Vegard’s law and superstructural phases in Al<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs(100) epitaxial heterostructures

The lattice constants of Al_xGa_1?x As epitaxial alloys with various AlAs (x) contents are determined for AlxGa_1?xAs/GaAs(100) heterostructures grown by MOC-hydride epitaxy using X-ray diffractometry and an X-ray back-reflection method. An ordered AlGaAs₂ (superstructural) phase is found in epitaxial heterostructures with x ≈ 0.50. The lattice constant of this phase is smaller than the lattice constants of an Al_0.50Ga_0.50As alloy and GaAs single-crystal substrate.     

Scanning electron microscopy of long-wavelength laser structures

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. Fiz. Tekh. Poluprovodn. 32, 1300–1305 (November 1998)     

Study of optical absorption in thin films of a-As2Se3 by photocapacitance spectroscopy

Photocapacitive spectroscopy is used for the first time to study optical absorption in thin films of a-As₂Se₃ for optical photons with energies below the gap width. Photocapacitance spectra are obtained over energies of 0.83–1.94 eV and used to characterize the density of localized states in the tail of the valence band and in deep states of charged defects. Aging and illumination of the film are found to affect the level of optical absorption by deep centers. Fiz. Tekh. Poluprovodn. 32, 490–493 (April 1998)     

Wannier-Stark states in a superlattice of InAs/GaAs quantum dots

Electron and hole emission from states of a ten-layer system of tunneling-coupled vertically correlated InAs/GaAs quantum dots (QDs) is studied experimentally by capacitance—voltage measurements and deep-level transient spectroscopy. The thickness of GaAs interlayers separating sheets of InAs QDs was ≈3 nm, as determined from transmission electron microscope images. It is found that the periodic multimo-dal DLTS spectrum of this structure exhibits a pronounced linear shift as the reverse-bias voltage U _r applied to the structure is varied. The observed behavior is a manifestation of the Wannier—Stark effect in the InAs/GaAs superlattice, where the presence of an external electric field leads to the suppression of coupling between the wave functions of electron states forming the miniband and to the appearance of a series of discrete levels called Wannier—Stark ladder states.     

Field-dependent photosensitivity of In-SiO2-Cd0.28Hg0.72Te metal-insulator-semiconductor structures with an opaque field electrode

The study of the photosensitivity of an In-SiO₂-Cd_0.28Hg_0.72Te metal-insulator-semiconductor structure with an opaque electrode is continued and the results are reported in this paper. The effect of a drastic decrease in photosensitivity with increasing inversion voltage is considered. This effect manifests itself both under unmodulated illumination (measurements of photocapacitance) and under modulated illumination (measurements of photovoltage), with the onset of a decrease in photovoltage coming ahead of that in photocapacitance. It is believed that this effect is caused by an increase in the longitudinal resistance of the inversion layer and by the anomalous generation of charge carriers at the semiconductor-insulator interface; as a result of the latter, the resistance of the induced p-n junction decreases.     

Specific features of nanosize object formation in an InSb/InAs system by metal-organic vapor-phase epitaxy

InSb quantum dashes (up to 4 × 10⁹ cm^?2) and quantum dots (QDs) (7 × 10⁹ cm^?2) were produced on InAs (100) substrates by the standard method of metal-organic vapor-phase epitaxy in the temperature range 420–440°C. A transformation of the shape and size of the quantum dashes is observed depending on the technological conditions of epitaxial deposition (quality of the matrix surface, growth temperature, flow rate, ratio between Group-V and -III elements in the gas phase, etc.). Control over the diffusion rate of reagents on the surface of the matrix based on an InAs epitaxial layer leads to a change in the transverse dimensions of the quantum dashes being deposited within the range 150–500 nm in length and 100–150 nm in width, respectively, with their height remaining at 50 nm. InSb QDs are grown on the surface of the InAs substrate at T = 440°C. A bimodal size distribution of the nano-objects is observed: there are small (average height 15 nm; average diameter 60 nm) and large (average height 25 nm; average diameter 110 nm) QDs.     

Problems of the design, construction, and operation of depots with anti-seepage protection for the storage of industrial wastes

Conclusions  1. Existing recommendations on the design, construction, and operation of waste dumps for industrial establishments do not correspond to requirements of nature-preserving legislation; this gives rise to the need for development of a unified regulatory document on the fulfillment of design documentation for waste dumps, which do not require burial and which are subject to subsequent utilization. 2. Scientific-research, design, and other organizations having work experience with industrial establishments storing wastes in dumps should participate in the development of the regulatory documents. In that case, attention should be focused on the development of a procedure for evaluating the effect of dumps on environment as a function of geological, hydrogeological, hydrological, and other conditions for sites at which dumps are located. 3. The reliable shielding of dumps, which guarantees that no surface, soil, and ground water will be polluted by seepage flows and which permits the storage of wastes of various risk categories, is one of the most important conditions for the ecological safety of dumps. 4. The method that we have developed for shielding large horizontal and inclined areas, which utilizes chemical silting of the pores of the underlying soils and ensures a given permeability, makes it possible to build shields with a sufficiently high degree of operational reliability. 5. The reagents used to create the gel-forming solutions do not exert a negative influence on the environment, since the gel is in a bound and water-insoluble form and does not pass from the soil layer being shielded into the underlying water-bearing horizons. Translated from Gidrotekhnicheskoe Stroitel’stvo, No, 5, pp. 30–34, May, 1998.     

Changes in the length of internal state codes with the aim at minimizing the power consumption of finite-state machines

Two heuristic techniques intended to encode the finite-state machine (FSM) internal states with the aim at decreasing the power consumption have been discussed. In the first approach, internal state codes are assumed to have the constant length. The second approach is based on code lengths varying from the minimum value to the level not leading to a decrease in power consumption. It is demonstrated that the second technique has a low computational complexity, making it possible to use FSMs with a large number of states. It has been ascertained experimentally that the FSM consumed power inherent to the NOVA algorithm can be decreased by 39% on the average (or by 68% with the use of certain benchmarks) via the first technique. In several cases, the second approach enables us to diminish the consumed power by 34% in comparison with the first one. Practical recommendations for the use of each technique, as well as the promising directions of further investigations, are presented.     

The influence of gain saturation on the output power of quantum-well semiconductor lasers

The light-power characteristic of a quantum-well semiconductor laser is theoretically studied taking into account the gain saturation effect. It is shown that, at high drive current densities, this light-current characteristic becomes nonlinear. The results obtained are in a good agreement with the experimental data.     

Formation of graphite/sic structures by the thermal decomposition of silicon carbide

The conditions in which carbon layers are synthesized on the surface of silicon carbide (SiC) wafers by thermal decomposition are studied. The effect of temperature and composition of the gas atmosphere on the structural properties of the layers being synthesized is analyzed. The conditions in which continuous graphite films with both single-crystal and polycrystalline structure can be obtained are determined.