Surface-acoustic-wave filters with a high input power for a nominal frequency of 2170 MHz for communication systems and radar and telecommunications equipment

The basic design of microwave filters based on surface acoustic waves with a high input power for specialized communication systems and radar and telecommunications equipment is developed.     

Adaptive control of the car motion of a monorail road

Construction of the mathematical model of the car motion, identification of the model parameters, and filtering of the coordinates of the car motion in a monorail road are considered. The law of control of the car motion that ensures an acceptable quality of operation of the control system is selected. Simulation confirming the serviceability of the obtained algorithms and the whole control system is performed.     

Photoluminescence of silicon after deposition of polycrystalline diamond films

Low-temperature (5K) photoluminescence of silicon substrates in the range 0.8–1.2 eV is studied before and after deposition of polycrystalline diamond films. The diamond films were deposited in the microwave plasma onto high-purity dislocation-free silicon (with the resitivity ρ ≈ 3 kΩ cm) subjected to mechanical polishing or more delicate chemical and mechanical polishing. The deposition temperature was 750–850°C. In the photoluminescence spectra of the samples with the substrates polished chemically and mechanically, two lines, D ₁ and D ₂, corresponding to the dislocation-related emission are recorded. Generation of dislocations in the substrates is caused by efficient adhesion of the diamond film and, as a result, by internal stresses that relax with the formation of dislocations. The experimental spectra are practically identical to the photoluminescence spectra observed in silicon (ρ ≈ 100 Ω cm) with the density of dislocations ∼10⁴ cm⁻².     

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.     

Temperature dependence of the effective coefficient of Auger recombination in 1.3 μm InAs/GaAs QD lasers

Semiconductor laser heterostructures containing five and ten sheets of InAs/GaAs QDs on GaAs substrates, with an emission wavelength of ～1.3 μm, have been studied. Dependences of the nonradiative lifetime and effective Auger coefficient in QDs are obtained from an analysis of temperature and current dependences of the efficiency of spontaneous radiative recombination. The zero-threshold Auger recombination channel in QDs is shown to dominate at low (below 200 K) temperature, whereas at higher temperatures the quasithreshold channel becomes dominant. The effective 3D Auger coefficient is estimated in the approximation of a spherical QD, and a good agreement with the experimental data is obtained.     

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.