B. V. Pushnyi

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.

Photovoltaic converters of concentrated sunlight, based on InGaAsP(1.0 eV)/InP heterostructures

Results obtained in the development of a metal-organic vapor-phase epitaxy (MOVPE) technology and in studies of the electrical parameters of photovoltaic converters based on heterostructures in the InP/InGaAsP system for the spectral range 0.95–1.2 μm are presented. A MOVPE technique is developed for obtaining and doping InGaAsP solid solutions around the spinodal dissociation region with a band-gap width of about 1.0 eV. Photovoltaic converters of 1000-× concentrated sunlight are fabricated.

Powerful InAsSbP/InAsSb light emitting diodes grown by MOVPE

Mid-infrared light-emitting diodes (LEDs) operating in the 3.3-4.5 μm wavelength range at room temperature are produced on the basis of InAsSbP/InAsSb heterostructures. The photoluminescence of InAsSb layers and electroluminescence properties of LEDs are investigated. LEDs light-current characteristics are also studied. Fabricated were LEDs of A and B type, A being preferential for currents in excess of 200 mA, and B being better for the current range 0-200 mA. When operating at 5% duty cycle, at room temperature wavelength λ = 3.4 μm the pulse power of the diodes is measured as 1.2 mW under 1.3 A drive current.

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.

Characteristics of stimulated emission from an optically pumped GaN/AlGaN double heterostructure

The luminescence properties of a GaN/Al0.1Ga0.9N double heterostructure grown by vapor-phase deposition from organometallic compounds are studied. When luminescence is observed from the end, the radiation intensity shows a sharply defined threshold dependence on the pump density. The threshold excitation density at T=77 K was ∼40 kW/cm2 and the wavelength of the stimulated emission was λ=357 nm. The long-wavelength shift of the emission line at high pump densities may be attributed to renormalization of the band gap caused by many-particle interactions in the electron-hole plasma.

InAs/GaSb superlattices fabricated by metalorganic chemical vapor deposition

The possibility of fabricating InAs/GaSb strained-layer superlattices by metalorganic chemical vapor deposition has been experimentally demonstrated. The results of transmission electron microscopy and photoluminescence spectroscopy investigations showed that the obtained structures comprise an InAs?GaSb superlattice on a GaSb substrate consisting of 2-nm-thick InAs and 3.3-nm-thick GaSb layers.

Study of postgrowth processing in the fabrication of quantum-cascade lasers

The special postgrowth processing of structures for quantum-cascade lasers is studied. The processing includes regrowth with a high-resistivity material (indium phosphide) with a carrier concentration of n ≈ 5 × 1010 cm−3, photolithography with various wet chemical etchants, and the fabrication of special contacts providing enhanced heat removal. The use of modified postgrowth processing provides necessary parameters satisfying requirements for high-quality devices.

Preparation of a strip structure for quantum-cascade lasers

A method for overgrowing laser stripe structures with high-ohmic indium phosphide to bound the domain of current flow and to improve heat dissipation is presented. Overgrowing was performed using metal-organic chemical-vapor deposition. It is shown that the method makes it possible to obtain high-quality epitaxial layers and defectless overgrowth boundaries without special processing of the structures after photolithography. All the InP layers were n-conductive, the specific resistance was ρ ∼ 5 × 104 Ω cm, and the carrier concentration was n ∼ 5 × 1010 cm−3. The characteristics of the grown InP layers permit one to obtain high-quality quantum-cascade lasers.

Properties of narrow-bandgap (0.3–0.48 eV) A3B5 solid solution epilayers grown by metal-organic chemical vapor deposition

Processes of epitaxial growth of narrow-bandgap (with bandgap value Eg ≈ 0.3−0.48 eV) solid solutions GaInAsSb and InAsPSb on InAs substrates by metal-organic chemical vapor deposition at low pressure (76 Torr) are investigated. It is shown that, under chosen growth conditions, the InAsPSb epilayers have high crystalline quality, while the solid solutions Ga1−xInxAsySb1−y and InAsyPzSb1 − y − z have compositions close to InAs (0.86 < x < 0.93, 0.62 < y < 0.9, 0.17 < z < 0.26) and manifest photoluminescence at room temperature.

Internal microstrain and distribution of composition and cathodoluminescence over lapped AlxGa1−xN epilayers on sapphire

Structural properties and spatial inhomogeneity of MOCVD-grown AlxGa1−xN layers on (0001) sapphire substrates were studied. A nonuniform distribution of Al across the epilayer was observed in layers grown at constant flux rates of precursors. The model of compositionally graded layer formation is proposed on the basis of cathodoluminescence and X-ray data. It is established that homogeneous samples can be obtained by increasing the flux rate of trimethylaluminum at the initial stage of epilayer growth compared with that in all further stages. Lowering the growth rate reduces strain in epitaxial AlxGa1−xN layers. The influence of strain on the luminescence properties of the layers is discussed.