Liquid Phase Epitaxial GaAs Research Articles

Liquid-phase epitaxy of GaAs by temperature difference method to realize wide lateral growth

Abstract A new experimental setup for temperature difference method (TDM) was designed and their growth parameters were optimized for GaAs growth on (0 0 1) GaAs substrates. In the setup, the substrate is directly cooled by flowing H 2 to the backside. This is very useful to locally cool the substrate with an extreme high efficiency, which helps to prevent the mixture of growth modes between TDM and other growth modes like step cooling. The cross-sectional observations of scanning electron microscope show that the growth rate was roughly proportional to the H 2 flow, and the thickness of the growth was also proportional to the growth time. This indicates that the growth was chiefly driven by the temperature difference in the melt. Although the grown layers were not extremely uniform, the growth rate of more than 3 μm/h was achieved. A very thick layer as thick as 360 μm was obtained by increasing the growth time up to 100 h. TDM was also applied to microchannel epitaxy of GaAs. A microchannel epitaxial layer whose width is as large as 84 μm was laterally grown with a fine ratio of the width to the thickness of 13.

Characterization of liquid phase epitaxial GaAs for blocked-impurity-band far-infrared detectors

GaAs blocked-impurity-band (BIB) photoconductor detectors have the potential to become the most sensitive, low noise detectors in the far-infrared below 45.5cm−1 (⩾220μm). We have studied the characteristics of liquid phase epitaxial GaAs films relevant to BIB detector production, including impurity band formation and the infrared absorption of the active section of the device. Knowledge of the far-infrared absorption spectrum as a function of donor concentration combined with variable temperature Hall effect and resistivity studies leads us to conclude that the optimal concentration for the absorbing layer of a GaAs BIB detector lies between 1×1015 and 6.7×1015cm−3. At these concentrations there is significant wave function overlap which in turn leads to absorption beyond the 1s ground to 2p bound excited state transition of 35.5cm−1 (282μm). There still remains a gap between the upper edge of the donor band and the bottom of the conduction band, a necessity for proper BIB detector operation.

GaAs and AlGaAs photodiodes for ionizing radiation detectors

In this work we present large area AlGaAs photodiodes for detecting the luminescent light of crystal scintillators in detectors of ionizing radiation, fabricated by low-temperature variant of the liquid-phase epitaxy (LPE) method. They exhibit a low leakage current (lower than 10 −12 A/cm 2), a high quantum efficiency for wide spectral range (400–900 nm) and a high operating temperature (up to 120 °C). P-i-n GaAs detectors on the base of high purity LPE GaAs material grown by LPE are suggested as an alternative to those on the base of semi-insulating (SI) GaAs material. The use of high purity GaAs instead SI GaAs material much reduces charge carrier trap concentrations and make it possible for p-i-n photodiode to obtain a high charge collection efficiency at low bias voltages. The calculated electrical characteristics show that low capacitance and low dark current can be realised in these photodiodes.

Muon dynamics in GaAs LPE lightly doped material: initial RFμSR study

The first (RF)μSR data is presented on high-quality liquid-phase epitaxy (LPE) grown GaAs, material known to have a defect concentration comparable to its dopant levels. Our initial data on two n-type samples is compared to results in commercial semi-insulating material and to the better understood situation in Si. Some preliminary interpretations are given.

Praseodymium added GaAs liquid phase epitaxy and its Schottky diode application

Pr 2O 3-added GaAs liquid phase epitaxy (LPE) has been studied. Due to the gettering effect of the rare earth (RE) elements low oxide surfaces and high purity GaAs epilayers are obtained and examined. After epitaxial growth, the samples are prepared by a standard Schottky diode (SD) fabrication process. The variations in the electrical properties of these SDs are reported. For an embodiment with a Schottky barrier height (SBH) above 0.94 eV, a leakage current of around 0.7×10 −6 A and a breakdown voltage of 140 V is obtained at a Pr 2O 3 addition ratio of 0.05 mg per gram of gallium. These SDs were also irradiated by gamma rays for study of radiation hardness. After 4 h irradiation, all samples are initially out of function. However, 4 h later, due to natural annealing, the Pr 2O 3-added samples can recover up to 72% of their original SBH values. Furthermore, after a further 24 h, the tendency to recover is saturated and a 17% SBH retardation still remains. During this period, the appropriate Pr 2O 3-added SDs (#508 & #509) show better radiation hardness than the one (#501) with no addition.

Characterization of GaAs liquid-phase epitaxy layers grown in a BN boat

GaAs liquid-phase epitaxy layers were grown in a BN boat using the melt-baking growth technique. Free-carrier concentration and mobility, photoluminescence at 11.5 K and electrooptical properties were studied to determine the quality of the layers. All the layers grown using this BN boat have a p-i-n structure possibly formed by the presence of nitrogen and silicon impurities.

Growth of high purity liquid phase epitaxial GaAs in a silica growth system

Liquid phase epitaxial gallium arsenide layers, greater than 200 μm thickness and with a low net carrier concentration ( N A,D ≈ 10 13 cm −3) have been grown in a silicia growth system with silica crucibles. Analysis of electrical and chemical defects was carried out using capacitance-voltage ( C V) measurements, deep level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS). Details of the growth procedure are given and it is shown that silicon incorporation in the growth layer is not suppressed by the addition of ppm levels of oxygen to the main hydrogen flow.

A neutron damage study of liquid phase epitaxial GaAs and high purity silicon

Neutron irradiation studies of silicon and liquid phase epitaxial (LPE) GaAs Schottky barrier radiation detectors were carried out using 1.1 MeV fast neutrons produced using the Australian Nuclear Science and Technology Organisation's 3 MeV Van de Graaff accelerator. Neutrons were provided by bombardment of a 7Li target with 3 MeV protons to a maximum fluence of 7 × 10 13 neutrons cm −2. Neutron damage to the detectors was characterised using capacitive deep level transient spectroscopy, optical deep level transient conductance spectroscopy, current-voltage measurements and capacitance-voltage measurements. The degradation of 241Am spectra was also observed.

Liquid Phase Epitaxy of GaAs by yo-yo solute feeding method

Liquid Phase Epitaxy of GaAs by yo-yo solute feeding method

Investigation of GaAs growth from Bi-based melts for solar cells

Bismuth was studied as an alternative to Ga and Sn solvents for liquid phase epitaxy of GaAs. GaAs solubility in Bi was measured at T < 600°C. Sn and Zn were studied as dopants for the growth of n- and p-GaAs, respectively.

LPE GaAs as an X-ray detector for astronomy

Gallium arsenide detectors offer an attractive alternative to silicon for high energy X-ray (> 10 keV) astrophysics. Thick (130 μm) detectors fabricated from GaAs grown using the liquid phase epitaxy (LPE) process are now achieving an energy resolution which is approaching that needed in astrophysics. At the same time progress continues to be made in the field of true imaging optics at these high energies using multi-layer reflective surfaces and it is now not unreasonable to imagine a hard X-ray astrophysics mission with grazing incidence optics and a GaAs solid state position sensitive spectrometer in the focal plane. A brief introduction to hard X-ray astrophysics and optics is given. Results obtained with an LPE GaAs device are presented including both detector performance and the electrical characteristics. At room temperature a resolution of ∼ 2.8 keV HWHM was achieved.

A photoluminescence and photocapacitance study of GaAs:In and GaAs:Sb layers grown by liquid-phase epitaxy

Results of Hall, photoluminescence and photocapacitance measurements performed on GaAs layers grown by liquid-phase epitaxy (LPE) and doped with various amounts of indium (In) and antimony (Sb) are presented. Hall measurements show that such doping marginally enhances the mobility in a certain optimum doping range. Near-band-edge photoluminescence spectra indicate the presence of CAs and SiAs as major acceptor impurities in lightly In-doped material. The latter impurity is not detected in heavily In-doped GaAs layers or in Sb-doped layers with either low and high doping density. Photocapacitance measurements reveal the presence of hole traps A and B, reported previously in undoped LPE GaAs. Indium doping reduces the total density of these traps. Furthermore, Sb doping induces a very sharp fall in the density of trap B. The results indicate that the hole trap B may be related to a GaAs antisite defect.

Dominant Traps in Liquid Phase Epitaxial GaAs Studied by Controlled Doping with Indium and Antimony

AbstractPhotocapacitance measurements in the photon energy range of 0.64 to 1.27 eV are done on GaAs layers grown by liquid phase epitaxy (LPE) and doped with varying amounts of indium (In) and antimony (Sb). Two hole traps with optical ionization energies of 0.65 and 0.79 eV are revealed in the material which are assumed to be two levels associated with the hole trap B reported in the literature. In addition, the hole trap A, usually found in LPE GaAs is also detected here by optical deep level transient spectroscopy (ODLTS) technique. The results of trap density measurements, as functions of isoelectronic doping concentration, indicate that VGa is an active constituent of the hole traps in LPE GaAs. The concentration of the 0.79 eV trap is found to be reduced in the material with high concentration of Sb. The analysis of photocapitance data using the existing theoretical models indicates the presence of an electron trap with activation energy of 0.75 eV in the heavily Sb‐doped material. This trap may be identified with the second charge state of the SbGa electron trap, obtained previously in bulk and metalorganic vapor phase epitaxial GaAs doped with Sb. The sharp reduction of the 0.79 eV hole trap density in Sb‐doped materials is explained by assuming the complex GaAsV, as its source.

Monomolecular steps of ultra-low density on (100) growth faces of liquid phase epitaxial GaAs

Steps of monolayer height, when in low density present on facets of liquid phase epitaxial GaAs, constitute almost atomically flat growth faces. We achieve a ration of monostep spacing to step height as high as 10 6: 1 on (100)-oriented facets. The 2.85 Å high monosteps arrange themselves inside closely adjoining square-shaped facets. The development of the facets is initiated by mesas of 0.5 × 0.5 mm 2 area, which are produced on the substrate prior to epitaxy. The monosteps on the facets appear in spiral or concentric patterns or in arrays of nearly straight steps. We have correlated the different monostep patterns with their particular step generation mechanism. The monosteps are mapped by optical and atomic force microscopy.

Liquid phase epitaxy of n-type GaAs from Bi solution

Liquid phase epitaxy of GaAs from Bi melt was studied for growth temperatures between 670–750○C. The layers were characterized by Van der Pauw and photoluminescence measurements. All epitaxial layers were n-type and exhibit low compensation and electron mobilities up to 6×104 cm2/V s at 77 K. A gradual increase in the n-type doping was observed with growth temperature. Intentional doping of GaAs with Sn leads to a Sn distribution coefficient ∼60 times larger for the Bi melt in comparison to the Ga melt. Extremely low compensation of the Sn-doped layers (K≤0.1 for Nd=2.5×1017 cm−3) is obtained.

Si Acceptors and their Passivation by Hydrogen in p-Type Liquid Phase Epitaxial and Molecular Beam Epitaxial GaAs

Si Acceptors and their Passivation by Hydrogen in p-Type Liquid Phase Epitaxial and Molecular Beam Epitaxial GaAs

Schottky barrier height modification on high-purity LPE GaAs following a sulphur-based etch

Nuclear radiation detectors constructed from GaAs Schottky barrier structures require control of barrier height if high resolution is to be reproducibly obtained. The authors have therefore studied the variation of device barrier height after treatment with common etching solutions. The heights of Au and Al Schottky barriers on respective samples of n- and p-type liquid-phase epitaxial GaAs were found from reverse bias I-V measurements subsequent to etching with aqua regia and 3H2SO4:H2O2:H2O (3:1:1). An increase in barrier height observed after the 3:1:1 etch was found to be a consequence of sulphur contamination. This result is consistent with those reported for deliberate sulphur passivation of GaAs. Low diode ideality factors, from 1.007 to 1.064, were measured for layers with carrier concentrations in the range 4*1014 cm-3 to 2.5*1016 cm-3. A comparison was made between samples etched in the 3:1:1 solution at 5 degrees C and at 100 degrees C. C-V measurements gave anomalously large barrier heights for those samples etched at 5 degrees C, indicating the formation of a significant interfacial layer prior to Schottky barrier metallization, while X-ray photoelectron spectroscopy measurements confirmed the presence of a large oxide layer. No such anomalies were observed for the samples etched in 3:1:1 at 100 degrees C.

Kinetics of Long Term Finite Melt Liquid Phase Epitaxyal Growth of GaAs and GaAlAs Layers. I. Gallium Arsenide

AbstractA model is proposed for a description of the growth kinetics of long term finite melt liquid phase epitaxy of GaAs and GaAlAs layers. The applicability region of the model is discussed. The correct liquidus, the temperature dependence of the diffusion coefficients, the precise concentration profiles of the components of the melt, and the non‐equilibrium construction of atoms in the layer are taken into account. The influence of the crystallisation reaction at the surface of the layer is considered, and different temperature regimes of the process can be treated. Temperature dependences of the Al and As diffusion coefficients in the melt are determined, based on comparison between theoretical and experimental results for the thicknesses and the concentration profile of GaAs and GaAlAs growon (etched) layers.

Gamma Induced Centres in Liquid Phase Epitaxial Gallium Arsenide

Poole-Frenkel pairs in liquid phase epitaxial Gallium Arsenide induced by gamma irradiation are described. These defects are shown to be easily annealed out, with the device metallisation intact, at 200°C. Preliminary investigations indicate the usefulness of Liquid Phase Epitaxial (LPE) GaAs for high energy particle detection.

Amphoteric behaviour of germanium during liquid phase epitaxy of GaAs from bismuth-gallium melts

The electrical properties of (100)-, (111)A- and (111)B-oriented layers of GaAs doped with the amphoteric impurity germanium have been studied. The layers were grown from the mixed Ga-Bi melts ranging from pure Ga to pure Bi solvent. Hall measurements showed that the properties of p- as well as n-type conductivity layers depend on crystallographic orientation over the whole range of solvent composition. The hole concentration dependence on bismuth content in the solvent for (111)B-oriented layers, at constant germanium concentration in the liquid phase, differed qualitatively from those of the other orientations. This is caused by a higher degree of compensation in p-GaAs:Ge (111)B-oriented layers. In general, the experimental results are in satisfactory agreement with Zschauer and Vogel's model, but for (111)B surface an additional nonequilibrium concentration of the arsenic vacancies must be assumed. It is also shown that the main factor, governing the incorporation of Ge into Ga or As sublattices of GaAs, during LPE from mixed Ga-Bi melts, is the change of gallium and arsenic concentrations in the liquid phase.