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The aim of the work was to create a selective gas sensor for hydrogen sulphide. As a result of adding ammonia to the zinc acetate solution, centrifuging the obtained zinc hydroxide and subsequent calcination, a polydisperse zinc oxide powder with a grain size of 5–50 nm was obtained. The material was characterized using X-ray phase analysis and transmission electron microscopy. Subsequently, silver nitrate and terpeniol were added to the zinc oxide nanopowder to form a paste. The gas-sensitive material was obtained by applying the resulting paste on a special dielectric substrate and subsequent calcination, as a result of which the terpeniol burned out, and the silver nitrate turned into an oxide (the mass fraction of the silver was 3%). A non-stationary temperature mode for the operation of the sensor was selected, in which, after rapidheating of the sensor to 450 °C (2 seconds), slow (13 seconds) cooling to 100 °C occurred. Each subsequent heating-cooling cycle with a total period of 15 seconds began immediately after the end of the previous cycle. The use of an unsteady temperature mode in combination with the selection of the composition of the gas-sensitive layer made it possible to obtain a response of 200 for a hydrogen sulphide concentration of 1 ppm. Along with an increase in sensitivity, a significant increase in selectivity was also observed. The cross-sensitivity for the determination of hydrogen sulphide and other reducing gases (CO, NH3, H2) was more than three orders of magnitude. Thus, this sensor can be used to detect hydrogen sulphide even in the presence of interfering components. The use of highly selective sensors in the tasks of qualitative andquantitative analysis can significantly simplify the calibration in comparison with “electronic nose” devices. Devices based on highly selective sensors do not require the use of mathematical methods for processing multidimensional data arrays.

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The effect of band-to-band illumination on noise spectra has been investigated in n-GaAs with an equilibrium concentration . The theoretical predictions of Levinshtien et al have been compared in detail with experimental results. A new local level has been observed and investigated using the technique of level recharging by minority carriers. The capture cross section of this level depends exponentially on temperature: . The level parameters: activation energy , level energy , capture cross section and trap concentration have been determined. Using band-to-band illumination techniques the parameters of a trap investigated recently by Copland have been redetermined. It has been shown that band-to-band illumination is a very effective tool in noise spectroscopy.

It has been shown that the low-frequency 1/f1.5 noise in GaAs and SiC, and occasionally in Si, exists in the temperature region where a generation-recombination (GR) noise predominates that is due to a local level. The 1/f1.5 noise can be accounted for by energy level broadening, which inevitably occurs in any real crystal as a result of structural or doping inhomogeneities and defects. GR noise simulations were performed for GaAs and SiC, taking into account the effect of broadening. It has been shown that, to explain the experimental results, consideration must be given to the exponential energy dependence of the capture cross section sigma n= sigma 0 exp(-E1/kT) and the dependence of the energy E1 on the level position E0. The simulated and experimental results are in good agreement.

The turn-on process and the steady state current-voltage characteristics have been investigated in 4H-SiC thyristors with a forward breakover voltage close to 700 V and pulse switch current density of 16 000 A/cm2. The rise current constant, τr, has been found to decrease monotonically with temperature: τr, ≈ 10.5 nsec at T = 300 K and τr ≈ 1.2 nsec at T = 500 K at high bias Uo ≥ 300 V. The value of τr ≈ 1.2 nsec is the lowest observed value for SiC thyristors. At very high current density, j ≥ 5 103 A/cm2, the residual voltage drop for 4H-SiC thyristors is lower than for identically rated Si thyristors. The voltage drop Udo decreases monotonically with temperature.