In-situ ellipsometric studies of optical and surface properties of GaAs(100) at elevated temperatures

NASA Technical Reports Server (NTRS)

Yao, Huade; Snyder, Paul G.

1991-01-01

A rotating-polarizer ellipsometer was attached to an ultrahigh vacuum (UHV) chamber. A GaAs(100) sample was introduced into the UHV chamber and heated at anumber of fixed elevated temperatures, without arsenic overpressure. In-situ spectroscopic ellipsometric (SE) measurements were taken, through a pair of low-strain quartz windows, to monitor the surface changes and measure the pseudodielectric functions at elevated temperatures. Real-time data from GaAs surface covered with native oxide showed clearly the evolution of oxide desorption at approximately 580 C. In addition, surface degradation was found before and after the oxide desorption. An oxide free and smooth GaAs surface was obtained by depositing an arsenic protective coating onto a molecular beam epitaxy grown GaAs surface. The arsenic coating was evaporated immediately prior to SE measurements. A comparison showed that our room temperature data from this GaAs surface, measured in the UHV, are in good agreement with those in the literature obtained by wet-chemical etching. The surface also remained clean and smooth at higher temperatures, so that reliable temperature-dependent dielectric functions were obtained.

Surface science analysis of GaAs photocathodes following sustained electron beam delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

2012-06-01

Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes,more » which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.« less

Atomic-scale luminescence measurement and theoretical analysis unveiling electron energy dissipation at a p-type GaAs(110) surface.

PubMed

Imada, Hiroshi; Miwa, Kuniyuki; Jung, Jaehoon; Shimizu, Tomoko K; Yamamoto, Naoki; Kim, Yousoo

2015-09-11

Luminescence of p-type GaAs was induced by electron injection from the tip of a scanning tunnelling microscope into a GaAs(110) surface. Atomically-resolved photon maps revealed a significant reduction in luminescence intensity at surface electronic states localized near Ga atoms. Theoretical analysis based on first principles calculations and a rate equation approach was performed to describe the perspective of electron energy dissipation at the surface. Our study reveals that non-radiative recombination through the surface states (SS) is a dominant process for the electron energy dissipation at the surface, which is suggestive of the fast scattering of injected electrons into the SS.

Heteroepitaxial growth of GaAs on (100) Ge/Si using migration enhanced epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanoto, H.; Loke, W. K.; Yoon, S. F.

In this paper, heteroepitaxial growth of GaAs on nominal (100) Ge/Si substrate was investigated. The root-mean square surface roughness of the sample where the first few monolayers of the GaAs were nucleated by migration enhanced epitaxy (MEE) is four times smaller compared to the sample without such a process, indicating better surface planarity. From the (004) x-ray diffraction rocking curve measurement, the full width at half maximum of the GaAs layer nucleated by MEE is 40% lower compared to that of the GaAs layer without such a process, indicating better crystal quality. Furthermore, it was found that the sample wheremore » the GaAs layer was nucleated by MEE experienced early relaxation. As the MEE process promotes two-dimensional growth, the GaAs layer where nucleation was initiated by such a process has fewer islandlike formations. This leads to a pseudomorphically grown GaAs layer, which experiences higher strain compared to the GaAs layer with more islandlike formations, where most relaxation occurs on the free surface of the islands. Therefore, for the same layer thickness, the GaAs layer on (100) Ge/Si substrate where nucleation was initiated by MEE relaxed first.« less

Optimization of conditions for thermal smoothing GaAs surfaces

NASA Astrophysics Data System (ADS)

Akhundov, I. O.; Kazantsev, D. M.; Kozhuhov, A. S.; Alperovich, V. L.

2018-03-01

GaAs thermal smoothing by annealing in conditions which are close to equilibrium between the surface and vapors of As and Ga was earlier proved to be effective for the step-terraced surface formation on epi-ready substrates with a small root-mean-square roughness (Rq ≤ 0.15 nm). In the present study, this technique is further developed in order to reduce the annealing duration and to smooth GaAs samples with a larger initial roughness. To this end, we proposed a two-stage anneal with the first high-temperature stage aimed at smoothing "coarse" relief features and the second stage focused on "fine" smoothing at a lower temperature. The optimal temperatures and durations of two-stage annealing are found by Monte Carlo simulations and adjusted after experimentation. It is proved that the temperature and duration of the first high-temperature stage are restricted by the surface roughening, which occurs due to deviations from equilibrium conditions.

Integration of GaAs vertical-cavity surface emitting laser on Si by substrate removal

NASA Astrophysics Data System (ADS)

Yeh, Hsi-Jen J.; Smith, John S.

1994-03-01

The successful integration of strained quantum well InGaAs vertical-cavity surface-emitting lasers (VCSELs) on both Si and Cu substrates was described using a GaAs substrate removal technique. The GaAs VCSEL structure was metallized and bonded to the Si substrate after growth. The GaAs substrate was then removed by selective chemical wet etching. Finally, the bonded GaAs film metallized on the top (emitting) side and separate lasers were defined. This is the first time a VCSEL had been integrated on a Si substrate with its substrate removed. The performance enhancement of GaAs VCSELs bonded on good thermal conductors are demonstrated.

Surface intervalley scattering on GaAs(110) studied with picosecond laser photoemission

NASA Astrophysics Data System (ADS)

Haight, R.; Silberman, J. A.

1990-01-01

Laser-based photoemission sources provide the unique opportunity to study dynamic electronic processes at surfaces and interfaces. Using angle-resolved, laser photoemission with < 1 ps time resolution, we have directly observed a new surface band at the X¯ point in the GaAs(110) surface Brillouin zone. The appearance of electron population in this valley occurs only as a result of scattering from the directly photoexcited valley at overlineГ. The momentum resolution of our experiment has permitted us to isolate the dynamic electron population changes at both overlineГ and X¯ and to deduce the scattering time between the two valleys.

Advanced GaAs Process Modeling. Volume 1

DTIC Science & Technology

1989-05-01

COSATI CODES 18 . SUBJECT TERMS (Continue on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP Gallium Arsenide, MESFET, Process...Background 9 3.2 Model Calculations 10 3.3 Conclusions 17 IV. ION-IMPLANTATION INTO GaAs PROFILE DETERMINATION 18 4.1 Ion Implantation Profile...Determination in GaAs 18 4.1.1. Background 18 4.1.2. Experimental Measurements 20 4.1.3. Results 22 4.1.3.1 Ion-Energy Dependence 22 4.1.3.2. Tilt and Rotation

Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

PubMed

Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

2012-07-01

Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

Structural Study of GaAs(001):In 4×2 Surface

NASA Astrophysics Data System (ADS)

Lee, T.-L.; Zegenhagen, J.; Lyman, P. F.; Bedzyk, M. J.

1997-03-01

In a STM and LEED investigation (U. Resch-Esser et al., JVST B 13, 1672 (1995)), the indium-terminated GaAs(001) surface exhibited a (4×2) reconstruction. Based on this study, a dimer model, similar to that proposed by Biegelsen et al. (PRB 41, 5701(1990)) for the (4×2) clean surface, was proposed. However, the detailed local structure of the In ad-atoms was not resolvable from the STM image. In this work, we applied in situ x-ray standing wave (XSW) measurements to determine the surface structure of the GaAs(001) upon the adsorption of In at low coverages. The (4×2)/c(8×2) In-terminated GaAs(001) surface (Θ_In = 0.2 ML) was prepared by MBE. The (004) XSW measurement showed that the In ad-atoms were located 1.61 Åabove the (004) diffraction planes. At higher In coverages (up to 0.6 ML) the In (004) coherent fraction was small. This is consistent with the ladder-type pattern observed by STM at Θ_In > 0.5 ML, which indicated that there were two coexisting surface structures. For Θ_In = 0.2 ML, we found that our off-normal XSW measurements did not agree with the model proposed by Resch-Esser et al.. This work is sponsored by DOE-BES No. W-31-109-ENG-38 and by NSF No. DMR-9632472.

Implementation and Performance of GaAs Digital Signal Processing ASICs

NASA Technical Reports Server (NTRS)

Whitaker, William D.; Buchanan, Jeffrey R.; Burke, Gary R.; Chow, Terrance W.; Graham, J. Scott; Kowalski, James E.; Lam, Barbara; Siavoshi, Fardad; Thompson, Matthew S.; Johnson, Robert A.

1993-01-01

The feasibility of performing high speed digital signal processing in GaAs gate array technology has been demonstrated with the successful implementation of a VLSI communications chip set for NASA's Deep Space Network. This paper describes the techniques developed to solve some of the technology and implementation problems associated with large scale integration of GaAs gate arrays.

Surface ordering of (In,Ga)As quantum dots controlled by GaAs substrate indexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zh.M.; Seydmohamadi, Sh.; Lee, J.H.

Self-organized surface ordering of (In,Ga)As quantum dots in a GaAs matrix was investigated using stacked multiple quantum dot layers prepared by molecular-beam epitaxy. While one-dimensional chain-like ordering is formed on singular and slightly misorientated GaAs(100) surfaces, we report on two-dimensional square-like ordering that appears on GaAs(n11)B, where n is 7, 5, 4, and 3. Using a technique to control surface diffusion, the different ordering patterns are found to result from the competition between anisotropic surface diffusion and anisotropic elastic matrix, a similar mechanism suggested before by Solomon [Appl. Phys. Lett. 84, 2073 (2004)].

Surface reconstruction of GaAs(001) nitrided under the controlled As partial pressure [rapid communication

NASA Astrophysics Data System (ADS)

Imayoshi, Takahiro; Oigawa, Haruhiro; Shigekawa, Hidemi; Tokumoto, Hiroshi

2003-08-01

Under the controlled As partial pressure, the nitridation process of GaAs(0 0 1)-(2 × 4) surface was studied using a scanning tunneling microscope (STM) combined with an electron cyclotron resonance plasma-assisted molecular beam epitaxy system. With either prolonging the nitridation time or decreasing the As partial pressure, the previously reported (3 × 3) structure with two dimers per surface cell ((3 × 3)-2D) was found to progressively convert into a new (3 × 3) structure characterized by one dimer per surface cell ((3 × 3)-1D). Reversely the exposure to arsenic transformed the structure from (3 × 3)-1D to (3 × 3)-2D, suggesting that the topmost layer is composed of As 2-dimers. Based on these STM images together with the X-ray photoelectron spectroscopy data, we propose the new As 2-dimer coverage models to explain both (3 × 3)-1D and -2D structures involving the exchange reaction of arsenic with nitrogen in the subsurface region of GaAs.

Surface segregation and the Al problem in GaAs quantum wells

NASA Astrophysics Data System (ADS)

Chung, Yoon Jang; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

2018-03-01

Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped AlxGa1 -xAs /GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the AlxGa1 -xAs barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the AlxGa1 -xAs barrier beneath the QW is increased, which we attribute to the surface segregation of oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking.

Velocity surface measurements for ZnO films over /001/-cut GaAs

NASA Technical Reports Server (NTRS)

Kim, Yoonkee; Hunt, William D.; Liu, Yongsheng; Jen, Cheng-Kuei

1994-01-01

A potential application for a piezoelectic film deposited on a GaAs substrate is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the filmed structure is critical for the optimum design of such devices. In this article, the measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metallized ZnO/SiO2 or Si3N4/GaAs /001/-cut samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. Comparisons, such as measurement accuracy and tradeoffs, between the former (dry) and the latter (wet) method are given. It is found that near the group of zone axes (110) propagation direction the autocollimating SAW property of the bare GaAs changes into a noncollimating one for the layered structure, but a reversed phenomenon exists near the group of zone axes (100) direction. The passivation layer of SiO2 or Si3N4 (less than 0.2 micrometer thick) and the metallization layer change the relative velocity but do not significantly affect the velocity surface. On the other hand, the passivation layer reduces the propagation loss by 0.5-1.3 dB/microseconds at 240 MHz depending upon the ZnO film thickness. Our SAW propagation measurements agree well with theorectical calculations. We have also obtained the anisotropy factors for samples with ZnO films of 1.6, 2.8, and 4.0 micrometer thickness. Comparisons concerning the piezoelectric coupling and acoustic loss between dc triode and rf magnetron sputtered ZnO films are provided.

Sulfur doping of GaAs with (NH4)2Sx solution

NASA Astrophysics Data System (ADS)

Lee, Jong-Lam

1999-01-01

A novel technique for sulfur doping to GaAs was demonstrated. The surface of GaAs was treated with (NH4)2Sx solution, subsequent to annealing using either furnace or rapid thermal processing. Sulfur atoms adsorbed at the surface of GaAs during the (NH4)2Sx treatment diffuse into GaAs during the annealing. The diffusion profiles of sulfur in both types of annealing treatments show a concave shape from the GaAs surface. Diffusion constants of sulfur determined using the Boltzmann-Matano technique increase with the decrease of sulfur concentration via the depth from the surface of GaAs. This suggests that immobile sulfur donor SAs+ forms at the near surface interacts with a Ga divacancy, and results in the production of mobile As interstitials, IAs. The IAs moves fast toward the inside of GaAs and kickout the SAs+ donor, producing a fast diffusing species of interstitial S atoms. The diffusion coefficients of sulfur determined are 2.5×10-14 cm2/s at 840 °C and 5×10-12 cm2/s at 900 °C. The sulfur doping technique is applied to the fabrication of metal-semiconductor field-effect transistors (MESFETs). The MESFETs with 1.0 μm gate length exhibit transconductance of 190 mS/mm, demonstrating the applicability of this technique to the formation of active channel layer of MESFETs.

Chemical beam epitaxy of GaAs1-xNx using MMHy and DMHy precursors, modeled by ab initio study of GaAs(100) surfaces stability over As2, H2 and N2

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2017-06-01

Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

Ab initio study of GaAs(100) surface stability over As2, H2 and N2 as a model for vapor-phase epitaxy of GaAs1-xNx

NASA Astrophysics Data System (ADS)

Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

2015-12-01

GaAs(100) c(4×4) surfaces were examined by ab initio calculations, under As2, H2 and N2 gas mixed conditions as a model for GaAs1-xNx vapor-phase epitaxy (VPE) on GaAs(100). Using a simple model consisting of As2 and H2 molecules adsorptions and As/N atom substitutions, it was shown to be possible to examine the crystal growth behavior considering the relative stability of the resulting surfaces against the chemical potential of As2, H2 and N2 gases. Such simple model allows us to draw a picture of the temperature and pressure stability domains for each surfaces that can be linked to specific growth conditions, directly. We found that, using this simple model, it is possible to explain the different N-incorporation regimes observed experimentally at different temperatures, and to predict the transition temperature between these regimes. Additionally, a rational explanation of N-incorporation ratio for each of these regimes is provided. Our model should then lead to a better comprehension and control of the experimental conditions needed to realize a high quality VPE of GaAs1-xNx.

Use of a corrugated surface to enhance radiation tolerance in a GaAs solar cell

NASA Technical Reports Server (NTRS)

Leon, Rosa P.; Piszczor, Michael F., Jr.

1985-01-01

The use of a corrugated surface on a GaAs solar cell and its effects on radiation resistance were studied. A compute code was developed to determine the performance of the cell for various geometric parameters. The large optical absorption coefficient of GaAs allows grooves to be only 4-5 micrometers deep. Using accepted material parameters for GaAs solar cells the theoretical performances were compared for various corrugated cells before and after minority carrier diffusion length degradation. The total power output was maximized for both n(+)/p and p(+)/n cells. Optimum values of 1.0-1.5 and 5.0 micrometers for groove and ridge widths respectively were determined.

Relevance of GaAs(001) surface electronic structure for high frequency dispersion on n-type accumulation capacitance

NASA Astrophysics Data System (ADS)

Pi, T. W.; Chen, W. S.; Lin, Y. H.; Cheng, Y. T.; Wei, G. J.; Lin, K. Y.; Cheng, C.-P.; Kwo, J.; Hong, M.

2017-01-01

This study investigates the origin of long-puzzled high frequency dispersion on the accumulation region of capacitance-voltage characteristics in an n-type GaAs-based metal-oxide-semiconductor. Probed adatoms with a high Pauling electronegativity, Ag and Au, unexpectedly donate charge to the contacted As/Ga atoms of as-grown α2 GaAs(001)-2 × 4 surfaces. The GaAs surface atoms behave as charge acceptors, and if not properly passivated, they would trap those electrons accumulated at the oxide and semiconductor interface under a positive bias. The exemplified core-level spectra of the Al2O3/n-GaAs(001)-2 × 4 and the Al2O3/n-GaAs(001)-4 × 6 interfaces exhibit remnant of pristine surface As emission, thereby causing high frequency dispersion in the accumulation region. For the p-type GaAs, electrons under a negatively biased condition are expelled from the interface, thereby avoiding becoming trapped.

Room temperature lasing of GaAs quantum wire vertical-cavity surface-emitting lasers grown on (7 7 5) B GaAs substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Higuchi, Y.; Osaki, S.; Kitada, T.; Shimomura, S.; Takasuka, Y.; Ogura, M.; Hiyamizu, S.

2006-06-01

Self-organized GaAs/(GaAs) 4(AlAs) 2 quantum wires (QWRs) grown on (7 7 5) B-oriented GaAs substrates by molecular beam epitaxy have been applied to an active region of vertical-cavity surface-emitting lasers (VCSELs). The (7 7 5) B GaAs QWR-VCSEL with an aperture diameter of 3 μm lased at a wavelength of 765 nm with a threshold current of 0.38 mA at room temperature. This is the first demonstration of laser operation of the QWR-VCSEL by current injection. The light output was linearly polarized in the direction parallel to the QWRs due to the optical anisotropy of the self-organized (7 7 5) B GaAs QWRs.

GaAs High Breakdown Voltage Front and Back Side Processed Schottky Detectors for X-Ray Detection

DTIC Science & Technology

2007-11-01

front and back side processed, unintentionally doped bulk gallium -arsenic (GaAs) Schottky detectors and determined that GaAs detectors with a large...a few materials that fulfill these requirements are gallium -arsenic (GaAs) and cadmium-zinc-tellurium (CdZnTe or CZT). They are viable alternative...Whitehill, C.; Pospíšil, S.; Wilhem, I.; Doležal, Z.; Juergensen, H.; Heuken, M. Development of low-pressure vapour -phase epitaxial GaAs for medical imaging

Design optimization of GaAs betavoltaic batteries

NASA Astrophysics Data System (ADS)

Chen, Haiyanag; Jiang, Lan; Chen, Xuyuan

2011-06-01

GaAs junctions are designed and fabricated for betavoltaic batteries. The design is optimized according to the characteristics of GaAs interface states and the diffusion length in the depletion region of GaAs carriers. Under an illumination of 10 mCi cm-2 63Ni, the open circuit voltage of the optimized batteries is about ~0.3 V. It is found that the GaAs interface states induce depletion layers on P-type GaAs surfaces. The depletion layer along the P+PN+ junction edge isolates the perimeter surface from the bulk junction, which tends to significantly reduce the battery dark current and leads to a high open circuit voltage. The short circuit current density of the optimized junction is about 28 nA cm-2, which indicates a carrier diffusion length of less than 1 µm. The overall results show that multi-layer P+PN+ junctions are the preferred structures for GaAs betavoltaic battery design.

Photoelectron and Auger electron diffraction studies of a sulfur-terminated GaAs(001)-(2×6) surface

NASA Astrophysics Data System (ADS)

Shimoda, M.; Tsukamoto, S.; Koguchi, N.

1998-01-01

Core-level X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) have been applied to investigate the sulfur-terminated GaAs(001)-(2×6) surface. No forward scattering peaks were found in the XPD pattern of S 2s emission, indicating that adsorbed S atoms form a single layer on the GaAs substrate. In accordance with the zincblende structure of GaAs, the AED patterns of Ga L 3M 45M 45 and As L 3M 45M 45 emission almost coincide with each other, if one of the emissions is rotated by 90° around the [001] direction. This fact suggests that the diffraction patterns mainly reflect the structure of the bulk GaAs crystal. In order to investigate the surface structure, AED patterns in large polar angles were analyzed with single scattering cluster (SSC) calculations. The best result was obtained with a model cluster where the S-S bond length was set at 0.28 nm, 30% shorter than the corresponding length of the ideal (1×1) structure, and the adsorption height was set at 0.12-0.13 nm, 10% shorter than the ideal interlayer distance of GaAs(001) planes. These values are in good agreement with the results of STM measurements. A modulation of the inter-dimer distance was also found, suggesting the existence of missing dimers.

Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

NASA Technical Reports Server (NTRS)

Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

1988-01-01

The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

Image processing using Gallium Arsenide (GaAs) technology

NASA Technical Reports Server (NTRS)

Miller, Warner H.

1989-01-01

The need to increase the information return from space-borne imaging systems has increased in the past decade. The use of multi-spectral data has resulted in the need for finer spatial resolution and greater spectral coverage. Onboard signal processing will be necessary in order to utilize the available Tracking and Data Relay Satellite System (TDRSS) communication channel at high efficiency. A generally recognized approach to the increased efficiency of channel usage is through data compression techniques. The compression technique implemented is a differential pulse code modulation (DPCM) scheme with a non-uniform quantizer. The need to advance the state-of-the-art of onboard processing was recognized and a GaAs integrated circuit technology was chosen. An Adaptive Programmable Processor (APP) chip set was developed which is based on an 8-bit slice general processor. The reason for choosing the compression technique for the Multi-spectral Linear Array (MLA) instrument is described. Also a description is given of the GaAs integrated circuit chip set which will demonstrate that data compression can be performed onboard in real time at data rate in the order of 500 Mb/s.

Surface reflectance anisotropy of indium-terminated GaAs(100) surfaces

NASA Astrophysics Data System (ADS)

Springer, C.; Resch-Esser, U.; Goletti, C.; Richter, W.; Fimland, B. O.

1997-04-01

The growth of thin indium-layers on the GaAs(100) As-rich {(2 × 4)}/{c(2 × 8) } surface has been investigated by reflectance anisotropy spectroscopy (RAS), LEED and AES. Clean surfaces of the {(2 × 4)}/{c(2 × 8) } reconstruction were prepared in UHV by thermal desorption of a protective arsenic layer deposited on homoepitaxially grown MBE layers. Room temperature deposition of indium on the {(2 × 4)}/{c(2 × 8) } surface and subsequent annealing at 450°C leads to a 90° rotation of symmetry in the LEED pattern at a threshold coverage of 0.5 monolayers, i.e. a change from the {(2 × 4)}/{c(2 × 8) } to the {(4 × 2)}/{c(8 × 2) } reconstruction. The RAS spectra show the evolution of a distinct negative feature at 1.8 eV, that shifts to 2.1 eV after annealing, corresponding to optical transitions attributed to In-dimers orientated along the [011]-direction. AES analysis shows a change in growth mode beyond 0.5 ML indicating saturation of all available adsorption sites at this coverage and RAS spectra show a contribution from additional disordered In. The AES spectra display no evidence of a surface exchange reaction between gallium and arsenic atoms, thus indicating a surface termination by In-dimers adsorbed on a layer of As.

Kinetics of (2 × 4) → (3 × 1(6)) structural changes on GaAs(001) surfaces during the UHV annealing

NASA Astrophysics Data System (ADS)

Vasev, A. V.; Putyato, M. A.; Preobrazhenskii, V. V.

2018-06-01

The peculiarities of superstructural transition (2 × 4) → (3 × 1(6)) on the GaAs(001) surface were studied by the RHEED method in the conditions initiated by a sharp change of the arsenic flux. The specular beam intensities RHEED picture dependences on time were obtained during the transition. The measurement results were analyzed within the JMAK (Johnson - Melh - Avrami - Kolmogorov) kinetic model. It was established that the process of structural rearrangement proceeds in two stages and it is realized through the state of intermediate disordering, domains with different reconstructions being coexistent on the surface. The activation energies and phase transition velocities were determined for each of the stages. The procedure for precise determination of GaAs(001) surface temperature using the features of the α(2 × 4) → DO transition process kinetic was proposed. The results of this work allow us to broaden our understanding of the reconstruction transitions mechanisms. This information has a key (fundamental and applied) nature for the technologies of epitaxial growth of multilayer heterostructures, where the interface planarity and the sharpness of composition profile are of particular importance.

ZnO Films on {001}-Cut <110>-Propagating GaAs Substrates for Surface Acoustic Wave Device Applications

NASA Technical Reports Server (NTRS)

Kim, Yoonkee; Hunt, William D.; Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei

1995-01-01

A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110> -propagating GaAs substrates are investigated in this article, including SAW Velocity effective piezoelectric coupling constant, propagation loss. diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films or different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(exp 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2, or Si3N4 on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

The influence of surfaces on the transient terahertz conductivity and electron mobility of GaAs nanowires

NASA Astrophysics Data System (ADS)

Joyce, Hannah J.; Baig, Sarwat A.; Parkinson, Patrick; Davies, Christopher L.; Boland, Jessica L.; Tan, H. Hoe; Jagadish, Chennupati; Herz, Laura M.; Johnston, Michael B.

2017-06-01

Bare unpassivated GaAs nanowires feature relatively high electron mobilities (400-2100 cm2 V-1 s-1) and ultrashort charge carrier lifetimes (1-5 ps) at room temperature. These two properties are highly desirable for high speed optoelectronic devices, including photoreceivers, modulators and switches operating at microwave and terahertz frequencies. When engineering these GaAs nanowire-based devices, it is important to have a quantitative understanding of how the charge carrier mobility and lifetime can be tuned. Here we use optical-pump-terahertz-probe spectroscopy to quantify how mobility and lifetime depend on the nanowire surfaces and on carrier density in unpassivated GaAs nanowires. We also present two alternative frameworks for the analysis of nanowire photoconductivity: one based on plasmon resonance and the other based on Maxwell-Garnett effective medium theory with the nanowires modelled as prolate ellipsoids. We find the electron mobility decreases significantly with decreasing nanowire diameter, as charge carriers experience increased scattering at nanowire surfaces. Reducing the diameter from 50 nm to 30 nm degrades the electron mobility by up to 47%. Photoconductivity dynamics were dominated by trapping at saturable states existing at the nanowire surface, and the trapping rate was highest for the nanowires of narrowest diameter. The maximum surface recombination velocity, which occurs in the limit of all traps being empty, was calculated as 1.3  ×  106 cm s-1. We note that when selecting the optimum nanowire diameter for an ultrafast device, there is a trade-off between achieving a short lifetime and a high carrier mobility. To achieve high speed GaAs nanowire devices featuring the highest charge carrier mobilities and shortest lifetimes, we recommend operating the devices at low charge carrier densities.

Surface intervalley scattering on GaAs(110): Direct observation with picosecond laser photoemission

NASA Astrophysics Data System (ADS)

Haight, R.; Silberman, J. A.

1989-02-01

Angle-resolved laser photoemission investigations of the laser excited GaAs(110) surface have revealed a previously unobserved valley of the C3 unoccupied surface band whose minimum is at X¯ in the surface Brillouin zone. Electron population in this valley increases only as a result of scattering from the directly photoexcited valley at Γ¯. With high momentum resolution, we have isolated the dynamic electron population changes at both Γ¯ and X¯ and deduced the scattering time between the two valleys.

Native oxides formation and surface wettability of epitaxial III-V materials: The case of InP and GaAs

NASA Astrophysics Data System (ADS)

Gocalinska, A.; Rubini, S.; Pelucchi, E.

2016-10-01

The time dependent transition from hydrophobic to hydrophilic states of the metalorganic vapour phase epitaxy (MOVPE) grown InP, GaAs and InAs is systematically documented by contact angle measurements. Natural oxides forming on the surfaces of air-exposed materials, as well as the results of some typical wet chemical process to remove those oxides, were studied by X-ray photoemission spectroscopy (XPS), revealing, surprisingly, a fundamental lack of strong correlations between the surface oxide composition and the reported systematic changes in hydrophobicity.

Nitridation of porous GaAs by an ECR ammonia plasma

NASA Astrophysics Data System (ADS)

Naddaf, M.; Hullavarad, S. S.; Ganesan, V.; Bhoraskar, S. V.

2006-02-01

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 °C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 °C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

Picosecond Dynamics Of The GaAs (110) Surface Studied With Laser Photoemission

NASA Astrophysics Data System (ADS)

Haight, R.; Silberman, J. A.; Lilie, M. I.

1988-08-01

A novel laser system and detection scheme is described which has been developed to investigate the transient dynamics of photoexcited electrons at material surfaces and interfaces with photoemission. The excited carrier population on the surface of GaAs (110) and the related Cr/GaAs (110) surface has been studied with 1-2 picosecond time resolution. Studies reveal a rapid rise and fall of the photexcited carrier population at the clean semiconductor surface within 15 picoseconds of excitation. For times greater than 15 picoseconds the carrier density decays slowly. Studies of the photoexcited surface after deposition of small numbers of Cr atoms reveal a remarkable decrease in the carrier density observed at the surface for a coverage as low as .006 monolayer.

Comparative research on activation technique for GaAs photocathodes

NASA Astrophysics Data System (ADS)

Chen, Liang; Qian, Yunsheng; Chang, Benkang; Chen, Xinlong; Yang, Rui

2012-03-01

The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs-O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

New Passivation Methods of GaAs.

DTIC Science & Technology

1980-01-01

Fabrication of Thin Nitride Layers on GaAs 33 - 35 CHAPTER 7 Passivation of InGaAsP 36 - 37 CHAPTER 8 Emulsions on GaAs Surfaces 38 - 42 APPENDIX...not yet given any useful results. The deposition of SiO2 by using emulsions is pursued and first results on the possibility of GaAs doping are...glycol-tartaric acid based aqueous solution was used in order to anodically oxidise the gate notch after the source and drain ohmic contacts were formed

Fabrication and characterization of the noble metal nanostructures on the GaAs surface

NASA Astrophysics Data System (ADS)

Gladskikh, Polina V.; Gladskikh, Igor A.; Toropov, Nikita A.; Vartanyan, Tigran A.

2016-04-01

Self-assembled silver, gold, and copper nanostructures on the monocrystalline GaAs (100) wafer surface were obtained via physical vapor deposition and characterized by optical reflection spectroscopy, scanning electron microscopy, and current-voltage curve measurements. Reflection spectra of the samples with Ag equivalent thicknesses of 2, 5, 7.5, and 10 nm demonstrated wide plasmonic bands in the visible range of spectra. Thermal annealing of the nanostructures led to narrowing of the plasmonic bands of Au and Ag nanostructures caused by major transformations of the film morphology. While the as prepared films predominantly had a small scale labyrinth structure, after annealing well-separated nanoislands are formed on the gallium arsenide surface. A clear correlation between films morphology and their optical and electrical properties is elucidated. Annealing of the GaAs substrate with Ag nanostructures at 100 °C under control of the resistivity allowed us to obtain and fix the structure at the percolation threshold. It is established that the samples at the percolation threshold possess the properties of resistance switching and hysteresis.

Structural and optical properties of GaAs(100) with a thin surface layer doped with chromium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Fedyukin, A. V.; Arsentyev, I. N.

The aim of this study is to explore the structural and optical properties of single-crystal GaAs(100) doped with Cr atoms by burning them into the substrate at high temperatures. The diffusion of chromium into single-crystal GaAs(100) substrates brings about the formation of a thin (~20–40 μm) GaAs:Cr transition layer. In this case, chromium atoms are incorporated into the gallium-arsenide crystal lattice and occupy the regular atomic sites of the metal sublattice. As the chromium diffusion time is increased, such behavior of the dopant impurity yields changes in the energy structure of GaAs, a decrease in the absorption at free chargemore » carriers, and a lowering of the surface recombination rate. As a result, the photoluminescence signal from the sample is significantly enhanced.« less

Heterojunction photovoltaics using GaAs nanowires and conjugated polymers.

PubMed

Ren, Shenqiang; Zhao, Ni; Crawford, Samuel C; Tambe, Michael; Bulović, Vladimir; Gradecak, Silvija

2011-02-09

We demonstrate an organic/inorganic solar cell architecture based on a blend of poly(3-hexylthiophene) (P3HT) and narrow bandgap GaAs nanowires. The measured increase of device photocurrent with increased nanowire loading is correlated with structural ordering within the active layer that enhances charge transport. Coating the GaAs nanowires with TiO(x) shells passivates nanowire surface states and further improves the photovoltaic performance. We find that the P3HT/nanowire cells yield power conversion efficiencies of 2.36% under white LED illumination for devices containing 50 wt % of TiO(x)-coated GaAs nanowires. Our results constitute important progress for the use of nanowires in large area solution processed hybrid photovoltaic cells and provide insight into the role of structural ordering in the device performance.

Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Wu, Y.

1988-01-01

A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

Atomic structure of the GaAs(001)-c(4x4) surface: first-principles evidence for diversity of heterodimer motifs.

PubMed

Penev, E; Kratzer, P; Scheffler, M

2004-10-01

The GaAs(001)-c(4x4) surface was studied using ab initio atomistic thermodynamics based on density-functional theory calculations. We demonstrate that in a range of stoichiometries, between those of the conventional three As-dimer and the new three Ga-As-dimer models, there exists a diversity of atomic structures featuring Ga-As heterodimers. These results fully explain the experimental scanning tunneling microscopy images and are likely to be relevant also to the c(4x4)-reconstructed (001) surfaces of other III-V semiconductors.

Photoluminescence intensity enhancement of GaAs by vapor-deposited GaS - A rational approach to surface passivation

NASA Technical Reports Server (NTRS)

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

1993-01-01

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster (/t-Bu/GaS)4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally-characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

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.

GaAs MOEMS Technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

SPAHN, OLGA B.; GROSSETETE, GRANT D.; CICH, MICHAEL J.

2003-03-01

Many MEMS-based components require optical monitoring techniques using optoelectronic devices for converting mechanical position information into useful electronic signals. While the constituent piece-parts of such hybrid opto-MEMS components can be separately optimized, the resulting component performance, size, ruggedness and cost are substantially compromised due to assembly and packaging limitations. GaAs MOEMS offers the possibility of monolithically integrating high-performance optoelectronics with simple mechanical structures built in very low-stress epitaxial layers with a resulting component performance determined only by GaAs microfabrication technology limitations. GaAs MOEMS implicitly integrates the capability for radiation-hardened optical communications into the MEMS sensor or actuator component, a vitalmore » step towards rugged integrated autonomous microsystems that sense, act, and communicate. This project establishes a new foundational technology that monolithically combines GaAs optoelectronics with simple mechanics. Critical process issues addressed include selectivity, electrochemical characteristics, and anisotropy of the release chemistry, and post-release drying and coating processes. Several types of devices incorporating this novel technology are demonstrated.« less

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.

ZnO films on /001/-cut (110)-propagating GaAs substrates for surface acoustic wave device applications

NASA Technical Reports Server (NTRS)

Hickernell, Frederick S.; Higgins, Robert J.; Jen, Cheng-Kuei; Kim, Yoonkee; Hunt, William D.

1995-01-01

A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

InGaAs quantum dots grown on B-type high index GaAs substrates: surface morphologies and optical properties

NASA Astrophysics Data System (ADS)

Liang, B. L.; Wang, Zh M.; Mazur, Yu I.; Strelchuck, V. V.; Holmes, K.; Lee, J. H.; Salamo, G. J.

2006-06-01

We systematically investigated the correlation between morphological and optical properties of InGaAs self-assembled quantum dots (QDs) grown by solid-source molecular beam epitaxy on GaAs (n 11)B (n = 9, 8, 7, 5, 3, 2) substrates. Remarkably, all InGaAs QDs on GaAs(n 11)B under investigation show optical properties superior to those for ones on GaAs(100) as regards the photoluminescence (PL) linewidth and intensity. The morphology for growth of InGaAs QDs on GaAs (n 11)B, where n = 9, 8, 7, 5, is observed to have a rounded shape with a higher degree of lateral ordering than that on GaAs(100). The optical property and the lateral ordering are best for QDs grown on a (511)B substrate surface, giving a strong correlation between lateral ordering and PL optical quality. Our results demonstrate the potential for high quality InGaAs QDs on GaAs(n 11)B for optoelectronic applications.

Characterization of reclaimed GaAs substrates and investigation of reuse for thin film InGaAlP LED epitaxial growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Englhard, M.; Klemp, C.; Behringer, M.

This study reports a method to reuse GaAs substrates with a batch process for thin film light emitting diode (TF-LED) production. The method is based on an epitaxial lift-off technique. With the developed reclaim process, it is possible to get an epi-ready GaAs surface without additional time-consuming and expensive grinding/polishing processes. The reclaim and regrowth process was investigated with a one layer epitaxial test structure. The GaAs surface was characterized by an atomic force microscope directly after the reclaim process. The crystal structure of the regrown In{sub 0.5}(Ga{sub 0.45}Al{sub 0.55}){sub 0.5}P (Q{sub 55}) layer was investigated by high resolution x-raymore » diffraction and scanning transmission electron microscopy. In addition, a complete TF-LED grown on reclaimed GaAs substrates was electro-optically characterized on wafer level. The crystal structure of the epitaxial layers and the performance of the TF-LED grown on reclaimed substrates are not influenced by the developed reclaim process. This process would result in reducing costs for LEDs and reducing much arsenic waste for the benefit of a green semiconductor production.« less

Photoluminescence and capacitance voltage characterization of GaAs surface passivated by an ultrathin GaN interface control layer

NASA Astrophysics Data System (ADS)

Anantathanasarn, Sanguan; Hasegawa, Hideki

2002-05-01

A novel surface passivation technique for GaAs using an ultrathin GaN interface control layer (GaN ICL) formed by surface nitridation was characterized by ultrahigh vacuum (UHV) photoluminescence (PL) and capacitance-voltage ( C- V) measurements. The PL quantum efficiency was dramatically enhanced after being passivated by the GaN ICL structure, reaching as high as 30 times of the initial clean GaAs surface. Further analysis of PL data was done by the PL surface state spectroscopy (PLS 3) simulation technique. PL and C- V results are in good agreement indicating that ultrathin GaN ICL reduces the gap states and unpins the Fermi level, realizing a wide movement of Fermi level within the midgap region and reduction of the effective surface recombination velocity by a factor of 1/60. GaN layer also introduced a large negative surface fixed charge of about 10 12 cm -2. A further improvement took place by depositing a Si 3N 4 layer on GaN ICL/GaAs structure.

Lateral epitaxial overgowth of GaAs by organometallic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Gale, R. P.; Mcclelland, R. W.; Fan, J. C. C.; Bozler, C. O.

1982-01-01

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than five have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 microns thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

Engineering Controlled Spalling in (100)-Oriented GaAs for Wafer Reuse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sweet, Cassi A.; McNeely, Joshua E.; Gorman, Brian

Controlled spalling offers a way to cleave thin, single-crystal films or devices from wafers, particularly if the fracture planes in the material are oriented parallel to the wafer surface. Unfortunately, misalignment between the favored fracture planes and the wafer surface preferred for photovoltaic growth in (100)-oriented GaAs produces a highly faceted surface when subject to controlled spalling. This highly faceted cleavage surface is problematic in several ways: (1) it can result in large variations of spall depth due to unstable crack propagation; (2) it may introduce defects into the device zone or underlying substrate; and (3) it consumes many micronsmore » of material outside of the device zone. We present the ways in which we have engineered controlled spalling for (100)-oriented GaAs to minimize these effects. We expand the operational window for controlled spalling to avoid spontaneous spalling, find no evidence of dislocation activity in the spalled film or the parent wafer, and reduce facet height and facet height irregularity. Resolving these issues provides a viable path forward for reducing III-V device cost through the controlled spalling of (100)-oriented GaAs devices and subsequent wafer reuse when these processes are combined with a high-throughput growth method such as Hydride Vapor Phase Epitaxy.« less

Attractive interaction between Mn atoms on the GaAs(110) surface observed by scanning tunneling microscopy.

PubMed

Taninaka, Atsushi; Yoshida, Shoji; Kanazawa, Ken; Hayaki, Eiko; Takeuchi, Osamu; Shigekawa, Hidemi

2016-06-16

Scanning tunneling microscopy/spectroscopy (STM/STS) was carried out to investigate the structures of Mn atoms deposited on a GaAs(110) surface at room temperature to directly observe the characteristics of interactions between Mn atoms in GaAs. Mn atoms were paired with a probability higher than the random distribution, indicating an attractive interaction between them. In fact, re-pairing of unpaired Mn atoms was observed during STS measurement. The pair initially had a new structure, which was transformed during STS measurement into one of those formed by atom manipulation at 4 K. Mn atoms in pairs and trimers were aligned in the <110> direction, which is theoretically predicted to produce a high Curie temperature.

Surface Interaction Kinetics of GaAs (100) Surfaces Under Electron Cyclotron Resonance Nitrogen Plasma Exposure

NASA Astrophysics Data System (ADS)

O'Steen, M. L.; Hauenstein, R. J.; Bandić, Z. Z.; Feenstra, R. M.; Hwang, S. J.; McGill, T. C.

1996-03-01

GaN is a robust semiconducting material offering a large, direct bandgap appropriate for use in blue-green to UV light emitting diodes and laser diodes. Attainment of device quality GaN has been difficult due to the lack of substrate materials that are suitably matched to the unusually small lattice parameter of GaN. To better control heteroepitaxial growth quality, a fundamental study of the initial stages of GaN growth by Electron Cyclotron Resonance Nitrogen Plasma-Assisted Molecular Beam Epitaxy (ECR-MBE) has been performed. The effect of an ECR Nitrogen plasma on a GaAs (100) surface is examined through time resolved reflection high energy electron diffraction, high resolution x-ray diffraction, and cross-sectional scanning tunneling microscopy. Fully commensurate GaN_yAs_1-y/GaAs heterostructures involving ultrathin GaN_yAs_1-y layers are obtained, and thermally activated microscopic growth processes are identified and quantitatively characterized through the aid of a specially developed kinetic model. The implications for ECR-MBE growth of GaN/GaAs mutilayers is discussed.

Modified energetics and growth kinetics on H-terminated GaAs (110)

NASA Astrophysics Data System (ADS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

2013-10-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

GaAs Supercomputing: Architecture, Language, And Algorithms For Image Processing

NASA Astrophysics Data System (ADS)

Johl, John T.; Baker, Nick C.

1988-10-01

The application of high-speed GaAs processors in a parallel system matches the demanding computational requirements of image processing. The architecture of the McDonnell Douglas Astronautics Company (MDAC) vector processor is described along with the algorithms and language translator. Most image and signal processing algorithms can utilize parallel processing and show a significant performance improvement over sequential versions. The parallelization performed by this system is within each vector instruction. Since each vector has many elements, each requiring some computation, useful concurrent arithmetic operations can easily be performed. Balancing the memory bandwidth with the computation rate of the processors is an important design consideration for high efficiency and utilization. The architecture features a bus-based execution unit consisting of four to eight 32-bit GaAs RISC microprocessors running at a 200 MHz clock rate for a peak performance of 1.6 BOPS. The execution unit is connected to a vector memory with three buses capable of transferring two input words and one output word every 10 nsec. The address generators inside the vector memory perform different vector addressing modes and feed the data to the execution unit. The functions discussed in this paper include basic MATRIX OPERATIONS, 2-D SPATIAL CONVOLUTION, HISTOGRAM, and FFT. For each of these algorithms, assembly language programs were run on a behavioral model of the system to obtain performance figures.

Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes

DOE PAGES

Liu, Wei; Zhang, Shukui; Stutzman, Marcy; ...

2016-10-24

Bulk GaAs samples with different surface cleave planes were implanted with 100 and 10 000 V hydrogen ions inside an ultrahigh vacuum test apparatus to simulate ion back-bombardment of the photocathode inside a DC high voltage photogun. The photocathode yield, or quantum efficiency, could easily be recovered following implantation with 100 V hydrogen ions but not for 10 000 V ions. Moreover, the implantation damage with 10 000 V hydrogen ions was more pronounced for GaAs photocathode samples with (100) and (111A) cleave planes, compared to the photocathode with (110) cleave plane. Lastly, this result is consistent with enhanced ionmore » channeling for the (110) cleave plane compared to the other cleave planes, with ions penetrating deeper into the photocathode material beyond the absorption depth of the laser light and beyond the region of the photocathode where the photoemitted electrons originate.« less

Comparison of the reactivity of alkyl and alkyl amine precursors with native oxide GaAs(100) and InAs(100) surfaces

NASA Astrophysics Data System (ADS)

Henegar, A. J., , Dr.; Gougousi, T., , Prof.

2016-12-01

In this manuscript we compare the interaction of alkyl (trimethyl aluminum) and alkyl amine (tetrakis dimethylamino titanium) precursors during thermal atomic layer deposition with III-V native oxides. For that purpose we deposit Al2O3 and TiO2, using H2O as the oxidizer, on GaAs(100) and InAs(100) native oxide surfaces. We find that there are distinct differences in the behavior of the two films. For the Al2O3 ALD very little native oxide removal happens after the first few ALD cycles while the interaction of the alkyl amine precursor for TiO2 and the native oxides continues well after the surface has been covered with 2 nm of TiO2. This difference is traced to the superior properties of Al2O3 as a diffusion barrier. Differences are also found in the behavior of the arsenic oxides of the InAs and GaAs substrates. The arsenic oxides from the InAs surface are found to mix more efficiently in the growing dielectric film than those from the GaAs surface. This difference is attributed to lower native oxide stability as well as an initial diffusion path formation by the indium oxides.

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.

Fabrication of p(+)-n junction GaAs solar cells by a novel method

NASA Technical Reports Server (NTRS)

Ghandhi, S. K.; Mathur, G.; Rode, H.; Borrego, J. M.

1984-01-01

A novel method for making p(+)-n diffused junction GaAs solar cells, with the formation of a diffusion source, an anti-reflective coating, and a protective cover glass in a single chemical-vapor deposition operation is discussed. Consideration is given to device fabrication and to solar-cell characteristics. The advantages of the technique are that the number of process steps is kept to an absolute minimum, the fabrication procedure is low-cost, and the GaAs surface is protected during the entire operation.

Influence of GaAs substrate properties on the congruent evaporation temperature

NASA Astrophysics Data System (ADS)

Spirina, A. A.; Nastovjak, A. G.; Shwartz, N. L.

2018-03-01

High-temperature annealing of GaAs(111)A and GaAs(111)B substrates under Langmuir evaporation conditions was studied using Monte Carlo simulation. The maximal value of the congruent evaporation temperature was estimated. The congruent evaporation temperature was demonstrated to be dependent on the surface orientation and concentration of surface defects.

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.

Correlation study of sodium-atom chemisorption on the GaAs(110) surface

NASA Astrophysics Data System (ADS)

Song, K. M.; Khan, D. C.; Ray, A. K.

1994-01-01

Different possible adsorption sites of sodium atoms on a gallium arsenide surface have been investigated using ab initio self-consistent unrestricted Hartree-Fock total-energy cluster calculations with Hay-Wadt effective core potentials. The effects of electron correlation have been included by invoking the concepts of many-body perturbation theory and are found to be highly significant. We find that the Na-atom adsorption at a site modeled with an NaGa5As4H12 cluster is most favored energetically followed by Na adsorption at the site modeled with the NaGa4As5H12 cluster. The effects of charge transfer from Na to the GaAs surface as also possibilities of metallization are also analyzed and discussed.

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

NASA Astrophysics Data System (ADS)

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

2004-09-01

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

The electronic and optical properties of Cs adsorbed GaAs nanowires via first-principles study

NASA Astrophysics Data System (ADS)

Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu; Lu, Feifei

2018-07-01

In this study, we investigate the Cs adsorption mechanism on (110) surface of zinc-blende GaAs nanowire. The adsorption energy, work function, dipole moment, geometric structure, Mulliken charge distribution, charge transfer index, band structures, density of state and optical properties of Cs adsorption structures are calculated utilizing first-principles method based on density function theory. Total-energy calculations show that all the adsorption energies are negative, indicating that Cs adsorption process is exothermic and Cs covered GaAs nanowires are stable. The work function of nanowire surface has an obvious decrease after Cs adsorption. Besides, the ionization of nanowire surface is enhanced as well. More importantly, Cs adsorption contributes to a lower side shift of bands near Fermi level, and the corresponding band gap disappears. Additionally, the absorption peak and energy loss function after Cs adsorption are far higher than those before adsorption, implying better light absorption characteristic of nanowire surface after Cs adsorption. These theoretical calculations can directly guide the Cs activation experiment for negative electron affinity GaAs nanowire, and also lay a foundation for the further study of Cs/O co-adsorption on the nanowire surface.

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

NASA Astrophysics Data System (ADS)

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

2001-11-01

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

Core-level photoemission investigation of atomic-fluorine adsorption on GaAs(110)

NASA Astrophysics Data System (ADS)

McLean, A. B.; Terminello, L. J.; McFeely, F. R.

1989-12-01

The adsorption of atomic F on the cleaved GaAs(110) surface has been studied with use of high-resolution core-level photoelectron spectroscopy by exposing the GaAs(110) surfaces to XeF2, which adsorbs dissociatively, leaving atomic F behind. This surface reaction produces two chemically shifted components in the Ga 3d core-level emission which are attributed to an interfacial monofluoride and a stable trifluoride reaction product, respectively. The As 3d core level develops only one chemically shifted component and from its exposure-dependent behavior it is attributed to an interfacial monofluoride. Least-squares analysis of the core-level line shapes revealed that (i) the F bonds to both the anion and the cation , (ii) the GaF3 component (characteristic of strong interfacial reaction) and the surface core-level shifted component (characteristic of a well ordered, atomically clean surface) are present together over a relatively large range of XeF2 exposures, and (iii) it is the initial disruption of the GaAs(110) surface that is the rate-limiting step in this surface reaction. These results are compared with similar studies of Cl and O adsorption on GaAs(110).

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.

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.

Design and fabrication of GaAs OMIST photodetector

NASA Astrophysics Data System (ADS)

Kang, Xuejun; Lin, ShiMing; Liao, Qiwei; Gao, Junhua; Liu, Shi'an; Cheng, Peng; Wang, Hongjie; Zhang, Chunhui; Wang, Qiming

1998-08-01

We designed and fabricated GaAs OMIST (Optical-controlled Metal-Insulator-Semiconductor Thyristor) device. Using oxidation of AlAs layer that is grown by MBE forms the Ultra- Thin semi-Insulating layer (UTI) of the GAAS OMIST. The accurate control and formation of high quality semi-insulating layer (AlxOy) are the key processes for fabricating GaAs OMIST. The device exhibits a current-controlled negative resistance region in its I-V characteristics. When illuminated, the major effect of optical excitation is the reduction of the switching voltage. If the GaAs OMIST device is biased at a voltage below its dark switching voltage Vs, sufficient incident light can switch OMIST from high impedance low current 'off' state to low impedance high current 'on' state. The absorbing material of OMIST is GaAS, so if the wavelength of incident light within 600 to approximately 850 nm can be detected effectively. It is suitable to be used as photodetector for digital optical data process. The other attractive features of GaAs OMIST device include suitable conducted current, switching voltage and power levels for OEIC, high switch speed and high sensitivity to light or current injection.

Anisotropy in Ostwald ripening and step-terraced surface formation on GaAs(0 0 1): Experiment and Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Kazantsev, D. M.; Akhundov, I. O.; Shwartz, N. L.; Alperovich, V. L.; Latyshev, A. V.

2015-12-01

Ostwald ripening and step-terraced morphology formation on the GaAs(0 0 1) surface during annealing in equilibrium conditions are investigated experimentally and by Monte Carlo simulation. Fourier and autocorrelation analyses are used to reveal surface relief anisotropy and provide information about islands and pits shape and their size distribution. Two origins of surface anisotropy are revealed. At the initial stage of surface smoothing, crystallographic anisotropy is observed, which is caused presumably by the anisotropy of surface diffusion at GaAs(0 0 1). A difference of diffusion activation energies along [1 1 0] and [1 1 bar 0] axes of the (0 0 1) face is estimated as ΔEd ≈ 0.1 eV from the comparison of experimental results and simulation. At later stages of surface smoothing the anisotropy of the surface relief is determined by the vicinal steps direction. At the initial stage of step-terraced morphology formation the kinetics of monatomic islands and pits growth agrees with the Ostwald ripening theory. At the final stage the size of islands and pits decreases due to their incorporation into the forming vicinal steps.

Effects of ultrathin oxides in conducting MIS structures on GaAs

NASA Technical Reports Server (NTRS)

Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

1978-01-01

Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions

NASA Astrophysics Data System (ADS)

Bischoff, L.; Böttger, R.; Heinig, K.-H.; Facsko, S.; Pilz, W.

2014-08-01

Self-organization of surface patterns on GaAs under irradiation with heavy polyatomic Au ions has been observed. The patterns depend on the ion mass, and the substrate temperature as well as the incidence angle of the ions. At room temperature, under normal incidence the surface remains flat, whereas above 200 °C nanodroplets of Ga appear after irradiation with monatomic, biatomic as well as triatomic Au ions of kinetic energies in the range of 10-30 keV per atom. In the intermediate temperature range of 100-200 °C meander- and dot-like patterns form, which are not related to Ga excess. Under oblique ion incidence up to 45° from the surface normal, at room temperature the surface remains flat for mon- and polyatomic Au ions. For bi- and triatomic ions in the range of 60° ≤ α ≤ 70° ripple patterns have been found, which become shingle-like for α ≥ 80°, whereas the surface remains flat for monatomic ions.

Real-time detection of laser-GaAs interaction process

NASA Astrophysics Data System (ADS)

Jia, Zhichao; Li, Zewen; Lv, Xueming; Ni, Xiaowu

2017-05-01

A real-time method based on laser scattering technology was used to detect the interaction process of GaAs with a 1080 nm laser. The detector collected the scattered laser beam from the GaAs wafer. The main scattering sources were back surface at first, later turn into front surface and vapor, so scattering signal contained much information of the interaction process. The surface morphologies of GaAs with different irradiation times were observed using an optical microscope to confirm occurrence of various phenomena. The proposed method is shown to be effective for the real-time detection of GaAs. By choosing a proper wavelength, the scattering technology can be promoted in detection of thicker GaAs wafer or other materials.

GaAs nanopillar-array solar cells employing in situ surface passivation

PubMed Central

Mariani, Giacomo; Scofield, Adam C.; Hung, Chung-Hong; Huffaker, Diana L.

2013-01-01

Arrays of III–V direct-bandgap semiconductor nanopillars represent promising photovoltaic candidates due to their inherent high optical absorption coefficients and minimized reflection arising from light trapping, efficient charge collection in the radial direction and the ability to synthesize them on low-cost platforms. However, the increased surface area results in surface states that hamper the power conversion efficiency. Here, we report the first demonstration of GaAs nanopillar-array photovoltaics employing epitaxial passivation with air mass 1.5 global power conversion efficiencies of 6.63%. High-bandgap epitaxial InGaP shells are grown in situ and cap the radial p–n junctions to alleviate surface-state effects. Under light, the photovoltaic devices exhibit open-circuit voltages of 0.44 V, short-circuit current densities of 24.3 mA cm−2 and fill factors of 62% with high external quantum efficiencies >70% across the spectral regime of interest. A novel titanium/indium tin oxide annealed alloy is exploited as transparent ohmic anode. PMID:23422665

Transient surface states during the CBE growth of GaAs

NASA Astrophysics Data System (ADS)

Farrell, T.; Hill, D.; Joyce, T. B.; Bullough, T. J.; Weightman, P.

1997-05-01

We report the occurrence of a transient surface state during the initial stages of CBE GaAs(0 0 1) growth. The state was detected in real-time reflectance ( R) and reflectance anisotropy spectroscopy (RAS) growth monitoring. At low growth rates, less than 1 μm/h, beam equivalent pressure (BEP) of triethylgallium (TEG) < 2.5 × 10 -5 mbar there was no change in R and the RAS signal changed from its pre-growth value under arsenic stabilisation at the growth temperature to its "during growth" value upon admission of the TEG, with the familiar monolayer oscillations. At higher TEG BEPs there was a rapid increase in R at all monitoring wavelengths, followed by a monotonic decay to its pre-growth value. This transient increase in R was accompanied by a change in the RAS signal, the magnitude and sign of which varied with wavelength. The initial increase in R is shown to be associated with the development of a metallic-like surface whereas the changes in the RAS signal are consistent with the formation of Ga dimers.

Reflection high energy electron diffraction and reflectance difference studies of surface anisotropy in InGaAs chemical beam epitaxy on flat and vicinal (001) GaAs

NASA Astrophysics Data System (ADS)

Junno, B.; Paulsson, G.; Miller, M.; Samuelson, L.

1994-03-01

InGaAs quantum wells (QWs) were grown in a chemical beam epitaxy (CBE) machine with trimethylindium (TMI), triethylgallium (TEG) and tertiarybutylarsine (TBA) as precursors. Growth was monitored in-situ by reflectance difference (RD) and reflection high energy electron diffraction (RHEED), on both flat and vicinal (2° off in the <111> A direction) (001)GaAs substrates. The RD was monitored at 632.8 nm. At this wavelength the RD signal from a GaAs surface is primarily related to the absorption by Ga dimers. When InGaAs had been grown, both the average RD signal and the amplitude of the RD oscillations for the subsequent growth of GaAs increased significantly, compared to GaAs growth on GaAs. This In influence was found to persist even after the growth of 20-30 ML of pure GaAs. As a result we were able to monitor growth oscillations with RD and RHEED simultaneously during growth of quantum wells of InGaAs in GaAs. As a conclusion to these observations we suggest that the group III dimer bond concentration, detected in the RD signal, increases.

Growth of GaAs crystals from the melt in a partially confined configuration

NASA Technical Reports Server (NTRS)

Gatos, Harry C.; Lagowski, Jacek

1988-01-01

The experimental approach was directed along two main goals: (1) the implementation of an approach to melt growth in a partially confined configuration; and (2) the investigation of point defect interaction and electronic characteristics as related to thermal treatment following solidification and stoichiometry. Significant progress was made along both fronts. Crystal growth of GaAs in triangular ampuls was already carried out successfully and consistent with the model. In fact, pronounced surface tension phenomena which cannot be observed in ordinary confinement system were identified and should premit the assessment of Maragoni effects prior to space processing. Regarding thermal treatment, it was discovered that the rate of cooling from elevated temperatures is primarily responsible for a whole class of defect interactions affecting the electronic characteristics of GaAs and that stoichiometry plays a critical role in the quality of GaAs.

Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

NASA Astrophysics Data System (ADS)

Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

2014-12-01

High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

Characteristics of GaAs with inverted thermal conversion

NASA Technical Reports Server (NTRS)

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

1987-01-01

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

Dielectric functions, chemical and atomic compositions of the near surface layers of implanted GaAs by In+ ions

NASA Astrophysics Data System (ADS)

Kulik, M.; Kołodyńska, D.; Bayramov, A.; Drozdziel, A.; Olejniczak, A.; Żuk, J.

2018-06-01

The surfaces of (100) GaAs were irradiated with In+ ions. The implanted samples were isobaric annealed at 800 °C and then of dielectric function, the surface atomic concentrations of atoms and also the chemical composition of the near surface layers in these implanted semiconductor samples were obtained. The following investigation methods were used: spectroscopic ellipsometry (SE), Rutherford backscattering spectrometry analyses (RBSA) and X-ray photoelectron spectroscopy (XPS) in the study of the above mentioned quantities, respectively. The change of the shape spectra of the dielectric functions at about 3.0 eV phonon energy, diffusion of In+ ions as well as chemical composition changes were observed after ion implantation and the thermal treatment. Due to displacement of Ga ions from GaAs by the In+ ions the new chemical compound InAs was formed. The relative amounts Ga2O3 and As2O3 ratio increase in the native oxide layers with the fluences increase after the thermal treatment of the samples. Additionally, it was noticed that the quantities of InO2 increase with the increasing values of the irradiated ions before thermal treatment.

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.

Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

NASA Technical Reports Server (NTRS)

Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

1987-01-01

GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

Ultra-thin flexible GaAs photovoltaics in vertical forms printed on metal surfaces without interlayer adhesives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Juho; Song, Kwangsun; Kim, Namyun

2016-06-20

Wearable flexible electronics often require sustainable power sources that are also mechanically flexible to survive the extreme bending that accompanies their general use. In general, thinner microelectronic devices are under less strain when bent. This paper describes strategies to realize ultra-thin GaAs photovoltaics through the interlayer adhesiveless transfer-printing of vertical-type devices onto metal surfaces. The vertical-type GaAs photovoltaic devices recycle reflected photons by means of bottom electrodes. Systematic studies with four different types of solar microcells indicate that the vertical-type solar microcells, at only a quarter of the thickness of similarly designed lateral-type cells, generate a level of electric powermore » similar to that of thicker cells. The experimental results along with the theoretical analysis conducted here show that the ultra-thin vertical-type solar microcells are durable under extreme bending and thus suitable for use in the manufacturing of wearable flexible electronics.« less

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

NASA Astrophysics Data System (ADS)

Chen, C.-H.; Gösele, U. M.; Tan, T. Y.

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species SiGa+ and as shallow acceptor species SiAs-. The solubility of SiAs- is much lower than that of SiGa+ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is SiGa+ which will convert into SiAs- in accordance with their solubilities and that the point defect species governing the diffusion of SiGa+ are triply-negatively-charged Ga vacancies VGa3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n+-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently.

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.

Lightweight, Light-Trapped, Thin GaAs Solar Cells for Spacecraft Applications.

DTIC Science & Technology

1995-10-05

improve the efficiency of this type of cell. 2 The high efficiency and light weight of the cover glass supported GaAs solar cell can have a significant...is a 3-mil cover glass and 1-mil silicone adhesive on the front surface of the GaAs solar cell. Power Output 3000 400 -{ 2400 { N 300 S18200 W/m2...the ultra-thin, light-trapped GaAs solar ceill 3. Incorporate light trapping. 0 external quantum efficiency at 850 nm increased by 5.2% 4. Develop

The ZnSe(110) puzzle - Comparison with GaAs(110)

NASA Technical Reports Server (NTRS)

Duke, C. B.; Paton, A.; Kahn, A.; Tu, D.-W.

1984-01-01

The surface structure of monocrystalline ZnSe(110) and of 4-5-nm-thick ZnSe(110) layers epitaxially grown on GaAs(110) is investigated by means of elastic LEED and AES; the results are analyzed using the computer programs and R-factor methods of Duke et al. (1981 and 1983), presented in graphs and tables, and compared to those for GaAs(110). Significant differences are attributed to bond-length-conserving outward rotation of Se and inward rotation of Zn in the top layer, with an angle of 4 deg between the actual plane of the cation-anion chain and the truncated bulk surface. The R intensities measured for ZnSe(110) and GaAs(110) are given as Rx = 0.22 and RI = 0.21 and Rx = 0.24 and RI = 0.16, respectively.

Surface Passivation for 3-5 Semiconductor Processing: Stable Gallium Sulphide Films by MOCVD

NASA Technical Reports Server (NTRS)

Macinnes, Andrew N.; Jenkins, Phillip P.; Power, Michael B.; Kang, Soon; Barron, Andrew R.; Hepp, Aloysius F.; Tabib-Azar, Massood

1994-01-01

Gallium sulphide (GaS) has been deposited on GaAs to form stable, insulating, passivating layers. Spectrally resolved photoluminescence and surface recombination velocity measurements indicate that the GaS itself can contribute a significant fraction of the photoluminescence in GaS/GaAs structures. Determination of surface recombination velocity by photoluminescence is therefore difficult. By using C-V analysis of metal-insulator-semiconductor structures, passivation of the GaAs with GaS films is quantified.

Nanostructured GaAs solar cells via metal-assisted chemical etching of emitter layers.

PubMed

Song, Yunwon; Choi, Keorock; Jun, Dong-Hwan; Oh, Jungwoo

2017-10-02

GaAs solar cells with nanostructured emitter layers were fabricated via metal-assisted chemical etching. Au nanoparticles produced via thermal treatment of Au thin films were used as etch catalysts to texture an emitter surface with nanohole structures. Epi-wafers with emitter layers 0.5, 1.0, and 1.5 um in thickness were directly textured and a window layer removal process was performed before metal catalyst deposition. A nanohole-textured emitter layer provides effective light trapping capabilities, reducing the surface reflection of a textured solar cell by 11.0%. However, because the nanostructures have high surface area to volume ratios and large numbers of defects, various photovoltaic properties were diminished by high recombination losses. Thus, we have studied the application of nanohole structures to GaAs emitter solar cells and investigated the cells' antireflection and photovoltaic properties as a function of the nanohole structure and emitter thickness. Due to decreased surface reflection and improved shunt resistance, the solar cell efficiency increased from 4.25% for non-textured solar cells to 7.15% for solar cells textured for 5 min.

Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zech, E. S.; Chang, A. S.; Martin, A. J.

2013-08-19

We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

Crystal Growth of Device Quality Gaas in Space

NASA Technical Reports Server (NTRS)

Gatos, H. C.

1985-01-01

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

GaAs VLSI technology and circuit elements for DSP

NASA Astrophysics Data System (ADS)

Mikkelson, James M.

1990-10-01

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

ZnSe Window Layers for GaAs and GaInP2 Solar Cells

NASA Technical Reports Server (NTRS)

Olsen, Larry C.

1997-01-01

This report concerns studies of the use of n-type ZnSe as a window layer for n/p GaAs and GaInP2 solar cells. Emphasis was placed in this phase of the project on characterizing the interface between n-type ZnSe films grown on epi-GaAs films grown onto single crystal GaAs. Epi-GaAs and heteroepitaxial ZnSe films were grown by MOCVD with a Spire 50OXT Reactor. After growing epitaxial GaAs films on single crystal GaAs wafers, well-oriented crystalline ZnSe films were grown by MOCVD. ZnSe films were grown with substrate temperatures ranging from 250 C to 450 C. Photoluminescence studies carried out by researchers at NASA Lewis determined that the surface recombination velocity at a GaAs surface was significantly reduced after the deposition of a heteroepitaxial layer of ZnSe. The optimum temperature for ZnSe deposition appears to be on the order of 350 C.

Electrical and optical characterization of surface passivation in GaAs nanowires.

PubMed

Chang, Chia-Chi; Chi, Chun-Yung; Yao, Maoqing; Huang, Ningfeng; Chen, Chun-Chung; Theiss, Jesse; Bushmaker, Adam W; Lalumondiere, Stephen; Yeh, Ting-Wei; Povinelli, Michelle L; Zhou, Chongwu; Dapkus, P Daniel; Cronin, Stephen B

2012-09-12

We report a systematic study of carrier dynamics in Al(x)Ga(1-x)As-passivated GaAs nanowires. With passivation, the minority carrier diffusion length (L(diff)) increases from 30 to 180 nm, as measured by electron beam induced current (EBIC) mapping, and the photoluminescence (PL) lifetime increases from sub-60 ps to 1.3 ns. A 48-fold enhancement in the continuous-wave PL intensity is observed on the same individual nanowire with and without the Al(x)Ga(1-x)As passivation layer, indicating a significant reduction in surface recombination. These results indicate that, in passivated nanowires, the minority carrier lifetime is not limited by twin stacking faults. From the PL lifetime and minority carrier diffusion length, we estimate the surface recombination velocity (SRV) to range from 1.7 × 10(3) to 1.1 × 10(4) cm·s(-1), and the minority carrier mobility μ is estimated to lie in the range from 10.3 to 67.5 cm(2) V(-1) s(-1) for the passivated nanowires.

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.

The effect of (NH4)2Sx passivation on the (311)A GaAs surface and its use in AlGaAs/GaAs heterostructure devices.

PubMed

Carrad, D J; Burke, A M; Reece, P J; Lyttleton, R W; Waddington, D E J; Rai, A; Reuter, D; Wieck, A D; Micolich, A P

2013-08-14

We have studied the efficacy of (NH4)2Sx surface passivation on the (311)A GaAs surface. We report XPS studies of simultaneously-grown (311)A and (100) heterostructures showing that the (NH4)2Sx solution removes surface oxide and sulfidizes both surfaces. Passivation is often characterized using photoluminescence measurements; we show that while (NH4)2Sx treatment gives a 40-60 ×  increase in photoluminescence intensity for the (100) surface, an increase of only 2-3 ×  is obtained for the (311)A surface. A corresponding lack of reproducible improvement in the gate hysteresis of (311)A heterostructure transistor devices made with the passivation treatment performed immediately prior to gate deposition is also found. We discuss possible reasons why sulfur passivation is ineffective for (311)A GaAs, and propose alternative strategies for passivation of this surface.

Removal of ion-implanted photoresists on GaAs using two organic solvents in sequence

NASA Astrophysics Data System (ADS)

Oh, Eunseok; Na, Jihoon; Lee, Seunghyo; Lim, Sangwoo

2016-07-01

Organic solvents can effectively remove photoresists on III-V channels without damage or etching of the channel material during the process. In this study, a two-step sequential photoresist removal process using two different organic solvents was developed to remove implanted ArF and KrF photoresists at room temperature. The effects of organic solvents with either low molar volumes or high affinities for photoresists were evaluated to find a proper combination that can effectively remove high-dose implanted photoresists without damaging GaAs surfaces. The performance of formamide, acetonitrile, nitromethane, and monoethanolamine for the removal of ion-implanted ArF and KrF photoresists were compared using a two-step sequential photoresist removal process followed by treatment in dimethyl sulfoxide (DMSO). Among the various combinations, the acetonitrile + DMSO two-step sequence exhibited the best removal of photoresists that underwent ion implantation at doses of 5 × 1013-5 × 1015 atoms/cm2 on both flat and trench-structured GaAs surfaces. The ability of the two-step process using organic solvents to remove the photoresists can be explained by considering the affinities of solvents for a polymer and its permeability through the photoresist.

Formation of the InAs-, InSb-, GaAs-, and GaSb-polished surface

NASA Astrophysics Data System (ADS)

Levchenko, Iryna; Tomashyk, Vasyl; Stratiychuk, Iryna; Malanych, Galyna; Korchovyi, Andrii; Kryvyi, Serhii; Kolomys, Oleksandr

2018-04-01

The features of the InAs, InSb, GaAs, and GaSb ultra-smooth surface have been investigated using chemical-mechanical polishing with the (NH4)2Cr2O7-HBr-CH2(OH)CH2(OH)-etching solutions. The etching rate of the semiconductors has been measured as a function of the solution saturation by organic solvent (ethylene glycol). It was found that mechanical effect significantly increases the etching rate from 1.5 to 57 µm/min, and the increase of the organic solvent concentration promotes the decrease of the damaged layer-removing rate. According to AFM, RS, HRXRD results, the treatment with the (NH4)2Cr2O7-HBr-ethylene glycol solutions produces the clean surface of the nanosize level (R a < 0.5 nm).

Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces

NASA Technical Reports Server (NTRS)

Kashkarov, P. K.; Kazior, T. E.; Lagowski, J.; Gatos, H. C.

1983-01-01

An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies, internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7 + or - 0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.

High efficiency thin-film GaAs solar cells

NASA Technical Reports Server (NTRS)

Stirn, R. J.

1977-01-01

Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

Understanding the true shape of Au-catalyzed GaAs nanowires.

PubMed

Jiang, Nian; Wong-Leung, Jennifer; Joyce, Hannah J; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

2014-10-08

With increasing interest in nanowire-based devices, a thorough understanding of the nanowire shape is required to gain tight control of the quality of nanowire heterostructures and improve the performance of related devices. We present a systematic study of the sidewalls of Au-catalyzed GaAs nanowires by investigating the faceting process from the beginning with vapor-liquid-solid (VLS) nucleation, followed by the simultaneous radial growth on the sidewalls, and to the end with sidewall transformation during annealing. The VLS nucleation interface of our GaAs nanowires is revealed by examining cross sections of the nanowire, where the nanowire exhibits a Reuleaux triangular shape with three curved surfaces along {112}A. These curved surfaces are not thermodynamically stable and adopt {112}A facets during radial growth. We observe clear differences in radial growth rate between the ⟨112⟩A and ⟨112⟩B directions with {112}B facets forming due to the slower radial growth rate along ⟨112⟩B directions. These sidewalls transform to {110} facets after high temperature (>500 °C) annealing. A nucleation model is proposed to explain the origin of the Reuleaux triangular shape of the nanowires, and the sidewall evolution is explained by surface kinetic and thermodynamic limitations.

Quantum Information Processing with Large Nuclear Spins in GaAs Semiconductors

NASA Astrophysics Data System (ADS)

Leuenberger, Michael N.; Loss, Daniel; Poggio, M.; Awschalom, D. D.

2002-10-01

We propose an implementation for quantum information processing based on coherent manipulations of nuclear spins I=3/2 in GaAs semiconductors. We describe theoretically an NMR method which involves multiphoton transitions and which exploits the nonequidistance of nuclear spin levels due to quadrupolar splittings. Starting from known spin anisotropies we derive effective Hamiltonians in a generalized rotating frame, valid for arbitrary I, which allow us to describe the nonperturbative time evolution of spin states generated by magnetic rf fields. We identify an experimentally observable regime for multiphoton Rabi oscillations. In the nonlinear regime, we find Berry phase interference.

Quantum Dots obtained by LPE from under-saturated In-As liquid phases on GaAs substrates

NASA Astrophysics Data System (ADS)

Ortiz, F. E.; Mishurnyi, V.; Gorbatchev, A.; De Anda, F.; Prutskij, T.

2011-01-01

In this work we inform about quantum dots (QD) obtained by Liquid Phase Epitaxy (LPE) on GaAs substrates from under-saturated In-As liquid phases. In our processes, we have prepared saturated In-rich liquid phases by dissolving an InAs wafer at one of the temperatures interval from 450 to 414 C for 60 minutes. The contact between In-As liquid phase and the GaAs substrate was always done at a constant temperature of 444 C for 5 seconds. Thus, the growth temperature for most of the samples was higher than the liquidus temperature. We think that the growth driving force is related to a transient process that occurs when the system is trying to reach equilibrium. Under the atom force microscope (AFM) we have observed nano-islands on the surfaces of the samples obtained from under-saturated liquid phases prepared at 438, 432 and 426 C. The 25 K photoluminescence spectrum shows a peak at a 1.33 eV, in addition to the GaAs related line.

Block copolymer-templated chemistry on Si, Ge, InP, and GaAs surfaces.

PubMed

Aizawa, Masato; Buriak, Jillian M

2005-06-29

Patterning of semiconductor surfaces is an area of intense interest, not only for technological applications, such as molecular electronics, sensing, cellular recognition, and others, but also for fundamental understanding of surface reactivity, general control over surface properties, and development of new surface reactivity. In this communication, we describe the use of self-assembling block copolymers to direct semiconductor surface chemistry in a spatially defined manner, on the nanoscale. The proof-of-principle class of reactions evaluated here is galvanic displacement, in which a metal ion, M+, is reduced to M0 by the semiconductor, including Si, Ge, InP, and GaAs. The block copolymer chosen has a polypyridine block which binds to the metal ions and brings them into close proximity with the surface, at which point they undergo reaction; the pattern of resulting surface chemistry, therefore, mirrors the nanoscale structure of the parent block copolymer. This chemistry has the added advantage of forming metal nanostructures that result in an alloy or intermetallic at the interface, leading to strongly bound metal nanoparticles that may have interesting electronic properties. This approach has been shown to be very general, functioning on a variety of semiconductor substrates for both silver and gold deposition, and is being extended to organic and inorganic reactions on a variety of conducting, semiconducting, and insulating substrates.

Microprocessor design for GaAs technology

NASA Astrophysics Data System (ADS)

Milutinovic, Veljko M.

Recent advances in the design of GaAs microprocessor chips are examined in chapters contributed by leading experts; the work is intended as reading material for a graduate engineering course or as a practical R&D reference. Topics addressed include the methodology used for the architecture, organization, and design of GaAs processors; GaAs device physics and circuit design; design concepts for microprocessor-based GaAs systems; a 32-bit GaAs microprocessor; a 32-bit processor implemented in GaAs JFET; and a direct coupled-FET-logic E/D-MESFET experimental RISC machine. Drawings, micrographs, and extensive circuit diagrams are provided.

Prediction of dislocation generation during Bridgman growth of GaAs crystals

NASA Technical Reports Server (NTRS)

Tsai, C. T.; Yao, M. W.; Chait, Arnon

1992-01-01

Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

Prediction of dislocation generation during Bridgman growth of GaAs crystals

NASA Astrophysics Data System (ADS)

Tsai, C. T.; Yao, M. W.; Chait, Arnon

1992-11-01

Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

Directional and dynamic modulation of the optical emission of an individual GaAs nanowire using surface acoustic waves.

PubMed

Kinzel, Jörg B; Rudolph, Daniel; Bichler, Max; Abstreiter, Gerhard; Finley, Jonathan J; Koblmüller, Gregor; Wixforth, Achim; Krenner, Hubert J

2011-04-13

We report on optical experiments performed on individual GaAs nanowires and the manipulation of their temporal emission characteristics using a surface acoustic wave. We find a pronounced, characteristic suppression of the emission intensity for the surface acoustic wave propagation aligned with the axis of the nanowire. Furthermore, we demonstrate that this quenching is dynamical as it shows a pronounced modulation as the local phase of the surface acoustic wave is tuned. These effects are strongly reduced for a surface acoustic wave applied in the direction perpendicular to the axis of the nanowire due to their inherent one-dimensional geometry. We resolve a fully dynamic modulation of the nanowire emission up to 678 MHz not limited by the physical properties of the nanowires.

Self-assembled InAs quantum dot formation on GaAs ring-like nanostructure templates

PubMed Central

Strom, NW; Wang, Zh M; AbuWaar, ZY; Mazur, Yu I; Salamo, GJ

2007-01-01

The evolution of InAs quantum dot (QD) formation is studied on GaAs ring-like nanostructures fabricated by droplet homo-epitaxy. This growth mode, exclusively performed by a hybrid approach of droplet homo-epitaxy and Stransky-Krastanor (S-K) based QD self-assembly, enables one to form new QD morphologies that may find use in optoelectronic applications. Increased deposition of InAs on the GaAs ring first produced a QD in the hole followed by QDs around the GaAs ring and on the GaAs (100) surface. This behavior indicates that the QDs prefer to nucleate at locations of high monolayer (ML) step density.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luan, Chongbiao; Wang, Bo; Huang, Yupeng

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 ofmore » 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.« less

Chemical etching and organometallic chemical vapor deposition on varied geometries of GaAs

NASA Technical Reports Server (NTRS)

Bailey, Sheila G.; Landis, Geoffrey A.; Wilt, David M.

1989-01-01

Results of micron-spaced geometries produced by wet chemical etching and subsequent OMCVD growth on various GaAs surfaces are presented. The polar lattice increases the complexity of the process. The slow-etch planes defined by anisotropic etching are not always the same as the growth facets produced during MOCVD deposition, especially for deposition on higher-order planes produced by the hex groove etching.

Submilliampere continuous-wave room-temperature lasing operation of a GaAs mushroom structure surface-emitting laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y.J.; Dziura, T.G.; Wang, S.C.

1990-05-07

We report a GaAs mushroom structure surface-emitting laser at 900 nm with submilliampere (0.2--0.5 mA) threshold under room-temperature cw operation for the first time. The very low threshold current was achieved on devices which consisted of a 2--4 {mu}m diameter active region formed by chemical selective etching, and sandwiched between two Al{sub 0.05}Ga{sub 0.95} As/ Al{sub 0.53}Ga{sub 0.47} As distributed Bragg reflectors of very high reflectivity (98--99%) grown by metalorganic chemical vapor deposition.

Submilliampere continuous-wave room-temperature lasing operation of a GaAs mushroom structure surface-emitting laser

NASA Astrophysics Data System (ADS)

Yang, Ying Jay; Dziura, Thaddeus G.; Wang, S. C.; Hsin, Wei; Wang, Shyh

1990-05-01

We report a GaAs mushroom structure surface-emitting laser at 900 nm with submilliampere (0.2-0.5 mA) threshold under room-temperature cw operation for the first time. The very low threshold current was achieved on devices which consisted of a 2-4 μm diameter active region formed by chemical selective etching, and sandwiched between two Al0.05Ga0.95 As/ Al0.53Ga0.47 As distributed Bragg reflectors of very high reflectivity (98-99%) grown by metalorganic chemical vapor deposition.

Reflection high energy electron diffraction observation of surface mass transport at the two- to three-dimensional growth transition of InAs on GaAs(001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patella, F.; Arciprete, F.; Fanfoni, M.

2005-12-19

We have followed by reflection high-energy electron diffraction the nucleation of InAs quantum dots on GaAs(001), grown by molecular-beam epitaxy with growth interruptions. Surface mass transport gives rise, at the critical InAs thickness, to a huge nucleation of three-dimensional islands within 0.2 monolayers (ML). Such surface mass diffusion has been evidenced by observing the transition of the reflection high-energy electron diffraction pattern from two- to three-dimensional during the growth interruption after the deposition of 1.59 ML of InAs. It is suggested that the process is driven by the As{sub 2} adsorption-desorption process and by the lowering of the In bindingmore » energy due to compressive strain. The last condition is met first in the region surrounding dots at step edges where nucleation predominantly occurs.« less

Quantum Information Processing with Large Nuclear Spins in GaAs Semiconductors

NASA Astrophysics Data System (ADS)

Leuenberger, Michael N.; Loss, Daniel; Poggio, M.; Awschalom, D. D.

2003-03-01

We propose an implementation for quantum information processing based on coherent manipulations of nuclear spins I=3/2 in GaAs semiconductors. We describe theoretically an NMR method which involves multiphoton transitions and which exploits the nonequidistance of nuclear spin levels due to quadrupolar splittings. Starting from known spin anisotropies we derive effective Hamiltonians in a generalized rotating frame, valid for arbitrary I, which allow us to describe the nonperturbative time evolution of spin states generated by magnetic rf fields. We identify an experimentally observable regime for multiphoton Rabi oscillations. In the nonlinear regime, we find Berry phase interference. Ref: PRL 89, 207601 (2002).

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1983-01-01

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

Temporal behavior of RHEED intensity oscillations during molecular beam epitaxial growth of GaAs and AlGaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, Ming Y.; Haas, T. W.

1990-10-01

We present the temporal behavior of intensity oscillations in reflection high-energy electron diffraction (RHEED) during molecular beam epitaxial (MBE) growth of GaAs and A1GaAs on (1 1 1)B GaAs substrates. The RHEED intensity oscillations were examined as a function of growth parameters in order to provide the insight into the dynamic characteristics and to identify the optimal condition for the two-dimensional layer-by-layer growth. The most intense RHEED oscillation was found to occur within a very narrow temperature range which seems to optimize the surface migration kinetics of the arriving group III elements and the molecular dissodiative reaction of the group V elements. The appearance of an initial transient of the intensity upon commencement of the growth and its implications are described.

DFT algorithms for bit-serial GaAs array processor architectures

NASA Technical Reports Server (NTRS)

Mcmillan, Gary B.

1988-01-01

Systems and Processes Engineering Corporation (SPEC) has developed an innovative array processor architecture for computing Fourier transforms and other commonly used signal processing algorithms. This architecture is designed to extract the highest possible array performance from state-of-the-art GaAs technology. SPEC's architectural design includes a high performance RISC processor implemented in GaAs, along with a Floating Point Coprocessor and a unique Array Communications Coprocessor, also implemented in GaAs technology. Together, these data processors represent the latest in technology, both from an architectural and implementation viewpoint. SPEC has examined numerous algorithms and parallel processing architectures to determine the optimum array processor architecture. SPEC has developed an array processor architecture with integral communications ability to provide maximum node connectivity. The Array Communications Coprocessor embeds communications operations directly in the core of the processor architecture. A Floating Point Coprocessor architecture has been defined that utilizes Bit-Serial arithmetic units, operating at very high frequency, to perform floating point operations. These Bit-Serial devices reduce the device integration level and complexity to a level compatible with state-of-the-art GaAs device technology.

Structural and electronic properties of isovalent boron atoms in GaAs

NASA Astrophysics Data System (ADS)

Krammel, C. M.; Nattermann, L.; Sterzer, E.; Volz, K.; Koenraad, P. M.

2018-04-01

Boron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of BxGa1-xAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the <110 > directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.

Strain relaxation induced surface morphology of heterogeneous GaInNAs layers grown on GaAs substrate

NASA Astrophysics Data System (ADS)

Gelczuk, Ł.; Jóźwiak, G.; Moczała, M.; Dłużewski, P.; Dąbrowska-Szata, M.; Gotszalk, T. P.

2017-07-01

The partially-relaxed heterogeneous GaInNAs layers grown on GaAs substrate by atmospheric pressure vapor phase epitaxy (AP-MOVPE) were investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The planar-view TEM image shows a regular 2D network of misfit dislocations oriented in two orthogonal 〈1 1 0〉 crystallographic directions at the (0 0 1) layer interface. Moreover, the cross-sectional view TEM image reveals InAs-rich and V-shaped precipitates in the near surface region of the GaInNAs epitaxial layer. The resultant undulating surface morphology, known as a cross-hatch pattern, is formed as observed by AFM. The numerical analysis of the AFM image of the GaInNAs layer surface with the well-defined cross-hatch morphology enabled us to determine a lower bound of actual density of misfit dislocations. However, a close correspondence between the asymmetric distribution of interfacial misfit dislocations and undulating surface morphology is observed.

Testing a GaAs cathode in SRF gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, E.; Kewisch, J.; Ben-Zvi, I.

RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10{sup -12} Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs,more » we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the

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

DTIC Science & Technology

1992-12-01

AD-A258 814 EXCITATION AND DE -EXCITATION MECHANISMS OF Er-DOPED GaAs AND A1GaAs DISSERTATION David W. Elsaesser, Captain, USAF DTICY. ft £ICTE’’ )AN...0 8 1993U -o Wo- .%Approved for public release; Distribution unlimited 93 1 04 022 AFIT/DS/ENP/92-5 EXCITATION AND DE -EXCITATION MECHANISMS OF Er...public release; Distribution unlimited AFIT/DS/ENP/92D-005 EXCITATION AND DE -EXCITATION MECHANISMS OF Er-DOPED GaAs AND A1GaAs 4 toFlor -- David W

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...the best quality copy available. j C] " ------ GaAs Computer Technology (1) Wang Qiao-yu (Li-Shan Microelectronics Institute) Abstract: The paper

The very surface states on GaAs(001) surface by means of electronic and optical techniques

NASA Astrophysics Data System (ADS)

Placidi, Ernesto

2004-03-01

Until now, Reflectance-Anisotropy Spectroscopy (RAS) in the visible has been the most used technique to quantify the anisotropy of these surfaces [1]. Low-energy electrons are believed to perturb more than photons and have not been employed to this purpose, despite their shorter penetration depth. In our presentation we show experimental results of High-Resolution Electron-Energy-Loss Spectroscopy (HREELS) applied to investigate the anisotropy of the GaAs(001)-c(4x4) and beta2(2x4) surfaces. We demonstrate the higher surface sensitivity of HREELS compared to RAS. Measurements are performed on high-quality samples grown in situ by Molecular Beam Epitaxy (MBE). The loss spectra taken in the two orthogonal surface directions have different intensities, particularly close to the fundamental gap, where surface like resonances, involving dimers, are observed. We discuss our HREELS and RAS data to identify the source of the anisotropy close to the critical point transitions where surface and bulk like excitations coexist. Our data are in very good agreement with DFT-LDA calculations for loss energies up to 3.5 eV [2]. The exposure of the reconstructed surfaces to molecular oxygen affects strongly the spectral features. [1] D.E.Aspnes, J.P.Harbison, A.A.Studna, L.T.Florez, Phys. Rev. Lett. 59 (1987) 1687; I.Kamiya, D.E.Aspnes, L.T.Florez, and J.T.Harbison, Phys. Rev. B 46 (1992) 15894. [2] A.Balzarotti, F.Arciprete, M.Fanfoni, F.Patella, E. Placidi, G.Onida, R.Del Sole, Surf. Sci. Lett. 524, L71 (2003); A.Balzarotti, E.Placidi, F.Arciprete, M.Fanfoni, F.Patella, Physical Review B, 67 115332 (2003); F.Arciprete, C. Goletti, E. Placidi, M.Fanfoni, F.Patella, P. Chiaradia, C. Hogan and A. Balzarotti, Phys. Rev. B 68 125328 (2003).

GaAs Photovoltaics on Polycrystalline Ge Substrates

NASA Technical Reports Server (NTRS)

Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

2007-01-01

High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

Cathodoluminescence Characterization of Ion Implanted GaAs.

DTIC Science & Technology

1980-03-01

technique that can be used to characterize the semiconductor device "in situ" before further processing can save the Air Force valuable time as well...Patterson Air Force Base,Ohio i! i ill i I ;Wow AFIT/DS/PH/80- I.i1I LEVELOO CATHODOLUMINESCENCE CHARACTERIZATION OF ION IPLANTED GaAs D I SSERUrAT ION...CATODOLUMINESCENCE CHARACTERIZATION .’ a .... OF ION IMPLANTED GaAs’ - .. .. Dtriy’ t’ c:’/ A’: t 1. - Cc;-,P by an i’or Milton L one B.S., M.S. Major USAF Approved

Epitaxial lateral overgrowth of GaAs: effect of doping on LPE growth behaviour

NASA Astrophysics Data System (ADS)

Zytkiewicz, Z. R.; Dobosz, D.; Pawlowska, M.

1999-05-01

Results of epitaxial lateral overgrowth (ELO) of GaAs on (001) GaAs substrates by liquid phase epitaxy are reported. We show that by introducing Si, Sn or Te impurities to the Ga-As solution the vertical growth rate is reduced while the lateral growth rate is significantly enhanced, which leads to a growth habit modification. Furthermore, the impurity incorporation into the growing layer is different on the upper and side surfaces of the ELO, reflecting the fundamental differences between the lateral and vertical growth modes. This phenomenon can be applied for studying the temporal development of ELO layers.

GaAs quantum dots in a GaP nanowire photodetector

NASA Astrophysics Data System (ADS)

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

2018-03-01

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

A Theoretical Study of Bulk and Surface Diffusion Processes for Semiconductor Materials Using First Principles Calculations

NASA Astrophysics Data System (ADS)

Roehl, Jason L.

Diffusion of point defects on crystalline surfaces and in their bulk is an important and ubiquitous phenomenon affecting film quality, electronic properties and device functionality. A complete understanding of these diffusion processes enables one to predict and then control those processes. Such understanding includes knowledge of the structural, energetic and electronic properties of these native and non-native point defect diffusion processes. Direct experimental observation of the phenomenon is difficult and microscopic theories of diffusion mechanisms and pathways abound. Thus, knowing the nature of diffusion processes, of specific point defects in given materials, has been a challenging task for analytical theory as well as experiment. The recent advances in computing technology have been a catalyst for the rise of a third mode of investigation. The advent of tremendous computing power, breakthroughs in algorithmic development in computational applications of electronic density functional theory now enables direct computation of the diffusion process. This thesis demonstrates such a method applied to several different examples of point defect diffusion on the (001) surface of gallium arsenide (GaAs) and the bulk of cadmium telluride (CdTe) and cadmium sulfide (CdS). All results presented in this work are ab initio, total-energy pseudopotential calculations within the local density approximation to density-functional theory. Single particle wavefunctions were expanded in a plane-wave basis and reciprocal space k-point sampling was achieved by Monkhorst-Pack generated k-point grids. Both surface and bulk computations employed a supercell approach using periodic boundary conditions. Ga adatom adsorption and diffusion processes were studied on two reconstructions of the GaAs(001) surface including the c(4x4) and c(4x4)-heterodimer surface reconstructions. On the GaAs(001)- c(4x4) surface reconstruction, two distinct sets of minima and transition sites were

Inverted thermal conversion - GaAs, a new alternative material for integrated circuits

NASA Technical Reports Server (NTRS)

Lagowski, J.; Gatos, H. C.; Kang, C. H.; Skowronski, M.; Ko, K. Y.

1986-01-01

A new type of GaAs is developed which exhibits inverted thermal conversion (ITC); i.e., it converts from conducting to semiinsulating upon annealing at about 850 C. In device fabrication, its low resistivity prior to high-temperature processing differentiates ITC GaAs from the standard semiinsulating GaAs. The ITC characteristics are obtained through control of the concentration of the midgap donor EL2 based on heat treatment and crystal-growth modification. Thus EL2 does not exist in the conducting state of ITC GaAs. Conversion to the semiinsulating state during 850 C annealing is caused by the formation of EL2.

Investigation of the fabrication mechanism of self-assembled GaAs quantum rings grown by droplet epitaxy.

PubMed

Tong, C Z; Yoon, S F

2008-09-10

We have directly imaged the formation of a GaAs quantum ring (QR) using droplet epitaxy followed by annealing in arsenic ambient. Based on the atomic force micrograph measurement and the analysis of surface energy, we determine that the formation of self-assembled GaAs QRs is due to the gallium atom's diffusion and crystallization driven by the gradient of surface energy. The phenomenon that GaAs is etched by the gallium droplets is reported and analyzed. It has been demonstrated that the epitaxy layers, such as AlAs and InGaP, can be used as the etching stop layer and hence can be used to control the shape and height of the QRs.

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.

Paths to light trapping in thin film GaAs solar cells.

PubMed

Xiao, Jianling; Fang, Hanlin; Su, Rongbin; Li, Kezheng; Song, Jindong; Krauss, Thomas F; Li, Juntao; Martins, Emiliano R

2018-03-19

It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

Concepts for thin-film GaAs concentrator cells. [for solar photovoltaic space power systems

NASA Technical Reports Server (NTRS)

Spitzer, M. B.; Gale, R. P.; Mcclelland, R.; King, B.; Dingle, J.

1989-01-01

The development of advanced GaAs concentrator solar cells, and in particular, the use of CLEFT (cleavage of lateral epitaxial films for transfer) processes for formation of thin-film structures is reported. The use of CLEFT has made possible processing of the back, and cells with back surface grids are discussed. Data on patterned junction development are presented; such junctions are expected to be useful in back surface applications requiring point contacts, grating structures, and interdigitated back contacts. CLEFT concentrator solar cells with grids on the front and back surfaces are reported here; these cells are 4 microns thick and are bonded to glass covers for support. Air mass zero efficiency of 18.8 percent has been obtained for a CLEFT concentrator operating at 18.5 suns.

Morphological instability of GaAs (7 1 1)A: A transition between (1 0 0) and (5 1 1) terraces

NASA Astrophysics Data System (ADS)

Yazdanpanah, V. R.; Wang, Zh. M.; Salamo, G. J.

2005-06-01

We report on the use of reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) study that indicates that the GaAs (7 1 1)A is right at the transition between vicinal GaAs (1 0 0) and vicinal GaAs (5 1 1)A surfaces and that a variation of the As overpressure switches the surface morphology between the two vicinal surfaces. The steps on the vicinal (1 0 0) surface have a width of 1.5 nm creating a staircase surface with excellent possibilities for growth of quantum wells. As-rich conditions can be described by vicinal (5 1 1)A surfaces with a width of 3.5 nm. This surface could find applications as a template for quantum wire growth. The observation suggests that the transition between these two morphologies is understandable based on the increase in surface energy of a vicinal (1 0 0) surface as the step separation approaches the dimer reconstructed separation.

GaAs QWIP Array Containing More Than a Million Pixels

NASA Technical Reports Server (NTRS)

Jhabvala, Murzy; Choi, K. K.; Gunapala, Sarath

2005-01-01

A 1,024 x 1,024-pixel array of quantum-well infrared photodetectors (QWIPs) has been built on a 1.8 x 1.8- cm GaAs chip. In tests, the array was found to perform well in detecting images at wavelengths from 8 to 9 m in operation at temperatures between 60 and 70 K. The largest-format QWIP prior array that performed successfully in tests contained 512 x 640 pixels. There is continuing development effort directed toward satisfying actual and anticipated demands to increase numbers of pixels and pixel sizes in order to increase the imaging resolution of infrared photodetector arrays. A 1,024 x 1,024-pixel and even larger formats have been achieved in the InSb and HgCdTe material systems, but photodetector arrays in these material systems are very expensive and manufactured by fewer than half a dozen large companies. In contrast, GaAs-photodetector-array technology is very mature, and photodetectors in the GaAs material system can be readily manufactured by a wide range of industrial technologists, by universities, and government laboratories. There is much similarity between processing in the GaAs industry and processing in the pervasive silicon industry. With respect to yield and cost, the performance of GaAs technology substantially exceeds that of InSb and HgCdTe technologies. In addition, GaAs detectors can be designed to respond to any portion of the wavelength range from 3 to about 16 micrometers - a feature that is very desirable for infrared imaging. GaAs QWIP arrays, like the present one, have potential for use as imaging sensors in infrared measuring instruments, infrared medical imaging systems, and infrared cameras.

Design of quantum efficiency measurement system for variable doping GaAs photocathode

NASA Astrophysics Data System (ADS)

Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

2008-03-01

To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

Growth of semimetallic ErAs films epitaxially embedded in GaAs

NASA Astrophysics Data System (ADS)

Crook, Adam M.; Nair, Hari P.; Lee, Jong H.; Ferrer, Domingo A.; Akinwande, Deji; Bank, Seth R.

2011-10-01

We present models for the growth and electrical conductivity of ErAs films grown with the nanoparticle-seeded film growth technique. This growth mode overcomes the mismatch in rotational symmetry between the rocksalt ErAs crystal structure and the zincblende GaAs crystal structure. This results in films of ErAs grown through a thin film of GaAs that preserves the symmetry of the substrate. The conductivity of the films, as a function of film thickness, are investigated and a surface roughness model is used to explain observed trends. Transmission electron micrographs confirm the suppression of anti-phase domains. A simple diffusion model is developed to describe the diffusion and incorporation of surface erbium into subsurface ErAs layers and predict potential failure mechanisms of the growth method.

Structure, bonding nature, and binding energy of alkanethiolate on As-rich GaAs (001) surface: a density functional theory study.

PubMed

Voznyy, Oleksandr; Dubowski, Jan J

2006-11-30

Chemisorption of alkanethiols on As-rich GaAs (001) surface under a low coverage condition was studied using first principles density functional calculations in a periodic supercell approach. The thiolate adsorption site, tilt angle and its direction are dictated by the high directionality of As dangling bond and sulfur 3p orbital participating in bonding and steric repulsion of the first three CH2 units from the surface. Small charge transfer between thiolate and surface, strong dependence of total energy on tilt angle, and a relatively short length of 2.28 A of the S-As bond indicate the highly covalent nature of the bonding. Calculated binding energy of 2.1 eV is consistent with the available experimental data.

Hydride VPE: the unexpected process for the fast growth of GaAs and GaN nanowires with record aspect ratio and polytypism-free crystalline structure

NASA Astrophysics Data System (ADS)

André, Yamina; Trassoudaine, Agnès.; Avit, Geoffrey; Lekhal, Kaddour; Ramdani, Mohammed R.; Leroux, Christine; Monier, Guillaume; Varenne, Christelle; Hoggan, Philip; Castelluci, Dominique; Bougerol, Catherine; Réveret, François; Leymarie, Joël.; Petit, Elodie; Dubrovskii, Vladimir G.; Gil, Evelyne

2013-12-01

Hydride Vapor Phase Epitaxy (HVPE) makes use of chloride III-Cl and hydride V-H3 gaseous growth precursors. It is known as a near-equilibrium process, providing the widest range of growth rates from 1 to more than 100 μm/h. When it comes to metal catalyst-assisted VLS (vapor-liquid-solid) growth, the physics of HVPE growth is maintained: high dechlorination frequency, high axial growth rate of nanowires (NWs) up to 170 μm/h. The remarkable features of NWs grown by HVPE are the untapered morphology with constant diameter and the stacking fault-free crystalline phase. Record pure zinc blende cubic phase for 20 μm long GaAs NWs with radii of 10 and 5 nm is shown. The absence of wurtzite phase in GaAs NWs grown by HVPE whatever the diameter is discussed with respect to surface energetic grounds and kinetics. Ni assisted, Ni-Au assisted and catalyst-free HVPE growth of wurtzite GaN NWs is also addressed. Micro-photoluminescence spectroscopy analysis revealed GaN nanowires of great optical quality, with a FWHM of 1 meV at 10 K for the neutral donor bound exciton transition.

Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

NASA Astrophysics Data System (ADS)

Debehets, J.; Homm, P.; Menghini, M.; Chambers, S. A.; Marchiori, C.; Heyns, M.; Locquet, J. P.; Seo, J. W.

2018-05-01

In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-level pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.

GaAs Monolithic Microwave Subsystem Technology Base

DTIC Science & Technology

1980-01-01

To provide a captive source of reliable, high-quality GaAs substrates, a new crystal growth and substrate preparation facility which utilizes a high...Symp. GaAs and Related Compounds, Inst. Phys. Conf. Ser. 24, 6. 20. Wood, Woodcock and Harris (1978) GaAs and Related Compounds, Inst. Phys. Conf

Electro-optic investigation of the n-alkanethiol GaAs(001) interface: Surface phenomena and applications to photoluminescence-based biosensing

NASA Astrophysics Data System (ADS)

Marshall, Gregory M.

Semiconductor surfaces coupled to molecular structures derived from organic chemistry form the basis of an emerging class of field-effect devices. In addition to molecular electronics research, these interfaces are developed for a variety of sensor applications in the electronic and optical domains. Of practical interest are self-assembled monolayers (SAMs) comprised of n-alkanethiols [HS(CH2)n], which couple to the GaAs(001) surface through S-GaAs covalent bond formation. These SAMs offer potential functionality in terms of the requisite sensor chemistry and the passivation effect such coupling is known to afford. In this thesis, the SAM-GaAs interface is investigated in the context of a photonic biosensor based on photoluminescence (PL) variation. The scope of the work is categorized into three parts: i) the structural and compositional analysis of the surface using X-ray photoelectron spectroscopy (XPS), ii) the investigation of electronic properties at the interface under equilibrium conditions using infrared (IR) spectroscopy, the Kelvin probe method, and XPS, and iii) the analysis of the electro-optic response under steady-state photonic excitation, specifically, the surface photovoltage (SPV) and PL intensity. Using a partial overlayer model of angle-resolved XPS spectra in which the component assignments are shown to be quantitatively valid, the coverage fraction of methyl-terminated SAMs is shown to exceed 90%. Notable among the findings are a low-oxide, Ga-rich surface with elemental As present in sub-monolayer quantities consistent with theoretical surface morphologies. Modal analysis of transmission IR spectra show that the SAM molecular order is sufficient to support a Beer-Lambert determination of the IR optical constants, which yields the observation of a SAM-specific absorbance enhancement. By correlation of the IR absorbance with the SAM dipole layer potential, the enhancement mechanism is attributed to the vibrational moments added by the

Measurement of minority carrier diffusion lengths in GaAs nanowires by a nanoprobe technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Darbandi, A.; Watkins, S. P., E-mail: simonw@sfu.ca

Minority carrier diffusion lengths in both p-type and n-type GaAs nanowires were studied using electron beam induced current by means of a nanoprobe technique without lithographic processing. The diffusion lengths were determined for Au/GaAs rectifying junctions as well as axial p-n junctions. By incorporating a thin lattice-matched InGaP passivating shell, a 2-fold enhancement in the minority carrier diffusion lengths and one order of magnitude reduction in the surface recombination velocity were achieved.

Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

PubMed

Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

2016-06-01

Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

GaAs VLSI for aerospace electronics

NASA Technical Reports Server (NTRS)

Larue, G.; Chan, P.

1990-01-01

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

Surface Chemistry and Interface Evolution during the Atomic Layer Deposition of High-k Metal Oxides on InAs(100) and GaAs(100) Surfaces

NASA Astrophysics Data System (ADS)

Henegar, Alex J.

Device scaling has been key for creating faster and more powerful electronic devices. Integral circuit components like the metal-oxide semiconductor field-effect transistor (MOSFET) now rely on material deposition techniques, like atomic layer deposition (ALD), that possess atomic-scale thickness precision. At the heart of the archetypal MOSFET is a SiO2/Si interface which can be formed to near perfection. However when the thickness of the SiO 2 layer is shrunk down to a few nanometers several complications arise like unacceptably high leakage current and power consumption. Replacing Si with III-V semiconductors and SiO2 with high-k dielectric materials is appealing but comes with its own set of challenges. While SiO2 is practically defect-free, the native oxides of III-Vs are poor dielectrics. In this dissertation, the surface chemistry and interface evolution during the ALD of high-k metal oxides on Si(100), GaAs(100) and InAs(100) was studied. In particular, the surface chemistry and crystallization of TiO2 films grown on Si(100) was investigated using transmission Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Large, stable, and highly reactive anatase TiO2 grains were found to form during a post-deposition heat treatment after the ALD at 100 °C. The remainder of this work was focused on the evolution of the interfacial oxides during the deposition of TiO2 and Al2O3 on InAs(100) and GaAs(100) and during the deposition of Ta2O 5 on InAs(100). In summary the ALD precursor type, deposited film, and substrate had an influence in the evolution of the native oxides. Alkyl amine precursors fared better at removing the native oxides but the deposited films (TiO2 and Ta2O5) were susceptible to significant native oxide diffusion. The alkyl precursor used for the growth of Al 2O3 was relatively ineffective at removing the oxides but was

Investigation of ZnSe-coated silicon substrates for GaAs solar cells

NASA Technical Reports Server (NTRS)

Huber, Daniel A.; Olsen, Larry C.; Dunham, Glen; Addis, F. William

1993-01-01

Studies are being carried out to determine the feasibility of using ZnSe as a buffer layer for GaAs solar cells grown on silicon. This study was motivated by reports in the literature indicating ZnSe films had been grown by metallorganic chemical vapor deposition (MOCVD) onto silicon with EPD values of 2 x 10(exp 5) cm(sup -2), even though the lattice mismatch between silicon and ZnSe is 4.16 percent. These results combined with the fact that ZnSe and GaAs are lattice matched to within 0.24 percent suggest that the prospects for growing high efficiency GaAs solar cells onto ZnSe-coated silicon are very good. Work to date has emphasized development of procedures for MOCVD growth of (100) ZnSe onto (100) silicon wafers, and subsequent growth of GaAs films on ZnSe/Si substrates. In order to grow high quality single crystal GaAs with a (100) orientation, which is desirable for solar cells, one must grow single crystal (100) ZnSe onto silicon substrates. A process for growth of (100) ZnSe was developed involving a two-step growth procedure at 450 C. Single crystal, (100) GaAs films were grown onto the (100) ZnSe/Si substrates at 610 C that are adherent and specular. Minority carrier diffusion lengths for the GaAs films grown on ZnSe/Si substrates were determined from photoresponse properties of Al/GaAs Schottky barriers. Diffusion lengths for n-type GaAs films are currently on the order of 0.3 microns compared to 2.0 microns for films grown simultaneously by homoepitaxy.

Diffusion and interface evolution during the atomic layer deposition of TiO{sub 2} on GaAs(100) and InAs(100) surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Liwang; Gougousi, Theodosia, E-mail: gougousi@umbc.edu

2016-01-15

Atomic layer deposition is used to form TiO{sub 2} films from tetrakis dimethyl amino titanium and H{sub 2}O on native oxide GaAs(100) and InAs(100) surfaces. The evolution of the film/substrate interface is examined as a function of the deposition temperature (100–325 °C) using ex situ x-ray photoelectron spectroscopy. An increase in the deposition temperature up to 250 °C leads to enhancement of the native oxide removal. For depositions at 300 °C and above, interface reoxidation is observed during the initial deposition cycles but when the films are thicker than 3 nm, the surface oxides are removed steadily. Based on these observations, two distinct filmmore » growth regimes are identified; up to 250 °C, layer-by-layer dominates while at higher temperatures island growth takes over. Angle resolved x-ray photoelectron spectroscopy measurements performed on 3 nm TiO{sub 2} film deposited at 325 °C on both surfaces demonstrates a very important difference between the two substrates: for GaAs the native oxides remaining in the stack are localized at the interface, while for InAs(100), the indium oxides are mixed in the TiO{sub 2} film.« less

Aging behavior of Au-based ohmic contacts to GaAs

NASA Technical Reports Server (NTRS)

Fatemi, Navid S.

1989-01-01

Gold based alloys, commonly used as ohmic contacts for solar cells, are known to react readily with GaAs. It is shown that the contact interaction with the underlying GaAs can continue even at room temperature upon aging, altering both the electrical characteristics of the contacts and the nearby pn junction. Au-Ge-Ni as-deposited (no heat-treatment) contacts made to thin emitter (0.15 microns) GaAs diodes have shown severe shunting of the pn junction upon aging for several months at room temperature. The heat-treated contacts, despite showing degradation in contact resistance, did not affect the underlying pn junction. Au-Zn-Au contacts to p-GaAs emitter (0.2 microns) diodes, however, showed slight improvement in contact resistance upon 200 C isothermal annealing for several months, without degrading the pn junction. The effect of aging on electrical characteristics of the as-deposited and heat-treated contacts and the nearby pn junction, as well as on the surface morphology of the contacts are presented.

Aging behavior of Au-based ohmic contacts to GaAs

NASA Technical Reports Server (NTRS)

Fatemi, Navid S.

1988-01-01

Gold based alloys, commonly used as ohmic contacts for solar cells, are known to react readily with GaAs. It is shown that the contact interaction with the underlying GaAs can continue even at room temperature upon aging, altering both the electrical characteristics of the contacts and the nearby pn junction. Au-Ge-Ni as-deposited (no heat treatment) contacts made to thin emitter (0.15 micrometer) GaAs diodes have shown severe shunting of the pn junction upon aging for several months at room temperature. The heat-treated contacts, despite showing degradation in contact resistance did not affect the underlying pn junction. Au-Zn-Au contacts to p-GaAs emitter (0.2 micrometer) diodes, however, showed slight improvement in contact resistance upon 200 C isothermal annealing for several months, without degrading the pn junction. The effect of aging on electrical characteristics of the as-deposited and heat-treated contacts and the nearby pn junction, as well as on the surface morphology of the contacts are presented.

Self-catalyzed GaAs nanowires on silicon by hydride vapor phase epitaxy.

PubMed

Dong, Zhenning; André, Yamina; Dubrovskii, Vladimir G; Bougerol, Catherine; Leroux, Christine; Ramdani, Mohammed R; Monier, Guillaume; Trassoudaine, Agnès; Castelluci, Dominique; Gil, Evelyne

2017-03-24

Gold-free GaAs nanowires on silicon substrates can pave the way for monolithic integration of photonic nanodevices with silicon electronic platforms. It is extensively documented that the self-catalyzed approach works well in molecular beam epitaxy but is much more difficult to implement in vapor phase epitaxies. Here, we report the first gallium-catalyzed hydride vapor phase epitaxy growth of long (more than 10 μm) GaAs nanowires on Si(111) substrates with a high integrated growth rate up to 60 μm h -1 and pure zincblende crystal structure. The growth is achieved by combining a low temperature of 600 °C with high gaseous GaCl/As flow ratios to enable dechlorination and formation of gallium droplets. GaAs nanowires exhibit an interesting bottle-like shape with strongly tapered bases, followed by straight tops with radii as small as 5 nm. We present a model that explains the peculiar growth mechanism in which the gallium droplets nucleate and rapidly swell on the silicon surface but then are gradually consumed to reach a stationary size. Our results unravel the necessary conditions for obtaining gallium-catalyzed GaAs nanowires by vapor phase epitaxy techniques.

Detection of oxygen-related defects in GaAs by exo-electron emission spectroscopy

NASA Astrophysics Data System (ADS)

Hulluvarad, Shiva S.; Naddaf, M.; Bhoraskar, S. V.

2001-10-01

The influence of intentional introduction of oxygen, at the surface of GaAs, on its native surface states was studied. Oxygen was made to interact with the surface of GaAs by three different means: (1) by growing native oxides, (2) exposing to oxygen plasma in an electron cyclotron resonance (ECR) plasma reactor and by (3) high energy oxygen ion irradiation. Thermally stimulated exo-electron emission (TSEE) spectroscopy was used to estimate the relative densities and energies of the surface states induced by the three different modes of introducing oxygen. Out of the two native defect levels found in GaAs by TSEE; at 325 K (0.7 eV below Ec) and at 415 K (0.9 below Ec); the former is seen to get broadened or split into multiple peaks in each of the methods. Multiple peaks in TSEE signify the presence of a closely spaced band of defect levels. Therefore the results exclusively point out that oxygen-related complexes contribute to the formation of a band of defects centered at 325 K in TSEE which is correlated to an energy level 0.7 eV below Ec known as the EL2 defect level. The results reported in this paper thus confirm that the TSEE peak at 0.7 eV below Ec is related to oxygen induced defects whereas the peak at 0.9 eV is not affected by the presence of oxygen-related species.

Isolating GaSb membranes grown metamorphically on GaAs substrates using highly selective substrate removal etch processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavrova, Olga; Balakrishnan, Ganesh

2017-02-24

The etch rates of NH 4OH:H 2O 2 and C 6H 8O 7:H 2O 2 for GaAs and GaSb have been investigated to develop a selective etch for GaAs substrates and to isolate GaSb epilayers grown on GaAs. The NH 4OH:H 2O 2 solution has a greater etch rate differential for the GaSb/GaAs material system than C 6H 8O 7:H 2O 2 solution. The selectivity of NH 4OH:H 2O 2 for GaAs/GaSb under optimized etch conditions has been observed to be as high as 11471 ± 1691 whereas that of C 6H 8O 7:H 2O 2 has been measured upmore » to 143 ± 2. The etch contrast has been verified by isolating 2 μm thick GaSb epi-layers that were grown on GaAs substrates. GaSb membranes were tested and characterized with high-resolution X-Ray diffraction (HR-XRD) and atomic force microscopy (AFM).« less

GaAs Solar Cells Grown on Unpolished, Spalled Ge Substrates: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cavalli, Alessandro; Johnston, Steven; Sulas, Dana

Decreasing the cost of single-crystal substrates by wafer reuse techniques has long been sought for III-V solar cells. Controlled spalling of III-V devices is a possible pathway for epitaxial liftoff, which would help reduce costs, but chemo- mechanical polishing after liftoff tends to limit the potential cost savings. Growth on an unpolished spalled surface would be an additional step toward lower costs, but it is crucial to show high efficiency solar cell devices on these unprocessed substrates. In this study, we spalled 2-inch Ge wafers using a Ni stressor layer, and then grew GaAs solar cells by HVPE on themore » spalled Ge surface without any other surface treatment. We show a 12.8% efficient single-junction device, without anti-reflection coating, with quantum efficiency very close to identical devices grown by HVPE on non-spalled GaAs substrates. Demonstrating a high carrier collection on unpolished spalled wafers is a step toward reducing substrate-related liftoff and reuse costs.« less

Self-ordering of InAs nanostructures on (631)A/B GaAs substrates

NASA Astrophysics Data System (ADS)

Eugenio-López, Eric; Alejandro Mercado-Ornelas, Christian; Kisan Patil, Pallavi; Cortes-Mestizo, Irving Eduardo; Ángel Espinoza-Figueroa, José; Gorbatchev, Andrei Yu; Shimomura, Satoshi; Ithsmel Espinosa-Vega, Leticia; Méndez-García, Víctor Hugo

2018-02-01

The high order self-organization of quantum dots is demonstrated in the growth of InAs on a GaAs(631)-oriented crystallographic plane. The unidimensional ordering of the quantum dots (QDs) strongly depends on the As flux beam equivalent pressure (P As) and the cation/anion terminated surface, i.e., A- or B-type GaAs(631). The self-organization of QDs occurs for both surface types along [\\bar{1}13], while the QD shape and size distribution were found to be different for the self-assembly on the A- and B-type surfaces. In addition, the experiments showed that any misorientation from the (631) plane, which results from the buffer layer waviness, does not allow a high order of unidimensional arrangements of QDs. The optical properties were studied by photoluminescence spectroscopy, where good correspondence was obtained between the energy transitions and the size of the QDs.

Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

NASA Astrophysics Data System (ADS)

Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

2012-06-01

GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

HfO2 Gate Dielectric on (NH4)2S Passivated (100) GaAs Grown by Atomic Layer Deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, P.T.; /Stanford U., Materials Sci. Dept.; Sun, Y.

2007-09-28

The interface between hafnium oxide grown by atomic layer deposition and (100) GaAs treated with HCl cleaning and (NH{sub 4}){sub 2}S passivation has been characterized. Synchrotron radiation photoemission core level spectra indicated successful removal of the native oxides and formation of passivating sulfides on the GaAs surface. Layer-by-layer removal of the hafnia film revealed a small amount of As{sub 2}O{sub 3} formed at the interface during the dielectric deposition. Traces of arsenic and sulfur out-diffusion into the hafnia film were observed after a 450 C post-deposition anneal, and may be the origins for the electrically active defects. Transmission electron microscopymore » cross section images showed thicker HfO{sub 2} films for a given precursor exposure on S-treated GaAs versus the non-treated sample. In addition, the valence-band and the conduction-band offsets at the HfO{sub 2}/GaAs interface were deduced to be 3.18 eV and a range of 0.87-0.97 eV, respectively. It appears that HCl+(NH{sub 4})2{sub S} treatments provide a superior chemical passivation for GaAs and initial surface for ALD deposition.« less

Scanning tunneling microscope study of GaAs(001) surfaces grown by migration enhanced epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, J.; Gallagher, M.C.; Willis, R.F.

We report an investigation of the morphology of p-type GaAs(001) surfaces using scanning tunneling microscopy (STM). The substrates were prepared using two methods: migration enhanced epitaxy (MEE) and standard molecular-beam epitaxy (MBE). The STM measurements were performed ex situ using As decapping. Analysis indicates that the overall step density of the MEE samples decreases as the growth temperature is increased. Nominally flat samples grown at 300{degrees}C exhibited step densities of 10.5 steps/1000 {Angstrom} along [ 110] dropping to 2.5 steps at 580{degrees}C. MEE samples exhibited a lower step density than MBE samples. However as-grown surfaces exhibited a larger distribution ofmore » step heights. Annealing the samples reduced the step height distribution exposing fewer atomic layers. Samples grown by MEE at 580{degrees}C and annealed for 2 min displayed the lowest step density and the narrowest step height distribution. All samples displayed an anisotropic step density. We found a ratio of A-type to B-type steps of between 2 and 3 which directly reflects the difference in the incorporation energy at steps. The aspect ratio increased slightly with growth temperature. We found a similar aspect ratio on samples grown by MBE. This indicates that anisotropic growth during MEE, like MBE, is dominated by incorporation kinetics. MEE samples grown at 580{degrees}C and capped immediately following growth exhibited a number of {open_quotes}holes{close_quotes} in the surface. The holes could be eliminated by annealing the surface prior to quenching. 20 refs., 3 figs., 1 tab.« less

InP and GaAs characterization with variable stoichiometry obtained by molecular spray

NASA Technical Reports Server (NTRS)

Massies, J.; Linh, N. T.; Olivier, J.; Faulconnier, P.; Poirier, R.

1979-01-01

Both InP and GaAs surfaces were studied in parallel. A molecular spray technique was used to obtain two semiconductor surfaces with different superficial compositions. The structures of these surfaces were examined by electron diffraction. Electron energy loss was measured spectroscopically in order to determine surface electrical characteristics. The results are used to support conclusions relative to the role of surface composition in establishing a Schottky barrier effect in semiconductor devices.

Three-dimensional lattice rotation in GaAs nanowire growth on hydrogen-silsesquioxane covered GaAs (001) using molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Tran, Dat Q.; Pham, Huyen T.; Higashimine, Koichi; Oshima, Yoshifumi; Akabori, Masashi

2018-05-01

We report on crystallographic behaviors of inclined GaAs nanowires (NWs) self-crystallized on GaAs (001) substrate. The NWs were grown on hydrogen-silsesquioxane (HSQ) covered substrates using molecular beam epitaxy (MBE). Commonly, the epitaxial growth of GaAs < 111>B (B-polar) NWs is prominently observed on GaAs (001); however, we yielded a remarkable number of epitaxially grown GaAs < 111>A (A-polar) NWs in addition to the majorly obtained B-polar NWs. Such NW orientations are always accompanied by a typical inclined angle of 35° from (001) plane. NWs with another inclined angle of 74° were additionally observed and attributed to be < 111>-oriented, not in direct epitaxial relation with the substrate. Such 74° NWs' existence is related to first-order three-dimensional (3D) lattice rotation taking place at the very beginning of the growth. It turns out that spatially 60° lattice rotation around < 111> directions at GaAs seeds is essentially in charge of A- and B-polar 74° NWs. Transmission electron microscope observations reveal a high density of twinning in the B-polar NWs and twin-free characteristic in the A-polar NWs.

All-optical switching in GaAs microdisk resonators by a femtosecond pump-probe technique through tapered-fiber coupling.

PubMed

Lin, Yen-Chih; Mao, Ming-Hua; Lin, You-Ru; Lin, Hao-Hsiung; Lin, Che-An; Wang, Lon A

2014-09-01

We demonstrate ultrafast all-optical switching in GaAs microdisk resonators using a femtosecond pump-probe technique through tapered-fiber coupling. The temporal tuning of the resonant modes resulted from the refractive index change due to photoexcited carrier density variation inside the GaAs microdisk resonator. Transmission through the GaAs microdisk resonator can be modulated by more than 10 dB with a switching time window of 8 ps in the switch-off operation using pumping pulses with energies as low as 17.5 pJ. The carrier lifetime was fitted to be 42 ps, much shorter than that of the bulk GaAs, typically of the order of nanoseconds. The above observation indicates that the surface recombination plays an important role in increasing the switching speed.

Thermal stress cycling of GaAs solar cells

NASA Technical Reports Server (NTRS)

Janousek, B. K.; Francis, R. W.; Wendt, J. P.

1985-01-01

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

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.

Insertion of GaAs MMICs into EW systems

NASA Astrophysics Data System (ADS)

Schineller, E. R.; Pospishil, A.; Grzyb, J.

1989-09-01

Development activities on a microwave/mm-wave monolithic IC (MIMIC) program are described, as well as the methodology for inserting these GaAs IC chips into several EW systems. The generic EW chip set developed on the MIMIC program consists of 23 broadband chip types, including amplifiers, oscillators, mixers, switches, variable attenuators, power dividers, and power combiners. These chips are being designed for fabrication using the multifunction self-aligned gate process. The benefits from GaAs IC insertion are quantified by a comparison of hardware units fabricated with existing MIC and digital ECL technology and the same units manufactured with monolithic technology. It is found that major improvements in cost, reliability, size, weight, and performance can be realized. Examples illustrating the methodology for technology insertion are presented.

Defects in GaAs films grown by MOMBE

NASA Astrophysics Data System (ADS)

Werner, K.; Heinecke, H.; Weyers, M.; Lüth, H.; Balk, P.

1987-02-01

The nature and densities of the defects obtained in MOMBE GaAs films have been studied. In addition to particulate matter deposited on the surface, imperfections in the substrate will lead to defect generation. Furthermore, the rate of generation is strongly affected by the ratio of the pressures of the group III alkyl and the group V hydride in the molecular beams and by the growth temperature, also on defect-free substrates. Doping has no effect on the defect structure of the surface. By proper choice of experimental conditions defect densities below 100 cm -2 may be consistently obtained.

The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study.

PubMed

Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

2014-01-01

First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.

GaAsSb bandgap, surface fermi level, and surface state density studied by photoreflectance modulation spectroscopy

NASA Astrophysics Data System (ADS)

Hwang, J. S.; Tsai, J. T.; Su, I. C.; Lin, H. C.; Lu, Y. T.; Chiu, P. C.; Chyi, J. I.

2012-05-01

The bandgap, surface Fermi level, and surface state density of a series of GaAs1-xSbx surface intrinsic-n+ structures with GaAs as substrate are determined for various Sb mole fractions x by the photoreflectance modulation spectroscopy. The dependence of the bandgap on the mole composition x is in good agreement with previous measurements as well as predictions calculated using the dielectric model of Van Vechten and Bergstresser in Phys. Rev. B 1, 3551 (1970). For a particular composition x, the surface Fermi level is always strongly pinned within the bandgap of GaAs1-xSbx and we find its variation with composition x is well described by a function EF = 0.70 - 0.192 x for 0 ≦ x ≦ 0.35, a result which is notably different from that reported by Chouaib et al. [Appl. Phys. Lett. 93, 041913 (2008)]. Our results suggest that the surface Fermi level is pinned at the midgap of GaAs and near the valence band of the GaSb.

On the dissolution properties of GaAs in Ga

NASA Technical Reports Server (NTRS)

Davidson, M. C.; Moynahan, A. H.

1977-01-01

The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

A GaAs vector processor based on parallel RISC microprocessors

NASA Astrophysics Data System (ADS)

Misko, Tim A.; Rasset, Terry L.

A vector processor architecture based on the development of a 32-bit microprocessor using gallium arsenide (GaAs) technology has been developed. The McDonnell Douglas vector processor (MVP) will be fabricated completely from GaAs digital integrated circuits. The MVP architecture includes a vector memory of 1 megabyte, a parallel bus architecture with eight processing elements connected in parallel, and a control processor. The processing elements consist of a reduced instruction set CPU (RISC) with four floating-point coprocessor units and necessary memory interface functions. This architecture has been simulated for several benchmark programs including complex fast Fourier transform (FFT), complex inner product, trigonometric functions, and sort-merge routine. The results of this study indicate that the MVP can process a 1024-point complex FFT at a speed of 112 microsec (389 megaflops) while consuming approximately 618 W of power in a volume of approximately 0.1 ft-cubed.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, Harry C.; Lagowski, Jacek

1989-01-01

The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

NASA Astrophysics Data System (ADS)

Louarn, K.; Claveau, Y.; Marigo-Lombart, L.; Fontaine, C.; Arnoult, A.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

2018-04-01

In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm‑2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

Study of sulfur bonding on gallium arsenide (100) surfaces using supercritical fluid extraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabauy, P.; Darici, Y.; Furton, K.G.

1995-12-01

In the last decades Gallium Arsenide (GaAs) has been considered the semiconductor that will replace silicon because of its direct band gap and high electron mobility. Problems with GaAs Fermi level pinning has halted its widespread use in the electronics industry. The formation of oxides on GaAs results in a high density of surface states that effectively pin the surface Fermi level at the midgap. Studies on sulfur passivation have eliminated oxidation and virtually unpinned the Fermi level on the GaAs surface. This has given rise to interest in sulfur-GaAs bonds. In this presentation, we will discuss the types ofmore » sulfur bonds extracted from a sulfur passivated GaAs (100) using Supercritical Fluid (CO2) Extraction (SFE). SFE can be a valuable tool in the study of chemical speciations on semiconductor surfaces. The variables evaluated to effectively study the sulfur species from the GaAs surface include passivation techniques, supercritical fluid temperatures, densities, and extraction times.« less

I-V curve hysteresis induced by gate-free charging of GaAs nanowires' surface oxide

NASA Astrophysics Data System (ADS)

Alekseev, P. A.; Geydt, P.; Dunaevskiy, M. S.; Lähderanta, E.; Haggrén, T.; Kakko, J.-P.; Lipsanen, H.

2017-09-01

The control of nanowire-based device performance requires knowledge about the transport of charge carriers and its limiting factors. We present the experimental and modeled results of a study of electrical properties of GaAs nanowires (NWs), considering their native oxide cover. Measurements of individual vertical NWs were performed by conductive atomic force microscopy (C-AFM). Experimental C-AFM observations with numerical simulations revealed the complex resistive behavior of NWs. A hysteresis of current-voltage characteristics of the p-doped NWs as-grown on substrates with different types of doping was registered. The emergence of hysteresis was explained by the trapping of majority carriers in the surface oxide layer near the reverse-biased barriers under the source-drain current. It was found that the accumulation of charge increases the current for highly doped p+-NWs on n+-substrates, while for moderately doped p-NWs on p+-substrates, charge accumulation decreases the current due to blocking of the conductive channel of NWs.

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.

Technology requirements for GaAs photovoltaic arrays

NASA Technical Reports Server (NTRS)

Scott-Monck, J.; Rockey, D.

1981-01-01

An analysis based on percent GaAs solar cell weight and cost is performed to assess the utility of this cell for future space missions. It is shown that the GaAs substrate cost and the end-of-life (EOL) advantage the cell can provide over the space qualified silicon solar cell are the dominant factors determining potential use. Examples are presented to show that system level advantages resulting from reduction in solar panel area may warrant the use of GaAs at its current weight and projected initial cost provided the EOL advantage over silicon is at least 20 percent.

Molecular Beam Epitaxial Growth of GaAs on (631) Oriented Substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cruz Hernandez, Esteban; Rojas Ramirez, Juan-Salvador; Contreras Hernandez, Rocio

2007-02-09

In this work, we report the study of the homoepitaxial growth of GaAs on (631) oriented substrates by molecular beam epitaxy (MBE). We observed the spontaneous formation of a high density of large scale features on the surface. The hilly like features are elongated towards the [-5, 9, 3] direction. We show the dependence of these structures with the growth conditions and we present the possibility of to create quantum wires structures on this surface.

Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

NASA Astrophysics Data System (ADS)

Mieda, Eiko; Maeda, Tatsuro; Miyata, Noriyuki; Yasuda, Tetsuji; Kurashima, Yuichi; Maeda, Atsuhiko; Takagi, Hideki; Aoki, Takeshi; Yamamoto, Taketsugu; Ichikawa, Osamu; Osada, Takenori; Hata, Masahiko; Ogawa, Arito; Kikuchi, Toshiyuki; Kunii, Yasuo

2015-03-01

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.

Supernormal hardness increase of dilute Ga(As, N) thin films

NASA Astrophysics Data System (ADS)

Berggren, Jonas; Hanke, Michael; Luna, Esperanza; Trampert, Achim

2017-03-01

Hardness of epitaxial GaAs1-xNx films on GaAs(001) with different film thicknesses, varying from 80 to 700 nm, and nitrogen compositions x between zero (pure GaAs) and 0.031, were studied by means of nano-indentation. As a result, a disproportionate and monotonic increase by 17% in hardness was proved in the dilute range from GaAs to GaAs0.969N0.031. We are tracing this observation to solid solution strengthening, an extrinsic effect based on dislocation pinning due to interstitial nitrogen. On the other hand, intrinsic effects related to different electronegativities of As and N (i.e., altered bonding conditions) could be ruled out. Furthermore, in tensilely strained GaAs1-xNx layers, the appearance of cracks acts as the main strain relieving mechanism. A correlation between cracking and hardness reduction is investigated and discussed as a further relaxation pathway.

Kinetic modeling of microscopic processes during electron cyclotron resonance microwave plasma-assisted molecular beam epitaxial growth of GaN/GaAs-based heterostructures

NASA Astrophysics Data System (ADS)

Bandić, Z. Z.; Hauenstein, R. J.; O'Steen, M. L.; McGill, T. C.

1996-03-01

Microscopic growth processes associated with GaN/GaAs molecular beam epitaxy (MBE) are examined through the introduction of a first-order kinetic model. The model is applied to the electron cyclotron resonance microwave plasma-assisted MBE (ECR-MBE) growth of a set of δ-GaNyAs1-y/GaAs strained-layer superlattices that consist of nitrided GaAs monolayers separated by GaAs spacers, and that exhibit a strong decrease of y with increasing T over the range 540-580 °C. This y(T) dependence is quantitatively explained in terms of microscopic anion exchange, and thermally activated N surface-desorption and surface-segregation processes. N surface segregation is found to be significant during GaAs overgrowth of GaNyAs1-y layers at typical GaN ECR-MBE growth temperatures, with an estimated activation energy Es˜0.9 eV. The observed y(T) dependence is shown to result from a combination of N surface segregation/desorption processes.

Physical mechanism of coherent acoustic phonons generation and detection in GaAs semiconductor

NASA Astrophysics Data System (ADS)

Babilotte, P.; Morozov, E.; Ruello, P.; Mounier, D.; Edely, M.; Breteau, J.-M.; Bulou, A.; Gusev, V.

2007-12-01

We first describe the picosecond acoustic interferometry study of GaAs with two-colors pump-probe laser pulses. The dependence of the generation process on the pump wavelength and the detection process on the probe wavelength both can cause the shift in the phase of the Brillouin signal. Secondly, in order to distinguish the short high frequency wideband acoustic pulse from low frequency Brillouin contribution, we accomplished experiments with (100)GaAs semiconductor coated by a transparent and photoelastically inactive thin film, serving a delay line for the acoustic pulse. Even with highly penetrating pump light (approx 680nm), short acoustic disturbances of approx 7ps of duration have been registered.

Doping assessment in GaAs nanowires.

PubMed

Goktas, N Isik; Fiordaliso, E M; LaPierre, R R

2018-06-08

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p-n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs was studied. The GaAs NWs were grown on (111) Si by molecular beam epitaxy using the self-assisted method. The dopant incorporation in the self-assisted GaAs NWs was investigated using Raman spectroscopy, photoluminescence, secondary ion mass spectrometry and electron holography. Be-doped NWs showed similar carrier concentration as compared to thin film (TF) standards. However, Te-doped NWs showed at least a one order of magnitude lower carrier concentration as compared to TF standards. Dopant incorporation mechanisms in NWs are discussed.

Doping assessment in GaAs nanowires

NASA Astrophysics Data System (ADS)

Isik Goktas, N.; Fiordaliso, E. M.; LaPierre, R. R.

2018-06-01

Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p–n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs was studied. The GaAs NWs were grown on (111) Si by molecular beam epitaxy using the self-assisted method. The dopant incorporation in the self-assisted GaAs NWs was investigated using Raman spectroscopy, photoluminescence, secondary ion mass spectrometry and electron holography. Be-doped NWs showed similar carrier concentration as compared to thin film (TF) standards. However, Te-doped NWs showed at least a one order of magnitude lower carrier concentration as compared to TF standards. Dopant incorporation mechanisms in NWs are discussed.

Nonlinear response of GaAs gratings in the extraordinary transmission regime.

PubMed

Vincenti, Maria Antonietta; de Ceglia, Domenico; Scalora, Michael

2011-12-01

We theoretically describe a way to enhance harmonic generation from subwavelength slits milled on semiconductor substrates in strongly absorptive regimes. The metal-like response typical of semiconductors, like GaAs and GaP, triggers enhanced transmission and nonlinear optical phenomena in the deep UV range. We numerically study correlations between linear and nonlinear responses and their intricacies in infinite arrays, and highlight differences between nonlinear surface and magnetic sources, and intrinsic χ((2)) and χ((3)) contributions to harmonic generation. The results show promising efficiencies at wavelengths below 120 nm, and reveal coupling of TE and TM polarizations for pump and harmonic signals. A downconversion process that can regenerate pump photons with polarization orthogonal to the incident pump is also discussed. © 2011 Optical Society of America

Formation and photoluminescence of GaAs1-xNx dilute nitride achieved by N-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

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

2014-07-01

In this paper, we present the fabrication of dilute nitride semiconductor GaAs1-xNx by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1 = 0.38% and ximp2 = 0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs1-xNx samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1 = 0.38% and ximp2 = 0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.

Light-Emitting GaAs Nanowires on a Flexible Substrate.

PubMed

Valente, João; Godde, Tillmann; Zhang, Yunyan; Mowbray, David J; Liu, Huiyun

2018-06-18

Semiconductor nanowire-based devices are among the most promising structures used to meet the current challenges of electronics, optics and photonics. Due to their high surface-to-volume ratio and excellent optical and electrical properties, devices with low power, high efficiency and high density can be created. This is of major importance for environmental issues and economic impact. Semiconductor nanowires have been used to fabricate high performance devices, including detectors, solar cells and transistors. Here, we demonstrate a technique for transferring large-area nanowire arrays to flexible substrates while retaining their excellent quantum efficiency in emission. Starting with a defect-free self-catalyzed molecular beam epitaxy (MBE) sample grown on a Si substrate, GaAs core-shell nanowires are embedded in a dielectric, removed by reactive ion etching and transferred to a plastic substrate. The original structural and optical properties, including the vertical orientation, of the nanowires are retained in the final plastic substrate structure. Nanowire emission is observed for all stages of the fabrication process, with a higher emission intensity observed for the final transferred structure, consistent with a reduction in nonradiative recombination via the modification of surface states. This transfer process could form the first critical step in the development of flexible nanowire-based light-emitting devices.

High-temperature degradation-free rapid thermal annealing of GaAs and InP

NASA Astrophysics Data System (ADS)

Pearton, Stephen J.; Katz, Avishay; Geva, Michael

1991-04-01

Rapid thermal annealing of GaAs and InP within enclosed SiC-coated graphite susceptors is shown to eliminate slip formation during implant activation treatments and to provide much better protection against surface degradation at the edges of wafers compared to the more conventional proximity method. Two different types of susceptor were investigated-the first type must be charged with As or P prior to the annealing cycles while the second type incorporates small reservoirs into the susceptor which provide a continuous overpressure of the group V species. Degradation-free annealing of patterned metallized wafers is possible using the latter type of susceptor. The activation of Si and Be implants in GaAs by RTA is also discussed.

Manipulation of morphology and structure of the top of GaAs nanowires grown by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Li, Lixia; Pan, Dong; Yu, Xuezhe; So, Hyok; Zhao, Jianhua

2017-10-01

Self-catalyzed GaAs nanowires (NWs) are grown on Si (111) substrates by molecular-beam epitaxy. The effect of different closing sequences of the Ga and As cell shutters on the morphology and structural phase of GaAs NWs is investigated. For the sequences of closing the Ga and As cell shutters simultaneously or closing the As cell shutter 1 min after closing the Ga cell shutter, the NWs grow vertically to the substrate surface. In contrast, when the As cell shutter is closed first, maintaining the Ga flux is found to be critical for the following growth of GaAs NWs, which can change the growth direction from [111] to < 11\\bar{1}> . The evolution of the morphology and structural phase transition at the tips of these GaAs NWs confirm that the triple-phase-line shift mode is at work even for the growth with different cell shutter closing sequences. Our work will provide new insights for better understanding of the growth mechanism and realizing of the morphology and structure control of the GaAs NWs. Project supported partly by the MOST of China (No. 2015CB921503), the National Natural Science Foundation of China (Nos. 61504133, 61334006, 61404127), and Youth Innovation Promotion Association, CAS (No. 2017156).

Fundamental role of arsenic flux in nanohole formation by Ga droplet etching on GaAs(001)

PubMed Central

2014-01-01

Nanoholes with a depth in the range of tens of nanometers can be formed on GaAs(001) surfaces at a temperature of 500°C by local etching after Ga droplet formation. In this work, we demonstrate that the local etching or nanodrilling process starts when the Ga droplets are exposed to arsenic. The essential role of arsenic in nanohole formation is demonstrated sequentially, from the initial Ga droplets to the final stage consisting of nanoholes surrounded by ringlike structures at the surface and Ga droplets consumed. The kinetics of local etching depends on the arsenic flux intensity, while the ringlike structures are basically the same as those formed underneath the droplets in the absence of arsenic. These structures show motifs with well-defined crystalline facets that correspond to those expected from surface energy minimization. These experimental results are qualitatively analyzed for a better understanding of the nanohole formation underlying processes. PMID:24994962

Electrode pattern design for GaAs betavoltaic batteries

NASA Astrophysics Data System (ADS)

Haiyang, Chen; Jianhua, Yin; Darang, Li

2011-08-01

The sensitivities of betavoltaic batteries and photovoltaic batteries to series and parallel resistance are studied. Based on the study, an electrode pattern design principle of GaAs betavoltaic batteries is proposed. GaAs PIN junctions with and without the proposed electrode pattern are fabricated and measured under the illumination of 63Ni. Results show that the proposed electrode can reduce the backscattering and shadowing for the beta particles from 63Ni to increase the GaAs betavoltaic battery short circuit currents effectively but has little impact on the fill factors and ideal factors.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Placidi, E.; Dipartimento di Fisica, Universita di Roma 'Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy; Arciprete, F.

2012-10-01

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

Energetics and Dynamics of GaAs Epitaxial Growth via Quantum Wave Packet Studies

NASA Technical Reports Server (NTRS)

Dzegilenko, Fedor N.; Saini, Subhash (Technical Monitor)

1998-01-01

The dynamics of As(sub 2) molecule incorporation into the flat Ga-terminated GaAs(100) surface is studied computationally. The time-dependent Schrodinger equation is solved on a two-dimensional potential energy surface obtained using density functional theory calculations. The probabilities of trapping and subsequent dissociation of the molecular As(sub 2) bond are calculated as a function of beam translational energy and vibrational quantum number of As(sub 2).

Understanding and Curing Structural Defects in Colloidal GaAs Nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srivastava, Vishwas; Liu, Wenyong; Janke, Eric M.

2017-02-22

Nearly three decades since the first report on the synthesis of colloidal GaAs nanocrystals (NCs), the preparation and properties of this material remain highly controversial. Traditional synthetic routes either fail to produce the GaAs phase or result in materials that do not show expected optical properties such as excitonic transitions. In this work, we demonstrate a variety of synthetic routes toward crystalline GaAs NCs. By using a combination of Raman, EXAFS and transient absorption spectroscopies, we conclude that unusual optical properties of 2 colloidal GaAs NCs can be related to the presence of vacancies and lattice disorder. We introduce novelmore » molten salt based annealing approach to alleviate these structural defects and show the emergence of size-dependent excitonic transitions in colloidal GaAs quantum dots.« less

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.

Temperature effect on the coupling between coherent longitudinal phonons and plasmons in n -type and p -type GaAs

NASA Astrophysics Data System (ADS)

Hu, Jianbo; Zhang, Hang; Sun, Yi; Misochko, Oleg V.; Nakamura, Kazutaka G.

2018-04-01

The coupling between longitudinal optical (LO) phonons and plasmons plays a fundamental role in determining the performance of doped semiconductor devices. In this work, we report a comparative investigation into the dependence of the coupling on temperature and doping in n - and p -type GaAs by using ultrafast coherent phonon spectroscopy. A suppression of coherent oscillations has been observed in p -type GaAs at lower temperature, strikingly different from n -type GaAs and other materials in which coherent oscillations are strongly enhanced by cooling. We attribute this unexpected observation to a cooling-induced elongation of the depth of the depletion layer which effectively increases the screening time of the surface field due to a slow diffusion of photoexcited carriers in p -type GaAs. Such an increase breaks the requirement for the generation of coherent LO phonons and, in turn, LO phonon-plasmon coupled modes because of their delayed formation in time.

Gate Drain Underlapped-PNIN-GAA-TFET for Comprehensively Upgraded Analog/RF Performance

NASA Astrophysics Data System (ADS)

Madan, Jaya; Chaujar, Rishu

2017-02-01

This work integrates the merits of gate-drain underlapping (GDU) and N+ source pocket on cylindrical gate all around tunnel FET (GAA-TFET) to form GDU-PNIN-GAA-TFET. It is analysed that the source pocket located at the source-channel junction narrows the tunneling barrier width at the tunneling junction and thereby enhances the ON-state current of GAA-TFET. Further, it is obtained that the GDU resists the extension of carrier density (built-up under the gated region) towards the drain side (under the underlapped length), thereby suppressing the ambipolar current and reducing the parasitic capacitances of GAA-TFET. Consequently, the amalgamated merits of both engineering schemes are obtained in GDU-PNIN-GAA-TFET that thus conquers the greatest challenges faced by TFET. Thus, GDU-PNIN-GAA-TFET results in an up-gradation in the overall performance of GAA-TFET. Moreover, it is realised that the RF figure of merits FOMs such as cut-off frequency (fT) and maximum oscillation frequency (fMAX) are also considerably improved with integration of source pocket on GAA-TFET. Thus, the improved analog and RF performance of GDU-PNIN-GAA-TFET makes it ideal for low power and high-speed applications.

Crystal Orientation Controlled Photovoltaic Properties of Multilayer GaAs Nanowire Arrays.

PubMed

Han, Ning; Yang, Zai-Xing; Wang, Fengyun; Yip, SenPo; Li, Dapan; Hung, Tak Fu; Chen, Yunfa; Ho, Johnny C

2016-06-28

In recent years, despite significant progress in the synthesis, characterization, and integration of various nanowire (NW) material systems, crystal orientation controlled NW growth as well as real-time assessment of their growth-structure-property relationships still presents one of the major challenges in deploying NWs for practical large-scale applications. In this study, we propose, design, and develop a multilayer NW printing scheme for the determination of crystal orientation controlled photovoltaic properties of parallel GaAs NW arrays. By tuning the catalyst thickness and nucleation and growth temperatures in the two-step chemical vapor deposition, crystalline GaAs NWs with uniform, pure ⟨110⟩ and ⟨111⟩ orientations and other mixture ratios can be successfully prepared. Employing lift-off resists, three-layer NW parallel arrays can be easily attained for X-ray diffraction in order to evaluate their growth orientation along with the fabrication of NW parallel array based Schottky photovoltaic devices for the subsequent performance assessment. Notably, the open-circuit voltage of purely ⟨111⟩-oriented NW arrayed cells is far higher than that of ⟨110⟩-oriented NW arrayed counterparts, which can be interpreted by the different surface Fermi level pinning that exists on various NW crystal surface planes due to the different As dangling bond densities. All this indicates the profound effect of NW crystal orientation on physical and chemical properties of GaAs NWs, suggesting the careful NW design considerations for achieving optimal photovoltaic performances. The approach presented here could also serve as a versatile and powerful platform for in situ characterization of other NW materials.

High-reliability GaAs image intensifier with unfilmed microchannel plate

NASA Astrophysics Data System (ADS)

Bender, Edward J.; Estrera, Joseph P.; Ford, C. E.; Giordana, A.; Glesener, John W.; Lin, P. P.; Nico, A. J.; Sinor, Timothy W.; Smithson, R. H.

1999-07-01

Current GaAs image intensifier technology requires that the microchannel plate (MCP) have a thin dielectric film on the side facing the photocathode. This protective coating substantially reduces the amount of outgassing of ions and neutral species from the microchannels. The prevention of MCP outgassing is necessary in order to prevent the `poisoning' of the Cs:O surface on the GaAs photocathode. Many authors have experimented with omitting the MCP coating. The results of such experiments invariably lead to an intensifier with a reported useful life of less than 100 hours, due to contamination of the Cs:O layer on the photocathode. Unfortunately, the MCP film is also a barrier to electron transport within the intensifier. Substantial enhancement of the image intensifier operating parameters is the motivation for the removal of the MCP film. This paper presents results showing for the first time that it is possible to fabricate a long lifetime image intensifier with a single uncoated MCP.

Growth of GaAs “nano ice cream cones” by dual wavelength pulsed laser ablation

NASA Astrophysics Data System (ADS)

Schamp, C. T.; Jesser, W. A.; Shivaram, B. S.

2007-05-01

Harmonic generation crystals inherently offer the possibility of using multiple wavelengths of light in a single laser pulse. In the present experiment, the fundamental (1064 nm) and second harmonic (532 nm) wavelengths from an Nd:YAG laser are focused together on GaAs and GaSb targets for ablation. Incident energy densities up to about 45 J/cm 2 at 10 Hz with substrate temperatures between 25 and 600 °C for durations of about 60 s have been used in an ambient gas pressure of about 10 -6 Torr. The ablated material was collected on electron-transparent amorphous carbon films for TEM analysis. Apart from a high density of isolated nanocrystals, the most common morphology observed consists of a crystalline GaAs cone-like structure in contact with a sphere of liquid Ga, resembling an "ice cream cone", typically 50-100 nm in length. For all of the heterostuctures of this type, the liquid/solid/vacuum triple junction is found to correspond to the widest point on the cone. These heterostructures likely form by preferential evaporation of As from molten GaAs drops ablated from the target. The resulting morphology minimizes the interfacial and surface energies of the liquid Ga and solid GaAs.

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.

Stacking InAs quantum dots over ErAs semimetal nanoparticles on GaAs (0 0 1) using molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Zhang, Yuanchang; Eyink, Kurt G.; Grazulis, Lawrence; Hill, Madelyn; Peoples, Joseph; Mahalingam, Krishnamurthy

2017-11-01

Hybrid nanostructures are known to elicit an enhanced optical response. We study the directed alignment of ErAs metal nanoparticle (NP) and InAs quantum dot (QD) using molecular beam eptaxy (MBE) in a GaAs matrix. Due to high surface free energy caused by the crystal structure difference, overgrowth of an ErAs NP with GaAs forms a depression that condenses subsequent InAs adatoms to form an inverted QD self-aligned to the underlying ErAs NP. The ErAs NP growth, GaAs overgrowth, and InAs QD deposition were carefully controlled and studied with transmission electron microscopy (TEM) and atomic force microscopy (AFM) to investigate their effects on the QD-NP alignment.

Planar regions of GaAs (001) prepared by Ga droplet motion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Changxi, E-mail: changxi.zheng@monash.edu; Tang, Wen-Xin; Jesson, David E., E-mail: jessonDE@cardiff.ac.uk

2016-07-15

The authors describe a simple method for obtaining planar regions of GaAs (001) suitable for surface science studies. The technique, which requires no buffer layer growth, atomic hydrogen source, or the introduction of As flux, employs controllable Ga droplet motion to create planar trail regions during Langmuir evaporation. Low-energy electron microscopy/diffraction techniques are applied to monitor the droplet motion and characterize the morphology and the surface reconstruction. It is found that the planar regions exhibit atomic flatness at the level of a high-quality buffer layer.

Strain-driven growth of GaAs(111) quantum dots with low fine structure splitting

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yerino, Christopher D.; Jung, Daehwan; Lee, Minjoo Larry, E-mail: minjoo.lee@yale.edu

2014-12-22

Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting (FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSSmore » with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters.« less

Interface structure and composition of MoO3/GaAs(0 0 1)

NASA Astrophysics Data System (ADS)

Sarkar, Anirban; Ashraf, Tanveer; Grafeneder, Wolfgang; Koch, Reinhold

2018-04-01

We studied growth, structure, stress, oxidation state as well as surface and interface structure and composition of thermally-evaporated thin MoO3 films on the technologically important III/V-semiconductor substrate GaAs(0 0 1). The MoO3 films grow with Mo in the 6+  oxidation state. The electrical resistance is tunable by the oxygen partial pressure during deposition from transparent insulating to semi-transparant halfmetallic. In the investigated growth temperature range (room temperature to 200 °C) no diffraction spots are detected by x-ray diffraction. However, high resolution transmission electron microscopy reveals the formation of MoO3 nanocrystal grains with diameters of 5–8 nm. At the interface a  ≈3 nm-thick intermediate layer has formed, where the single-crystal lattice of GaAs gradually transforms to the nanocrystalline MoO3 structure. This interpretation is corroborated by our in situ and real-time stress measurements evidencing a two-stage growth process as well as by elemental interface analysis revealing coexistance of Ga, As, Mo, and oxygen in a intermediate layer of 3–4 nm.

Comparisons of single event vulnerability of GaAs SRAMS

NASA Astrophysics Data System (ADS)

Weatherford, T. R.; Hauser, J. R.; Diehl, S. E.

1986-12-01

A GaAs MESFET/JFET model incorporated into SPICE has been used to accurately describe C-EJFET, E/D MESFET and D MESFET/resistor GaAs memory technologies. These cells have been evaluated for critical charges due to gate-to-drain and drain-to-source charge collection. Low gate-to-drain critical charges limit conventional GaAs SRAM soft error rates to approximately 1E-6 errors/bit-day. SEU hardening approaches including decoupling resistors, diodes, and FETs have been investigated. Results predict GaAs RAM cell critical charges can be increased to over 0.1 pC. Soft error rates in such hardened memories may approach 1E-7 errors/bit-day without significantly reducing memory speed. Tradeoffs between hardening level, performance and fabrication complexity are discussed.

Formation and reconstruction of Se nanoislands at the surface of thin epitaxial ZnSe layers grown on GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlovskiy, V. I.; Krivobok, V. S., E-mail: krivobok@lebedev.ru; Kuznetsov, P. I.

2016-05-15

Strained epitaxial ZnSe layers are grown on GaAs substrates by the method of vapor-phase epitaxy from metal-organic compounds. It is found that Se nanoislands with a density of 10{sup 8} to 10{sup 9} cm{sup –2} are formed at the surface of such layers. It is established that an increase in the size of Se islands and a decrease in their density take place after completion of growth. Annealing in a H{sub 2} atmosphere at a temperature higher than 260°C leads to the disappearance of Se islands and to a decrease in the surface roughness. It is shown that annealing doesmore » not lead to deterioration of the structural perfection of the epitaxial ZnSe films; rather, annealing gives rise to a decrease in the intensity of impurity–defect luminescence and to an increase in the intensity of intrinsic radiation near the bottom of the exciton band.« less

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.

Nanopatterning as a Probe of Unstable Growth on GaAs(001)

NASA Astrophysics Data System (ADS)

Cosert, Krista; Lin, Chuan-Fu; Hammouda, Ajmi; Kan, Hung-Chih; Subrumaniam, Kanakaraju; Richardson, Chris; Phaneuf, Ray

2009-03-01

We report on observations of unstable growth on nanopatterned GaAs(001) surfaces. For growth at 500^oC, 1 ML/sec and an As2/Ga beam equivalent pressure ratio of 10:1, we find that grooves oriented at right angles to [110] produce a build up of ridges of GaAs at the upper edges, while for grooves oriented at right angles to [110] no ridges form; instead cusps evolve at the bottoms of such grooves [1]. The cusp-forming grooves show a pronounced initial amplification of depth during growth which changes with length/width ratio, and become more narrow. The ridge-forming grooves instead broaden during growth. We compare these experimental observations with kinetic Monte Carlo simulations in which a small anisotropic Ehrlich-Schwoebel barrier is included. [1] T. Tadayyon-Eslami, H.-C. Kan, L. C. Calhoun and R. J. Phaneuf, Phys. Rev. Lett. 97, 126101 (2006)

Ab initio-based approach to structural change of compound semiconductor surfaces during MBE growth

NASA Astrophysics Data System (ADS)

Ito, Tomonori; Akiyama, Toru; Nakamura, Kohji

2009-01-01

Phase diagrams of GaAs and GaN surfaces are systematically investigated by using our ab initio-based approach in conjunction with molecular beam epitaxy (MBE). The phase diagrams are obtained as a function of growth parameters such as temperature and beam equivalent pressure (BEP). The versatility of our approach is exemplified by the phase diagram calculations for GaAs(0 0 1) surfaces, where the stable phases and those phase boundaries are successfully determined as functions of temperature and As 2 and As 4 BEPs. The initial growth processes are clarified by the phase diagram calculations for GaAs(1 1 1)B-(2×2). The calculated results demonstrate that the As-trimer desorption on the GaAs(1 1 1)B-(2×2) with Ga adatoms occurs beyond 500-700 K while the desorption without Ga adatoms does beyond 800-1000 K. This self-surfactant effect induced by Ga adsorption crucially affects the initial growth of GaAs on the GaAs(1 1 1)B-(2×2). Furthermore, the phase diagram calculations for GaN(0 0 0 1) suggests that Ga adsorption or desorption during GaN MBE growth can easily change the pseudo-(1×1) to the (2×2)-Ga via newly found (1×1) and vice versa. On the basis of this finding, the possibility of ghost island formation during MBE growth is discussed.

Monolithic GaAs dual-gate FET phase shifter

NASA Astrophysics Data System (ADS)

Kumar, M.; Subbarao, S. N.; Menna, R.

1981-09-01

The objective of this program is to develop a monolithic GaAs dual-gate FET phase shifter, operating over the 4- to 8-GHz frequency band and capable of a continuously programmable phase shift from 0 deg through N times 360 deg where N is an integer. The phase shift is to be controllable to within +3 deg. This phase shifter will be capable of delivering an output power up to 0 dBm with an input and output VSWR of less than 1.5:1. Progress 1: The photomask of a 0 to 90 deg monolithic GaAs dual-gate FET phase shifter has been procured, and we are in the process of fabricating the phase shifter. 2: We have designed and fabricated a 50 ohm, 4-line interdigitated coupler. Also, we have designed and fabricated a 25-ohm, 6-line interdigitated coupler. The performance of both couplers agrees quite well with the theoretical results. Technical Problems: there was no major problem during this period.

On the origin of reflectance-anisotropy oscillations during GaAs (0 0 1) homoepitaxy

NASA Astrophysics Data System (ADS)

Ortega-Gallegos, J.; Guevara-Macías, L. E.; Ariza-Flores, A. D.; Castro-García, R.; Lastras-Martínez, L. F.; Balderas-Navarro, R. E.; López-Estopier, R. E.; Lastras-Martínez, A.

2018-05-01

We report on the first spectroscopic study of reflectance-anisotropy (RA) oscillations during molecular beam epitaxy (MBE) GaAs homoepitaxy. Real-time RA spectra measured during epitaxial growth were carried out with a recently developed rapid RA multichannel spectrometer with 100 ms per spectrum acquisition time. An analysis of the time-resolved RA spectra shows that RA oscillations are mostly due to the periodic modulation of the surface orthorhombic strain associated to surface reconstruction. Results reported here demonstrate the power of real-time RA spectroscopy as a probe for the study of epitaxial growth processes. In particular, given its sub monolayer surface-strain sensitivity, RA spectroscopy results a very convenient tool to study epitaxial growth mechanisms in real-time with sub monolayer resolution. This capability allows for real-time RA spectroscopy to be used as a probe for the in situ, real-time control of epitaxial growth, with the additional advantage of operating in higher pressure systems such as CVD, where RHEED monitoring cannot be implemented.

A Novel Growth Method To Improve the Quality of GaAs Nanowires Grown by Ga-Assisted Chemical Beam Epitaxy.

PubMed

García Núñez, Carlos; Braña, Alejandro F; López, Nair; García, Basilio J

2018-06-13

The successful synthesis of high crystalline quality and high aspect ratio GaAs nanowires (NWs) with a uniform diameter is needed to develop advanced applications beyond the limits established by thin film and bulk material properties. Vertically aligned GaAs NWs have been extensively grown by Ga-assisted vapor-liquid-solid (VLS) mechanism on Si(111) substrates, and they have been used as building blocks in photovoltaics, optoelectronics, electronics, and so forth. However, the nucleation of parasitic species such as traces and nanocrystals on the Si substrate surface during the NW growth could affect significantly the controlled nucleation of those NWs, and therefore the resulting performance of NW-based devices. Preventing the nucleation of parasitic species on the Si substrate is a matter of interest, because they could act as traps for gaseous precursors and/or chemical elements during VLS growth, drastically reducing the maximum length of grown NWs, affecting their morphology and structure, and reducing the NW density along the Si substrate surface. This work presents a novel and easy to develop growth method (i.e., without using advanced nanolithography techniques) to prevent the nucleation of parasitic species, while preserving the quality of GaAs NWs even for long duration growths. GaAs NWs are grown by Ga-assisted chemical beam epitaxy on oxidized Si(111) substrates using triethylgallium and tertiarybutylarsine precursors by a two-step-based growth method presented here; this method includes a growth interruption for an oxidation on air between both steps of growth, reducing the nucleation of parasitic crystals on the thicker SiO x capping layer during the second and longer growth step. VLS conditions are preserved overtime, resulting in a stable NW growth rate of around 6 μm/h for growth times up to 1 h. Resulting GaAs NWs have a high aspect ratio of 85 and average radius of 35 nm. We also report on the existence of characteristic reflection high

Combined experimental and theoretical study of fast atom diffraction on the β2(2×4) reconstructed GaAs(001) surface

NASA Astrophysics Data System (ADS)

Debiossac, M.; Zugarramurdi, A.; Khemliche, H.; Roncin, P.; Borisov, A. G.; Momeni, A.; Atkinson, P.; Eddrief, M.; Finocchi, F.; Etgens, V. H.

2014-10-01

A grazing incidence fast atom diffraction (GIFAD or FAD) setup, installed on a molecular beam epitaxy chamber, has been used to characterize the β2(2×4) reconstruction of a GaAs(001) surface at 530∘C under an As4 overpressure. Using a 400-eV 4He beam, high-resolution diffraction patterns with up to eighty well-resolved diffraction orders are observed simultaneously, providing a detailed fingerprint of the surface structure. Experimental diffraction data are in good agreement with results from quantum scattering calculations based on an ab initio projectile-surface interaction potential. Along with exact calculations, we show that a straightforward semiclassical analysis allows the features of the diffraction chart to be linked to the main characteristics of the surface reconstruction topography. Our results demonstrate that GIFAD is a technique suitable for measuring in situ the subtle details of complex surface reconstructions. We have performed measurements at very small incidence angles, where the kinetic energy of the projectile motion perpendicular to the surface can be reduced to less than 1 meV. This allowed the depth of the attractive van der Waals potential well to be estimated as -8.7 meV in very good agreement with results reported in literature.

Properties of epitaxial BaTiO{sub 3} deposited on GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contreras-Guerrero, R.; Droopad, R.; Veazey, J. P.

2013-01-07

Single crystal BaTiO{sub 3} (BTO) has been grown epitaxially on GaAs using molecular beam epitaxy with a 2 unit cell SrTiO{sub 3} nucleation layer. The oxide film is lattice-matched to GaAs through an in-plane rotation of 45 Degree-Sign relative to the (100) surface leading to c-axis orientation of the BaTiO{sub 3}. X-ray diffraction confirmed the crystallinity and orientation of the oxide film with a full width half maximum of 0.58 Degree-Sign for a 7.5 nm thick layer. Piezoresponse force microscopy was used to characterize the ferroelectric domains in the BaTiO{sub 3} layer, and a coercive voltage of 1-2 V andmore » piezoresponse amplitude {approx}5 pm/V was measured.« less

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

A Initio Theoretical Studies of Surfaces of Semiconductors

NASA Astrophysics Data System (ADS)

Wang, Jing

1993-01-01

The first semiconductor which we study with these techniques is the archetypal elemental semiconductor, silicon. We present the first extensive study of point defects on Si(100). We identify the principal defects and two primary mechanisms responsible for their dominance: the need to eliminate dangling bonds on the surface and the need to compensate the strain induced by topological effects. Furthermore, we present evidence that the presence of point defects on the Si(100) surface is not intrinsic to the ground state of the surface as a stress relieving mechanism but rather is due merely to thermal fluctuations. We address materials issues associated with the identification of the lowest energy surfaces of GaAs and the determination of the geometric structure of a GaAs crystallite growing freely in three dimensions. The fracture energies associated with (110), (100) and (111) interface planes are calculated and a Wulff construction indicates that an ideal stoichiometric GaAs crystal should be terminated with (110) surfaces. We investigate the more complex issues that arise on surfaces when aspects of these two semiconductors are mixed. We investigate the problem of growing GaAs on the Si(100) surface and demonstrate how and why the most fundamental properties of the resulting bulk GaAs material, such as its crystalline orientation, may depend sensitively on the interplay between growth conditions such as temperature and the properties of the Si surface. For stepped Si(100) -As, we show that the growth of As directly on top of the Si surface produces a metastable state, while the replacement of the original top Si layer leads to a lower energy configuration, with the rearrangement of the surface driven by the relaxation of stress by surface steps. Finally, we study delta -doping, where one attempts to grow a single layer of Si on a GaAs surface before continuing with the growth of bulk GaAs. We shall employ a slightly different modality of the ab initio approach. We

Growth features and spectroscopic structure investigations of nanoprofiled AlN films formed on misoriented GaAs substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seredin, P. V., E-mail: paul@phys.vsu.ru; Goloshchapov, D. L.; Lenshin, A. S.

Nanostructured aluminum-nitride films are formed by reactive ion-plasma sputtering onto GaAs substrates with different orientations. The properties of the films are studied via structural analysis, atomic force microscopy, and infrared and visible–ultraviolet spectroscopy. The aluminum-nitride films can have a refractive index in the range of 1.6–4.0 at a wavelength of ~250 nm and an optical band gap of ~5 eV. It is shown that the morphology, surface composition, and optical characteristics of AlN/GaAs heterophase systems can be controlled using misoriented GaAs substrates.

GaAs CLEFT solar cells for space applications. [CVD thin film growth technology

NASA Technical Reports Server (NTRS)

Fan, J. C. C.; Mcclelland, R. W.; King, B. D.

1984-01-01

Although GaAs solar cells are radiation-resistant and have high conversion efficiencies, there are two major obstacles that such cells must overcome before they can be widely adopted for space applications: GaAs wafers are too expensive and cells made from these wafers are too heavy. The CLEFT process permits the growth of thin single-crystal films on reusable substrates, resulting in a drastic reduction in both cell cost and cell weight. Recent advances in CLEFT technology have made it possible to achieve efficiencies of about 14 percent AM0 for 0.51-sq cm GaAs solar cells 5 microns thick with a 41-mil-thick coverglass. In preliminary experiments efficiencies close to 19 percent AM1 have been obtained for 10-micron-thick cells. It is suggested that the CLEFT technology should yield inexpensive, highly efficient modules with a beginning-of-life specific power close to 1 kW/kg (for a coverglass thickness of 4 mils).

Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE.

PubMed

Skibitzki, Oliver; Prieto, Ivan; Kozak, Roksolana; Capellini, Giovanni; Zaumseil, Peter; Arroyo Rojas Dasilva, Yadira; Rossell, Marta D; Erni, Rolf; von Känel, Hans; Schroeder, Thomas

2017-03-01

We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO 2 -mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

Long-term radiation effects on GaAs solar cell characteristics

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Doviak, M. J.

1978-01-01

This report investigates preliminary design considerations which should be considered for a space experiment involving Gallium Arsenide (GaAs) solar cells. The electron radiation effects on GaAs solar cells were conducted in a laboratory environment, and a statistical analysis of the data is presented. In order to augment the limited laboratory data, a theoretical investigation of the effect of radiation on GaAs solar cells is also developed. The results of this study are empirical prediction equations which can be used to estimate the actual damage of electrical characteristics in a space environment. The experimental and theoretical studies also indicate how GaAs solar cell parameters should be designed in order to withstand the effects of electron radiation damage.

Orientation-dependent surface core-level shifts and chemical shifts on clean and H 2S-covered GaAs

NASA Astrophysics Data System (ADS)

Ranke, W.; Finster, J.; Kuhr, H. J.

1987-08-01

Photoelectron spectra of the As 3d and Ga 3d core levels were studied in situ on a cylindrically shaped GaAs single crystal for the six inequivalent orientations (001), (113), (111), (110), (11¯1) and (11¯3). On the clean surface, prepared by molecular beam epitaxy (MBE), surface core levels are shifted by 0.25 to 0.55 eV towards smaller binding energy (BE) for As 3d and -0.25 to -0.35 eV towards higher BE for Ga, depending on orientation. Additional As causes As 3d contributions shifted between -0.45 and -0.7 eV towards higher BE. The position and intensity of them is influenced by H 2S adsorption. At 150 K, H 2S adsorbs preferentially on As sites. As chemical shifts appear at -0.6 to -0.9 eV towards higher BE. Simultaneously, As accumulation occurs on all orientations with the exception of (110). High temperature adsorption (550 K, 720 K) influences mainly the Ga 3d peaks. Two peaks shifted by about -0.45 and -0.8 eV towards higher Be were found which are attributed to Ga atoms with one or two sulfur ligands, respectively. At 720 K, also As depletion is observed. The compatibility of surface core-level positions and intensities with recent structural models for the (111) and (11¯1) surfaces is discussed.

Development of a 1K x 1K GaAs QWIP Far IR Imaging Array

NASA Technical Reports Server (NTRS)

Jhabvala, M.; Choi, K.; Goldberg, A.; La, A.; Gunapala, S.

2003-01-01

In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x1K), 8.4-9 microns infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.

GaAs thin films and methods of making and using the same

DOEpatents

Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

2016-06-14

Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

High-efficiency thin-film GaAs solar cells, phase2

NASA Technical Reports Server (NTRS)

Yeh, Y. C. M.

1981-01-01

Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

Ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Weiquan; Becker, Jacob; Liu, Shi

2014-05-28

This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In{sub 0.49}Ga{sub 0.51}P/GaAs/In{sub 0.49}Ga{sub 0.51}P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al{sub 0.52}In{sub 0.48}P layer with amore » textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF{sub 2}/ZnS anti-reflective coating demonstrated open-circuit voltages (V{sub oc}) up to 1.00 V, short-circuit current densities (J{sub sc}) up to 24.5 mA/cm{sup 2}, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated J{sub sc} and conversion efficiency of these devices are expected to reach 26.6 mA/cm{sup 2} and 20.7%, respectively.« less

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions

NASA Astrophysics Data System (ADS)

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-01

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

Optimization of GaAs Nanowire Pin Junction Array Solar Cells by Using AlGaAs/GaAs Heterojunctions.

PubMed

Wu, Yao; Yan, Xin; Wei, Wei; Zhang, Jinnan; Zhang, Xia; Ren, Xiaomin

2018-04-25

We optimized the performance of GaAs nanowire pin junction array solar cells by introducing AlGaAs/GaAs heterejunctions. AlGaAs is used for the p type top segment for axial junctions and the p type outer shell for radial junctions. The AlGaAs not only serves as passivation layers for GaAs nanowires but also confines the optical generation in the active regions, reducing the recombination loss in heavily doped regions and the minority carrier recombination at the top contact. The results show that the conversion efficiency of GaAs nanowires can be greatly enhanced by using AlGaAs for the p segment instead of GaAs. A maximum efficiency enhancement of 8.42% has been achieved in this study. And for axial nanowire, by using AlGaAs for the top p segment, a relatively long top segment can be employed without degenerating device performance, which could facilitate the fabrication and contacting of nanowire array solar cells. While for radial nanowires, AlGaAs/GaAs nanowires show better tolerance to p-shell thickness and surface condition.

LEED and AES characterization of the GaAs(110)-ZnSe interface

NASA Technical Reports Server (NTRS)

Tu, D.-W.; Kahn, A.

1984-01-01

In this paper, a study is conducted of the composition and structure of epitaxial ZnSe films grown by congruent evaporation on GaAs(110) at a rate of 2 A/min. It is found that the films grown on 300 C GaAs are nearly stoichiometric and form an abrupt interface with the substrate. Films grown at higher temperature (T greater than 350-400 C) are Se rich. The crystallinity of films grown at 300 C is good and their surface atomic geometry is identical to that of a ZnSe crystal. The GaAs-ZnSe interface geometry seems to be dominated by the Se-substrate bonds. The adsorption of Se, during the formation of very thin ZnSe films (2-3 A), produces a (1 x 2) LEED pattern and modifications of the LEED I-V profiles, which probably indicate a change in the substrate atomic relaxation.

Effects of doping impurity and growth orientation on dislocation generation in GaAs crystals grown from the melt: A qualitative finite-element study

NASA Astrophysics Data System (ADS)

Zhu, X. A.; Tsai, C. T.

2000-09-01

Dislocations in gallium arsenide (GaAs) crystals are generated by excessive thermal stresses induced during the crystal growth process. The presence of dislocations has adverse effects on the performance and reliability of the GaAs-based devices. It is well known that dislocation density can be significantly reduced by doping impurity atoms into a GaAs crystal during its growth process. A viscoplastic constitutive equation that couples the microscopic dislocation density with the macroscopic plastic deformation is employed in a crystallographic finite element model for calculating the dislocation density generated in the GaAs crystal during its growth process. The dislocation density is considered as an internal state variable and the drag stress caused by doping impurity is included in this constitutive equation. A GaAs crystal grown by the vertical Bridgman process is adopted as an example to study the influences of doping impurity and growth orientation on dislocation generation. The calculated results show that doping impurity can significantly reduce the dislocation density generated in the crystal. The level of reduction is also influenced by the growth orientation during the crystal growth process.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Klimov, E. A.; Vasiliev, A. L.

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 ofmore » 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.« less

Gallium arsenide (GaAs) solar cell modeling studies

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.

1980-01-01

Various models were constructed which will allow for the variation of system components. Computer studies were then performed using the models constructed in order to study the effects of various system changes. In particular, GaAs and Si flat plate solar power arrays were studied and compared. Series and shunt resistance models were constructed. Models for the chemical kinetics of the annealing process were prepared. For all models constructed, various parametric studies were performed.

Growth and characteristics of p-type doped GaAs nanowire

NASA Astrophysics Data System (ADS)

Li, Bang; Yan, Xin; Zhang, Xia; Ren, Xiaomin

2018-05-01

The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow. The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow. In addition, the I–V curves of GaAs NWs has been measured and the p-type dope concentration under the II/III ratio of 0.013 and 0.038 approximated to 1019–1020 cm‑3. Project supported by the National Natural Science Foundation of China (Nos. 61376019, 61504010, 61774021) and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Nos. IPOC2017ZT02, IPOC2017ZZ01).

Structural and optical characteristics of GaAs films grown on Si/Ge substrates

NASA Astrophysics Data System (ADS)

Rykov, A. V.; Dorokhin, M. V.; Vergeles, P. S.; Baidus, N. V.; Kovalskiy, V. A.; Yakimov, E. B.; Soltanovich, O. A.

2018-03-01

A GaAs/AlAs heterostructure and a GaAs film grown on Si/Ge substrates have been fabricated and studied. A Ge buffer on a silicon substrate was fabricated using the MBE process. A3B5 films were grown by MOCVD at low pressures. Photoluminescence spectroscopy was used to define the optical quality of A3B5 films. Structural properties were investigated using the electron beam induced current method. It was established that despite a rather high density of dislocations on the epitaxial layers, the detected photoluminescence radiation of layers indicates the acceptable crystalline quality of the top GaAs layer.

Imaging performance of a Timepix detector based on semi-insulating GaAs

NASA Astrophysics Data System (ADS)

Zaťko, B.; Zápražný, Z.; Jakůbek, J.; Šagátová, A.; Boháček, P.; Sekáčová, M.; Korytár, D.; Nečas, V.; Žemlička, J.; Mora, Y.; Pichotka, M.

2018-01-01

This work focused on a Timepix chip [1] coupled with a bulk semi-insulating GaAs sensor. The sensor consisted of a matrix of 256 × 256 pixels with a pitch of 55 μm bump-bonded to a Timepix ASIC. The sensor was processed on a 350 μm-thick SI GaAs wafer. We carried out detector adjustment to optimize its performance. This included threshold equalization with setting up parameters of the Timepix chip, such as Ikrum, Pream, Vfbk, and so on. The energy calibration of the GaAs Timepix detector was realized using a 241Am radioisotope in two Timepix detector modes: time-over-threshold and threshold scan. An energy resolution of 4.4 keV in FWHM (Full Width at Half Maximum) was observed for 59.5 keV γ-photons using threshold scan mode. The X-ray imaging quality of the GaAs Timepix detector was tested using various samples irradiated by an X-ray source with a focal spot size smaller than 8 μm and accelerating voltage up to 80 kV. A 700 μm × 700 μm gold testing object (X-500-200-16Au with Siemens star) fabricated with high precision was used for the spatial resolution testing at different values of X-ray image magnification (up to 45). The measured spatial resolution of our X-ray imaging system was about 4 μm.

Relation between trinucleotide GAA repeat length and sensory neuropathy in Friedreich's ataxia.

PubMed

Santoro, L; De Michele, G; Perretti, A; Crisci, C; Cocozza, S; Cavalcanti, F; Ragno, M; Monticelli, A; Filla, A; Caruso, G

1999-01-01

To verify if GAA expansion size in Friedreich's ataxia could account for the severity of sensory neuropathy. Retrospective study of 56 patients with Friedreich's ataxia selected according to homozygosity for GAA expansion and availability of electrophysiological findings. Orthodromic sensory conduction velocity in the median nerve was available in all patients and that of the tibial nerve in 46 of them. Data of sural nerve biopsy and of a morphometric analysis were available in 12 of the selected patients. The sensory action potential amplitude at the wrist (wSAP) and at the medial malleolus (m mal SAP) and the percentage of myelinated fibres with diameter larger than 7, 9, and 11 microm in the sural nerve were correlated with disease duration and GAA expansion size on the shorter (GAA1) and larger (GAA2) expanded allele in each pair. Pearson's correlation test and stepwise multiple regression were used for statistical analysis. A significant inverse correlation between GAA1 size and wSAP, m mal SAP, and percentage of myelinated fibres was found. Stepwise multiple regression showed that GAA1 size significantly affects electrophysiological and morphometric data, whereas duration of disease has no effect. The data suggest that the severity of the sensory neuropathy is probably genetically determined and that it is not progressive.

Comparison of photoemission characteristics between square and circular wire array GaAs photocathodes.

PubMed

Deng, Wenjuan; Peng, Xincun; Zou, Jijun; Wang, Weilu; Liu, Yun; Zhang, Tao; Zhang, Yijun; Zhang, Daoli

2017-11-10

Two types of negative electron affinity gallium arsenide (GaAs) wire array photocathodes were fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material. High density GaAs wire arrays with high periodicity and good morphology were verified using scanning electron microscopy, and photoluminescence spectra confirmed the wire arrays had good crystalline quality. Reflection spectra showed that circular GaAs wire arrays had superior light trapping compared with square ones. However, after Cs/O activation, the square GaAs wire array photocathodes showed enhanced spectral response. The integral sensitivity of the square wire array photocathodes was approximately 2.8 times that of the circular arrays.

Electrical properties of spin coated ultrathin titanium oxide films on GaAs

NASA Astrophysics Data System (ADS)

Dutta, Shankar; Pal, Ramjay; Chatterjee, Ratnamala

2015-04-01

In recent years, ultrathin (<50 nm) metal oxide films have been being extensively studied as high-k dielectrics for future metal oxide semiconductor (MOS) technology. This paper discusses deposition of ultrathin TiO2 films (˜10 nm) on GaAs substrates (one sulfur-passivated, another unpassivated) by spin coating technique. The sulfur passivation is done to reduce the surface states of GaAs substrate. After annealing at 400 °C in a nitrogen environment, the TiO2 films are found to be polycrystalline in nature with rutile phase. The TiO2 films exhibit consistent grain size of 10-20 nm with thickness around 10-12 nm. Dielectric constants of the films are found to be 65.4 and 47.1 corresponding to S-passivated and unpassivated substrates, respectively. Corresponding threshold voltages of the MOS structures are measured to be -0.1 V to -0.3 V for the S-passivated and unpassivated samples, respectively. The S-passivated TiO2 film showed improved (lower) leakage current density (5.3 × 10-4 A cm-2 at 3 V) compared to the unpassivated film (1.8 × 10-3 A/cm2 at 3 V). Dielectric breakdown-field of the TiO2 films on S-passivated and unpassivated GaAs samples are found to be 8.4 MV cm-1 and 7.2 MV cm-1 respectively.

Observation of linear I-V curves on vertical GaAs nanowires with atomic force microscope

NASA Astrophysics Data System (ADS)

Geydt, P.; Alekseev, P. A.; Dunaevskiy, M.; Lähderanta, E.; Haggrén, T.; Kakko, J.-P.; Lipsanen, H.

2015-12-01

In this work we demonstrate the possibility of studying the current-voltage characteristics for single vertically standing semiconductor nanowires on standard AFM equipped by current measuring module in PeakForce Tapping mode. On the basis of research of eight different samples of p-doped GaAs nanowires grown on different GaAs substrates, peculiar electrical effects were revealed. It was found how covering of substrate surface by SiOx layer increases the current, as well as phosphorous passivation of the grown nanowires. Elimination of the Schottky barrier between golden cap and the top parts of nanowires was observed. It was additionally studied that charge accumulation on the shell of single nanowires affects its resistivity and causes the hysteresis loops on I-V curves.

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

Photovoltaic Properties of p-Doped GaAs Nanowire Arrays Grown on n-Type GaAs(111)B Substrate

PubMed Central

2010-01-01

We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For the best sample, the conversion efficiency of 1.65% and the fill factor of 25% are obtained. PMID:20672038

Two-Photon Pumped Synchronously Mode-Locked Bulk GaAs Laser

NASA Astrophysics Data System (ADS)

Cao, W. L.; Vaucher, A. M.; Ling, J. D.; Lee, C. H.

1982-04-01

Pulses 7 picoseconds or less in duration have been generated from a bulk GaAs crystal by a synchronous mode-locking technique. The GaAs crystal was optically pumped by two-photon absorption of the emission from a mode-locked Nd:glass laser. Two-photon absorption as the means of excitation increases the volume of the gain medium by increasing the pene-tration depth of the pump intensity, enabling generation of intra-cavity pulses with peak power in the megawatt range. Tuning of the wavelength of the GaAs emission is achieved by varying the temperature. A tuning range covering 840 nm to 885 nm has been observed over a temperature range from 97°K to 260°K. The intensity of the GaAs emission has also been observed to decrease as the temperature of the crystal is increased.

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.

Microwave GaAs Integrated Circuits On Quartz Substrates

NASA Technical Reports Server (NTRS)

Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

1994-01-01

Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

Modeling of phase velocity and frequency spectrum of guided Lamb waves in piezoelectric-semiconductor multilayered structures made of AlAs and GaAs

NASA Astrophysics Data System (ADS)

Othmani, Cherif; Takali, Farid; Njeh, Anouar

2017-11-01

Modeling of guided Lamb waves propagation in piezoelectric-semiconductor multilayered structures made of AlAs and GaAs is evaluated in this paper. Here, the Legendre polynomial method is used to calculate dispersion curves, frequency spectrum and field distributions of guided Lamb waves propagation modes in AlAs, GaAs, AlAs/GaAs and AlAs/GaAs/AlAs-1/2/1 structures. In fact, formulations are given for open-circuit surface. Consequently, the polynomial method is numerically stable according to the total number of layers and the frequency range. This analysis is meaningful for the applications of the piezoelectric-semiconductor multilayered structures made of AlAs and GaAs such as in novel acoustic devices.

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

NASA Technical Reports Server (NTRS)

Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

1988-01-01

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

Pulse plating of Pt on n-GaAs ( 1 0 0 ) wafer surfaces: Synchrotron induced photoelectron spectroscopy and XPS of wet fabrication processes

NASA Astrophysics Data System (ADS)

Ensling, D.; Hunger, R.; Kraft, D.; Mayer, Th.; Jaegermann, W.; Rodriguez-Girones, M.; Ichizli, V.; Hartnagel, H. L.

2003-01-01

Preparation steps of Pt/n-GaAs Schottky contacts as applied in the fabrication process of varactor diode arrays for THz applications are analysed by photoelectron spectroscopy. Pulsed cathodic deposition of Pt onto GaAs (1 0 0) wafer surfaces from acidic solution has been studied by core level photoelectron spectroscopy using different excitation energies. A laboratory AlKα source as well as synchrotron radiation of hν=130 and 645 eV at BESSY was used. Chemical analyses and semiquantitative estimates of layer thickness are given for the natural oxide of an untreated wafer surface, a surface conditioning NH 3 etching step, and stepwise pulse plating of Pt. The structural arrangement of the detected species and interface potentials are considered.

Photoluminescence upconversion at GaAs /InGa P2 interfaces driven by a sequential two-photon absorption mechanism

NASA Astrophysics Data System (ADS)

Hylton, N. P.; Hinrichsen, T. F.; Vaquero-Stainer, A. R.; Yoshida, M.; Pusch, A.; Hopkinson, M.; Hess, O.; Phillips, C. C.; Ekins-Daukes, N. J.

2016-06-01

This paper reports on the results of an investigation into the nature of photoluminescence upconversion at GaAs /InGa P2 interfaces. Using a dual-beam excitation experiment, we demonstrate that the upconversion in our sample proceeds via a sequential two-photon optical absorption mechanism. Measurements of photoluminescence and upconversion photoluminescence revealed evidence of the spatial localization of carriers in the InGa P2 material, arising from partial ordering of the InGa P2 . We also observed the excitation of a two-dimensional electron gas at the GaAs /InGa P2 heterojunction that manifests as a high-energy shoulder in the GaAs photoluminescence spectrum. Furthermore, the results of upconversion photoluminescence excitation spectroscopy demonstrate that the photon energy onset of upconversion luminescence coincides with the energy of the two-dimensional electron gas at the GaAs /InGa P2 interface, suggesting that charge accumulation at the interface can play a crucial role in the upconversion process.

GaAs on Si epitaxy by aspect ratio trapping: Analysis and reduction of defects propagating along the trench direction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orzali, Tommaso, E-mail: tommaso.orzali@sematech.org; Vert, Alexey; O'Brien, Brendan

2015-09-14

The Aspect Ratio Trapping technique has been extensively evaluated for improving the quality of III-V heteroepitaxial films grown on Si, due to the potential for terminating defects at the sidewalls of SiO{sub 2} patterned trenches that enclose the growth region. However, defects propagating along the trench direction cannot be effectively confined with this technique. We studied the effect of the trench bottom geometry on the density of defects of GaAs fins, grown by metal-organic chemical vapor deposition on 300 mm Si (001) wafers inside narrow (<90 nm wide) trenches. Plan view and cross sectional Scanning Electron Microscopy and Transmission Electron Microscopy, togethermore » with High Resolution X-Ray Diffraction, were used to evaluate the crystal quality of GaAs. The prevalent defects that reach the top surface of GaAs fins are (111) twin planes propagating along the trench direction. The lowest density of twin planes, ∼8 × 10{sup 8 }cm{sup −2}, was achieved on “V” shaped bottom trenches, where GaAs nucleation occurs only on (111) Si planes, minimizing the interfacial energy and preventing the formation of antiphase boundaries.« less

Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Debehets, J.; Homm, P.; Menghini, M.

In this study, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-levelmore » pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH 4) 2S-solutions in an inert atmosphere (N 2-gas). Although the (NH 4) 2S-cleaning in N 2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH 4) 2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.« less

Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

DOE PAGES

Debehets, J.; Homm, P.; Menghini, M.; ...

2018-01-12

In this study, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-levelmore » pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH 4) 2S-solutions in an inert atmosphere (N 2-gas). Although the (NH 4) 2S-cleaning in N 2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH 4) 2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.« less

Rare-earth gate oxides for GaAs MOSFET application

NASA Astrophysics Data System (ADS)

Kwon, Kwang-Ho; Yang, Jun-Kyu; Park, Hyung-Ho; Kim, Jongdae; Roh, Tae Moon

2006-08-01

Rare-earth oxide films for gate dielectric on n-GaAs have been investigated. The oxide films were e-beam evaporated on S-passivated GaAs, considering interfacial chemical bonding state and energy band structure. Rare-earth oxides such as Gd 2O 3, (Gd xLa 1- x) 2O 3, and Gd-silicate were employed due to high resistivity and no chemical reaction with GaAs. Structural and bonding properties were characterized by X-ray photoemission, absorption, and diffraction. The electrical characteristics of metal-oxide-semiconductor (MOS) diodes were correlated with material properties and energy band structures to guarantee the feasibility for MOS field effect transistor (FET) application. Gd 2O 3 films were grown epitaxially on S-passivated GaAs (0 0 1) at 400 °C. The passivation induced a lowering of crystallization temperature with an epitaxial relationship of Gd 2O 3 (4 4 0) and GaAs (0 0 1). A better lattice matching relation between Gd 2O 3 and GaAs substrate was accomplished by the substitution of Gd with La, which has larger ionic radius. The in-plane relationship of (Gd xLa 1- x) 2O 3 (4 4 0) with GaAs (0 0 1) was found and the epitaxial films showed an improved crystalline quality. Amorphous Gd-silicate film was synthesized by the incorporation of SiO 2 into Gd 2O 3. These amorphous Gd-silicate films excluded defect traps or current flow path due to grain boundaries and showed a relatively larger energy band gap dependent on the contents of SiO 2. Energy band parameters such as Δ EC, Δ EV, and Eg were effectively controlled by the film composition.

Failure Mechanisms of GaAs Transistors - A Literature Survey

DTIC Science & Technology

1990-03-01

doping profile cannot be as sharp as with epitaxial methods. This is the result of the statistics of the implantation and the general diffusion that...Speed GaAs Logic Gates 5.1 GaAs PLANAR TRANSITOR STRUCTURES USED IN IC’S Some planar transistor structures used in IC’s with examples of the

Photon counting microstrip X-ray detectors with GaAs sensors

NASA Astrophysics Data System (ADS)

Ruat, M.; Andrä, M.; Bergamaschi, A.; Barten, R.; Brückner, M.; Dinapoli, R.; Fröjdh, E.; Greiffenberg, D.; Lopez-Cuenca, C.; Lozinskaya, A. D.; Mezza, D.; Mozzanica, A.; Novikov, V. A.; Ramilli, M.; Redford, S.; Ruder, C.; Schmitt, B.; Shi, X.; Thattil, D.; Tinti, G.; Tolbanov, O. P.; Tyazhev, A.; Vetter, S.; Zarubin, A. N.; Zhang, J.

2018-01-01

High-Z sensors are increasingly used to overcome the poor efficiency of Si sensors above 15 keV, and further extend the energy range of synchrotron and FEL experiments. Detector-grade GaAs sensors of 500 μm thickness offer 98% absorption efficiency at 30 keV and 50% at 50 keV . In this work we assess the usability of GaAs sensors in combination with the MYTHEN photon-counting microstrip readout chip developed at PSI. Different strip length and pitch are compared, and the detector performance is evaluated in regard of the sensor material properties. Despite increased leakage current and noise, photon-counting strips mounted with GaAs sensors can be used with photons of energy as low as 5 keV, and exhibit excellent linearity with energy. The charge sharing is doubled as compared to silicon strips, due to the high diffusion coefficient of electrons in GaAs.

Reflectance-difference spectroscopy of GaAs crystal growth by OMCVD

NASA Astrophysics Data System (ADS)

Colas, Etienne G.; Aspnes, David E.; Bhat, Rajaram J.; Studna, A. A.; Koza, M. A.; Keramidas, Vassilis G.

1990-02-01

This paper summarizes results of our investigations of growth on (001) and (110) GaAs by atmospheric-pressure organometallic chemical vapor deposition (OMCVD). We follow evolutions of surface species to a sensitivity of 0.01 monolayer (ML) on a time scale of 0.1 s under alternating flows of trimethylgallium (TMG) and arsine (AsH3) as functions of partial pressure, sample temperature, and surface orienta-tion. The reaction of TMG with an AsH3-saturated (001) surface is rate-limited by com-petition between desorption and decomposition of TMG molecules chemisorbed to surface lattice sites via an excluded-volume mechanism, while the reaction of AsH3 with the TMG-saturated (001) surface is essentially instantaneous. In contrast, TMG reacts essentially instantaneously with the AsH3 -saturated (110) surface while the AsH3 reaction with the TMG-saturated (110) surface is the rate-limiting step. However, the latter rate is not intrinsic to the AsH3-surface reaction but appears to be determined by desorption of adsorbed species that block active sites.

Laser Induced Electrodeposition on Polyimide and GaAs Substrates

DTIC Science & Technology

1983-10-01

6 3.1 Laser Gold Plating on Undoped Ga As Substrate ........... 6 3.1.1 Deposit Formation...22 iv LIST OF ILLUSTRATIONS Figure Page 1. Experimental Set-Up . . . . . .................. 4 2. Laser Gold Pla’ting Undoped GaAs (100...9 3. Laser Gold Plating Undoped GaAs (100) Deposit Resistance Measurement ......................... .10 4. Laser Gold Plating on Polyimide

Amplification in Double Heterostructure GaAs Lasers.

DTIC Science & Technology

1981-03-15

done, for example, in the book by Siegman . When the laser signal which is to be amplified is a single mode, it is important to include the possibility...k A’AD-A097 862 AEROSPACE CORP EL SEGUNDO CA ELECTRONICS RESEARCH LAP) P 5 20/5 I AMPLIFICATION IN DOUBLE HETEROSTRUCTURE GAAS LASERS .(U IMAR al E...GARMIRE, M CHANG F04701-80-C-0081I UNCLASSIFIED TR GO81(6930 03)-2 SD-TA8-30 NL Amplification in Double Heterostructure GaAs Lasers E. GARMIRE nd M

Dynamics of reflection high-energy electron diffraction intensity oscillations during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates

NASA Astrophysics Data System (ADS)

Yen, M. Y.; Haas, T. W.

1990-06-01

We have observed intensity oscillations in reflection high-energy electron diffraction during molecular beam epitaxial growth of GaAs on (111)B GaAs substrates. These oscillations only exist over a narrow range of growth conditions and their behavior is strongly dependent on the migration kinetics of group III and the molecular dissociative reaction of group V elements.

Formation of III–V ternary solid solutions on GaAs and GaSb plates via solid-phase substitution reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasil’ev, V. I.; Gagis, G. S., E-mail: galina.gagis@gmail.com; Kuchinskii, V. I.

2015-07-15

Processes are considered in which ultrathin layers of III–V ternary solid solutions are formed via the delivery of Group-V element vapors to GaAs and GaSb semiconductor plates, with solid-phase substitution reactions occurring in the surface layers of these plates. This method can form defect-free GaAs{sup 1–x}P{sup x}, GaAs{sup x}Sb{sup 1–x}, and GaP{sup x}Sb{sup 1–x} layers with thicknesses of 10–20 nm and a content x of the embedded components of up to 0.04.

Enhancement of photoluminescence intensity of GaAs with cubic GaS chemical vapor deposited using a structurally designed single-source precursor

NASA Technical Reports Server (NTRS)

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

1993-01-01

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster /(t-Bu)GaS/4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

GaAs Coupled Micro Resonators with Enhanced Sensitive Mass Detection

PubMed Central

Chopard, Tony; Lacour, Vivien; Leblois, Therese

2014-01-01

This work demonstrates the improvement of mass detection sensitivity and time response using a simple sensor structure. Indeed, complicated technological processes leading to very brittle sensing structures are often required to reach high sensitivity when we want to detect specific molecules in biological fields. These developments constitute an obstacle to the early diagnosis of diseases. An alternative is the design of coupled structures. In this study, the device is based on the piezoelectric excitation and detection of two GaAs microstructures vibrating in antisymmetric modes. GaAs is a crystal which has the advantage to be micromachined easily using typical clean room processes. Moreover, we showed its high potential in direct biofunctionalisation for use in the biological field. A specific design of the device was performed to improve the detection at low mass and an original detection method has been developed. The principle is to exploit the variation in amplitude at the initial resonance frequency which has in the vicinity of weak added mass the greatest slope. Therefore, we get a very good resolution for an infinitely weak mass: relative voltage variation of 8%/1 fg. The analysis is based on results obtained by finite element simulation. PMID:25474375

Growth mechanism of GaAs1-xSbx ternary alloy thin film on MOCVD reactor using TMGa, TDMAAs and TDMASb

NASA Astrophysics Data System (ADS)

Suhandi, A.; Tayubi, Y. R.; Arifin, P.

2016-04-01

Metal Organic Chemical Vapor Deposition (MOCVD) is a method for growing a solid material (in the form of thin films, especially for semiconductor materials) using vapor phase metal organic sources. Studies on the growth mechanism of GaAs1-xSbx ternary alloy thin solid film in the range of miscibility-gap using metal organic sources trimethylgallium (TMGa), trisdimethylaminoarsenic (TDMAAs), and trisdimethylaminoantimony (TDMASb) on MOCVD reactor has been done to understand the physical and chemical processes involved. Knowledge of the processes that occur during alloy formation is very important to determine the couple of growth condition and growth parameters are appropriate for yield high quality GaAs1-xSbx alloy. The mechanism has been studied include decomposition of metal organic sources and chemical reactions that may occur, the incorporation of the alloy elements forming and the contaminants element that are formed in the gown thin film. In this paper presented the results of experimental data on the growth of GaAs1-xSbx alloy using Vertical-MOCVD reactor to demonstrate its potential in growing GaAs1-xSbx alloy in the range of its miscibility gap.

Structural properties of GaAsN grown on (001) GaAs by metalorganic molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ok, Young-Woo; Choi, Chel-Jong; Seong, Tae-Yeon; Uesugi, K.; Suemune, I.

2001-07-01

Detailed transmission electron microscopy (TEM) and transmission electron diffraction (TED) examination has been made of metalorganic molecular beam epitaxial GaAsN layers grown on (001) GaAs substrates. TEM results show that lateral composition modulation occurs in the GaAs1-xNx layer (x 6.75%). It is shown that increasing N composition and Se (dopant) concentration leads to poor crystallinity. It is also shown that the addition of Se increases N composition. Atomic force microscopy (AFM) results show that the surfaces of the samples experience a morphological change from faceting to islanding, as the N composition and Se concentration increase. Based on the TEM and AFM results, a simple model is given to explain the formation of the lateral composition modulation.

Reflection Properties of Metallic Gratings on ZnO Films over GaAs Substrates

NASA Technical Reports Server (NTRS)

Hickernell, Fred S.; Kim, Yoonkee; Hunt, William D.

1994-01-01

A potential application for piezoelectric film deposited on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Metallic gratings are basic elements required for the construction of such devices, and analyzing the reflectivity and the velocity change due to metallic gratings is often a critical design parameter. In this article, Datta and Hunsinger technique is extended to the case of a multilayered structure, and the developed technique is applied to analyze shorted and open gratings on ZnO films sputtered over (001)-cut (110)-propagating GaAs substrates. The analysis shows that zero reflectivity of shorted gratings can be obtained by a combination of the ZnO film and the metal thickness and the metalization ratio of the grating. Experiments are performed on shorted and an open gratings (with the center frequency of about 180 MHz) for three different metal thicknesses over ZnO films which are 0.8 and 2.6 micrometers thick. From the experiments, zero reflectivity at the resonant frequency of the grating is observed for a reasonable thickness (h/Alpha = 0.5%) of aluminum metalization. The velocity shift between the shorted and the open grating is also measured to be 0.18 MHz and 0.25 MHz for 0.8 and 1.6 micrometers respectively. The measured data show relatively good agreement with theoretical predictions.

Multilayer-Grown Ultrathin Nanostructured GaAs Solar Cells as a Cost-Competitive Materials Platform for III-V Photovoltaics.

PubMed

Gai, Boju; Sun, Yukun; Lim, Haneol; Chen, Huandong; Faucher, Joseph; Lee, Minjoo L; Yoon, Jongseung

2017-01-24

Large-scale deployment of GaAs solar cells in terrestrial photovoltaics demands significant cost reduction for preparing device-quality epitaxial materials. Although multilayer epitaxial growth in conjunction with printing-based materials assemblies has been proposed as a promising route to achieve this goal, their practical implementation remains challenging owing to the degradation of materials properties and resulting nonuniform device performance between solar cells grown in different sequences. Here we report an alternative approach to circumvent these limitations and enable multilayer-grown GaAs solar cells with uniform photovoltaic performance. Ultrathin single-junction GaAs solar cells having a 300-nm-thick absorber (i.e., emitter and base) are epitaxially grown in triple-stack releasable multilayer assemblies by molecular beam epitaxy using beryllium as a p-type impurity. Microscale (∼500 × 500 μm 2 ) GaAs solar cells fabricated from respective device layers exhibit excellent uniformity (<3% relative) of photovoltaic performance and contact properties owing to the suppressed diffusion of p-type dopant as well as substantially reduced time of epitaxial growth associated with ultrathin device configuration. Bifacial photon management employing hexagonally periodic TiO 2 nanoposts and a vertical p-type metal contact serving as a metallic back-surface reflector together with specialized epitaxial design to minimize parasitic optical losses for efficient light trapping synergistically enable significantly enhanced photovoltaic performance of such ultrathin absorbers, where ∼17.2% solar-to-electric power conversion efficiency under simulated AM1.5G illumination is demonstrated from 420-nm-thick single-junction GaAs solar cells grown in triple-stack epitaxial assemblies.

Developing Low-Noise GaAs JFETs For Cryogenic Operation

NASA Technical Reports Server (NTRS)

Cunningham, Thomas J.

1995-01-01

Report discusses aspects of effort to develop low-noise, low-gate-leakage gallium arsenide-based junction field-effect transistors (JFETs) for operation at temperature of about 4 K as readout amplifiers and multiplexing devices for infrared-imaging devices. Transistors needed to replace silicon transistors, relatively noisy at 4 K. Report briefly discusses basic physical principles of JFETs and describes continuing process of optimization of designs of GaAs JFETs for cryogenic operation.

The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model.

PubMed

Ezzatizadeh, Vahid; Pinto, Ricardo Mouro; Sandi, Chiranjeevi; Sandi, Madhavi; Al-Mahdawi, Sahar; Te Riele, Hein; Pook, Mark A

2012-04-01

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a dynamic GAA repeat expansion mutation within intron 1 of the FXN gene. Studies of mouse models for other trinucleotide repeat (TNR) disorders have revealed an important role of mismatch repair (MMR) proteins in TNR instability. To explore the potential role of MMR proteins on intergenerational GAA repeat instability in FRDA, we have analyzed the transmission of unstable GAA repeat expansions from FXN transgenic mice which have been crossed with mice that are deficient for Msh2, Msh3, Msh6 or Pms2. We find in all cases that absence of parental MMR protein not only maintains transmission of GAA expansions and contractions, but also increases GAA repeat mutability (expansions and/or contractions) in the offspring. This indicates that Msh2, Msh3, Msh6 and Pms2 proteins are not the cause of intergenerational GAA expansions or contractions, but act in their canonical MMR capacity to protect against GAA repeat instability. We further identified differential modes of action for the four MMR proteins. Thus, Msh2 and Msh3 protect against GAA repeat contractions, while Msh6 protects against both GAA repeat expansions and contractions, and Pms2 protects against GAA repeat expansions and also promotes contractions. Furthermore, we detected enhanced occupancy of Msh2 and Msh3 proteins downstream of the FXN expanded GAA repeat, suggesting a model in which Msh2/3 dimers are recruited to this region to repair mismatches that would otherwise produce intergenerational GAA contractions. These findings reveal substantial differences in the intergenerational dynamics of expanded GAA repeat sequences compared with expanded CAG/CTG repeats, where Msh2 and Msh3 are thought to actively promote repeat expansions. Copyright © 2012 Elsevier Inc. All rights reserved.

The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model

PubMed Central

Ezzatizadeh, Vahid; Pinto, Ricardo Mouro; Sandi, Chiranjeevi; Sandi, Madhavi; Al-Mahdawi, Sahar; te Riele, Hein; Pook, Mark A.

2013-01-01

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a dynamic GAA repeat expansion mutation within intron 1 of the FXN gene. Studies of mouse models for other trinucleotide repeat (TNR) disorders have revealed an important role of mismatch repair (MMR) proteins in TNR instability. To explore the potential role of MMR proteins on intergenerational GAA repeat instability in FRDA, we have analyzed the transmission of unstable GAA repeat expansions from FXN transgenic mice which have been crossed with mice that are deficient for Msh2, Msh3, Msh6 or Pms2. We find in all cases that absence of parental MMR protein not only maintains transmission of GAA expansions and contractions, but also increases GAA repeat mutability (expansions and/or contractions) in the offspring. This indicates that Msh2, Msh3, Msh6 and Pms2 proteins are not the cause of intergenerational GAA expansions or contractions, but act in their canonical MMR capacity to protect against GAA repeat instability. We further identified differential modes of action for the four MMR proteins. Thus, Msh2 and Msh3 protect against GAA repeat contractions, while Msh6 protects against both GAA repeat expansions and contractions, and Pms2 protects against GAA repeat expansions and also promotes contractions. Furthermore, we detected enhanced occupancy of Msh2 and Msh3 proteins downstream of the FXN expanded GAA repeat, suggesting a model in which Msh2/3 dimers are recruited to this region to repair mismatches that would otherwise produce intergenerational GAA contractions. These findings reveal substantial differences in the intergenerational dynamics of expanded GAA repeat sequences compared with expanded CAG/CTG repeats, where Msh2 and Msh3 are thought to actively promote repeat expansions. PMID:22289650

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.

N/P GaAs concentrator solar cells with an improved grid and bushbar contact design

NASA Technical Reports Server (NTRS)

Desalvo, G. C.; Mueller, E. H.; Barnett, A. M.

1985-01-01

The major requirements for a solar cell used in space applications are high efficiency at AMO irradiance and resistance to high energy radiation. Gallium arsenide, with a band gap of 1.43 eV, is one of the most efficient sunlight to electricity converters (25%) when the the simple diode model is used to calculate efficiencies at AMO irradiance, GaAs solar cells are more radiation resistant than silicon solar cells and the N/P GaAs device has been reported to be more radiation resistant than similar P/N solar cells. This higher resistance is probably due to the fact that only 37% of the current is generated in the top N layer of the N/P cell compared to 69% in the top layer of a P/N solar cell. This top layer of the cell is most affected by radiation. It has also been theoretically calculated that the optimized N/P device will prove to have a higher efficiency than a similar P/N device. The use of a GaP window layer on a GaAs solar cell will avoid many of the inherent problems normally associated with a GaAlAs window while still proving good passivation of the GaAs surface. An optimized circular grid design for solar cell concentrators has been shown which incorporates a multi-layer metallization scheme. This multi-layer design allows for a greater current carrying capacity for a unit area of shading, which results in a better output efficiency.

Multiband corrections for the semi-classical simulation of interband tunneling in GaAs tunnel junctions

NASA Astrophysics Data System (ADS)

Louarn, K.; Claveau, Y.; Hapiuk, D.; Fontaine, C.; Arnoult, A.; Taliercio, T.; Licitra, C.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

2017-09-01

The aim of this study is to investigate the impact of multiband corrections on the current density in GaAs tunnel junctions (TJs) calculated with a refined yet simple semi-classical interband tunneling model (SCITM). The non-parabolicity of the considered bands and the spin-orbit effects are considered by using a recently revisited SCITM available in the literature. The model is confronted to experimental results from a series of molecular beam epitaxy grown GaAs TJs and to numerical results obtained with a full quantum model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We emphasize the importance of considering the non-parabolicity of the conduction band by two different measurements of the energy-dependent electron effective mass in N-doped GaAs. We also propose an innovative method to compute the non-uniform electric field in the TJ for the SCITM simulations, which is of prime importance for a successful operation of the model. We demonstrate that, when considering the multiband corrections and this new computation of the non-uniform electric field, the SCITM succeeds in predicting the electrical characteristics of GaAs TJs, and are also in agreement with the quantum model. Besides the fundamental study of the tunneling phenomenon in TJs, the main benefit of this SCITM is that it can be easily embedded into drift-diffusion software, which are the most widely-used simulation tools for electronic and opto-electronic devices such as multi-junction solar cells, tunnel field-effect transistors, or vertical-cavity surface-emitting lasers.

Arsine flow requirement for the flow modulation growth of high purity GaAs using adduct-grade triethylgallium

NASA Astrophysics Data System (ADS)

Pitts, B. L.; Emerson, D. T.; Shealy, J. R.

1992-10-01

Using arsine and triethylgallium with flow modulation, organometallic vapor phase epitaxy can produce high purity GaAs layers with V/III molar ratios near unity. We have estimated that under appropriate growth conditions the arsine incorporation efficiency into epitaxial GaAs can exceed 30%. The arsine flow requirement for obtaining good morphology has been identified over a range of substrate temperatures using adduct-grade triethylgallium. The process described reduces the environmental impact and life safety risk of the hydride based organometallic vapor phase epitaxial method.

Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

GaAs Spectrometer for Electron Spectroscopy at Europa

NASA Astrophysics Data System (ADS)

Lioliou, G.; Barnett, A. M.

2016-12-01

We propose a GaAs based electron spectrometer for a hypothetical future mission orbiting Europa. Previous observations at Europa's South Pole with the Hubble Space Telescope of hydrogen Lyman-α and oxygen OI 130.4 nm emissions were consistent with water vapor plumes [Roth et al., 2014, Science 343, 171]. Future observations and analysis of plumes on Europa could provide information about its subsurface structure and the distribution of liquid water within its icy shells [Rhoden at al. 2015, Icarus 253, 169]. In situ low energy (1keV - 100keV) electron spectroscopy along with UV imaging either in situ or with the Hubble Space Telescope Wide Field Camera 3 or similar would allow verification of the auroral observations being due to electron impact excitation of water vapor plumes. The proposed spectrometer includes a novel GaAs p+-i-n+ photodiode and a custom-made charge-sensitive preamplifier. The use of an early prototype GaAs detector for direct electron spectroscopy has already been demonstrated in ground based applications [Barnett et al., 2012, J. Instrum. 7, P09012]. Based on previous radiation hardness measurements of GaAs, the expected duration of the mission without degradation of the detector performance is estimated to be 4 months. Simulations and laboratory experiments characterising the detection performance of the proposed system are presented.

Photo-recovery of electron-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Meulenberg, Andrew

1995-01-01

The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has produced some unexpected and important results. Two results, independent of the coverslide coatings, are of particular importance in terms of the predictability of GaAs solar-array lifetime in space: ( 1) The GaAs/Ge solar cells used for this series of tests displayed a much higher radiation degradation than that predicted based on JPL Solar Cell Radiation Handbook data. Covered cells degraded more in Isc than did bare cells. Short-term illumination at 60 C did not produce significant recovery (-1%) of the radiation damage. (2) However, electron radiation damage to these GaAs solar celIs anneals at 40 C when exposed to approximately 1 sun AM0 UV light sources for extended periods. The effect appears to be roughly linear with time (-1% of lsc per 1000 UVSH), is large (greater than or equal to 3%), and has not yet saturated (at 3000 hours). This photo-recovery of radiation damage to GaAs solar cells is a new effect and potentially important to the spacecraft community. The figure compares the effects of extended UV on irradiated and unirradiated GaAs solar cells with INTELSAT-6 Si cells. The effect and its generality, the extent of and conditions for photo-recovery, and the implications of such recovery for missions in radiation environments have not yet been determined.

Defect interactions in GaAs single crystals

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1984-01-01

The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

Free Carrier Induced Spectral Shift for GaAs Filled Metallic Hole Arrays

DTIC Science & Technology

2012-03-13

Bahae , G. I . Stegeman, K. Al-hemyari, J. S. Aitchison, and C. N. Ironside, “Limitation due to three-photon absorption on the useful spectral range...Free carrier induced spectral shift for GaAs filled metallic hole arrays Jingyu Zhang 1,2,* , Bin Xiang 3 , Mansoor Sheik- Bahae 4 , and S. R. J...OCIS codes: (310.6628) Subwavelength structures;(190.4350) Nonlinear optics at surfaces References and links 1. J. M. Luther, P. K. I . Jain, T. Ewers

Heteroepitaxial growth of Ge films on (100) GaAs by pyrolysis of digermane

NASA Astrophysics Data System (ADS)

Eres, Djula; Lowndes, Douglas H.; Tischler, J. Z.; Sharp, J. W.; Geohegan, D. B.; Pennycook, S. J.

1989-08-01

Pyrolysis of high-purity digermane (Ge2 H6 ) has been used to grow epitaxial Ge films of high crystalline quality on (100) GaAs substrates in a low-pressure environment. X-ray double-crystal diffractometry shows that fully commensurate, coherently strained epitaxial Ge films can be grown on (100) GaAs at digermane partial pressures of 0.05-40 mTorr for substrate temperatures of 380-600 °C. Amorphous films also were deposited. Information about the crystalline films surface morphology, growth mode, and microstructure was obtained from scanning electron microscopy, cross-section transmission electron microscopy, and in situ reflectivity measurements. The amorphous-to-crystalline transition temperature and the morphology of the crystalline films were both found to depend on deposition conditions (primarily the incidence rate of Ge-bearing species and the substrate temperature). Epitaxial growth rates using digermane were found to be about two orders of magnitude higher than rates using germane (GeH4 ) under similar experimental conditions.

Optimization of the interfacial misfit array growth mode of GaSb epilayers on GaAs substrate

NASA Astrophysics Data System (ADS)

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

2018-02-01

The growth of undoped GaSb epilayers on GaAs (0 0 1) substrates with 2° offcut towards 〈1 1 0〉, by molecular beam epitaxy system (MBE) at low growth temperature is reported. The strain due to the lattice mismatch of 7.78% is relieved spontaneously at the interface by using interfacial misfit array (IMF) growth mode. Three approaches of this technique are investigated. The difference consists in the steps after the growth of GaAs buffer layer. These steps are the desorption of arsenic from the GaAs surface, and the cooling down to the growth temperature, under or without antimony flux. The X-ray analysis and the transmission electron microscopy point out that desorption of arsenic followed by the substrate temperature decreasing under no group V flux leads to the best structural and crystallographic properties in the GaSb layer. It is found that the 2 μm-thick GaSb is 99.8% relaxed, and that the strain is relieved by the formation of a periodic array of 90° pure-edge dislocations along the [1 1 0] direction with a periodicity of 5.6 nm.

Molecular beam epitaxial growth of high-quality InSb on InP and GaAs substrates

NASA Technical Reports Server (NTRS)

Oh, J. E.; Bhattacharya, P. K.; Chen, Y. C.; Tsukamoto, S.

1989-01-01

Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures.

Simulation of the transient indiffusion-segregation process of triply negatively charged Ga vacancies in GaAs and AlAs/GaAs superlattices

NASA Astrophysics Data System (ADS)

You, Horng-Ming; Gösele, Ulrich M.; Tan, Teh Y.

1993-08-01

In GaAs and AlAs/GaAs superlattice crystals containing n-type regions, several sets of recent experimental results obtained from diffusion studies require the interpretation that the responsible point defect species, the triply negatively charged Ga vacancy (VGa3-), has attained its thermal equilibrium concentration (CVGa3-eq) at the onset of an experiment. This could be due to either the fact that under heavy n-doping conditions CVGa3-eq is fairly temperature independent, or the fact that the transient process of populating VGa3- from an undersaturated to the appropriate CVGa3-eq value via indiffusion from the surfaces to the interior of the crystals is extremely rapid. We have simulated the transient process of populating VGa3- to the crystal interior. The experiments use crystals consisting of adjacent intrinsic and n-type regions for which CVGa3-eq values are different, leading to the simultaneous occurrence of VGa3- diffusion and segregation phenomena. A diffusion-segregation equation has been derived and subsequently used in the simulation calculations. The simulation results showed that, as long as n-type regions are involved, such transient processes are ineffective and therefore cannot explain the experimental requirement that VGa3- is already present in the appropriate CVGa3-eq(n) value at the onset of an experiment. On the other hand, the transient process is sufficiently rapid for the purely intrinsic crystal cases. These simulation results support our recent finding that the CVGa3-eq(n) values are essentially temperature independent, obtained via a thermodynamic treatment.

Transient GaAs plasmonic metasurfaces at terahertz frequencies

DOE PAGES

Yang, Yuanmu; Kamaraju, N.; Campione, Salvatore; ...

2016-12-09

Here we demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to moremore » complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. In conclusion, the platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.« less

Spin-lattice relaxation of optically polarized nuclei in p -type GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Cherbunin, R. V.; Sokolov, P. S.; Yakovlev, D. R.; Bayer, M.; Suter, D.; Kavokin, K. V.

2018-04-01

Spin-lattice relaxation of the nuclear spin system in p -type GaAs is studied using a three-stage experimental protocol including optical pumping and measuring the difference of the nuclear spin polarization before and after a dark interval of variable length. This method allows us to measure the spin-lattice relaxation time T1 of optically pumped nuclei "in the dark," that is, in the absence of illumination. The measured T1 values fall into the subsecond time range, being three orders of magnitude shorter than in earlier studied n -type GaAs. The drastic difference is further emphasized by magnetic-field and temperature dependencies of T1 in p -GaAs, showing no similarity to those in n -GaAs. This unexpected behavior finds its explanation in the spatial selectivity of the optical pumping in p -GaAs, that is only efficient in the vicinity of shallow donors, together with the quadrupole relaxation of nuclear spins, which is induced by electric fields within closely spaced donor-acceptor pairs. The developed theoretical model explains the whole set of experimental results.

Study of Carbon Nanotubes as Etching Masks and Related Applications in the Surface Modification of GaAs-based Light-Emitting Diodes.

PubMed

Jin, Yuanhao; Li, Qunqing; Chen, Mo; Li, Guanhong; Zhao, Yudan; Xiao, Xiaoyang; Wang, Jiaping; Jiang, Kaili; Fan, Shoushan

2015-09-02

The surface modification of LEDs based on GaAs is realized by super-aligned multiwalled carbon nanotube (SACNT) networks as etching masks. The surface morphology of SACNT networks is transferred to the GaAs. It is found that the light output power of LEDs based on GaAs with a nanostructured surface morphology is greatly enhanced with the electrical power unchanged. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

DTIC Science & Technology

1994-02-28

from the bandgap discontinuity (as was proposed in my publications [1,2]). Also, by using superlattice structure A1GaAs / GaAs: Er / AlGaAs, we could...n ipact ightemiting evic 10 3. The AlGaAs/GaAs: Er/A1GaAs superlattice structure. For the first time we designed the unipolar n’ - superlattice - n...structure as shown in Figure 5. The GaAs: Er/Alo.45Gao.55As superlattice was grown by MBE on an n’ GaAs: Si substrate. It consisted of 60 periods of

Crystal growth of GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.; Pawlowicz, L. M.; Dabkowski, F.; Li, C. J.

1984-01-01

It is shown that stoichiometry variations in the GaAs melt during growth constitute the most critical parameter regarding defect formations and their interactions; this defect structure determines all relevant characteristics of GaAs. Convection in the melt leads to stoichiometric variations. Growth in axial magnetic fields reduces convection and permits the study of defect structure. In order to control stoichiometry in space and to accommodate expansion during solidification, a partially confined configuration was developed. A triangular prism is employed to contain the growth melt. This configuration permits the presence of the desired vapor phase in contact with the melt for controlling the melt stoichiometry.

Investigation of the interface characteristics of Y2O3/GaAs under biaxial strain, triaxial strain, and non-strain conditions

NASA Astrophysics Data System (ADS)

Shi, Li-Bin; Liu, Xu-Yang; Dong, Hai-Kuan

2016-09-01

We investigate the interface behaviors of Y2O3/GaAs under biaxial strain, triaxial strain, and non-strain conditions. This study is performed by first principles calculations based on density functional theory (DFT). First of all, the biaxial strain is realized by changing the lattice constants in ab plane. Averaged electrostatic potential (AEP) is aligned by establishing Y2O3 and GaAs (110) surfaces. The band offsets of Y2O3/GaAs interface under biaxial strain are investigated by generalized gradient approximation and Heyd-Scuseria-Ernzerhof (HSE) functionals. The interface under biaxial strain is suitable for the design of metal oxide semiconductor (MOS) devices because the valence band offsets (VBO) and conduction band offsets (CBO) are larger than 1 eV. Second, the triaxial strain is applied to Y2O3/GaAs interface by synchronously changing the lattice constants in a, b, and c axis. The band gaps of Y2O3 and GaAs under triaxial strain are investigated by HSE functional. We compare the VBO and CBO under triaxial strain with those under biaxial strain. Third, in the absence of lattice strain, the formation energies, charge state switching levels, and migration barriers of native defects in Y2O3 are assessed. We investigate how they will affect the MOS device performance. It is found that VO+2 and Oi-2 play a very dangerous role in MOS devices. Finally, a direct tunneling leakage current model is established. The model is used to analyze current and voltage characteristics of the metal/Y2O3/GaAs.

A model for proton-irradiated GaAs solar cells

NASA Technical Reports Server (NTRS)

Wilson, J. W.; Walker, G. H.; Outlaw, R. A.; Stock, L. V.

1982-01-01

A simple model for proton radiation damage in GaAs heteroface solar cells is developed. The model includes the effects of spatial nonuniformity of low energy proton damage. Agreement between the model and experimental proton damage data for GaAs heteroface solar cells is satisfactory. An extension of the model to include angular isotropy, as is appropriate for protons in space, is shown to result in significantly less cell damage than for normal proton incidence.

Focusing effect of bent GaAs crystals for γ-ray Laue lenses: Monte Carlo and experimental results

NASA Astrophysics Data System (ADS)

Virgilli, E.; Frontera, F.; Rosati, P.; Bonnini, E.; Buffagni, E.; Ferrari, C.; Stephen, J. B.; Caroli, E.; Auricchio, N.; Basili, A.; Silvestri, S.

2016-02-01

We report on results of observation of the focusing effect from the planes (220) of Gallium Arsenide (GaAs) crystals. We have compared the experimental results with the Monte Carlo simulations of the focusing capability of GaAs tiles performed with a dedicated ray-tracer. The GaAs tiles were bent using a lapping process developed at the cnr/imem - Parma (Italy) in the framework of the laue project, funded by ASI, dedicated to build a broad band Laue lens prototype for astrophysical applications in the hard X-/soft γ-ray energy range (80-600 keV). We present and discuss the results obtained from their characterization, mainly in terms of focusing capability. Bent crystals will significantly increase the signal to noise ratio of a telescope based on a Laue lens, consequently leading to an unprecedented enhancement of sensitivity with respect to the present non focusing instrumentation.

Low temperature plasma enhanced CVD epitaxial growth of silicon on GaAs: a new paradigm for III-V/Si integration

NASA Astrophysics Data System (ADS)

Cariou, Romain; Chen, Wanghua; Maurice, Jean-Luc; Yu, Jingwen; Patriarche, Gilles; Mauguin, Olivia; Largeau, Ludovic; Decobert, Jean; Roca I Cabarrocas, Pere

2016-05-01

The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion, and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs.

Structural modifications of silicon-implanted GaAs induced by the athermal annealing technique

NASA Astrophysics Data System (ADS)

Qadri, S. B.; Yousuf, M.; Kendziora, C. A.; Nachumi, B.; Fischer, R.; Grun, J.; Rao, M. V.; Tucker, J.; Siddiqui, S.; Ridgway, M. C.

2004-12-01

We have used high-resolution X-ray diffraction and Raman spectroscopy to investigate structural modifications inside and outside the focal region of Si-implanted GaAs samples that have been irradiated at high power by a focused short-pulse laser. Si atoms implanted into the GaAs matrix generate exciton-induced local lattice expansion, resulting in a satellite on the lower-angle side of the Bragg peak. After the laser pulse irradiation, surface features inside and outside the focal spot suggest the presence of Bernard convection cells, indicating that a rapid melting and re-crystallization has taken place. Moreover, the laser irradiation induces a compressive strain inside the focal spot, since the satellite appears on the higher-angle side of the Bragg peak. The stress maximizes at the center of the focal spot and extends far outside the irradiated area (approximately 2.5-mm away from the bull’s eye), suggesting the propagation of a laser-induced mechanical wave. The maximum compressive stress inside the focal spot corresponds to 2.7 GPa. Raman spectra inside the focal spot resemble that of pristine GaAs, indicating that rapid melting has introduced significant heterogeneity, with zones of high and low Si concentration. X-ray measurements indicate that areas inside the focal spot and annealed areas outside of the focal spot contain overtones of a minor tetragonal distortion of the lattice, consistent with the observed relaxation of Raman selection rules when compared with the parent zinc-blende structure.

Modelling of double air-bridged structured inductor implemented by a GaAs integrated passive device manufacturing process

NASA Astrophysics Data System (ADS)

Li, Yang; Yao, Zhao; Zhang, Chun-Wei; Fu, Xiao-Qian; Li, Zhi-Ming; Li, Nian-Qiang; Wang, Cong

2017-05-01

In order to provide excellent performance and show the development of a complicated structure in a module and system, this paper presents a double air-bridge-structured symmetrical differential inductor based on integrated passive device technology. Corresponding to the proposed complicated structure, a new manufacturing process fabricated on a high-resistivity GaAs substrate is described in detail. Frequency-independent physical models are presented with lump elements and the results of skin effect-based measurements. Finally, some key features of the inductor are compared; good agreement between the measurements and modeled circuit fully verifies the validity of the proposed modeling approach. Meanwhile, we also present a comparison of different coil turns for inductor performance. The proposed work can provide a good solution for the design, fabrication, modeling, and practical application of radio-frequency modules and systems.

OM-VPE growth of Mg-doped GaAs. [OrganoMetallic-Vapor Phase Epitaxy

NASA Technical Reports Server (NTRS)

Lewis, C. R.; Dietze, W. T.; Ludowise, M. J.

1982-01-01

The epitaxial growth of Mg-doped GaAs by the organometallic vapor phase epitaxial process (OM-VPE) has been achieved for the first time. The doping is controllable over a wide range of input fluxes of bis (cyclopentadienyl) magnesium, (C5H5)2Mg, the organometallic precursor to Mg.

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

NASA Astrophysics Data System (ADS)

Perl, E. E.; Kuciauskas, D.; Simon, J.; Friedman, D. J.; Steiner, M. A.

2017-12-01

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 °C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 °C, we measure VOC that is ˜50 mV higher for the GaAs solar cell and ˜60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-type GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 °C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 °C to 400 °C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4× reduction in the effective lifetime and ˜40× increase in the surface recombination velocity as the temperature is increased from 25 °C to 400 °C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 °C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

DOE PAGES

Perl, E. E.; Kuciauskas, D.; Simon, J.; ...

2017-12-21

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-typemore » GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.« less

Identification of the limiting factors for high-temperature GaAs, GaInP, and AlGaInP solar cells from device and carrier lifetime analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perl, E. E.; Kuciauskas, D.; Simon, J.

We analyze the temperature-dependent dark saturation current density and open-circuit voltage (VOC) for GaAs, GaInP, and AlGaInP solar cells from 25 to 400 degrees C. As expected, the intrinsic carrier concentration, ni, dominates the temperature dependence of the dark currents. However, at 400 degrees C, we measure VOC that is ~50 mV higher for the GaAs solar cell and ~60-110 mV lower for the GaInP and AlGaInP solar cells compared to what would be expected from commonly used solar cell models that consider only the ni2 temperature dependence. To better understand these deviations, we measure the carrier lifetimes of p-typemore » GaAs, GaInP, and AlGaInP double heterostructures (DHs) from 25 to 400 degrees C using time-resolved photoluminescence. Temperature-dependent minority carrier lifetimes are analyzed to determine the relative contributions of the radiative recombination, interface recombination, Shockley-Read-Hall recombination, and thermionic emission processes. We find that radiative recombination dominates for the GaAs DHs with the effective lifetime approximately doubling as the temperature is increased from 25 degrees C to 400 degrees C. In contrast, we find that thermionic emission dominates for the GaInP and AlGaInP DHs at elevated temperatures, leading to a 3-4x reduction in the effective lifetime and ~40x increase in the surface recombination velocity as the temperature is increased from 25 degrees C to 400 degrees C. These observations suggest that optimization of the minority carrier confinement layers for the GaInP and AlGaInP solar cells could help to improve VOC and solar cell efficiency at elevated temperatures. We demonstrate VOC improvement at 200-400 degrees C in GaInP solar cells fabricated with modified AlGaInP window and back surface field layers.« less

Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Debehets, J.; Homm, P.; Menghini, M.

In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate detector and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-level. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-levelmore » pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs. This work has been funded by J.D.'s PhD fellowship of the Fund of Scientific Research-Flanders (FWO-V) (Dossier No. 11U4516N). P.H. acknowledges support from Becas Chile-CONICYT. This research was also supported by the FWO Odysseus Program, the Belgian Hercules Stichting with the Project No. Her/08/25 and AKUL/13/19 and the KU Leuven project GOA "Fundamental challenges in Semiconductor Research". The authors would also like to thank Bastiaan Opperdoes and Ludwig Henderix for technical support. The work was supported by the U.S. Department of Energy (USDOE), Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and performed in the Environmental Molecular

High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

NASA Technical Reports Server (NTRS)

Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.

2005-01-01

III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge

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.

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.

Properties of TiO2 thin films and a study of the TiO2-GaAs interface

NASA Technical Reports Server (NTRS)

Chen, C. Y.; Littlejohn, M. A.

1977-01-01

Titanium dioxide (TiO2) films prepared by chemical vapor deposition were investigated in this study for the purpose of the application in the GaAs metal-insulator-semiconductor field-effect transistor. The degree of crystallization increases with the deposition temperature. The current-voltage study, utilizing an Al-TiO2-Al MIM structure, reveals that the d-c conduction through the TiO2 film is dominated by the bulk-limited Poole-Frenkel emission mechanism. The dependence of the resistivity of the TiO2 films on the deposition environment is also shown. The results of the capacitance-voltage study indicate that an inversion layer in an n-type substrate can be achieved in the MIS capacitor if the TiO2 films are deposited at a temperature higher than 275 C. A process of low temperature deposition followed by the pattern definition and a higher temperature annealing is suggested for device fabrications. A model, based on the assumption that the surface state densities are continuously distributed in energy within the forbidden band gap, is proposed to interpret the lack of an inversion layer in the Al-TiO2-GaAs MIS structure with the TiO2 films deposited at 200 C.

Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots.

PubMed

Nichol, John M; Harvey, Shannon P; Shulman, Michael D; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I; Halperin, Bertrand I; Yacoby, Amir

2015-07-17

The central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spin-orbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electron-nuclear system, despite weak spin-orbit coupling in GaAs. Using Landau-Zener sweeps to measure static and dynamic properties of the electron spin-flip probability, we observe that the size of the spin-orbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spin-orbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spin-orbit coupling in central-spin systems.

Single quantum dot emission by nanoscale selective growth of InAs on GaAs: A bottom-up approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patella, F.; Arciprete, F.; Placidi, E.

2008-12-08

We report on single dot microphotoluminescence ({mu}PL) emission at low temperature and low power from InAs dots grown by molecular beam epitaxy in nanoscale holes of a SiO{sub 2} mask deposited on GaAs(001). By comparing atomic force microscopy measurements with {mu}PL data, we show that the dot sizes inside the nanoholes are smaller than those of the dots nucleated on the extended GaAs surface. PL of dots spans a wide energy range depending on their size and on the thickness and composition of the InGaAs capping layer. Time-resolved PL experiments demonstrate a negligible loss of radiative recombination efficiency, proving highlymore » effective in the site-controlled dot nucleation.« less

High-efficiency GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy

PubMed Central

2011-01-01

We report the initial results of GaAs and GaInP solar cells grown by all solid-state molecular-beam-epitaxy (MBE) technique. For GaAs single-junction solar cell, with the application of AlInP as the window layer and GaInP as the back surface field layer, the photovoltaic conversion efficiency of 26% at one sun concentration and air mass 1.5 global (AM1.5G) is realized. The efficiency of 16.4% is also reached for GaInP solar cell. Our results demonstrate that the MBE-grown phosphide-contained III-V compound semiconductor solar cell can be quite comparable to the metal-organic-chemical-vapor-deposition-grown high-efficiency solar cell. PMID:22040124

Formation of embedded plasmonic Ga nanoparticle arrays and their influence on GaAs photoluminescence

NASA Astrophysics Data System (ADS)

Kang, M.; Jeon, S.; Jen, T.; Lee, J.-E.; Sih, V.; Goldman, R. S.

2017-07-01

We introduce a novel approach to the seamless integration of plasmonic nanoparticle (NP) arrays into semiconductor layers and demonstrate their enhanced photoluminescence (PL) efficiency. Our approach utilizes focused ion beam-induced self-assembly of close-packed arrays of Ga NPs with tailorable NP diameters, followed by overgrowth of GaAs layers using molecular beam epitaxy. Using a combination of PL spectroscopy and electromagnetic computations, we identify a regime of Ga NP diameter and overgrown GaAs layer thickness where NP-array-enhanced absorption in GaAs leads to enhanced GaAs near-band-edge (NBE) PL efficiency, surpassing that of high-quality epitaxial GaAs layers. As the NP array depth and size are increased, the reduction in spontaneous emission rate overwhelms the NP-array-enhanced absorption, leading to a reduced NBE PL efficiency. This approach provides an opportunity to enhance the PL efficiency of a wide variety of semiconductor heterostructures.

Photoemission study of CaF2- and SrF2-GaAs(110) interfaces formed at room temperature

NASA Astrophysics Data System (ADS)

Mao, D.; Young, K.; Kahn, A.; Zanoni, R.; McKinley, J.; Margaritondo, G.

1989-06-01

Interfaces formed by evaporating CaF2 or SrF2 on room-temperature GaAs(110) are studied with synchrotron-radiation photoemission spectroscopy. The fluoride films grow uniformly on the GaAs surface. The deposition of CaF2 and SrF2 induces a large initial band bending on p-type GaAs (~0.9 eV) and a small initial band bending on n-type GaAs (~0.25 eV). The valence band is dominated by the F 2p peak which shifts toward high binding energies by ~1.5 eV after the deposition of >=16 Å fluoride. This shift reflects an increase in the valence-band offset between the two materials as the film forms. The final band offsets are estimated at 7.7 and 8.0 eV for CaF2 and SrF2, respectively, and are in qualitative agreement with those expected from the fluoride-Si data. Core-level measurements indicate that no reaction or decomposition of the MF2 molecule takes place at the interface. The F 2s core-level line shape and the increase in the binding-energy separation of F 2s and Ca 3p with increasing coverage suggest the presence of an interface F component. Contrary to the CaF2/Si case, no measurable Ca-substrate bonding effect is observed. The dissociative effect of uv irradiation on the CaF2 film is also investigated.

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.

Investigation of high efficiency GaAs solar cells

NASA Technical Reports Server (NTRS)

Olsen, Larry C.; Dunham, Glen; Addis, F. W.; Huber, Dan; Linden, Kurt

1989-01-01

Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies.

Intermixing optical and microwave signals in GaAs microstrip circuits for phase-locking applications

NASA Astrophysics Data System (ADS)

Li, Ming G.; Chauchard, Eve A.; Lee, Chi H.; Hung, Hing-Loi A.

1990-12-01

The microwave modulation of the interference generated by optical beams that are reflected from the top and bottom surfaces of GaAs substrate adjacent to a microstrip line is studied. The detected modulation is used to directly characterize the electrooptic effect. This optical-microwave intermixing technique is applied to phase-lock a free-running microwave oscillator with picosecond laser pulses. One potential application of this technique is for the optical on-wafer characterization of MMICs.

MEDIPIX: a VLSI chip for a GaAs pixel detector for digital radiology

NASA Astrophysics Data System (ADS)

Amendolia, S. R.; Bertolucci, E.; Bisogni, M. G.; Bottigli, U.; Ceccopieri, A.; Ciocci, M. A.; Conti, M.; Delogu, P.; Fantacci, M. E.; Maestro, P.; Marzulli, V.; Pernigotti, E.; Romeo, N.; Rosso, V.; Rosso, P.; Stefanini, A.; Stumbo, S.

1999-02-01

A GaAs pixel detector designed for digital mammography, equipped with a 36-channel single photon counting discrete read-out electronics, was tested using a test object developed for quality control purposes in mammography. Each pixel was 200×200 μm 2 large, and 200 μm deep. The choice of GaAs with respect to silicon (largely used in other applications and with a more established technique) has been made because of the much better detection efficiency at mammographic energies, combined with a very good charge collection efficiency achieved thanks to new ohmic contacts. This GaAs detector is able to perform a measurement of low-contrast details, with minimum contrast lower (nearly a factor two) than that typically achievable with standard mammographic film+screen systems in the same conditions of clinical routine. This should allow for an earlier diagnosis of breast tumour masses. Due to these encouraging results, the next step in the evolution of our imaging system based on GaAs detectors has been the development of a VLSI front-end prototype chip (MEDIPIX ) in order to cover a much larger diagnostic area. The chip reads 64×64 channels in single photon counting mode, each one 170 μm wide. Each channel contains also a test input where a signal can be simulated, injecting a known charge through a 16 f F capacitor. Fake signals have been injected via the test input measuring and equalizing minimum thresholds for all the channels. On an average, in most of the performing chips available up to now, we have found that it is possible to set a threshold as low as 1800 electrons with an RMS of 150 electrons (10 standard deviations lower than the 20 keV photon signal roughly equivalent to 4500 electrons). The detector, bump-bonded to the chip, will be tested and a ladder of detectors will be prepared to be able to scan large surface objects.

Response of GaAs charge storage devices to transient ionizing radiation

NASA Astrophysics Data System (ADS)

Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

Enhancement of conductance of GaAs sub-microwires under external stimuli

NASA Astrophysics Data System (ADS)

Qu, Xianlin; Deng, Qingsong; Zheng, Kun

2018-03-01

Semiconductors with one dimension on the micro-nanometer scale have many unique physical properties that are remarkably different from those of their bulk counterparts. Moreover, changes in the external field will further modulate the properties of the semiconductor micro-nanomaterials. In this study, we used focused ion beam technology to prepare freestanding ⟨111⟩-oriented GaAs sub-microwires from a GaAs substrate. The effects of laser irradiation and bending or buckling deformation induced by compression on the electrical transport properties of an individual GaAs sub-microwire were studied. The experimental results indicate that both laser irradiation and bending deformation can enhance their electrical transport properties, the laser irradiation resulted in a conductance enhancement of ˜30% compared to the result with no irradiation, and in addition, bending deformation changed the conductance by as much as ˜180% when the average strain was approximately 1%. The corresponding mechanisms are also discussed. This study provides beneficial insight into the fabrication of electronic and optoelectronic devices based on GaAs micro/nano-wires.

GaAs digital dynamic IC's for applications up to 10 GHz

NASA Astrophysics Data System (ADS)

Rocchi, M.; Gabillard, B.

1983-06-01

To evaluate the potentiality of GaAs MESFET's as transmitting gates, dynamic TT-bar flip-flops have been fabricated using a self-aligned planar process. The maximum operating frequency is 10.2 GHz, which is the best speed performance ever reported for a digital circuit. The performance of the transmitting gates within the circuits are discussed in detail. Speed improvement and topological simplification of fully static LSI subsystems are investigated.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1985-01-01

The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

Fabrication, testing and reliability modeling of copper/titanium-metallized GaAs MESFETs and HEMTs for low-noise applications

NASA Astrophysics Data System (ADS)

Feng, Ting

Today, GaAs based field effect transistors (FETs) have been used in a broad range of high-speed electronic military and commercial applications. However, their reliability still needs to be improved. Particularly the hydrogen induced degradation is a large remaining issue in the reliability of GaAs FETs, because hydrogen can easily be incorporated into devices during the crystal growth and virtually every device processing step. The main objective of this research work is to develop a new gate metallization system in order to reduce the hydrogen induced degradation from the gate region for GaAs based MESFETs and HEMTs. Cu/Ti gate metallization has been introduced into the GaAs MESFETs and HEMTs in our work in order to solve the hydrogen problem. The purpose of the use of copper is to tie up the hydrogen atoms and prevent hydrogen penetration into the device active region as well as to keep a low gate resistance for low noise applications. In this work, the fabrication technology of GaAs MESFETs and AlGaAs/GaAs HEMTs with Cu/Ti metallized gates have been successfully developed and the fabricated Cu/Ti FETs have shown comparable DC performance with similar Au-based GaAs FETs. The Cu/Ti FETs were subjected to temperature accelerated testing at NOT under 5% hydrogen forming gas and the experimental results show the hydrogen induced degradation has been reduced for the Cu/Ti FETs compared to commonly used AuPtTi based GaAs FETs. A long-term reliability testing for Cu/Ti FETs has also been carried out at 200°C and up to 1000hours and testing results show Cu/Ti FETs performed with adequate reliability. The failure modes were found to consist of a decrease in drain saturation current and pinch-off voltage and an increase in source ohmic contact resistance. Material characterization tools including Rutherford backscattering spectroscopy and a back etching technique were used in Cu/Ti GaAs FETs, and pronounced gate metal copper in-diffusion and intermixing compounds at the

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

First tests of Timepix detectors based on semi-insulating GaAs matrix of different pixel size

NASA Astrophysics Data System (ADS)

Zaťko, B.; Kubanda, D.; Žemlička, J.; Šagátová, A.; Zápražný, Z.; Boháček, P.; Nečas, V.; Mora, Y.; Pichotka, M.; Dudák, J.

2018-02-01

In this work, we have focused on Timepix detectors coupled with the semi-insulating GaAs material sensor. We used undoped bulk GaAs material with the thickness of 350 μm. We prepared and tested four pixelated detectors with 165 μm and 220 μm pixel size with two versions of technology preparation, without and with wet chemically etched trenches around each pixel. We have carried out adjustment of GaAs Timepix detectors to optimize their performance. The energy calibration of one GaAs Timepix detector in Time-over-threshold mode was performed with the use of 241Am and 133Ba radioisotopes. We were able to detect γ-photons with the energy up to 160 keV. The X-ray imaging quality of GaAs Timepix detector was tested with X-ray source using various samples. After flat field we obtained very promising imaging performance of tested GaAs Timepix detectors.

Tight-binding analysis of Si and GaAs ultrathin bodies with subatomic wave-function resolution

NASA Astrophysics Data System (ADS)

Tan, Yaohua P.; Povolotskyi, Michael; Kubis, Tillmann; Boykin, Timothy B.; Klimeck, Gerhard

2015-08-01

Empirical tight-binding (ETB) methods are widely used in atomistic device simulations. Traditional ways of generating the ETB parameters rely on direct fitting to bulk experiments or theoretical electronic bands. However, ETB calculations based on existing parameters lead to unphysical results in ultrasmall structures like the As-terminated GaAs ultrathin bodies (UTBs). In this work, it is shown that more transferable ETB parameters with a short interaction range can be obtained by a process of mapping ab initio bands and wave functions to ETB models. This process enables the calibration of not only the ETB energy bands but also the ETB wave functions with corresponding ab initio calculations. Based on the mapping process, ETB models of Si and GaAs are parameterized with respect to hybrid functional calculations. Highly localized ETB basis functions are obtained. Both the ETB energy bands and wave functions with subatomic resolution of UTBs show good agreement with the corresponding hybrid functional calculations. The ETB methods can then be used to explain realistically extended devices in nonequilibrium that cannot be tackled with ab initio methods.

Performance and temperature dependencies of proton irradiated n/p and p/n GaAs and n/p silicon cells

NASA Technical Reports Server (NTRS)

Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.

1985-01-01

n/p homojunction GaAs cells are found to be more radiation resistant than p/n heteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increased temperature dependency of maximum power for the GaAs n/p cells is attributed to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

GaAs laser diode pumped Nd:YAG laser

NASA Technical Reports Server (NTRS)

Conant, L. C.; Reno, C. W.

1974-01-01

A 1.5-mm by 3-cm neodymium-ion doped YAG laser rod has been side pumped using a GaAs laser diode array tuned to the 8680-A absorption line, achieving a multimode average output power of 120 mW for a total input power of 20 W to the final-stage laser diode drivers. The pumped arrangement was designed to take advantage of the high brightness of a conventional GaAs array as a linear source by introducing the pump light through a slit into a close-wrapped gold coated pump cavity. This cavity forms an integrating chamber for the pump light.

Monolithic high voltage nonlinear transmission line fabrication process

DOEpatents

Cooper, Gregory A.

1994-01-01

A process for fabricating sequential inductors and varactor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varactor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process.

Growth and Photovoltaic Properties of High-Quality GaAs Nanowires Prepared by the Two-Source CVD Method.

PubMed

Wang, Ying; Yang, Zaixing; Wu, Xiaofeng; Han, Ning; Liu, Hanyu; Wang, Shuobo; Li, Jun; Tse, WaiMan; Yip, SenPo; Chen, Yunfa; Ho, Johnny C

2016-12-01

Growing high-quality and low-cost GaAs nanowires (NWs) as well as fabricating high-performance NW solar cells by facile means is an important development towards the cost-effective next-generation photovoltaics. In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method. The high V/III ratio and precursor concentration enabled by this two-source configuration can significantly benefit the NW growth and suppress the crystal defect formation as compared with the conventional one-source system. Since less NW crystal defects would contribute fewer electrons being trapped by the surface oxides, the p-type conductivity is then greatly enhanced as revealed by the electrical characterization of fabricated NW devices. Furthermore, the individual single NW and high-density NW parallel arrays achieved by contact printing can be effectively fabricated into Schottky barrier solar cells simply by employing asymmetric Ni-Al contacts, along with an open circuit voltage of ~0.3 V. All these results indicate the technological promise of these high-quality two-source grown GaAs NWs, especially for the realization of facile Schottky solar cells utilizing the asymmetric Ni-Al contact.

Probability of twin formation on self-catalyzed GaAs nanowires on Si substrate

PubMed Central

2012-01-01

We attempted to control the incorporation of twin boundaries in self-catalyzed GaAs nanowires (NWs). Self-catalyzed GaAs NWs were grown on a Si substrate under various arsenic pressures using molecular beam epitaxy and the vapor-liquid-solid method. When the arsenic flux is low, wurtzite structures are dominant in the GaAs NWs. On the other hand, zinc blende structures become dominant as the arsenic flux rises. We discussed this phenomenon on the basis of thermodynamics and examined the probability of twin-boundary formation in detail. PMID:23043754

Large Signal Modeling and Analysis of the GaAs MESFET.

DTIC Science & Technology

1986-07-09

various dimensions and physical parameters. A powerful computer aided design system can be developed by automating the circuit element and parameter...circuit model of the GaAs MESFET to aid in the designs of microwave MESFET circuits. The circuit elements of this model are obtained either directly...34. -. ’ Abstract The purpose of this work is to develop a large signal signal lumped circuit model of the GaAs MESFET to aid In the designs of microwave MESFET

Giant and reversible enhancement of the electrical resistance of GaAs1-xNx by hydrogen irradiation

NASA Astrophysics Data System (ADS)

Alvarez, J.; Kleider, J.-P.; Trotta, R.; Polimeni, A.; Capizzi, M.; Martelli, F.; Mariucci, L.; Rubini, S.

2011-08-01

The electrical properties of untreated and hydrogen-irradiated GaAs1-xNx are investigated by conductive-probe atomic force microscopy (CP-AFM). After hydrogen irradiation, the resistance R of GaAs1-xNx increases by more than three orders of magnitude while that of a N-free GaAs reference slightly decreases. Thermal annealing at 550 °C of H-irradiated GaAs1-xNx restores the pristine electrical properties of the as-grown sample thus demonstrating that this phenomenon is fully reversible. These effects are attributed to the nitrogen-hydrogen complexes that passivate N in GaAs1-xNx (thus restoring the energy gap of N-free GaAs) and, moreover, reduce the carrier scattering time by more than one order of magnitude. This opens up a route to the fabrication of planar conductive/resistive/conductive heterostructures with submicrometer spatial resolution, which is also reported here.

Germanium diffusion with vapor-phase GeAs and oxygen co-incorporation in GaAs

NASA Astrophysics Data System (ADS)

Wang, Wei-Fu; Cheng, Kai-Yuan; Hsieh, Kuang-Chien

2018-01-01

Vapor-phase germanium diffusion has been demonstrated in Zn-doped and semi-insulating GaAs in sealed ampoules with GeAs powders and excess arsenic. Secondary-ion-mass spectroscopy (SIMS) profiles indicate the presence of unintentional co-incorporation of oxygen in high densities (>1017/cm3) along with diffused germanium donors whose concentration (>>1018/cm3) determined by electro-chemical capacitance-voltage (ECV) profiler shows significant compensation near the surface. The source of oxygen mainly originates from the GeAs powder which contains Ge-O surface oxides. Variable-temperature photoluminescence (PL) shows that in GeAs-diffused samples, a broad peak ranging from 0.86-1.38 eV with the peak position around 1.1 eV predominates at low temperatures while the near band-edge luminescence quenches. The broad band is attributed to the GeGa-VGa self-activated (SA) centers possibly associated with nearby oxygen-related defect complex, and its luminescence persists up to 400 K. The configurational-coordinate modeling finds that the SA defect complex has a thermal activation energy of 150-180 meV and a vibrational energy 26.8 meV. The presence of oxygen does not much affect the SA emission intensity but may have influenced the peak position, vibration frequency and activation energy as compared to other common donor-VGa defects in GaAs.

The growth of low band-gap InAs on (111)B GaAs substrates

NASA Technical Reports Server (NTRS)

Welser, R. E.; Guido, L. J.

1995-01-01

The use of low band-gap materials is of interest for a number of photovoltaic and optoelectronic applications, such as bottom cells of optimized multijunction solar cell designs, long wavelength light sources, detectors, and thermophotovoltaics. However, low band-gap materials are generally mismatched with respect to lattice constant, thermal expansion coefficient, and chemical bonding to the most appropriate commercially available substrates (Si, Ge, and GaAs). For the specific case of III-V semiconductor heteroepitaxy, one must contend with the strain induced by both lattice constant mismatch at the growth temperature and differences in the rates of mechanical deformation during the cool down cycle. Several experimental techniques have been developed to minimize the impact of these phenomena (i.e., compositional grading, strained layer superlattices, and high-temperature annealing). However, in highly strained systems such as InAs-on-GaAs, three-dimensional island formation and large defect densities (greater than or equal to 10(exp 8)/ cm(exp -2)) tend to limit their applicability. In these particular cases, the surface morphology and defect density must be controlled during the initial stages of nucleation and growth. At the last SPRAT conference, we reported on a study of the evolution of InAs islands on (100) and (111)B GaAs substrates. Growth on the (111)B orientation exhibits a number of advantageous properties as compared to the (100) during these early stages of strained-layer epitaxy. In accordance with a developing model of nucleation and growth, we have deposited thin (60 A - 2500 A), fully relaxed InAs films on (111)B GaAs substrates. Although thicker InAs films are subject to the formation of twin defects common to epitaxy on the (111)B orientation, appropriate control of the growth parameters can greatly minimize their density. Using this knowledge base, InAs films up to 2 microns in thickness with improved morphology and structural quality have

Monolithic high voltage nonlinear transmission line fabrication process

DOEpatents

Cooper, G.A.

1994-10-04

A process for fabricating sequential inductors and varistor diodes of a monolithic, high voltage, nonlinear, transmission line in GaAs is disclosed. An epitaxially grown laminate is produced by applying a low doped active n-type GaAs layer to an n-plus type GaAs substrate. A heavily doped p-type GaAs layer is applied to the active n-type layer and a heavily doped n-type GaAs layer is applied to the p-type layer. Ohmic contacts are applied to the heavily doped n-type layer where diodes are desired. Multiple layers are then either etched away or Oxygen ion implanted to isolate individual varistor diodes. An insulator is applied between the diodes and a conductive/inductive layer is thereafter applied on top of the insulator layer to complete the process. 6 figs.

Electric field effects on the optical properties of buckled GaAs monolayer

NASA Astrophysics Data System (ADS)

Bahuguna, Bhagwati Prasad; Saini, L. K.; Sharma, Rajesh O.

2018-04-01

Buckled GaAs monolayer has a direct band gap semiconductor with energy gap of 1.31 eV in the absence of electric field. When we applied transverse electric field, the value of band gap decreases with increasing of electric field strength. In our previous work [1], it is observed that the buckled GaAs monolayer becomes metallic at 1.3 V/Å. In the present work, we investigate the optical properties such as photon energy-dependent dielectric functions, extinction coefficient, refractive index, absorption spectrum and reflectivity of buckled GaAs monolayer in the semiconducting phase i.e. absence of external electric field and metallic phase i.e. presence of external electric field using density functional theory.

Gallium arsenide processing for gate array logic

NASA Technical Reports Server (NTRS)

Cole, Eric D.

1989-01-01

The development of a reliable and reproducible GaAs process was initiated for applications in gate array logic. Gallium Arsenide is an extremely important material for high speed electronic applications in both digital and analog circuits since its electron mobility is 3 to 5 times that of silicon, this allows for faster switching times for devices fabricated with it. Unfortunately GaAs is an extremely difficult material to process with respect to silicon and since it includes the arsenic component GaAs can be quite dangerous (toxic) especially during some heating steps. The first stage of the research was directed at developing a simple process to produce GaAs MESFETs. The MESFET (MEtal Semiconductor Field Effect Transistor) is the most useful, practical and simple active device which can be fabricated in GaAs. It utilizes an ohmic source and drain contact separated by a Schottky gate. The gate width is typically a few microns. Several process steps were required to produce a good working device including ion implantation, photolithography, thermal annealing, and metal deposition. A process was designed to reduce the total number of steps to a minimum so as to reduce possible errors. The first run produced no good devices. The problem occurred during an aluminum etch step while defining the gate contacts. It was found that the chemical etchant attacked the GaAs causing trenching and subsequent severing of the active gate region from the rest of the device. Thus all devices appeared as open circuits. This problem is being corrected and since it was the last step in the process correction should be successful. The second planned stage involves the circuit assembly of the discrete MESFETs into logic gates for test and analysis. Finally the third stage is to incorporate the designed process with the tested circuit in a layout that would produce the gate array as a GaAs integrated circuit.

Nuclear spin warm up in bulk n -GaAs

NASA Astrophysics Data System (ADS)

Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

2016-08-01

We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2013 CFR

2013-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2012 CFR

2012-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2010 CFR

2010-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2014 CFR

2014-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

Code of Federal Regulations, 2011 CFR

2011-10-01

... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

Real-time observation of FIB-created dots and ripples on GaAs

NASA Astrophysics Data System (ADS)

Rose, F.; Fujita, H.; Kawakatsu, H.

2008-01-01

We report a phenomenological study of Ga dots and ripples created by a focused ion beam (FIB) on the GaAs(001) surface. Real-time observation of dot diffusion and ripple formation was made possible by recording FIB movies. In the case of FIB irradiation with a 40 nA current of Ga+ ions accelerated under 40 kV with an incidence angle of θ = 30°, increasing ion dose gives rise to three different regimes. In Regime 1, dots with lateral sizes in the range 50-460 nm are formed. Dots diffuse under continuous sputtering. In Regime 2, dots self-assemble into Bradley and Harper (BH) type ripples with a pseudo-period of λ = 1150 ± 25 nm. In Regime 3, ripples are eroded and the surface topology evolves into microplanes. In the case of normal incidence, FIB sputtering leads only to the formation of dots, without surface rippling.

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.

Interface dynamics and crystal phase switching in GaAs nanowires

NASA Astrophysics Data System (ADS)

Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M.

2016-03-01

Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

Periodic annealing of radiation damage in GaAs solar cells

NASA Technical Reports Server (NTRS)

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

1980-01-01

Continuous annealing of GaAs solar cells is compared with periodic annealing to determine their relative effectiveness in minimizing proton radiation damage. It is concluded that continuous annealing of the cells in space at 150 C can effectively reduce the proton radiation damage to the GaAs solar cells. Periodic annealing is most effective if it can be initiated at relatively low fluences (approximating continuous annealing), especially if low temperatures of less than 200 C are to be used. If annealing is started only after the fluence of the damaging protons has accumulated to a high value 10 to the 11th power sq/pcm), effective annealing is still possible at relatively high temperatures. Finally, since electron radiation damage anneals even more easily than proton radiation damage, substantial improvements in GaAs solar cell life can be achieved by incorporating the proper annealing capabilities in solar panels for practical space missions where both electron and proton radiation damage have to be minimized.

Interface dynamics and crystal phase switching in GaAs nanowires.

PubMed

Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A; Ross, Frances M

2016-03-17

Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Juang, Bor-Chau, E-mail: bcjuang@ucla.edu; Laghumavarapu, Ramesh B.; Foggo, Brandon J.

There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAsmore » substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.« less

Disruption of Higher Order DNA Structures in Friedreich’s Ataxia (GAA)n Repeats by PNA or LNA Targeting

PubMed Central

Bergquist, Helen; Rocha, Cristina S. J.; Álvarez-Asencio, Rubén; Nguyen, Chi-Hung; Rutland, Mark. W.; Smith, C. I. Edvard; Good, Liam; Nielsen, Peter E.; Zain, Rula

2016-01-01

Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigenetic modifications. With the aim of interfering with higher order H-DNA (like) DNA structures within pathological (GAA)n expansions, we examined sequence-specific interaction of peptide nucleic acid (PNA) with (GAA)n repeats of different lengths (short: n=9, medium: n=75 or long: n=115) by chemical probing of triple helical and single stranded regions. We found that a triplex structure (H-DNA) forms at GAA repeats of different lengths; however, single stranded regions were not detected within the medium size pathological repeat, suggesting the presence of a more complex structure. Furthermore, (GAA)4-PNA binding of the repeat abolished all detectable triplex DNA structures, whereas (CTT)5-PNA did not. We present evidence that (GAA)4-PNA can invade the DNA at the repeat region by binding the DNA CTT strand, thereby preventing non-canonical-DNA formation, and that triplex invasion complexes by (CTT)5-PNA form at the GAA repeats. Locked nucleic acid (LNA) oligonucleotides also inhibited triplex formation at GAA repeat expansions, and atomic force microscopy analysis showed significant relaxation of plasmid morphology in the presence of GAA-LNA. Thus, by inhibiting disease related higher order DNA structures in the Frataxin gene, such PNA and LNA oligomers may have potential for discovery of drugs aiming at recovering Frataxin expression. PMID:27846236

The effect of V/III ratio on the morphology and structure of GaAs nanowires by MOCVD

NASA Astrophysics Data System (ADS)

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

2018-05-01

In this paper, GaAs nanowires with different V/III ratios (70, 140, 280 and 560) were vertically grown from bottom to top on GaAs substrates by using metal organic chemical vapor deposition based on gold assisted vapor-liquid-solid mechanism. It is found that the growth rate of nanowires is inversely proportional to their V/III ratio. And the V/III ratio can also change nanowire growth type. For the nanowire with small V/III ratios (≤280), the reactants are most from those atoms merged in the catalyst. But, for the nanowire with V/III ratio 560, the contribution mainly comes from the diffusions of atoms pyrolyzed on the surface of the nanowire and the substrate. A shrunken neck under the catalyst is observed in TEM characterizations. These results will provide a theoretical basis for potential practical applications of nanowire-based devices.

830-nm Polarization Controlled Lasing of InGaAs Quantum Wire Vertical-Cavity Surface-Emitting Lasers Grown on (775)B GaAs Substrates by Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Higuchi, Yu; Osaki, Shinji; Sasahata, Yoshifumi; Kitada, Takahiro; Shimomura, Satoshi; Ogura, Mutsuo; Hiyamizu, Satoshi

2007-02-01

We report the first demonstration of room temperature (RT) current injection lasing of vertical-cavity surface-emitting lasers (VCSELs), with self-organized InGaAs/(GaAs)6(AlAs)1 quantum wires (QWRs) in their active region, grown on (775)B-oriented GaAs substrates by molecular beam epitaxy. A (775)B InGaAs QWR-VCSEL with an aperture diameter of 4 μm lased at a wavelength of 829.7 nm and a threshold current of 0.7 mA at RT. The light output was linearly polarized in the direction parallel to the QWRs due to optical anisotropy of the self-organized (775)B InGaAs QWRs.

Radial Growth of Self-Catalyzed GaAs Nanowires and the Evolution of the Liquid Ga-Droplet Studied by Time-Resolved in Situ X-ray Diffraction.

PubMed

Schroth, Philipp; Jakob, Julian; Feigl, Ludwig; Mostafavi Kashani, Seyed Mohammad; Vogel, Jonas; Strempfer, Jörg; Keller, Thomas F; Pietsch, Ullrich; Baumbach, Tilo

2018-01-10

We report on a growth study of self-catalyzed GaAs nanowires based on time-resolved in situ X-ray structure characterization during molecular-beam-epitaxy in combination with ex situ scanning-electron-microscopy. We reveal the evolution of nanowire radius and polytypism and distinguish radial growth processes responsible for tapering and side-wall growth. We interpret our results using a model for diameter self-stabilization processes during growth of self-catalyzed GaAs nanowires including the shape of the liquid Ga-droplet and its evolution during growth.

A comparison of GaAs and Si hybrid solar power systems

NASA Technical Reports Server (NTRS)

Heinbockel, J. H.; Roberts, A. S., Jr.

1977-01-01

Five different hybrid solar power systems using silicon solar cells to produce thermal and electric power are modeled and compared with a hybrid system using a GaAs cell. Among the indices determined are capital cost per unit electric power plus mechanical power, annual cost per unit electric energy, and annual cost per unit electric plus mechanical work. Current costs are taken to be $35,000/sq m for GaAs cells with an efficiency of 15% and $1000/sq m for Si cells with an efficiency of 10%. It is shown that hybrid systems can be competitive with existing methods of practical energy conversion. Limiting values for annual costs of Si and GaAs cells are calculated to be 10.3 cents/kWh and 6.8 cents/kWh, respectively. Results for both systems indicate that for a given flow rate there is an optimal operating condition for minimum cost photovoltaic output. For Si cell costs of $50/sq m optimal performance can be achieved at concentrations of about 10; for GaAs cells costing 1000/sq m, optimal performance can be obtained at concentrations of around 100. High concentration hybrid systems offer a distinct cost advantage over flat systems.

Basic mechanisms study for MIS solar cell structures on GaAs

NASA Technical Reports Server (NTRS)

Fonash, S. J.

1978-01-01

The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

Photoelectrochemical Water Oxidation by GaAs Nanowire Arrays Protected with Atomic Layer Deposited NiO x Electrocatalysts

NASA Astrophysics Data System (ADS)

Zeng, Joy; Xu, Xiaoqing; Parameshwaran, Vijay; Baker, Jon; Bent, Stacey; Wong, H.-S. Philip; Clemens, Bruce

2018-02-01

Photoelectrochemical (PEC) hydrogen production makes possible the direct conversion of solar energy into chemical fuel. In this work, PEC photoanodes consisting of GaAs nanowire (NW) arrays were fabricated, characterized, and then demonstrated for the oxygen evolution reaction (OER). Uniform and periodic GaAs nanowire arrays were grown on a heavily n-doped GaAs substrates by metal-organic chemical vapor deposition selective area growth. The nanowire arrays were characterized using cyclic voltammetry and impedance spectroscopy in a non-aqueous electrochemical system using ferrocene/ferrocenium (Fc/Fc+) as a redox couple, and a maximum oxidation photocurrent of 11.1 mA/cm2 was measured. GaAs NW arrays with a 36 nm layer of nickel oxide (NiO x ) synthesized by atomic layer deposition were then used as photoanodes to drive the OER. In addition to acting as an electrocatalyst, the NiO x layer served to protect the GaAs NWs from oxidative corrosion. Using this strategy, GaAs NW photoanodes were successfully used for the oxygen evolution reaction. This is the first demonstration of GaAs NW arrays for effective OER, and the fabrication and protection strategy developed in this work can be extended to study any other nanostructured semiconductor materials systems for electrochemical solar energy conversion.

Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

NASA Technical Reports Server (NTRS)

Bhasin, K. B.; Ponchak, G. E.; Kascak, T. J.

1985-01-01

Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

Effect of Ion Sputtering on Interface Chemistry and Electrical Properties of an Gaas (100) Schottky Contacts

NASA Technical Reports Server (NTRS)

Wang, Y. X.; Holloway, P. H.

1984-01-01

Auger and electron photoelectron spectroscopy were used to measure the extent of As depletion during 1 keV to 5 keV argon sputtering of GaAs surfaces. This depletion was correlated with a general decrease in the barrier height of the rectifying Au contact deposited in situ. However, nondestructive angle resolved XPS measurements showed As was depleted at the outer surface more by 1 keV than 3 keV argon. These effects are explained based on a combined work effective work function model and creation of a donor like surface damage layer. The donor layer was correlated with As depletion by sputtering. Deep level trap formation and annealing of sputtering effects were studied.

Scanning tunneling microscopy studies of Si donors (Si[sub Ga]) in GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, J.F.; Liu, X.; Newman, N.

1994-03-07

We report scanning tunneling microscopy (STM) studies of Si substitutional donors (Si[sub Ga]) in GaAs that reveal delocalized and localized electronic features corresponding to Si[sub Ga] in the top few layers of the (110) cleavage surface. The delocalized features appear as protrusions a few nm in size, superimposed on the background lattice. These features are attributed to enhanced tunneling due to the local perturbation of the band bending by the Coulomb potential of subsurface Si[sub Ga]. In contrast, STM images of surface Si[sub Ga] show very localized electronic structures, in good agreement with a recent theoretical prediction [J. Wang [italmore » et] [ital al]., Phys. Rev. B 47, 10 329 (1993)].« less

Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (0 0 1) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Ha, Minh Thien Huu; Hoang Huynh, Sa; Binh Do, Huy; Nguyen, Tuan Anh; Luc, Quang Ho; Chang, Edward Yi

2017-08-01

High quality 40 nm GaSb thin film was grown on the zero off-cut Si (0 0 1)-oriented substrate using metalorganic chemical vapor deposition with the temperature-graded GaAs buffer layer. The growth time of the GaAs nucleation layer, which was deposited at a low temperature of 490 °C, is systematically investigated in this paper. Cross-sections of the high resolution transmission electron microscopy images indicate that the GaAs compound formed 3D-islands first before to quasi-2D islands, and finally formed uniform GaAs layer. The optimum thickness of the 490 °C-GaAs layer was found to be 10 nm to suppress the formation of antiphase domain boundaries (APDs). The thin GaAs nucleation layer had a root-mean-square surface roughness of 0.483 nm. This allows the continued high temperature GaAs buffer layer to be achieved with low threading dislocation density of around 7.1  ×  106 cm-2 and almost invisible APDs. Finally, a fully relaxed GaSb film was grown on the top of the GaAs/Si heterostructure using interfacial misfit dislocation growth mode. These results indicate that the GaSb epitaxial layer can be grown on Si substrate with GaAs buffer layer for future p-channel metal-oxide-semiconductor field effect transistors (MOSFETs) applications.

High purity low dislocation GaAs single crystals

NASA Technical Reports Server (NTRS)

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

1982-01-01

Recent advances in GaAs bulk crystal growth using the LEC (liquid encapsulated Czochralski) technique are described. The dependence of the background impurity concentration and the dislocation density distribution on the materials synthesis and growth conditions were investigated. Background impurity concentrations as low as 4 x 10 to the 15th power were observed in undoped LEC GaAs. The dislocation density in selected regions of individual ingots was very low, below the 3000 cm .3000/sq cm threshold. The average dislocation density over a large annular ring on the wafers fell below the 10000/sq cm level for 3 inch diameter ingots. The diameter control during the program advanced to a diameter variation along a 3 inch ingot less than 2 mm.

Highly efficient single-junction GaAs thin-film solar cell on flexible substrate.

PubMed

Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

2016-07-20

There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.

Radiation testing of GaAs on CRRES and LIPS experiment

NASA Technical Reports Server (NTRS)

Trumble, T. M.; Masloski, K.

1984-01-01

The radiation damage of solar cells has become a prime concern to the U.S. Air Force due to longer satellite lifetime requirements. Flight experiments were undertaken on the Navy Living Plume Shield (LPS) satellite and the NASA/Air Force Combined Release and Radiation Effects Satellite (CRRES) to complement existing radiation testing. Each experiment, the rationale behind it, and its approach and status are presented. The effect of space radiation on gallium arsenide (GaAs) solar cells was the central parameter investigated. Specifications of the GaAs solar cells are given.

Visualization of carrier dynamics in p(n)-type GaAs by scanning ultrafast electron microscopy

PubMed Central

Cho, Jongweon; Hwang, Taek Yong; Zewail, Ahmed H.

2014-01-01

Four-dimensional scanning ultrafast electron microscopy is used to investigate doping- and carrier-concentration-dependent ultrafast carrier dynamics of the in situ cleaved single-crystalline GaAs(110) substrates. We observed marked changes in the measured time-resolved secondary electrons depending on the induced alterations in the electronic structure. The enhancement of secondary electrons at positive times, when the electron pulse follows the optical pulse, is primarily due to an energy gain involving the photoexcited charge carriers that are transiently populated in the conduction band and further promoted by the electron pulse, consistent with a band structure that is dependent on chemical doping and carrier concentration. When electrons undergo sufficient energy loss on their journey to the surface, dark contrast becomes dominant in the image. At negative times, however, when the electron pulse precedes the optical pulse (electron impact), the dynamical behavior of carriers manifests itself in a dark contrast which indicates the suppression of secondary electrons upon the arrival of the optical pulse. In this case, the loss of energy of material’s electrons is by collisions with the excited carriers. These results for carrier dynamics in GaAs(110) suggest strong carrier–carrier scatterings which are mirrored in the energy of material’s secondary electrons during their migration to the surface. The approach presented here provides a fundamental understanding of materials probed by four-dimensional scanning ultrafast electron microscopy, and offers possibilities for use of this imaging technique in the study of ultrafast charge carrier dynamics in heterogeneously patterned micro- and nanostructured material surfaces and interfaces. PMID:24469803

Visualization of carrier dynamics in p(n)-type GaAs by scanning ultrafast electron microscopy.

PubMed

Cho, Jongweon; Hwang, Taek Yong; Zewail, Ahmed H

2014-02-11

Four-dimensional scanning ultrafast electron microscopy is used to investigate doping- and carrier-concentration-dependent ultrafast carrier dynamics of the in situ cleaved single-crystalline GaAs(110) substrates. We observed marked changes in the measured time-resolved secondary electrons depending on the induced alterations in the electronic structure. The enhancement of secondary electrons at positive times, when the electron pulse follows the optical pulse, is primarily due to an energy gain involving the photoexcited charge carriers that are transiently populated in the conduction band and further promoted by the electron pulse, consistent with a band structure that is dependent on chemical doping and carrier concentration. When electrons undergo sufficient energy loss on their journey to the surface, dark contrast becomes dominant in the image. At negative times, however, when the electron pulse precedes the optical pulse (electron impact), the dynamical behavior of carriers manifests itself in a dark contrast which indicates the suppression of secondary electrons upon the arrival of the optical pulse. In this case, the loss of energy of material's electrons is by collisions with the excited carriers. These results for carrier dynamics in GaAs(110) suggest strong carrier-carrier scatterings which are mirrored in the energy of material's secondary electrons during their migration to the surface. The approach presented here provides a fundamental understanding of materials probed by four-dimensional scanning ultrafast electron microscopy, and offers possibilities for use of this imaging technique in the study of ultrafast charge carrier dynamics in heterogeneously patterned micro- and nanostructured material surfaces and interfaces.

Enhanced second-harmonic generation from resonant GaAs gratings.

PubMed

de Ceglia, D; D'Aguanno, G; Mattiucci, N; Vincenti, M A; Scalora, M

2011-03-01

We theoretically study second harmonic generation in nonlinear, GaAs gratings. We find large enhancement of conversion efficiency when the pump field excites the guided mode resonances of the grating. Under these circumstances the spectrum near the pump wavelength displays sharp resonances characterized by dramatic enhancements of local fields and favorable conditions for second-harmonic generation, even in regimes of strong linear absorption at the harmonic wavelength. In particular, in a GaAs grating pumped at 1064 nm, we predict second-harmonic conversion efficiencies approximately 5 orders of magnitude larger than conversion rates achievable in either bulk or etalon structures of the same material.

Scanning microwave microscopy applied to semiconducting GaAs structures

NASA Astrophysics Data System (ADS)

Buchter, Arne; Hoffmann, Johannes; Delvallée, Alexandra; Brinciotti, Enrico; Hapiuk, Dimitri; Licitra, Christophe; Louarn, Kevin; Arnoult, Alexandre; Almuneau, Guilhem; Piquemal, François; Zeier, Markus; Kienberger, Ferry

2018-02-01

A calibration algorithm based on one-port vector network analyzer (VNA) calibration for scanning microwave microscopes (SMMs) is presented and used to extract quantitative carrier densities from a semiconducting n-doped GaAs multilayer sample. This robust and versatile algorithm is instrument and frequency independent, as we demonstrate by analyzing experimental data from two different, cantilever- and tuning fork-based, microscope setups operating in a wide frequency range up to 27.5 GHz. To benchmark the SMM results, comparison with secondary ion mass spectrometry is undertaken. Furthermore, we show SMM data on a GaAs p-n junction distinguishing p- and n-doped layers.

Selective Area Growth of GaAs on Si Patterned Using Nanoimprint Lithography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warren, Emily L.; Makoutz, Emily A.; Horowitz, Kelsey A. W.

Heteroepitaxial selective area growth (SAG) of GaAs on patterned Si substrates is a potential low-cost approach to integrate III-V and Si materials for tandem or multijunction solar cells. The use of nanoscale openings in a dielectric material can minimize nucleation-related defects and allow thinner buffer layers to be used to accommodate lattice mismatch between Si and an epitaxial III-V layer. For photovoltaic applications, the cost of patterning and growth, as well as the impact on the performance of the Si bottom cell must be considered. We present preliminary results on the use of soft nanoimprint lithography (SNIL) to create patternedmore » nucleation templates for the heteroepitaxial SAG of GaAs on Si. We demonstrate that SNIL patterning of passivating layers on the Si substrate improves measured minority carrier properties relative to unprotected Si. Cost modeling of the SNIL process shows that adding a patterning step only adds a minor contribution to the overall cost of a tandem III-V/Si solar cell, and can enable significant savings if it enables thinner buffer layers.« less

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.

Theoretical and experimental study of highly textured GaAs on silicon using a graphene buffer layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alaskar, Yazeed; Arafin, Shamsul; Lin, Qiyin

2015-09-01

A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (..theta..-2..theta.. scan, ..omega..-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smoothmore » GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.« less

Bistable Vertical-Cavity Surface-Emitting Laser. Structures on GaAs and Si Substrates

DTIC Science & Technology

1994-06-01

vertical - cavity surface - emitting lasers ( VCSELs ) [1,5,6 of publications below], fabrication processes to realize low...May 91 through 1 June 94 R&T Number: Contract / Grant Number: N00014-91-J-1952 Contract / Grant Title: Bistable Vertical - Cavity Surface - Emitting Laser ...T.J. Rogers, B.G. Streetman, S.C. Smith, and R.D. Burnham, "Cascadabity of an Optically Iathing Vertical - Cavity Surface - Emitting Laser

GaAs1-xBix/GaNyAs1-y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics.

PubMed

Broderick, Christopher A; Jin, Shirong; Marko, Igor P; Hild, Konstanze; Ludewig, Peter; Bushell, Zoe L; Stolz, Wolfgang; Rorison, Judy M; O'Reilly, Eoin P; Volz, Kerstin; Sweeney, Stephen J

2017-04-19

The potential to extend the emission wavelength of photonic devices further into the near- and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs 1-x Bi x /GaN y As 1-y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs 0.967 Bi 0.033 /GaN 0.062 As 0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications.

GaAs1-xBix/GaNyAs1-y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics

NASA Astrophysics Data System (ADS)

Broderick, Christopher A.; Jin, Shirong; Marko, Igor P.; Hild, Konstanze; Ludewig, Peter; Bushell, Zoe L.; Stolz, Wolfgang; Rorison, Judy M.; O'Reilly, Eoin P.; Volz, Kerstin; Sweeney, Stephen J.

2017-04-01

The potential to extend the emission wavelength of photonic devices further into the near- and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1-xBix/GaNyAs1-y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications.

Fermi level pinning at epitaxial Si on GaAs(100) interfaces

NASA Astrophysics Data System (ADS)

Silberman, J. A.; de Lyon, T. J.; Woodall, J. M.

1991-12-01

GaAs Schottky barrier contacts and metal-insulator-semiconductor structures that include thin epitaxial Si interfacial layers operate in a manner consistent with an unpinned Fermi level at the GaAs interface. These findings raise the question of whether this effect is an intrinsic property of the epitaxial GaAs(100)-Si interface. We have used x-ray photoemission spectroscopy to monitor the Fermi level position during in situ growth of thin epitaxial Si layers. In particular, films formed on heavily doped n- and p-type substrates were compared so as to use the large depletion layer fields available with high impurity concentration as a field-effect probe of the interface state density. The results demonstrate that epitaxial bonding at the interface alone is insufficient to eliminate Fermi level pinning, indicating that other mechanisms affect the interfacial charge balance in the devices that utilize Si interlayers.

Diffused junction p(+)-n solar cells in bulk GaAs. II - Device characterization and modelling

NASA Technical Reports Server (NTRS)

Keeney, R.; Sundaram, L. M. G.; Rode, H.; Bhat, I.; Ghandhi, S. K.; Borrego, J. M.

1984-01-01

The photovoltaic characteristics of p(+)-n junction solar cells fabricated on bulk GaAs by an open tube diffusion technique are presented in detail. Quantum efficiency measurements were analyzed and compared to computer simulations of the cell structure in order to determine material parameters such as diffusion length, surface recombination velocity and junction depth. From the results obtained it is projected that proper optimization of the cell parameters can increase the efficiency of the cells to close to 20 percent.

Improved interfacial and electrical properties of GaAs metal-oxide-semiconductor capacitors with HfTiON as gate dielectric and TaON as passivation interlayer

NASA Astrophysics Data System (ADS)

Wang, L. S.; Xu, J. P.; Zhu, S. Y.; Huang, Y.; Lai, P. T.

2013-08-01

The interfacial and electrical properties of sputtered HfTiON on sulfur-passivated GaAs with or without TaON as interfacial passivation layer (IPL) are investigated. Experimental results show that the GaAs metal-oxide-semiconductor capacitor with HfTiON/TaON stacked gate dielectric annealed at 600 °C exhibits low interface-state density (1.0 × 1012 cm-2 eV-1), small gate leakage current (7.3 × 10-5 A cm-2 at Vg = Vfb + 1 V), small capacitance equivalent thickness (1.65 nm), and large equivalent dielectric constant (26.2). The involved mechanisms lie in the fact that the TaON IPL can effectively block the diffusions of Hf, Ti, and O towards GaAs surface and suppress the formation of interfacial As-As bonds, Ga-/As-oxides, thus unpinning the Femi level at the TaON/GaAs interface and improving the interface quality and electrical properties of the device.

Structures, Properties and Defects of SrTiO3/GaAs Hetero-interfaces

NASA Astrophysics Data System (ADS)

Hong, Liang; Bhatnagar, Kunal; Droopad, Ravi; Öğüt, Serdar; Klie, Robert

SrTiO3 thin film can be epitaxially grown on GaAs substrate and used as a platform for growing other oxides to create functional metal-oxide-semiconductor devices, where a high-quality SrTiO3/GaAs interface is essential. We studied the structural and electronic properties of SrTiO3/GaAs hetero-interfaces at atomic level using scanning transmission electron microscopy and first-principles calculations. Our results suggest the preferred termination of GaAs (001) is significantly dependent on the oxygen concentration in the first oxide layer. The favorable interface structure is characterized as oxygen-deficient SrO in contact with arsenic and is observed in both experiment and simulation. The electronic properties are calculated and found to be tunable by interfacial defects such as oxygen, gallium and arsenic vacancies. This work was supported by the National Science Foundation (Grant No. DMR-1408427). This work made use of instruments in the Electron Microscopy Service and the High Performance Computing Clusters at University of Illinois at Chicago.

Accelerated GaAs growth through MOVPE for low-cost PV applications

NASA Astrophysics Data System (ADS)

Ubukata, Akinori; Sodabanlu, Hassanet; Watanabe, Kentaroh; Koseki, Shuichi; Yano, Yoshiki; Tabuchi, Toshiya; Sugaya, Takeyoshi; Matsumoto, Koh; Nakano, Yoshiaki; Sugiyama, Masakazu

2018-05-01

The high growth rate of epitaxial GaAs was investigated using a novel horizontal metalorganic vapor phase epitaxy (MOVPE) reactor, from the point of view of realizing low-cost photovoltaic (PV) solar cells. The GaAs growth rate exhibited an approximately linear relationship with the amount of trimethylgalium (TMGa) supplied, up to a rate of 90 μm/h. The distribution of growth rate was observed for a two-inch wafer, along the flow direction, and the normalized profile of the distribution was found to be independent of the precursor input, from 20 to 70 μm/h. These tendencies indicated that significant parasitic prereaction did not occur in the gaseous phase, for this range of growth rate. GaAs p-n single-junction solar cells were successfully fabricated at growth rates of 20, 60, and 80 μm/h. The conversion efficiency of the cell grown at 80 μm/h was comparable to that of the 20 μm/h cell, indicating the good quality and properties of GaAs. The epitaxial growth exhibited good uniformity, as evidenced by the uniformity of the cell performance across the wafer, from the center to the edge. The result indicated the potential of high-throughput MOVPE for low-cost production, not only for PV devices but also for other semiconductor applications.

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.

Orientation and temperature dependent adsorption of H 2S on GaAs: Valence band photoemission

NASA Astrophysics Data System (ADS)

Ranke, W.; Kuhr, H. J.; Finster, J.

A cylindrically shaped GaAs single crystal was used to study the adsorption of H 2S on the six inequivalent orientations (001), (113), (111), (110), (111) and (113) by angle resolved valence band photoelectron spectroscopy and surface dipole measurements. Adsorption at 150 K on the surface prepared by molecular beam epitaxy (MBE) yields similar adsorbate induced emission on all orientations which were ascribed to SH radicals. On (110), where preferential adsorption occurs additional features from molecular H 2S are observed. The adsorbate spectra at 720 K are ascribed to atomic sulphur. On the surface prepared by ion bombardment and annealing, defect enhanced adsorption occurs in the range (111)-(113). The adsorbate spectra are very similar to those on the MBE surface at 720 K. Thus, no new species are adsorbed on defects but only sticking probability and penetration capability are increased.

Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

NASA Technical Reports Server (NTRS)

Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

2003-01-01

NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

Alternatives to Arsine: The Atmospheric Pressure Organometallic Chemical Vapor Deposition Growth of GaAs Using Triethylarsenic.

DTIC Science & Technology

1987-08-15

SUPPLEMENTARY NOTATION 17. COSATI CODES 18 SUBJECT TERMS (Corinue on reverse if necessary and identify by block number) FIELD GROUP SUB-GROUP Epitaxy GaAs 9...Zr leiK m I141’ FIGURES 1 . Effect of Growth Parameters on Residual Doping Type ................... 7 2. Photoluminescence Spectrum of a GaAs Epilayer... 1 3 Successful homoepitaxial growth of high purity, unintentionally doped GaAs epilayers by organometallic chemical vapor deposition (OMCVD) has

Overcoming Ehrlich-Schwöbel barrier in (1 1 1)A GaAs molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ritzmann, Julian; Schott, Rüdiger; Gross, Katherine; Reuter, Dirk; Ludwig, Arne; Wieck, Andreas D.

2018-01-01

In this work, we first study the effect of different growth parameters on the molecular beam epitaxy (MBE) growth of GaAs layers on (1 1 1)A oriented substrates. After that we present a method for the MBE growth of atomically smooth layers by sequences of growth and annealing phases. The samples exhibit low surface roughness and good electrical properties shown by atomic force microscopy (AFM), scanning electron microscopy (SEM) and van-der-Pauw Hall measurements.

Imaging surface plasmon polaritons using proximal self-assembled InGaAs quantum dots

NASA Astrophysics Data System (ADS)

Bracher, Gregor; Schraml, Konrad; Blauth, Mäx; Wierzbowski, Jakob; López, Nicolás Coca; Bichler, Max; Müller, Kai; Finley, Jonathan J.; Kaniber, Michael

2014-07-01

We present optical investigations of hybrid plasmonic nanosystems consisting of lithographically defined plasmonic Au-waveguides or beamsplitters on GaAs substrates coupled to proximal self-assembled InGaAs quantum dots. We designed a sample structure that enabled us to precisely tune the distance between quantum dots and the sample surface during nano-fabrication and demonstrated that non-radiative processes do not play a major role for separations down to ˜ 10 nm. A polarized laser beam focused on one end of the plasmonic nanostructure generates propagating surface plasmon polaritons that, in turn, create electron-hole pairs in the GaAs substrate during propagation. These free carriers are subsequently captured by the quantum dots ˜ 25 nm below the surface, giving rise to luminescence. The intensity of the spectrally integrated quantum dot luminescence is used to image the propagating plasmon modes. As the waveguide width reduces from 5 μ m to 1 μ m, we clearly observe different plasmonic modes at the remote waveguide end, enabling their direct imaging in real space. This imaging technique is applied to a plasmonic beamsplitter facilitating the determination of the splitting ratio between the two beamsplitter output ports as the interaction length L i is varied. A splitting ratio of 50:50 is observed for L i ˜ 9 ± 1 μ m and 1 μ m wide waveguides for excitation energies close to the GaAs band edge. Our experimental findings are in good agreement with mode profile and finite difference time domain simulations for both waveguides and beamsplitters.

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

NASA Astrophysics Data System (ADS)

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

2013-09-01

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

The importance of scattering, surface potential, and vanguard counter-potential in terahertz emission from gallium arsenide

NASA Astrophysics Data System (ADS)

Cortie, D. L.; Lewis, R. A.

2012-06-01

It is well established that under excitation by short (<1 ps), above-band-gap optical pulses, semiconductor surfaces may emit terahertz-frequency electromagnetic radiation via photocarrier diffusion (the dominant mechanism in InAs) or photocarrier drift (dominant in GaAs). Our three-dimensional ensemble Monte Carlo simulations allow multiple physical parameters to vary over wide ranges and provide unique direct insight into the factors controlling terahertz emission. We find for GaAs (in contrast to InAs), scattering and the surface potential are key factors. We further delineate in GaAs (as in InAs) the role of a vanguard counter-potential. The effects of varying dielectric constant, band-gap, and effective mass are similar in both emitter types.

Negative differential velocity in ultradilute GaAs1-xNx alloys

NASA Astrophysics Data System (ADS)

Vogiatzis, N.; Rorison, J. M.

2011-04-01

We present theoretical results on steady state characteristics in bulk GaAs1-xNx alloys (x ≤ 0.2) using the single electron Monte-Carlo method. Two approaches have been used; the first assumes a GaAs band with a strong nitrogen scattering resonance and the second uses the band anti-crossing model, in which the localized N level interacts with the GaAs band strongly perturbing the conduction band. In the first model we observe two negative differential velocity peaks, the lower one associated with nitrogen scattering while the higher one with polar optical phonon emission accounting for the nonparabolicity effect. In the second model one negative differential velocity peak is observed associated with polar optical phonon emission. Good agreement with experimental low field mobility is obtained from the first model. We also comment on the results from both Models when the intervalley Г → L transfer is accounted for.

Intrinsic Spin-Hall Effect in n-Doped Bulk GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-01-15

We show that the bulk Dresselhauss (k{sup 3}) spin-orbit coupling term leads to an intrinsic spin-Hall effect in n-doped bulk GaAs, but without the appearance of uniform magnetization. The spin-Hall effect in strained and unstrained bulk GaAs has been recently observed experimentally by Kato et. al. [1]. We show that the experimental result is quantitatively consistent with the intrinsic spin-Hall effect due to the Dresselhauss term, when lifetime broadening is taken into account. On the other hand, extrinsic contribution to the spin-Hall effect is several orders of magnitude smaller than the observed effect.

Terahertz pulse induced intervalley scattering in photoexcited GaAs.

PubMed

Su, F H; Blanchard, F; Sharma, G; Razzari, L; Ayesheshim, A; Cocker, T L; Titova, L V; Ozaki, T; Kieffer, J-C; Morandotti, R; Reid, M; Hegmann, F A

2009-06-08

Nonlinear transient absorption bleaching of intense few-cycle terahertz (THz) pulses is observed in photoexcited GaAs using opticalpump--THz-probe techniques. A simple model of the electron transport dynamics shows that the observed nonlinear response is due to THz-electric- field-induced intervalley scattering over sub-picosecond time scales as well as an increase in the intravalley scattering rate attributed to carrier heating. Furthermore, the nonlinear nature of the THz pulse transmission at high peak fields leads to a measured terahertz conductivity in the photoexcited GaAs that deviates significantly from the Drude behavior observed at low THz fields, emphasizing the need to explore nonlinear THz pulse interactions with materials in the time domain.

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.

Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shang-Hua; Jarrahi, Mona; Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095

2015-09-28

We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more thanmore » 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.« less

Time-resolved photoluminescence characterization of GaAs nanowire arrays on native substrate

NASA Astrophysics Data System (ADS)

Dagytė, Vilgailė; Barrigón, Enrique; Zhang, Wei; Zeng, Xulu; Heurlin, Magnus; Otnes, Gaute; Anttu, Nicklas; Borgström, Magnus T.

2017-12-01

Time-resolved photoluminescence (TRPL) measurements of nanowires (NWs) are often carried out on broken-off NWs in order to avoid the ensemble effects as well as substrate contribution. However, the development of NW-array solar cells could benefit from non-destructive optical characterization to allow faster feedback and further device processing. With this work, we show that different NW array and substrate spectral behaviors with delay time and excitation power can be used to determine which part of the sample dominates the detected spectrum. Here, we evaluate TRPL characterization of dense periodic as-grown GaAs NW arrays on a p-type GaAs substrate, including a sample with uncapped GaAs NWs and several samples passivated with AlGaAs radial shell of varied composition and thickness. We observe a strong spectral overlap of substrate and NW signals and find that the NWs can absorb part of the substrate luminescence signal, thus resulting in a modified substrate signal. The level of absorption depends on the NW-array geometry, making a deconvolution of the NW signal very difficult. By studying TRPL of substrate-only and as-grown NWs at 770 and 400 nm excitation wavelengths, we find a difference in spectral behavior with delay time and excitation power that can be used to assess whether the signal is dominated by the NWs. We find that the NW signal dominates with 400 nm excitation wavelength, where we observe two different types of excitation power dependence for the NWs capped with high and low Al composition shells. Finally, from the excitation power dependence of the peak TRPL signal, we extract an estimate of background carrier concentration in the NWs.

Experimental investigation of millimeter-wave GaAs TED oscillators cooled to cryogenic temperatures

NASA Astrophysics Data System (ADS)

Rydberg, Anders; Kollberg, Erik

1988-03-01

The output power and operating (bias) point for 80-100-GHz GaAs TED oscillators have been investigated for temperatures between 300 and 40 K. It is shown experimentally that the power can be increased by as much as nearly four times by cooling the oscillator. The thermal design of the oscillator was studied for GaAs and InP TED oscillators.

Single crystal and polycrystalline GaAs solar cells using AMOS technology

NASA Technical Reports Server (NTRS)

Stirn, R. J.; Yeh, Y. C. M.

1976-01-01

A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

Effect of H{sup +} implantation on the optical properties of semi-insulating GaAs crystals in the IR spectral region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klyui, N. I.; Lozinskii, V. B., E-mail: lvb@isp.kiev.ua; Liptuga, A. I.

2017-03-15

The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interactionmore » of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.« less

Wafer-Fused Orientation-Patterned GaAs

DTIC Science & Technology

2008-02-13

frequencies utilizing existing industrial foundries. 15. SUBJECT TERMS Orientation-patterned Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase... Gallium Arsenide, hydride vapor phase epitaxy, quasi-phase-matching, nonlinear frequency conversion 1. INTRODUCTION Quasi-phase-matching (QPM)1...and E. Lallier, “Second harmonic generation of CO2 laser using thick quasi-phase-matched GaAs layer grown by hydride vapour phase epitaxy

High power cascaded mid-infrared InAs/GaSb light emitting diodes on mismatched GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Provence, S. R., E-mail: sydney-provence@uiowa.edu; Ricker, R.; Aytac, Y.

2015-09-28

InAs/GaSb mid-wave, cascaded superlattice light emitting diodes are found to give higher radiance when epitaxially grown on mismatched GaAs substrates compared to lattice-matched GaSb substrates. Peak radiances of 0.69 W/cm{sup 2}-sr and 1.06 W/cm{sup 2}-sr for the 100 × 100 μm{sup 2} GaSb and GaAs-based devices, respectively, were measured at 77 K. Measurement of the recombination coefficients shows the shorter Shockley-Read-Hall recombination lifetime as misfit dislocations for growth on GaAs degrade the quantum efficiency only at low current injection. The improved performance on GaAs was found to be due to the higher transparency and improved thermal properties of the GaAs substrate.

Analysis of GAA/TTC DNA triplexes using nuclear magnetic resonance and electrospray ionization mass spectrometry.

PubMed

Mariappan, S V Santhana; Cheng, Xun; van Breemen, Richard B; Silks, Louis A; Gupta, Goutam

2004-11-15

The formation of a GAA/TTC DNA triplex has been implicated in Friedreich's ataxia. The destabilization of GAA/TTC DNA triplexes either by pH or by binding to appropriate ligands was analyzed by nuclear magnetic resonance (NMR) and positive-ion electrospray mass spectrometry. The triplexes and duplexes were identified by changes in the NMR chemical shifts of H8, H1, H4, 15N7, and 15N4. The lowest pH at which the duplex is detectable depends upon the overall stability and the relative number of Hoogsteen C composite function G to T composite function A basepairs. A melting pH (pHm) of 7.6 was observed for the destabilization of the (GAA)2T4(TTC)2T4(CTT)2 triplex to the corresponding Watson-Crick duplex and the T4(CTT)2 overhang. The mass spectrometric analyses of (TTC)6.(GAA)6 composite function(TTC)6 triplex detected ions due to both triplex and single-stranded oligonucleotides under acidic conditions. The triplex ions disappeared completely at alkaline pH. Duplex and single strands were detectable only at neutral and alkaline pH values. Mass spectrometric analyses also showed that minor groove-binding ligands berenil, netropsin, and distamycin and the intercalating ligand acridine orange destabilize the (TTC)6.(GAA)6 composite function (TTC)6 triplex. These NMR and mass spectrometric methods may function as screening assays for the discovery of agents that destabilize GAA/TTC triplexes and as general methods for the characterization of structure, dynamics, and stability of DNA and DNA-ligand complexes.

Protective capping and surface passivation of III-V nanowires by atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhaka, Veer, E-mail: veer.dhaka@aalto.fi; Perros, Alexander; Kakko, Joona-Pekko

2016-01-15

Low temperature (∼200 °C) grown atomic layer deposition (ALD) films of AlN, TiN, Al{sub 2}O{sub 3}, GaN, and TiO{sub 2} were tested for protective capping and surface passivation of bottom-up grown III-V (GaAs and InP) nanowires (NWs), and top-down fabricated InP nanopillars. For as-grown GaAs NWs, only the AlN material passivated the GaAs surface as measured by photoluminescence (PL) at low temperatures (15K), and the best passivation was achieved with a few monolayer thick (2Å) film. For InP NWs, the best passivation (∼2x enhancement in room-temperature PL) was achieved with a capping of 2nm thick Al{sub 2}O{sub 3}. All othermore » ALD capping layers resulted in a de-passivation effect and possible damage to the InP surface. Top-down fabricated InP nanopillars show similar passivation effects as InP NWs. In particular, capping with a 2 nm thick Al{sub 2}O{sub 3} layer increased the carrier decay time from 251 ps (as-etched nanopillars) to about 525 ps. Tests after six months ageing reveal that the capped nanostructures retain their optical properties. Overall, capping of GaAs and InP NWs with high-k dielectrics AlN and Al{sub 2}O{sub 3} provides moderate surface passivation as well as long term protection from oxidation and environmental attack.« less

GaAs1−xBix/GaNyAs1−y type-II quantum wells: novel strain-balanced heterostructures for GaAs-based near- and mid-infrared photonics

PubMed Central

Broderick, Christopher A.; Jin, Shirong; Marko, Igor P.; Hild, Konstanze; Ludewig, Peter; Bushell, Zoe L.; Stolz, Wolfgang; Rorison, Judy M.; O’Reilly, Eoin P.; Volz, Kerstin; Sweeney, Stephen J.

2017-01-01

The potential to extend the emission wavelength of photonic devices further into the near- and mid-infrared via pseudomorphic growth on conventional GaAs substrates is appealing for a number of communications and sensing applications. We present a new class of GaAs-based quantum well (QW) heterostructure that exploits the unusual impact of Bi and N on the GaAs band structure to produce type-II QWs having long emission wavelengths with little or no net strain relative to GaAs, while also providing control over important laser loss processes. We theoretically and experimentally demonstrate the potential of GaAs1−xBix/GaNyAs1−y type-II QWs on GaAs and show that this approach offers optical emission and absorption at wavelengths up to ~3 µm utilising strain-balanced structures, a first for GaAs-based QWs. Experimental measurements on a prototype GaAs0.967Bi0.033/GaN0.062As0.938 structure, grown via metal-organic vapour phase epitaxy, indicate good structural quality and exhibit both photoluminescence and absorption at room temperature. The measured photoluminescence peak wavelength of 1.72 μm is in good agreement with theoretical calculations and is one of the longest emission wavelengths achieved on GaAs to date using a pseudomorphically grown heterostructure. These results demonstrate the significant potential of this new class of III-V heterostructure for long-wavelength applications. PMID:28422129

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.

Image quality of a pixellated GaAs X-ray detector

NASA Astrophysics Data System (ADS)

Sun, G. C.; Makham, S.; Bourgoin, J. C.; Mauger, A.

2007-02-01

X-ray detection requires materials with large atomic numbers Z in order to absorb the radiation efficiently. In case of X-ray imaging, fluorescence is a limiting factor for the spatial resolution and contrast at energies above the kα threshold. Since both the energy and yield of the fluorescence of a given material increase with the atomic number, there is an optimum value of Z. GaAs, which can now be epitaxially grown as self-supported thick layers to fulfil the requirements for imaging (good homogeneity of the electronic properties) corresponds to this optimum. Image performances obtained with this material are evaluated in terms of line spread function and modulation transfer function, and a comparison with CsI is made. We evaluate the image contrast obtained for a given object contrast with GaAs and CsI detectors, in the photon energy range of medical applications. Finally, we discuss the minimum object size, which can be detected by these detectors in of mammography conditions. This demonstrates that an object of a given size can be detected using a GaAs detector with a dose at least 100 times lower than using a CsI detector.

Spectrally resolved localized states in GaAs 1– xBi x

DOE PAGES

Christian, Theresa M.; Alberi, Kirstin; Beaton, Daniel A.; ...

2017-02-01

In this study, the role of localized states and their influence on the broader band structure remains a crucial question in understanding the band structure evolution in GaAs 1-xBi x. Here in this work, we present clear spectroscopic observations of recombination at several localized states in GaAs 1-xBi x. Sharp and recognizable photoluminescence features appear in multiple samples and redshift as a function of GaBi fraction between x = 0.16% and 0.4% at a linearized rate of 34 meV per % Bi, weaker than the redshift associated with band-to-band recombination. Interpreting these results in terms of radiative recombination between localizedmore » holes and free electrons sheds light on the relative movement of the conduction band minimum and the characteristics of localized bismuth-related trap states in GaAs 1-xBi x alloys.« less

Optical detectors for GaAs MMIC integration: Technology assessment

NASA Technical Reports Server (NTRS)

Claspy, P. C.; Bhasin, K. B.

1989-01-01

Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

Interface shape and crystallinity in LEC GaAs

NASA Astrophysics Data System (ADS)

Tower, J. P.; Tobin, R.; Pearah, P. J.; Ware, R. M.

1991-12-01

Growth striation mapping was used to relate the growth interface shape to crystallinity failure modes in LEC growth of undoped <100> GaAs. The onset of twinning and polycrystallinity were both found to depend on the interface shape near the crystal periphery. The origins of polycrystalline growth were investigated in 8 kg, 3-inch and 4-inch diameter crystals. Interface maps of these crystals show that polycrystalline growth begins when the growth interface periphery turns down, independent of the shape of the central portions. The cause of initial grain boundary formation was found to be included gallium droplets which originate on the surface and migrate through the crystal toward the growth interface. Twinning occurs on {111} facets, usually during shoulder growth. Growth striations show that the sequence of events leading to twin formation consists of deep facet growth, followed by meltback and rapid regrowth. We found it possible to avoid twinning by reducing melt instabilities or by reducing the extent of facet growth.

New method for MBE growth of GaAs nanowires on silicon using colloidal Au nanoparticles

NASA Astrophysics Data System (ADS)

Bouravleuv, A.; Ilkiv, I.; Reznik, R.; Kotlyar, K.; Soshnikov, I.; Cirlin, G.; Brunkov, P.; Kirilenko, D.; Bondarenko, L.; Nepomnyaschiy, A.; Gruznev, D.; Zotov, A.; Saranin, A.; Dhaka, V.; Lipsanen, H.

2018-01-01

We present a new method for the deposition of colloidal Au nanoparticles on the surface of silicon substrates based on short-time Ar plasma treatment without the use of any polymeric layers. The elaborated method is compatible with molecular beam epitaxy, which allowed us to carry out the detailed study of GaAs nanowire synthesis on Si(111) substrates using colloidal Au nanoparticles as seeds for their growth. The results obtained elucidated the causes of the difference between the initial nanoparticle sizes and the diameters of the grown nanowires.

Gallium arsenide (GaAs) (001) after sublimation of arsenic (As) thin-film cap, by XPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Engelhard, Mark H.; Lyubinetsky, Andre; Baer, Don R.

2016-12-01

Survey and high energy resolution spectra are reported for MBE grown GaAs (001) that had been capped with As. The As cap was removed by heating in situ prior to analysis. The current data expands upon the spectral regions previously reported in Surface Science Spectra. High energy resolution spectral features reported include: 2p, 3s, 3p, 3d, and L3M45M45 peaks for As; 2p, 3s, 3p, 3d, and L3M45M45 peaks for Ga; and the valance band region.

Control of Polarization of Vertical-Cavity Surface - Lasers

NASA Astrophysics Data System (ADS)

Sun, Decai

1995-01-01

To date, most vertical-cavity surface-emitting lasers (VCSELs) have been fabricated from structures grown on GaAs (InP) substrates oriented in the (001) crystallographic axis. For the most part, these devices have exhibited linear, but random polarization states with no definite relationship to the in-plane crystallographic axes. The control of the polarization states of these devices is important for polarization-sensitive applications. Such applications include magneto-optic disk recording and coherent detection in advanced communication systems. In this thesis, a novel approach for controlling the polarization eigen-states of VCSELs is investigated. The approach utilizes anisotropic optical properties found in quantum wells (QW) oriented in directions other than the (001) to stabilize their polarization states. Specifically, the (110) direction is chosen for this work. An analysis of the in-plane optical matrix element connected with the gain coefficient of (In,Ga)As/GaAs QW structures grown on (110) GaAs substrates is conducted. It is found that the in-plane gain distribution is elliptically anisotropic--with a maximum directed along the (110) - (110) crystallographic axis. The design and growth of (In,Ga)As/GaAs QW VCSEL structures is studied in this work. The transition wavelengths of the (001) - and (110) -oriented (In,Ga)As/GaAs QW structures are calculated using a finite QW model. Distributed Bragg reflector mirrors consisting of GaAs/AlAs quarter wave layers are modeled using a characteristic matrix method. Threshold gain, internal and differential quantum efficiencies are analyzed. The growth of III-V compounds on (110) GaAs substrates by molecular beam epitaxy is investigated. High quality materials are successfully grown on the misoriented (110) GaAs substrates tilted by 6^circ toward the (111)B surface. (In,Ga)As/GaAs QW VCSEL structures are grown on (001) and (110) GaAs substrates. (In,Ga)As/GaAs QW VCSELs are fabricated from structures grown on the

Optically controlled phased array antenna concepts using GaAs monolithic microwave integrated circuits

NASA Technical Reports Server (NTRS)

Kunath, R. R.; Bhasin, K. B.

1986-01-01

The desire for rapid beam reconfigurability and steering has led to the exploration of new techniques. Optical techniques have been suggested as potential candidates for implementing these needs. Candidates generally fall into one of two areas: those using fiber optic Beam Forming Networks (BFNs) and those using optically processed BFNs. Both techniques utilize GaAs Monolithic Microwave Integrated Circuits (MMICs) in the BFN, but the role of the MMIC for providing phase and amplitude variations is largely eliminated by some new optical processing techniques. This paper discusses these two types of optical BFN designs and provides conceptual designs of both systems.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galiev, G. B.; Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru; Buriakov, A. M.

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

Homojunction GaAs solar cells grown by close space vapor transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boucher, Jason W.; Ritenour, Andrew J.; Greenaway, Ann L.

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,more » and ultimately wider band gap window or surface passivation layers, are required to increase the efficiency.« less

The 20 GHz power GaAs FET development

NASA Technical Reports Server (NTRS)

Crandell, M.

1986-01-01

The development of power Field Effect Transistors (FET) operating in the 20 GHz frequency band is described. The major efforts include GaAs FET device development (both 1 W and 2 W devices), and the development of an amplifier module using these devices.

Cryogenic measurements of aerojet GaAs n-JFETs

NASA Technical Reports Server (NTRS)

Goebel, John H.; Weber, Theodore T.

1993-01-01

The spectral noise characteristics of Aerojet gallium arsenide (GaAs) junction field effect transistors (JFET's) have been investigated down to liquid-helium temperatures. Noise characterization was performed with the field effect transistor (FET) in the floating-gate mode, in the grounded-gate mode to determine the lowest noise readings possible, and with an extrinsic silicon photodetector at various detector bias voltages to determine optimum operating conditions. The measurements indicate that the Aerojet GaAs JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to silicon (Si) metal oxide semiconductor field effect transistor (MOSFET's) operating at liquid helium temperatures, and is equal to the best Si n channel junction field effect transistor (n-JFET's) operating at 300 K.

First-principles study of structural, electronic, and optical properties of surface defects in GaAs(001) - β2(2x4)

NASA Astrophysics Data System (ADS)

Bacuyag, Dhonny; Escaño, Mary Clare Sison; David, Melanie; Tani, Masahiko

2018-06-01

We performed first-principles calculations based on density functional theory (DFT) to investigate the role of point defects in the structural, electronic, and optical properties of the GaAs(001)- β2(2x4). In terms of structural properties, AsGa is the most stable defect structure, consistent with experiments. With respect to the electronic structure, band structures revealed the existence of sub-band and midgap states for all defects. The induced sub-bands and midgap states originated from the redistributions of charges towards these defects and neighboring atoms. The presence of these point defects introduced deep energy levels characteristic of EB3 (0.97 eV), EL4 (0.52 eV), and EL2 (0.82 eV) for AsGa, GaAs, GaV, respectively. The optical properties are found to be strongly related to these induced gap states. The calculated onset values in the absorption spectra, corresponding to the energy gaps, confirmed the absorption below the known bulk band gap of 1.43 eV. These support the possible two-step photoabsorption mediated by midgap states as observed in experiments.

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.

A capacitive power sensor based on the MEMS cantilever beam fabricated by GaAs MMIC technology

NASA Astrophysics Data System (ADS)

Yi, Zhenxiang; Liao, Xiaoping

2013-03-01

In this paper, a novel capacitive power sensor based on the microelectromechanical systems (MEMS) cantilever beam at 8-12 GHz is proposed, fabricated and tested. The presented design can not only realize a cantilever beam instead of the conventional fixed-fixed beam, but also provide fine compatibility with the GaAs monolithic microwave integrated circuit (MMIC) process. When the displacement of the cantilever beam is very small compared with the initial height of the air gap, the capacitance change between the measuring electrode and the cantilever beam has an approximately linear dependence on the incident radio frequency (RF) power. Impedance compensating technology, by modifying the slot width of the coplanar waveguide transmission line, is adopted to minimize the effect of the cantilever beam on the power sensor; its validity is verified by the simulation of high frequency structure simulator software. The power sensor has been fabricated successfully by Au surface micromachining using polyimide as the sacrificial layer on the GaAs substrate. Optimization of the design with impedance compensating technology has resulted in a measured return loss of less than -25 dB and an insertion loss of around 0.1 dB at 8-12 GHz, which shows the slight effect of the cantilever beam on the microwave performance of this power sensor. The measured capacitance change starts from 0.7 fF to 1.3 fF when the incident RF power increases from 100 to 200 mW and an approximate linear dependence has been obtained. The measured sensitivities of the sensor are about 6.16, 6.27 and 6.03 aF mW-1 at 8, 10 and 12 GHz, respectively.

Imaging surface plasmon polaritons using proximal self-assembled InGaAs quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bracher, Gregor; Schraml, Konrad; Blauth, Mäx

2014-07-21

We present optical investigations of hybrid plasmonic nanosystems consisting of lithographically defined plasmonic Au-waveguides or beamsplitters on GaAs substrates coupled to proximal self-assembled InGaAs quantum dots. We designed a sample structure that enabled us to precisely tune the distance between quantum dots and the sample surface during nano-fabrication and demonstrated that non-radiative processes do not play a major role for separations down to ∼10 nm. A polarized laser beam focused on one end of the plasmonic nanostructure generates propagating surface plasmon polaritons that, in turn, create electron-hole pairs in the GaAs substrate during propagation. These free carriers are subsequently captured bymore » the quantum dots ∼25 nm below the surface, giving rise to luminescence. The intensity of the spectrally integrated quantum dot luminescence is used to image the propagating plasmon modes. As the waveguide width reduces from 5 μm to 1 μm, we clearly observe different plasmonic modes at the remote waveguide end, enabling their direct imaging in real space. This imaging technique is applied to a plasmonic beamsplitter facilitating the determination of the splitting ratio between the two beamsplitter output ports as the interaction length L{sub i} is varied. A splitting ratio of 50:50 is observed for L{sub i}∼9±1 μm and 1 μm wide waveguides for excitation energies close to the GaAs band edge. Our experimental findings are in good agreement with mode profile and finite difference time domain simulations for both waveguides and beamsplitters.« less

X-ray photoelectron spectroscopic study of the oxide removal mechanism of GaAs /100/ molecular beam epitaxial substrates in in situ heating

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Lewis, B. F.; Grunthaner, F. J.

1983-01-01

A standard cleaning procedure for GaAs (100) molecular beam epitaxial (MBE) substrates is a chemical treatment with a solution of H2SO4/H2O2/H2O, followed by in situ heating prior to MBE growth. X-ray photoelectron spectroscopic (XPS) studies of the surface following the chemical treatment show that the oxidized As is primarily As(+ 5). Upon heating to low temperatures (less than (350 C) the As(+ 5) oxidizes the substrate to form Ga2O3 and elemental As, and the As(+ 5) is reduced to As(+ 3) in the process. At higher temperatures (500 C), the As(+ 3) and elemental As desorb, while the Ga(+ 3) begins desorbing at about 600 C.

Quantum-confinement effects on conduction band structure of rectangular cross-sectional GaAs nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, H., E-mail: tanaka@semicon.kuee.kyoto-u.ac.jp; Morioka, N.; Mori, S.

2014-02-07

The conduction band structure and electron effective mass of GaAs nanowires with various cross-sectional shapes and orientations were calculated by two methods, a tight-binding method and an effective mass equation taking the bulk full-band structure into account. The effective mass of nanowires increases as the cross-sectional size decreases, and this increase in effective mass depends on the orientations and substrate faces of nanowires. Among [001], [110], and [111]-oriented rectangular cross-sectional GaAs nanowires, [110]-oriented nanowires with wider width along the [001] direction showed the lightest effective mass. This dependence originates from the anisotropy of the Γ valley of bulk GaAs. Themore » relationship between effective mass and bulk band structure is discussed.« less

New dynamic FET logic and serial memory circuits for VLSI GaAs technology

NASA Technical Reports Server (NTRS)

Eldin, A. G.

1991-01-01

The complexity of GaAs field effect transistor (FET) very large scale integration (VLSI) circuits is limited by the maximum power dissipation while the uniformity of the device parameters determines the functional yield. In this work, digital GaAs FET circuits are presented that eliminate the DC power dissipation and reduce the area to 50% of that of the conventional static circuits. Its larger tolerance to device parameter variations results in higher functional yield.

Photoreflectance from GaAs and GaAs/GaAs interfaces

NASA Astrophysics Data System (ADS)

Sydor, Michael; Angelo, James; Wilson, Jerome J.; Mitchel, W. C.; Yen, M. Y.

1989-10-01

Photoreflectance from semi-insulating GaAs, and GaAs/GaAs interfaces, is discussed in terms of its behavior with temperature, doping, epilayer thickness, and laser intensity. Semi-insulating substrates show an exciton-related band-edge signal below 200 K and an impurity-related photoreflectance above 400 K. At intermediate temperatures the band-edge signal from thin GaAs epilayers contains a contribution from the epilayer-substrate interface. The interface effect depends on the epilayer's thickness, doping, and carrier mobility. The effect broadens the band-edge photoreflectance by 5-10 meV, and artifically lowers the estimates for the critical-point energy, ECP, obtained through the customary third-derivative functional fit to the data.

Theoretical aspects of studies of oxide and semiconductor surfaces using low energy positrons

NASA Astrophysics Data System (ADS)

Fazleev, N. G.; Maddox, W. B.; Weiss, A. H.

2011-01-01

This paper presents the results of a theoretical study of positron surface and bulk states and annihilation characteristics of surface trapped positrons at the oxidized Cu(100) single crystal and at both As- and Ga-rich reconstructed GaAs(100) surfaces. The variations in atomic structure and chemical composition of the topmost layers of the surfaces associated with oxidation and reconstructions and the charge redistribution at the surfaces are found to affect localization and spatial extent of the positron surface-state wave functions. The computed positron binding energy, work function, and annihilation characteristics reveal their sensitivity to charge transfer effects, atomic structure and chemical composition of the topmost layers of the surfaces. Theoretical positron annihilation probabilities with relevant core electrons computed for the oxidized Cu(100) surface and the As- and Ga-rich reconstructed GaAs(100) surfaces are compared with experimental ones estimated from the positron annihilation induced Auger peak intensities measured from these surfaces.

Gallium arsenide (GaAs) power conversion concept

NASA Technical Reports Server (NTRS)

Nussberger, A. A.

1980-01-01

A summary design analysis of a GaAs power conversion system for the solar power satellite (SPS) is presented. Eight different satellite configuration options for the solar arrays are compared. Solar cell annealing effects after proton irradiation are considered. Mass estimates for the SPS and the effect of solar cell parameters on SPS array design are discussed.

Influence of ion-implanted profiles on the performance of GaAs MESFET's and MMIC amplifiers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlidis, D.; Cazaux, J.L.; Graffeuil, J.

1988-04-01

The RF small-signal performance of GaAs MESFET's and MMIC amplifiers as a function of various ion-implanted profiles is theoretically and experimentally investigated. Implantation energy, dose, and recess depth influence are theoretically analyzed with the help of a specially developed device simulator. The performance of MMIC amplifiers processed with various energies, doses, recess depths, and bias conditions is discussed and compared to experimental characteristics. Some criteria are finally proposed for the choice of implantation conditions and process in order to optimize the characteristics of ion-implanted FET's and to realize process-tolerant MMIC amplifiers.

GaAs photovoltaics and optoelectronics using releasable multilayer epitaxial assemblies.

PubMed

Yoon, Jongseung; Jo, Sungjin; Chun, Ik Su; Jung, Inhwa; Kim, Hoon-Sik; Meitl, Matthew; Menard, Etienne; Li, Xiuling; Coleman, James J; Paik, Ungyu; Rogers, John A

2010-05-20

Compound semiconductors like gallium arsenide (GaAs) provide advantages over silicon for many applications, owing to their direct bandgaps and high electron mobilities. Examples range from efficient photovoltaic devices to radio-frequency electronics and most forms of optoelectronics. However, growing large, high quality wafers of these materials, and intimately integrating them on silicon or amorphous substrates (such as glass or plastic) is expensive, which restricts their use. Here we describe materials and fabrication concepts that address many of these challenges, through the use of films of GaAs or AlGaAs grown in thick, multilayer epitaxial assemblies, then separated from each other and distributed on foreign substrates by printing. This method yields large quantities of high quality semiconductor material capable of device integration in large area formats, in a manner that also allows the wafer to be reused for additional growths. We demonstrate some capabilities of this approach with three different applications: GaAs-based metal semiconductor field effect transistors and logic gates on plates of glass, near-infrared imaging devices on wafers of silicon, and photovoltaic modules on sheets of plastic. These results illustrate the implementation of compound semiconductors such as GaAs in applications whose cost structures, formats, area coverages or modes of use are incompatible with conventional growth or integration strategies.

Hb Beograd [beta121(GH4)Glu-->Val, GAA-->GTA] in the Turkish population.

PubMed

Atalay, Ayfer; Koyuncu, Hasan; Köseler, Aylin; Ozkan, Anzel; Atalay, Erol O

2007-01-01

Hb Beograd [beta121(GH4)Glu-->Val, GAA-->GTA] is a rare variant first reported in Yugoslavia and then in Turkey, Australia and New Zealand. We report two further unrelated cases from Turkey. The importance of identifying Hb Beograd at the molecular level, especially in regions where Hb D-Los Angeles [beta121(GH4)Glu-->Gln, GAA-->CAA] is prevalent, is emphasized.

28 percent efficient GaAs concentrator solar cells

NASA Technical Reports Server (NTRS)

Macmillan, H. F.; Hamaker, H. C.; Kaminar, N. R.; Kuryla, M. S.; Ladle Ristow, M.

1988-01-01

AlGaAs/GaAs heteroface solar concentrator cells which exhibit efficiencies in excess of 27 percent at high solar concentrations (over 400 suns, AM1.5D, 100 mW/sq cm) have been fabricated with both n/p and p/n configurations. The best n/p cell achieved an efficiency of 28.1 percent around 400 suns, and the best p/n cell achieved an efficiency of 27.5 percent around 1000 suns. The high performance of these GaAs concentrator cells compared to earlier high-efficiency cells was due to improved control of the metal-organic chemical vapor deposition growth conditions and improved cell fabrication procedures (gridline definition and edge passivation). The design parameters of the solar cell structures and optimized grid pattern were determined with a realistic computer modeling program. An evaluation of the device characteristics and a discussion of future GaAs concentrator cell development are presented.

Interpolative modeling of GaAs FET S-parameter data bases for use in Monte Carlo simulations

NASA Technical Reports Server (NTRS)

Campbell, L.; Purviance, J.

1992-01-01

A statistical interpolation technique is presented for modeling GaAs FET S-parameter measurements for use in the statistical analysis and design of circuits. This is accomplished by interpolating among the measurements in a GaAs FET S-parameter data base in a statistically valid manner.

GaAs monolithic RF modules for SARSAT distress beacons

NASA Technical Reports Server (NTRS)

Cauley, Michael A.

1991-01-01

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

Low temperature growth and electrical characterization of insulators for GaAs MISFETS

NASA Technical Reports Server (NTRS)

Borrego, J. M.; Ghandhi, S. K.

1981-01-01

Progress in the low temperature growth of oxides and layers on GaAs and the detailed electrical characterization of these oxides is reported. A plasma anodization system was designed, assembled, and put into operation. A measurement system was assembled for determining capacitance and conductance as a function of gate voltage for frequencies in the range from 1 Hz to 1 MHz. Initial measurements were carried out in Si-SiO2 capacitors in order to test the system and in GaAs MIS capacitors abricated using liquid anodization.

Photoluminescence Study of N-Type Thermal Conversion in Semi-Insulating GaAs.

DTIC Science & Technology

1982-12-01

free electron to the crystal. For example, in GaAs, a tellurium atom on an arsenic site (TeAs) or a silicon atom on a gallium site (SiGa) are donor atoms...Photoconductivity Photoluminescenc Silicon, SiGa 5.81 6.80 Germanium, GeGa 6.08 Sulfur, SAs 6.10 Selenium, SeAs 5.89 6.10 Tellurium , TeAs When an electron...34 to the neutral donor or acceptor (Ref 16:15). The following excitonic com- plexes have been observed in GaAs: (i) exciton bound to a neutron donor at

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.

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

NASA Astrophysics Data System (ADS)

Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

2018-05-01

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

Surface Modification and Surface - Subsurface Exchange Processes on Europa

NASA Astrophysics Data System (ADS)

Phillips, Cynthia B.; Molaro, Jamie; Hand, Kevin P.

2017-10-01

The surface of Jupiter’s moon Europa is modified by exogenic processes such as sputtering, gardening, radiolysis, sulfur ion implantation, and thermal processing, as well as endogenic processes including tidal shaking, mass wasting, and the effects of subsurface tectonic and perhaps cryovolcanic activity. New materials are created or deposited on the surface (radiolysis, micrometeorite impacts, sulfur ion implantation, cryovolcanic plume deposits), modified in place (thermal segregation, sintering), transported either vertically or horizontally (sputtering, gardening, mass wasting, tectonic and cryovolcanic activity), or lost from Europa completely (sputtering, plumes, larger impacts). Some of these processes vary spatially, as visible in Europa’s leading-trailing hemisphere brightness asymmetry.Endogenic geologic processes also vary spatially, depending on terrain type. The surface can be classified into general landform categories that include tectonic features (ridges, bands, cracks); disrupted “chaos-type” terrain (chaos blocks, matrix, domes, pits, spots); and impact craters (simple, complex, multi-ring). The spatial distribution of these terrain types is relatively random, with some differences in apex-antiapex cratering rates and latitudinal variation in chaos vs. tectonic features.In this work, we extrapolate surface processes and rates from the top meter of the surface in conjunction with global estimates of transport and resurfacing rates. We combine near-surface modification with an estimate of surface-subsurface (and vice versa) transport rates for various geologic terrains based on an average of proposed formation mechanisms, and a spatial distribution of each landform type over Europa’s surface area.Understanding the rates and mass balance for each of these processes, as well as their spatial and temporal variability, allows us to estimate surface - subsurface exchange rates over the average surface age (~50myr) of Europa. Quantifying the

Surface Modification and Surface - Subsurface Exchange Processes on Europa

NASA Astrophysics Data System (ADS)

Phillips, C. B.; Molaro, J.; Hand, K. P.

2017-12-01

The surface of Jupiter's moon Europa is modified by exogenic processes such as sputtering, gardening, radiolysis, sulfur ion implantation, and thermal processing, as well as endogenic processes including tidal shaking, mass wasting, and the effects of subsurface tectonic and perhaps cryovolcanic activity. New materials are created or deposited on the surface (radiolysis, micrometeorite impacts, sulfur ion implantation, cryovolcanic plume deposits), modified in place (thermal segregation, sintering), transported either vertically or horizontally (sputtering, gardening, mass wasting, tectonic and cryovolcanic activity), or lost from Europa completely (sputtering, plumes, larger impacts). Some of these processes vary spatially, as visible in Europa's leading-trailing hemisphere brightness asymmetry. Endogenic geologic processes also vary spatially, depending on terrain type. The surface can be classified into general landform categories that include tectonic features (ridges, bands, cracks); disrupted "chaos-type" terrain (chaos blocks, matrix, domes, pits, spots); and impact craters (simple, complex, multi-ring). The spatial distribution of these terrain types is relatively random, with some differences in apex-antiapex cratering rates and latitudinal variation in chaos vs. tectonic features. In this work, we extrapolate surface processes and rates from the top meter of the surface in conjunction with global estimates of transport and resurfacing rates. We combine near-surface modification with an estimate of surface-subsurface (and vice versa) transport rates for various geologic terrains based on an average of proposed formation mechanisms, and a spatial distribution of each landform type over Europa's surface area. Understanding the rates and mass balance for each of these processes, as well as their spatial and temporal variability, allows us to estimate surface - subsurface exchange rates over the average surface age ( 50myr) of Europa. Quantifying the timescale

Displacement damage and predicted non-ionizing energy loss in GaAs

NASA Astrophysics Data System (ADS)

Gao, Fei; Chen, Nanjun; Hernandez-Rivera, Efrain; Huang, Danhong; LeVan, Paul D.

2017-03-01

Large-scale molecular dynamics (MD) simulations, along with bond-order interatomic potentials, have been applied to study the defect production for lattice atom recoil energies from 500 eV to 20 keV in gallium arsenide (GaAs). At low energies, the most surviving defects are single interstitials and vacancies, and only 20% of the interstitial population is contained in clusters. However, a direct-impact amorphization in GaAs occurs with a high degree of probability during the cascade lifetime for Ga PKAs (primary knock-on atoms) with energies larger than 2 keV. The results reveal a non-linear defect production that increases with the PKA energy. The damage density within a cascade core is evaluated, and used to develop a model that describes a new energy partition function. Based on the MD results, we have developed a model to determine the non-ionizing energy loss (NIEL) in GaAs, which can be used to predict the displacement damage degradation induced by space radiation on electronic components. The calculated NIEL predictions are compared with the available data, thus validating the NIEL model developed in this study.

GaAs Optoelectronic Integrated-Circuit Neurons

NASA Technical Reports Server (NTRS)

Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

1992-01-01

Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

First results from GaAs double-sided detectors

NASA Astrophysics Data System (ADS)

Beaumont, S. P.; Bertin, R.; Booth, C. N.; Buttar, C.; Carraresi, L.; Cindolo, F.; Colocci, M.; Combley, F. H.; D'Auria, S.; del Papa, C.; Dogru, M.; Edwards, M.; Foster, F.; Francescato, A.; Gowdy, S.; Gray, R.; Hill, G.; Hou, Y.; Houston, P.; Hughes, G.; Jones, B. K.; Lynch, J. G.; Lisowski, B.; Matheson, J.; Nava, F.; Nuti, M.; O'Shea, V.; Pelfer, P. G.; Raine, C.; Santana, J.; Saunders, I. J.; Seller, P. H.; Shankar, K.; Sharp, P. H.; Skillicorn, I. O.; Sloan, T.; Smith, K. M.; ten Have, I.; Turnbull, R. M.; Vanni, U.; Zichichi, A.

1994-09-01

Preliminary results are presented on the performance of double-sided microstrip detectors using Schottky contacts on both sides of a semi-insulating (SI) GaAs substrate wafer, after exposure to 10 14 neutrons cm -2 at the ISIS facility. A qualitative explanation of the device behaviour is given.

Expanded GAA repeats impair FXN gene expression and reposition the FXN locus to the nuclear lamina in single cells.

PubMed

Silva, Ana M; Brown, Jill M; Buckle, Veronica J; Wade-Martins, Richard; Lufino, Michele M P

2015-06-15

Abnormally expanded DNA repeats are associated with several neurodegenerative diseases. In Friedreich's ataxia (FRDA), expanded GAA repeats in intron 1 of the frataxin gene (FXN) reduce FXN mRNA levels in averaged cell samples through a poorly understood mechanism. By visualizing FXN expression and nuclear localization in single cells, we show that GAA-expanded repeats decrease the number of FXN mRNA molecules, slow transcription, and increase FXN localization at the nuclear lamina (NL). Restoring histone acetylation reverses NL positioning. Expanded GAA-FXN loci in FRDA patient cells show increased NL localization with increased silencing of alleles and reduced transcription from alleles positioned peripherally. We also demonstrate inefficiencies in transcription initiation and elongation from the expanded GAA-FXN locus at single-cell resolution. We suggest that repressive epigenetic modifications at the expanded GAA-FXN locus may lead to NL relocation, where further repression may occur. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Room Temperature Sensing Achieved by GaAs Nanowires and oCVD Polymer Coating.

PubMed

Wang, Xiaoxue; Ermez, Sema; Goktas, Hilal; Gradečak, Silvija; Gleason, Karen

2017-06-01

Novel structures comprised of GaAs nanowire arrays conformally coated with conducting polymers (poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(3,4-ethylenedioxythiophene-co-3-thiophene acetic acid) display both sensitivity and selectivity to a variety of volatile organic chemicals. A key feature is room temperature operation, so that neither a heater nor the power it would consume, is required. It is a distinct difference from traditional metal oxide sensors, which typically require elevated operational temperature. The GaAs nanowires are prepared directly via self-seeded metal-organic chemical deposition, and conducting polymers are deposited on GaAs nanowires using oxidative chemical vapor deposition (oCVD). The range of thickness for the oCVD layer is between 100 and 200 nm, which is controlled by changing the deposition time. X-ray diffraction analysis indicates an edge-on alignment of the crystalline structure of the PEDOT coating layer on GaAs nanowires. In addition, the positive correlation between the improvement of sensitivity and the increasing nanowire density is demonstrated. Furthermore, the effect of different oCVD coating materials is studied. The sensing mechanism is also discussed with studies considering both nanowire density and polymer types. Overall, the novel structure exhibits good sensitivity and selectivity in gas sensing, and provides a promising platform for future sensor design. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct determination of minority carrier diffusion lengths at axial GaAs nanowire p-n junctions.

PubMed

Gutsche, Christoph; Niepelt, Raphael; Gnauck, Martin; Lysov, Andrey; Prost, Werner; Ronning, Carsten; Tegude, Franz-Josef

2012-03-14

Axial GaAs nanowire p-n diodes, possibly one of the core elements of future nanowire solar cells and light emitters, were grown via the Au-assisted vapor-liquid-solid mode, contacted by electron beam lithography, and investigated using electron beam induced current measurements. The minority carrier diffusion lengths and dynamics of both, electrons and holes, were determined directly at the vicinity of the p-n junction. The generated photocurrent shows an exponential decay on both sides of the junction and the extracted diffusion lengths are about 1 order of magnitude lower compared to bulk material due to surface recombination. Moreover, the observed strong diameter-dependence is well in line with the surface-to-volume ratio of semiconductor nanowires. Estimating the surface recombination velocities clearly indicates a nonabrupt p-n junction, which is in essential agreement with the model of delayed dopant incorporation in the Au-assisted vapor-liquid-solid mechanism. Surface passivation using ammonium sulfide effectively reduces the surface recombination and thus leads to higher minority carrier diffusion lengths. © 2012 American Chemical Society

Temperature dependent GaAs MMIC radiation effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, W.T.; Roussos, J.A.; Gerdes, J.

1993-12-01

The temperature dependence of pulsed neutron and flash x-ray radiation effects was studied in GaAs MMICs. Above room temperature the long term current transients are dominated by electron trapping in previously existing defects. At low temperature in the range 126 to 259 K neutron induced lattice damage appears to play an increasingly important role in producing long term current transients.

Design and implementation of GaAs HBT circuits with ACME

NASA Technical Reports Server (NTRS)

Hutchings, Brad L.; Carter, Tony M.

1993-01-01

GaAs HBT circuits offer high performance (5-20 GHz) and radiation hardness (500 Mrad) that is attractive for space applications. ACME is a CAD tool specifically developed for HBT circuits. ACME implements a novel physical schematic-capture design technique where designers simultaneously view the structure and physical organization of a circuit. ACME's design interface is similar to schematic capture; however, unlike conventional schematic capture, designers can directly control the physical placement of both function and interconnect at the schematic level. In addition, ACME provides design-time parasitic extraction, complex wire models, and extensions to Multi-Chip Modules (MCM's). A GaAs HBT gate-array and semi-custom circuits have been developed with ACME; several circuits have been fabricated and found to be fully functional .

E+ Transition in GaAs1-xNx and GaAs1-xBix Due to Isoelectronic-Impurity-Induced Perturbation of the Conduction Band

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fluegel, B.; Mascarenhas, A.; Ptak, A. J.

2007-01-01

An above-band-gap transition E{sub +} is experimentally observed in the dilute GaAs{sub 1-x}Bi{sub x} alloy. Precise measurements at very low dilutions are made of the above-band-gap transition E{sub +} that is observed in GaAs{sub 1-x}N{sub x}, making it possible to compare the behavior of the different isoelectronic traps Bi and N in the common host GaAs with respect to their perturbation to the host electronic structure. We suggest that the origin of the E{sub +} level observed in GaAs is not the isolated isoelectronic impurity level N{sub x}, as is presumed in the band-anticrossing model, but rather the isoelectronic-impurity-induced perturbationmore » of the conduction band L{sub 6}{sup c}.« less

Effect of thermal annealing on the photoluminescence of structures with InGaAs/GaAs quantum wells and a low-temperature GaAs layer δ-doped with Mn

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalentyeva, I. L.; Vikhrova, O. V., E-mail: istery@rambler.ru; Danilov, Yu. A.

2016-11-15

The effects of isochronal thermal annealing (at 325–725°C) on the radiative properties of InGaAs/GaAs nanoheterostructures containing a low-temperature GaAs layer δ-doped with Mn grown by laser deposition are studied. A decrease in the photoluminescence intensity and increase in the ground transition energy are observed upon thermal impact for quantum wells located near the low-temperature GaAs layer. The distribution of Mn atoms in the initial and annealed structures is obtained by secondary-ion mass spectrometry. A qualitative model of the observed effects of thermal annealing on the radiative properties of the structures is discussed; this model takes into account two main processes:more » diffusion of point defects (primarily gallium vacancies) from the GaAs coating layer deep into the structure and Mn diffusion in both directions by the dissociation mechanism. Magnetization studies show that, as a result of thermal annealing, an increase in the proportion of the ferromagnetic phase at room temperature (presumably, MnAs clusters) in the low-temperature GaAs coating layer takes place.« less

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).

Dual-gate GaAs FET switches

NASA Astrophysics Data System (ADS)

Vorhaus, J. L.; Fabian, W.; Ng, P. B.; Tajima, Y.

1981-02-01

A set of multi-pole, multi-throw switch devices consisting of dual-gate GaAs FET's is described. Included are single-pole, single-throw (SPST), double-pole, double-throw (DPDT), and single-pole four-throw (SP4T) switches. Device fabrication and measurement techniques are discussed. The device models for these switches were based on an equivalent circuit of a dual-gate FET. The devices were found to have substantial gain in X-band and low Ku-band.

Second harmonic generation in photonic crystal cavities in (111)-oriented GaAs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buckley, Sonia, E-mail: bucklesm@stanford.edu; Radulaski, Marina; Vučković, Jelena

2013-11-18

We demonstrate second harmonic generation at telecommunications wavelengths in photonic crystal cavities in (111)-oriented GaAs. We fabricate 30 photonic crystal structures in both (111)- and (100)-oriented GaAs and observe an increase in generated second harmonic power in the (111) orientation, with the mean power increased by a factor of 3, although there is a large scatter in the measured values. We discuss possible reasons for this increase, in particular, the reduced two photon absorption for transverse electric modes in (111) orientation, as well as a potential increase due to improved mode overlap.

Crystal growth of device quality GaAs in space

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1986-01-01

It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

A two layer hermetic-like coating process for on-wafer encapsulation of GaAs MMIC`s