Study of semiconductor heterojunctions of zinc selenide, gallium arsenide, and germanium
Fabrication and properties of gallium arsenide and zinc selenide junctions with germanium, and of gallium arsenide-zinc selenide heterojunctions
Feucht, D. L.↗
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Low temperature recombination and trapping analysis in high purity gallium arsenide by microwave photodielectric techniques
Some physical theories pertinent to the measurement properties of gallium arsenide are presented and experimental data are analyzed. A model for explaining recombination and trapping high purity gallium arsenide, valid below 77 K is assembled from points made at various places and an appraisal is given of photodielectric techniques for material property studies.
Khambaty, M. B.↗
Development of gallium arsenide solar cells
The potential of ion implantation as a means of developing gallium arsenide solar cells with high efficiency performance was investigated. Computer calculations on gallium arsenide cell characteristics are presented to show the effects of surface recombination, junction space-charge recombination, and built-in fields produced by nonuniform doping of the surface region. The fabrication technology is summarized. Electrical and optical measurements on samples of solar cells are included.
Source record↗
Electrical contacts to ion cleaned n-type gallium arsenide.
The electrical current through silver contacts evaporated onto n-type gallium arsenide is reported as a function of surface treatment. Contacts to untreated gallium arsenide exhibit the expected high resistance. Surface cleaning by argon ion bombardment reduces the resistance by three orders of magnitude. The electrical resistance beyond 850 eV increases rapidly with ion bombardment energy. The resistance minimum at 850 eV is explained semiquantitatively in terms of a balance between cleaning and surface damage.
Walker, G. H.↗
The 13.9 GHz short pulse radar noise figure measurements utilizing silicon and gallium-arsenide mixer diodes
An analysis was made on two commercially available silicon and gallium arsenide Schottky barrier diodes. These diodes were selected because of their particularly low noise figure in the frequency range of interest. The specified noise figure for the silicon and gallium arsenide diodes were 6.3 db and 5.3 db respectively when functioning as mixers in the 13.6 GHz region with optimum local oscillator drive.
Dombrowski, M.↗
Radiation damage of gallium arsenide production cells
High efficiency liquid phase epitaxy (LPE) gallium arsenide cells were irradiated with 1 Mev electrons up to fluences of 1 times 10 to the 16th power cm-2. Measurements of spectral response and dark and illuminated I-V data were made at each fluence and then, using computer codes, the experimental data was fitted to gallium arsenide cell models. In this way it was possible to determine the extent of the damage, and hence damage coefficients in both the emitter and base of the cell.
Mardesich, N.↗
Bit-systolic arithmetic arrays using dynamic differential gallium arsenide circuits
A new family of gallium arsenide circuits for fine grained bit-systolic arithmetic arrays is introduced. This scheme combines features of two recent techniques of dynamic gallium arsenide FET logic and differential dynamic single-clock CMOS logic. The resulting circuits are fast and compact, with tightly constrained series FET propagation paths, low fanout, no dc power dissipation, and depletion FET implementation without level shifting diodes.
Beagles, Grant↗
Window structure for passivating solar cells based on gallium arsenide
Passivated gallium arsenide solar photovoltaic cells with high resistance to moisture and oxygen are provided by means of a gallium arsenide phosphide window graded through its thickness from arsenic rich to phosphorus rich.
Barnett, Allen M.↗
Ternary rare-earth zinc arsenides REZn{sub 1-x}As{sub 2} (RE=La-Nd, Sm)
The ternary rare-earth zinc arsenides REZn{sub 1-x}As{sub 2} (RE=La-Nd, Sm) were prepared by reaction of the elements at 800 deg. C. Single-crystal and powder X-ray diffraction analysis revealed a defect SrZnBi{sub 2}-type average structure for the La member (Pearson symbol tI16, space group I4/mmm, Z=4; a=4.0770(9) A, c=20.533(5) A), in contrast to defect HfCuSi{sub 2}-type average structures for the remaining RE members (Pearson symbol tP8, space group P4/nmm, Z=2; a=4.0298(5)-3.9520(4) A, c=10.222(1)-10.099(1) A in the progression from Ce to Sm). The homogeneity range is not appreciable (estimated to be narrower than 0.6<1-x<0.7 in SmZn{sub 1-x}As{sub 2}) and the formula REZn{sub 0.67}As{sub 2} likely represents the Zn-rich phase boundary. The Ce-Nd members are Curie-Weiss paramagnets. LaZn{sub 0.67}As{sub 2} shows activated behavior in its electrical resistivity, whereas SmZn{sub 0.67}As{sub 2} exhibits anomalies in its temperature dependence of the electrical resistivity. - Graphical abstract: LaZn{sub 1-x}As{sub 2} adopts a SrZnBi{sub 2}-type structure whereas the remaining members of the REZn{sub 1-x}As{sub 2} series (RE=Ce-Nd, Sm) adopt a HfCuSi{sub 2}-type structure. Highlights: > REZn{sub 1-x}As{sub 2} adopts SrZnBi{sub 2}-type (RE=La) or HfCuSi{sub 2}-type (RE=Ce-Nd, Sm) structures. > Trends in RE substitution and local distortion around Zn-centered tetrahedra can be rationalized by geometrical factors. > Zn vacancies occur to reduce Zn-As and As-As antibonding interactions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Impacts of point defects on shallow doping in cubic boron arsenide: A first principles study
Cubic boron arsenide (BAs) stands out as a promising material for advanced electronics, thanks to its exceptional thermal conductivity and ambipolar mobility. However, effective control of p- and n-type doping in BAs poses a significant challenge, mostly as a result of the influence of defects. In the present study, we employed density functional theory (DFT) to explore the impacts of the common point defects and impurities on p-type doping of Be B and Si As , and on n-type doping of Si B and Se As . We found that the most favorable point defects formed by C, O, and Si are C As , O B O As , Si As , C As Si B , and O B Si As , which have formation energies of less than 1.5 eV. While the O impurity detrimentally affects both p- and n-type dopings, C and Si impurities are harmful for n-type dopings, making n-type doping a potential challenge. Interestingly, the antisite defect pair A s B B As benefits both p- and n-type doping. Finally, the doping limitation analysis presented in this study can potentially pave the way for strategic development in the area of BAs-based electronics.
36 MATERIALS SCIENCE↗
High Pressure X-ray Diffraction Study on Icosahedral Boron Arsenide (B12As2)
The high pressure properties of icosahedral boron arsenide (B12As2) were studied by in situ X-ray diffraction measurements at pressures up to 25.5 GPa at room temperature. B12As2 retains its rhombohedral structure; no phase transition was observed in the pressure range. The bulk modulus was determined to be 216 GPa with the pressure derivative 2.2. Anisotropy was observed in the compressibility of B12As2-c-axis was 16.2% more compressible than a-axis. The boron icosahedron plays a dominant role in the compressibility of boron-rich compounds.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Nanoscale interlayer defects in iron arsenides
Using a local real-space microscopy probe, we investigate evidence of nanoscale interlayer defects along the c-crystallographic direction in BaFe 2 As 2 (‘122’) based iron-arsenide superconductors. We find ordered 122 atomic arrangements within the ab -plane, and within regions of ~10 to 20 nm size perpendicular to this plane. While the FeAs substructure is very rigid, Ba ions are relatively weakly bound and can be displaced from the 122, forming stacking faults resulting in the physical separation of the 122 between adjacent ordered domains. The evidence for interlayer defects between the FeAs superconducting planes gives perspective on the minimal connection between interlayer chemical disorder and high-temperature superconductivity. Specifically, the Cooper pairs may be finding a way around such localized interlayer defects through a percolative path of the ordered layered 122 lattice that may not affect T c .
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Rapid microwave synthesis of the iron arsenides NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO
Graphical abstract: For the first time, a rapid method for synthesizing NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO is reported. This method uses 2.45 GHz microwave radiation and an additional microwave susceptor to drive the reaction. The superconducting properties NdFe{sub 0.9}Co{sub 0.1}AsO of microwave synthesized materials match well with those reported previously. Highlights: Black-Right-Pointing-Pointer Microwave assisted solid state synthesis of NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO is reported. Black-Right-Pointing-Pointer Synthesis of high quality samples is achieved after 50 min microwave exposure. Black-Right-Pointing-Pointer Physical properties of microwave samples match those prepared conventionally. -- Abstract: The future of iron pnictide superconductors in technology is still undecided. While these materials are now known to possess relatively high critical temperatures and critical magnetic fields, processing methods for these superconductors are still in the development stage. Recently we have been investigating possible ways to speed up the synthetic process for obtaining polycrystalline iron arsenide superconductors and other transition metal pnictides. Here we report the synthesis of NdFeAsO and NdFe{sub 0.9}Co{sub 0.1}AsO in less than 1 h total exposure to microwave radiation using an additional microwave susceptor to surround the reaction ampoule. Structure and property measurements reveal the samples to be of high quality and superconducting when Co doped.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Persistent hot carrier diffusion in boron arsenide single crystals imaged by ultrafast electron microscopy
Cubic boron arsenide (BAs) is promising for microelectronics thermal management because of its high thermal conductivity. Recently, its potential as an optoelectronic material is also being explored. However, it remains challenging to measure its photocarrier transport properties because of small sizes of available high-quality crystals. Here, we use scanning ultrafast electron microscopy (SUEM) to directly visualize the diffusion of photocarriers in BAs single crystals. Surprisingly, we observed ambipolar diffusion at low optical fluence with persistent hot carrier dynamics for above 200 ps, which can likely be attributed to the large frequency gap between acoustic and optical phonons, the same feature that is responsible for the high thermal conductivity. At higher optical fluence, we observed spontaneous electron-hole separation. Our results show BAs is an attractive optoelectronic material combining high thermal conductivity and excellent photocarrier transport properties. Finally, our study also demonstrates the capability of SUEM to probe photocarrier transport in emerging materials.
36 MATERIALS SCIENCE↗
Carrier-Transport Study of Gallium Arsenide Hillock Defects
Abstract Single-crystalline gallium arsenide (GaAs) grown by various techniques can exhibit hillock defects on the surface when sub-optimal growth conditions are employed. The defects act as nonradiative recombination centers and limit solar cell performance. In this paper, we applied near-field transport imaging to study hillock defects in a GaAs thin film. On the same defects, we also performed near-field cathodoluminescence, standard cathodoluminescence, electron-backscattered diffraction, transmission electron microscopy, and energy-dispersive X-ray spectrometry. We found that the luminescence intensity around the hillock area is two orders of magnitude lower than on the area without hillock defects in the millimeter region, and the excess carrier diffusion length is degraded by at least a factor of five with significant local variation. In conclusion, the optical and transport properties are affected over a significantly larger region than the observed topography and crystallographic and chemical compositions associated with the defect.
14 SOLAR ENERGY↗
CO{sub 2} laser-based dispersion interferometer utilizing orientation-patterned gallium arsenide for plasma density measurements
A dispersion interferometer based on the second-harmonic generation of a carbon dioxide laser in orientation-patterned gallium arsenide has been developed for measuring electron density in plasmas. The interferometer includes two nonlinear optical crystals placed on opposite sides of the plasma. This instrument has been used to measure electron line densities in a pulsed radio-frequency generated argon plasma. A simple phase-extraction technique based on combining measurements from two successive pulses of the plasma has been used. The noise-equivalent line density was measured to be 1.7 × 10{sup 17} m{sup −2} in a detection bandwidth of 950 kHz. One of the orientation-patterned crystals produced 13 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 13 W of peak power. Two crystals arranged sequentially produced 58 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 37 W of peak power.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch
Properties of ultrafast switching in a bulk gallium arsenide (GaAs) avalanche semiconductor switch based on semi-insulating wafer, triggered by an optical pulse, were analyzed using physics-based numerical simulations. It has been demonstrated that when a voltage with amplitude of 5.2 kV is applied, after an exciting optical pulse with energy of 1 μJ arrival, the structure with thickness of 650 μm reaches a high conductivity state within 110 ps. Carriers are created due to photons absorption, and electrons and holes drift to anode and cathode terminals, respectively. Static ionizing domains appear both at anode and cathode terminals, and create impact-generated carriers which contribute to the formation of electron-hole plasma along entire channel. When the electric field in plasma region increases above the critical value (∼4 kV/cm) at which the electrons drift velocity peaks, a domain comes into being. An increase in carrier concentration due to avalanche multiplication in the domains reduces the domain width and results in the formation of an additional domain as soon as the field outside the domains increases above ∼4 kV/cm. The formation and evolution of multiple powerfully avalanching domains observed in the simulations are the physical reasons of ultrafast switching. The switch exhibits delayed breakdown with the characteristics affected by biased electric field, current density, and optical pulse energy. The dependence of threshold energy of the exciting optical pulse on the biased electric field is discussed.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Structure and electrical characterization of gallium arsenide nanowires with different V/III ratio growth parameters
Gallium arsenide (GaAs) nanowires were grown vertically on GaAs(111)B substrate by gold-assisted using metal-organic chemical vapour deposition. Field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and conductivity atomic force microscopy (CAFM) analysis were carried out to investigate the effects of V/III ratio on structural properties and current-voltage changes in the wires. Results show that GaAs NWs grow preferably in the wurtzite crystal structure than zinc blende crystal structure with increasing V/III ratio. Additionally, CAFM studies have revealed that zincblende nanowires indicate ohmic characteristic compared to oscillation current occurred for wurtzite structures. The GaAs NWs with high quality structures are needed in solar cells technology for trapping energy that directly converts of sunlight into electricity with maximum capacity.
36 MATERIALS SCIENCE↗