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Doping processes of silicon carbide crystals with scandium are investigated. It is shown that the scandium solubility in SiC is limited within the 1800 to 2600°C temperature range and amounts to (2 to 3) × 1017 cm−3. On doping silicon carbide crystals with scandium the VLS growth mechanism is possible. The luminescence spectra of the crystals are studied. It is found that nitrogen actively affects the luminescence intensity of silicon carbide doped with scandium. The depth of the radiative recombination centre in SiC (Sc) which is acceptor like is found to be 0.24 eV. [Russian Text Ignored].

The paper summarizes the results of studies concerned with the processes of growing large silicon carbide single crystals of only one polytype. Vacuum sublimation has been found to be a suitable method of crystal growth. Mass-transfer aspects of crystal growth processes are analyzed, and the conditions of growing crystals of various polytypic structures are discussed. The as-grown crystals are suitable for the production of semiconductor devices.

Parathion and methyl parathion adsorbed at high loads on clays and similar surfaces exhibited properties of a bulk phase, such as a well-defined solubility and a characteristic X-ray powder diffraction (XRD) pattern, different from those of the free substances. The aqueous solubility of parathion condensed at these surfaces was as low as 1.2 μg/ml as compared to 14 μg/ml for free parathion. The BET isotherm described the behavior of the investigated surface condensates even though these condensates were different from the multilayer adsorption for which the BET isotherm was originally developed. The XRD patterns of parathion and methyl parathion adsorbed on Na-bentonite exhibited reflections which were shifted towards higher angles as compared with the XRD patterns of the free compounds. This is in agreement with the lower solubility of the surface condensates. The properties of these condensates were easily controlled by the choice of adsorbent as well as by the choice of conditions under whch they were prepared. The existence of such surface-condensed phases and the manipulation of their properties can be utilized for the slow-release formulation of organophosphate esters which is important, for example, in pesticides application.

A qualitative dependence of polytype structures 6H, 15R, and 3C on the partial pressure of nitrogen in the interval 4 to 760 Torr is obtained by optical and X-ray studies of SiC epitaxial layers, grown by recrystallization in the gaseous phase at 1900 to 2300°C. The morphological peculiarities of β-SiC epitaxial layers, grown on the (0001) and (0001) faces of the α-SiC substrate are determined. The strained regions of the α-SiC monocrystals, due to inhomogeneous nitrogen-doping, are established by optical and X-ray methods. The effect of nitrogen on the polytype stability of SiC is the basis of the discussion of the experimental data. [Russian Text Ignored]

The kinetics of silicon carbide synthesis plays an important part in the formation of polytypes during the growth of crystals and epitaxial layers. The results obtained permit to develop a technique of plotting kinetic phase diagrams with the polytypes shown for silicon carbide. In particular, these phase diagrams accomodate quite well the conditions of production (rather high growth rates at comparatively low temperatures of growing) of crystals and epitaxial layers of β-SiC from solutions in silicon melts and at decomposition in hydrogen of methyl-trichlorosilane and other silicon-and carbon-containing organic compounds. [Russian text Ignored.]

A thermodynamic analysis of the equilibrium in the SiC-H2 system has been carried out at various constant pressures (1, 5 × 10-1, and 10-2 atm) over the 1500–3000 K temperature range. On the basis of thermodynamic analysis data it has been established that the stoichiometric relationship of the silicon- and carbon-containing components in the vapour phase greatly depends on the hydrogen temperature and pressure. This dependence is to be taken into account when analysing the processes of diffusion mass-transfer and heterogeneous interactions in the course of growing silicon carbide epitaxial layers. “The extent of development” of silicon carbide-hydrogen interactions has been estimated, and it has been found that for all H2 pressures studied in the 1850–2350 K temperature range, the reaction accompanied by the formation of gaseous silicon and C2H2 is the most likely.

The growth kinetics of silicon carbide epitaxial layers from the vapour phase using the “sandwich” method has been investigated and the limiting stages of the growth process have been established as a function of the argon pressure in the growth zone. The methods of determining the temperature gradient and its distribution in the high-temperature furnaces have been developed. On the basis of analysis of mass transfer efficiency and kinetics as well as the calculations of vapour pressures in the temperature change of 1800–3000 K, it has been shown that silicon in the vapour phase acts as a “transporting agent” during the growth of silicon carbide crystals and epitaxial layers.

Results of an experimental study are shown concerning the local heat transfer during a pneumatic transport of graphite particles (mean size 0.180 mm and 0.065 mm) through a horizontal duct (diameter 18.8 mm).

Results are given of tests on the drag of graphite particles, sizes 100 and 200μ, pneumatically transported through horizontal and vertical pipes 5.33, 8.16, and 18.8 mm in diameter.

The present paper gives results of sublimation growth studies of SiC crystals. From these results one can conclude that the vapour-liquid-solid (VLS) growth mechanism as well as the vapour-solid (VS) mechanism is possible for SiC crystals grown by the sublimation method. For the studies of SiC crystals grown by the sublimation method the authors have prepared pure single crystals as well as crystals doped with nitrogen, boron, aluminium, beryllium, scandium, and lanthanum.

Synthesis, study and application of increasingly more complex crystalline structures are one of the most important tendencies in physics and the science of materials of solid-state electronics. The creation of A3B5 compounds and multi-component solid solutions based on these compounds, superlattices, complex ceramic high-temperature superconductors and other materials made it possible to enlarge substantially the possibilities of solid-state electronics, to create devices with wider ranges of operating characteristics and functional possibilities.

Polytypic crystals of semiconductors, dielectrics and magnetic materials attract an increasing attention in science and technology. On one hand, the phenomenon of polytypism is one of the fundamental problems of solid-state physics; its solution would make it possible to elucidate- the problem of the interconnection of different structures and intraatomic forces acting in crystals. On the other hand, the polytypic difference in crystals is most strongly expressed in electro-physical properties, which makes their application promising, mainly in semiconductor electronics. Thus, the difficulties of producing modulated structures in polytypic crystals can be overcome since these crystals form a class of one-dimensional natural superlattices.

High-purity, semi-insulating (HPSI) 4H-SiC crystals with diameters up to 75 mm have been grown by the seeded sublimation technique without the intentional introduction of elemental deep-level dopants, such as vanadium. Wafers cut from these crystals exhibit homogeneous activation energies near mid gap and thermally stable semi-insulating (SI) behavior (>109 ohm-cm) throughout device processing. Secondary ion mass spectroscopy, deep-level transient spectroscopy, optical admittance spectroscopy, and electron paramagnetic resonance data suggest that the SI behavior originates from several deep levels associated with intrinsic point defects. Micropipe densities in HPSI substrates have been demonstrated to be as low as 10 cm−2 in 2-in. substrates, and the room-temperature thermal conductivity of this material is near the theoretical maximum of 5 W/cm·K for 4H-SiC. Devices fabricated on these HPSI wafers do not exhibit any substrate related back-gating effects and have power densities as high as 5.2 W/mm with 63% power added efficiency.