K.E. Singer

A photoluminescence and Hall‐effect study of GaSb grown by molecular‐beam epitaxy

Unintentionally doped gallium antimonide has been grown by molecular‐beam epitaxy on gallium arsenide and gallium antimonide. Substrate temperatures in the range 480 to 620 °C and antimony to gallium flux ratios from 0.65 : 1 to 6.5 : 1 have been investigated. The deposition conditions have been related to growth morphology and to the electrical and optical properties of the epitaxial films. A strong correlation has been found between the quality of the layers and the degree of excess antimony flux; the best material in terms of both optical and electrical properties was obtained with the minimum antimony stable growth at a particular substrate temperature. All the material exhibited residual p‐type behavior. The lowest hole concentration achieved was 7.8×1015 cm−3 with a corresponding room‐temperature mobility of 950 cm2/V s. The narrowest PL (photoluminescence) features observed were peaks associated with bound exciton transitions with half‐widths of 2–3 meV.

Growth and structural characterization of molecular beam epitaxial erbium-doped GaAs

Abstract Elemental erbium from a thermal effusion cell has been used to dope gallium arsenide grown by molecular beam epitaxy with erbium concentrations of 4 × 10 16 to 2 × 10 20 cm -3 . No incorporation dependence on substrate temperature was observed over the range 540–630°C. Transmission electron microscopy has revealed a solubility limit of erbium in GaAs of approximately 7 × 10 17 cm -3 at 580°C. Above this concentration, erbium is incorporated primarily as near spherical micro-precipitates which possess a cubic (rocksalt) structure consistent with their chemical composition being ErAs. The precipitate size during the molecular beam epitaxial growth is dependent primarily on the substrate temperature and can be controlled in the 10–20 A range. Larger precipitates produce misfit dislocations and are no longer spherical. The mechanism represents a simple method for the fabrication of quantum dots distributed uniformly in three dimensions.

Thermal stability of epitaxial Al/GaAs Schottky barriers prepared by molecular-beam epitaxy

The effect of annealing on the electrical characteristics of epitaxial aluminum/gallium arsenide Schottky barriers prepared by molecular‐beam epitaxy has been studied and compared with the annealing behavior of polycrystalline aluminum contacts deposited in a conventional evaporation system. It was found that the epitaxial contacts showed remarkably stable electrical characteristics, the forward characteristics remaining exponential over 6 decades of current after annealing for 1 h at 500 °C, with a slight degradation of n value from 1.01 to 1.02 and a very small recombination component. In the reverse direction, the characteristics improved on annealing, with a reduction in current from 9×10−10 to 6×10−11 A at a reverse bias of 1 V. In contrast, the polycrystalline contacts showed a pronounced recombination component after annealing, with an increase in n to between 1.05 and 1.09, and a significant degradation in reverse characteristics. Auger depth profiling showed that the epitaxial contacts exhibited ...

Spectroscopic studies of shallow defects in MBE GaSb

Abstract GaSb is an important material for long wavelength optoelectronic technologies, but much more information on its defect structure is required. In this paper we describe detailed photoluminescence spectroscopy on a series of unintentionally-doped (p-type) GaSb layers. We have resolved several excitonic and associated non-excitonic transitions. We find that the defect structure of some MBE layers exhibit similarity to that of material grown by all other major techniques. However, some defects appear to be unique to MBE growth, and in our best layers these defect transitions dominate. We report detailed behaviour of several luminescence features. A temperature dependence and excitation level study of the so-called native double acceptor has been made which confirms the DAP nature of this low temperature transition, and yields the associated donor binding energy. We have also demonstrated that the 801 meV line (also unique to MBE), located in the acceptor bound exciton spectral region, is not excitonic in nature, and we comment on the possible origin of this defect.

Self‐organizing growth of erbium arsenide quantum dots and wires in gallium arsenide by molecular beam epitaxy

Gallium arsenide doped with erbium has been grown by molecular beam epitaxy. At growth temperatures in the range 540–605 °C, and with arsenic to gallium flux ratios of 2 and more, the erbium forms uniform crystalline microprecipitates of ErAs when the concentration exceeds 7×1017 cm−3. The diameter can be varied in the range 11–21 A by altering the growth temperature. Reducing the arsenic to gallium flux ratio to close to stoichiometry changes the growth mode to one yielding quantum wires aligned in the growth direction. Subtle changes in growth conditions lead to bifurcated structures, which we refer to as quantum trees.

The effects of vacuum conditions on epitaxial Al/GaAs contacts formed by molecular‐beam epitaxy

The effects of the quality of the vacuum on the epitaxy of aluminum on (100) gallium arsenide have been investigated. It was found that leaving the ion gauge running during the cooling down of the GaAs prior to the deposition of the Al and the presence of a helium cryopump both affected the nature of the epitaxy and the height of the resulting Schottky barrier. Reproducible results were only obtained with the ion gauge off and the cryopump on. The Al film was found to take up the (100) orientation irrespective of the reconstruction of the GaAs surface [c(2×8), c(4×4), or (4×6)]. The height of the Schottky barrier on n‐type GaAs was 0.77±0.01 eV, and was independent of the GaAs reconstruction. The I‐V characteristics were the most nearly ideal that have been reported, a plot of log{I/[1−exp(−qV/kT)]} vs V being linear over the whole voltage range from +0.5 to −1.0 V, with an ideality factor of 1.01 which can be explained solely in terms of image‐force lowering. The barrier height on p‐type GaAs was 0.64±0....

Deep donors in GaSb grown by molecular beam epitaxy

A deep state possessing similar properties to those reported for DX centers in the AlGaAs system has been observed at atmospheric pressure in GaSb moderately doped with sulfur. The first detailed deep level transient spectroscopy study of this material has revealed a large energy barrier to electron capture and a correspondingly small capture cross section for this deep level. The deep level activity of selenium‐ and tellurium‐doped GaSb has also been investigated.

Insitu, near‐ideal epitaxial Al/AlxGa1−xAs Schottky barriers formed by molecular beam epitaxy

The Schottky barrier height of in situ epitaxial aluminum on AlxGa1−xAs was measured as a function of aluminum mole fraction from x=0 to x=1, using I/V, C/V and activation energy plots of current‐voltage dependence on temperature. The excellent electrical properties of the molecular beam epitaxy grown AlGaAs layers, with residual deep levels concentrations of less than 1014 cm−3 combined with the in situ deposition of single‐crystal epitaxial aluminum resulted in extremely high quality Schottky diodes from x=0 (GaAs) to x=1 (AlAs) with accurately exponential current‐voltage characteristics over up to 10 decades and with ideality factors less than 1.03. Both the C−2−V and activation energy plots were linear and yielded barrier heights in very good agreement with the I/V ones. The near‐ideal characteristics of these diodes were compared with several models of Schottky barrier formation and the dependence of the Schottky barrier height on the aluminum mole fraction was found to agree with the anion vacancy m...

Insitu Schottky contacts to molecular‐beam epitaxially grown gallium antimonide

Rectifying contacts have been made by depositing epitaxial films of aluminum on both homo‐ and heteroepitaxial layers of n‐type GaSb grown by molecular‐beam epitaxy. The barrier heights determined from the current‐voltage and capacitance‐voltage characteristics of these contacts were 0.54 and 0.56 eV, respectively. The significance of these results is briefly discussed.

Electrical properties of indium doped GaAs layers grown by MBE

Abstract The use of indium doping in bulk grown GaAs has recieved much attention as a way of reducing the defect concentration as revealed by the etch pit density. In this work we report similar indium doping studies in MBE grown GaAs. n-Type GaAs has been grown with indium concentrations up to 0.1 at % and at substrate temperatures from 540 to 580°C. We have made measurements of the free carrier concentration using C-V and Hall measurements, Hall mobility, 4 K photoluminescence and deep level concentrations. For a given substrate growth temperature, the most obvious effect of indium doping is to give an increase in the measured free electron concentration. This correlates with a higher 77 K mobility which suggests a reduction in the degree of compensation. The indium also leads to an order of magnitude reduction in the intensity of deep level-related PL features. The use of indium at normal GaAs growth temperature (580°C) is made difficult by re-evaporation. However, indium doping does allow the growth of high electrical quality GaAs at reduced temperatures, which is of particular benefit for the growth of GaAs on top of single crystal aluminium layers.