Studies of physical phenomena in semiconductor nanostructures using samples with laterally nonuniform layers. Photoluminescence of structures with n-type δ-doped layers

Photoluminescence of a structure based on GaAs with δ-doped n-type layers is studied experimentally at 77 K in the context of a previously suggested spectral-correlative method for investigating semiconductor structures with laterally nonuniform layers. This method makes it possible to study (for the same sample) the features of the observed multicomponent photoluminescence spectrum in relation to two parameters, i.e., the distance between the δ-doped layers and the width of a narrow InGaAs quantum well located between these layers. The results obtained make it possible to relate the observed exponential increase in the intensity of photoluminescence from the region of δ-doped layers as these parameters are varied to the variation in the ratio between the concentration of the holes laterally localized in the minimums of the fluctuation potential and that of free two-dimensional holes. An effect of stabilization of the energy position of the photoluminescence spectral lines is observed; this effect is related to the localization of holes in the potential well between the δ-doped layers. The experimental data obtained are consistent with the results of our numerical calculations.     

High-temperature thermal-insulation Tizolit articles

High-temperature thermal insulation Tizolit articles made from mulit-silica fibers are reviewed. The basic stages of the technology are discussed and the values of the physico-technical properties of the articles are presented. The indicators of the properties of Tizolit articles are compared to articles produced by certain Russian and foreign manufacturers of this type of product.     

Optical gas analyzer intended to monitor gas emissions in the atmosphere

The optical gas analyzer based on a semiconductor laser is proposed in the variant applicable for remote monitoring of methane emissions on territories with gas-transport systems. The optimized configuration of a gas analyzer, which allows more accurate control of gas emissions in the atmosphere, has been developed. An approach based on the use of an optical fiber amplifier is proposed to increase the range of action of such devices.     

Microelectromechanical System for Controlling Flow Past an Airfoil: Pressure Transducers

A technology is developed for making single-chip diaphragm pressure sensors with polycrystalline-silicon piezoresistive elements on a monocrystalline-silicon substrate. It allows one to produce piezoresistive elements with a conductivity–temperature characteristic that neutralizes the temperature dependence of piezoresistive sensitivity. Sensors with a 1.8 × 1.8-mm² diaphragm are designed and fabricated by the above technology for pressures ranging from 1 to 10⁵ Pa, showing a maximum sensitivity of 10^–6 Pa^–1. The sensors are tested in aerodynamic experiments on monitoring the flow past a model wing of finite span at angles of attack close to the stall angle.     

Application of Triggered Vacuum Switches in a High-Voltage High-Speed Protective Device

The possibility of using triggered vacuum switches in a high-voltage high-speed protective shunting device that consists of several switches connected in series is considered. The probability of a breakdown in such a device at a uniform voltage division between switches was studied theoretically and experimentally. A circuit for controlling the protective device is proposed. The results of the development and tests of protective devices for 80 and 120 kV, based on two and three switches connected in series, are presented.     

Optimization of a variable-frequency induction motor drive with a scalar control system

The structure of an upgraded frequency control system and procedures for calculating control laws for induction motor drives under static and dynamic conditions are considered. The results of mathematical simulation and experimental investigation of the processes in a standard and an upgraded scalar control system are discussed.