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Equilibrium distributions of misfit dislocation density along the growth direction of metamorphic buffer layers InxAl1–xAs/GaAs with maximum In content xmax > 0.77 and different non-linear graded composition profiles are calculated. The effect of the initial In composition (n = 2) of InxAl1–xAs buffer layer with convex-graded (xmin) composition profile on misfit dislocation density as well as amount of residual stresses at its top part is considered. Using computational approach, it was shown that a dislocation-free region is formed under thin tensile- strained GaAs layer (1–10 nm) inserted into InAlAs metamorphic buffer layer, which agrees with experimental data obtained early by transmission electron microscopy. Novel non-linear graded composition profile of metamorphic buffer layer has been proposed, which results in twice reduction of misfit dislocation density as compared to the convex-graded one. In addition, equilibrium distributions of misfit dislocation density in the HEMT heterostructures with two-dimensional electron channel InxAl1–xAs, which are based on In0.75Ga0.25As/In0.75Al0.25As metamorphic buffer layer of various designs, are calculated. The values of inverse steps (A), representing the difference between the maximum In content of InxAl1–xAs (xmax) and In content of In0.75Al0.25As virtual substrate, at which relaxation of the elastic strains in 2D channel In0.75Ga0.25As/In0.75Al0.25As doesn't occur, are calculated for metamorphic buffer layers InxAl1–xAs with convex-graded and optimized non-linear graded composition profiles. [ABSTRACT FROM AUTHOR]

Characteristics of photoconductive antennas (PCAs) based on InGaAs/InAs/InAlAs superlattice heterostructures exhibiting different types of elastic strain in the layers are compared experimentally. THz signals, noise characteristics, and signal-to-noise ratios of the PCA-detectors were compared by means of a laboratory pulsed time-domain THz spectrometer at different levels of average optical-probe power. A larger detection bandwidth in entire range of probe power is demonstrated experimentally for PCA-detectors based on superlattice heterostructures exhibiting both compressive and tensile strain compared to lattice-matched superlattice heterostructures. It can thus be stated that modification of properties of superlattice heterostructures by introducing strain in the crystal lattice represents a universal and relatively efficient method of improving characteristics of PCAs based on such heterostructures, which allows using these PCAs for development of THz spectroscopy and imaging systems. [ABSTRACT FROM AUTHOR]

Metamorphic InAs(Sb)/InGaAs/InAlAs quantum-confined heterostructures with thin (1–5 nm) strongly mismatched GaAs and InAs inserts in a gradient metamorphic InxAl1−xAs buffer layer have been grown on GaAs (001) substrates by molecular beam epitaxy. It has been shown that the use of a 5-nm GaAs insert in the region of a metamorphic buffer layer at x ~ 0.37 almost doubles the photoluminescence intensity at 300 K (λ ~ 3.5 μm) from an InAs/InGaAs quantum well with a monolayer InSb insert. This is explained by an increase in the hole localization energy in InSb measured by photomodulation reflection Fourier transform infrared spectroscopy. This increase is due to increased elastic stresses in the quantum well because of a decreased density of threading dislocations in this structure caused by the introduction of an additional inverse step into the metamorphic buffer layer in the form of a 5-nm GaAs layer. The introduction of a 5-nm InAs layer into the metamorphic buffer layer violates its functions as a dislocation filter, leading to a higher density of dislocations in the quantum well region and to an order of magnitude decrease in the luminescence intensity. [ABSTRACT FROM AUTHOR]

The electrophysical properties of InSb/AlInSb/AlSb heterostructures with a high electron concentration are reported. We have observed anisotropy of the electron concentration and mobility measured at a low magnetic field in the [110] and $$\left[ {1\bar 10} \right]$$ crystallographic directions. It has been established by analysis of Shubnikov-de Haas oscillations that the conductivity through the two-dimensional electron channel InSb/AlInSb quantum well (QW) does not depend on the crystallographic direction. However, the magnetic-field dependences of the Hall coefficient and resistivity of the structures reveal a strong influence of the crystallographic directions. This has allowed one to conclude that the anisotropy of the electron transport parameters in the QW structures measured at low magnetic fields correspond to parasitic conductivity through the AlInSb buffer layer with two pronounced anisotropic contributions: the influence of metallic In nanoclusters inhomogeneously distributed within the buffer layer and conductivity of the near-interface layer with a high anisotropic density of extended defects. [ABSTRACT FROM AUTHOR]

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 AlAlSb 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. [ABSTRACT FROM AUTHOR]

Photoluminescence and electroluminescence in InSb/InAs heterostructures with ultrathin InSb insertions grown by molecular-beam epitaxy have been systematically studied. Measurements were made in the temperature range from 2 to 300 K on a large set of samples of various designs, with both the InAs matrix and ultrathin InSb insertions grown by different methods. The primary goal of the study was to identify the main radiative recombination channels in these heterostructures. It is shown that optical transitions associated with acceptor impurity centers in the InAs matrix represent an important mechanism diminishing the efficiency of luminescence from InSb insertions at room temperature. The results obtained are important for development of optimal growth modes and design of the active region of light-emitting devices based on quantum-confined InSb/InAs structures emitting in the range 3–5 μm. [ABSTRACT FROM AUTHOR]

GaAs/GaSb type-II quantum-dot heterostructures were grown by molecular-beam epitaxy. The circularly polarized photoluminescence of these samples in a magnetic field up to 4.7 T in the Faraday configuration was investigated. It was found that the emission from quantum dots in a magnetic field is σ−-polarized, which corresponds to the electron-spin component along the magnetic-field vector of +1/2. The degree of polarization increases with increasing excitation intensity. The observed effect is explained in terms of spin injection from the GaSb matrix, where spin orientation appears owing to the Zeeman splitting of the conduction band. An increase in the degree of polarization occurs due to a reduction in the charge-carrier radiative lifetime in type-II quantum dots with increasing excitation level. [ABSTRACT FROM AUTHOR]

The lasing of an injection-pumped p-AlGaAsSb/n[SUP0]-InAs/n-CdMgSe double hybrid heterostructure in the mid-IR range is demonstrated for the first time. The lasing wavelength λ is 2.775 μm, and the threshold current density J[SUBth] = 3-4 kA/cm[SUP2] at T = 77 K. The structure grown by two-stage molecular-beam epitaxy is characterized by extremely high (∼1.5 eV) asymmetric potential barriers for electrons and holes in the InAs active region. The output power of spontaneous emission for round-mesa diodes atT = 300 K was no less than 0.3 mW. [ABSTRACT FROM AUTHOR]

Heterostructures with a single InAs[sub 1-x]Sb[sub x]/AlSb[sub 1-y]As[sub y] quantum well (QW) on (001) GaSb substrates have been grown by MBE and studied using X-ray diffraction, transmission electron microscopy, and photoluminescence (PL) spectroscopy. High-intensity PL was observed at a temperature of 80 K, with a peak half-width of 30-50 meV and a peak wavelength in the range from 2 to 4.5 µm, depending on the QW width, which varied between 4 and 20 nm, respectively. The fundamental absorption edge of such QWs was calculated for a wide range of alloy compositions, x and y. Good correlation between the experimental and calculated dependences of the band gap on the InAsSb/AlSbAs QW thickness was obtained. [ABSTRACT FROM AUTHOR]

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 selfassembled 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. [ABSTRACT FROM AUTHOR]

Far infrared radiation from type-II heterostructures is observed. The samples used for the observations have the form of ten-period cascade structures, each period containing InAs and AlGaAsSb quantum wells separated by a variband barrier. The results of studying the vertical transport and the electroluminescence testify that the radiation is caused by transitions between the electron and hole states existing in the adjacent quantum wells. © 2002 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

New possibilities of scanning electron microscopy, using secondary- and reflected-electron signals, for determining the position of heteroboundaries in long-wavelength laser structures are reported. The formation of the indicated signals in structures of mid-infrared-range lasers of a new type based on type-II GaInAsSb/InGaAsSb heterostructures as well as in the conventional InAsSb/InAsSbP heterostructures is analyzed. The observed characteristic features of the formation of secondary- and reflected-electron signals in these structures as compared with the well-studied AlGaAs/GaAs structures are explained. The results obtained are necessary for accurate determination of an important laser parameter — the position of the p-n junction. It is shown that it is best to use the reflected-electron signal. [ABSTRACT FROM AUTHOR]

Lasing at 3.075μm(T=60K) 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. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

A mid-IR laser based on a hybrid pseudomorphic AlGaAsSb/InAs/CdMgSe heterostructure with a III-V/II-VI heterovalent interface at the 0.6-µm-InAs active region has been fabricated by molecular-beam epitaxy on p[sup +]-InAs substrate. It provides ∼1.5-eV asymmetric barriers for both electrons and holes in InAs, inhibiting carrier leakage from the active region. Despite a nonoptimal defect density at the CdMgSe/InAs interface (10[sup 6]-10[sup 7] cm[sup -2]), the structure demonstrates lasing at ∼2.78 µm (up to 100 K) under pulse injection pumping with the threshold current density of 3-4 kA/cm². The proposed design is promising for high-power mid-IR lasers operating at room temperature. [ABSTRACT FROM AUTHOR]

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 ΔE[sub C]=1.28 eV and ΔE[sub V]∼1.6 eV. The type of band lineups at a coherent InAs/Cd[sub 1-x]Mg[sub x]Se interface is discussed for 0≤x≤0.15. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is shown that an array of two-dimensional islands is formed during the growth of ultrathin (∼1.5 monolayers) InSb layers on a GaSb (100) surface by molecular beam epitaxy. After the deposition of several InSb layers separated by narrow barriers, islands of subsequent rows are formed on top of islands of the first row (vertical correlation effect). The formation of islands is confirmed by analysis of the photoluminescence spectra. [ABSTRACT FROM AUTHOR]

The first AlGaAsSb/InGaAsSb phototransistors with a cutoff wavelength (50% of peak responsivity) of 2.4 µm operating in a broad range of temperatures are reported. These devices are also the first AlGaAsSb/InGaAsSb heterojunction phototransistors (HPT) grown by molecular beam epitaxy (MBE). The new MBE-grown HPT exhibited both high responsivity R (up to 2334 A/W for λ=2.05 µm at-20°C) and specific detectivity D* (up to 2.1×1011 cmHz1/2/W for λ=2.05µm at -20°C). [ABSTRACT FROM AUTHOR]

Results obtained from the fabrication and characterisation of double heterostructure AlGaAsSb/AlGaSb pin photodetectors designed for 1.55 μm wavelength are reported. The photodetectors were fabricated using a customised inductively coupled plasma etching process, and exhibited high external quantum efficiency and record speed characteristics (3 dB bandwidth of 10 GHz). [ABSTRACT FROM AUTHOR]

Electron spin polarization up to 100% has been observed in type-II narrow-gap heterostructures with ultrathin InSb insertions in an InAs matrix via investigation of circularly polarized photoluminescence in an external magnetic field applied in Faraday geometry. The polarization degree decreases drastically, changes its sign, and saturates finally at the value of 10% in the limit of either high temperature or strong excitation. The observed effect is explained in terms of strong Zeemsn splitting of the electron conduction band in the InAs matrix and a heavy-hole state confined in the InSb insertion, due to s large intrinsic g factor of both types of carriers. The hole ground state in a monolayer-scale InSb/InAs quantum well, calculated using a tight-binding approach, fits well the observed emission wavelength. Temperature dependence of the emission polarization degree is in good agreement with its theoretical estimation performed in the framework of a proposed phenomenological model. [ABSTRACT FROM AUTHOR]