V. A. Solov’ev

The TESIS experiment on the CORONAS-PHOTON spacecraft

On February 26, 2009, the first data was obtained in the TESIS experiment on the research of the solar corona using imaging spectroscopy. The TESIS is a part of the scientific equipment of the CORONAS-PHO-TON spacecraft and is designed for imaging the solar corona in soft X-ray and extreme ultraviolet regions of the spectrum with high spatial, spectral, and temporal resolutions at altitudes from the transition region to three solar radii. The article describes the main characteristics of the instrumentation, management features, and operation modes.

Room-temperature midinfrared electroluminescence from asymmetric AlSbAs/InAs/CdMgSe heterostructures grown by molecular beam epitaxy

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III–V part) and CdMgSe/CdSe (as a II–VI part), has been proposed as a basic element of a midinfrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy and has exhibited an intense long-wavelength electroluminescence at 3.12 μm (300 K). A less than 10 times reduction of electroluminescence intensity from 77 to 300 K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ΔEC=1.28 eV and ΔEV∼1.6 eV. The type of band lineups at a coherent InAs/Cd1−xMgxSe interface is discussed for 0⩽x⩽0.15.

Midinfrared injection-pumped laser based on a III–V/II–VI hybrid heterostructure with submonolayer InSb insets

Lasing at 3.075 μm (T = 60 K) in a regime of pulsed injection pumping has been obtained in an AlGaAsSb/InAs/CdMgSe double hybrid heterostructure with the active region comprising an InAs layer with submonolayer InSb insets. The electroluminescence (EL) spectrum of the heterostructure has been studied for various values of the pumping current up to the stimulated emission threshold. An increase in the pumping current leads to a short-wavelength shift and a change in the EL band structure, which is explained by the occupation of higher states by the charge carriers in InSb quantum dots and/or in the adjacent InAsSb layer.

Features of molecular-beam epitaxy and structural properties of AlInSb-based heterostructures

AlInSb layers are grown on highly lattice-mismatched GaAs (100) substrates by molecular-beam epitaxy (MBE) and studied in situ by reflection high-energy electron diffraction and ex situ by scanning and transmission electron microscopy (SEM and TEM). It is shown that one feature of AlInSb/GaAs heterostructure features is a high probability of forming microtwins; methods for decreasing their concentration are proposed. To initiate AlInSb growth on GaAs substrates under high lattice-mismatch (∼14.5%) conditions and to stimulate the transition to 2D growth, the GaAs layer surface was preliminarily exposed to an antimony flux followed by deposition of an intermediate AlSb buffer layer. The optimization of initial MBE growth stages of Sb-containing layers on the GaAs surface allows a decrease in the defect density in the GaAs/AlInSb heterostructures more than by two orders of magnitude, including a drastic decrease in the microtwin density. Optimal MBE growth conditions for AlxAl1 − xSb are determined in a wide composition range (0 < x < 0.3). The TEM and SEM studies confirm the high structural quality of grown GaAs/AlInSb heterostructures. Hall-effect measurements showed the dependence of the carrier mobility and concentration on the aluminum content in AlInSb layers and allowed preliminary conclusions on scattering mechanisms.

Special features of Sb2 and Sb4 incorporation in MBE-grown AlGaAsSb alloys

AlGaAsSb and GaAsSb alloys of different composition were grown by molecular-beam epitaxy (MBE) on GaSb, InAs, and GaAs substrates, using both conventional and cracker antimony effusion cells. The incorporation coefficients of dimer and tetramer antimony molecules, which totally describe the kinetic processes on the growth surface, were calculated. The differences in the incorporation of Sb2 and Sb4 molecules in MBE-grown GaAsSb alloys are shown. The effect of the MBE-growth parameters (substrate temperature and incident fluxes of group-V and group-III elements) on the composition of (Al,Ga)AsSb alloys and the incorporation coefficient of Sb was studied in detail. The incorporation coefficients of tetramer and dimer antimony molecules were found to vary over a wide range, depending on the substrate temperature and the ratio between the arrival rates of the group-III and the group-V elements.

Optical Properties of Epitaxial Al x In 1- x Sb Alloy Layers

Optical studies of unstrained narrow-gap AlxIn1 − xSb semiconductor alloy layers are carried out. The layers are grown by molecular-beam epitaxy on semi-insulating GaAs substrates with an AlSb buffer. The composition of the alloys is varied within the range of x = 0–0.52 and monitored by electron probe microanalysis. The band gap Eg is determined from the fundamental absorption edge with consideration for the nonparabolicity of the conduction band. The refined bowing parameter in the experimental dependence Eg(x) for the AlxIn1 − xSb alloys is 0.32 eV. This value is by 0.11 eV smaller than the commonly referred one.

Metamorphic InAs/InGaAs/InAlAs quantum wells with submonolayer InSb insertions emitted in the mid-infrared spectral range

Metamorphic InAs/InGaAs/InAlAs quantum wells with submonolayer InSb insertions have been grown for the first time by molecular beam epitaxy on GaAs (001) substrates using a graded InAlAs buffer layer with increasing In composition. The given nanoheterostructures demonstrate an intense photoluminescence at a wavelength of over of over 3 μm (80 K), which is shifted toward longer wavelengths as compared with that of the structures without InSb insertions.

Molecular beam epitaxy of thermodynamically metastable GaInAsSb alloys for medium IR-range photodetectors

The features of growth of GaInAsSb alloy with In content as high as 25 mol % lattice-matched to GaSb by molecular beam epitaxy are studied. These alloys are promising for use as the active region of photodetector structures of the mid-infrared range. The results of the study of these alloys by double-crystal X-ray diffractometry, scanning electron microscopy, and photoluminescence are presented. It is shown that the GaxIn1 − xAsySb1 − y alloys with x < 0.8 grown at 500°C show the degradation of structural and optical properties as the layer thickness is increased. In layers with thicknesses above the critical one, spinodal decomposition is observed in complete agreement with thermodynamic calculations of the location of the boundaries of immiscibility regions. The possibilities to optimize the molecular beam growth of the GaxIn1 − xAsySb1 − y alloys (x < 0.75) with high optical and structural quality, as well as the characteristics of photodetectors based on the GaInAsSb/AlGaAsSb heterostructures, are discussed.

3C-SiC p-n structures grown by sublimation on 6H-SiC substrates

Sublimation epitaxy in a vacuum has been employed to grow n-and p-type 3C-SiC layers on 6H-SiC substrates. Diodes have been fabricated on the basis of the p-n structure obtained, and their parameters have been studied by measuring their current-voltage and capacitance-voltage characteristics and by applying the DLTS and electroluminescence methods. It is shown that the characteristics of the diodes studied are close to those of diodes based on bulk 3C-SiC. A conclusion is made that sublimation epitaxy can be used to fabricate 3C-SiC p-n structures on substrates of other silicon carbide polytypes.

GaAs in GaSb: Strained nanostructures for mid-infrared optoelectronics

Molecular beam epitaxy was used for the first time to grow novel GaAs/GaSb heterostructures with ultrathin (0.8–3 monolayers) GaAs layers embedded in GaSb. These structures were studied by X-ray diffraction, transmission electron microscopy, and photoluminescence. By contrast to known structures with self-assembled quantum dots, GaAs layers in GaAs/GaSb structures are subject to elastic tensile stresses due to 7% lattice mismatch. The structures exhibit intense photoluminescence in the 2 µm region at low temperatures. Quantum-dimensional islands are formed in the structure at a nominal GaAs layer thickness exceeding 1.5 monolayers. The band alignment of the structures is of type II.