V. M. Daniltsev

Control of charge transport mode in the Schottky barrier by δ-doping: Calculation and experiment for Al/GaAs

The possibility of controlling the effective barrier height in Schottky diodes by introducing a δ-doped layer near the metal-semiconductor contact is considered. A decrease in the effective barrier height is caused by the increased role of carrier tunneling through the barrier. A complete quantum-mechanical numerical simulation of the effect of the δ-layer parameters (concentration and depth) on the current-voltage characteristics of modified diodes was carried out for the Schottky barrier contacts to n-GaAs. The simulation results were found to fit well the experimental characteristics of diodes produced by metal-organic chemical vapor epitaxy. The studies carried out made it possible to choose the optimal δ-layer parameters to produce low-barrier (about 0.2 eV) diodes with a reasonable nonideality factor (n≤1.5). Such structures can be employed to fabricate microwave detector diodes without bias.

Microstructure and properties of aluminum contacts formed on GaAs(100) by low pressure chemical vapor deposition with dimethylethylamine Alane source

We report on a low pressure chemical vapor deposition of metallic thin aluminum films on GaAs (001) with a dimethylethylamine alane (DMEAA) source and H2 as a carrier gas. The deposition temperatures varied in the range 130–360°C. Integrated volumes for Al (111), (100), (110)R, and (110) grains were estimated by the x-ray diffraction technique and the growth temperature values preferred for every type of grains were observed. The experimentally observed dominance of Al(110)R over Al(110), irrespective of the substrate miscut direction, supports the GaAs(100) inner anisotropy effect on the Al grain orientation. Electrical resistivity was 5 ·cm for the best Al films. The Schottky barrier heights were near a 0.7 eV level and the ideality factor n=1.1. Nonalloyed ohmic contacts were fabricated on an n-type GaAs epitaxial layer with an additional set of Si-layers near the Al/GaAs interface. Specific contact resistance, c=7 cm2, was measured. Best contacts were obtained at a deposition temperature lower than 250°C.

Features of GaN Growth Attained by Metal-Organic Vapor-Phase Epitaxy in a Low-Pressure Reactor

The properties of GaN layers grown by metal-organic vapor-phase epitaxy on sapphire substrates at atmospheric and reduced pressures were studied. The surface morphology, crystalline, luminescence, and electric transport properties of these structures were comparatively analyzed. The depth profiles of elements were measured using secondary-ion mass spectrometry. The carrier distribution in heavily doped structures with p-n junctions was analyzed by electrochemical C–V profiling. It was shown that GaN layers grown in a low-pressure reactor feature improved structural, electric, and optical characteristics.

Electrical isolation of a silicon δ-doped layer in GaAs by ion irradiation

The electrical isolation of a n-type δ-doped layer embedded into undoped GaAs was studied using proton or helium ion bombardment. The threshold dose for isolation Dth of the δ-doped layer was found to be ≈2 times higher than that predicted for thick doped layers of similar carrier concentration. The thermal stability of the isolation, i.e., the persistence of sheet resistance Rs at values >109Ω/□ after subsequent thermal annealing, is limited to temperatures below 400 °C. This temperature limit for the thermal stability Tsm is markedly lower than those observed in wider doped layers in which Tsm is ≅650 °C. A previously isolated δ-doped layer presents p-type conductivity after annealing at temperatures >600 °C .

Analysis of the composition of (Al,Ga)As alloys by secondary ion mass spectroscopy and X-ray diffractometry

Calibration lines for the layer-by-layer analysis of the concentration of matrix elements in AlxGa1 − xAs layers are obtained using a TOF.SIMS-5 secondary-ion mass spectrometer. The alloy concentration for the set of test samples was independently measured by high-resolution X-ray diffractometry allowing for deviation of the lattice constants and elastic moduli from Vegard’s law. It is shown that when using Cs+ sputtering ions and a Bi+ beam in secondary-ion mass spectrometry, the dependence of the intensity ratio Y(CsAl+)/Y(CsAs+) on x(AlAs) is close to linear for positive ions; and when detecting negative ions, the dependence Y(Al2As−)/Y(As−) on x is close to linear. These data allow us to normalize the profiles of layer-by-layer analysis in the AlxGa1 − xAs/GaAs system. In addition, a simple variant for the introduction of corrections to the deviation from Vegard’s law in the X-ray data is suggested.

Heavily doped GaAs:Te layers grown by MOVPE using diisopropyl telluride as a source

The capabilities of GaAs epitaxial layers extremely heavily doped with tellurium by metal-organic vapor-phase epitaxy using diisopropyl telluride as a source are studied. It is shown that tellurium incorporation into GaAs occurs to an atomic concentration of 1021 cm–3 without appreciable diffusion and segregation effects. Good carrier concentrations (2 × 1019 cm–3) and specific contact resistances of non-alloyed ohmic contacts (1.7 × 10–6 Ω cm2) give grounds to use such layers to create non-alloyed ohmic contacts in electronic devices. A sharp decrease in the electrical activity of Te atoms, a decrease in the electron mobility, and an increase in the contact resistance at atomic concentrations above 2 × 1020 cm–3 are detected.

Effect of rapid thermal annealing on the parameters of gallium-arsenide low-barrier diodes with near-surface δ-doping

The results of experimental studies of the effect of rapid thermal annealing on low-barrier diode structures used in the fabrication of microwave detectors for imaging arrays are indicative of an increase in the effective barrier height. Assuming that this effect is related to the diffusion spreading of the silicon δ-doped layer, which determines charge transport in the modified diode, a theoretical model is developed and the diffusion coefficient for silicon in the near-surface region of gallium arsenide (D ≈ 2 × 10−14 cm2/s at 600°C) is estimated. A comparison with published data makes it possible to assume that diffusion in the near-surface layers is greatly facilitated compared to that in the bulk. It is suggested that the cause of acceleration of the diffusion can be a high electric field formed by the charged plane of the detector and it can also be related to an increased density of defects near the surface. The practical result consists in the emerging possibility of increasing (within a certain range) the effective barrier height in the grown structures, which will make it possible to adapt the parameters of low-barrier diodes to the optimal value in order to obtain sensitive detectors.

Intraband photoconductivity induced by interband illumination in InAs/GaAs heterostructures with quantum dots

The effect of lateral intraband photoconductivity in undoped InAs/GaAs heterostructures with quantum dots (QDs) has been studied, with QD levels populated with carriers by means of interband optical excitation of varied power at different wavelengths. In the absence of interband illumination, no photoconductivity is observed in the mid-IR spectral range. At the same time, additional exposure of the structures to visible or near-IR light gives rise to a strong photoconductivity signal in the mid-IR spectral range (3–5 μm), associated with intraband transitions in QDs. The signal is observed up to a temperature of ∼200 K. Use of interband optical pumping makes the intraband photoconductivity signal stronger, compared with similar structures in which doping serves to populate QD levels.

Anisotropic piezoeffect in microelectromechanical systems based on epitaxial Al0.5Ga0.5As/AlAs heterostructures

AbstractA microelectromechanical system is created that has the form of a cantilever-fitted microbar with a cross-sectional area of several square micrometers. The system is formed by applying epitaxial AlGaAs layers on the GaAs(001) surface and selective chemical etching of the AlAs layer lying under the bar. Two micro-cantilevers that are made on the same GaAs(001) wafer and directed along the [110] and [1