the semi-insulating electrical properties.

  20. 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.

  1. Characterization of Heavily Doped ALUMINUM(X)GALLIUM(1 -X)ARSENIDE:TELLURIUM Grown on Semi-Insulating Gallium-Arsenide

    NASA Astrophysics Data System (ADS)

    Malloy, Kevin John

    The ability to dope a semiconductor into near metallic conduction widens its usefulness as a material and thereby permits the construction of new devices. Aluminum Gallium Arsenide is no exception. Heavily doped n-type Aluminum Gallium Arsenide has important device applications in tandem junction solar cells and in high electron mobility transistors. Aluminum Gallium Arsenide heavily doped with Tellurium was grown on semi-insulating Gallium Arsenide using liquid phase epitaxy. It was found that the addition of 0.4 atomic percent Tellurium to the melt reduced the Aluminum content of solid Aluminum Gallium Arsenide by up to 20 percent. A model was offered for this behavior involving a differential in the degree of association between Aluminum-Tellurium and Gallium-Tellurium in the liquid phase epitaxial melt. The electrical properties of n-type Aluminum Gallium Arsenide grown on semi-insulating Gallium Arsenide were modeled as a two sheet conductor. The two conductors consisted of the epitaxial n-type Aluminum Gallium Arsenide layer and the induced two dimensional electron gas present at the n-type Aluminum Gallium Arsenide-Gallium Arsenide heterojunction. This model showed the two dimensional electron gas as responsible for the constant low temperature carrier concentration observed experimentally. It also successfully explained the observation of a slope equal to the donor ionization potential instead of the donor ionization potential divided by two in the plot of the log of the carrier concentration versus reciprocal temperature. Because of the chemically independent nature of the deep donor ionization potential in Aluminum Gallium Arsenide, a minima interaction model was introduced to describe the donor level. The major matrix elements were determined to be V(,LX) = 4mV (+OR-) 1mV and V(,LL) = 40mV (+OR-) 10mV. These minima interaction matrix elements were an order of magnitude larger than suggested by theory, thus indicating the possible non-coulombic nature of

  2. EL2 distributions in doped and undoped liquid encapsulated Czochralski GaAs. [deep donor concentration

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Yang, J.

    1983-01-01

    The longitudinal and radial distributions of EL2 in undoped semi-insulating and intentionally doped n-type GaAs crystals grown by the liquid encapsulated Czochralski technique are compared. Longitudinal profiles in undoped crystals are controlled by changes in melt stoichiometry as the crystal is pulled from the melt. EL2 profiles along crystals doped above about 1 x 10 to the 17th/cu cm, on the other hand, are controlled primarily by the carrier concentration as a result of the suppression of EL2 by free electrons. Radial EL2 profiles are typically W shaped and M shaped in undoped and doped (above threshold) crystals, respectively. The origin of these radial profiles is discussed in terms of residual stress, melt stoichiometry, and the suppresion of EL2 by electrons. The results are also discussed in the light of the antisite model for EL2.

  3. EL2 distributions in doped and undoped liquid encapsulated Czochralski GaAs. [deep donor concentration

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Yang, J.

    1983-01-01

    The longitudinal and radial distributions of EL2 in undoped semi-insulating and intentionally doped n-type GaAs crystals grown by the liquid encapsulated Czochralski technique are compared. Longitudinal profiles in undoped crystals are controlled by changes in melt stoichiometry as the crystal is pulled from the melt. EL2 profiles along crystals doped above about 1 x 10 to the 17th/cu cm, on the other hand, are controlled primarily by the carrier concentration as a result of the suppression of EL2 by free electrons. Radial EL2 profiles are typically W shaped and M shaped in undoped and doped (above threshold) crystals, respectively. The origin of these radial profiles is discussed in terms of residual stress, melt stoichiometry, and the suppresion of EL2 by electrons. The results are also discussed in the light of the antisite model for EL2.

  4. 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.

  5. 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.

  6. 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.

  7. Carbon doping of GaAs NWs

    NASA Astrophysics Data System (ADS)

    Salehzadeh Einabad, Omid

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

  8. 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.

  9. The influence of the scatter of heat flux at the m/c interface on the frequency of appearance of poly body and twin defects during 6″ semi-insulating GaAs crystal growth by the VGF method

    NASA Astrophysics Data System (ADS)

    Marchenko, Marina P.; Liu, Weiguo; Badawi, M. Hani; Yin, Phil

    2008-04-01

    The challenge of increasing and maintaining a high yield for 6″ GaAs crystal growth is of utmost importance for meeting the price requirements dictated by today's requirements for semi-insulating GaAs substrates. For maintaining a low dislocation density in the grown ingots, the growth process time is typically long and, sometimes, the final ingots may exhibit twins and poly-crystalline formation. These defects may occur at the beginning of the cylindrical part of the ingot, or even at the conical part of pBN crucible so the whole ingot is rejected. On the other hand, these defects may appear further away from the seed and the location of the onset of these defects will determine the extent of the useful (production worthy) crystal length, also known as "yield". The reasons for the onset of these defects are, however, not fully understood [M. Jurisch, F. Borner, Th. Bunger, St. Eichler, T. Flade, U. Kretser, A. Kohler, J. Stenzenberger, B. Weinert. J. Crystal Growth 275 (2005) 283]. In this study, we conducted numerical simulation using the transient two-dimensional mathematical model of the GaAs crystal growth by vertical gradient freeze method (VGF-method). We defined a new parameter " A" that is equal to the scatter of heat fluxes at m/c interface. Our study showed that some correlation exists between the defect appearance and A-value at m/c interface close to crucible wall. We have found that the frequency of a totally bad crystal length is higher if the A-value exceeds a certain value. Close to the crystal tail the scatter must be less than a defined A-value at the beginning of crystallization. Reduction in A-value was found to occur due to anomalies in the melt flow close to the m/c interface and crucible wall leading to the higher frequency of defects close to the crystal tail. Based on the correlation found, we developed a new technology regime that results in crystals grown with a lower frequency of defect occurrence at crucible wall.

  10. 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.

  11. 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.

  12. A simple and reliable method of thermoelectic effect spectroscopy for semi-insulating III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Huang, Z. C.; Xie, K.; Wie, C. R.

    1991-08-01

    We have developed a simpler and more reliable method of thermoelectric effect spectroscopy (TEES), eliminating the second heater in the technique. We have applied this method to the deep level studies in the semi-insulating undoped or Cr-doped GaAs materials and in the GaAs epitaxial layers grown at a low temperature by molecular beam epitaxy. We have found that the electrical contacts made on front and back surfaces of the sample are more reliable for the TEES measurement than both contacts made on the same surface. In this contact arrangement, the temperature difference of about 1-2 K between the back and front surfaces is enough to produce a clear and reliable TEES data, without the need for a second heater. The results obtained by TEES are consistent with the results obtained by photoinduced transient spectroscopy (PITS) and by thermally stimulated current (TSC) measurements. The TEES results clearly distinguish between the electron traps and the hole traps. We discuss the results on the various semi-insulating GaAs samples and the advantages and limitations of the TEES technique.

  13. GaAs MESFET with lateral non-uniform doping

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    An analytical model of the GaAs MESFET with arbitrary non-uniform doping is presented. Numerical results for linear lateral doping profile are given as a special case. Theoretical considerations predict that better device linearity and improved F(T) can be obtained by using linear lateral doping when doping density increases from source to drain.

  14. Mixed conduction in semi-insulating gallium arsenide

    NASA Astrophysics Data System (ADS)

    Winter, J. J.; Leupold, H. A.; Ross, R. L.; Ballato, A.

    1982-12-01

    Hall effect and conductivity measurements made on semi-insulating bulk GaAs are examined by a new approach to mixed conduction analysis. Based on Fermi level and electron mobility analyses of conductivity and Hall coefficient, it uses revised values of effective densities of states at the band edges, and electron/hole mobility ratios recently adopted by other workers. The treatment provides a visual analysis of the system in terms of the electrical parameters and impurity densities, and establishes criteria for the onset of mixed conduction.

  15. Formation of a semi-insulating layer in n-type 4H-SiC by electron irradiation

    SciTech Connect

    Kaneko, Hiromi; Kimoto, Tsunenobu

    2011-06-27

    Electron irradiation has been applied to the formation of a semi-insulating 4H-SiC(0001) layer. The resistivity of the semi-insulating layer, which was irradiated with a fluence of 1.9 x 10{sup 18} cm{sup -2} at 400 keV, exceeded 10{sup 10{Omega}} cm at room temperature. From capacitance-voltage characteristics of Schottky structure, the depth of the semi-insulating layer was estimated to be 10 {mu}m, indicating that the whole region of lightly-doped n-type epilayer was converted to the semi-insulating layer by electron irradiation. The semi-insulating property can be ascribed to electron trapping at the Z{sub 1/2} and EH{sub 6/7} centers generated by electron irradiation. The threshold energy for the generation of Z{sub 1/2} center was about 100 keV.

  16. Cooperative transition of electronic states of antisite As defects in Be-doped low-temperature-grown GaAs layers

    NASA Astrophysics Data System (ADS)

    Ambri Mohamed, Mohd; Tien Lam, Pham; Bae, K. W.; Otsuka, N.

    2011-12-01

    Magnetic properties resulting from localized spins associated with antisite arsenic ions AsGa+ in Be-doped low-temperature-grown GaAs (LT-GaAs) layers were studied by measuring the magnetization of lift-off samples. With fast cooling, the magnetization of samples at 1.8 K becomes significantly lower than that expected from Curie-type paramagnetism in the range of the applied field to 7 T, and a transition from low magnetization to the magnetization of paramagnetism occurs upon the heating of samples to 4.5 K. With slow cooling, on the other hand, samples have a paramagnetic temperature dependence throughout the measurement-temperature range. The magnetization was found to decrease monotonically when a sample was kept at a fixed low temperature. These observations are explained by the cooperative transition of electron states of AsGa defects, which is closely related to the normal-metastable state transition of EL2 defects in semi-insulating GaAs. The results of the magnetization measurements in the present study suggest that AsGa+ ions are spontaneously displaced at low temperature without photoexcitation in Be-doped LT-GaAs. The similarity of the transition observed in this system to the normal-metastable state transition of the EL2 defect was also suggested by first-principle calculations of the electron state of an AsGa defect with a doped Be atom.

  17. 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).

  18. Electronic properties of delta -doped GaAs

    NASA Astrophysics Data System (ADS)

    Gold, A.; Ghazali, A.; Serre, J.

    1992-07-01

    For temperature zero the authors study the effects of disorder on the electronic properties of the two-dimensional electron gas which exists in planar-doped ( delta -doped) GaAs. The density of states, the Fermi level, the single-particle relaxation time and the electron mobility are calculated as functions of the dopant concentration. The transition from a band tail to an impurity band and the nature of the metal-insulator transition are discussed. The authors compare the theoretical results on the mobility with some available experimental data.

  19. Epitaxial Growth of Semi-Insulating GaAs

    DTIC Science & Technology

    1980-01-01

    83 APPENDIX - Van der Pauw Measurements of High-Resistivity Materials .... 84 vi LIST OF ILLUSTRATIONS...79 A-I. Schematic of guarded high-impedance van der Pauw system ......... 84 .i xi hL LIST OF TABLES * Table Page 1. Van der Pauw Measurement...this method has been described previously in the literature [I], we have been able to grow thicker layers than that achieved previously. Van der Pauw measurements

  20. Epitaxial Growth of Semi-Insulating GaAs

    DTIC Science & Technology

    1978-03-01

    CA 95051 Mr. R . Bell, K 101 Varlan Associates 6ll Hansen Way Palo Äl^o, CA 9^301+ \\ Mr. R . Bierl Raytheon Compa 28 Seyon Street Walthon, MA...BASI Program Code No. 7D10 78 Monitored by Office of Naval Research Arlington, Virginia 22217 Under Contract No. N 00014077 C 0542 06 - • r ...Supervisor and S. T. Jolly is the Project Scientist. D. S. Yaney and D. R . Capewell also participated in the research project. £> iii/iv 1 r

  1. Novel ways to grow thermally stable semi-insulating InP-based layers

    NASA Astrophysics Data System (ADS)

    Bimberg, D.; Dadgar, A.; Heitz, R.; Knecht, A.; Krost, A.; Kuttler, M.; Scheffler, H.; Näser, A.; Srocka, B.; Wolf, T.; Zinke, T.; Hyeon, J. Y.; Wernik, S.; Schumann, H.

    1994-12-01

    Semi-insulating InP is generally grown by Fe doping. In contact with p-type layers, however, semi-insulating characteristics turn out to be difficult to reproduce because of pronounced interdiffusion of Fe and p-type dopants. Co-doping of InP:Fe with Ti is shown to be a universal process for the preparation of thermally stable high-resistivity layers. Fe + Ti co-doping can compensate both excess shallow donors and excess shallow acceptors up to concentrations of 8 × 10 16 and 2 × 10 16 cm -3, respectively. In contrast to InP:Fe, resistivities in excess of 10 7 Ω cm are obtained in contact with both symmetric n- and p-type current injecting contacts. Moreover, co-doping of semi-insulating InP:Fe with Ti is found to suppress the interdiffusion of Fe and p-type dopants. Therefore, the out-diffusion and accumulation of Fe in other regions of complex device structures can be significantly reduced. A comprehensive model accounting for these phenomena is presented. A totally different way to produce thermally more stable semi-insulating InP layers is to replace Fe by a less diffusive deep acceptor. We propose the 4d transition metal Rh as a potential alternative. The diffusion of Rh is shown to be practically nonexistent and near-midgap Rh levels are found by means of DLTS in InP at Ev + 730 meV and in InGaAs at Ec - 380 meV below the conduction band. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.

  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. Optimum doping achieves high quantum yields in GaAs photoemitters

    NASA Technical Reports Server (NTRS)

    Sonnenberg, H.

    1971-01-01

    Experimental data indicate that optimum doping exists. Measured quantum yield curves indicate optimum overall response is obtained in GaAs emitters with doping in high 10 to the 18th power per cu cm range. Doping for optimum response is not necessarily in this range.

  4. Terahertz refractive anisotropy on femtosecond laser pulse ablated semi-insulating gallium arsenide surface

    NASA Astrophysics Data System (ADS)

    Zhao, Zhenyu; Song, Zhiqiang; Bai, Feng; Shi, Wangzhou; Zhao, Quan-Zhong

    2017-04-01

    We present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of <100>-oriented semi-insulating gallium arsenide (SI-GaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the gap of columns of micro-ripples when the polarization of THz is parallel to the micro-ripples, while no electric energy localization occurs when the polarization of THz is perpendicular to the micro-ripples. We found that the laser ablation process can induce a periodic distribution of n-type GaAs at the surface of SI-GaAs. These n-type GaAs micro-ripples work as plasmonic resonators, which are proposed to be the origin of the induced refractive index anisotropy.

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    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.

  7. 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.

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

    PubMed Central

    2011-01-01

    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 × 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. PMID:27502686

  10. Microscopic identification of native donor Ga-vacancy complexes in Te-doped GaAs

    NASA Astrophysics Data System (ADS)

    Gebauer, J.; Lausmann, M.; Staab, T. E. M.; Krause-Rehberg, R.; Hakala, M.; Puska, M. J.

    1999-07-01

    Native vacancies in Te-doped (5×1016-5×1018 cm-3) GaAs were investigated by means of positron lifetime and Doppler-broadening coincidence spectroscopy. The experimental data were related to theoretical calculations of the positron lifetime and the annihilation momentum distribution. Monovacancies were observed in all Te-doped GaAs samples under study. It will be shown that they can directly be identified to be Ga-vacancy-TeAs-donor complexes. These complexes are the dominating type of vacancy defects in the doping range under observation.

  11. Quantum confinement: A route to enhance the Curie temperature of Mn doped GaAs

    NASA Astrophysics Data System (ADS)

    Mandal, Basudeb; Chandra, Hirak Kumar; Kumari, Poonam; Mahadevan, Priya

    2017-07-01

    The electronic structure of Mn doped GaAs and GaN have been examined within a multiband Hubbard model. By virtue of the positioning of the Mn d states, Mn doped GaAs is found to belong to the p -d metal regime of the Zaanen-Sawatzky-Allen phase diagram and its variants, while Mn doping in GaN belongs to the covalent insulator regime. Their location in the phase diagram also determines how they would behave under quantum confinement which would increase the charge transfer energy. The ferromagnetic stability of Mn doped GaAs, we find, increases with confinement therefore providing a route to higher ferromagnetic transition temperatures.

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

    PubMed

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

    2016-11-11

    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.

  13. 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.

  14. 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.

  15. Dopant mapping of Be δ-doped layers in GaAs tailored by counterdoping using scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Ebert, Ph.; Landrock, S.; Chiu, Y. P.; Breuer, U.; Dunin-Borkowski, R. E.

    2012-11-01

    The effect of counterdoping on the Be dopant distribution in delta (δ)-doped layers embedded in Si-doped and intrinsic GaAs is investigated by cross-sectional scanning tunneling microscopy. δ-doped layers in intrinsic GaAs exhibit a large spreading, whereas those surrounded by Si-doped GaAs remain spatially localized. The different spreading is explained by the Fermi-level pinning at the growth surface, which leads to an increased Ga vacancies concentration with increasing Si counterdoping. The Ga vacancies act as sinks for the diffusing Be dopant atoms, hence retarding the spreading.

  16. Determination of the charge carrier compensation mechanism in Te-doped GaAs by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Gebauer, J.; Weber, E. R.; Jäger, N. D.; Urban, K.; Ebert, Ph.

    2003-03-01

    We identified the charge carrier compensation mechanism in Te-doped GaAs with atomically resolved scanning tunneling microscopy. Three types of defects were found: tellurium donors (TeAs), Ga vacancies (VGa), and Ga vacancy-donor complexes (VGa-TeAs). We show quantitatively that the compensation in Te-doped bulk GaAs is exclusively caused by vacancy-donor complexes in contrast to Si-doped GaAs. This is explained with the Fermi-level effect as the universal mechanism leading to Ga vacancy formation in n-doped GaAs, and a Coulomb interaction leading to the formation of the complexes. The quantification of the carrier compensation yields a -3e charge state of VGa in bulk GaAs.

  17. Observation of As-Grown Defects in Zn-Doped GaAs by Positron Lifetime Spectra

    NASA Astrophysics Data System (ADS)

    Wang, Zhu; Wang, Shao-Jie; Chen, Zhi-Quan

    2000-11-01

    Positron lifetime spectra were measured for the Zn-doped p-type GaAs. In comparing the horizontal-Bridgman-method-grown and the floating-zone-method grown p-type GaAs with the liquid-encapsulation-Czochralski-grown p-type GaAs samples, positron trapping into vacancy type defects was observed in the former two grown p-type GaAs. Shallow positron traps were detected, and the dominant ones were attributed to acceptor the in p-type GaAs.

  18. 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.

  19. Temperature and intensity dependence of photorefractive effect in GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Partovi, Afshin

    1986-01-01

    The photorefractive effect in semi-insulating Cr-doped GaAs as measured by the beam coupling technique was investigated as functions of temperature (295-386 K) and intensity (0.15-98 mW/sq cm of 1.15-micron light beams from a He-Ne laser). Results show that the photorefractive effect deteriorates rapidly over a narrow range of temperature as temperature rises, and that this characteristic temperature increases with the logarithm of beam intensity. The observed phenomenon is attributed to the competing effects of the dark- and light-induced conductivities.

  20. Can electrical deactivation of highly Si-doped GaAs be explained by autocompensation

    SciTech Connect

    Schuppler, S.; Adler, D.L.; Pfeiffer, L.N.; West, K.W.; Chaban, E.E.; Citrin, P.H. )

    1993-10-25

    Using near-edge x-ray absorption fine structure, the first experimental determination of Si atom concentrations occupying As sites in Si-doped GaAs (100) is reported. The measurements reveal that at high doping levels ([approx gt]10[sup 19] cm[sup [minus]3]) in molecular-beam-epitaxy-grown samples, the number of such [ital p]-type Si atoms is insufficient to account for the observed large reduction of free-carriers.

  1. Towards low-dimensional hole systems in Be-doped GaAs nanowires.

    PubMed

    Ullah, A R; Gluschke, J G; Krogstrup, P; Sørensen, C B; Nygård, J; Micolich, A P

    2017-03-01

    GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly confined 0D and 1D hole systems with strong spin-orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowly doped nanowires and inability to reach a clear off-state under gating for the highly doped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio [Formula: see text], and sub-threshold slope 50 mV/dec at [Formula: see text] K. Lastly, we made a device featuring a moderately doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantisation highlighting the potential for future quantum device studies in this material system.

  2. Towards low-dimensional hole systems in Be-doped GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Ullah, A. R.; Gluschke, J. G.; Krogstrup, P.; Sørensen, C. B.; Nygård, J.; Micolich, A. P.

    2017-03-01

    GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly confined 0D and 1D hole systems with strong spin–orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowly doped nanowires and inability to reach a clear off-state under gating for the highly doped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio ∼ {10}4, and sub-threshold slope 50 mV/dec at T=4 K. Lastly, we made a device featuring a moderately doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantisation highlighting the potential for future quantum device studies in this material system.

  3. 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.

  4. 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.

  5. 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.

  6. Carbon doping in GaAs grown by MOVPE with trimethylgallium and triethylarsenic

    NASA Astrophysics Data System (ADS)

    Pak, Kangsa; Ashizuka, Kazuaki; Fukazawa, Hidetaka; Yamashita, Seiji; Takano, Yasushi; Yonezu, Hiroo

    1990-12-01

    Heavily carbon doped GaAs epitaxial layers were grown by low-pressure MOVPE using TMGa and TEAs as the source materials. GaAs epitaxial layers with hole concentrations up to 2.4×10 20 cm -3 were obtained. The hole concentrations of the films increased as the growth temperature (500-600°C) and/or the growth pressure (10-100 Torr) decreased, and were less dependent on V/III molar ratio (10-30). The uniform incorporation of carbon atoms during the growth was confirmed from SIMS measurements.

  7. 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.

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

    SciTech Connect

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

    2016-05-02

    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 × 10{sup 17} cm{sup −3} (lightly doped), to 1.5 × 10{sup 18} cm{sup −3} (moderately doped), to 3.5 × 10{sup 18} cm{sup −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.

  9. 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

    2017-01-01

    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.

  10. Radiation Resistance Study of Semi-Insulating GaAs-Based Radiation Detectors to Extremely High Gamma Doses

    NASA Astrophysics Data System (ADS)

    Ly Anh, T.; Perd'ochová, A.; Nečas, V.; Pavlicová, V.

    2006-01-01

    In our previous paper [V. Nečas et al.: Nucl. Inst. and Meth. A 458 (2001) 348-351] we reported on the study on radiation stability of semi-insulating (SI) LEG GaAs detectors to doses of photons from 60Co up to 19.2 kGy. Later we presented a study, which covered radiation hardness to the same doses on the base of detector material itself, where strong dependence has been proved [T. Ly Anh et al., Proceedings of the XII th International Conference on Semiconducting and Insulating Materials (SIMC-XII-2002). Smolenice Castle, Slovakia (2002) 292-295 (0-7803-7418-5)]. In this paper we present both the key electrical and detection characteristics of SI GaAs radiation detectors prepared using substrates from four various supplies and two different types of contacts, which were exposed to several gamma doses from 60Co up to the integral dose of about 1 MGy. The obtained results show that SI LEG GaAs detectors provide good spectroscopic performances and even their slight improvement after low to middle gamma irradiation doses (3 -10 kGy) was observed. Further dose exposure caused the degradation of detection properties with an extreme and following improvement depending on detector material properties. SI GaAs detector still retains its working capabilities even after very high doses applied, up to 1 MGy.

  11. Design considerations for a GaAs nipi doping superlattice solar cell

    NASA Technical Reports Server (NTRS)

    Clark, Ralph; Goradia, Chandra; Brinker, David

    1987-01-01

    A new GaAs nipi doping superlattice solar cell structure is presented, which holds promise for high efficiency coupled with very high radiation tolerance. The structure has all contacts on the unilluminated side. Design constraints are presented which this structure must satisfy in order to exhibit high efficiency and high radiation tolerance. The results of self-consistent quantum mechanical calculations are presented which show that a viable design of this cell would include relatively thick n and p layers which are fairly heavily doped.

  12. Synthesis solute diffusion growth of bulk GaAs: Effects of growth temperature and stoichiometry

    NASA Astrophysics Data System (ADS)

    Markov, A. V.; Biberin, V. I.; Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Gavrin, V. N.; Kalikhov, A. V.; Kozlova, J. P.; Veretenkin, E. P.; Bowles, T. J.

    2007-07-01

    Bulk GaAs crystals were grown by synthesis solute diffusion (SSD) technique in a wide range of growth temperatures between 990 and 1150 °C. Electrical properties of these crystals were studied by means of van der Pauw, admittance spectroscopy, deep levels transient spectroscopy and photoinduced current spectroscopy techniques. It was shown that the main defects determining the properties were the GaAs antisites acceptors and the A center acceptors with the levels, respectively, Ev +0.078 eV and Ev +0.43 eV. The conductivity of the grown crystals was p-type and showed a pronounced maximum at a level of 10 4-10 5 Ω cm for growth temperatures between 1020 and 1080 °C. If the crystals were additionally compensated either by unintentional Si donors contamination from quartz crucibles or by intentional light Te doping one could get semi-insulating material with the room temperature resistivity higher than 10 6 Ω cm. The Fermi level in such crystals was pinned near Ec -0.8 eV, i.e. close to the EL2 donors. Measurements by deep levels transient spectroscopy on n-type doped crystals or by low frequency capacitance-voltage on semi-insulating crystals showed that the density of EL2 in these samples was in the low 10 14 cm -3 and that thus the EL2 donors were not the main compensating agents.

  13. Divacancy complexes induced by Cu diffusion in Zn-doped GaAs

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    Positron annihilation spectroscopy was applied to investigate the nature and thermal behavior of defects induced by Cu diffusion in Zn-doped p-type GaAs crystals. Cu atoms were intentionally introduced in the GaAs lattice through thermally activated diffusion from a thin Cu capping layer at 1100 °C under defined arsenic vapor pressure. During isochronal annealing of the obtained Cu-diffused GaAs in the temperature range of 450-850 K, vacancy clusters were found to form, grow and finally disappear. We found that annealing at 650 K triggers the formation of divacancies, whereas further increasing in the annealing temperature up to 750 K leads to the formation of divacancy-copper complexes. The observations suggest that the formation of these vacancy-like defects in GaAs is related to the out-diffusion of Cu. Two kinds of acceptors are detected with a concentration of about 1016 - 1017 cm-3, negative ions and arsenic vacancy copper complexes. Transmission electron microscopy showed the presence of voids and Cu precipitates which are not observed by positron measurements. The positron binding energy to shallow traps is estimated using the positron trapping model. Coincidence Doppler broadening spectroscopy showed the presence of Cu in the immediate vicinity of the detected vacancies. Theoretical calculations suggested that the detected defect is VGaVAs-2CuGa.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Optical properties of heavily doped GaAs nanowires and electroluminescent nanowire structures.

    PubMed

    Lysov, A; Offer, M; Gutsche, C; Regolin, I; Topaloglu, S; Geller, M; Prost, W; Tegude, F-J

    2011-02-25

    We present GaAs electroluminescent nanowire structures fabricated by metal organic vapor phase epitaxy. Electroluminescent structures were realized in both axial pn-junctions in single GaAs nanowires and free-standing nanowire arrays with a pn-junction formed between nanowires and substrate, respectively. The electroluminescence emission peak from single nanowire pn-junctions at 10 K was registered at an energy of around 1.32 eV and shifted to 1.4 eV with an increasing current. The line is attributed to the recombination in the compensated region present in the nanowire due to the memory effect of the vapor-liquid-solid growth mechanism. Arrayed nanowire electroluminescent structures with a pn-junction formed between nanowires and substrate demonstrated at 5 K a strong electroluminescence peak at 1.488 eV and two shoulder peaks at 1.455 and 1.519 eV. The main emission line was attributed to the recombination in the p-doped GaAs. The other two lines correspond to the tunneling-assisted photon emission and band-edge recombination in the abrupt junction, respectively. Electroluminescence spectra are compared with the micro-photoluminescence spectra taken along the single p-, n- and single nanowire pn-junctions to find the origin of the electroluminescence peaks, the distribution of doping species and the sharpness of the junctions.

  19. Zn-doping of GaAs nanowires grown by Aerotaxy

    NASA Astrophysics Data System (ADS)

    Yang, Fangfang; Messing, Maria E.; Mergenthaler, Kilian; Ghasemi, Masoomeh; Johansson, Jonas; Wallenberg, L. Reine; Pistol, Mats-Erik; Deppert, Knut; Samuelson, Lars; Magnusson, Martin H.

    2015-03-01

    Nanowires were grown by means of a novel aerosol-based method called Aerotaxy. Here an aerosol of Au catalyst nanoparticles in N2 is mixed with MOVPE precursors in a flow-through reactor at atmospheric pressure, whereby nanowires are produced continuously in high concentrations. We demonstrate the possibility of in situ doping of the NWs and the realization of well-controlled p-type GaAs nanowires using this Aerotaxy method. By controlling the cracking and concentration of the precursors, p-doped GaAs nanowires could be grown exhibiting a wide range of Zn doping levels. DEZn was used as the dopant source and the injected DEZn/TMGa ratio was varied from 0.1% to 3.4%. The morphology, the crystalline structure and the composition of the nanowires were studied using SEM, TEM and XEDS. The nanowires were grown straight without any significant tapering and this ideal morphology could be maintained up to an injected DEZn/TMGa ratio of 3.4%. The nanowires typically grew in the <111> direction with a pure zincblende structure, but by increasing the DEZn flow the number of twinning defects increased which we ascribe to Zn incorporation. Elemental analysis shows a high Zn content in the catalyst particle and also a gradient in the Zn content along the nanowire. The samples were analyzed optically using photoluminescence (PL). From the result we estimated the free hole concentration induced by Zn acceptors to be 1×1020 cm-3 for DEZn/TMGa ratio of 3.4%. To our knowledge this is the first report on in situ doping of GaAs nanowires grown by Aerotaxy.

  20. Long-lived electron spins in a modulation doped (100) GaAs quantum well

    NASA Astrophysics Data System (ADS)

    Colton, John; Meyer, David; Clark, Ken; Craft, Daniel; Tanner, Jane; Park, Tyler; White, Phil

    2013-03-01

    We have measured T1 spin lifetimes of a 14 nm modulation-doped (100) GaAs quantum well using a time-resolved pump-probe Kerr rotation technique. The quantum well was selected by tuning the wavelength of the probe laser. T1 lifetimes in excess of 1 microsecond were measured at 1.5 K and 5.5 T, exceeding the typical T2* lifetimes that have been measured in GaAs and II-VI quantum wells by orders of magnitude. We observed effects from nuclear polarization, which were largely removable by simultaneous nuclear magnetic resonance, along with two distinct lifetimes under some conditions that likely result from probing two differently-localized subsets of electrons.

  1. Long-lived electron spins in a modulation doped (100) GaAs quantum well

    NASA Astrophysics Data System (ADS)

    Colton, J. S.; Meyer, D.; Clark, K.; Craft, D.; Cutler, J.; Park, T.; White, P.

    2012-10-01

    We have measured T1 spin lifetimes of a 14 nm modulation-doped (100) GaAs quantum well using a time-resolved pump-probe Kerr rotation technique. The quantum well was selected by tuning the wavelength of the probe laser. T1 lifetimes in excess of 1 μs were measured at 1.5 K and 5.5 T, exceeding the typical T2* lifetimes that have been measured in GaAs and II-VI quantum wells by orders of magnitude. We observed effects from nuclear polarization, which were largely removable by simultaneous nuclear magnetic resonance, along with two distinct lifetimes under some conditions that likely result from probing two differently localized subsets of electrons.

  2. 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.

  3. Photoluminescence of individual doped GaAs /AlGaAs nanofabricated quantum dots

    NASA Astrophysics Data System (ADS)

    Kalliakos, Sokratis; García, César Pascual; Pellegrini, Vittorio; Zamfirescu, Marian; Cavigli, Lucia; Gurioli, Massimo; Vinattieri, Anna; Pinczuk, Aron; Dennis, Brian S.; Pfeiffer, Loren N.; West, Ken W.

    2007-04-01

    Dilute arrays of GaAs /AlGaAs modulation-doped quantum dots with same sizes fabricated by electron beam lithography and low impact reactive ion etching exhibit highly uniform luminescence lines. Single quantum dots display spectral emission with peak energies and linewidths linked largely to the geometrical diameter of the dot and to the built-in electron population. Multicharged excitonic and biexcitonic emission intensities have activation energy of about 2meV. These results highlight the potential of high quality nanofabricated quantum dots for applications in areas that require fine control of optical emission.

  4. Inhibition of Te surfactant effect on surface morphology of heavily Te-doped GaAs

    NASA Astrophysics Data System (ADS)

    Paquette, Bernard; Ilahi, Bouraoui; Aimez, Vincent; Arès, Richard

    2013-11-01

    The surface morphology and incorporation behavior of heavily Te-doped GaAs were studied for various growth parameters by chemical beam epitaxy (CBE). The Te precursor, DIPTe (diisopropyl telluride), acts as a volatile dopant in the growth temperature range of 475-595 °C. Electrical activation of Te is increased for lower growth temperatures. The Te surfactant effect was shown to lead to three-dimensional growth, which greatly affected the resulting surface morphology. We have shown that growth parameters can be tuned to reduce the Te surfactant effect through kinetic limitation, thus obtaining improved surface morphologies.

  5. Laser Annealing of GaAs

    DTIC Science & Technology

    1978-12-01

    annealing implanted layers. Sheet resistance measurements made on the irradiated semi- insulating GaAs samples indicate no significant change in the... sheet resistance after laser irradiation (typical decrease in the sheet resistance after laser irradiation was found to be less than a factor of two...OF THE SHEET - RESISTANCE (P ) THE EFFECTIVE SHEET ELECTRON CONCENTRATION (N ), AND THE EFFECTIVE MOBILITY _u)FOR SEMIb- INSULATING GaAs IMPLANTED WITH

  6. Effects of Zn doping in the substrate on the quantum well intermixing in GaAs/Al0.24Ga0.76As single quantum well structures

    NASA Astrophysics Data System (ADS)

    Zhao, Feng; Choi, In Wang; Hing, Peter; Yuan, Shu; Ong, Teik Kooi; Ooi, Boon Siew; Jiang, Jian; Chan, Michael C. Y.; Surya, Charles C.; Li, E. Herbert

    2000-10-01

    N diffusion usually enhances the intermixing in GaAs/AlGaAs quantum well structure. However, Krames et al reported the reduction of layer intermixing in GaAs/AlGaAs quantum well heterostructures by an initial low-temperature 'blocking' Zn diffusion. Zn is commonly used as the dopant of the p-type GaAs substrate. To the best of our knowledge, the effect of Zn diffusion from the Zn-doped GaAs substrate on the intermixing has not been studied. In this work, we report the suppression of GaAs/AlGaAs quantum well intermixing by Zn doping in the GaAs substrate. Three samples with single GaAs/Al0.24Ga0.76As quantum wells were used in the work, all grown together by molecular beam epitaxy, but on three different substrates: Zn-doped p-type GaAs, Si-doped n-type GaAs, and semi-insulating GaAs. The samples were annealed together in a rapid thermal processor at temperatures around 900 degrees C. Photoluminescence measurements were then performed to characterize the samples. The samples with Zn-doped GaAs substrate shows more than 50 percent suppression of quantum well intermixing compared to the other two samples. It is due to Zn diffusion from the substrate into the quantum well, which induces the reduction in the number of group-III vacancies in the quantum well structure.

  7. 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.

  8. Improved short-channel GaAs MESFET's by use of higher doping concentration

    NASA Astrophysics Data System (ADS)

    Daembkes, H.; Brockerhoff, W.; Heime, K.; Cappy, A.

    1984-08-01

    GaAs MESFET's with highly doped channels up to 5 x 10 to the 18th per cu cm and with both micrometer and submicrometer gates were fabricated and evaluated. FET's with 1.2 micron gates show an extrinsic transconductance of more than 250 mS/mm, cutoff frequencies around 20 GHz, and a noise figure of 2 dB at 8 GHz with 9-dB associated gain. Breakdown voltage is higher than 6 V. FET's with 1.2- and 0.4-micron gates were simultaneously fabricated on the same wafer to investigate short-channel effects. The short-channel devices show a good saturation behavior and no shift in the threshold voltage compared to the long-channel devices thus demonstrating a pronounced alleviation of short-channel effects as experienced for 1 x 10 to the 17th per cu cm doping levels. The influence of doping concentration on the performance of devices with micrometer and submicrometer gates upon doping concentration is investigated by detailed computer simulations. Good agreement between theoretical and experimental results is obtained. From these results improved technological approaches are pointed out.

  9. GaAs microcrystals selectively grown on silicon: Intrinsic carbon doping during chemical beam epitaxy with trimethylgallium

    NASA Astrophysics Data System (ADS)

    Molière, T.; Jaffré, A.; Alvarez, J.; Mencaraglia, D.; Connolly, J. P.; Vincent, L.; Hallais, G.; Mangelinck, D.; Descoins, M.; Bouchier, D.; Renard, C.

    2017-01-01

    The monolithic integration of III-V semiconductors on silicon and particularly of GaAs has aroused great interest since the 1980s. Potential applications are legion, ranging from photovoltaics to high mobility channel transistors. By using a novel integration method, we have shown that it is possible to achieve heteroepitaxial integration of GaAs crystals (typical size 1 μ m) on silicon without any structural defect such as antiphase domains, dislocations, or stress, usually reported for direct GaAs heteroepitaxy on silicon. However, concerning their electronic properties, conventional free carrier characterization methods are impractical due to the micrometric size of GaAs crystals. In order to evaluate the GaAs material quality for optoelectronic applications, a series of indirect analyses such as atom probe tomography, Raman spectroscopy, and micro-photoluminescence as a function of temperature were performed. These revealed a high content of partially electrically active carbon originating from the trimethylgallium used as the Ga precursor. Nevertheless, the very good homogeneity observed by this doping mechanism and the attractive properties of carbon as a dopant once controlled to a sufficient degree are a promising route to device doping.

  10. Optical and magnetic properties of Mn{sup +}-implanted GaAs

    SciTech Connect

    Shon, Yoon; Park, Y.S.; Chung, K.J.; Fu, D.J.; Kim, D.Y.; Kim, H.S.; Kim, H.J.; Kang, T.W.; Kim, Yongmin; Fan, X.J.; Park, Y.J.

    2004-12-15

    Neutron-transmutation-doped GaAs samples were prepared by irradiating the middle-level neutrons into the semi-insulating GaAs grown by a liquid encapsulated Czochralski method and subsequently implanted with Mn{sup +}. The characteristics of the Mn{sup +}-implanted neutron-transmutation-doped GaAs (namely, the implantation of Mn{sup +} subsequent to neutron-transmutation-doping) were investigated by various measurements. The result of the energy dispersive x-ray peak displayed an injected Mn concentration of 9.65%. The photoluminescence peaks related to carbon and germanium acceptors were resolved, and the peaks related to Mn due to a neutral Mn acceptor were evidently observed. It is found that the proper activation for the neutral Mn acceptor starts from a relatively low annealing temperature of 600 deg. C for 15 min. The atomic force microscopy and magnetic forcemicroscopy images showed that magnetic clusters were well formed. The ferromagnetic hysteresis loop measured at 10 K was observed, and the temperature-dependent magnetization revealed that the two different phases exist at 135 and 360 K. The Curie temperature (T{sub c}{approx}360 K) is caused by MnAs, which agrees with the clusters of the magnetic force microscopy image.

  11. Effect of doped substrates on the growth of GaAs nanowires via metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Peng, Yan; Guo, Jingwei; La, Dongsheng; Xu, Zhaopeng; Wang, Haiyan

    2017-08-01

    Vertical GaAs nanowires were grown on different doped substrates via Metal Organic Chemical Vapor Deposition by catalyst assisted vapor-liquid-solid mechanism. It is found that both n and p type doped substrates affect catalyst distribution during the formation of alloy catalysts. The catalyst density decreases with an increase in the doping concentration of the substrates. In the growth of GaAs nanowires, the growth rate, which is mostly determined by the atoms diffusion from the pyrolysis of precursors on the surface of nanowires and substrates, is proportional to the catalyst densities. Moreover, the structures of as-grown nanowires are all pure zinc blende without any defects. These results will be valuable for the applications of nanowire-based optical and electrical devices.

  12. 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.

  13. Influence of stoichiometry and doping on vacancies in n-type GaAs

    NASA Astrophysics Data System (ADS)

    Gebauer, J.; Lausmann, M.; Redmann, F.; Krause-Rehberg, R.

    1999-12-01

    Native vacancies in n-type, Te-doped GaAs (n=5×1016-5×1018 cm-3) were studied by means of positron annihilation. We investigated the influence of doping, thermal treatment, and stoichiometry adjusted by changing the As pressure during annealing. Negatively charged monovacancies were found in all Te-doped samples under investigation. By using positron lifetime spectroscopy in conjunction with measurements of the annihilation momentum distribution and theoretical calculations, they can directly be identified to be VGa-TeAs complexes. After thermal treatment at 1100°C the density of the vacancies cv increases with the As pressure (pAs) like cv=0.1cdp1/4As where cd is the donor concentration. For such a treatment, cv depends only on pAs but not on the thermal history. The vacancy concentration was found to increase slightly with decreasing annealing temperature at a given pAs. This can be explained by the so-called Fermi level effect, i.e. the dependence of the equilibrium concentration of charged point defects on the position of the Fermi level.

  14. 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

    2016-06-17

    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.

  15. 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.

  16. Influence of photoexcitation on hopping conduction in neutron-transmutation-doped GaAs

    SciTech Connect

    Satoh, M.; Kawahara, H.; Kuriyama, K.; Kawakubo, T.; Yoneda, K.; Kimura, I.

    1988-02-15

    The nature of the tunneling-assisted hopping conduction in neutron-transmutation-doped GaAs has been studied under photoexcitation with a photon energy of 1.32 eV. It is found that the dopants activated by annealing around 400 /sup 0/C provide the electrons to the defect levels originating the hopping conduction even when under photoexcitation. The hopping conduction under photoexcitation is affected by quenching in photoconductance below 120 K concerned with the main electron trap (EL2) and/or the As antisite defect (As/sub Ga/) induced by the neutron irradiation. The photoconductance of the samples with a lower radiation damage, As/sub Ga/less than or equal to1 x 10/sup 18/ cm/sup -3/, consists of the coexistence of the hopping and band conductions.

  17. 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

  18. Optical absorption by free holes in heavily doped GaAs

    NASA Technical Reports Server (NTRS)

    Huberman, M. L.; Ksendzov, A.; Larsson, A.; Terhune, R.; Maserjian, J.

    1991-01-01

    Optical absorption in p-type GaAs with hole concentrations between 10 exp 19 and 10 exp 20/cu cm has been measured for wavelengths between 2 and 20 microns and compared with results of theoretical calculations. In contrast to previous measurements at lower doping levels, the occupied hole states are far from the zone center, where the heavy- and light-hole bands become parallel. This gives rise to a large joint density of states for optical transitions. It is found that the overall magnitude of the observed absorption is explained correctly by the theory, with both the free-carrier (indirect) and the inter-valence-band (direct) transitions contributing significantly to the total absorption. The strength of the absorption (a about 20,000/cm for N(A) = 5 x 10 exp 19/cu cm) is attractive for long-wavelength infrared-detector applications.

  19. Optical absorption by free holes in heavily doped GaAs

    NASA Astrophysics Data System (ADS)

    Huberman, M. L.; Ksendzov, A.; Larsson, A.; Terhune, R.; Maserjian, J.

    1991-07-01

    Optical absorption in p-type GaAs with hole concentrations between 10 exp 19 and 10 exp 20/cu cm has been measured for wavelengths between 2 and 20 microns and compared with results of theoretical calculations. In contrast to previous measurements at lower doping levels, the occupied hole states are far from the zone center, where the heavy- and light-hole bands become parallel. This gives rise to a large joint density of states for optical transitions. It is found that the overall magnitude of the observed absorption is explained correctly by the theory, with both the free-carrier (indirect) and the inter-valence-band (direct) transitions contributing significantly to the total absorption. The strength of the absorption (a about 20,000/cm for N(A) = 5 x 10 exp 19/cu cm) is attractive for long-wavelength infrared-detector applications.

  20. 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.

  1. Two acceptor levels and hopping conduction in Mn-doped GaAs

    NASA Astrophysics Data System (ADS)

    Kajikawa, Yasutomo

    2017-01-01

    By analysing the experimental data of the temperature-dependent Hall-effect measurements, an additional acceptor level has been confirmed to exist in Mn-doped p-GaAs besides the isolated substitutional Mn acceptor level. It is found that, in most of the investigated samples, the room-temperature hole concentration is governed by the additional acceptor level rather than the isolated substitutional Mn acceptor level. The concentration of the additional acceptor level is found to increase almost in proportion to the square of the concentration of the isolated substitutional Mn acceptors, suggesting that the additional acceptor level is related to Mn dimers. This suggests that the ferromagnetism observed in more heavily Mn-doped GaAs may be attributed to Mn clusters. For some of the samples in which the characteristic of nearest-neighbour hopping conduction in the substitutional Mn acceptor impurity band is evident, the hopping activation energy is deduced and is proved to increase in proportion to the cube root of the concentration of the substitutional Mn acceptors.

  2. 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.

  3. Crossover from negative to positive magnetoresistance in a Si delta-doped GaAs single quantum well

    NASA Astrophysics Data System (ADS)

    Lo, Shun-Tsung; Chen, Kuang Yao; Su, Yi-Chun; Liang, C.-T.; Chang, Y. H.; Kim, Gil-Ho; Wu, J.-Y.; Lin, Sheng-Di

    2010-07-01

    We have performed magnetoresistance measurements on a Si delta-doped GaAs single quantum well. With increasing temperature T, a crossover from negative magnetoresistance (NMR) to positive magnetoresistance (PMR) can be observed. Our experimental results suggest that such a crossover corresponds to a transition from variable range hopping regime to activated electron transport. This is also consistent with the measured non-monotonic carrier density dependence on T.

  4. Preparation of Large-Diameter GaAs Crystals.

    DTIC Science & Technology

    1981-09-18

    implantation as a reliable, cost-effective fabrication technology for high-performance GaAs MESFET and integrated circuits . To address these problems, the...have been prepared by in-situ synthesis and pulled from pyrolytic boron nitride (PBN) crucibles, and improved FET channels by direct ion-implantation of...viii SUMMARY Significant progress has been made toward developing large- diai.3ter, semi-insulating GaAs crystals of improved quality by LEC growth for

  5. Barrier-height measurement for a gallium arsenide metal-semi-insulator interface

    SciTech Connect

    Ayzenshtat, G. I. Lelekov, M. A.; Tolbanov, O. P.

    2007-11-15

    The I-V characteristics of structures from semi-insulating gallium arsenide with different contacts are analyzed. The Schottky barrier height was measured using two procedures; its values obtained for vanadium-based contacts amount to 0.81 {+-} 0.02 V.

  6. 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.

  7. Excitation and de-excitation mechanisms of Er-doped GaAs and AlGaAs

    NASA Astrophysics Data System (ADS)

    Elsaesser, David W.

    1992-12-01

    Electrical and optical characterization have been performed on GaAs and Al(x)Ga(1-x)As samples doped with Er either by ion implantation or during Molecular Beam Epitaxial (MBE) growth. Deep Level Transient Spectroscopy (DLTS) and Temperature-Dependent Hall Effect (TDH) measurements indicated the presence of two hole traps in Er-doped GaAs, at 35 and 360 meV above the valence band maximum. The former (shallower) center was thought to be due to Er substituting for a Ga atom (ErGa) and giving rise to an isoelectronic impurity potential. The second center was attributed to an Er atom occupying an interstitial position (Er(i)). Annealing studies performed on Er-implanted GaAs indicated that the ErGa center preferentially formed at higher annealing temperatures (greater than 850 C), with the Er(i) reaching a maximum concentration at an annealing temperature of around 750 C. Optical characterization performed by Photoluminescence (PL) measurements showed that the Er(i) center gave a much stronger Er-related intra-4f shell emission. Mechanisms for the excitation of the 4f shells of these two centers are discussed. Similar optically active Eri centers may be forming in AlGaAs.

  8. Growth of n-doped GaAs nanowires by Au-assisted metalorganic chemical vapor deposition: effect of flux rates of n-type dopants

    NASA Astrophysics Data System (ADS)

    Guo, Jingwei; Huang, Hui; Liu, Minjia; Ren, Xiaomin; Cai, Shiwei; Wang, Wei; Wang, Qi; Huang, Yongqing; Zhang, Xia

    2010-12-01

    N-doped GaAs nanowires (NWs) were grown on GaAs (111) B substrate by means of vapor-liquid-solid (VLS) mechanism in a metalorganic chemical vapor deposition (MOCVD) system. Two flux rates of n-type dopants used for GaAs NWs growth were researched. For comparison, undoped GaAs NWs were grown at the same conditions. It is found that all NWs are vertical to the substrate and no lateral growth occurs. The growth rate is proportional the flux rates of n dopant. It is observed that there is Gibbs-Thomson effect in doped NWs. Pure zinc blende structures without any stacking faults from bottom to top for all three samples were achieved.

  9. Enhancement of intensity-dependent absorption in InP and GaAs at 1.9 microns by doping

    NASA Technical Reports Server (NTRS)

    Li, N.-L.; Bass, M.; Swimm, R.

    1985-01-01

    It is pointed out that the study of intensity-dependent absorption (IDA) in general, and two-photon absorption (TPA), in particular, has suffered from experimental difficulties and inadequate theoretical models. Bass et al. (1979) could improve the experimental situation by making use of laser calorimetry to obtain directly the TPA coefficient of a medium with a high degree of sensitivity. In the present investigation, the employed technique has been used to study the effect of deep level dopants on IDA in InP and GaAs. It is found that the coefficient for IDA is strongly dependent on the presence of Fe in InP and Cr in GaAs. The conducted investigation had the objective to examine the effect of deep level impurities on IDA processes in InP and GaAs. Fe-doped InP and Cr-doped GaAs were compared with undoped crystals.

  10. Carbon doping for the GaAs base layer of Heterojunction Bipolar Transistors in a production scale MOVPE reactor

    NASA Astrophysics Data System (ADS)

    Brunner, F.; Bergunde, T.; Richter, E.; Kurpas, P.; Achouche, M.; Maaßdorf, A.; Würfl, J.; Weyers, M.

    2000-12-01

    In this work different approaches for carbon doping of GaAs in MOVPE are compared with respect to their growth- and device-related material properties. Doping levels up to 6×10 19 cm -3 and smooth surface morphologies are achieved with either intrinsically (TMG and AsH 3 or TMAs) or extrinsically (CBr 4) doped layers. Despite comparable structural and majority carrier properties differences in GaInP/GaAs-HBT device performance depending on base doping conditions are obtained. Devices with an intrinsically doped base layer (TMG+AsH 3) show superior transistor performance with a current gain to base sheet resistance ratio ( β/ Rsb) exceeding 0.5 for base thicknesses as large as 120 nm. The use of either CBr 4 or TMAs as base growth precursors results in reduced current gains ( β/ Rsb⩽0.3). It is shown that the achieved HBT current gain is directly related to recombination centers in the heavily doped base layer depending on doping method.

  11. Self-consistent calculations and design considerations for a GaAs nipi doping superlattice solar cell

    NASA Technical Reports Server (NTRS)

    Clark, Ralph O.; Goradia, Chandra; Brinker, David

    1987-01-01

    The authors present design constraints which show that a previously proposed GaAs nipi doping superlattice solar cell structure would not work as an efficient space solar cell. A structure based on the CLEFT process, which shows promise of being an efficient cell with very high radiation tolerance, is proposed. In order to test theoretically its viability and to optimize its design, self-consistent quantum mechanical calculations were made for a number of thicknesses of the n, i, and p layers and the dopings in the n and p layers. These results show that: 1) an i layer is not necessary; in fact, its presence makes it difficult to satisfy one of the key constraints; 2) a near-optimum design with 750-A thick n and p layers with dopings of 2.5E18/cu cm and a selective contact separation of 20 microns would yield both high efficiency and very high radiation tolerance.

  12. Self-consistent calculations and design considerations for a GaAs nipi doping superlattice solar cell

    NASA Technical Reports Server (NTRS)

    Clark, Ralph O.; Goradia, Chandra; Brinker, David

    1987-01-01

    The authors present design constraints which show that a previously proposed GaAs nipi doping superlattice solar cell structure would not work as an efficient space solar cell. A structure based on the CLEFT process, which shows promise of being an efficient cell with very high radiation tolerance, is proposed. In order to test theoretically its viability and to optimize its design, self-consistent quantum mechanical calculations were made for a number of thicknesses of the n, i, and p layers and the dopings in the n and p layers. These results show that: 1) an i layer is not necessary; in fact, its presence makes it difficult to satisfy one of the key constraints; 2) a near-optimum design with 750-A thick n and p layers with dopings of 2.5E18/cu cm and a selective contact separation of 20 microns would yield both high efficiency and very high radiation tolerance.

  13. 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.

  14. Effects of rapid thermal annealing on two-dimensional delocalized electronic states of the epitaxial N δ-doped layer in GaAs

    SciTech Connect

    Ogawa, Yasuhiro; Harada, Yukihiro; Baba, Takeshi; Kaizu, Toshiyuki; Kita, Takashi

    2016-03-14

    We have conducted rapid thermal annealing (RTA) for improving the two-dimensional (2D) arrangement of electronic states in the epitaxial nitrogen (N) δ-doped layer in GaAs. RTA rearranged the N-pair configurations in the GaAs (001) plane and reduced the number of non-radiative recombination centers. Furthermore, a Landau shift, representing the 2D delocalized electronic states in the (001) plane, was observed at around zero magnetic field intensity in the Faraday configuration.

  15. 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.

  16. Emission-wavelength tuning of InAs quantum dots grown on nitrogen-δ-doped GaAs(001)

    SciTech Connect

    Kaizu, Toshiyuki; Taguchi, Kohei; Kita, Takashi

    2016-05-21

    We studied the structural and photoluminescence (PL) characteristics of InAs quantum dots (QDs) grown on nitrogen (N) δ-doped GaAs(001). The emission wavelength for low-density N-δ doping exhibited a blueshift with respect to that for undoped GaAs and was redshifted with increasing N-sheet density. This behavior corresponded to the variation in the In composition of the QDs. N-δ doping has two opposite and competing effects on the incorporation of Ga atoms from the underlying layer into the QDs during the QD growth. One is the enhancement of Ga incorporation induced by the lattice strain, which is due to the smaller radius of N atoms. The other is an effect blocking for Ga incorporation, which is due to the large bonding energy of Ga-N or In-N. At a low N-sheet density, the lattice-strain effect was dominant, while the blocking effect became larger with increasing N-sheet density. Therefore, the incorporation of Ga from the underlying layer depended on the N-sheet density. Since the In-Ga intermixing between the QDs and the GaAs cap layer during capping also depended on the size of the as-grown QDs, which was affected by the N-sheet density, the superposition of these three factors determined the composition of the QDs. In addition, the piezoelectric effect, which was induced with increased accumulation of lattice strain and the associated high In composition, also affected the PL properties of the QDs. As a result, tuning of the emission wavelength from 1.12 to 1.26 μm was achieved at room temperature.

  17. 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.

  18. Optical power-driven electron spin relaxation regime crossover in Mn-doped bulk GaAs

    NASA Astrophysics Data System (ADS)

    Münzhuber, F.; Kiessling, T.; Ossau, W.; Molenkamp, L. W.; Astakhov, G. V.

    2015-09-01

    We demonstrate tunability of the electron spin lifetime in Mn-doped GaAs by purely optical means. The observed behavior stems from a crossover of the electron spin relaxation rate with increasing excitation density, first decreasing due to the exchange interaction of Mn bound holes with Mn ions, and then increasing again as the valence band is populated and Bir-Aranov-Pikus relaxation sets in. On this account, we explain the complex spatial spin polarization profiles emerging from inhomogeneous optical excitation, which are the result of the combined action of this nonmonotonic spin relaxation characteristics and the intricate photocarrier decay dynamics.

  19. Microstructure and contact resistance temperature dependence of Pt/Ti ohmic contact to Zn-doped GaAs

    NASA Astrophysics Data System (ADS)

    Katz, A.; Nakahara, S.; Savin, W.; Weir, B. E.

    1990-10-01

    Ohmic contacts to p-GaAs, Zn doped at 5×1018 and 1×1019 cm-3, with the best specific contact resistance of 1.2×10-5 and 2.4×10-6 Ω cm2, respectively, have been formed with deposited layers of Ti and Pt. These layers, which were sequentially evaporated and then rapid thermally processed at 450 °C for 30 s, contained an interfacial layer constituted mainly of the TiAs phase adjacent to the substrate and the TixGa1-x solid solution in between it and the Ti layer. In addition, a significant amount of the Pt3Ti intermetallic was found at the Ti/Pt interface. The same metallization scheme, applied to 1×1018 cm-3 Zn-doped GaAs, produced a Schottky contact for the as-deposited and heat-treated samples. The temperature dependence characteristic of the specific contact resistance of the as-deposited Pt/Ti contacts to 5×1018 and 1×1019 cm-3 Zn-doped GaAs revealed a thermionic emission dominated carrier transport mechanism with an apparent barrier height of about 0.118 and 0.115 eV, respectively. This mechanism remained as the dominated one for the heat-treated contacts to the lower doped substrate. The contact resistance of the heat-treated contacts to the more heavily doped substrate, however, revealed a weaker temperature dependence. This indicates a conversion to a mixture of thermionic and field-emission carrier transport mechanisms across the interfacial barrier, and a reduced barrier height to a minimum value of 0.068 eV measured after sintering at 450 °C.

  20. Photoluminescence of Undoped, Semi-Insulating, and Mg-Implanted Indium Phosphide.

    DTIC Science & Technology

    1979-12-01

    PH/79D-8 PHOTOLUMINESCENCE OF UNDOPED, SEMI-INSULATING, AND Mg- IMPLANTED INDIUM PHOSPHIDE THESIS Presented to the Faculty of the School of Engineering...Unannealed, Unimplanted and Mg- Implanted InP:Fe at 500 K ...... 132 Appendix H: Photoluminescence of Mg- Implanted , 750* C Annealed InP:Fe at 50 K...136 Appendix I: Photoluminescence of Mg- Implanted , 7000 C Annealed InP:Fe at 4.20 K ..................... 146 Appendix J

  1. Excitation and De-Excitation Mechanisms of Er-Doped GaAs and A1GaAs.

    DTIC Science & Technology

    1992-12-01

    laser, which operates on internal transitions in the unfilled 4f shell of the RE ion neodymium (Nd 3 +) in yttrium aluminum garnet (YAG = Y3Ah5O 1 2... operation , as well as a much smaller shift in the mode wavelength with temperature (,,hAPC) as compared to laser structures without Er-doping (,,5 APC...Techniques ......................................... 18 3.1. Hall Effect Measurements ................................... 18 3.1.1. Temperature

  2. Effect of Sb composition on the conduction type and photoluminescence of heavily Sn-doped GaAs1-xSbx

    NASA Astrophysics Data System (ADS)

    Sasaki, T.; Jinbo, Y.; Uchitomi, N.

    2006-09-01

    Heavily Sn-doped GaAs1-xSbx epitaxial films were grown on SI-GaAs (001) substrates by solid source molecular beam epitaxy. A 5 nm-thick AlSb buffer layer was employed to relax the lattice mismatch between the epilayer and the substrate. X-ray diffraction (XRD), Hall effect measurements and photoluminescence measurements were performed to characterize the epitaxial films. The heavily Sn-doped GaAs1-xSbx / AlSb films with x 0.24 indicated n-type conduction while the epitaxial films with x 0.43 indicated p-type conduction.

  3. 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.

  4. 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.

  5. The effect of doping on low temperature growth of high quality GaAs nanowires on polycrystalline films

    NASA Astrophysics Data System (ADS)

    DeJarld, Matt; Teran, Alan; Luengo-Kovac, Marta; Yan, Lifan; Moon, Eun Seong; Beck, Sara; Guillen, Cristina; Sih, Vanessa; Phillips, Jamie; Mirecki Milunchick, Joanna

    2016-12-01

    The increasing demand for miniature autonomous sensors requires low cost integration methods, but to date, material limitations have prevented the direct growth of optically active III-V materials on CMOS devices. We report on the deposition of GaAs nanowires on polycrystalline conductive films to allow for direct integration of optoelectronic devices on dissimilar materials. Undoped, Si-doped, and Be-doped nanowires were grown at Ts = 400 °C on oxide (indium tin oxide) and metallic (platinum and titanium) films. Be-doping is shown to significantly reduce the nanowire diameter and improve the nanowire aspect ratio to 50:1. Photoluminescence measurements of Be-doped nanowires are 1-2 orders of magnitude stronger than undoped and Si-doped nanowires and have a thermal activation energy of 14 meV, which is comparable to nanowires grown on crystalline substrates. Electrical measurements confirm that the metal-semiconductor junction is Ohmic. These results demonstrate the feasibility of integrating nanowire-based optoelectronic devices directly on CMOS chips.

  6. The effect of doping on low temperature growth of high quality GaAs nanowires on polycrystalline films.

    PubMed

    DeJarld, Matt; Teran, Alan; Luengo-Kovac, Marta; Yan, Lifan; Moon, Eun Seong; Beck, Sara; Guillen, Cristina; Sih, Vanessa; Phillips, Jamie; Milunchick, Joanna Mirecki

    2016-12-09

    The increasing demand for miniature autonomous sensors requires low cost integration methods, but to date, material limitations have prevented the direct growth of optically active III-V materials on CMOS devices. We report on the deposition of GaAs nanowires on polycrystalline conductive films to allow for direct integration of optoelectronic devices on dissimilar materials. Undoped, Si-doped, and Be-doped nanowires were grown at Ts  = 400 °C on oxide (indium tin oxide) and metallic (platinum and titanium) films. Be-doping is shown to significantly reduce the nanowire diameter and improve the nanowire aspect ratio to 50:1. Photoluminescence measurements of Be-doped nanowires are 1-2 orders of magnitude stronger than undoped and Si-doped nanowires and have a thermal activation energy of 14 meV, which is comparable to nanowires grown on crystalline substrates. Electrical measurements confirm that the metal-semiconductor junction is Ohmic. These results demonstrate the feasibility of integrating nanowire-based optoelectronic devices directly on CMOS chips.

  7. Physical property analysis of C-doped GaAs as function of the carrier concentration grown by MOCVD using elemental arsenic as precursor

    NASA Astrophysics Data System (ADS)

    Díaz-Reyes, J.; Avendaño, M. A.; Galván-Arellano, M.; Peña-Sierra, R.

    2006-03-01

    This work presents the characterization of GaAs layers grown in a metallic-arsenic-based-MOCVD system. The gallium precursor was the compound trimethylgallium (TMG) and elemental arsenic as precursor of arsenic. The most important parameters of the growth process include the substrate temperature and the composition of the carrier gas; an N2+H2 gas mixture. The influence of carbon doping on the optical and electrical properties of GaAs layers have been studied by photoluminescence (PL) spectroscopy, Photoreflectance (PR) and Hall Effect measurements. To carry out doping with carbon in the range of around 1016 to 1020 cm-3, it was necessary to modifying the hydrogen activity in the reacting atmosphere with the control of the N{2}+H{2}, mixture which was used as carrier gas. The PL response of the samples is strongly dependent on the growth temperature and showed mainly two radiative transitions, band-to-band and band-to C-acceptor. PR spectra present transitions associated to GaAs. Besides, short period oscillations near the GaAs band-gap energy are observed, interpreted as Franz-Keldysh oscillations associated to the hole-ionized acceptor (h-A-) pair modulations. For investigating the chemical bonds of impurity-related species in the GaAs layers optical absorption was measured using a FT-IR spectrometer. Device quality GaAs layers have been grown in a broad range of growth temperatures.

  8. Low temperature planar regrowth of semi-insulating InP by low pressure hydride vapour phase epitaxy for device application

    NASA Astrophysics Data System (ADS)

    Alexandre, F.; Parillaud, O.; Nguyen, D. C.; Azoulay, R.; Quillec, M.; Bouchoule, S.; Le Mestreallan, G.; Juhel, M.; Le Roux, G.; Rao, E. V. K.

    1998-05-01

    The growth of both undoped and iron doped InP on planar as well as non-planar (0 0 1)InP substrates has been explored using low pressure hydride vapour phase epitaxy (LP-HVPE) in the temperature range of 500-620°C. Secondary ion mass spectroscopy (SIMS), X-ray diffraction and photoluminescence measurements have shown no drastic degradation in the crystal quality with decreasing growth temperature. The Fe incorporation in the layers is found to be independent of the substrate temperature ( Ts) and in all experiments semi-insulating InP : Fe layers with resistivities close to 10 9 Ω cm have been obtained. A perfect growth selectivity with no deposition on masked areas and a good planarized regrowth on mesas has been demonstrated even at low Ts.

  9. Influence of low-temperature annealing on Schottky barrier height and surface electrical properties of semi-insulating CdTe

    NASA Astrophysics Data System (ADS)

    Rejhon, M.; Franc, J.; Zázvorka, J.; Dědič, V.; Kunc, J.

    2017-08-01

    We investigated the influence of low-temperature annealing in ambient air on the fundamental properties of semi-insulating CdTe doped with In and Cl in planar configuration, with gold and indium contacts prepared by evaporation at temperatures up to 373 K. The Au contact was formed by a central electrode and a guard ring, which allows us to separate bulk and surface leakage currents. We measured I-V characteristics and ellipsometry after each annealing step at room temperature. We determined that the change of the Schottky barrier height is responsible for the change of the bulk current, while the surface leakage current is affected by TeO2 layer thickness.

  10. GaInP/GaAs tandem solar cells with highly Te- and Mg-doped GaAs tunnel junctions grown by MBE

    NASA Astrophysics Data System (ADS)

    Zheng, Xin-He; Liu, San-Jie; Xia, Yu; Gan, Xing-Yuan; Wang, Hai-Xiao; Wang, Nai-Ming; Yang, Hui

    2015-10-01

    We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction (TJ) with using tellurium (Te) and magnesium (Mg) as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy (MBE) at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm2. The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 mA/cm2, but a low open-circuit voltage range of 1.4 V˜1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy (SIMS) analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended GaAs n++/p++ junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of ˜ 2.5 × 1020 in GaAs could cause a lattice strain of 10-3 in magnitude and thus a surface roughening, which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell. Project supported by the SINANO-SONY Joint Program (Grant No. Y1AAQ11001), the National Natural Science Foundation of China (Grant No. 61274134), the USCB Start-up Program (Grant No. 06105033), and the International Cooperation Projects of Suzhou City, China (Grant No. SH201215).

  11. Three-fold Symmetric Doping Mechanism in GaAs Nanowires.

    PubMed

    Dastjerdi, M H T; Fiordaliso, E M; Leshchenko, E D; Akhtari-Zavareh, A; Kasama, T; Aagesen, M; Dubrovskii, V G; LaPierre, R R

    2017-10-11

    A new dopant incorporation mechanism in Ga-assisted GaAs nanowires grown by molecular beam epitaxy is reported. Off-axis electron holography revealed that p-type Be dopants introduced in situ during molecular beam epitaxy growth of the nanowires were distributed inhomogeneously in the nanowire cross-section, perpendicular to the growth direction. The active dopants showed a remarkable azimuthal distribution along the (111)B flat top of the nanowires, which is attributed to preferred incorporation along 3-fold symmetric truncated facets under the Ga droplet. A diffusion model is presented to explain the unique radial and azimuthal variation of the active dopants in the GaAs nanowires.

  12. Implementation of Neural Network Method to Investigate Defect Centers in Semi-Insulating Materials

    NASA Astrophysics Data System (ADS)

    Jankowski, S.; Wierzbowski, M.; Kaminski, P.; Pawlowski, M.

    A neural network (NN) method has been proposed as a new algorithm for extraction of defect centers parameters in semi-insulating materials from experimental data obtained by photoinduced transient spectroscopy (PITS). The new algorithm is applied to investigate irradiation-induced defect centers in high resistive silicon. The folds on the PITS spectral surface formed due to the presence of defect levels are best fitted with a two-dimensional approximation function with implementation of the NN learning process. As a result, the Arrhenius plots for defect centers are obtained and the parameters of these centers are determined.

  13. Carrier compensation in semi-insulating CdTe: First-principles calculations

    SciTech Connect

    Du, Mao-Hua; Singh, David J

    2008-01-01

    Carrier compensation in semi-insulating CdTe has been attributed to the compensation of surplus shallow acceptors by deep donors, usually assumed to be Te antisites. However, our first-principles calculations show that intrinsic defects should not have a significant effect on the carrier compensation due either to lack of deep levels near midgap or to low defect concentration. We demonstrate that an extrinsic defect, OTe-H complex, may play an important role in the carrier compensation in CdTe because of its amphoteric character and reasonably high concentration. Our findings have important consequences for improving device performance in CdTe-based radiation detectors and solar cells.

  14. Compensation Mechanism in High Purity Semi-Insulating 4H-SiC

    DTIC Science & Technology

    2007-01-01

    online 15 March 2007 A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect TDH , thermal and...optical admittance spectroscopies, and secondary ion mass spectrometry SIMS. Thermal activation energies from TDH varied from a low of 0.55 eV to a...high of 1.65 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to

  15. Persistent photoconductivity in uniforndy and selectively silicon doped AlAs / GaAs short period superlattices

    NASA Astrophysics Data System (ADS)

    Jeanjean, P.; Sicart, J.; Robert, J. L.; Mollot, F.; Planel, R.

    1991-04-01

    Hall and photo-Hall measurements have been carried out between 4 K et 400 K on MBE deposited AlAs / GaAs superiattices (SPS) with short period (25 Å < P < 50 Å) SPSs were uniformly or selectively doped with silicon. Galvanomagnetic measurements show that SPSs exhibited an electrical behaviour similar to that of AlxGal{1-x}As : Si alloy (0.32 < x < 0.35). The Hall mobility was increased under illumination and persistent photoconductivity (PPC) was observed at low temperature (DX center). Ibermal annealing of PPC was performed by increasing the measurement temperature. Two plateaus are observed in the n_H(T) curves in uniformly doped SPSs whereas only one plateau was present in selectively doped SPSs. These experimental results are interpreted in terms of the multibarrier model of the DX center recently proposed in AIxGal{1-x}As: Si. Nous présentons des résultats de mesures d'effet Hall et photo-Hall obtenus entre 4 K et 400 K dans des superréseaux AlAs / GaAs de courtes périodes (25 Å < P < 50 Å) déposées par MBE et dopées au silicium de manière uniforme ou sélectivement dans GaAs. Les mesures de concentration de porteurs et de mobilité par effet Hall à l'obscurité montrent que ce type de SPS (short period superiattice) présente un comportement électrique voisin de l'alliage AIxGal{1-x}As: Si de teneur en aluminium équivalente (0.32 < x < 0.35). Les mesures de photo-Hall à basse température montrent que ces SPS présentent également une photeconductivité persistente (PPC) et une augmentation de mobilité sous éclairement. La présence d'un plateau de PPC à basse temperature (T< 90 K) est caractéristique du centre métastable DX dans tous les cas. Des mesures de décroissance du nombre de porteurs mesurés à l'obscurité aprés éclairement quand la température augmente (capture thermique), mettent en évidence la présence de deux plateaux correspondant à deux barrières thermiques de l'état métastable du centre DX dans les SPS

  16. Improvement in GaAs Device Yield and Performance through Substrate Defect Gettering

    DTIC Science & Technology

    1980-06-01

    defects will be retained at tempera- tures aproaching those normally encountered in routine device fabrication or processing procedures. Therefore, we...insulating GaAs wafers or direct ion implantation and annealing of bulk insulating substrates. The latter method would appear to be straight forward process...capsulated Czochralski (LEC) growth methods to reduce the residual donor level and, thereby, produce semi-insulating GaAs without the intentional addition

  17. Factors influencing doping control and abrupt metallurgical transitions during atmospheric pressure MOVPE growth of AlGaAs and GaAs

    NASA Astrophysics Data System (ADS)

    Roberts, J. S.; Mason, N. J.; Robinson, M.

    1984-09-01

    Atmospheric pressure MOVPE of GaAs and AlGaAs has been investigated using two gas handling systems and a conventional horizontal reactor. Initially a simple source/carrier gas manifold design was assessed but severe retention of reagents in the pipework resulted in poor control of doping and interface abruptness. However, integration of the reagent and carrier gas in a pressure balanced vent/run configuration gave a significant improvement. AlGaAs/GaAs multilayers and n +/n - GaAs transitions have been used to assess the performance of both systems. Abrupt p-type doping transitions using bis-cyclopentadienylmagnesium proved unsuccessful as long doping tails were observed.

  18. In Situ Selected Area Doping of GaAs by Molecular Beam Epitaxy.

    DTIC Science & Technology

    1985-07-01

    utilized a multichambered, cyropumped, LN shrouded, homebuilt MBE apparatus. The MBE system consists of three chambers: a load-lock chamber, an antechamber... homebuilt apparatus. The three chambers consist of a * load-lock chamber for fast introduction of the GaAs substrate wafers into vacuum, an

  19. 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.

  20. Thermal annealing behavior of deep levels in Rh-doped n-type MOVPE GaAs

    NASA Astrophysics Data System (ADS)

    Naz, Nazir A.; Qurashi, Umar S.; Zafar Iqbal, M.

    2009-12-01

    We report the results of isochronal annealing study of deep levels in Rh-doped n-type GaAs grown by metal-organic vapor phase epitaxy (MOVPE). Deep level transient spectroscopy (DLTS) technique has been employed to study the effects of annealing on deep levels in Rh-doped p+nn+ junction samples. A majority-carrier emitting band of deep levels along with a high temperature peak (RhE1), corresponding to deep level energy position Ec-0.92 eV and a minority-carrier emitting band of deep levels are identified with Rh-impurity prior to thermal annealing of our samples. In addition to these Rh-related deep levels, the well-known native defect EL2 at Ec-0.79 eV is observed in majority-carrier emission spectra and two inadvertent deep-level defects, H1 at Ev+0.09 eV and H3 at Ev+0.93 eV, usually observed in reference (without Rh) samples, are also detected in the minority-carrier emission spectra of Rh-doped samples. At least one level is found to be introduced at Ec-0.13 eV in Rh-doped samples at about the same temperature position as the level E(A)1, observed in reference samples, as a result of isochronal annealing, while the other two levels observed in reference samples could not be seen in annealed Rh-doped samples. Data on the annealing behavior and other characteristics of both Rh-related bands of deep levels observed in majority- and minority-carrier emission DLTS spectra, as well as for the high temperature Rh-related electron-emission peak, are presented. Possible interpretations of these results for the nature and structure of the different deep-level defects are discussed.

  1. 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.

  2. Identifying and quantifying point defects in semiconductors using x-ray-absorption spectroscopy: Si-doped GaAs

    SciTech Connect

    Schuppler, S.; Adler, D.L.; Pfeiffer, L.N.; West, K.W.; Chaban, E.E.; Citrin, P.H.

    1995-04-15

    Both the type and concentration of point defects responsible for the observed poor electrical activity of highly Si-doped GaAs have been determined using near-edge and extended x-ray-absorption fine structure (NEXAFS and EXAFS). The measurements were made possible using a combination of synchrotron beamline features, fluorescence detection, and GaAs(311){ital A} samples. Because Si can occupy both {ital n}-type Ga and {ital p}-type As sites, the electrical deactivation has generally been attributed to acceptor-Si atoms trapping free-electron carriers. However, the present NEXAFS data directly measure upper limts on the concentration of Si atoms occupying such {ital p}-type As sites, showing that only about half of the observed electrical inactivity is due to this autocompensation mechanism. Identification of the dominant defects responsible for the additionally missing carriers is provided by the EXAFS data, which reveal a comparatively large number of neutral Si{sub Ga}-Si{sub As} dimers and small Si{sub {ital n}} clusters. Implications of these findings and a comparison with local vibrational mode spectroscopy and scanning tunneling microscopy methods are discussed.

  3. Photoreflectance analysis of annealed vanadium-doped GaAs thin films grown by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Bilel, C.; Zaied, I.; Bchetnia, A.; Rebey, A.; El Jani, B.

    2015-09-01

    In this study, we investigate the optical properties of annealed vanadium-doped GaAs films grown on GaAs substrates by metalorganic vapor phase epitaxy. The temperature dependence of the photoreflectance (PR) of as-grown GaAs:V films has been studied. We used the fit with Third-Derivative Functional Form model to evaluate the physical parameters. The temperature dependence of band gap and spin-orbit energies can be described by the Bose-Einstein statistical expression. The PR spectra of the samples are measured after thermal annealing in order to check any improvement in the optical quality of the material. The PR signal amplitude of GaAs:V samples decreased after thermal annealing. Degradation of the PR signal for annealing temperature at about 850 °C is observed revealing a poor quality of the layer surface states and an important density of the recombination centers. The lock-in phase analysis of PR spectra allows to determine the time constant for GaAs:V sample before and after thermal annealing.

  4. 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.

  5. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    NASA Astrophysics Data System (ADS)

    Schulthess, T. C.; Temmerman, W. M.; Szotek, Z.; Svane, A.; Petit, L.

    2007-04-01

    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 the 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 photoemission experiments.

  6. 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.

  7. 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.

  8. 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.

  9. Critical metal-insulator transition due to nuclear quantum effects in Mn-doped GaAs

    NASA Astrophysics Data System (ADS)

    Bae, Soungmin; Raebiger, Hannes

    2016-12-01

    Mn-doped GaAs exhibits a critical metal-insulator transition at the Mn concentration of xcrit≈1 % . Our self-interaction corrected first principles calculation shows that for Mn concentrations x ≳1 % , hole carriers are delocalized in host valence states, and for x ≲1 % , holes tend to be trapped in impurity-band-like states. We further show that for a finite range of concentrations around xcrit the system exhibits a nonadiabatic superposition of these states, i.e., a mixing of electronic and nuclear wave functions. This means that the phase transition is continuous, and its criticality is caused by quantum effects of the atomic nuclei. In other words, the apparently electronic phase transition from the insulator to metal state cannot be described by electronic effects alone.

  10. High-purity semi-insulating 4H-SiC for microwave device applications

    NASA Astrophysics Data System (ADS)

    Jenny, J. R.; Malta, D. P.; Müller, St G.; Powell, A. R.; Tsvetkov, V. F.; Hobgood, H. Mcd; Glass, R. C.; Carter, C. H., Jr.

    2003-05-01

    High-purity, semi-insulating (HPSI) 4H-SiC crystals with diameters up to 75 mm have been grown by the seeded sublimation technique without the intentional introduction of elemental deep-level dopants, such as vanadium. Wafers cut from these crystals exhibit homogeneous activation energies near mid gap and thermally stable semi-insulating (SI) behavior (>109 ohm-cm) throughout device processing. Secondary ion mass spectroscopy, deep-level transient spectroscopy, optical admittance spectroscopy, and electron paramagnetic resonance data suggest that the SI behavior originates from several deep levels associated with intrinsic point defects. Micropipe densities in HPSI substrates have been demonstrated to be as low as 10 cm-2 in 2-in. substrates, and the room-temperature thermal conductivity of this material is near the theoretical maximum of 5 W/cm·K for 4H-SiC. Devices fabricated on these HPSI wafers do not exhibit any substrate related back-gating effects and have power densities as high as 5.2 W/mm with 63% power added efficiency.

  11. Passivation of carbon acceptors during growth of carbon-doped GaAs, InGaAs, and HBTs by MOCVD

    SciTech Connect

    Stockman, S.A.; Hanson, A.W.; Lichtenthal, S.M.; Fresina, M.T.; Hoefler, G.E.; Hsieh, K.C.; Stillman, G.E. )

    1992-12-01

    Carbon doped p-type GaAs and In[sub 0.53]Ga[sub 0.47]As epitaxial layers were grown by low-pressure metalorganic chemical vapor deposition using CCl[sub 4] as the carbon source. Low-temperature post-growth annealing resulted in a significant increase in the hole concentration for both GaAs and In[sub 0.53]Ga[sub 0.47]As, especially at high doping levels. The most heavily doped GaAs sample had a hole concentration of 3.6 [times] 10[sup 20] cm[sup [minus]3] after a 5 minute anneal at approximately 400[degree]C in N[sub 2], while the hole concentration in In[sub 0.53]Ga[sub 0.47]As reached 1.6 [times] 10[sup 19] cm[sup [minus]3] after annealing. This behavior is attributed to hydrogen passivation of carbon acceptors. Post-growth cool-down in an AsH[sub 3]/H[sub 2] ambient was found to be the most important factor affecting the degree of passivation for single, uncapped GaAs layers. No evidence of passivation is observed in the base region of InGaP/GaAs HBTs grown at approximately 625[degree]C. The effect of n-type cap layers and cool-down sequence on passivation of C-doped InGaAs grown at approximately 525[degree] shows that hydrogen can come from AsH[sub 3], PH[sub 3], or H[sub 2], and can be incorporated during growth and post-growth cool-down. In the case of InP/InGaAs HBTs, significant passivation was found to occur in the C-doped base region. 28 refs., 5 figs., 2 tabs.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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 n2DA and n2DB, and the same well width. The Thomas-Fermi approximation, the semi-empirical sp3s* 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.

  13. 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.

  14. 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.

  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. 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.

  17. 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.

  18. 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.

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

    PubMed

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

    2014-09-07

    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.

  20. Thermally stimulated current spectroscopy on silicon planar-doped GaAs samples

    NASA Astrophysics Data System (ADS)

    Rubinger, R. M.; Bezerra, J. C.; Chagas, E. F.; González, J. C.; Rodrigues, W. N.; Ribeiro, G. M.; Moreira, M. V. B.; de Oliveira, A. G.

    1998-10-01

    Using thermally stimulated current (TSC) spectroscopy we have identified the presence of several deep traps in low temperature grown (LTG) nonintentionally doped bulk molecular beam epitaxy (MBE)-GaAs and silicon planar-doped MBE-GaAs samples. The experiments of TSC spectroscopy were carried out on a LTG MBE-GaAs epilayer grown at 300 °C and the planar-doped layer with a nominal silicon concentration of 3.4×1012cm-2. The LTG nonintentionally doped bulk MBE-GaAs sample shows three peaks in the TSC spectra but the planar-doped MBE-GaAs sample shows spectra similar to those of bulk samples grown by the liquid-encapsulated Czochralski and vertical gradient freeze methods. The main achievement is the experimental evidence that the potential well present in the planar-doped sample is effective in detecting the presence of different deep traps previously not seen in LTG bulk MBE-GaAs epilayers due to a shorter carrier lifetime (about 10-12 s) in the conduction band which occurs due to EL2-like deep traps recombination. This fact is evidenced by a strong hopping conduction in LTG bulk MBE-GaAs samples at temperatures lower than 300 K, but not in planar-doped MBE-GaAs samples because the two-dimensional electron gas has a higher mobility than lateral LTG bulk MBE-GaAs epilayers.

  1. 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).

  2. 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).

  3. Femtosecond energy relaxation of nonthermal electrons injected in p-doped GaAs base of a heterojunction bipolar transistor

    NASA Astrophysics Data System (ADS)

    Prabhu, S. S.; Vengurlekar, A. S.

    2001-07-01

    We study femtosecond relaxation of minority carriers (electrons) injected into a heavily p-doped base of a heterojunction bipolar transistor (HBT). Here, we consider the case of p-doped GaAs, to be specific. The electrons are assumed to have a peaked energy distribution at t=0, with kinetic energies a few hundred meV above the conduction band threshold. We solve the time dependent Boltzmann equation governing the dynamics of these electrons. The main feature of this work is a detailed calculation of the time dependent nonthermal, nonequilibrium electron energy distribution, that relaxes due to single particle excitations via electron-hole scattering and interaction with coupled optical phonon-hole plasmon modes in the sub and picosecond time domains. We highlight the significant role that the electron-hole scattering plays in this relaxation. The majority carriers (holes) are assumed to remain in quasiequilibrium with the lattice, taken to be at room temperature (or at 77 K). We present calculations of electron energy relaxation with the hole density varied from 1×1018 to 1×1020cm-3. In the initial, subpicosecond stages of the relaxation, the energy distribution evolves into two major components: a quasiballistic but broad component, at energies near the injection energy, and an energy relaxed component near E=0. The latter becomes dominant in a picosecond or so. The electrons with an initial mean velocity of ˜1.5×108cm/s attain a cooler distribution with a mean velocity of ˜4×107 cm/s within about 1 ps for p doping in excess of 1×1019 cm-3. The temporal evolution of average velocity of the electrons should be useful in obtaining values of the base width suitable for effective operation of HBTs.

  4. Compensation mechanism in liquid encapsulated Czochralski GaAs Importance of melt stoichiometry

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Elliott, K. R.; Kirkpatrick, C. G.; Yu, P. W.

    1982-01-01

    It is shown that the key to reproducible growth of undoped semi-insulating GaAs by the liquid encapsulated Czochralski (LEC) technique is the control over the melt stoichiometry. Twelve crystals were grown from stoichiometric and nonstoichiometric melts. The material was characterized by secondary ion mass spectrometry, localized vibrational mode far infrared spectroscopy, Hall-effect measurements, optical absorption, and photoluminescence. A quantitative model for the compensation mechanism in the semi-insulating material was developed based on these measurements. The free carrier concentration is controlled by the balance between EL2 deep donors and carbon acceptors; furthermore, the incorporation of EL2 is controlled by the melt stoichiometry, increasing as the As atom fraction in the melt increases. As a result, semi-insulating material can be grown only from melts above a critical As composition. The practical significance of these results is discussed in terms of achieving high yield and reproducibility in the crystal growth process.

  5. Germanium- and tellurium-doped GaAs for non-alloyed {ital p}-type and {ital n}-type ohmic contacts

    SciTech Connect

    Park, J.; Barnes, P.A.; Lovejoy, M.L.

    1995-08-14

    Epitaxial ohmic contacts to GaAs were grown by liquid phase epitaxy. Heavily Ge-doped GaAs was grown to prepare ohmic contacts to {ital p}-GaAs while Te was used for the {ital n}-type contacts. Hall measurements were carried out for the samples grown from melts in which the mole fraction of Ge was varied between 1.55 atomic % and 52.2 atomic %, while the Te mole fractions varied between 0.03% and 0.5%. Specific contact resistance, {ital r}{sub {ital c}}, as low as {ital r}{sub {ital cp}}=2.9{times}10{sup {minus}6} ohm-cm{sup 2} for Ge doping of {ital p}=({ital N}{sub {ital a}}{minus}{ital N}{sub {ital d}})=6.0{times}10{sup 19} holes/cm{sup 3} was measured for {ital p}-contacts and {ital r}{sub {ital cn}}=9.6{times}10{sup {minus}5} ohm-cm{sup 2 }was measured for Te doping of {ital n}=({ital N}{sub {ital d}}{minus}{ital N}{sub {ital a}})=8.9{times}10{sup 18} electrons/cm{sup 3 }for GaAs metallized with non-alloyed contacts of Ti/Al. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  6. Germanium- and tellurium-doped GaAs for non-alloyed p-type and n-type ohmic contacts

    NASA Astrophysics Data System (ADS)

    Park, Joongseo; Barnes, Peter A.; Lovejoy, Michael L.

    1995-08-01

    Epitaxial ohmic contacts to GaAs were grown by liquid phase epitaxy. Heavily Ge-doped GaAs was grown to prepare ohmic contacts to p-GaAs while Te was used for the n-type contacts. Hall measurements were carried out for the samples grown from melts in which the mole fraction of Ge was varied between 1.55 atomic % and 52.2 atomic %, while the Te mole fractions varied between 0.03% and 0.5%. Specific contact resistance, rc, as low as rcp=2.9×10-6 ohm-cm 2 for Ge doping of p=(Na-Nd)=6.0×1019 holes/cm3 was measured for p-contacts and rcn=9.6×10-5 ohm-cm2 was measured for Te doping of n=(Nd-Na)=8.9×1018 electrons/cm3 for GaAs metallized with non-alloyed contacts of Ti/Al.

  7. Development of bulk GaAs room temperature radiation detectors

    SciTech Connect

    McGregor, D.S.; Knoll, G.F. . Dept. of Nuclear Engineering); Eisen, Y. . Soreq Nuclear Research Center); Brake, R. )

    1992-10-01

    This paper reports on GaAs, a wide band gap semiconductor with potential use as a room temperature radiation detector. Various configurations of Schottky diode detectors were fabricated with bulk crystals of liquid encapsulated Czochralski (LEC) semi-insulating undoped GaAs material. Basic detector construction utilized one Ti/Au Schottky contact and one Au/Ge/Ni alloyed ohmic contact. Pulsed X-ray analysis indicated pulse decay times dependent on bias voltage. Pulse height analysis disclosed non-uniform electric field distributions across the detectors tentatively explained as a consequence of native deep level donors (EL2) in the crystal.

  8. Infrared absorption related to the metastable state of arsenic antisite defects in electron-irradiated GaAs

    SciTech Connect

    Kuisma, S.; Saarinen, K.; Hautojaervi, P.; Corbel, C.

    1996-12-31

    A metastable irradiation-induced vacancy is detected by positrons in semi-insulating GaAs. The vacancy is associated with the metastable state of an irradition-induced As-antisite-related defect. This metastable state absorbs IR light in contrast to the metastable state of the As-antisite-related native EL2 defect. This property can be explained by the presence of other defects complexed with the As antisite in electron-irradiated GaAs.

  9. 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.

  10. Highly efficient and electrically robust carbon irradiated semi-insulating GaAs based photoconductive terahertz emitters

    NASA Astrophysics Data System (ADS)

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S. S.; Nanal, Vandana; Pillay, R. G.

    2014-02-01

    We demonstrate here an efficient photoconductive THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters (PCEs) by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 μm deep, we have created lot of defects and decreased the lifetime of photo-excited carriers inside the substrate. Depending on the irradiation dose, we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the device. This has resulted in increasing maximum cut-off of the applied voltage across PCE electrodes to operate the device without thermal breakdown from ˜35 V to >150 V for the 25 μm electrode gaps. At optimum operating conditions, carbon irradiated (1014 ions/cm2) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ˜800.

  11. Optical-Electrical Characteristics and Carrier Dynamics of Semi-Insulation GaAs by Terahertz Spectroscopic Technique

    NASA Astrophysics Data System (ADS)

    Han, Xiao-Wei; Hou, Lei; Yang, Lei; Wang, Zhi-Quan; Zhao, Meng-Meng; Shi, Wei

    2016-12-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 61575161 and 61427814, the National Basic Research Program of China under Grant No 2014CB339800, the Foundation of Shaanxi Key Science and Technology Innovation Team under Grant No 2014KTC-13, and the Special Financial Grant from the China Postdoctoral Science Foundation under Grant No 2013T60883.

  12. 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.

  13. III-nitride heterostructure field-effect transistors grown on semi-insulating GaN substrate without regrowth interface charge

    NASA Astrophysics Data System (ADS)

    Liu, J. P.; Ryou, J.-H.; Yoo, D.; Zhang, Y.; Limb, J.; Horne, C. A.; Shen, S.-C.; Dupuis, R. D.; Hanser, A. D.; Preble, E. A.; Evans, K. R.

    2008-03-01

    Charge is observed at the regrowth interface for heterostructure field-effect transistors (HFETs) grown on semi-insulating (SI) bulk GaN substrates, even with Fe doping in the regrown buffer layer for reduction of the interface charge. Ultraviolet photoenhanced chemical (PEC) etching is used to treat the surface of SI bulk GaN substrates. Employing optimized etching conditions, a very smooth surface is achieved for the bulk GaN substrate after the etching. The charge at the regrowth interface is eliminated for HFETs grown on etched SI GaN substrates. Secondary ion mass spectrometry measurements show that the Si impurity concentration at the regrowth interface for HFETs grown on etched SI GaN substrates is much lower than that for HFETs grown on unetched SI GaN substrates, which suggests that the charge-containing layer on the SI substrate is removed by PEC etching and that the effects of the reduced charge layer near the regrowth interface can be eliminated by Fe doping for HFETs grown on etched SI substrates.

  14. Investigation of New SemiInsulating Behavior of III-V Compounds

    DTIC Science & Technology

    1990-02-28

    encapsulated Czochralski and horizontal Bridgman techniques and in epitaxial crystals prepared by liquid-phase electroepitaxy. By employing deep-level...com- crystals by LEG9 ") and horizontal Bridgman (HB)-" tech- plexes could be responsible for deep levels in GaAs. 1 7 niques has also been reported...Fig. 7) became direct band-gap semiconductors (GaAs and CdSe ) and was clearly visible after quenching of the absorption. explained in terms of a

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

    SciTech Connect

    Norseng, Marshall Stephen

    1999-12-01

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

  16. Intermediate Band Performance of GaSb Type-II Quantum Dots Located in n-Doped Region of GaAs Solar Cells

    NASA Astrophysics Data System (ADS)

    Kechiantz, Ara; Afanasev, Andrei

    2013-03-01

    The intermediate band (IB) electronic states assist sub-bandgap photons in generation of additional photocurrent in single-junction solar cells. Such non-linear effect of resonant two-photon absorption of concentrated sunlight attracts much attention because it promises up to 63% conversion efficiency in IB solar cells. The main obstacle to achieving high performance is involvement of IB-states in electron-hole recombination that is drastically increasing the dark current and reducing the open circuit voltage of IB solar cells. The IB-states can be composed of quantum dots (QDs). Concentration of sunlight limits recombination through type-II QD IB-states located outside of the depletion region. In this work we model GaAs solar cell with strained GaSb type-II QDs separated from the depletion region. The focus is on type-II QDs located in n-doped region of p-n-junction. Our calculation shows that photovoltaic performance can be essentially improved by concentration of sunlight, and that this improvement is highly sensitive to the doping of materials and the shape of potential barriers surrounding type-II QDs. For instance, strained GaSb type-II QDs may increase the performance of GaAs solar cell by 20% compared to the reference GaAs solar cell without QDs.

  17. 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.

  18. GaAs Self-Aligned JFETS with Carbon-Doped P+ Region

    SciTech Connect

    Allerman, A.A.; Baca, A.G.; Chang, P.C.; Drummond, T.J.

    1999-02-15

    Self-aligned JFETs with a carbon-doped p{sup +} region have been reported for the first time. For these JFETs, both the channel and p{sup +} region were grown by metal organic chemical vapor deposition (MOCVD) and are termed epitaxial JFETs in this study. The epitaxial JFETs were compared to ion implanted JFETs of similar channel doping and threshold voltage. Both JFETs were fabricated using the same self-aligned process for doping the source and drain regions of the JFET and for eliminating excess gate capacitance of conventional JFETs. The gate turn-on voltage for the epitaxial JFETs was 1.06 V, about 0.1 V higher than for the implanted JFETs. The reverse breakdown voltage was similar for both JFETs but the reverse gate leakage current of the epitaxial JFETs was 1-3 orders of magnitude less than the implanted JFETs. The epitaxial JFETs also showed higher transconductance and lower knee voltage than the implanted JFETs.

  19. A New Radiation Hard Semiconductor — Semi-Insulating GaN: Photoelectric Properties

    NASA Astrophysics Data System (ADS)

    Vaitkus, J.; Gaubas, E.; Kazukauskas, V.; Blue, A.; Cunningham, W.; Rahman, M.; Smith, K.; Sakai, S.

    2005-06-01

    The anticipated upgrade of the CERN Large Hadron Collider to ten times brighter luminosity poses a severe challenge to semiconductor detectors in the CERN experiments. The suitability of semi-insulating GaN (SI-GaN), proposed as an alternative to silicon for the fabrication of radiation hard detectors, is investigated here in MOCVD GaN layers grown on sapphire. The electrical properties of SI-GaN were studied by dc and microwave techniques, and defect parameters determined by the method of thermally stimulated currents. Variations of charge collection efficiency (CCE) in SI-GaN diodes induced by ionizing radiation of 5.48 MeV alpha particles were revealed. Samples were also irradiated by X-rays, reactor neutrons and high-energy proton fluences of up to 1016 cm-2. The high radiation hardness of SI-GaN was demonstrated by the modest reduction in CCE, from 92% to 77%, in the material irradiated by neutrons (up to a fluence of 1015 cm-2). The CCE was unaffected by an X-rays dose of 600 MRad), but decreased to a few % after proton and neutron fluences of 1016 cm-2. The electrical characteristics vary more significantly, depending on irradiation type and dose. Fast decay components and a significant role of percolation effects are observed in the photoconductivity transients.

  20. Gamma-Ray Response of Semi-Insulating CdMnTe Crystals

    SciTech Connect

    Kim, K.H.; Cho, S.H.; Suh, J.H.; Hong, J.; Kim, S.U.

    2009-06-10

    Semi-insulating Cd{sub 0.9}Mn{sub 0.1}Te:In crystals are grown by vertical Bridgman method. The segregation coefficient of Mn in CdTe is nearly 1 so that all the CdMnTe samples obtained from one ingot have nearly a same Mn composition. Also sulfur-based passivation effectively prevent the formation of Te-oxide but large amount of Mn exist as a MnO on the CdMnTe surface. The resistivity of CdMnTe samples are low 10{sup 10} Omegacm and well resolved {sup 241}Am gamma peaks are seen for all detectors. The difference in spectral response can be attributed to the effect of excess Te and conductivity change due to over-compensation induced by indium segregation in CdMnTe. The mobility-lifetime products evaluated from the dependence of peak location on the bias voltage are 1 times 10{sup -3} cm{sup 2}/V. The higher mobility-lifetime products in our CdMnTe crystals than other previous reports are assumed due to minimization of impurity contents in MnTe by several zone refining process.

  1. Compensation mechanism in high purity semi-insulating 4H-SiC

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Mitchell, William D.; Smith, H. E.; Landis, G.; Smith, S. R.; Glaser, E. R.

    2007-03-01

    A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect (TDH), thermal and optical admittance spectroscopies, and secondary ion mass spectrometry (SIMS). Thermal activation energies from TDH varied from a low of 0.55eV to a high of 1.65eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to different charge balance equations and comparison of the fitting results with SIMS measurements indicated that the deep levels are acceptorlike even though they are in the upper half of the band gap. Carrier concentration measurements indicated that the deep levels are present in concentrations in the low 1015cm-3 range, while SIMS results demonstrate nitrogen and boron concentrations in the low to mid-1015-cm-3 range. The results suggest that compensation in this material is a complex process involving multiple deep levels.

  2. Femtosecond energy relaxation of nonthermal electrons injected in p-doped GaAs base of a heterojunction bipolar transistor

    SciTech Connect

    Prabhu, S. S.; Vengurlekar, A. S.

    2001-07-01

    We study femtosecond relaxation of minority carriers (electrons) injected into a heavily p-doped base of a heterojunction bipolar transistor (HBT). Here, we consider the case of p-doped GaAs, to be specific. The electrons are assumed to have a peaked energy distribution at t=0, with kinetic energies a few hundred meV above the conduction band threshold. We solve the time dependent Boltzmann equation governing the dynamics of these electrons. The main feature of this work is a detailed calculation of the time dependent nonthermal, nonequilibrium electron energy distribution, that relaxes due to single particle excitations via electron{endash}hole scattering and interaction with coupled optical phonon-hole plasmon modes in the sub and picosecond time domains. We highlight the significant role that the electron-hole scattering plays in this relaxation. The majority carriers (holes) are assumed to remain in quasiequilibrium with the lattice, taken to be at room temperature (or at 77 K). We present calculations of electron energy relaxation with the hole density varied from 1{times}10{sup 18} to 1{times}10{sup 20}cm{sup {minus}3}. In the initial, subpicosecond stages of the relaxation, the energy distribution evolves into two major components: a quasiballistic but broad component, at energies near the injection energy, and an energy relaxed component near E=0. The latter becomes dominant in a picosecond or so. The electrons with an initial mean velocity of {similar_to}1.5{times}10{sup 8}cm/s attain a cooler distribution with a mean velocity of {similar_to}4{times}10{sup 7}cm/s within about 1 ps for p doping in excess of 1{times}10{sup 19}cm{sup {minus}3}. The temporal evolution of average velocity {l_angle}v{r_angle} of the electrons should be useful in obtaining values of the base width suitable for effective operation of HBTs. {copyright} 2001 American Institute of Physics.

  3. Comparison of Intersubband GaAs/AlGaAs Multiple Quantum Well Infrared Photodetectors on GaAs and GaAs-on-Si Subtrates

    NASA Technical Reports Server (NTRS)

    Sengupta, D.; Gunapala, S.; George, T.; Bandara, S.; Chang-Chien, C. N.; Leon, R.; Kayali, S.; Kuo, H.; Fang, W.; Liu, H.; Stillman, G.

    1998-01-01

    We have successfully fabricated intersubband GaAs/AlGaAs quantum well infrared photodetectors grown on GaAs-on-Si substrate and evaluated their structural, electrical, and optical characteristics. We have found that the performance is comparable to a similar detector structure grown on a semi-insulating GaAs substrate.

  4. Fabrication of Ohmic contact on semi-insulating 4H-SiC substrate by laser thermal annealing

    NASA Astrophysics Data System (ADS)

    Cheng, Yue; Lu, Wu-yue; Wang, Tao; Chen, Zhi-zhan

    2016-06-01

    The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρc) is 1.97 × 10-3 Ω.cm2, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC.

  5. An optimal annealing technique for ohmic contacts to ion-implanted n-layers in semi-insulating indium phosphide

    NASA Astrophysics Data System (ADS)

    Pande, K. P.; Martin, E.; Gutierrez, D.; Aina, O.

    1987-03-01

    An optimal annealing process was developed for sintering AuGe ohmic contacts to ion-implanted semi-insulating InP substrates. Contacts were annealed using a standard furnace, graphite strip heater and a lamp annealer. Alloying at 375°C for 3 min was found to be most suitable for achieving good contact morphology and lowest contact resistivity. Of the three techniques, the lamp annealing technique was found to give the best results when contacts were annealed under a SiO 2 cap. Contact resistivity as low as 8 × 10 -6 cm 2 was obtained for ion-implanted n+ layers in semi-insulating InP.

  6. Fabrication of Ohmic contact on semi-insulating 4H-SiC substrate by laser thermal annealing

    SciTech Connect

    Cheng, Yue; Lu, Wu-yue; Wang, Tao; Chen, Zhi-zhan

    2016-06-14

    The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρ{sub c}) is 1.97 × 10{sup −3} Ω·cm{sup 2}, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC.

  7. An Analytical Model for Silicon-on-Insulator Reduced Surface Field Devices with Semi-Insulating Polycrystalline Silicon Shielding Layer

    NASA Astrophysics Data System (ADS)

    Ho, Chi-Hon; Liao, Chien-Nan; Chien, Feng-Tso; Tsai, Yao-Tsung

    2008-07-01

    An analytical model is presented to determine the potential and electric field distribution along the semiconductor surface of new silicon-on-insulator (SOI) reduced surface field (RESURF) device. The SOI structure is characterized by a semi-insulating polycrystalline silicon (SIPOS) layer inserted between a silicon layer and a buried oxide. An improvement in the breakdown voltage due to the presence of the SIPOS shielding layer is demonstrated. Numerical simulations using medici are shown to support the analytical model.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Carrier and defect dynamics in photoexcited semi-insulating epitaxial GaN layers

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Juršėnas, S.; Miasojedovas, S.; Vaitkus, J.; Žukauskas, A.

    2004-10-01

    Transients of fast free-carrier recombination and of multitrapping processes, determined by different types of defects, have been traced by photoluminescence (PL) and contact photoconductivity (CPC) in semi-insulating GaN epitaxial layers. To eliminate effects caused by the electrodes, the CPC decays were supplemented with noninvasive microwave absorption transients. The lifetimes of fast recombination and initial free-carrier capture processes were evaluated using ultraviolet (UV) time-resolved photoluminescence transients. The UV PL band peaked at 3.42 eV with contributions from both stimulated and spontaneous emission was attributed to band-to-band recombination. At the highest excitations, the initial PL decay time exhibited a value of 880 ps due to nonradiative free-carrier recombination. The radiative centers were revealed in continuous-wave PL spectra, where the UV band was accompanied with the bands of blue (B) PL, peaked in the range of 2.82-3.10 eV, and yellow (Y) PL, peaked at 2.19 eV, ascribed to dislocations and bulk donor-acceptor recombination, respectively. The time scale of the relaxation rate exhibited a crossover from picoseconds for stimulated emission to hundreds of nanoseconds for multitrapping. In the asymptotic part, a stretched-exponent decay on the millisecond scale was observed with the disorder factor of α =0.7. The asymptotic decay is explained by competition of centers of nonradiative recombination within bulk of the material and trapping attributed to the dislocations. Behavior of the dislocation-attributed capture centers was simulated using a model of capture cross section, which depends on the excess carrier concentration via screening.

  15. Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping

    PubMed Central

    2012-01-01

    Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV). PACS: 81.15.Gh. PMID:22297193

  16. Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping.

    PubMed

    Dalapati, Goutam Kumar; Shun Wong, Terence Kin; Li, Yang; Chia, Ching Kean; Das, Anindita; Mahata, Chandreswar; Gao, Han; Chattopadhyay, Sanatan; Kumar, Manippady Krishna; Seng, Hwee Leng; Maiti, Chinmay Kumar; Chi, Dong Zhi

    2012-02-02

    Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV).PACS: 81.15.Gh.

  17. Rapid evaluation of doping-spike carrier concentration levels in millimetre-wave GaAs Gunn diodes with hot-electron injection

    NASA Astrophysics Data System (ADS)

    Farrington, N. E. S.; Carr, M. W.; Missous, M.

    2010-12-01

    This paper describes a novel method for fast, accurate evaluation of doping-spike carrier concentrations in hot-electron injected GaAs Gunn diodes. The technique relies on current asymmetry measurements obtained using pulsed-dc testing of on-wafer quasi-planar Gunn diode test structures, which removes the need for full device fabrication. Small changes in carrier concentration can easily be detected (at a nominal value of 1 × 1018 cm-3) and a greater sensitivity than conventional techniques is demonstrated at the doping levels used. In addition, test structure fabrication can be integrated into the initial Gunn diode front side production process allowing a rapid in-process test to be carried out thus leading to a significant reduction in material characterization cycle time.

  18. Nonlinear optical properties of asymmetric n-type double δ-doped GaAs quantum well under intense laser field

    NASA Astrophysics Data System (ADS)

    Sari, Huseyin; Kasapoglu, Esin; Yesilgul, Unal; Sakiroglu, Serpil; Ungan, Fatih; Sökmen, Ismail

    2017-09-01

    The effect of non-resonant intense laser field on the intersubband-related optical absorption coefficient and refractive index change in the asymmetric n-type double δ-doped GaAs quantum well is theoretically investigated. The confined energy levels and corresponding wave functions of this structure are calculated by solving the Schrödinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. The optical responses are reported as a function of the δ-doped impurities density and the applied non-resonant intense laser field. Additionally, the calculated results also reveal that the non-resonant intense laser field can be used as a way to control the electronic and optical properties of the low dimensional semiconductor nano-structures.

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

    SciTech Connect

    Chang, Yoon Jung Woo, Jason C. S.; Simmonds, Paul J.

    2016-04-18

    Using an aspect ratio trapping technique, we demonstrate molecular beam epitaxy of GaAs nanostubs on Si(001) substrates. Nanoholes in a SiO{sub 2} 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{sup +}–Si/n{sup +}–GaAs p–n diodes.

  20. 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.

  1. 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.

  2. Inherent photoluminescence Stokes shift in GaAs.

    PubMed

    Ullrich, Bruno; Singh, Akhilesh K; Barik, Puspendu; Xi, Haowen; Bhowmick, Mithun

    2015-06-01

    The intrinsic photoluminescence Stokes shift, i.e., the energy difference between optical band gap and emission peak, of 350 μm thick semi-insulating GaAs wafers is found to be 4 meV at room temperature. The result is based on the determination of the optical bulk band gap from the transmission trend via modified Urbach rule whose result is confirmed with the transmission derivative method. The findings reveal the detailed balance of the optically evoked transitions and disclose the intrinsic link between Stokes shift and the Urbach tail slope parameter.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Direct identification of interstitial Mn in heavily p-type doped GaAs and evidence of its high thermal stability

    SciTech Connect

    Pereira, L. M. C.; Wahl, U.; Correia, J. G.; Decoster, S.; Vantomme, A.; Silva, M. R. da; Araujo, J. P.

    2011-05-16

    We report on the lattice location of Mn in heavily p-type doped GaAs by means of {beta}{sup -} emission channeling from the decay of {sup 56}Mn. The majority of the Mn atoms substitute for Ga and up to 31% occupy the tetrahedral interstitial site with As nearest neighbors. Contrary to the general belief, we find that interstitial Mn is immobile up to 400 deg. C, with an activation energy for diffusion of 1.7-2.3 eV. Such high thermal stability of interstitial Mn has significant implications on the strategies and prospects for achieving room temperature ferromagnetism in Ga{sub 1-x}Mn{sub x}As.

  8. Alloy formation during molecular beam epitaxy growth of Si-doped InAs nanowires on GaAs[111]B

    PubMed Central

    Davydok, Anton; Rieger, Torsten; Biermanns, Andreas; Saqib, Muhammad; Grap, Thomas; Lepsa, Mihail Ion; Pietsch, Ullrich

    2013-01-01

    Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiOx layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, the formation of a Ga0.2In0.8As alloy was observed if the growth was performed on samples covered by a defective oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Ga concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers. PMID:24046494

  9. Alloy formation during molecular beam epitaxy growth of Si-doped InAs nanowires on GaAs[111]B.

    PubMed

    Davydok, Anton; Rieger, Torsten; Biermanns, Andreas; Saqib, Muhammad; Grap, Thomas; Lepsa, Mihail Ion; Pietsch, Ullrich

    2013-08-01

    Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiO x layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, the formation of a Ga0.2In0.8As alloy was observed if the growth was performed on samples covered by a defective oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Ga concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers.

  10. Electrical properties of Mg-doped GaAs and AlxGa1-xAs (x<=0.36)

    NASA Astrophysics Data System (ADS)

    Csontos, L.; Podor, Balint; Somogyi, K.; Andor, L.

    1992-08-01

    Mg-doped GaAs and AlxGa1-xAs (x

  11. Electronic spin polarization and the spin-dependent bandstructure in GaAs probed by optically pumped NMR

    SciTech Connect

    Crooker, Scott A; Ramaswamy, Kannan; Mui, Stacy; Hayes, Sophia E; Pan, Xingyuan; Sanders, Gary D; Stanton, Christopher J

    2008-01-01

    High resolution optically pumped NMR (OPNMR) experiments are used to resolve fine features in the spin-dependent electronic structure of the valence bands in semi-insulating GaAs. By theoretically calculating oscillations in the OPNMR signal intensity with respect to the excitation energy, we have mapped out the conduction band electronic spin polarization under optical pumping. Comparison with a theoretical analysis of the oscillatory experimental features allows the extraction of semiconductor energy band parameters.

  12. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Anomalous behaviours of terahertz reflected waves transmitted from GaAs induced by optical pumping

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Lei; Zhou, Qing-Li; Zhao, Dong-Mei; Zhang, Cun-Lin

    2009-12-01

    Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers. It is observed that, at high pump powers, the reflection peaks flip to the opposite polarity and dramatically enhance as the pump arrival time approaches the reflected wave of the terahertz pulse. The abnormal polarity-flip and enhancement can be interpreted by the pump-induced enhancement in the photoconductivity of GaAs and half-wave loss. Moreover, the carrier relaxation processes and surface states filling in GaAs are also studied in these measurements.

  13. Liquid encapsulated Czochralski growth of low dislocation GaAs

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Holmes, D. E.

    1982-01-01

    The availability of high-quality, large-diameter GaAs substrates is key to the successful development and production of high-speed GaAs devices and high-efficiency GaAs solar cells. The liquid encapsulated Czochralski (LEC) technique has provided a means for producing large-diameter GaAs. Progress in improving the LEC growth process which has resulted in 3-inch GaAs crystals with exceptionally low dislocation densities and reduced propensity for twinning is reported. Undoped, semi-insulating GaAs ingots were grown in a Melbourn high-pressure LEC system. The effects of seed perfection, seed necking, cone angle, melt stoichiometry, ambient pressure, thickness of the B2O3 encapsulating layer, and diameter control on the dislocation density were investigated. The material was characterized by preferential etching and X-ray topography. It is shown that 3-inch diameter substrates can be produced with dislocation densities as low as 6000 per sq cm through proper selection and control of growth parameters. Also, the incidence of twinning can be reduced significantly by growing from slightly As-rich melts.

  14. Quantitative analysis of the effects of vertical magnetic fields on microsegregation in Te-doped LEC GaAs

    NASA Technical Reports Server (NTRS)

    Carlson, D. J.; Witt, A. F.

    1992-01-01

    Using near-IR transmission microscopy with computational absorption analysis, the effects of axial magnetic fields on micro- and macrosegregation during LP-LEC growth of GaAs were quantitatively investigated with a spatial resolution approaching 2 microns. Segregation inhomogeneities exceeding one order of magnitude are found to be related to fluid dynamics of the melt. The applicability of the BPS theory as well as the nonapplicability of the Cochran analysis are established.

  15. Deep-defect-induced quenching effects in semi-insulating GaN layers detected by photoelectrical spectroscopic techniques

    NASA Astrophysics Data System (ADS)

    Witte, H.; Krtschil, A.; Lisker, M.; Schrenk, E.; Christen, J.; Krost, A.; Kuhn, B.; Scholz, F.

    2003-06-01

    Quenching effects induced by additional below-bandgap illumination in undoped semi-insulating GaN were investigated using optical admittance spectroscopy (OAS) and photocurrent (PC) spectroscopy as well as optically excited, thermally stimulated currents (TSC). In OAS and PC, a decrease of defect-related signals due to the quenching light was observed. The thermal quenching of the defect band between 2.7 and 3.3 eV shows a good agreement with thermal emissions as measured by TSC, indicating the same defects cause the optical transitions in OAS/PC and the thermal transitions in TSC. The thermal emission in the temperature region between 250 and 300 K, which is responsible for the thermal quenching of the blue band (BB) in OAS, also shows an optical quenching under below-bandgap excitation.

  16. Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

    SciTech Connect

    Pousset, J.; Farella, I.; Cola, A.; Gambino, S.

    2016-03-14

    We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

  17. Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

    NASA Astrophysics Data System (ADS)

    Pousset, J.; Farella, I.; Gambino, S.; Cola, A.

    2016-03-01

    We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

  18. 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.

  19. Terahertz emission enhancement in semi-insulating gallium arsenide integrated with subwavelength one-dimensional metal line array.

    PubMed

    Faustino, Maria Angela B; Lopez, Lorenzo P; Pauline Afalla, Jessica; Muldera, Joselito; Hermosa, Nathaniel; Salvador, Arnel A; Somintac, Armando S; Estacio, Elmer S

    2016-10-01

    A one-order-of-magnitude terahertz (THz) emission enhancement in the transmission geometry, over a 0.7-THz broadband range, was observed in semi-insulating gallium arsenide (SI-GaAs) integrated with a subwavelength one-dimensional metal line array (1DMLA). THz emission of the 1DMLA samples showed an intensity increase and exhibited a full-width-at-half-maximum broadening relative to the emission of the bare substrate. Improved index matching could not account for the observed phenomenon. A nonlinear dependence of the integrated THz emission intensity on the number of illuminated lines and on the pump power was observed. The actual origin of the increased THz emission is still under investigation. At present, it is attributed to extraordinary optical transmission.

  20. 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.

  1. 4H-SiC Schottky barrier diodes with semi-insulating polycrystalline silicon field plate termination

    NASA Astrophysics Data System (ADS)

    Yuan, Hao; Tang, Xiao-Yan; Zhang, Yi-Men; Zhang, Yu-Ming; Song, Qing-Wen; Yang, Fei; Wu, Hao

    2014-05-01

    Based on the theoretical analysis of the 4H-SiC Schottky-barrier diodes (SBDs) with field plate termination, 4H-SiC SBD with semi-insulating polycrystalline silicon (SIPOS) FP termination has been fabricated. The relative dielectric constant of the SIPOS dielectric first used in 4H-SiC devices is 10.4, which is much higher than that of the SiO2 dielectric, leading to benefitting the performance of devices. The breakdown voltage of the fabricated SBD could reach 1200 V at leakage current 20 μA, about 70% of the theoretical breakdown voltage. Meanwhile, both of the simulation and experimental results show that the length of the SIPOS FP termination is an important factor for structure design.

  2. Defect levels of semi-insulating CdMnTe:In crystals

    NASA Astrophysics Data System (ADS)

    Kim, K. H.; Bolotinikov, A. E.; Camarda, G. S.; Hossain, A.; Gul, R.; Yang, G.; Cui, Y.; Prochazka, J.; Franc, J.; Hong, J.; James, R. B.

    2011-06-01

    Using photoluminescence (PL) and current deep-level transient spectroscopy (I-DLTS), we investigated the electronic defects of indium-doped detector-grade CdMnTe:In (CMT:In) crystals grown by the vertical Bridgman method. We similarly analyzed CdZnTe:In (CZT:In) and undoped CdMnTe (CMT) crystals grown under the amount of same level of excess Te and/or indium doping level to detail the fundamental properties of the electronic defect structure more readily. Extended defects, existing in all the samples, were revealed by synchrotron white beam x-ray diffraction topography and scanning electron microscopy. The electronic structure of CMT is very similar to that of CZT, with shallow traps, A-centers, Cd vacancies, deep levels, and Te antisites. The 1.1-eV deep level, revealed by PL in earlier studies of CZT and CdTe, were attributed to dislocation-induced defects. In our I-DLTS measurements, the 1.1-eV traps showed different activation energies with applied bias voltage and an exponential dependence on the trap-filling time, which are typical characteristics of dislocation-induced defects. We propose a new defect-trap model for indium-doped CMT crystals.

  3. Analysis and comparison of the breakdown performance of semi-insulator and dielectric passivated Si strip detectors

    NASA Astrophysics Data System (ADS)

    Ranjan, Kirti; Bhardwaj, Ashutosh; Namrata; Chatterji, Sudeep; Srivastava, Ajay K.; Shivpuri, R. K.

    2002-12-01

    The harsh radiation environment in future high-energy physics (HEP) experiments like LHC provides a challenging task to the performance of Si microstrip detectors. Normal operating condition for silicon detectors in HEP experiments are in most cases not as favourable as for experiments in nuclear physics. In HEP experiments the detector may be exposed to moisture and other adverse atmospheric environment. It is therefore utmost important to protect the sensitive surfaces against such poisonous effects. These instabilities can be nearly eliminated and the performance of Si detectors can be improved by implementing suitably passivated metal-overhang structures. This paper presents the influence of the relative permittivity of the passivant on the breakdown performance of the Si detectors using computer simulations. The semi-insulator and the dielectric passivated metal-overhang structures are compared under optimal conditions. The influence of various parameters such as passivation layer thickness, junction depth, metal-overhang width, device depth, substrate resistivity and fixed oxide charge on the junction breakdown voltage of these structures is extensively studied. The results presented in this work clearly demonstrate the superiority of the metal-overhang structure design employing semi-insulator passivated structures over dielectric passivated ones in realising a given breakdown voltage. The effect of bulk damage caused by hadron environment in the passivated Si detectors is simulated, to a first order approximation, by varying effective carrier concentration (calculated using Hamburg Model) and minority carrier lifetime. This approach allows getting an insight of the device behaviour after radiation damage by evaluating the electric field distribution, and thus proves helpful in predicting some interesting results.

  4. The investigation of custom grown vertical zone melt semi-insulating bulk gallium arsenide as a radiation spectrometer

    SciTech Connect

    McGregor, D.S.; Antolak, A.J.; Chui, H.C.

    1996-06-01

    Vertical zone melt (VZM) bulk GaAs boules have been zone refined (ZR) and zone leveled (ZL) to reduce EL2 deep donor levels and impurity concentrations with the intent of improving properties for gamma ray detectors. Zr and Zl GaAs boules had background impurity levels and deep donor EL2 concentrations near or below detectable limits. The crystal mosaic of the material at locations near the seed end was slightly superior to commercial liquid encapsulated Czochralski (LEC) material, and nearly equivalent to commercial vertical gradient freeze (VGF) material. The crystal mosaic in ZL material degraded towards the tail end. The homogeneity of the electrical properties for the ZL and ZR VZM material was inferior compared to commercially available bulk GaAs material. Post growth annealing may help to homogenize some electrical properties of the material. The charge collection efficiency of the ZR GaAs detectors was only 30% maximum, and only 25% maximum for the ZL GaAs detectors. Resulting gamma ray spectra was poor from detectors fabricated with the ZL or ZR VZM material. Detectors fabricated from material that was both ZR and ZL did not demonstrate gamma ray resolution, and operated mainly as counters. The poor spectroscopic performance is presently attributed to the inhomogeneity of the electrical properties of the ZR and ZL GaAs materials. Comparisons are made with detectors fabricated from VGF SI bulk GaAs.

  5. Nonlinear optical properties of GaAs at 1. 06 micron, picosecond pulse investigation and applications

    SciTech Connect

    Cui, A.G.

    1992-01-01

    The author explores absorptive and refractive optical nonlinearities at 1.06 [mu]m in bulk, semi-insulating, undoped GaAs with a particular emphasis on the influence of the native deep-level defect known as EL2. Picosecond pump-probe experimental technique is used to study the speed, magnitude, and origin of the absorptive and refractive optical nonlinearities and to characterize the dynamics of the optical excitation of EL2 in three distinctly different undoped, semi-insulating GaAs samples. Intense optical excitation of these materials leads to the redistribution of charge among the EL2 states resulting in an absorptive nonlinearity due to different cross sections for electron and hole generation through this level. This absorptive nonlinearity is used in conjunction with the linear optical properties of the material and independent information regarding the EL2 concentration to extract the cross section ratio [sigma][sub p]/[sigma][sub e] [approx equal]0.8, where [sigma][sub p](e) is the absorption cross section for hole (electron) generation from EL2[sup +] (EL2[sup 0]). The picosecond pump-probe technique can be used to determine that EL2/EL2[sup +]density ratio in an arbitrary undoped, semi-insulating GaAs sample. The author describes the use of complementary picosecond pump-probe techniques that are designed to isolate and quantify cumulative and instantaneous absorptive and refractive nonlinear processes. Numerical simulations of the measurements are achieved by solving Maxwell equations with the material equations in a self-consistent manner. The numerical analysis together with the experimental data allows extraction of a set of macroscopic nonlinear optical parameters in undoped GaAs. The nonlinearities in this material have been used to construct three proof-of-principle nonlinear optical devices for use at 1.06 [mu]m: (1) a weak beam amplifier, (2) a polarization rotation optical switch, and (3) optical limiters.

  6. Structural properties of pressure-induced structural phase transition of Si-doped GaAs by angular-dispersive X-ray diffraction

    NASA Astrophysics Data System (ADS)

    Lin, Kung-Liang; Lin, Chih-Ming; Lin, Yu-Sheng; Jian, Sheng-Rui; Liao, Yen-Fa; Chuang, Yu-Chun; Wang, Chuan-Sheng; Juang, Jenh-Yih

    2016-02-01

    Pressure-induced phase transitions in n-type silicon-doped gallium arsenide (GaAs:Si ) at ambient temperature were investigated by using angular-dispersive X-ray diffraction (ADXRD) under high pressure up to around 18.6 (1) GPa, with a 4:1 (in volume ratio) methanol-ethanol mixture as the pressure-transmitting medium. In situ ADXRD measurements revealed that n-type GaAs:Si starts to transform from zinc- blende structure to an orthorhombic structure [GaAs-II phase], space group Pmm2, at 16.4 (1) GPa. In contrast to previous studies of pure GaAs under pressure, our results show no evidence of structural transition to Fmmm or Cmcm phase. The fitting of volume compression data to the third-order Birch-Murnaghan equation of state yielded that the zero-pressure isothermal bulk moduli and the first-pressure derivatives were 75 (3) GPa and 6.4 (9) for the B3 phase, respectively. After decompressing to the ambient pressure, the GaAs:Si appears to revert to the B3 phase completely. By fitting to the empirical relations, the Knoop microhardness numbers are between H PK = 6.21 and H A = 5.85, respectively, which are substantially smaller than the values of 7-7.5 for pure GaAs reported previously. A discontinuous drop in the pressure-dependent lattice parameter, N- N distances, and V/ V 0 was observed at a pressure of 11.5 (1) GPa, which was tentatively attributed to the pressure-induced dislocation activities in the crystal grown by vertical gradient freeze method.

  7. A p-type-doped quantum dot superluminescent LED with broadband and flat-topped emission spectra obtained by post-growth intermixing under a GaAs proximity cap.

    PubMed

    Zhang, Z Y; Jiang, Q; Luxmoore, I J; Hogg, R A

    2009-02-04

    Broadband superluminescent light emitting diodes are realized by a post-growth annealing process, on modulation p-doped multiple InAs/InGaAs/GaAs quantum dot layer structures, under a GaAs proximity cap. The device exhibits a large and flat emission with spectral width up to 132 nm at 2 mW. This is mainly attributed to the reduction of the energy separation between the ground state and the excited state, in addition to the optical quality of the intermixed modulation p-doped quantum dot materials being comparable to that of the as-grown sample.

  8. Semi insulating CdTe:Cl after elimination of inclusions and precipitates by post grown annealing

    SciTech Connect

    Franc, J.; Belas, E.; Bug?r, M.; Hl?dek, P.; Grill, R.; Yang, G.; Cavallini, A.; Fraboni, B.; Castaldini, A.; Assali, S.

    2012-11-01

    We present in this contribution results of two-step annealing, when the CdTe:Cl doped samples are at first annealed under Cd overpressure to remove inclusions and the re-annealed under Te overpressure to restore the high resistivity state. Investigation of samples after Cd rich annealing by infrared microscope has proven, that all inclusions are removed. Also Te nano precipitates were strongly influenced by the annealing process. The resistivity of the samples after Te-rich annealing was restored to values ( ~ 108-109Ωcm). We observed, however, decrease of mobility-lifetime product of electrons from 10-3cm2/Vs to 10-4cm2/Vs. In order to understand the reason of this decrease we performed a study of point defects before and after annealing by thermoelectric effect spectroscopy. It shows a decrease of concentrations of most deep levels after two-step annealing. This behavior is completely different compared to past annealing studies, where concentration of deep levels strongly increased after annealing. The only level with an increased concentration in the current study is the midgap level (E ~ 0.8 eV). At the same time we observed increase of micro-twins in the samples investigated by transmission electron microscopy. The decrease of charge collection efficiency after two-step annealing may be therefore connected with re-arrangement of near midgap levels due to increase of concentrations of structure defects (micro twins, dislocations) that accumulate in their surroundings point defects with energy ~ 0.75 eV.

  9. Characterization Of Thermal Annealing Of Implanted GaAs Using Raman Scattering

    NASA Astrophysics Data System (ADS)

    Yaney, Perry P.; Baird, William E., Jr.; Park, Y. S.

    1981-04-01

    Raman spectra were recorded in backscattering from (100) oriented, Cr-doped, semi-insulating crystalline wafers of GaAs to characterize the changes introduced by implan-tation and by encapsulation and thermal anneal15ing. The studies were carried out at 300 and 100K. Implant fluences of lx1012 to 1x1015 S-ions/cm2 at 120 keV were used. Annealing temperatures ranged from 750 to 950°C for 15 minutes. The encapsulation was by means of rf-plasma-deposited Si3N4 films. The characteristics of a fixed annealing pro-cedure as a function of fluence and a fixed fluence at different annealing temperatures were determined. Unprocessed samples and a laser-annealed sample were studied. A pulsed, doubled YAG laser at 532 nm was used with about 16 mW of incident power in a 0.12-mm-diameter spot. A "triple" spectrometer, gated photon counting and computer pro-cessing of data were used. Following are the results: (1) the intensity of the LO pho-non line strongly varied with both implant dosage and annealing including a five-fold enhancement at 1012 S-ions/cm2 fluence, (2) the LO mode "softened" apparently due to implant-induced bond weakening, (3) polycrystalline and amorphous conditions of the implanted layer were identified, (4) thermal annealing itself was found to introduce disorder in the surface, at least for temperatures above 850°C, and (5) removal of amor-phous regions by laser annealing was observed.

  10. GaAs thin film epitaxy and x-ray detector development

    NASA Astrophysics Data System (ADS)

    Wynne, Dawnelle I.; Cardozo, B.; Haller, Eugene E.

    1999-10-01

    We report on the growth of high purity n-GaAs using Liquid Phase Epitaxy and on the fabrication of Schottky barrier diodes for use as x-ray detectors using these layers. Our epilayers are grown form an ultra-pure Ga solvent in a graphite boat in a hydrogen atmosphere. Growth is started at a temperature of approximately 800 degrees C; the temperature is ramped down at 2 degrees C/min. to room temperature. Our best epilayers show a net-residual-donor concentration of approximately 2 X 1012 cm-3, measured by Hall effect. Electron mobilities as high as 150,000 cm2 V-1 s-1 at 77K have been obtained. The residual donors have been analyzed by far IR photothermal ionization spectroscopy and found to be sulfur and silicon. Up to approximately 200 micrometers of epitaxial GaAs have been deposited using several sequential growth runs on semi-insulating and n+-doped substrates. Schottky barrier diodes have been fabricated using this epitaxial material and have been electrically characterized by current-voltage and capacitance-voltage measurements. The Schottky barriers are formed by electron beam evaporation of Pt films. The ohmic contacts are made by electron beam evaporated and alloyed Ni-Ge-Au films on the backside of the substrate. Several of our diodes exhibit dark currents of the order of 0.3-3.3 nA/mm2 at reverse biases depleting approximately 50 micrometers of the epilayer. Electrical characteristics and preliminary performance results of our Schottky diodes using 109Cd and 241Am gamma and x- ray radiation will be discussed.

  11. Multiple-Scale Analysis of Charge Transport in Semiconductor Radiation Detectors: Application to Semi-Insulating CdZnTe

    NASA Astrophysics Data System (ADS)

    Bale, Derek S.; Szeles, Csaba

    2009-01-01

    The transport, trapping, and subsequent detrapping of charge in single crystals of semi-insulating cadmium zinc telluride (CdZnTe) has been analyzed using multiple-scale perturbation techniques. This method has the advantage of not only treating impulse charge generation typical in spectroscopic analysis, but also a large class of continuous generation sources more relevant to high-flux x-ray imaging applications. We first demonstrate that the multiple-scale solutions obtained for small-current transients induced by an impulse generation of charge are consistent with well-known exact solutions. Further, we use the multiple-scale solutions to derive an analytic generalization of the Hecht equation that incorporates detrapping over times much longer than the carrier transit time (i.e., delayed signal components). The method is then applied to a continuous charge generation source that approximates that of an x-ray source. The space-time solutions obtained are relevant to detector design in high-flux x-ray imaging applications. Throughout this work the multiple-scale solutions are compared with exact solutions as well as full numerical solutions of the fundamental charge conservation equations.

  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. Combined effects of the intense laser field, electric and magnetic fields on the optical properties of n-type double δ-doped GaAs quantum well

    NASA Astrophysics Data System (ADS)

    Sari, H.; Kasapoglu, E.; Sakiroglu, S.; Yesilgul, U.; Ungan, F.; Sökmen, I.

    2017-06-01

    In the present work, the effects of the non-resonant intense laser field, electric and magnetic fields on the optical properties, such as linear, third order nonlinear and the total optical absorption coefficient and refractive index changes associated with the intersubband transitions between the ground and the first excited states in the n-type double δ-doped GaAs quantum well is theoretically studied by solving the Schrödinger equation in the laser-dressed confinement potential within the framework of effective mass approximation. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. Our numerical results show that the optical absorption coefficient and refractive index change are quite sensitive to the applied external fields, such as non-resonant intense laser field, electric and magnetic fields. The obtained results can be applied for the design of various optoelectronic devices based on the intersubband transitions of electrons.

  14. Effect of quantum dot position and background doping on the performance of quantum dot enhanced GaAs solar cells

    SciTech Connect

    Driscoll, Kristina Bennett, Mitchell F.; Polly, Stephen J.; Forbes, David V.; Hubbard, Seth M.

    2014-01-13

    The effect of the position of InAs quantum dots (QD) within the intrinsic region of pin-GaAs solar cells is reported. Simulations suggest placing the QDs in regions of reduced recombination enables a recovery of open-circuit voltage (V{sub OC}). Devices with the QDs placed in the center and near the doped regions of a pin-GaAs solar cell were experimentally investigated. While the V{sub OC} of the emitter-shifted device was degraded, the center and base-shifted devices exhibited V{sub OC} comparable to the baseline structure. This asymmetry is attributed to background doping which modifies the recombination profile and must be considered when optimizing QD placement.

  15. Development and characterization of zone melt growth GaAs for gamma-ray detectors

    SciTech Connect

    King, S.E.; Dietrich, H.B.; Henry, R.L.; Katzer, D.S.; Moore, W.J.; Phillips, G.W.; Mania, R.C.

    1996-06-01

    GaAs is a potentially attractive material for room temperature x-ray and {gamma}-ray spectrometers. To date, the only high resolution GaAs devices were produced by epitaxial growth. The usefulness of detectors made from bulk grown semi-insulating (SI) GaAs has been limited by low charge collection efficiency caused, it is believed, by the high density of EL2 deep donor defects. Vertical zone melt (VZM) growth of GaAs has recently been developed at the Naval Research Laboratory. Zone refining and zone leveling techniques were used with VZM to reduce the level of impurities and the EL2 defects in bulk SI-GaAs. Schottky barrier and PIN diodes have been fabricated from the newly grown material. These devices were characterized using {alpha} particles and {gamma}-rays. In this paper, the measurements and analysis of the first VZM GaAs devices are presented and compared with commercially available GaAs. The intent is to test the hypothesis that high purity, low defect GaAs material growth could lead to improved radiation detectors.

  16. Electron-paramagnetic-resonance study of the isolated arsenic antisite in electron irradiated GaAs and its relation to the EL2 center

    SciTech Connect

    Rong, F.C.; Buchwald, W.R.; Harmatz, M.; Poindexter, E.H. ); Warren, W.L. )

    1991-10-28

    Arsenic antisites produced in GaAs by room-temperature electron irradiation (RTEI) are examined by electron paramagnetic resonance (EPR). For the first time, this RTEI antisite, which has been believed to be the isolated antisite, is found to be metastable. The most efficient photon energy for photoquenching is found to be approximately 1.15 eV, which is very close to that observed for the well-known EL2 center in undoped semi-insulating GaAs. However, the thermal recovery temperature is about 200--250 K, much higher than that for the EL2 center.

  17. Improvement of radiation stability of semi-insulating gallium arsenide crystals by deposition of diamond-like carbon films

    NASA Astrophysics Data System (ADS)

    Klyui, N. I.; Lozinskii, V. B.; Liptuga, A. I.; Izotov, V. Yu.; Han, Wei; Liu, Bingbing

    2016-12-01

    We studied the properties of optical elements for the IR spectral range based on semi-insulating gallium arsenide (SI-GaAs) and antireflecting diamond-like carbon films (DLCF). Particular attention has been paid to the effect of penetrating γ-radiation on transmission of the developed optical elements. A Co60 source and step-by-step gaining of γ-irradiation dose were used for treatment of both an initial SI-GaAs crystal and DLCF/SI-GaAs structures. It was shown that DLCF deposition essentially increases degradation resistance of the SI-GaAs-based optical elements to γ-radiation. Particularly, the transmittance of the DLCF/SI-GaAs structure after γ-irradiation with a dose 9ṡ104 Gy even exceeds that of initial structures. The possible mechanism that explains the effect of γ-radiation on the SI-GaAs crystals and the DLCF/SI-GaAs structures at different irradiation doses was proposed. The effect of small doses is responsible for non-monotonic transmission changes in both SI-GaAs crystals and DLCF/SI-GaAs structures. At further increasing the γ-irradiation dose, the variation of properties of both DLCF and SI-GaAs crystal influences on the transmission of DLCF/SI-GaAs system. At high γ-irradiation dose 1.4ṡ105 Gy, passivation of radiation defects in the SI-GaAs bulk by hydrogen diffused from DLCF leads to increasing the degradation resistance of the SI-GaAs crystals coated with DLCF as compared with the crystals without DLCF.

  18. High Energy Neutron Irradiation Effects in GaAs Modulation-Doped Field Effect Transistors (MODFETS): Threshold Voltage

    DTIC Science & Technology

    1989-06-15

    PREFACE We would like to thank B. K. Janousek, W. E. Yamada, and L. W. Aukerman for their technical assistance in this study. Aceession For [iTIS CRA...Doped GaAs-(AlGa)As Heterostructures," Surface Science, 132, 519-526, (1983). 8. L. W. Aukerman , "Radiation-Produced Energy Levels in Compound Semi...conductors," J. Appl. Phys. LO, 1239-1243, (Aug. 1959). 9. L. W. Aukerman , "Radiation Effects," in Semiconductors and Semimetals: Physics of III-V

  19. Luminescence and Electroluminescence of Nd, Tm and Yb Doped GaAs and some II-Vi Compounds

    DTIC Science & Technology

    1994-02-28

    isoelectronic trap. We have evidence that II-VI semiconductors, ZnTe doped with oxygen -electron the other RE ions in IlI-V semiconductors can occupy traps...act as donors exciton. or acceptors. The important roles of oxygen on RE It has been well established that the "simple" isoelect- luminescence have...agreement with experimnt, over a wide rang of genration rates. T electric field InP:.Yb photoun~escence quenching was investigated and reported for the

  20. Electrochemical capacitance-voltage measurements and modeling of GaAs nanostructures with delta-doped layers

    NASA Astrophysics Data System (ADS)

    Shestakova, L.; Yakovlev, G.; Zubkov, V.

    2017-03-01

    The paper presents the results of electrochemical capacitance-voltage profiling and simulation of quantum-sized semiconductor structures with quantum wells and delta-doped layers based on gallium arsenide. The experimental ECV data were obtained by superposition of measured capacitance-voltage characteristics during the gradual etching of the nanostructure. As a result of simulation, the concentration distribution and energy lineups for structures with delta-layers and quantum wells in gallium arsenide were calculated. The results of simulation are in qualitative agreement with the experimental results and data found in literature.

  1. Comparative evaluation of InAs/GaSb superlattices for mid infrared detection: p-i-n versus residual doping

    NASA Astrophysics Data System (ADS)

    Korkmaz, Melih; Kaldirim, Melih; Arikan, Bulent; Serincan, Uğur; Aslan, Bulent

    2015-08-01

    We report on the opto-electronic characterization of an InAs/GaSb superlattice (SL) midwave infrared p-i-n photodetector structure (pin-SL) in comparison with the same structure with no intentional doping (i-SL). Both structures were grown on an n-GaSb substrate using molecular beam epitaxy. The nominally undoped structure (i-SL) presented p-i-n like behavior and showed a photovoltaic mode photoresponse due to the residual doping and native defects in this material system. For ˜77 K operation, 0.76 and 0.11 A W-1 responsivity values were obtained at 4 μm from the pin-SL and i-SL structures, respectively. Activation energy analysis showed that the recombination current was dominant in both structures but different recombination centers were involved. The same i-SL structure was also grown on a semi-insulating (SI)-GaAs substrate to study the contribution of the substrate to the carrier density in the SL layers. Temperature dependent Hall effect measurements showed that the nominally undoped structure presented both n-type and p-type conductivities; however, the temperature at which the carrier type switched polarity was observed to be at higher values when the i-SL structure was grown on the SI-GaAs substrate. In addition, a higher carrier density was observed for i-SL on the GaSb substrate than on the GaAs substrate.

  2. Pt/Ti ohmic contacts to ultrahigh carbon-doped p-GaAs formed by rapid thermal processing

    NASA Astrophysics Data System (ADS)

    Katz, A.; Abernathy, C. R.; Pearton, S. J.

    1990-03-01

    Increasing the concentration of the carbon dopants in p-GaAs layers grown on semi-insulating substrates to levels of 1×1020 to 5×1020 cm-3 enables the formation of an ohmic contact with low resistance using the refractory Pt/Ti metallization. These contacts showed ohmic behavior prior to any heat treatment with specific contact resistance as low as 7×10-6 Ω cm2 (0.08 Ω mm) for the lower doping level and 8×10-7 Ω cm2 (0.04 Ω mm) for the higher level. Small improvements in the specific resistance of the former contact were achieved by rapid thermal processing at a temperature of 450 °C for 30 s, which yielded a value of 4.9×10-6 Ω cm2. The electrical nature of the contact to the heavily doped GaAs was not affected by heat treatments at temperatures up to 450 °C. Rapid thermal processing of these contacts at higher temperatures, however, caused an increase in the contact resistance which was correlated to the expanded Ti/GaAs and Pt/GaAs interfacial reactions. Current-voltage characteristics were found to be temperature independent. This suggested that the field emission quantum-mechanical tunneling was the dominant carrier transport mechanism in these contacts.

  3. Photo-carrier and Electronic Studies of Silicon-Doped GaAs Grown by MBE Using PCR

    NASA Astrophysics Data System (ADS)

    Villada, J. A.; Jiménez-Sandoval, S.; López-López, M.; Mendoza, J.; Espinosa-Arbeláez, D. G.; Rodríguez-García, M. E.

    2010-05-01

    Photo-carrier radiometry (PCR) has been used to study the distribution of impurities and the lattice damage in silicon-doped gallium arsenide in a noncontact way. The results from the PCR study are correlated with Hall effect measurements. Samples for this study were grown by molecular beam epitaxy. Of all possible parameters that can be manipulated, the silicon effusion cell temperature was the only one that was varied, in order to obtain samples with different silicon concentrations. The distribution of impurities was obtained by scanning the surface of each sample. The PCR amplitude and phase images were obtained as a function of the x- y position. According to the PCR images, it is evident that the impurities are not uniformly distributed across the sample. From these images, the average value of the amplitude and phase data across the surface was obtained for each sample in order to study the PCR signal behavior as a function of the silicon effusion cell temperature.

  4. Conference on Semi-Insulating III-V Materials (2nd), held 19-21 Apr 82, Evian (France),

    DTIC Science & Technology

    1983-02-28

    Dist Special 19. KEY WORDS (Continue on reverse side If neceary mud Identity by block numb ) Semiconductor devices Field effect transitors Integrated...Sun Tongnien (Hebei Semiconductor pit density. The W Research Institute, People’swith the etch ites of w Republic of China), and a compre-was...of impurities in touched on the topic of residual III-V semiconductors . The boron impurities in undoped GaAs, techniques discussed included a topic

  5. Deep level defect studies in semi-insulating 4H- and 6H-silicon carbide using optical admittance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Wonwoo

    The objective of this study is to determine the deep vanadium defect levels in semi-insulating 4H- and 6H- silicon carbide using optical admittance spectroscopy. Also infrared spectroscopy and electron paramagnetic resonance spectroscopy are conducted to support the evidence of vanadium donor and acceptor levels obtained from OAS measurements. Vanadium acts as an amphoteric impurity in silicon carbide with a V3+/4+ acceptor level and V4+/5+ donor level. Although the value for the donor level is well established, the V3+/4+ defect level remains controversial. OAS shows that the vanadium donor level is isolated near Ec-1.7 eV, and the vanadium acceptor level is located at Ec-0.75 eV at a cubic site and Ec-0.94 eV at a hexagonal site in 4H-SiC, while the vanadium donor level of 6H-SiC samples is about Ec-1.5 eV. The acceptor levels of 6H-SiC were assigned to Ec-0.67 eV, E c -0.70 eV at two cubic sites, and Ec-0.87 eV at a hexagonal site. IR spectra demonstrated that the signatures of the vanadium V 3+ and V4+ charge states are present in the samples. EPR and photo-induced EPR are used to identify the V3+/4+ and V4+/5+ levels as well as the V3+ and V 4+ charge states. EPR spectra represent both V3+ and V4+ in 4H- and 6H samples consistent with FTIR data. EPR and photo-induced EPR suggest that the va nadium acceptor level is between 0.7 eV and 0.86 eV, while the donor level is near Ec-1.5 eV in 6H-SiC. The donor level of 4H-SiC is located at Ec-1.6 eV. Thus, the data obtained from EPR and FTIR support the assignment of the vanadium defect levels determined by OAS. Vanadium complexes induced by other elements such as titanium, hydrogen, and nitrogen atoms are also observed in OAS spectra and will be discussed in the text.

  6. 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.

  7. 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.

  8. Multiple Applications of GaAs semiconductors

    NASA Astrophysics Data System (ADS)

    Martel, Jenrené; Wonka, Willy

    2003-03-01

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

  9. 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.

  10. Enhanced NMR with Optical Pumping Yields (75)As Signals Selectively from a Buried GaAs Interface.

    PubMed

    Willmering, Matthew M; Ma, Zayd L; Jenkins, Melanie A; Conley, John F; Hayes, Sophia E

    2017-03-22

    We have measured the (75)As signals arising from the interface region of single-crystal semi-insulating GaAs that has been coated and passivated with an aluminum oxide film deposited by atomic layer deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective optical pumping, the laser restricts the volume from which OPNMR signals are collected. Here, OPNMR signals were obtained from the interface region and distinguished from signals arising from the bulk. The interface region is highlighted by interactions that disrupt the cubic symmetry of the GaAs lattice, resulting in quadrupolar satellites for nuclear [Formula: see text] isotopes, whereas NMR of the "bulk" lattice is nominally unsplit. Quadrupolar splitting at the interface arises from strain based on lattice mismatch between the GaAs and ALD-deposited aluminum oxide due to their different coefficients of thermal expansion. Such spectroscopic evidence of strain can be useful for measuring lattice distortions at heterojunction boundaries and interfaces.

  11. Stoichiometry-controlled compensation in liquid encapsulated Czochralski GaAs

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Elliott, K. R.; Kirkpatrick, C. G.

    1982-01-01

    It is shown that the electrical compensation of undoped GaAs grown by the liquid encapsulated Czochralski technique is controlled by the melt stoichiometry. The concentration of the deep donor EL2 in the crystal depends on the As concentration in the melt, increasing from about 5 x 10 to the 15th per cu cm to 1.7 x 10 to the 16th per cu cm as the As atom fraction increases from 0.48 to 0.51. Furthermore, it is shown that the free-carrier concentration of semi-insulating GaAs is determined by the relative concentrations of EL2 and carbon acceptors. As a result, semi-insulating material can be obtained only above a critical As concentration (0.475-atom fraction in the material here) where the concentration of EL2 is sufficient to compensate residual acceptors. Below the critical As concentration the material is p type due to excess acceptors.

  12. Investigation of GaAs photoconductive switches triggered by 900nm semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Ma, Deming; Shi, Wei; Ma, Xiangrong; Wang, Xinmei; Pei, Tao

    2008-12-01

    Experiment of a lateral semi-insulating GaAs photoconductive semiconductor switch (SI-GaAs PCSS) with different electrode gaps triggered by 900nm semiconductor laser is reported. With the biased voltage of 0.2KV~3.0KV, the linear electrical pulse is outputted by SI-GaAs PCSS. When laser energy is very low, the semi-insulating GaAs PCSS with 1.5mm electrode gap is triggered by laser pulse, the output electrical pulse samples is instable. When the energy of the laser increases, the amplitude and the width of the electrical pulse also increase. It indicates that a stable electrical pulse is obtained while laser energy is high. With the biased voltage of 2.8kV, the SI-GaAs PCSS with 3mm electrode gap is triggered by laser pulse about 10nJ in 200ns at 900nm. The SI-GaAs PCSS switches a electrical pulse with a voltage up to 80V. The absorption mechanism by Franz-Keldysh effect under high-intensity electric field and EL2 deep level defects is discussed.

  13. Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yulei; Zhou, Qing-li; Zhang, Cunlin

    2010-11-01

    The ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs have been investigated in detail by using terahertz pump-emission technique. Through theoretical modeling based on Hertz vector potential, it is found that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed subsequent to the excitation of pump pulse, and our modeling gives successful analyses for the dynamics of photogenerated carriers in the GaAs. We attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperaturedependent measurements are also performed to verify this model.

  14. EL2 distributions in vertical gradient freeze GaAs crystals

    SciTech Connect

    Gray, M.L.; Sargent, L.; Blakemore, J.S.; Parsey J.M. Jr.; Clemans, J.E.

    1988-06-15

    Spatial distributions of EL2 in undoped, semi-insulating GaAs crystals grown by a novel vertical gradient freeze (VGF) method are reported. As a result of the low-temperature gradients present during growth and post-solidification cooling, these crystals exhibit lower EL2 concentrations and lower dislocation densities than liquid-encapsulated Czochralski crystals. Both the EL2 distribution and dislocation density over the area of a wafer do not display the fourfold symmetric pattern prevalent for LEC-grown GaAs. The radial distributions of EL2 in as-grown VGF crystals have been found to be independent of the dislocation density. Axial and radial Hall-effect measurements are included. Thermal activation energies are also presented and the compensation mechanism for this material is discussed.

  15. The Investigation of Ion Implantation as a Technique for Manufacturing GaAs Magneto-Sensitive Detectors

    NASA Astrophysics Data System (ADS)

    Karlova, G. F.; Avdochenko, B. I.

    2017-01-01

    This paper studies thin active layers of n-n i and n +-n-n i -types produced by means of silicon ion implantation into a semi-insulating GaAs substrate. The results of these structures’ physical parameters investigation are presented. Based on the structures the Hall-effect sensors are designed that have the linearity of Hall voltage dependency on magnetic density UH(B) of at least 1% in the range of up to B<1.2 T.

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

    DOE PAGES

    Ritenour, Andrew J.; Boucher, Jason W.; DeLancey, Robert; ...

    2014-09-01

    The high balance-of-system costs of photovoltaic (PV) installations indicate that reductions in cell $/W costs alone are likely insufficient for PV electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which yield both high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III-V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the difficulty of scaling the metal-organic chemical vapor deposition (MOCVD) process, which relies on expensive reactors and employs toxic and pyrophoric gas-phase precursors suchmore » as arsine and trimethyl gallium, respectively. In this study, we describe GaAs films made by an alternative close-spaced vapor transport (CSVT) technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient in order to deposit crystalline films with similar electronic properties to that of GaAs deposited by MOCVD. CSVT is similar to the vapor transport process used to deposit CdTe thin films and is thus a potentially scalable low-cost route to GaAs thin films.« less

  17. 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

    The high balance-of-system costs of photovoltaic (PV) installations indicate that reductions in cell $/W costs alone are likely insufficient for PV electricity to reach grid parity unless energy conversion efficiency is also increased. Technologies which yield both high-efficiency cells (>25%) and maintain low costs are needed. GaAs and related III-V semiconductors are used in the highest-efficiency single- and multi-junction photovoltaics, but the technology is too expensive for non-concentrated terrestrial applications. This is due in part to the difficulty of scaling the metal-organic chemical vapor deposition (MOCVD) process, which relies on expensive reactors and employs toxic and pyrophoric gas-phase precursors such as arsine and trimethyl gallium, respectively. In this study, we describe GaAs films made by an alternative close-spaced vapor transport (CSVT) technique which is carried out at atmospheric pressure and requires only bulk GaAs, water vapor, and a temperature gradient in order to deposit crystalline films with similar electronic properties to that of GaAs deposited by MOCVD. CSVT is similar to the vapor transport process used to deposit CdTe thin films and is thus a potentially scalable low-cost route to GaAs thin films.

  18. Application of a Resistance Heater to the MOCVD (Metal-Organic Chemical Vapor Deposition) Growth of Undoped and Se-Doped GaAS.

    DTIC Science & Technology

    1985-03-08

    concentration and mobilities of the epitaxial layers were determined at room temperature and liquid-nitrogen temperature (77 K) by the van der Pauw technique’ for...mobility versus total impurity concentration for bulk GaAs (Ref. 7). 13 REFERENCES 1. van der Pauw , L. J., PhlisRes ep. 13, 1 (1958). 2. Binet, M., Electron

  19. INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Doping inhomogeneities and behavior of compensation of n-type GaAs and InP

    NASA Astrophysics Data System (ADS)

    Wruck, D.; Knauer, A.

    1988-11-01

    A comparison was made of the distributions of Sn and of the chalcogens S and Se in InP and GaAs, determined from infrared absorption and the Hall effect. An analysis was made of the possible cause of the difference between the values of the degree of compensation determined by the two methods.

  20. 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.

  1. Transient space charge limited current spectroscopy method of measuring the position and concentration of trap levels in semi-insulating materials

    NASA Astrophysics Data System (ADS)

    Yuan, S. H.; Pardavi-Horvath, M.; Wigen, P. E.

    1988-11-01

    A new method is reported to measure the position and concentration of trap levels in semi-insulating materials where the regular deep level transient spectroscopy method is not applicable. In the proposed method, a transient space charge limited current (TSCLC) associated with the trap levels is measured using a capacitance balanced square wave voltage source, a voltage limiter-amplifier and a double box car averager. The TSCLC method is demonstrated on a p-type Y2.01Ca0.99Ge0.91Fe4.09O12 magnetic garnet sample ρ300=107 Ω cm. The trap level is located at 0.36 eV above the valence band edge and the concentration of the trapped holes is found to be 1013-1015 cm-3.

  2. On the relation between deep level compensation, resistivity and electric field in semi-insulating CdTe:Cl radiation detectors

    NASA Astrophysics Data System (ADS)

    Cola, Adriano; Farella, Isabella; Pousset, Jeremy; Valletta, Antonio

    2016-12-01

    A compensation model for semi-insulating CdTe:Cl based on a single dominant deep level 0.725 eV above the valence band is proposed. The model is corroborated by experimental evidence: resistivity measurements as a function of temperature on bulk crystals and stationary electric field distributions in Ohmic/Schottky radiation detectors, obtained by the Pockels effect. The latter are in close agreement with the numerical solutions of transport equations when considering the deep centre concentration in the range 2 - 4 × 1012 cm-3, and a compensation ratio R = 2.1, this one being consistent with an original ambipolar analysis of resistivity. More generally, the approach elucidates the role of electrical contacts and deep levels in controlling the electric fields in devices based on compensated materials.

  3. Thermally stimulated current spectroscopy applied on defect characterization in semi-insulating Cd0.9Zn0.1Te

    NASA Astrophysics Data System (ADS)

    Nan, Ruihua; Jie, Wanqi; Zha, Gangqiang; Wang, Bei; Yu, Hui

    2012-12-01

    Defects exhibiting trapping behaviors in semi-insulating (SI) materials were investigated by thermally stimulated current (TSC) spectroscopy. The variation of measurement conditions during the initial photoexcitation and thermal emission, such as the heating rate, bias voltage, illumination time and delay time, may bring some significant effects on TSC spectra, leading to incomplete characterization of trap levels. In this work, defects with deep levels in the band gap of SI-Cd0.9Zn0.1Te crystal, grown by the modified vertical Bridgman (MVB) method, were studied via TSC measurements. TSC measurement of the SI-CZT sample was performed with the optimized measurement conditions. Ten different traps and a deep donor (EDD) level were characterized from the as-obtained spectrum in the temperature range from 25 to 310 K with the aid of simultaneous multiple peak analysis (SIMPA). The origins of these traps were identified in detail as well.

  4. Analysis of intensity dependent near-bandedge absorption in semi-insulating 4H–SiC for photoconductive switch applications

    NASA Astrophysics Data System (ADS)

    Meyers, V.; Chowdhury, A. R.; Mauch, D.; Dickens, J. C.; Neuber, A. A.; Joshi, R. P.

    2017-04-01

    We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulating 4H–SiC material. Data from as-received samples show a monotonic decrease in α with incident energy density, with a pronounced change in slope at around 10 mJ cm‑2. Annealed samples, on the other hand, exhibit an experimental trend of increasing α with intensity. Qualitative explanation of the observed behavior is presented that probes the possible role of spontaneous and stimulated emission for as-received samples. With annealing, trap related recombination is strongly reduced leading to higher carrier densities and increased free-carrier absorption with incident intensity. The role of band-filling and permittivity changes are shown to be inconsequential, while changes in internal fields could contribute to decreases in absorption.

  5. 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.

  6. 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.

  7. 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.

  8. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Lei; Zhou, Qing-Li; Zhang, Cun-Lin

    2009-10-01

    This paper investigates the ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs in detail by using a terahertz pump-emission technique. Based on theoretical modelling, it finds that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed after the excitation of pump pulse and we attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperature-dependent measurements are also performed to verify this trapping model.

  9. High-speed digital ICs - A comparison between silicon and GaAs

    NASA Astrophysics Data System (ADS)

    Ricco, Bruno

    1986-06-01

    High electron mobility and semi-insulating characteristics make GaAs a semiconductor material ideally suited for very fast logics. Nevertheless, for such purposes it must compete with the fully mature LSI and VLSI technologies of silicon. The choice depends on applications and technology options. If MESFETs are rated against Si MOSFETs and bipolar transistors, the scale of circuit integration plays a fundamental role. For fewer than a few hundred gates per chip, GaAs can provide circuits that are two to four times faster although the cost per bit is significantly higher; thus GaAs circuits seem attractive only for required performances above a few gigahertz (beyond the reach of silicon devices). The brighter perspectives for GaAs come from the potential of heterostructure devices which are under development and showing great promise. Sophisticated processing steps (such as molecular beam epitaxy) are still under development and still need to be assessed regarding their viability for circuit mass production. Various logics are compared.

  10. Crystallization of semi-insulating HVPE-GaN with solid iron as a source of dopants

    NASA Astrophysics Data System (ADS)

    Iwinska, M.; Piotrzkowski, R.; Litwin-Staszewska, E.; Ivanov, V. Yu.; Teisseyre, H.; Amilusik, M.; Lucznik, B.; Fijalkowski, M.; Sochacki, T.; Takekawa, N.; Murakami, H.; Bockowski, M.

    2017-10-01

    Gallium nitride crystals were grown by hydride vapor phase epitaxy using solid iron as a source of dopants. Three crystal growth processes were performed at constant HCl flow over the solid iron and with different gallium chloride flows. High structural quality ammonothermal GaN was used as seed material. No yellow luminescence and only weak near band edge luminescence were visible in all grown crystals. A sharp peak was observed at 1.298 eV. This was shown before as an intrinsic transition of Fe impurity in GaN. The grown crystals were highly resistive at room temperature. High-temperature Hall effect measurements revealed n-type conductivity with activation energy equal to 1.8 eV. Secondary ion mass spectrometry indicated the presence of manganese in all three samples. The concentration of manganese was always higher than concentration of iron in the doped GaN.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  13. Deep levels induced by high fluence proton irradiation in undoped GaAs diodes

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Polenta, L.; Canali, C.; Nava, F.; Ferrini, R.; Galli, M.

    1998-12-31

    Semi-insulating liquid encapsulated Czochralski grown GaAs has been investigated after irradiation at high fluences of high-energy protons. Electron beam induced current observations of scanning electron microscopy evidenced a radiation stimulated ordering. An analysis has been carried out of the deep levels associated with defects as a function of the irradiation fluence, using complementary current transient spectroscopies. By increasing the irradiation fluence, the concentration of the native traps at 0.37 eV together with that of the EL2 defect significantly increases and, at the same time, two new electron traps at 0.15 eV and 0.18 eV arise and quickly increase in density.

  14. Modification of GaAs surface by low-current Townsend discharge

    NASA Astrophysics Data System (ADS)

    Gurevich, E. L.; Kittel, S.; Hergenröder, R.; Astrov, Yu A.; Portsel, L. M.; Lodygin, A. N.; Tolmachev, V. A.; Ankudinov, A. V.

    2010-07-01

    The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 µA cm-2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (<1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (<10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase.

  15. Deep levels in undoped horizontal Bridgman GaAs by Fourier transform photoconductivity and Hall effect

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Brown, Gail J.; Rea, Laura S.; Smith, S. R.

    1992-01-01

    Deep levels between 0.1 and 1.0 eV in semi-insulating and high resistivity undoped horizontal Bridgman GaAs have been studied by temperature-dependent Hall effect (TDH) and Fourier transform photoconductivity (FTPC). Activation energies at 0.77, 0.426, and 0.15 eV have been observed by TDH. Photoionization thresholds at 1.0, 0.8, 0.56, 0.44, and 0.25 are reported. The photoconductivity thresholds at 0.56 and 0.25 eV are reported for the first time. New features in the 0.44 eV threshold suggest that the defect responsible for this level has a small lattice relaxation and Frank-Condon shift. Possible associations of the FTPC and TDH energies with the deep-level transient spectroscopy levels EL2, EL3, and EL6 are presented.

  16. GaAs core--shell nanowires for photovoltaic applications.

    PubMed

    Czaban, Josef A; Thompson, David A; LaPierre, Ray R

    2009-01-01

    We report the use of Te as an n-type dopant in GaAs core-shell p-n junction nanowires for use in photovoltaic devices. Te produced significant change in the morphology of GaAs nanowires grown by the vapor-liquid-solid process in a molecular beam epitaxy system. The increase in radial growth of nanowires due to the surfactant effect of Te had a significant impact on the operating characteristics of photovoltaic devices. A decrease in solar cell efficiency occurred when the Te-doped GaAs growth duration was increased.

  17. The effect of the intense laser field on the electronic states and optical properties of n-type double δ-doped GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Kasapoglu, E.; Yesilgul, U.; Ungan, F.; Sökmen, I.; Sari, H.

    2017-02-01

    In this work, within the effective mass approximation we have performed a theoretical study of electronic states, the intersubband-related optical absorption coefficient and relative refractive index change properties in the GaAs-based double δ-doped quantum well under non-resonant intense laser field. By solving the Schrödinger equation in the laser-dressed confinement potential, we calculated eigenvalues and corresponding eigenfunctions as an intense laser parameter. We concluded that the separation between ground and first excited energy levels in the double δ-doped quantum well increases in energy by the increase of the laser field intensity and this effect leads to an optical blue-shift in intersubband transitions. Therefore a significant tunability of the optical transitions in double δ-doped quantum well can be achieved by modulating the intensity of the intense laser field.

  18. Nondestructive three-dimensional observation of defects in semi-insulating 6H-SiC single-crystal wafers using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST)

    NASA Astrophysics Data System (ADS)

    Wutimakun, Passapong; Buteprongjit, Chumpol; Morimoto, Jun

    2009-07-01

    Peripheral and central areas of a semi-insulating 6H-SiC single-crystal wafer were examined using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST). The form and density of the defects in each area were observed by SLM. We reconstructed three-dimensional (3D) IR-LST images of scatterers by stacking 2D layer-by-layer IR-LST images on different planes. Using these 3D IR-LST images, variations in the defect distribution with depth were observed for the first time. To study the defect distribution and defect form in detail, we observed the defect configuration in the same volume as for 3D IR-LST images by magnified SLM and merged the images from the two techniques. Information on defects obtained using this approach will be very important in the development of high-quality semi-insulating silicon carbide (SiC) substrates.

  19. Self-compensation limited conductivity in semi-insulating indium-doped Cd0.9Zn0.1Te crystals

    NASA Astrophysics Data System (ADS)

    Kosyachenko, L. A.; Melnychuk, S. V.; Maslyanchuk, O. L.; Sklyarchuk, V. M.; Sklyarchuk, O. F.; Fiederle, M.; Lambropoulos, C. P.

    2012-07-01

    Cd0.9Zn0.1Te:In crystals with semi-intrinsic conductivity have been investigated. Temperature dependence of their electrical characteristics shows a number of unconventional peculiarities: the thermal activation energy of conductivity is "anomalously" low (0.60-0.62 eV); the resistivity at elevated temperatures is greater than its intrinsic value for Cd0.9Zn0.1Te; the inversion of the conduction from n- to p-type occurs at a temperature slightly above 300 K, etc. The observed features are explained in terms of statistics of electrons and holes in a semiconductor containing a self-compensation complex, whose concentration is much higher than those of uncontrolled (background) impurities and defects. Comparison of the calculation results and experimental data leads to the conclusion that the donor level, which is far distant from the middle of the band gap, dominates in the conductivity of the material and its compensation is virtually complete (Na/Nd = 0.99996-0.99998) as predicted by theory.

  20. 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.

  1. 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.

  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. Absorption edge determination of thick GaAs wafers using surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Sharma, T. K.; Porwal, S.; Kumar, R.; Kumar, Shailendra

    2002-04-01

    A procedure for choosing the appropriate chopping frequency (f) for the surface photovoltage spectroscopy (SPS) measurements in order to obtain the absorption related features is presented. We could obtain the absorption edge of thick n+ GaAs wafer (thickness ≈700 μm) by performing SPS measurements at f⩾1 kHz at room temperature (300 K). The similar information for semi-insulating (SI) GaAs could not be obtained due to the carrier trapping at deep levels or surface states at 300 K. However, we could obtain the absorption edge of SI-GaAs by performing SPS measurements at 395 K at f=3 kHz. Here, we demonstrate the capability of the SPS technique to measure large absorption coefficient (α) values for thick wafers by performing SPS measurements and normalizing this with the reported α value at one wavelength in the above band gap region. For comparison, we also perform quasisimultaneous SPS and transmission spectroscopy (TS) measurements. The SPS technique could provide α values up to 104cm-1 for 700-μm-thick GaAs wafers, whereas TS could only measure α values up to about 15 cm-1. An improved design of the sample holder for measuring the surface photovoltage in the chopped light geometry, which increases the signal strength by reducing the gap between the top electrode and the wafer in a controlled manner, is presented. This ensures that there is no sample damage or contamination.

  4. Low contrast imaging with a GaAs pixel digital detector

    NASA Astrophysics Data System (ADS)

    Amendolia, S. R.; Bisogni, M. G.; Bottigli, U.; Ciocci, M. A.; Delogu, P.; Dipasquale, G.; Fantacci, M. E.; Giannelli, M.; Maestro, P.; Marzulli, V. M.; Pernigotti, E.; Rosso, V.; Stefanini, A.; Stumbo, S.

    2000-08-01

    A digital mammography system based on a GaAs pixel detector has been developed by the INFN (Istituto Nazionale di Fisica Nucleare) collaboration MED46. The high atomic number makes the GaAs a very efficient material for low energy X-ray detection (10-30 keV is the typical energy range used in mammography). Low contrast details can be detected with a significant dose reduction to the patient. The system presented in this paper consists of a 4096 pixel matrix built on a 200 /spl mu/m thick semi-insulating GaAs substrate. The pixel size is 170/spl times/170 /spl mu/m/sup 2/ for a total active area of 1.18 cm/sup 2/. The detector is bump-bonded to a VLSI front-end chip which implements a single-photon counting architecture. This feature allows to enhance the radiographic contrast detection with respect to charge integrating devices. The system has been tested by using a standard mammographic tube. Images of mammographic phantoms will be presented and compared with radiographs obtained with traditional film/screen systems. Monte Carlo simulations have been also performed to evaluate the imaging capability of the system. Comparison with simulations and experimental results will be shown.

  5. Effect of the Photoquenching of EL2 in GaAs Substrate on the Piezoelectric Photothermal and Surface Photovoltage Spectra of a GaAs Single Quantum Well Confined by GaAs/AlAs Short-Period Superlattices

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Fukuyama, Atsuhiko; Akashi, Yoshito; Ikari, Tetsuo

    2008-01-01

    Two nondestructive techniques, surface photovoltage (SPV) and piezoelectric photothermal (PPT) spectroscopies, were adopted to investigate a GaAs single quantum well (SQW) confined by GaAs/AlAs short-period superlattices (SPSs) fabricated on a semi-insulating (SI) GaAs substrate, whose absorption spectra cannot be obtained easily using conventional techniques. Excitonic absorptions associated with subband transitions in a GaAs SQW and SPSs were clearly observed. We also examined how a SI-GaAs substrate affects the PPT and SPV spectra, particularly the effect of the photoquenching of the deep donor level EL2. It was found that the photoquenching of EL2 causes a significant change in the total built-in potential at the interface between the epitaxial layers and the substrate, and affected the signal intensities observed in the PPT and SPV spectra. The present experimental results have shown that a large amount of carrier leakage occurs from a GaAs SQW and SPSs to the sample surface, even in the presence of Al0.3Ga0.7As buffer layers.

  6. 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.

  7. 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.

  8. ZnSe Window Layers for GaAs and GaInP2 Solar Cells

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.

    1995-01-01

    This report concerns studies of the use of ZnSe as a window layer for GaAs solar cells. Well-oriented crystalline ZnSe films on (100) single crystal GaAs substrates were grown by MOCVD. In particular, ZnSe films were grown by reacting a zinc adduct with hydrogen selenide at temperatures in the range of 200 C to 400 C. X-ray diffraction studies and images obtained with an atomic force microscope determined that the films were highly oriented but were polycrystalline. Particular emphasis was placed on the use of a substrate temperature of 350 C. Using iodine as a dopant, n-type ZnSe films with resistivities in the range of .01 to .05 ohm-cm were grown on semi-insulating GaAs. Thus procedures have been developed for investigating the utility of n-type ZnSe window layers on n/p GaAs structures. Studies of recombination at n-ZnSe/n-GaAs interfaces in n-ZnSe/n-GaAs/p-GaAs cell structures are planned for future work.

  9. LSI/VLSI (Large Scale Integration/Very Large Scale Integration) ion implanted GaAs (Gallium Arsenide) IC processing

    NASA Astrophysics Data System (ADS)

    Zucca, R. R.; Kirkpatrick, C. G.; Asbeck, P. M.; Eisen, F. H.; Lee, C. P.

    1984-01-01

    This report covers a program designed to realize the full potential of GaAs integrated circuits by expanding and improving fabrication and material techniques. The main accomplishment of the program was the successful implementation of the fabrication of integrated circuits on 3-inch diameter GaAs wafers. In addition, this program covered many activities related to GaAs IC processing. These include: work on semi-insulating material growth and characterization, investigation of ion implantation techniques (work carried out at the California Institute of Technology); evaluation of device uniformity, and investigation of its controlling factors; investigation of metallization yield and reliability, and improvements of processing techniques resulting from this study; design and testing of a multiplier and programmable shift registers/pattern generators; evaluation of mask programmable logic arrays to meet ERADCOMs needs for high performance communication systems; investigation of the hardness of GaAs ICs to total dose and transient ionizing radiation, and modelling of MESFET devices (this work carried out at North Carolina State University).

  10. Migration processes of the As interstitial in GaAs

    NASA Astrophysics Data System (ADS)

    Wright, A. F.; Modine, N. A.

    2016-12-01

    Thermal migration processes of the As interstitial in GaAs were investigated using density-functional theory and the local-density approximation for exchange and correlation. The lowest-energy processes were found to involve the -1, 0, and +1 charge states, and to produce migration along ⟨110⟩-type directions. In the -1 and 0 charge states, migration proceeds via hops between split-interstitial stable configurations at bulk As sites through bridging saddle-point configurations in which the interstitial atom is equidistant from two adjacent bulk As sites. In the +1 charge state, the roles of these two configurations are approximately reversed and migration proceeds via hops between bridging stable configurations through higher-energy split-interstitial stable configurations bounded by a pair of distorted split-interstitial saddle-point configurations. The predicted activation energies for migration in the 0 and +1 charge states agree well with measurements in semi-insulating and p-type material, respectively. Also consistent with experiments, the approximate reversal of the stable and saddle-point configurations between the 0 and +1 charge states is predicted to enable carrier-induced migration with a residual activation energy of 0.05 eV.

  11. The Stark effect on a bound hole in δ-acceptor doped GaAs/ Al xGa 1- xAs heterostructures

    NASA Astrophysics Data System (ADS)

    Łusakowski, J.; Friedland, K. J.; Ploog, K.

    2007-05-01

    There are only a few experimental reports on measurements of the Stark effect on shallow acceptors. We show that measurements of the degree of circular polarization of the luminescence originating from a free-to-bound Γ6→Γ8 transition allows us to determine the dipole moment of a substitutional acceptor in a crystal of Td symmetry. We suggest the performance of such experiments in a single GaAs/GaAlAs heterostructure δ-doped with acceptors. Thus we propose an experimental method for investigation of the Stark effect in solids.

  12. Intense laser field effects on the intersubband optical absorption and refractive index change in the δ -doped GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Sari, H.; Yesilgul, U.; Ungan, F.; Sakiroglu, S.; Kasapoglu, E.; Sökmen, I.

    2017-04-01

    In this paper, we have investigated the effects of the non-resonant intense laser field on the electronic and optical properties such as linear, nonlinear and the total optical absorption coefficient and refractive index change for transitions between two lower-lying electronic states in the GaAs-based δ -doped quantum well. Within the effective mass approximation, we calculated the eigenvalues and corresponding eigenfunctions as a function of the intense laser parameter by solving the Schrödinger equation in the laser-dressed confinement potential. The analytical expressions of the linear and third-order non-linear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism. The obtained results show that the separation between ground and first excited energy levels in the δ -doped quantum well decreases in energy by the increase of the laser field intensity and this effect leads to an optical red-shift in the intersubband transitions. This behavior gives us a new degree of freedom in tunability of different device applications based on the optical transitions.

  13. Electrodeposition of Metal on GaAs Nanowires

    NASA Astrophysics Data System (ADS)

    Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

    2010-10-01

    Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

  14. THz conductivity of semi-insulating and magnetic CoFe2O4 nano-hollow structures through thermally activated polaron

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Serita, Kazunori; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-11-01

    Herein, terahertz (THz) time domain spectroscopy is used to measure the complex conductivity of semi-insulating CoFe2O4 nanoparticles (NPs) and nano-hollow spheres (NHSs) with different diameters ranging from 100 to 350 nm having a nanocrystalline shell thickness of 19 to 90 nm, respectively. Interestingly, the magnitude of conductivity for CoFe2O4 NPs and NHSs of same average diameter (˜100 nm) for a given frequency of 0.3 THz is found to be 0.33 S/m and 9.08 S/m, respectively, indicating that the hollow structure exhibits greater THz conduction in comparison to its solid counterpart. Moreover, THz conductivity can be tailored by varying the nano-shell thickness of NHSs, and a maximum conductivity of 15.61 S/m is observed at 0.3 THz for NHSs of average diameter 250 nm. A detailed study reveals that thermally activated polaronic hopping plays the key role in determining the electrical transport property of CoFe2O4 nanostructures, which is found to solely depend on their magnitude of THz absorptivity. The non-Drude conductivity of all CoFe2O4 nanostructures is well described by the Polaron model instead of the Drude-Smith model, which is relevant for backscattering of free electrons in a nanostructured material. The Polaron model includes intra-particle and interparticle polaronic conductivities for closely spaced magnetic nanostructures and provides a mean free path of 29 nm for CoFe2O4 NPs of diameter 100 nm, which is comparable with its average crystallite size, indicating the applicability of the developed model for nanomaterials where charge transport is determined by polaronic hopping. Finally, we have demonstrated the morphology and size dependent magnetic measurements of ferrimagnetically aligned CoFe2O4 nanostructures through a vibrating sample magnetometer in the temperature range of 80-250 K, revealing that the disordered surface spin layer of nanostructures significantly controls their magnetism.

  15. Delta-doping of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schubert, E. F.

    2005-08-01

    Part I: 1. Introduction E. F. Schubert; Part II: 2. Electronic structure of delta-doped semiconductors C. R. Proetto; Part III: 3. Recent progress in delta-like confinement of impurities in GaAs K. H. Ploog; 4. Flow-rate modulation epitaxy (FME) of III-V semiconductors T. Makimoto and Y. Horikoshi; 5. Gas source molecular beam epitaxy (MBE) of delta-doped III-V semiconductors D. Ritter; 6. Solid phase epitaxy for delta-doping in silicon I. Eisele; 7. Low temperature MBE of silicon H.-J. Gossmann; Part IV: 8. Secondary ion mass spectrometry of delta-doped semiconductors H. S. Luftmann; 9. Capacitance-voltage profiling E. F. Schubert; 10. Redistribution of impurities in III-V semiconductors E. F. Schubert; 11. Dopant diffusion and segregation in delta-doped silicon films H.-J. Gossmann; 12. Characterisation of silicon and delta-doped structures in GaAs R. C. Newman; 13. The DX-center in silicon delta-doped GaAs and AlxGa1-xAs P. M. Koenraad; Part V: 14. Luminescence and ellipsometry spectroscopy H. Yao and E. F. Schubert; 15. Photoluminescence and Raman spectroscopy of single delta-doped III-V semiconductor heterostructures J. Wagner and D. Richards; 16. Electron transport in delta-doped quantum wells W. T. Masselink; 17. Electron mobility in delta-doped layers P. M. Koenraad; 18. Hot electrons in delta-doped GaAs M. Asche; 19. Ordered delta-doping R. L. Headrick, L. C. Feldman and B. E. Weir; Part IV: 20. Delta-doped channel III-V field effect transistors (FETs) W.-P. Hong; 21. Selectively doped heterostructure devices E. F. Schubert; 22. Silicon atomic layer doping FET K. Nakagawa and K. Yamaguchi; 23. Planar doped barrier devices R. J. Malik; 24. Silicon interband and intersubband photodetectors I. Eisele; 25. Doping superlattice devices E. F. Schubert.

  16. 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.

  17. Electrical properties of molecular beam epitaxial GaAs grown at 300-450{degrees}C

    SciTech Connect

    Look, D.C.; Robinson, G.D.; Sizelove, J.R.; Stutz, C.E.

    1993-12-01

    We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate temperatures of 300-450{degrees}C. Layers grown from 350-450{degrees}C are semi-insulating (resistivity greater than 10{sup 7}{Omega}-cm), as grown, because of an As{sub Ga}-related donor (not EL2) at E{sub c} - 0.65 eV. The donor concentrations are about 2 x 10{sup 18} cm{sup -3} and 2 x 10{sup 17} cm{sup -3} at growth temperatures of 300 and 400{degrees}C, respectively, and acceptor concentrations are about an order of magnitude lower. Relatively high mobilities ({approximately}5000 cm{sup 2}/V s) along with the high resistivities make this material potentially useful for certain device applications. 8 refs., 2 figs., 2 tabs.

  18. Positively charged manganese acceptor disclosed by photoluminescence spectra in an n-i-p-i-n heterostructure with a Mn-doped GaAs base

    NASA Astrophysics Data System (ADS)

    Shen, C.; Wang, L. G.; Zheng, H. Z.; Zhu, H.; Chen, L.; Zhao, J. H.

    2011-05-01

    A type of manganese impurity center with two holes bound in it is disclosed in a lightly Mn-doped base layer of an n-i-p-i-n heterostructure. In addition to the intensively investigated (e, AMn0) peak, a photoluminescence (PL) peak appears at 820.3 nm under zero bias and is continuously shifted to 822.5 nm by negatively biasing the structure. Its circular polarization has the same polarity as PL (e, AMn0), and has a magnetic dependence fitted by a paramagnetic Brillouin function with S = 1/2 and g = 2.09. These observations are consistent with the physical picture that in the AMn+ center both the - 3/2 and the - 1/2 holes occupy the lowest 1S hydrogenic orbit with their spins parallel to each other and antiparallel to the 5/2 local spin of the 3d shell. This spin coupling picture in the AMn+ center has been confirmed by a modified numerical calculation based upon effective mass theory. The feature of the ability to tune the impurity level of the AMn+ center makes it attractive for optically and electrically manipulating local magnetic spins in semiconductors.

  19. Modelling of OPNMR phenomena using photon energy-dependent in GaAs and InP

    NASA Astrophysics Data System (ADS)

    Wheeler, Dustin D.; Willmering, Matthew M.; Sesti, Erika L.; Pan, Xingyuan; Saha, Dipta; Stanton, Christopher J.; Hayes, Sophia E.

    2016-12-01

    We have modified the model for optically-pumped NMR (OPNMR) to incorporate a revised expression for the expectation value of the z-projection of the electron spin, and apply this model to both bulk GaAs and a new material, InP. This expression includes the photon energy dependence of the electron polarization when optically pumping direct-gap semiconductors in excess of the bandgap energy, Eg . Rather than using a fixed value arising from coefficients (the matrix elements) for the optical transitions at the k = 0 bandedge, we define a new parameter, Sopt (Eph) . Incorporating this revised element into the expression for , we have simulated the photon energy dependence of the OPNMR signals from bulk semi-insulating GaAs and semi-insulating InP. In earlier work, we matched calculations of electron spin polarization (alone) to features in a plot of OPNMR signal intensity versus photon energy for optical pumping (Ramaswamy et al., 2010). By incorporating an electron spin polarization which varies with pump wavelength into the penetration depth model of OPNMR signal, we are able to model features in both III-V semiconductors. The agreement between the OPNMR data and the corresponding model demonstrates that fluctuations in the OPNMR intensity have particular sensitivity to light hole-to-conduction band transitions in bulk systems. We provide detailed plots of the theoretical predictions for optical pumping transition probabilities with circularly-polarized light for both helicities of light, broken down into illustrative plots of optical magnetoabsorption and spin polarization, shown separately for heavy-hole and light-hole transitions. These plots serve as an effective roadmap of transitions, which are helpful to other researchers investigating optical pumping effects.

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

    PubMed

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

    2012-05-07

    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.

  1. Magnetic-field dependence of the optical Overhauser effect in GaAs

    SciTech Connect

    Kuhns, P.L.; Kleinhammes, A.; Schmiedel, T.; Moulton, W.G.; Chabrier, P.; Sloan, S.; Hughes, E.; Bowers, C.R.

    1997-03-01

    When nuclear spin order is induced by optical excitation near the band gap of a semiconductor such as GaAs, the effect is referred to as optical pumping. This paper presents measurements of the optical pumping rate in semi-insulating GaAs over the magnetic field range of 0{minus}24 T at temperatures of 1.5 K and 4.2 K. The enhanced nuclear polarization was sampled by radio wave detected NMR. The data were recorded using Bitter- type magnets which permitted rapid ramping between the pumping and sampling fields in a time short compared to the nuclear spin lattice relaxation time in the dark. The field dependence has been fitted to a relaxation model which includes spin diffusion and dark relaxation terms. Fits were obtained by fixing the g factor to its literature value. The fitted parameters include the correlation time for electron spin-density fluctuations, the average hyperfine field, and the nuclear spin diffusion coefficient. {copyright} {ital 1997} {ital The American Physical Society}

  2. 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.

  3. Effects of EL2 deep level in GaAs photoconductive switch

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Liu, Rui; Wang, Jing-li

    2009-07-01

    The semi-insulating (SI) GaAs photoconductive switch is considered to be the higher efficient THz source recently. In order to make good use of the photoconductive switch to generate the more efficient THz wave, SI-GaAs photoconductive switch's working mechanism is discussed from the respect of EL2 deep level in this paper. It has three operation modes. The SI-GaAs material has many kinds of intrinsic-defects. One of the more notable defects is EL2 deep level. The EL2 level can become an impactful electron trap in the linear operation mode; The EL2 level is also the necessary condition of nonlinear (also known as Lock-on) operation mode emerging in III-V semiconductors such as GaAs and InP. At the same time, the compound operation mode is substantial related with the conversion from neutral energy level EL20 to metastable energy level EL2* and singly ionized energy level EL2+ in semiconductor under the light. So in this paper the effects of EL2 deep level are analyzed in photoconductive switch' there operation modes.

  4. Performances of SI GaAs detectors fabricated with implanted ohmic contacts

    SciTech Connect

    Nava, F.; Alietti, M.; Canali, C.; Chiossi, C. |; Cavallini, A. |; Papa, C. del |; Re, V. |; Lanzieri, C.

    1996-06-01

    The slow component of the output pulse of Semi-Insulating (SI) Gallium Arsenide (GaAs) particle detectors, which affects charge collection efficiency (cce), has been generally attributed to trapping/detrapping effects. However, most of the detectors analyzed in the literature can only be operated below the voltage V{sub d} necessary to extend the electric field all the way to the ohmic contact, making difficult to distinguish between the effect of the non-active part of the detector and that of trapping/detrapping. To do that, the authors have carefully analyzed the output signals of SI GaAs detectors, operated below and above V{sub d} and irradiated with {sup 241}Am {alpha} particles. When the detector is biased below V{sub d} the output signals are affected also by the non-active part of the detector itself, while, when the detector is operated above V{sub d}, the output signals are only affected by trapping/detrapping of charge carriers. The authors found that trapping/detrapping is only relevant for the hole contribution to the signal. Trapping/detrapping effects are in agreement with the characteristics of deep levels present in the detectors as analyzed by means of PICTS (Photo Induced Current Transient Spectroscopy) and P-DLTS (Photo Deep Level Transient Spectroscopy).

  5. The Features of GaAs and GaP Semiconductor Cathodes in an Infrared Converter System

    NASA Astrophysics Data System (ADS)

    Kurt, H. Hilal; Tanrıverdi, Evrim

    2017-07-01

    The aim of this study is to examine the electrical and optical comparative analysis of semi-insulating GaAs and GaP photoconductive electrodes in an infrared converter system with a resistivity of >107 Ω cm for the same interelectrode distance d and gas pressure p experimentally and theoretically, when the discharge cell has been filled by argon. To provide the stability of the semiconductor electrode in Ar media, the experiments were carried out in Townsend and glow discharge regimes for various parameter sets of pressure, interelectrode gap and discharge voltage. When the discharge exceeds a critical voltage value, some N-shape CVC s, which stem from both semiconductors and Ar gas, have been observed. To compare the features of the GaAs and GaP cathodes, the COMSOL multiphysics programme is used under the Ar media. The mean electron energy, thermal velocity, surface charge density, space charge and initial electron densities, and electron mobilities have been calculated for both semiconductor materials. It has been found that the electron mobility μe, electron thermal velocity, surface charge density σ and mean electron energy of GaAs is higher than those of GaP; hence, GaAs has better opto-electronic features compared to GaP. In addition, the experiments on the optical explorations prove that GaAs exhibit better optical response in the infrared region. The explored transport characteristics of the semiconductor electrodes are of importance, and they have to be taken into account when studying plasma cells.

  6. Method of Making Self-Aligned GAAS/ALGAAS FET’s.

    DTIC Science & Technology

    having a predetermined crystalline structure is obtained having a heavily doped top GaAs layer, having a heavily doped AlGaAs layer under the top layer...recess is wider at the base of the recess than at the top of the recess because of the predetermined crystalline structure and the orientation-dependent

  7. Graphitized carbon on GaAs(100) substrates

    SciTech Connect

    Simon, J.; Simmonds, P. J.; Lee, M. L.; Woodall, J. M.

    2011-02-14

    We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp{sup 2}-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5-3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.

  8. Electrical and structural characterization of GaAs on InP grown by OMCVD; application to GaAs MESFETs

    NASA Astrophysics Data System (ADS)

    Azoulay, R.; Clei, A.; Dugrand, L.; Draïdia, auN.; Leroux, G.; Biblemont, S.

    1991-01-01

    The growth of GaAs on InP has attracted considerable interest recently because of the possibility of integration of GaAs electronic devices and 1.3 μm optical devices on the same wafer. In this work, we have investigated the growth of GaAs MESFETs and doped channel MIS-like FETs on InP by atmospheric pressure OMCVD. Because of the difference between the thermal expansion coefficient of GaAs and InP, the layers are under biaxial strain. The lowest FWHM of the (004) reflection curve of the double crystal X-ray diffraction spectra is 110 arc sec for a 12 μm thick layer. We have investigated the influence of the substrate temperature and of the arsine molar fraction on the residual carrier concentration of layers grown side by side on GaAs and on InP. The GaAs layers grown on InP are much more compensated than the layers grown on GaAs, indicating a higher incorporation of impurities. On MESFETs grown on InP, gm = 200mS/mm with Fmax higher than 30 GHz. On doped-channel MIS-like FETs on InP, we have measured gm = 145mS/mm.

  9. 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.

  10. 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.

  11. Cubic GaS: A Surface Passivator For GaAs

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; Barron, Andrew R.; Power, Michael B.; Jenkins, Phillip P.; Macinnes, Andrew N.

    1994-01-01

    Thin films of cubic form of gallium sulfide (GaS) formed on surfaces of gallium arsenide (GaAs) substrates via metal/organic chemical vapor deposition (MOCVD). Deposited cubic GaS, crystalline lattice matched to substrate GaAs, neutralizes electrically active defects on surfaces of both n-doped and p-doped GaAs. Enabling important GaAs-based semiconducting materials to serve as substrates for metal/insulator/semiconductor (MIS) capacitors. Cubic GaS enables fabrication of ZnSe-based blue lasers and light-emitting diodes. Because GaS is optically transparent, deposited to form window layers for such optoelectronic devices as light-emitting diodes, solar optical cells, and semiconductor lasers. Its transparency makes it useful as interconnection material in optoelectronic integrated circuits. Also useful in peeled-film technology because selectively etched from GaAs.

  12. 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.

  13. Monolithic Series-Interconnected GaInAsSb/AlGaAsSb Thermophotovoltaic Devices Wafer Bonded to GaAs

    NASA Astrophysics Data System (ADS)

    Wang, C. A.; Huang, R. K.; Connors, M. K.; Shiau, D. A.; Murphy, P. G.; O'Brien, P. W.; Anderson, A. C.; Donetsky, D.; Anikeev, S.; Belenky, G.; Luryi, S.; Nichols, G.

    2004-11-01

    GaInAsSb/AlGaAsSb/GaSb epitaxial layers were wafer bonded to semi-insulating GaAs wafers for monolithic series interconnection of thermophotovoltaic (TPV) devices. SiOx/Ti/Au was used as a bonding layer to provide electrical isolation and to serve as an internal back-surface reflector (BSR). The minority-carrier lifetime in WB BSR structures is more than two times longer than that of control structures without a BSR. WB GaInAsSb/AlGaAsSb TPV cells were fabricated and monolithically interconnected in series. These cells exhibit nearly linear voltage building. At a short-circuit current density of 0.4 A/cm2, Voc of a single TPV cell is 0.2 V, compared to 0.37 and 1.8 V for 2- and 10-junction series-interconnected TPV cells, respectively.

  14. Neutron irradiation effects on the infrared absorption of the EL2 defect in GaAs: New interpretation for the intracenter transition

    SciTech Connect

    Manasreh, M.O.; Fischer, D.W.; Covington, B.C.

    1988-04-15

    The effect of neutron irradiation on the optical properties of the EL2 center in semi-insulating GaAs was studied using the infrared absorption technique. The results show that the absorption band known as the intracenter transition between 1.03 and 1.27 eV is decreased by neutron irradiation. This absorption band is interpreted as a charge-transfer transition between the As/sub Ga/ antisite and an X component(s) assuming that EL2equivalentAs/sub Ga/+X. The neutron irradiation increases the As/sub Ga/ antisite concentration and reduces the EL2 concentration. The reduction of the EL2 concentration is due to the decrease of the X-component concentration. The zero-phonon line observed at 1.039 eV may not be an internal optical excitation within the isolated As/sub Ga/ antisite.

  15. Two orders of magnitude reduction in the temperature dependent resistivity of Ga1-xMnxAs grown on (6 3 1) GaAs insulating substrates

    NASA Astrophysics Data System (ADS)

    Rangel-Kuopp, Victor-Tapio; Martinez-Velis, Isaac; Gallardo-Hernandez, Salvador; Lopez-Lopez, Maximo

    2013-12-01

    The temperature dependent van der Pauw (T-Pauw) technique was used to investigate the resistivity of three Ga1-xMnxAs layers grown on (6 3 1) GaAs semi-insulating substrates. The samples had Mn concentration of 3.52×l020 cm-3, 5.05×1020 cm-3 and 1.12×l021 cm-3, corresponding to Mn cell effusion temperature TMn of 700 °C, 715 °C and 745 °C, respectively. They were compared to samples grown under the same conditions but on (0 0 1) GaAs semi-insulating substrates. For the sample grown at TMn=700 °C on a (6 3 1) substrate, a two orders of magnitude decrease in the resistivity is observed, when compared with the sample grown on a (0 0 1) substrate. For the sample grown at TMn=715 °C the decrease is approximately four times, while for the sample grown at TMn=745 °C the decrease is approximately forty times. We plotted the resistivities as a function of temperature in Arrhenius plots, where we extracted two activation energies, the smallest one between 6 and 11 meV, and the largest one between 25 and 183 meV. Both activation energies increased as TMn increased. These results are in agreement with SIMS analysis where we observed that manganese concentration in the (6 3 1) orientation growth is around two order of magnitude larger than in the samples grown in the (0 0 1) orientation substrate.

  16. Modelling of OPNMR phenomena using photon energy-dependent 〈Sz〉 in GaAs and InP.

    PubMed

    Wheeler, Dustin D; Willmering, Matthew M; Sesti, Erika L; Pan, Xingyuan; Saha, Dipta; Stanton, Christopher J; Hayes, Sophia E

    2016-12-01

    We have modified the model for optically-pumped NMR (OPNMR) to incorporate a revised expression for the expectation value of the z-projection of the electron spin, 〈Sz〉 and apply this model to both bulk GaAs and a new material, InP. This expression includes the photon energy dependence of the electron polarization when optically pumping direct-gap semiconductors in excess of the bandgap energy, Eg. Rather than using a fixed value arising from coefficients (the matrix elements) for the optical transitions at the k=0 bandedge, we define a new parameter, Sopt(Eph). Incorporating this revised element into the expression for 〈Sz〉, we have simulated the photon energy dependence of the OPNMR signals from bulk semi-insulating GaAs and semi-insulating InP. In earlier work, we matched calculations of electron spin polarization (alone) to features in a plot of OPNMR signal intensity versus photon energy for optical pumping (Ramaswamy et al., 2010). By incorporating an electron spin polarization which varies with pump wavelength into the penetration depth model of OPNMR signal, we are able to model features in both III-V semiconductors. The agreement between the OPNMR data and the corresponding model demonstrates that fluctuations in the OPNMR intensity have particular sensitivity to light hole-to-conduction band transitions in bulk systems. We provide detailed plots of the theoretical predictions for optical pumping transition probabilities with circularly-polarized light for both helicities of light, broken down into illustrative plots of optical magnetoabsorption and spin polarization, shown separately for heavy-hole and light-hole transitions. These plots serve as an effective roadmap of transitions, which are helpful to other researchers investigating optical pumping effects.

  17. Incorporation of the dopants Si and Be into GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Hilse, M.; Ramsteiner, M.; Breuer, S.; Geelhaar, L.; Riechert, H.

    2010-05-01

    We studied the doping with Si and Be of GaAs nanowires (NWRs) grown by molecular beam epitaxy. Regarding the NW morphology, no influence was observed for Si doping but high Be doping concentrations cause a kinking and tapering of the NWRs. We investigated local vibrational modes by means of resonant Raman scattering to determine the incorporation sites of the dopant atoms. For Si doping, both donors on Ga sites and acceptors on As sites have been observed. Be was found to be incorporated as an acceptor on Ga sites. However, at high doping concentration, Be is also incorporated on interstitial sites.

  18. Vacancy-associated Te sites in GaAs

    NASA Astrophysics Data System (ADS)

    Wuyts, K.; Langouche, G.; van Rossum, M.; Silverans, R. E.

    1992-03-01

    Defect structures, observed by 129I Mössbauer spectroscopy in high-dose Te-doped GaAs, are identified by a reference study of the semiconducting compound Ga2Te3. The formation of TeAs-VGa complexes (tellurium atoms quasisubstitutional on an As site with a gallium vacancy in the first-neighbor shell) is proposed, in agreement with theoretical predictions. The relevance of this assignment in relation to the earlier proposed Te DX configuration is also discussed.

  19. 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.

  20. Heterostructure design optimization for laser cooling of GaAs

    NASA Astrophysics Data System (ADS)

    Imangholi, B.; Wang, C.; Soto, E.; Sheik-Bahae, M.; Stintz, A.; Malloy, K.; Nuntawong, N.; Epstein, R.

    2007-02-01

    Doping of the clad layers in thin GaAs/GaInP heterostructures, displaces the band energy discontinuity, modifies the carrier concentration in the active GaAs region and changes the quality of the hetero-interfaces. As a result, internal and consequently external quantum efficiencies in the double heterostructure are affected. In this paper, the interfacial quality of GaAs/GaInP heterostructure is systematically investigated by adjusting the doping level and type (n or p) of the cladding layer. An optimum structure for laser cooling applications is proposed.

  1. Characterization of Si volume- and delta-doped InGaAs grown by molecular beam epitaxy

    SciTech Connect

    Fedoryshyn, Y.; Kaspar, P.; Jaeckel, H.; Beck, M.

    2010-05-15

    Bulk InGaAs layers were grown at 400 deg. C lattice-matched to InP semi-insulating substrates by molecular beam epitaxy. Si doping of the layers was performed by applying volume- and delta-doping techniques. The samples were characterized by capacitance-voltage, van der Pauw-Hall, secondary ion mass spectroscopy and photoluminescence measurements. Good agreement in terms of dependence of mobility and Burstein-Moss shift shift on doping concentration in samples doped by the two different techniques was obtained. Amphoteric behavior of Si was observed at doping concentrations higher than {approx}2.9x10{sup 19} cm{sup -3} in both delta- and volume-doped samples. Degradation of InGaAs crystalline quality occurred in samples with Si concentrations higher than {approx}4x10{sup 19} cm{sup -3}.

  2. 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.

  3. Characterization of defect levels in semi-insulating 6H-SiC by means of photoinduced transient spectroscopy and modulated photocurrent technique.

    PubMed

    Longeaud, C; Kleider, J P; Kaminski, P; Kozlowski, R; Miczuga, M

    2009-01-28

    Parameters of electrically active defect centres in vanadium-doped 6H silicon carbide (6H-SiC:V) were investigated by means of the photoinduced transient spectroscopy (PITS) and modulated photocurrent (MPC) method. After a short description of the two techniques, experimental results are presented and briefly compared. Our aim is mainly to understand and explain these experimental results. In particular, in the PITS technique a shallow level seems to be at the origin of negative photoconductivity. Besides, in the same temperature range hole and electron levels can be detected at the same time. Finally, the detection of a given level seems to depend on the photon flux used to perform the PITS experiment. As far as the MPC experiment is concerned, it has put into evidence a very efficient shallow level. A numerical calculation was developed to simulate both experiments in order to understand the experimental results. By means of this simulation, we have explained all the phenomena observed experimentally in each technique and we propose a simple model for the distribution of electrically active defect centres in 6H-SiC:V crystals.

  4. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy.

    PubMed

    Ohno, Takeo; Oyama, Yutaka

    2012-02-01

    In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE), in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm(-2). They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor.

  5. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

    PubMed Central

    Ohno, Takeo; Oyama, Yutaka

    2012-01-01

    In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE), in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor. PMID:27877466

  6. 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.

  7. Experimental studies of the charge limit phenomenon in NEA GaAs photocathodes

    SciTech Connect

    Tang, H.; Alley, R.K.; Aoyagi, H.; Clendenin, J.E.; Frisch, J.C.; Mulhollan, G.A.; Saez, P.J.; Schultz, D.C.; Turner, J.L.

    1994-06-01

    Negative electron affinity GaAs photocathodes have been in continuous use at SLAC for generating polarized electron beams since early 1992. If the quantum efficiency of a GaAs cathode is below a critical value, the maximum photoemitted charge with photons of energies close to the band gap in a 2-ns pulse is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this novel charge limit phenomenon in a variety of GaAs photocathodes of different structures and doping densities. We find that the charge limit is strongly dependent on the cathode`s quantum efficiency and the extraction electric field, and to a lesser degree on the excitation laser wavelength. In addition, we show that the temporal behavior of the charge limit depends critically on the doping density.

  8. Microstructural properties of phosphorus-doped p-type ZnO grown by radio-frequency magnetron sputtering

    SciTech Connect

    Oh, Min-Suk; Hwang, Dae-Kue; Choi, Yong-Seok; Kang, Jang-Won; Park, Seong-Ju; Hwang, Chi-Sun; Cho, Kyoung Ik

    2008-09-15

    Phosphorus (P)-doped ZnO thin films were grown by radio-frequency magnetron sputtering to study the microstructural properties of p-type ZnO. As-grown P-doped ZnO, a semi-insulator, was converted to p-type ZnO after being annealed at 800 deg. C in an N{sub 2} ambient. X-ray diffraction, secondary-ion-mass spectrometry, and Hall effect measurements indicated that P{sub 2}O{sub 5} phases in as-grown P-doped ZnO disappeared after thermal annealing to form a substitutional P at an O lattice site, which acts as an acceptor in P-doped ZnO. Transmission electron microscopy showed that the formation of stacking faults was facilitated to release the strain in P-doped ZnO during post-thermal annealing.

  9. Investigation of Schottky Barrier on GaAs and InP Using a Multi-Disciplined Approach

    DTIC Science & Technology

    1990-10-29

    more optimum metal contacts and Schottky barriers on GaAs and for increasing productivity and reliability of monolithic as well as individual GaAs...Since this overall study was motivated by a desire to understand GaAs (as well as InP and other 3-5) interfaces on an atomic level , we recognized...properly manipulating the native defects and impurity doping near the interface. This is supported by results of studies by others as well as

  10. 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.

  11. 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.

  12. Enhanced solar energy harvesting using top n-contact GaAs solar cell

    NASA Astrophysics Data System (ADS)

    Das, N. C.

    2015-05-01

    We fabricated single-junction solar cell on molecular beam epitaxially grown p-n junction on n-type gallium arsenide (GaAs) substrate. We used a germanium (Ge)/gold (Au)/nickel (Ni)/Au metal contact from the top side on a highly doped n+ epitaxial layer as well as the bottom side on an n-type GaAs substrate. We observed 10-15% increase in solar cell power when the top contact is used for the n+ GaAs epi layer compared to the bottom side n-type GaAs substrate. Solar cell fill factor, sheet, and shunt resistances are same for both the top and bottom contact type devices. We also observed higher external quantum efficiency (EQE) for top contact devices compared to bottom contact devices. We conclude that to achieve higher power, it is advantageous to use an n-type contact from a highly doped top n+ epitaxial layer rather than a bottom n-type GaAs substrate.

  13. Differences in stability and repeatability between GaAs and GaAlAs photocathodes

    NASA Astrophysics Data System (ADS)

    Xu, Yuan; Zhang, Yijun; Feng, Cheng; Shi, Feng; Zou, Jijun; Chen, Xinlong; Chang, Benkang

    2016-12-01

    For the applications in vacuum photodetectors and photoinjectors, a crucial limiting factor for conventional GaAs photocathodes is the limited lifetime, depending on the Cs-O activation layer vulnerable to the harmful residual gases. In order to develop a type of GaAs-based photocathode with good stability and repeatability, Cs/O activation and multiple recesiation experiments under the same preparation condition were performed on reflection-mode exponential-doped GaAs and GaAlAs photocathodes grown by metalorganic vapor phase epitaxy, and quantum efficiency and photocurrent decay were measured after activation and recesiation. The experimental results show that the photoemission characteristics on cathode degradation and repeatability are different between GaAs and GaAlAs photocathodes. In an unsatisfactory vacuum system, the operational lifetime for GaAlAs photocathode is nearly twice longer than that for GaAs photocathode after Cs/O activation under a high intensity illumination. After multiple recesiations, the quantum efficiency and operational lifetime for GaAlAs photocathode remain nearly unchanged, while those for GaAs photocathode become lower and lower with the increase of recesiation cycles, which reflects the superiority in stability and repeatability for GaAlAs photocathode in contrast to GaAs photocathode operating in the poor vacuum environment.

  14. Fracture mechanics evaluation of GaAs

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1984-01-01

    A data base of mechanical and fracture properties for GaAs was generated. The data for single crystal GaAs will be used to design reusable GaAs solar modules. Database information includes; (1) physical property characterizations; (2) fracture behavior evaluations; and (3) strength of cells determined as a function of cell processing and material parameters.

  15. Epitaxial two-dimensional nitrogen atomic sheet in GaAs

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  16. 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.

  17. Lifetime measurements by open circuit voltage decay in GaAs and InP diodes

    NASA Technical Reports Server (NTRS)

    Bhimnathwala, H. G.; Tyagi, S. D.; Bothra, S.; Ghandhi, S. K.; Borrego, J. M.

    1990-01-01

    Minority carrier lifetimes in the base of solar cells made on GaAs and InP were measured by the open-circuit voltage decay method. The measurement technique and the conditions under which the minority carrier lifetimes can be measured are described. Minority carrier lifetimes ranging from 1.6 to 34 ns in InP of different doping concentrations were measured. A minority carrier lifetime of 6 ns was measured in n-type GaAs, which agrees well with the lifetime of 5.7 ns measured by transient microwave reflection.

  18. 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.

  19. GaAs Computer Technology

    DTIC Science & Technology

    1992-01-07

    AD-A259 259 FASTC-ID FOREIGN AEROSPACE SCIENCE AND TECHNOLOGY CENTER GaAs COMPUTER TECHNOLOGY (1) by Wang Qiao-yu 93-00999 Distrir bution t,,,Nm ted...FASTC- ID(RS)T-0310-92 HUMAN TRANSLATION FASTC-ID(RS)T-0310-92 7 January 1993 GaAs COMPUTER TECHNOLOGY (1) By: Wang Qiao-yu English pages: 6 Source...SCIENCE AND DO NOT NECESSARILY REFLECT THE POSITION OR TECHNOLOGY CENiER OPINION OF THE FOREIGN AEROSPACE SCIENCE AND WPAFB, OHIO TECHNOLOGY CENTER

  20. Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111) A substrates

    NASA Astrophysics Data System (ADS)

    Galiev, G. B.; Klimov, E. A.; Vasiliev, A. L.; Imamov, R. M.; Pushkarev, S. S.; Trunkin, I. N.; Maltsev, P. P.

    2017-01-01

    The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111) A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in "low-temperature" GaAs serve as formation centers of arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100-150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111) A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150-200 nm.

  1. Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge substrates

    NASA Astrophysics Data System (ADS)

    Brammertz, Guy; Mols, Yves; Degroote, Stefan; Motsnyi, Vasyl; Leys, Maarten; Borghs, Gustaaf; Caymax, Matty

    2006-05-01

    Thin epitaxial GaAs films, with thickness varying from 140 to 1000 nm and different Si doping levels, were grown at 650 °C by organometallic vapor phase epitaxy on Ge substrates and analyzed by low-temperature photoluminescence (PL) spectroscopy. All spectra of thin GaAs on Ge show two different structures, one narrow band-to-band (B2B) structure at an energy of ~1.5 eV and a broad inner-band-gap (IB) structure at an energy of ~1.1 eV. Small strain in the thin GaAs films causes the B2B structure to be separated into a light-hole and a heavy-hole peak. At 2.5 K the good structural quality of the thin GaAs films on Ge can be observed from the narrow excitonic peaks. Peak widths of less than 1 meV are measured. GaAs films with thickness smaller than 200 nm show B2B PL spectra with characteristics of an n-type doping level of approximately 1018 at./cm3. This is caused by heavy Ge diffusion from the substrate into the GaAs at the heterointerface between the two materials. The IB structure observed in all films consists of two Gaussian peaks with energies of 1.04 and 1.17 eV. These deep trapping states arise from Ge-based complexes formed within the GaAs at the Ge-GaAs heterointerface, due to strong diffusion of Ge atoms into the GaAs. Because of similarities with Si-based complexes, the peak at 1.04 eV was identified to be due to a GeGa-GeAs complex, whereas the peak at 1.17 eV was attributed to the GeGa-VGa complex. The intensity of the IB structure decreases strongly as the GaAs film thickness is increased. PL intensity of undoped GaAs films containing antiphase domains (APDs) is four orders of magnitude lower than for similar films without APDs. This reduction in intensity is due to the electrically active Ga-Ga and As-As bonds at the boundaries between the different APDs. When the Si doping level is increased, the PL intensity of the APD-containing films is increased again as well. A film containing APDs with a Si doping level of ~1018 at./cm3 has only a factor 10

  2. Transient Velocity Assessment in Gallium Arsenide, and of Other GaAs Characteristics Related to Device Functions

    DTIC Science & Technology

    2012-03-29

    GaAs, two-terminal devices such as N+N-N+ diodes, and three-terminal devices (such as MESFETs and bipolar transistors ) are treated. We have chosen...Cornell group is no longer working on the standard MESFET. Their planar-doped barrier transistor is a vertically oriented device that uses a barrier...made a few hundred angstroms thick. Figure 7 shows an energy diagram of the planar doped barrier transistor mentioned above. A second possibility

  3. Influence of SiCl sub 4 reactive ion etching on the electrical characteristics of GaAs

    SciTech Connect

    Lootens, D. , Laboratorium voor Elektromagnetisme en Acoustica , Sint-Pietersnieuwstraat 41, B-9000 Gent ); Clauws, P. ); Van Daele, P.; Demeester, P. , Laboratorium voor Elektromagnetisme en Acoustica , Sint-Pietersnieuwstraat 41, B-9000 Gent )

    1991-05-05

    SiCl{sub 4}-RIE causes electrical damage to GaAs strongly related to doping type and level. Changes in C-V and DLTS-measurements can be related to EL2-defects. Explanations for observed differences in n-type and p-type material will be presented.

  4. Electrical and Optical Properties of Au-Catalyzed GaAs Nanowires Grown on Si (111) Substrate by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Wang, Chiu-Yen; Hong, Yu-Chen; Ko, Zong-Jie; Su, Ya-Wen; Huang, Jin-Hua

    2017-04-01

    In this study, defect-free zinc blende GaAs nanowires on Si (111) by molecular beam epitaxy (MBE) growth are systematically studied through Au-assisted vapor-liquid-solid (VLS) method. The morphology, density, and crystal structure of GaAs nanowires were investigated as a function of substrate temperature, growth time, and As/Ga flux ratio during MBE growth, as well as the thickness, annealing time, and annealing temperature of Au film using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), cathodoluminescence (CL), and Raman spectroscopy. When the As/Ga flux ratio is fixed at 25 and the growth temperature at 540 °C, the GaAs nanowires exhibit a defect-free zinc blende structure with uniform and straight morphology. According to the characteristics of GaAs nanowires grown under varied conditions, a growth mechanism for defect-free zinc blende GaAs nanowires via Au-assisted vapor-liquid-solid (VLS) method is proposed. Finally, doping by Si and Be of nanowires is investigated. The results of doping lead to GaAs nanowires processing n-type and p-type semiconductor properties and reduced electrical resistivity. This study of defect-free zinc blende GaAs nanowire growth should be of assistance in further growth and applications studies of complex III-V group nanostructures.

  5. Spectroscopic constants and potential energy curves of GaAs, GaAs +, and GaAs -

    NASA Astrophysics Data System (ADS)

    Balasubramanian, K.

    1990-02-01

    Twenty electronic states of GaAs, 12 electronic states of GaAs +, and 13 electronic states of GaAs - are investigated using relativistic ab initio complete active space MCSCF (CASSCF) followed by large-scale configuration interaction calculations which included up to 700 000 configurations. Potential energy curves and spectroscopic constants of all these states of three radicals are obtained. Spectroscopic constants of low-lying states of GaAs are in very good agreement with both experiment and all-electron results. Two nearly-degenerate states of 2Σ +, 2Π ( 2Σ + lower) symmetries are found as candidates for the ground state of GaAs -. The GaAs - negative ion is found to be more stable compared to the neutral GaAs ( De(GaAs -) = 3 eV). The electron affinity of GaAs is computed as 0.89 and 1.3 eV at the FOCI and SOCI levels of theory, respectively. Calculated potential energy curves of GaAs are in accord with the experimentally observed predissociation in the 3Π( III) - X3Σ- system.

  6. Two-dimensional simulation for the GaAs V-groove gate MESFET's

    NASA Astrophysics Data System (ADS)

    Wang, Y. J.; Lu, S. S.

    1999-02-01

    V-groove gate MESFET's were investigated in this paper by 2D simulation. In these devices, an interesting drain-induced-carrier-accumulation (DICA) effect was found. This effect could explain the origin of the output conductance and the dependence of the pinch-off voltages on the drain bias (i.e. short-channel effect). An analytical formula with physical meaning parameters for describing the DICA effect were also proposed. In addition, different substrate effects (including the undoped GaAs, undoped Al 0.3Ga 0.7As and p-doped GaAs substrates) on the V-groove gate MESFET's were simulated. The simulated I- V characteristics of the three devices with the different substrates exhibited short channel effects but the mechanisms of the short channel effect were found different. In the device with undoped GaAs substrate, the mechanism of the short-channel effect was due to the leakage current in the substrate. However, in that with the undoped AlGaAs substrate, it was the DICA effect. As for the device with the p-doped GaAs substrate, both the leakage current and the DICA were found.

  7. Incorporation and thermal stability of defects in highly p-conductive non-stoichiometric GaAs : Be

    NASA Astrophysics Data System (ADS)

    Specht, P.; Cich, M. J.; Zhao, R.; Gebauer, J.; Luysberg, M.; Weber, E. R.

    2001-12-01

    Non-stoichiometric GaAs is known to contain a high concentration of native point defects. The dominant defect in the epilayers is the arsenic antisite (As Ga), a deep double donor, which is incorporated at low growth temperatures (commonly between 200°C and 300°C) in molecular beam epitaxy (MBE). Consequently, p-doping of non-stoichiometric GaAs is difficult because large concentrations of acceptors are compensated by the As Ga. Recently, we found that despite this compensation effect we can achieve p-conductive GaAs : Be with almost one order of magnitude higher Be-doping than previously obtained in MBE grown GaAs. The kinetics of dopant incorporation during MBE growth at these low growth temperatures seem to allow pushing the doping concentration further beyond thermal equilibrium. The epilayers, which are about 1 μm thick, are pseudomorphic with a lattice mismatch to the substrate of up to Δ c/ c=-0.4%. They remain free of structural defects such as dislocations and stacking faults. After annealing at 600 oC only the highest doped epilayers show a reduction in the Be concentration although the layers remain ultrahigh p-conductive. The increased incorporation of Be as well as its unusual stability in non-stoichiometric GaAs is likely influenced by the native defects in these layers, double positively charged As Ga defects and probably neutral gallium vacancies ( VGa). This novel material which is solely achievable through low-temperature growth may significantly enhance III-V semiconductor applicability due to ultrahigh doping capability with increased thermal stability.

  8. Effects of various dopants on properties of GaAs tunneling junctions and p-i-n solar cells

    NASA Astrophysics Data System (ADS)

    Sodabanlu, Hassanet; Watanabe, Kentaroh; Sugiyama, Masakazu; Nakano, Yoshiaki

    2017-08-01

    Several GaAs tunneling junctions (TJs) and p-i-n single junction solar cells grown using a planetary metalorganic vapor phase epitaxy (MOVPE) reactor utilizing various dopant species including Zn, C, S, and Te were investigated. The incorporation of Te atoms into GaAs was approximately two orders larger than that of S atoms. Although only 30% of Te atoms could be electrically activated, a carrier concentration of 1019 cm-3 was achieved. Highly C-doped GaAs was successfully obtained by decreasing the growth temperature and increasing the amount of H2 carrier gas in order to prevent the predecomposition of CBr4 dopant gas. A hole concentration of about 1020 cm-3 was realized with a growth temperature of 450 °C. The C-Te-doped GaAs TJ exhibited the best ohmic tunneling behavior with a resistivity of 12.5 mΩ·cm2, while the others had diode characteristics. The GaAs solar cell grown with the Zn-S dopant showed the highest conversion efficiency ascribed to a longer minority carrier lifetime.

  9. 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.

  10. 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.

  11. Comparison of degradation and recaesiation between GaAs and AlGaAs photocathodes in an unbaked vacuum system.

    PubMed

    Feng, Cheng; Zhang, Yijun; Shi, Feng; Qian, Yunsheng; Cheng, Hongchang; Zhang, Junju; Liu, Xinxin; Zhang, Xiang

    2017-03-20

    The lifetime and reliability of a photocathode during operation are always raised problems and the photocathode performance depends on the vacuum condition. With the purpose of investigating the stability and reliability of a GaAs-based photocathode in a harsher vacuum environment, reflection-mode exponential-doped GaAs and AlGaAs photocathodes are metalorganic vapor-phase epitaxial grown and then (Cs, O) activated inside an unbaked vacuum chamber. The degraded photocurrents are compared after activation and recaesiations between GaAs and AlGaAs photocathdoes under illumination with an equal initial photocurrent and an equal optical flux, respectively. It is found that the performance on degradation and recaesiations between GaAs and AlGaAs photocathodes are different. In the unbaked vacuum system, the stability of an AlGaAs photocathode after (Cs, O) activation is always better than that of a GaAs photocathode. After multiple recaesiations, the photocurrent decay curves of the AlGaAs photocathode are nearly coincident, which means a nearly constant operational lifetime. Moreover, operational lifetime of an AlGaAs photocathode is longer than that of a GaAs photocathode, which further illuminates that AlGaAs photocathodes are superior to GaAs photocathodes in stability and repeatability under markedly harsher vacuum conditions.

  12. GaAs MMIC phase shifters

    NASA Astrophysics Data System (ADS)

    Lane, A. A.; Myers, F. A.

    This paper describes the design and performance of various GaAs MMIC phase shifters specifically designed for electronically scanned antennas. Phase shifting is achieved by using GaAs FETs to switch various circuits to realize the required functions. Some preliminary results on novel components and high packing density techniques leading to truly effective multifunction circuits are described.

  13. 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.

  14. 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.

  15. GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Conway, E. J.

    1982-01-01

    The major thrusts proposed for GaAs were increased efficiency and improved radiation damage data. Current laboratory production cells consistently achieve 16 percent AMO one-Sun efficiency. The user community wants 18-percent efficient cells as soon as possible, and such a goal is though to be achievable in 2 years with sufficient research funds. A 20-percent research cell is considered the efficiency limit with current technology, and such a cell seems realizable in approximately 4 years. Future efficiency improvements await improved substrates and materials. For still higher efficiencies, concentrator cells and multijunction cells are proposed as near-term directions.

  16. Characterization of as-grown and annealed GaAs: Structural defects and electrical properties

    SciTech Connect

    Lee, B.T.

    1988-07-01

    Structural defects in GaAs related to excess As were characterized and their behavior upon heat treatments studied. The observed defects included precipitates and dislocations. Results showed most of the precipitates in As-rich GaAs to the rhombohedral arsenic. Two exceptions were observed in an In-doped LEC (liguid encapsulated Czochralski) GaAs, which were As-rich but could not be further identified. Some of the observed As precipitates showed a simple orientation relationship with the matrix which yields structural coherence between As precipitates and GaAs matrix. Other As precipitates showed less coherent orientation. The dislocation loops in As-rich GaAs consisted a faulted loop with Shockley type Burgers vector and a perfect loop associated with an extra /l brace/111/r brace/ plane. It was proposed that these loops were formed as a result of dual condensation of both excess As interstitials and Ga vacancies, followed by generation and movement of Shockley partial dislocations. These precipitates and dislocation loops disappear after annealing, indicating a solvus temperature between 600--700/degree/C. The EL2 concentration increased as the defects dissolved, showing the defects to be the source of the excess As required to form EL2. The implication is that the As interstitial and Ga vacancies coexist in GaAs at high temperatures, which indicates that these point defects are responsible for the formation of arsenic antisites by direct combination. During the cooling period, they freeze into the matrix as point defects during a rapid cooling and condense as dislocation loops and precipitates during very slow cooling, in the dislocation-free region of the crystals. Around dislocations, the excess As precipitates heterogeneously even during rapid cooling. 217 refs.

  17. Wafer Bonding and Epitaxial Transfer of GaSb-based Epitaxy to GaAs for Monolithic Interconnection of Thermophotovoltaic Devices

    SciTech Connect

    C.A. Wang; D.A. Shiau; P.G. Murphy; P.W. O'brien; R.K. Huang; M.K. Connors; A.C. Anderson; D. Donetsky; S. Anikeev; G. Belenky; D.M. Depoy; G. Nichols

    2003-06-16

    GaInAsSb/AlGaAsSb/InAsSb/GaSb epitaxial layers were bonded to semi-insulating GaAs handle wafers with SiO{sub x}/Ti/Au as the adhesion layer for monolithic interconnection of thermophotovoltaic (TPV) devices. Epitaxial transfer was completed by removal of the GaSb substrate, GaSb buffer, and InAsSb etch-stop layer by selective chemical etching. The SiO{sub x}/TiAu provides not only electrical isolation, but also high reflectivity and is used as an internal back-surface reflector. Characterization of wafer-bonded epitaxy by high-resolution x-ray diffraction and time-decay photoluminescence indicates minimal residual stress and enhancement in optical quality. 0.54-eV GaInAsSb cells were fabricated and monolithically interconnected in series. A 10-junction device exhibited linear voltage building with an open-circuit voltage of 1.8 V.

  18. Radiation effects in GaAs AMOS solar cells

    NASA Technical Reports Server (NTRS)

    Shin, B. K.; Stirn, R. J.

    1979-01-01

    The results of radiation damage produced in AMOS (Antireflecting-Metal-Oxide-Semiconductor) cells with Sb2O3 interfacial oxide layers by 1-MeV electrons are presented. The degradation properties of the cells as a function of irradiation fluences were correlated with the changes in their spectral response, C-V, dark forward, and light I-V characteristics. The active n-type GaAs layers were grown by the OM-CVD technique, using sulfur doping in the range between 3 x 10 to the 15th power and 7 x 10 to the 16th power/cu cm. At a fluence of 10 to the 16th power e/sq cm, the low-doped samples showed I sub sc degradation of 8% and V sub oc degradation of 8%. The high-doped samples showed I sub sc and V sub oc degradation of 32% and 1%, respectively, while the fill factor remained relatively unchanged for both. AMOS cells with water vapor-grown interfacial layers showed no significant change in V sub oc.

  19. Sn nanothreads in GaAs: experiment and simulation

    NASA Astrophysics Data System (ADS)

    Semenikhin, I.; Vyurkov, V.; Bugaev, A.; Khabibullin, R.; Ponomarev, D.; Yachmenev, A.; Maltsev, P.; Ryzhii, M.; Otsuji, T.; Ryzhii, V.

    2016-12-01

    The gated GaAs structures like the field-effect transistor with the array of the Sn nanothreads was fabricated via delta-doping of vicinal GaAs surface by Sn atoms with a subsequent regrowth. That results in the formation of the chains of Sn atoms at the terrace edges. Two device models were developed. The quantum model accounts for the quantization of the electron energy spectrum in the self-consistent two-dimensional electric potential, herewith the electron density distribution in nanothread arrays for different gate voltages is calculated. The classical model ignores the quantization and electrons are distributed in space according to 3D density of states and Fermi-Dirac statistics. It turned out that qualitatively both models demonstrate similar behavior, nevertheless, the classical one is in better quantitative agreement with experimental data. Plausibly, the quantization could be ignored because Sn atoms are randomly placed along the thread axis. The terahertz hot-electron bolometers (HEBs) could be based on the structure under consideration.

  20. Bismuth alloying properties in GaAs nanowires

    SciTech Connect

    Ding, Lu; Lu, Pengfei; Cao, Huawei; Cai, Ningning; Yu, Zhongyuan; Gao, Tao; Wang, Shumin

    2013-09-15

    First-principles calculations have been performed to investigate the structural, electronic and optical properties of bismuth alloying in GaAs nanowires. A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration and the band edge shifts when spin–orbit coupling (SOC) is considered. The insertion of Bi atom leads to hybridization of Ga/As/Bi p states which contributes a lot around Fermi level. Scissor effect is involved. The optical properties are presented, including dielectric function, optical absorption spectra and reflectivity, which are also varied with the increasing of Bi concentrations. - Graphical abstract: Top view of Bi-doped GaAs nanowires. Ga, As, and Bi atoms are denoted with grey, purple and red balls, respectively. Display Omitted - Highlights: • A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. • The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration. • The band edge shifts when spin–orbit coupling (SOC) is considered. • The insertion of Bi atom leads to hybridization of Ga/As/Bi p states.

  1. Anisotropic transport in modulation doped quantum well structures

    NASA Technical Reports Server (NTRS)

    Radulescu, D. C.; Wicks, G. W.; Schaff, W. J.; Calawa, A. R.; Eastman, L. F.

    1987-01-01

    The degree of anisotropy in the anisotropic electron transport that has been observed in GaAs modulation-doped quantum wells grown by MBE on Al(0.3)Ga(0.7)As is related to the thickness and growth parameters of this substrate, which is grown just prior to the inverted interface. It is presently observed that the inverted interface has an anisotropic roughness which affects the 77 K low field electron transport parallel to the interface, and gives rise to anisotropic electron scattering in the GaAs modulation-doped quantum well.

  2. Patterned radial GaAs nanopillar solar cells.

    PubMed

    Mariani, Giacomo; Wong, Ping-Show; Katzenmeyer, Aaron M; Léonard, Francois; Shapiro, Joshua; Huffaker, Diana L

    2011-06-08

    Photovoltaic devices using GaAs nanopillar radial p-n junctions are demonstrated by means of catalyst-free selective-area metal-organic chemical vapor deposition. Dense, large-area, lithographically defined vertical arrays of nanowires with uniform spacing and dimensions allow for power conversion efficiencies for this material system of 2.54% (AM 1.5 G) and high rectification ratio of 213 (at ±1 V). The absence of metal catalyst contamination results in leakage currents of ∼236 nA at -1 V. High-resolution scanning photocurrent microscopy measurements reveal the independent functioning of each nanowire in the array with an individual peak photocurrent of ∼1 nA at 544 nm. External quantum efficiency shows that the photocarrier extraction highly depends on the degenerately doped transparent contact oxide. Two different top electrode schemes are adopted and characterized in terms of Hall, sheet resistance, and optical transmittance measurements.

  3. Ab Initio Investigation of the Structural, Electronic and Optical Properties of Cubic GaAs1- x P x Ternary Alloys Under Hydrostatic Pressure

    NASA Astrophysics Data System (ADS)

    Moussa, R.; Abdiche, A.; Abbar, B.; Guemou, M.; Riane, R.; Murtaza, G.; Omran, SAAD Bin; Khenata, R.; Soyalp, F.

    2015-12-01

    The structural, electronic and optical properties of the GaAs1- x P x ternary alloys together with their binary GaP and GaAs compounds were investigated in the zinc-blende (ZB) phase using the density functional theory. The lattice constant of the GaAs compound decreases while its bulk modulus increases when the doping concentration of the P dopant is increased. In addition, both parameters (lattice constant and bulk modulus) show small deviations from the linear concentration dependence. The energy band gap of the GaAs compound is of the direct nature, which increases with the increase in the P dopant concentration, whereas at higher P dopant concentration, the band gap shifts from direct to indirect character. On the other hand, the hydrostatic pressure has a significant effect on the band structure of the investigated compounds where the binary GaAs compound changes from a direct band gap semiconductor to an indirect band gap semiconductor at P ≥ 5 GPa. Furthermore, the pressure-dependence of the optical properties of the GaAs, GaP and GaAs0.75P0.25 alloy were also investigated, where the calculated zero frequency refractive index and the dielectric function are also compared with the experimental results as well as with different empirical models.

  4. 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.

  5. 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.

  6. 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.

  7. Interplay between quantum well width and interface roughness for electron transport mobility in GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Kamburov, D.; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

    2016-12-01

    We report transport mobility measurements for clean, two-dimensional (2D) electron systems confined to GaAs quantum wells (QWs), grown via molecular beam epitaxy, in two families of structures, a standard, symmetrically doped GaAs set of QWs with Al0.32Ga0.68As barriers and one with additional AlAs cladding surrounding the QWs. Our results indicate that the mobility in narrow QWs with no cladding is consistent with existing theoretical calculations where interface roughness effects are softened by the penetration of the electron wave function into the adjacent low barriers. In contrast, data from AlAs-clad wells show a number of samples where the 2D electron mobility is severely limited by interface roughness. These measurements across three orders of magnitude in mobility provide a road map of reachable mobilities in the growth of GaAs structures of different electron densities, well widths, and barrier heights.

  8. High-efficiency, radiation-resistant GaAs space cells

    NASA Technical Reports Server (NTRS)

    Bertness, K. A.; Ristow, M. Ladle; Grounner, M.; Kuryla, M. S.; Werthen, J. G.

    1991-01-01

    Although many GaAs solar cells are intended for space applicatons, few measurements of cell degradation after radiation are available, particularly for cells with efficiencies exceeding 20 percent (one-sun, AMO). Often the cell performance is optimized for the highest beginning-of-life (BOL) efficiency, despite the unknown effect of such design on end-of-life (EOL) efficiencies. The results of a study of the radiation effects on p-n GaAs cells are presented. The EOL efficiency of GaAs space cell can be increased by adjusting materials growth parameters, resulting in a demonstration of 16 percent EOL efficiency at one-sun, AMO. Reducing base doping levels to below 3 x 10(exp 17)/cu m and decreasing emitter thickness to 0.3 to 0.5 micron for p-n cells led to significant improvements in radiation hardness as measured by EOL/BOL efficiency ratios for irradiation of 10(exp -15)/sq cm electrons at 1 MeV. BOL efficiency was not affected by changes in emitter thickness but did improve with lower base doping.

  9. Pulse transformer for GaAs laser

    NASA Technical Reports Server (NTRS)

    Rutz, E. M.

    1976-01-01

    High-radiance gallium arsenide (GaAs) laser operating at room temperature is utilized in optical navigation system. For efficient transformer-to-laser impedance match, laser should be connected directly to pulse transformer secondary winding.

  10. Ohmic contact to GaAs semiconductor

    NASA Technical Reports Server (NTRS)

    Hovel, H. J.; Woodall, J. M.

    1980-01-01

    Multimetallic layers produce stable, low-resistance contacts for p-type GaAs and p-type GaAlAs devices. Contacts present no leakage problems, and their series resistance is too small to measure at 1 Sun intensity. Ohmic contacts are stable and should meet 20-year-life requirement at 150 C for GaAs combined photothermal/photovoltaic concentrators.

  11. GaAs homojunction solar cell development

    NASA Technical Reports Server (NTRS)

    Flood, D. J.; Swartz, C. K.; Hart, R. E., Jr.

    1980-01-01

    The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells.

  12. Direct-bonded four-junction GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Jingman, Shen; Lijie, Sun; Kaijian, Chen; Wei, Zhang; Xunchun, Wang

    2015-06-01

    Direct wafer bonding technology is able to integrate two smooth wafers and thus can be used in fabricating III-V multijunction solar cells with lattice mismatch. In order to monolithically interconnect between the GaInP/GaAs and InGaAsP/InGaAs subcells, the bonded GaAs/InP heterojunction must be a highly conductive ohmic junction or a tunnel junction. Three types of bonding interfaces were designed by tuning the conduction type and doping elements of GaAs and InP. The electrical properties of p-GaAs (Zn doped)/n-InP (Si doped), p-GaAs (C doped)/n-InP (Si doped) and n-GaAs (Si doped)/n-InP (Si doped) bonded heterojunctions were analyzed from the I-V characteristics. The wafer bonding process was investigated by improving the quality of the sample surface and optimizing the bonding parameters such as bonding temperature, bonding pressure, bonding time and so on. Finally, GaInP/GaAs/InGaAsP/InGaAs 4-junction solar cells have been prepared by a direct wafer bonding technique with the high efficiency of 34.14% at the AM0 condition (1 Sun). Project supported by the Shanghai Rising-Star Program (No. 14QB1402800).

  13. High Resistivity Molecular Beam Epitaxial AlGaAs for Device Applications.

    DTIC Science & Technology

    1980-02-01

    V MESFET technology requires, in part, the improvement of semi-insulating materials used in today’s device fabrication. The properties of currently...overall improvement in low temperature Hall mobility. Several techniques have been used to characterize AlGaAs properties. Basic determinations of impurity...available chromium-doped GaAs substrates impose restrictions on the performance of devices and monolithic circuits presently being produced in research

  14. Low resistance Pd/Zn/Pd Au ohmic contacts to P-type gaas

    NASA Astrophysics Data System (ADS)

    Bruce, R.; Clark, D.; Eicher, S.

    1990-03-01

    Many optoelectronic devices require contacts to p-doped epitaxial layers. To achieve low contact resistance, the semiconductor has to be doped to high levels. The p-dopants most commonly used are Be, Mg, and Zn. The contacts were formed by the sequential e-beam evaporation of 10 nm Pd, ≤5 nm Zn, 20 nm Pd and 40 nm Au layers onto a 0.2 μm thick Be-doped (5 × 1018 cm) GaAs layer grown by MBE. The minimum contact resistance of 0.04 Ω-mm (≤1 × 10-7 Ω-cm2), as measured using the transmission line method, was obtained for contacts annealed at 500° C for 30s. These are the lowest contact resistance values reported to date for alloyed contacts to p-GaAs.

  15. 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.

  16. Sulfur passivation and contact methods for GaAs nanowire solar cells.

    PubMed

    Tajik, N; Peng, Z; Kuyanov, P; LaPierre, R R

    2011-06-03

    The effect of sulfur passivation on core-shell p-n junction GaAs nanowire (NW) solar cells has been investigated. Devices of two types were investigated, consisting of indium tin oxide contact dots or opaque Au finger electrodes. Lateral carrier transport from the NWs to the contact fingers was achieved via a p-doped GaAs surface conduction layer. NWs between the opaque contact fingers had sidewall surfaces exposed for passivation by sulfur. The relative cell efficiency increased by 19% upon passivation. The contribution of the thin film grown between the NWs to the total cell efficiency was estimated by removing the NWs using a sonication procedure. Mechanisms of carrier transport and photovoltaic effects are discussed on the basis of spatially resolved laser scanning measurements.

  17. Spatial distribution of carbon and native defects in large-diameter bulk grown GaAs

    SciTech Connect

    Walukiewicz, W.; Bourret, E.; Yau, W.F.; Mc Murray, R.E. Jr.; Haller, E.E.; Bliss, D.

    1987-04-01

    Different spectroscopic techniques have been combined to measure concentrations of carbon on arsenic sites and of neutral EL2. Utilizing the recently found dependence of the high resolution local vibrational mode spectrum on the charge state of the carbon acceptors we have been able to separately determine concentrations of neutral and ionized carbon after EL2 has been optically quenched. The concentration of ionized carbon shows a very distinct W-shaped variation across the wafer whereas the total carbon concentration is close to constant. The variations are caused by the nonuniform distribution of donors which are shallower than EL2. The account for the commonly observed variations of the near infrared absorption. Radiotracer experiments with GaAs crystals intentionally doped with /sup 14/C showed that carbon is very homogeneously distributed in GaAs grown by horizontal Bridgman method. No correlation between the distribution of carbon and dislocations has been found. 17 refs., 5 figs.

  18. GALLIUM ARSENIDE (GaAs)

    NASA Astrophysics Data System (ADS)

    Levinshtein, M. E.; Rumyantsev, S. L.

    The following sections are included: * Basic Parameters at 300 K * Band Structure and Carrier Concentration * Temperature Dependences * Dependences on Hydrostatic Pressure * Energy Gap Narrowing at High Doping Levels * Effective Masses * Donors and Acceptors * Electrical Properties * Mobility and Hall Effect * Transport Properties in High Electric Field * Impact Ionization * Recombination Parameters * Optical Properties * Thermal Properties * Mechanical Properties, Elastic Constants, Lattice Vibrations, Other Properties * References

  19. 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.

  20. 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.

  1. Growth of high-quality p-type GaAs epitaxial layers using carbon tetrabromide by gas source molecular-beam epitaxy and molecular-beam epitaxy

    SciTech Connect

    Houng, Y.M.; Lester, S.D.; Mars, D.E.

    1993-05-01

    Heavily C-doped p-type GaAs epitaxial films have been grown using carbon tetrabromide (CBr{sub 4}) as a dopant source in both gas source molecular-beam epitaxy (GSMBE) and molecular-beam epitaxy (MBE). It was found that CBr;{sub 4} has a great potential as a p-type dopant source for use in a conventional MBE chamber without any major modification of its pumping system because of its high-doping efficiency and low gas load. Hole concentrations in excess of 1x10{sup 20} cm{sup {minus}3} have been measured in CBr{sub 4}-doped GaAs grown from both the MBE or GSMBE techniques, using As{sub 4} or AsH{sub 3}, respectively. A Hall mobility of > 80 cm{sup 2}/V s was measured in layers with doping level of 5x10{sup 19} cm{sup {minus}3}, which is comparable to that from chemical beam exitaxially (CBE) grown TMGa-doped GaAs. Under GSMBE and MBE modes, the doping memory effect in AlGaAs was greatly reduced using CBr{sub 4} as compared to TMGa doping source. GSMBE grown heterojunction bipolar transistors with a CBr{sub 4} as compared to TMGa doping source. GSMBE grown heterojunction bipolar transistors with a CBr{sub 4}-doped base layer have a current gain as high as 79 and a base sheet resistance as low as 225 {Omega}/{open_square}. 15 refs., 4 figs., 1 tab.

  2. 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.

  3. Above bandgap luminescence of p-type GaAs epitaxial layers

    NASA Astrophysics Data System (ADS)

    Sapriel, J.; Chavignon, J.; Alexandre, F.; Azoulay, R.; Sermage, B.; Rao, K.; Voos, M.

    1991-08-01

    New photoluminescence bands are observed in p-type GaAs epitaxial layers at 300 and 80 K, above the bandgap. These bands are independent of the nature of the dopant (Zn, Be, C) and of the growth technique (MBE or MOCVD). Their intensities increase as a function of the p doping (1 × 10 17 < p < 2 × 10 20cm-3) and peak at energies which correspond to transitions between the Γ 6, L 6 and X 6 minima of the conduction band and the Γ 8 and Γ 7 maxima of the valence band.

  4. 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.

  5. GaAs solar cell test facility

    NASA Astrophysics Data System (ADS)

    Kawashima, M.; Hosoda, Y.; Suzawa, C.; Shimada, T.; Motoyoshi, K.; Sasatani, Y.

    1982-01-01

    A hybrid type (electricity and heat) GaAs solar cell test facility has been made to evaluate total characteristics of GaAs cell and to study the energy conversion system. The size of a solar collector is 3.4 m x 2.1 m and 60 GaAs cells with Fresnel lenses are attached on it. The solar collector is controlled by a microcomputer to track the sun. Electric energy produced by the cells is stored in a lead-acid battery and then supplied to the load through a DC-AC inverter. The microcomputer also controls the data acquisition in parallel with tracking. This paper presents an overview of the facility and the experimental results of power generation obtained to date.

  6. 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.

  7. 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.

  8. 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.

  9. Ion Implanted GaAs I.C. Process Technology

    DTIC Science & Technology

    1981-07-01

    in ion implantation in GaAs, coupled with better control of the substrate material. 1 Once ion implantation became a reliable processing technology it... Processing Technology for Planar GaAs Integrated Circuits," GaAs IC Symposium, Lake Tahoe, CA., Sept. 1979. 20. R.C. Eden, "GaAs Integrated Circuit Device...1980. 25. B.M. Welch, "Advances in GaAs LSI!VLSI Processing Technology ," Sol. St. Tech., Feb. 1980, pp. 95-101. 27. R. Zucca, B.M. Welch, P.M

  10. GaAs nanowire array solar cells with axial p-i-n junctions.

    PubMed

    Yao, Maoqing; Huang, Ningfeng; Cong, Sen; Chi, Chun-Yung; Seyedi, M Ashkan; Lin, Yen-Ting; Cao, Yu; Povinelli, Michelle L; Dapkus, P Daniel; Zhou, Chongwu

    2014-06-11

    Because of unique structural, optical, and electrical properties, solar cells based on semiconductor nanowires are a rapidly evolving scientific enterprise. Various approaches employing III-V nanowires have emerged, among which GaAs, especially, is under intense research and development. Most reported GaAs nanowire solar cells form p-n junctions in the radial direction; however, nanowires using axial junction may enable the attainment of high open circuit voltage (Voc) and integration into multijunction solar cells. Here, we report GaAs nanowire solar cells with axial p-i-n junctions that achieve 7.58% efficiency. Simulations show that axial junctions are more tolerant to doping variation than radial junctions and lead to higher Voc under certain conditions. We further study the effect of wire diameter and junction depth using electrical characterization and cathodoluminescence. The results show that large diameter and shallow junctions are essential for a high extraction efficiency. Our approach opens up great opportunity for future low-cost, high-efficiency photovoltaics.

  11. 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.

  12. Defect studies in low-temperature-grown GaAs

    SciTech Connect

    Bliss, David Emory

    1992-11-01

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

  13. 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.

  14. Electron channel mobility in silicon-doped Ga2O3 MOSFETs with a resistive buffer layer

    NASA Astrophysics Data System (ADS)

    Wong, Man Hoi; Sasaki, Kohei; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2016-12-01

    The electron mobility in depletion-mode lateral β-Ga2O3(010) metal-oxide-semiconductor field-effect transistors (MOSFETs) with an n-channel formed by Si-ion (Si+) implantation doping was extracted using low-field electrical measurements on FET structures. An undoped Ga2O3 buffer layer protected the channel against charge compensation by suppressing outdiffusion of deep Fe acceptors from the semi-insulating substrate. The molecular beam epitaxy growth temperature was identified as a key process parameter for eliminating parasitic conduction at the buffer/substrate growth interface. Devices with a resistive buffer showed room temperature channel mobilities of 90-100 cm2 V-1 s-1 at carrier concentrations of low- to mid-1017 cm-3, with small in-plane mobility anisotropy of 10-15% ascribable to anisotropic carrier scattering.

  15. Characterization of LT GaAs carrier lifetime in multilayer GaAs epitaxial wafers by the transient reflectivity technique

    SciTech Connect

    McMorrow, D.; Melinger, J.S.; Campbell, A.B.; Knudson, A.R.; Buchner, S.; Ikossi-Anastasiou, K.; Moss, S.C.; Engelhardt, D.; Childs, T.

    1997-12-01

    A methodology for determining the carrier lifetime of LT GaAs buffer layers in GaAs multilayer wafers utilizing the femtosecond transient reflectivity technique is introduced. Experimental results and computer simulations performed as a function of the LT GaAs growth temperature are presented for the multilayer GaAs structures that are used for device fabrication. The markedly non-exponential nature of the measured transients is a consequence of the multilayer structure of the wafers. The carrier lifetime measurements are correlated with available SEU data measured for structures fabricated with LT GaAs buffers with different growth temperatures.

  16. 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.

  17. 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.

  18. 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.

  19. Image transfer in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory; Rau, Mann-Fu; Wang, Faa-Ching

    1987-01-01

    Image transfer from one beam to the other using counterpropagation beam coupling in GaAs was demonstrated. Good image quality was achieved. The results also reveal that local birefringence due to the residual stress/strain field in the crystal can degrade the image quality.

  20. 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.

  1. Image transfer in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory; Rau, Mann-Fu; Wang, Faa-Ching

    1987-01-01

    Image transfer from one beam to the other using counterpropagation beam coupling in GaAs was demonstrated. Good image quality was achieved. The results also reveal that local birefringence due to the residual stress/strain field in the crystal can degrade the image quality.

  2. 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.

  3. Dilute nitride and GaAs n-i-p-i solar cells.

    PubMed

    Mazzucato, Simone; Royall, Benjamin; Ketlhwaafetse, Richard; Balkan, Naci; Salmi, Joel; Puustinen, Janne; Guina, Mircea; Smith, Andy; Gwilliam, Russell

    2012-11-20

    We demonstrate for the first time the operation of GaInNAs and GaAs n-i-p-i doping solar cells with ion-implanted selective contacts. Multiple layers of alternate doping are grown by molecular beam epitaxy to form the n-i-p-i structure. After growth, vertical selective contacts are fabricated by Mg and Si ion implantation, followed by rapid thermal annealing treatment and fabrication into circular mesa cells. As means of characterisation, spectral response and illuminated current-voltage (I-V) were measured on the samples. The spectral response suggests that all horizontal layers are able to contribute to the photocurrent. Performance of the devices is discussed with interest in the n-i-p-i structure as a possible design for the GaInP/GaAs/GaInNAs tandem solar cell.

  4. Magneto-transport properties of exfoliated graphene on GaAs

    NASA Astrophysics Data System (ADS)

    Woszczyna, Mirosław; Friedemann, Miriam; Pierz, Klaus; Weimann, Thomas; Ahlers, Franz J.

    2011-08-01

    We studied the magneto-transport properties of graphene prepared by exfoliation on a III-V semiconductor substrate. Tuneability of the carrier density of graphene was achieved by using a doped GaAs substrate as a back-gate. A GaAs/AlAs multilayer, designed to render the exfoliated graphene flakes visible, also provides the required back-gate insulation. Good tuneability of the graphene carrier density is obtained, and the typical Dirac resistance characteristic is observed despite the limited height of the multilayer barrier as compared to the usual SiO2 oxide barrier on doped silicon. In a magnetic field, weak localization effects as well as the quantum Hall effect of a graphene monolayer are studied.

  5. Dilute nitride and GaAs n-i-p-i solar cells

    PubMed Central

    2012-01-01

    We demonstrate for the first time the operation of GaInNAs and GaAs n-i-p-i doping solar cells with ion-implanted selective contacts. Multiple layers of alternate doping are grown by molecular beam epitaxy to form the n-i-p-i structure. After growth, vertical selective contacts are fabricated by Mg and Si ion implantation, followed by rapid thermal annealing treatment and fabrication into circular mesa cells. As means of characterisation, spectral response and illuminated current–voltage (I-V) were measured on the samples. The spectral response suggests that all horizontal layers are able to contribute to the photocurrent. Performance of the devices is discussed with interest in the n-i-p-i structure as a possible design for the GaInP/GaAs/GaInNAs tandem solar cell. PMID:23167964

  6. Ion Implanted Gaas Integrated Optics Fabrication Technology

    NASA Astrophysics Data System (ADS)

    Mentzer, M. A.; Hunsperger, R. G.; Bartko, J.; Zavada, J. M.; Jenkinson, H. A.

    1985-01-01

    Ion implantation of semiconductor materials is a fabrication technique that offers a number of distinct advantages for the formation of guided-wave components and microelectronic devices. Implanted damage and dopants produce optical and electronic changes that can be utilized for sensing and signal processing applications. GaAs is a very attractive material for optical fabrication since it is transparent out to the far infrared. It can be used to fabricate optical waveguides, directional couplers, EO modulators, and detectors, as well as other guided wave structures. The presence of free carriers in GaAs lowers the refractive index from that of the pure semiconductor material. This depression of the refractive index is primarily due to the negative contribution of the free carrier plasma to the dielectric constant of the semiconductor. Bombardment of n-type GaAs by protons creates damage sites near the surface of the crystal structure where free carriers are trapped. This "free carrier compensated" region in the GaAs has a higher refractive index than the bulk region. If the compensated region is sufficiently thick and has a refractive index which is sufficiently larger than that of the bulk n-type region, an optical waveguide is formed. In this paper, a description of ion implantation techniques for the fabrication of both planar and channel integrated optical structures in GaAs is presented, and is related to the selection of ion species, implant energy and fluence, and to the physical processes involved. Lithographic technology and masking techniques are discussed for achieving a particular desired implant profile. Finally, the results of a set of ion implantation experiments are presented.

  7. Contact properties to CVD-graphene on GaAs substrates for optoelectronic applications.

    PubMed

    Babichev, A V; Gasumyants, V E; Egorov, A Yu; Vitusevich, S; Tchernycheva, M

    2014-08-22

    The optimization of contacts between graphene and metals is important for many optoelectronic applications. In this work, we evaluate the contact resistance and sheet resistance of monolayer and few-layered graphene with different metallizations using the transfer length method (TLM). Graphene was obtained by the chemical vapor deposition technique (CVD-graphene) and transferred onto GaAs and Si/SiO₂ substrates. To account for the quality of large-area contacts used in a number of practical applications, a millimeter-wide TLM pattern was used for transport measurements. Different metals--namely, Ag, Pt, Cr, Au, Ni, and Ti--have been tested. The minimal contact resistance Rc obtained in this work is 11.3 kΩ μm for monolayer CVD-graphene, and 6.3 kΩ μm for a few-layered graphene. Annealing allows us to decrease the contact resistance Rc and achieve 1.7 kΩm μm for few-layered graphene on GaAs substrate with Au contacts. The minimal sheet resistance Rsh of few-layered graphene transferred to GaAs and Si/SiO₂ substrates are 0.28 kΩ/□ and 0.27 kΩ/□. The Rsh value of monolayer graphene on the GaAs substrate is 8 times higher (2.3 kΩ/□), but it reduces for the monolayer graphene on Si/SiO₂ (1.4 kΩ/□). For distances between the contacts below 5 μm, a considerable reduction in the resistance per unit length was observed, which is explained by the changes in doping level caused by graphene suspension at small distances between contact pads.

  8. Zn diffusion in Al/0.7/Ga/0.3/As compared with that in GaAs. [solar cells

    NASA Technical Reports Server (NTRS)

    Flat, A.; Milnes, A. G.; Feucht, D. L.

    1977-01-01

    Zinc was diffused into 4 times 10 to the 17th per cu cm n-type Al(0.7)Ga(0.3)As grown by liquid-phase epitaxy and also into n-type 2 times 10 to the 17th per cu cm doped GaAs slices at 600, 650, and 750 C. The Zn diffusion coefficient in the Al(0.7)Ga(0.3)As was about one order of magnitude larger than in GaAs. The significance of this fact is that diffusion of Zn through a 0.5 micron Al(0.7)Ga(0.3)As layer appears to be possible with adequate control of the junction depth in the underlying GaAs.

  9. 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.

  10. 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.

  11. Laser doping and metallization of wide bandgap materials: silicon carbide, gallium nitride, and aluminum nitride

    NASA Astrophysics Data System (ADS)

    Salama, Islam Abdel Haleem

    A laser direct write and doping (LDWD) system is designed and utilized for direct metallization and selective area doping in different SiC polytypes, GaN and in dielectrics including AlN. Laser direct metallization in 4H- and 6H-SiC generates metal-like conductive phases that are produced as both rectifying and ohmic contacts without metal deposition. Nd:YAG (lambda = 532, 1064 nm) nanosecond pulsed laser irradiation in SiC induces carbon-rich conductive phases by thermal decomposition of SiC while UV excimer (lambda = 193 nm) laser irradiation produces a silicon-rich phase due to selective carbon photoablation. Linear transmission line method (TLM) pattern is directly fabricated in single crystals SiC by pulsed laser irradiation allowing characterization of the laser fabricated metal-like contacts. Activation of a self focusing effect at the frequency doubled Nd:YAG laser irradiation (lambda = 532 nm) allows to fabricate buried metal like contacts in SiC wafers while maintaining their device-ready surface condition. Gas immersion laser doping (GILD) and laser doping from a molten precursor are utilized to dope both GaN and SiC. Trimethylaluminum (TMAl) and nitrogen are the precursors used to produce p-type and n-type doped SiC; respectively. Nd:YAG and excimer laser nitrogen doping in SiC epilayer and single crystal substrates increases the dopant concentration by two orders of magnitude and produces both deep (500--600 nm) and shallow (50 nm) junctions, respectively. Laser assisted effusion/diffusion is introduced and utilized to dope Al in SiC wafers. Using this technique, a150 nm p-type doped junction is fabricated in semi-insulating 6H- and n-type doped 4H-SiC wafers. Laser-induced p-type doping of Mg in single crystal GaN is conducted using Bis-magnesium dihydrate [Mg(TMHD)2]. Mg concentration and penetration depth up to 10 20--1021 cm-3 and 5mum, respectively are achieved using various laser doping techniques. Laser direct writing and doping (LDWD) is a

  12. Te incorporation in GaAs1-xSbx nanowires and p-i-n axial structure

    NASA Astrophysics Data System (ADS)

    Ahmad, Estiak; Kasanaboina, P. K.; Karim, M. R.; Sharma, M.; Reynolds, C. L.; Liu, Y.; Iyer, S.

    2016-12-01

    We report on in situ Te-doping in GaAs1-xSbx nanowires (NWs) grown via self-assisted molecular beam epitaxy. Enhanced Te incorporation in the NW at higher Te cell temperature was attested by the broadening of the x-ray diffraction peak and the presence of a strong coupled-LO phonon mode in the Raman spectra. Te-doping was estimated from the shift in the coupled-LO phonon mode to be ˜2.0 × 1018/cm3. The surfactant nature of the Te modulated the growth kinetics, which was manifested in an enhanced radial growth rate with improved photoluminescence (PL) characteristics at both room temperature (RT) and 4 K. No noticeable planar defects were observed as ascertained from the high-resolution transmission electron microscopy images and selected-area electron diffraction patterns. Finally, we demonstrate the experimental realization of a GaAs1-xSbx axial p-type/intrinsic/n-type (p-i-n) structure on a Si substrate with Te as the n-type dopant. The GaAs1-xSbx p-i-n NW structures exhibited rectifying current-voltage (I-V) behavior. The dopant concentration and the transport parameters estimated from the PL spectra and I-V curve were found to be in good agreement.

  13. Growth of GaAs in a rotating disk MOCVD reactor

    NASA Astrophysics Data System (ADS)

    Thompson, A. G.; Sundaram, V. S.; Girard, G. R.; Fraas, L. M.

    1989-04-01

    We report the growth of GaAs homoepitaxial films from trimethylgallium and arsine in a multi-wafer rotating disk reactor. In this configuration the substrates are mounted on a disk that is spun at high speed (> 1000 rpm) in a sub-atmospheric (<100 Torr) environment. The spinning disk pumps the reactant and carrier gases radially outwards; under optimum conditions, convective recirculating cells are avoided, thus facilitating rapid transitions in doping and composition in the grown layers. In this paper we look at the morphology, growth rate and electrical properties of the GaAs epitaxial layers as a function of substrate temperature, V/III ratio, dopant type, spin speed and hydrogen carrier flow conditions. These results are compared with those obtained in conventional MOCVD reactors. Silicon and tellurium doping over a wide range of carrier concentrations has been achieved with excellent mobilities and uniformity across the wafers. Preliminary results on MESFET's fabricated from n +/n/buffer structures show good device characteristics.

  14. 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.

  15. 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).

  16. Experimental and theoretical study of passively Q-switched Yb:YAG laser with GaAs saturable absorber near 1050 nm

    NASA Astrophysics Data System (ADS)

    Chu, Hongwei; Zhao, Shengzhi; Yang, Kejian; Li, Yuefei; Li, Dechun; Li, Guiqiu; Zhao, Jia; Qiao, Wenchao; Xu, Xiaodong; Di, Juqing; Zheng, Lihe; Xu, Jun

    2014-03-01

    A diode-end-pumped passively Q-switched ytterbium-doped yttrium aluminum garnet (Yb:YAG) laser with gallium arsenide (GaAs) wafer as saturable absorber has been realized. In the experiment, two pieces of GaAs wafers with respective thicknesses of 400 and 700 μm were used respectively. The output laser characteristics such as the pulse duration, single pulse energy and peak power, have been measured. By using thicker GaAs wafer as saturable absorber, a minimum pulse duration of 3.5 ns was obtained with an average output power of 361 mW and a pulse repetition rate (PRR) of 25 kHz, corresponding to a single pulse energy of 19.6 μJ and a peak power of 5.7 kW. With a 400 μm-thick GaAs wafer as saturable absorber, a maximum output power of 469 mW was achieved. The central wavelength of the laser was measured to be 1050.4 nm at pump power of 7.8 W and dual wavelength operation peaked at 1049.3 nm and 1051.6 nm was observed at a high pump power of 10 W. By considering Gaussian spatial distribution and the thermal effects in the gain medium, the coupled rate equations for passively Q-switched Yb:YAG laser with GaAs saturable absorber were given.

  17. 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.

  18. 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.

  19. 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.

  20. Rapid thermal annealing of Be, Si, and Zn implanted GaAs using an ultrahigh power argon arc lamp

    NASA Astrophysics Data System (ADS)

    Tabatabaie-Alavi, K.; Masum Choudhury, A. N. M.; Fonstad, C. G.; Gelpey, J. C.

    1983-09-01

    The use of a 100-kW water-walled dc argon lamp to anneal ion-implanted GaAs is reported. Annealing cycles of 3 and 10 s and peak temperatures from 950 to 1200 C have been used to anneal Be, Si, and Zn implanted following representative implant schedules of technological importance. It is demonstrated that this technique is superior to conventional furnace anneal techniques in terms of the doping profiles, peak carrier concentrations, activation efficiencies (particularly at high doses), and mobilities achieved. The annealing technique should be applicable to large volume GaAs integrated circuit production and 100-mm-diam wafers can be annealed in a single exposure with better than 2 percent temperature uniformity (Si data).

  1. High-Temperature In situ Deformation of GaAs Micro-pillars: Lithography Versus FIB Machining

    NASA Astrophysics Data System (ADS)

    Chen, M.; Wehrs, J.; Michler, J.; Wheeler, J. M.

    2016-11-01

    The plasticity of silicon-doped GaAs was investigated between 25°C and 400°C using microcompression to prevent premature failure by cracking. Micropillars with diameters of 2.5 μm were fabricated on a < 100rangle -oriented GaAs single crystal by means of both conventional lithographic etching techniques and focused ion beam machining and then compressed in situ in the scanning electron microscope (SEM). A transition in deformation mechanisms from partial dislocations to perfect dislocations was found at around 100°C. At lower temperatures, the residual surface layer from lithographic processing was found to provide sufficient constraint to prevent crack opening, which resulted in a significant increase in ductility over FIB-machined pillars. Measured apparent activation energies were found to be significantly lower than previous bulk measurements, which is mostly attributed to the silicon dopant and to a lesser extent to the size effect.

  2. Excitons Bound to Nitrogen Pairs in GaAs as Seen by Photoluminescence of High Spectral and Spatial Resolution

    SciTech Connect

    Karaiskaj, D.; Mascarenhas, A.; Klem, J. F.; Volz, K.; Stolz, W.; Adamcyk, M.; Tiedje, T.

    2007-01-01

    High resolution photoluminescence (PL) spectroscopy was performed on high quality bulk GaAs, lightly doped with the nitrogen isoelectronic impurity. The shallowest nitrogen pair bound exciton center labeled as X{sub 1} revealed a total of six transitions. The photoluminescence lines from a small ensemble of nitrogen centers showed polarization dependent intensity. High spectral resolution PL spectroscopy was combined with confocal spectroscopy experiments performed on a GaAs:N/AlGaAs heterostructure. The high spatial resolution achieved by this technique enables us to localize and examine individual nitrogen bound excitons. Similar spectral structure and polarization dependence was observed for individual N-pair centers in GaAs. Both techniques support the C{sub 2v} symmetry of such isoelectronic impurity centers. The comparison between the PL spectra from an ensemble of nitrogen pairs and individual centers demonstrate the ability of the single impurity technique to lift the orientational degeneracy.

  3. 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.

  4. GaAs FET microwave oscillators

    NASA Astrophysics Data System (ADS)

    Sautereau, J.-F.

    Techniques for establishing the temporal stability of functioning of GaAs FETs are presented, along with a theory of negative resistance oscillators and an analysis of noise in GaAs FETs. Conditions of stable oscillation are discussed, as are techniques for designing solid state devices. An analog microwave circuit is described and is characterized in terms of inherent nonlinearities, which allows precise determination of the period, power, and harmonic distortion for the output signal. A coefficient is defined for expressing low frequency noise in microwave terms and methods for minimizing oscillator noise are presented, based on results from experimentation in X-band and low frequency devices. A computer model is developed which includes allowances for constantly repartitioned circuitry looping impedances. The model is concluded to be useful for the design of integrated monolithic microwave circuits.

  5. LSI/VLSI Ion Implanted GaAs IC Processing

    DTIC Science & Technology

    1982-02-10

    insulating High Speed Logic Ion Implantation GaAs IC FET Integrated Circuits MESFET 20. ABSTRACT (Coalki. on.. roersie if oookay and IdoeI by WOOe tw**, This...The goal of this program is to realize the full potential of GaAs digital integrated circuits employing depletion mode MESFETs by developing the...Processing. The main objective of this program is to realize the full potential of GaAs digital integrated circuits by expanding and improving

  6. 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.

  7. Fabrication and properties of Sb-doped ZnO thin films grown by radio frequency (RF) magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Chen, Nuofu; Yin, Zhigang; Yang, Fei; Peng, Changtao

    2006-04-01

    Sb-doped and undoped ZnO thin films were deposited on Si (1 0 0) substrates by radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that all the films had polycrystalline wurtzite structure and c-axis preferred orientation. Room temperature Hall measurements showed that the as-grown films were n-type and conducting ( ρ˜1-10 Ω cm). Annealing in a nitrogen ambient at 400 °C for 1 h made both samples highly resistive ( ρ>10 3 Ω cm). Increasing the annealing temperature up to 800 °C, the resistivity of the undoped ZnO film decreased gradually, but it increased for the Sb-doped ZnO film. In the end, the Sb-doped ZnO film annealed at 800 °C became semi-insulating with a resistivity of 10 4 Ω cm. In addition, the effects of annealing treatment and Sb-doping on the structural and electrical properties are discussed.

  8. An Electron-Beam Controlled Semiconductor Switch

    DTIC Science & Technology

    1989-11-01

    Lakdawala, Old Dominion University. The behavior of semi- insulating GaAs is investigated in the Pulsed mode under strong electric fields. In particular...published yet. 3 I (8)I I 6. Measurements of the current-voltage characteristics of semi- insulating GaAs were per- formed with the purpose of...MD, May 1989 [9] David C. Stoudt, K.H. Schoenbach and V.K. Lakdawala, "THE ELECTRICAL CHARACTERISTICS OF SEMI- INSULATING Gais FOR HIGH POWER

  9. New Passivation Methods for GaAs

    DTIC Science & Technology

    1975-01-01

    a shutter for a short ........ t .. Tl() to cover all freely exposed elements present in the chamber with an Aluminium film which will avoid oxidation...formation of an insulating layer by suitable means on the free surface to prevent carrier injection from outside and to improve the overall dielectric...conducting layers in the coses of both GaAs and GaAQ2,s. In order to prevent mixingj up cf 5lifferent dopants, a thorough cleaning procedure was appliecd

  10. Passivation of GaAs Surfaces.

    DTIC Science & Technology

    1980-08-15

    hour at indicated temperatures. Each symbol indicates one of four pieces of the same starting crystal . Three of the pieces were treated four times. The...Each symbol indicates one of four pieces of the same starting crystal . Three of the pieces were treated three times ................................ 9... crystal 11 11. Luminescence intensity of GaAs treated in ammonia plasma at 575*C as a function of treatment time. Each symbol represents one of five

  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. Characteristic measurement for femtosecond laser pulses using a GaAs PIN photodiode as a two-photon photovoltaic receiver

    NASA Astrophysics Data System (ADS)

    Chen, Junbao; Xia, Wei; Wang, Ming

    2017-06-01

    Photodiodes that exhibit a two-photon absorption effect within the spectral communication band region can be useful for building an ultra-compact autocorrelator for the characteristic inspection of optical pulses. In this work, we develop an autocorrelator for measuring the temporal profile of pulses at 1550 nm from an erbium-doped fiber laser based on the two-photon photovoltaic (TPP) effect in a GaAs PIN photodiode. The temporal envelope of the autocorrelation function contains two symmetrical temporal side lobes due to the third order dispersion of the laser pulses. Moreover, the joint time-frequency distribution of the dispersive pulses and the dissimilar two-photon response spectrum of GaAs and Si result in different delays for the appearance of the temporal side lobes. Compared with Si, GaAs displays a greater sensitivity for pulse shape reconstruction at 1550 nm, benefiting from the higher signal-to-noise ratio of the side lobes and the more centralized waveform of the autocorrelation trace. We also measure the pulse width using the GaAs PIN photodiode, and the resolution of the measured full width at half maximum of the TPP autocorrelation trace is 0.89 fs, which is consistent with a conventional second-harmonic generation crystal autocorrelator. The GaAs PIN photodiode is shown to be highly suitable for real-time second-order autocorrelation measurements of femtosecond optical pulses. It is used both for the generation and detection of the autocorrelation signal, allowing the construction of a compact and inexpensive intensity autocorrelator.

  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. Carbon doping of III-V compound semiconductors

    SciTech Connect

    Moll, Amy Jo

    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 > 1014/cm2. 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.

  16. 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.

  17. Effect of defects due to lattice mismatch between GaAs and InP materials on gate-leakage current and microwave noise of GaAs MESFETS on InP substrates

    NASA Astrophysics Data System (ADS)

    Chertouk, Mourad; Boudiaf, A.; Azoulay, Rozette; Clei, A.

    1993-11-01

    The effect of traps due to lattice mismatch between GaAs and InP materials on the reverse current of Schottky diodes is demonstrated by the temperature dependence of the current, which exhibits a S.R.H. component at low reverse bias (also present in GaAs/GaAs with activation energy 0.125 eV) and a trap assisted tunneling one at high reverse bias (not observed in GaAs/GaAs). A model is developed which takes into account the temperature and channel doping level dependence. Application of this model to 0.25 micrometers gate GaAs MESFETs gives a good agreement with gate leakage current behavior as a function of drain and gate bias, for 6 X 1017 cm-3 and 1018 cm-3 channel doping. The excess gate-drain assisted tunneling current in 1018 cm-3 doped channel does not affect the MESFETs dc and microwave performances. However, the microwave noise (Fmin) is increased.

  18. Ruthenium related deep-level defects in n-type GaAs

    NASA Astrophysics Data System (ADS)

    Naz, Nazir A.; Qurashi, Umar S.; Majid, A.; Zafar Iqbal, M.

    2009-12-01

    Deep-level transient spectroscopy (DLTS) has been used to investigate deep levels in n-type Ru-doped GaAs grown by low-pressure metal-organic chemical-vapor deposition (LP-MOCVD). DLTS scans over a wide temperature range (12-470 K) reveal two prominent deep-level peaks associated with Ru, when compared with control samples with no deliberate Ru-doping. The well-known mid-gap defect EL2 is also observed in these scans. The Ru-related deep levels, Ru1 and Ru2, correspond to energy positions Ec-0.46 eV and Ec-0.57 eV in the upper-half-bandgap of GaAs. No prominent deep levels associated with Ru are observed in the lower half-bandgap in the injection DLTS spectra; only the three inadvertent levels already present in the as-grown, control material are observed in these spectra. Although a possible Ru-related peak may be present with a rather small concentration in these injection DLTS spectra, it is difficult to clearly identify this peak also present in the control (as-grown, without Ru) samples at a closely similar position. Interestingly, doping with Ru reveals an interesting significant suppression of the pre-existing deep levels, including EL2. Detailed emission rate signatures are presented for the Ru-related deep levels and analyzed to obtain the relevant deep-level characteristics. Both Ru1 and Ru2 are found to show strong dependence on electric field, as demonstrated by the shift in the corresponding DLTS peak positions with the applied reverse bias during electron emission.

  19. Study of silicon incorporation from SiH 4 in GaAs layers grown by metalorganic vapor phase epitaxy using tertiarybutylarsine

    NASA Astrophysics Data System (ADS)

    Redwing, J. M.; Simka, H.; Jensen, K. F.; Kuech, T. F.

    1994-12-01

    The incorporation of silicon from SiH 4 into GaAs grown using tertiarybutylarsine (t-C 4H 9AsH 2 or TBAs) as the group V source has been investigated. The dependence of silicon incorporation on growth conditions was used to evaluate the role of gas phase and surface chemistry in the doping process. The use of TBAs results in a greater SiH 4 doping efficiency and weaker dependence on growth temperature than is typically observed with AsH 3. The doping is insensitive to gas residence time with AsH 3 and TBAs, indicating that the process is limited by heterogeneous chemistry in both cases. AsH 3 addition to layers grown at a constant TBAs/TMGa ratio results in a rapid decrease in Si incorporation. A surface kinetic-limited process is proposed to describe this behaviour. The influence of TBAs on SiH 4 doping chemistry was also found to improve the doping uniformity of GaAs films grown in our metalorganic vapor phase epitaxy (MOVPE) reactor.

  20. Effects of substrates on Raman spectroscopy in chemical vapor deposition grown graphene transferred with poly (methyl methacrylate)

    NASA Astrophysics Data System (ADS)

    Gui, Yangyang; Sun, Hengchao; Yan, Hui; Wang, Hao; Zhang, Yongzhe; Song, Xue Mei; Jia, Rui

    2017-09-01

    Graphene on copper foil produced through chemical vapor deposition has been transferred to different substrates and the Raman signatures from graphene on semi-insulating GaAs, n-GaAs, SiO2 (300 nm)/Si, boron-doped Si, phosphorus-doped Si have been studied. It is found that all the material varieties, morphology and lattice of substrates can influence the Raman scattering spectra from graphene. The obtained results are important for nanometrology of graphene and graphene based devices.

  1. Gallium Arsenide Field Effect Transistors with Semi-Insulated Gates.

    DTIC Science & Technology

    1977-09-01

    Zo \\ ‘ \\ I t LA 4’ N — 0N N N N (‘-1 — — (w9p) pappy -J~MOd 56 - . - LI -V_~~~~~~ - -~~~~~~~~~~~~ - V- —- VV ~~ V~~~~~ -V -~~~~ - - - - - - - V

  2. 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.

  3. GaAs IMPATT diodes for microstrip circuit applications.

    NASA Technical Reports Server (NTRS)

    Wisseman, W. R.; Tserng, H. Q.; Shaw, D. W.; Mcquiddy, D. N.

    1972-01-01

    GaAs IMPATT diodes with plated heat sinks are shown to be particularly well suited for microstrip circuit applications. Details of materials growth and device fabrication procedures are given, and experimental results are presented for a GaAs IMPATT microstrip oscillator operating at X band.

  4. GaAs IMPATT diodes for microstrip circuit applications.

    NASA Technical Reports Server (NTRS)

    Wisseman, W. R.; Tserng, H. Q.; Shaw, D. W.; Mcquiddy, D. N.

    1972-01-01

    GaAs IMPATT diodes with plated heat sinks are shown to be particularly well suited for microstrip circuit applications. Details of materials growth and device fabrication procedures are given, and experimental results are presented for a GaAs IMPATT microstrip oscillator operating at X band.

  5. 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.

  6. 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.

  7. 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.

  8. Peeled film GaAs solar cell development

    NASA Astrophysics Data System (ADS)

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

    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.

  9. 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.

  10. 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.

  11. The capability comparison of high-performance GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Wang, Hui; Chang, Benkang; Zou, Jijun; Li, Ming; Du, Xiaoqing; Yang, Zhi

    2006-09-01

    High-performance reflection-mode GaAs photocathode (named cathode 1 for short) with the integral sensitivity of 2140μA/lm is prepared by adopting "high-low temperature" two-step activation and using heavily p-type Be-doped GaAs materials, which is grown by molecular beam epitaxy (MBE) technique. Moreover, spectral response characteristic and cathodes performance parameters of two cathodes are obtained by spectral response database we compiled, one is the reflection-mode photocathode (named cathode 2 for short) with the integral sensitivity of 1800μA/lm reported by G. H. Olsen in the 70s; the other is the transmission-mode photocathode (named cathode 3 for short) with the integral sensitivity 3070μA/lm reported by O. H. W. Siegmund in 2003. A transmission-mode cathode (named cathode 4 for short) is acquired by computer simulation on the basis of cathode 1, and its integral sensitivity is 1907μA/lm, then we compare the reflection-mode cathodes (cathode 1 and cathode 2) and the transmission-mode cathodes (cathode 3 and cathode 4), respectively, and analyze the cause for performance difference among these cathodes, the results show that the surface escape probability of cathode 1 reach to 0.62, which is lower slightly that of cathode 2, so preparation technique of cathode 1 has gotten higher the surface escape probability, but the electron diffusion length of cathode 1 and the back interface recombination velocity of cathode 4 is not better compared to cathode 2 or cathode 3. Which shows preparation technique of cathode 1 obtains better surface barrier, it need to be optimized all the same for achieving higher performance GaAs photocathodes.

  12. 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.

  13. 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.

  14. 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.

  15. Hole-Impeded-Doping-Superlattice LWIR Detectors

    NASA Technical Reports Server (NTRS)

    Maserjian, Joseph

    1991-01-01

    Hole-Impeded-Doping-Superlattice (HIDS) InAs devices proposed for use as photoconductive or photovoltaic detectors of radiation in long-wavelength infrared (LWIR) range of 8 to 17 micrometers. Array of HIDS devices fabricated on substrates GaAs or Si. Radiation incident on black surface, metal contacts for picture elements serve as reactors, effectively doubling optical path and thereby increasing absorption of photons. Photoconductive detector offers advantages of high gain and high impedance; photovoltaic detector offers lower noise and better interface to multiplexer readouts.

  16. Hole-Impeded-Doping-Superlattice LWIR Detectors

    NASA Technical Reports Server (NTRS)

    Maserjian, Joseph

    1991-01-01

    Hole-Impeded-Doping-Superlattice (HIDS) InAs devices proposed for use as photoconductive or photovoltaic detectors of radiation in long-wavelength infrared (LWIR) range of 8 to 17 micrometers. Array of HIDS devices fabricated on substrates GaAs or Si. Radiation incident on black surface, metal contacts for picture elements serve as reactors, effectively doubling optical path and thereby increasing absorption of photons. Photoconductive detector offers advantages of high gain and high impedance; photovoltaic detector offers lower noise and better interface to multiplexer readouts.

  17. Effects of surface reconstruction on the epitaxial growth of III-Sb on GaAs using interfacial misfit array

    NASA Astrophysics Data System (ADS)

    Jia, Bo Wen; Tan, Kian Hua; Loke, Wan Khai; Wicaksono, Satrio; Yoon, Soon Fatt

    2017-03-01

    The effects of pre-growth Sb reconstruction on a GaAs surface on the epitaxial growth of III-Sb (GaSb and InSb) on a (100) GaAs substrate using interfacial misfit array were investigated. All samples exhibited smooth surface with a root mean square (r.m.s.) roughness below 1.5 nm and nearly 100% relaxation. Modeling indicated that the distribution and types of misfit dislocations can be evaluated using a reciprocal space map (RSM) of the x-ray measurements. The interfacial misfit (IMF) arrays in III-Sb/GaAs samples were characterized by RSMs of high-resolution x-ray diffraction (XRD) and transmission electron microscopy (TEM). The RSM results suggest that all samples exhibited highly uniformly distributed misfit dislocations, and pre-growth (2 × 8) Sb surface reconstruction promoted the formation of 90° dislocations in an IMF array. Hall measurements of unintentionally doped GaSb and InSb layers also suggested that the highest motilities at both 77 K and 300 K were achieved at the samples grown on GaAs with pre-growth (2 × 8) Sb reconstruction.

  18. Impurity incorporation in orientation patterned GaAs grown by low pressure HVPE

    NASA Astrophysics Data System (ADS)

    Snure, M.; Jiménez, J.; Hortelano, V.; Swider, S.; Mann, M.; Tassev, V.; Lynch, C.; Bliss, D.

    2012-08-01

    Orientation-patterned GaAs (OP-GaAs) has shown promise as an efficient frequency-shifted laser source over the range of 2-12 μm. In order to make OP-GaAs a viable source, efficiency and output power must be significantly increased, which requires minimizing major sources of loss. Low pressure HVPE has been adopted as the most suitable technique for regrowth of thick high quality GaAs layers on OP templates. We have explored process parameters in bulk and OP material to identify and control the sources of point defects, a key contributor to optical losses. Growth on OP templates with periodic [001] and [00-1] domains results in domain specific surface orientation, which should have inhomogeneous defect incorporation. Hall measurements, SIMS depth profiling, and cathodoluminescence (CL) were used to identify point defects in bulk and OP-GaAs. It was found that Si impurities are the primary source of donors, while VGa were identified as the primary source of acceptors. In order to study the incorporation of impurities in OP-GaAs samples, we intentionally doped samples with Si to increase CL and SIMS detectability. Spatially resolved CL and SIMS revealed regions with significant differences in the defect concentration, which can affect device output.

  19. 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.

  20. 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.