T. S. Lagunova

MOCVD Growth and Mg-Doping of InAs Layers

Epitaxial layers of Mg-doped InAs were grown by MOCVD, and electrical properties of these layers were studied. The doping with magnesium in the course of MOCVD growth allows one to obtain strongly compensated p-InAs with a high hole density (p≈2×1018 cm−3) and a low carrier mobility (μ≈50 cm2/(V s)) at T=300 K. When the samples are lightly doped with Mg, neutral impurities are bound with Mg, and n-type InAs layers with a carrier mobility exceeding that in undoped samples are formed.

Electrical properties of GaSb-based solid solutions (GaInAsSb, GaAlSb, GaAlAsSb) and their compositional dependence

The electrical properties of GaSb and solid solutions based on it (GaInAsSb, GaAlSb, GaAlAsSb) have been investigated. It is shown that the current-carrier concentration and mobility in all these materials are determined mainly by VGaGaSb structural defects, with their concentration decreasing almost linearly with decrease of the GaSb content of the solid solution. The dependence of the parameters of the solid solutions on the concentration of these structural defects is determined. The possibility of reducing their concentration by using the neutral solvent Pb and rare-earth elements is demonstrated.

Magnetotransport in a semimetal channel in p-Ga1−xInxAsySb1−y/p-InAs heterostructures with various compositions of the solid solution

Magnetotransport properties of an electron channel at the heteroboundary in type II separated p-Ga1−xInxAsySb1−y/p-InAs heterostructures grown by LPE (x=0.09–0.22) were studied in the temperature range of 77–300 K. It is shown that an electron channel, which is formed at the heteroboundary and has high mobility μ=(3–5)×104 cm2 V−1 s−1, exists throughout the whole composition range. The band diagram of the heterostructures under study is discussed, and some parameters of the electron channel are evaluated. It is found that the electron channel with high mobility persists up to room temperature. Type II GaInAsSb/p-InAs heterostructures can find application in new Hall sensor devices with an electron channel at the heteroboundary.

Transition from the type-II broken-gap heterojunction to the staggered one in the GaInAsSb/InAs(GaSb) system

Conditions for the transition from the staggered heterojunction to the type-II broken-gap one were considered for isolated Ga1−xInxAsySb1−y/InAs(GaSb) heterostructures in relation to the quaternary alloy composition. Energy-band diagrams of such heterojunctions were estimated and energy band offsets Δ at the heterointerface were determined. It was experimentally found that the type-II broken-gap heterojunction in the Ga1−xInxAsySb1−y/p-InAs structure is observed in the entire range of composition parameters under study, 0.03 < x < 0.23, and becomes staggered in the range 0.3 < x < 1. In p-Ga1−xInxAsySb1−y/p-GaSb heterostructures with the indium content 0.85 < x < 0.92 in the solid phase, the p-type conductivity is observed, which is indicative of the staggered heterojunction. At x > 0.92, the contribution of electrons of the semimetal channel at the heterointerface to the total conductivity was observed, as well as the transition from the staggered heterojunction to the type-II broken-gap one.

Electrical properties of epitaxial indium arsenide and narrow band solid solutions based on it

The electrical properties of epitaxial InAs and solid solutions based on it (InGaAsSb, InAsSbP, InAsGa, InAsP) have been investigated. It is shown that intentionally undoped crystals have n-type conductivity, which is determined by shallow donor impurities (E1=0.002–0.003 eV) and structural defects (E2=0.02–0.03 eV and E3=0.09–0.10 eV). It is shown that growth of epitaxial InAs using the neutral solvent Pb and also rare-earth elements makes it possible to reduce the electron density by almost an order of magnitude (to levels as low as 3×1015 cm−3) due to due to a decrease in the density of structural defects.

Interface roughness scattering in type II broken-gap GaInAsSb/InAs single heterostructures

The effect of the interface roughness (IFR) scattering on the carrier mobility in type II broken-gap p-GaInAsSb/p-InAs heterostructures with self-consistent quantum wells at the interface has been studied experimentally. It was found that the low-temperature mobility decreases as μ∼d2 when the quantum well width at the interface changes from 400 to 50 A upon raising the acceptor (Zn) doping level of the quaternary layer. It was established that the IFR scattering governs the low-temperature mobility in the two-dimensional electron channel at the heterointerface. The parameters of the IFR scattering, roughness height Δ=12 A, and correlation length Λ=100 A were evaluated on the basis of structural, photoluminescent, and magnetotransport data.

Magnetotransport properties of type II heterojunctions based on GaInAsSb/InAs and GaInAsSb/GaSb

The results of detailed study of the magnetotransport properties of broken-gap type II heterojunctions in a GaInAsSb/InAs(GaSb) system are reported. An electron channel with a high charge-carrier mobility (as high as 50000–60000 cm2/(V s)) is observed and studied for the first time in an isotype broken-gap p-GaInAsSb/p-InAs heterostructure. The effects of electron-channel depletion and semimetal-semiconductor transition in the case of heavy doping of the quaternary alloy with acceptors are studied. Magnetotransport properties at temperatures of 4.2–200 K are studied in detail. Data on the energy spectrum and parameters of two-dimensional charge carriers at the heteroboundary are obtained. It is ascertained experimentally that, depending on the composition, either staggered (at x = 0.85) or broken-gap (at x = 0.95) heterojunctions can be formed in the Ga1−xInxAsySb1−y/GaSb, which is confirmed by theoretical calculations. The anomalous Hall effect and negative magnetoresistance were observed in GaInAsSb/InAs:Mn grown on substrates doped heavily with Mn magnetic acceptor impurity so that the hole concentration was as high as p > 5 × 1018 cm−3; these phenomena are caused by exchange interaction of Mn ions in InAs with high-mobility charge carriers in the electron channel at the heterointerface.

Characterization of light-emitting diodes based on InAsSbP/InAsSb structures grown by metal-organic vapor-phase epitaxy

Light-emitting diodes for the wavelength range λ=3.3–4.5 µm were fabricated on the basis of InAsSbP/InAsSb heterostructures grown by metal-organic vapor-phase epitaxy. The use of vapor-phase epitaxy made it possible to appreciably increase the phosphorus content in barrier layers (up to 50%) in comparison with that attainable in the case of liquid-phase epitaxy; correspondingly, it was possible to improve confinement of charge carriers in the active region of the structures. Photoluminescent properties of InAsSb layers, electroluminescent properties of light-emitting diodes, and dependences of the emission power on current were studied. Two types of light-emitting diodes were fabricated: (i) with extraction of emission through the substrate (type A) and (ii) with extraction of emission through the epitaxial layer (type B). The light-emitting diodes operating in the pulse mode (with a relative pulse duration of 20) had an emission power of 1.2 mW at room temperature.

Influence of tellurium impurity on the Properties of Ga1−XInXAsYSb1−Y (X>0.22) solid solutions

The influence of tellurium impurity on the electrical properties of Ga1−XInXAsYSb1−Y (X=0.22 and X=0.24) solid solutions grown by liquid-phase epitaxy from lead-containing solution-melts was studied. Defect healing was shown to take place at low tellurium doping levels (XTeL<2×10−5 at. %) in inhomogeneous highly compensated p-type solid solutions. Thus, it is possible to produce slightly compensated p-type materials with a low density of impurities and structural defects. High doping levels allow production of n-type materials with the electron density n=1017–1019 cm−3. Electroluminescence spectra of n-GaInAsSb/p-GaSb heterostructures are promising for the development of light-emitting diodes with a wavelength λ=2.0–2.5 µm.

Depletion of the inverse electron channel at the type-II heterojunction in the system p-GaInAsSb/p-InAs

Magnetotransport and the electron channel parameters are investigated in p-GaInAsSb/p-InAs heterojunctions as functions of the acceptor doping level of the quaternary (GaInAsSb) layer. An abrupt decrease in the carrier mobility with increased doping level in these heterojunctions is observed. This decrease can be attributed to the narrowing and depletion of the channel near the interface and strong localization of electrons in potential wells at the interface.