Liquid Phase Epitaxial GaAs Research Articles

On the role of space-charge scattering in epitaxial GaAs

Electron mobility was measured in liquid phase epitaxial GaAs of moderate purity. The relevant charge carrier scattering mechanisms were investigated. It is found that the measured mobility can only be interpreted taking into account scattering on space-charge regions besides lattice and impurity scattering. The implications of space-charge scattering are discussed and it is suggested that this scattering mechanism is an almost universally occurring phenomenon in GaAs and presumably in other compound semiconductors, too. [Russian Text Ignored]

Liquid phase epitaxial growth of six-layer GaAs/(GaAl)As structures for injection lasers with 0.04 μm thick centre layer

Multilayer liquid phase epitaxy of GaAs and (GaAl)As from Ga solution, using a rotary graphite crucible in a vertical furnace, has been developed so that GaAs layers down to less than 0.04 μm thickness and (GaAl)As layers down to less than 0.08 μm thickness can be grown reproducibly on GaAs substrates. Five layer (+ contacting layer) localised gain injection lasers made from these slices give very consistent performance. During growth reasonable equilibrium is maintained in the melts, cooled at 0.2 °C/min, by allowing solid to float on the top at the growth temperature. The small supersaturation which remains is counteracted by a vertical temperature gradient of about 2.5°C/cm (slice hotter than solution). Analysis shows that the solute transport in the growth of (GaAl)As is by diffusion, but that a more rapid process occurs in the growth of GaAs, possibly constitutional convection.

LPE GaAs for microwave applications

The liquid phase epitaxial (LPE) growth method has been successfully used to fabricate GaAs microwave device structures. General material requirements for the GaAs microwave devices currently of interest are reviewed in this paper. An LPE technology based on a multiple-well graphite slider boat, utilized for growth of multilayer structures, is described. Selection of dopants and control of unwanted background impurities are discussed in detail. Doping profiles and rf performance data on Gunn and Avalanche devices are presented to define the state-of-the-art in GaAs LPE capability.

A quartz sliding boat for GaAs liquid phase epitaxy

A new sliding boat configuration for liquid phase epitaxy is described. The design is simple enough for the boat to be made of quartz. Such a quartz boat has been used to grow undoped GaAs layers with carrier concentrations in the 10 14 cm -3 range. The boat was also used for the growth of p-n junctions.

Effects of dislocation density on the properties of liquid phase epitaxial GaAs

A study has been made of the effect of dislocation density on the properties of p-type GaAs (Ge-doped, p = 1 × 1019 cm−3) grown homoepitaxially on GaAs and heteroepitaxially on GaP. It has been found that dislocation densities > 5 × 106 cm−2 reduce the minority-carrier diffusion length in the p-type material and, consistent with this reduction, degrade the junction electroluminescence and p-layer photoluminescence. At high dislocation densities (> 5 × 106 cm−2), it is also found that subgrains form in the GaAs epitaxial layers grown either heteroepitaxially on GaP or homoepitaxially on GaAs. It is surmised that the dislocations polygonize during growth to form subgrain boundaries rather than form due to nucleation at the substrate. Finally, the results indicate that the electron diffusion length is limited to the average dislocation spacing with the dislocations acting as nonradiative recombination centers for electrons.

Heterojunction cold-cathode electron emitters of (AlGa) As-GaAs

New cold-cathode electron emitters designed for vacuum tube have been developed based on the use of liquid phase epitaxy, (AlGa) As-GaAs heterojunctions and negative-electron affinity GaAs surfaces. An important part of the device is the lateral confinement of the current flow to the desired emitting surface by a novel fabrication technique. It has been shown that devices operating at practical efficiencies and emission current densities can be reproducibly fabricated and activated. The electron energy distribution has been determined. The half width of the energy distribution is 160 meV (compared to ≈ 220 meV for a thermionic cathode at 1000 °K) and is consistent with theoretical calculations based on the energy loss of the electrons in the GaAs space charge region near the surface. While this distribution is wider than kT, it contains a relatively small high energy component. It is the high energy component which is the most troublesome aspect of the thermionic cathode emission. Some of the major factors affecting cathode life have been studied, and the following conclusions have been reached: (1) A decrease in negative electron affinity occurs mainly during electron emission from the activated surface and results from electron-stimulated desorption from the anode; (2) a decrease in negative electron affinity is due, at least in part, to the physical adsorption of impurities released from the anode rather than to a loss of cesium and/or oxygen; (3) oxygen physically adsorbed on the activated surface is a specific impurity which causes a severe reduction in negative electron; (4) cathode stability can be greatly improved by a number of techniques including operation at low anode voltages and magnetic field deflection to prevent the incidence on the cathode surface of impurities released from the anode.

Performance of GaAs Surface-Barrier Detectors Made from High-Purity Gallium Arsenide

Gallium arsenide surface barrier diodes have been fabricated from high purity level materials. These devices have an Au surface barrier having a depletion layer thickness of from 70μmto 1 mm and an area of from 3mm2-27mm2. These devices have been operated as α-particles, / ß-ray, and γ-ray spectrometers and detectors. The best energy resolutions taken with a GaAs detector made from liquid phase epitaxial GaAs wafer were 20keV (fwhm) and 8 keV for 5.486 MeV α-particles from 241Am and 115 keV conversion electrons from 57Co at room temperature, respectively. For room temperature applications, a simple charge sensitive preamplifier was constructed using two FETs and one OP amp. The combination of a encapsulated GaAs detector and two small semiconductor thermoelements (electrical cooling device) was studied to make a simple X-or γ-ray spectrometer. A special tiny GaAs detector was also fabricated as in vivo ß-ray counting detector in biomedical applications. The energy per electron-hole pair (ϵ) in GaAs was measured at 4.35 + 0.02 eV for α-particles with a linear variation with bandgap energy (Eg) of 2.53 over a temperature range of 1950°K to 330°K, and 4.57 eV for conversion electrons (115keV) at 300°K, respectively. The ϵ vs Eg relationship was also investigated for Ge, Si, GaAs and CdTe using experimental values and led to ϵ = 2. 596 Eg + 0.714 (eV) with correlation coefficient of 0.999 at 300°K. The related problems for intrinsic material constant (ϵ) are discussed for several semiconductor materials.

Interface Effects on the Spectral Response of Liquid Phase Epitaxial n-GaAs Radiation Detectors

Two undesirable features exhibited by gold surface barrier detectors from liquid phase epitaxial (LPE) n-GaAs are the variation in pulse height response with bias and multi-peaking effects near full depletion. Capacitative attenuation by the high resistivity epitaxy-substrate interface (ESI) layer is considered to be the origin of these effects. Such anomalous interface layers are well known in the application of LPE GaAs to Gunn oscillator devices and a review of their properties is presented. The response of detectors at room temperature when subjected to IR illumination was markedly improved in the multi-peaking region and slow components in the pulse rise time were removed. The presence of a deep level acceptor in the ESI layer 0.31 - 0.76 eV from the valence band is inferred. Other methods for the reduction of ESI effects are discussed.

Computer simulations of liquid phase epitaxy of GaAs in Ga solution

Numerical methods have been used to calculate the concentration profiles of solute at successive intervals of time in front of a crystal interface growing under the normal conditions of liquid phase epitaxy. Such methods are necessary due to the complexity of the boundary conditions. The concentration gradient at the interface can be used to calculate the growth rate, and hence the amount etched or grown as a function of time can be obtained. The basic model considers purely diffusive transport of material and two variants on this have been used: the first is similar with a mechanism to simulate homogeneous nucleation at a critical super-saturation in the solution, while the second is a case of boundary layer diffusion in an otherwise well mixed solution. Comparison with experimental results indicates that the boundary layer diffusion model is generally applicable to the vertical substrate geometry while the bulk diffusion model is more applicable to the system where a solution covers a horizontal substrate.

A deep level in Zn-doped liquid phase epitaxial GaAs

A deep level in Zn-doped liquid phase epitaxial GaAs

Electroluminescence Characteristics and Efficiency of GaAs:Si Diodes

The peak wavelength, spectral half-width, and efficiency of liquid-phase epitaxial GaAs:Si diodes were determined as a function of silicon concentration in the melt. The peak of the emission spectrum could be shifted from about 9200 to 10 000 Å by varying the silicon concentration. For all wavelengths investigated, uncoated diodes with 6% efficiency could be made, with some going as high as 10%. External room-temperature dc efficiencies up to 32% were measured on diodes provided with high-index glass domes. The spectral half-width was found to increase with silicon concentration, and was especially large for growth on the 111B plane. The internal absorption loss was found to be significant for all peak wavelengths. These findings are discussed in the light of current models of recombination processes in heavily doped semiconductors.

Constitutional supercooling in GaAs liquid phase epitaxy

The diffusion equation is solved for the epitaxial crystallization of gallium arsenide from gallium solution. The melt was assumed to be cooled at a constant rate and phase equilibrium was assumed at the freezing epitaxial interface. The minimum temperature gradient allowed to avoid constitutional supercooling was calculated for the cases of a semi-infinite and a finite melt. The latter case is much more favorable for the growth of thin smooth layers. The difficiencies of the present technology in this respect are pointed out.

Efficient AlxGa1-xAs injection lasers

This paper describes the characteristics of Al x Ga 1-x As injection lasers fabricated by an epitaxial growth process based on the solution growth technique. Efficient room temperature lasers (exterior differential quantum efficiency of about 15-20%) with threshold current densities of 40,000-50,000 A/cm2have been fabricated which emit in the wavelength range of 9000 to 8250A. It is noteworthy that the near-field emission patterns of these lasers are quite uniform -- an important consideration for practical use. We have also measured the temperature dependence of the threshold current density of these diodes and found a ratio of about 40 to 1 between 77°K and 300°K which is typical for liquid-phase epitaxial GaAs lasers. A further point of interest is the variation of laser wavelength with temperature. We find that the peak shifts by about 530A between 77°K and 300°K. At 77°K efficient ( \sim40% efficient) stimulated emission has been observed in the visible range of the spectrum (6900A). Diodes which simultaneously lase at two wavelengths at 100°K and below (in the visible and infrared portion of the spectrum) have also been fabricated by varying the alloy composition within two to three microns of the p-n junction. These devices will be described.