Effects of Heat-Treatment Duration and Dislocation Density on the Transport Properties of Semi-insulating Gallium Arsenide Crystals

Data are presented on carrier mobility and strain in semi-insulating undoped gallium arsenide crystals containing different dislocation densities and annealed at 900°C for various lengths of time. The effect of the dislocations is found to depend on heat-treatment time, which is attributed to changes in the composition of defect clouds, in particular, owing to As diffusion.     

An Energy Source Based on Helical Explosion–Magnetic Generators for High-Impedance Loads

A transportable standard module developed at the Institute of Experimental Physics as a component of an energy source for modeling current pulses of positive lightning is described. The source is designed as a combination of several unified helical explosion–magnetic generators with output transformers and an inner diameter of the stator of 200 mm. According to our calculations, the source generates current pulses with an amplitude of up to 100 kA in loads with an inductance of 100 H and a resistance of several tens of ohms. The results from testing a typical module operating with a circuit having an inductance of 100 H and a resistance of 4 are presented. The experimental data coincide well with the results of a mathematical simulation of the module's operation.     

Application of magnesia concrete and brick for the lining of electric furnaces

Conclusions Self-setting magnesia concrete and solutions are applicable for the lining of electric furnaces in the form of blocks.The testing of magnesia concrete and basic brick blocks is recommended on an industrial level for the verification of their effectiveness in electric furnaces of different capacity.     

A Helical Magnetic-Cumulation Generator with a Compact Transformer

Experimental data on a helical magnetic-cumulation generator with an output step-up transformer formed by two coaxial solenoids is presented. The inner diameter of the helix is 50 mm. Compared with the transformers described earlier, this transformer has a smaller size. The transformer can feed an energy of 1 kJ into a 100-H high-impedance load.     

Effect of irradiation on the properties of nanocrystalline silicon carbide films

The effect of irradiation with electrons on the optical and electrical properties of the nanocrystalline rhombohedral 21R-SiC and 27R-SiC films is studied. The cycles of irradiation of nanocrystalline SiC films on sapphire substrates with electrons with the energy 10 MeV are conducted in the range of fluences from 5 × 10¹⁴ to 9 × 10¹⁹ cm^?2. It is established that, at the irradiation doses above 10¹⁹ cm^?2, the optical absorption of the films at the photon energies E > E _g becomes less efficient than the optical absorption of unirradiated films. It is established that the Urbach energy as a function of the irradiation dose exhibits a minimum at the dose ～10¹⁷ cm^?2 for the 21R-SiC films and ～5 × 10¹⁷ cm^?2 for the 27R-SiC films, suggesting that radiation induces some ordering in the films. As the dose is increased from 5 × 10¹⁷ up to 9 × 10¹⁹ cm^?2, an increase in the Urbach energy and a decrease in the optical band gap are observed. The effect is attributed to an increase in the concentration of radiation defects in the films.     

Whispering-gallery and Luneburg-lens effects in a beam-fed circularly layered dielectric cylinder

The whispering-gallery (WG) mode excitation and Luneburg (1941) lens (LL) effects are studied for a lossy circularly layered dielectric cylinder illuminated by a beam field. The latter is simulated by the complex source-point (CSP) beam. Exact series solution to the wave scattering problem is used to obtain the far-field patterns and directivity. The WG mode effect is shown to undermine the LL performance.