Search

We have analyzed phase equilibria in the Si–C–H–Ar system during silicon carbide ingot growth by the modified Lely method. The results indicate that the addition of even small amounts of hydrogen to an inert carrier gas leads to a sharp increase in the rate of carbon transport through the gas phase, mediated by volatile hydrocarbons, primarily acetylene, and prevents carbon enrichment in the solid source and corrosion of the graphite equipment in the single-crystal seed region.

The optical and photovoltaic properties of two-component TPP–Yt0.95Er0.05VO4 films prepared by the spincoating method are for the first time studied. A 30% increase in the photovoltage (PV) of TPP: Yt0.95Er0.05VO4 = 3: 2 films on silicon carbide (SiC) supports as compared to TPP one-component films is observed. In contrast, for films on tin dioxide (SnO2) supports, the PV drops by 35–96% as the TPP content in the film decreases from 80 to 20%. The properties of the films are monitored by atomic force microscopy. The highest roughness of the films corresponds to a 40–60% TPP content.

Model concepts concerning control over the formation of oxide layers during the course of oxidation are developed on the basis of experimental results of studies of systematic features of the formation of nanostructured layers after diffusion annealing. Data on a variation in the composition of oxide phases as the extent of deviation from stoichiometry is changed in the initial lead chalcogenide are presented. Model concepts related to the possibility of varying the thickness of the coating oxide phases using annealing in an oxygen-containing medium are developed. It is shown that annealing in an iodine atmosphere ensures the effective penetration of oxygen into the grains, which is necessary for an increase in the photoluminescence efficiency.

The growth of 4 H-polytype silicon carbide ingots by the modified Lely method on (10 $$ \bar 1 $$ 0) seeds has been investigated. It is shown that this seed plane allows intense ingot outgrowth. Single-crystal ingots up to 60 mm in diameter can be obtained at growth rates below 0.6 mm/h. Investigation of the defect structure showed that the grown ingots are practically micropipe-free but contain stacking faults and carbon inclusions.

The problem of the appearance of carbon inclusions in single-crystal silicon carbide ingots grown by the modified Lely method (the so-called graphitization of the ingot) is analyzed. It is shown that the process of graphitization of the ingot is not related to a deficit of silicon in the growth cell; in contrast, it is excess of silicon at the growth surface that inhibits the ingot growth rate and gives rise to intense corrosion of the graphite fittings.

The aim of the present paper is to discuss our results of the investigation (both theoretical and experimental) of mass transfer in the β-SiC–α-SiC system in conditions of about zero temperature gradient. Growth temperature was in the range 1800–2300°C. Modeling of growth of silicon carbide crystals have been carried out both for vacuum (10−3 Pa) and for a gas (nitrogen, argon or their mixture) atmosphere. The gas pressure was in the range 102–105 Pa. Growth rate in the range from 0.01 to 1.5 mm/h for growth in vacuum and 0.001–0.15 mm/h for growth in gas have been calculated. Experimental results obtained are in a good agreement with theoretically predicted ones.

A modified Ludeke model assuming that interfacial defect states are responsible for the formation of the Schottky barrier is applied to calculate the barrier heights Φbn in the systems 〈Ag, Au〉-〈3C-, 6H-SiC〉. Excellent agreement with experimental data is obtained. The calculation also shows that the concentration of silicon vacancies determining the Φbn value depends only slightly on the nature of the metal constituent of the contact.

The results obtained in measuring the Schottky barrier height Φ b n for a chromium contact with 8H-, 6H-, 15R-, 27R-and 4H-SiC silicon carbide polytypes with n-type conduction are analyzed in terms of a simple model. It is shown that the Φ b n value is proportional to the concentration of silicon vacancies in the polytypes. The results of Φ b n measurements for palladium and platinum contacts to silicon carbide polytypes are discussed.

The distribution of the elements in naturally faceted PbTe and Pb0.8Sn0.2Te single crystals doped with zinc and cadmium is analyzed. The results show the formation of a multilayer structure with an outer layer of ZnTe (CdTe) on top of a metallic sublayer.

The thermodynamic analysis of high temperature processes in the SiC-N 2 system has been carried out at different initial pressures of nitrogen in the closed system 4, 200, 400, 600, 760, 1140 and 1520 Torr in the temperature interval (1500–3000) K. On the basis of thermodynamic analysis data it has been established that the stoichiometric relationship of silicon and carbon containing components in the vapour phase greatly depends on nitrogen pressure and temperature and this dependence is to be taken into account when analysing the phenomena of luminescence and polytypism in the course of growing silicon carbide monocrystals and epitaxial layers from the vapour phase. The “extent of development” of silicon carbide/nitrogen interaction reactions has been estimated and it has been shown that to certain temperatures (which depend on initial nitrogen pressure i P N 2 and shift toward higher temperatures under the increase of i P N 2 ) it is most likely the reaction, accompanied by the formation of liquid silicon and gaseous cyanogen.

The results of the study of SiC epitaxial layer growth kinetics in the system SiC-C are reported. The effects of temperature, pressure and heterogeneous reactions during the epitaxial layer formation have been studied in vacuum and at different partial pressures of argon in the system. An analysis of the experimental results was made on the basis of the theory of mass transfer by diffusion, taking into consideration the surface reactions. The dependence of the total supersaturation on the velocity of the epitaxial layer growth has been proposed. It has been established that above a certain pressures of argon in the system, and depending on the temperature of growth, the process is controlled primarily by mass transfer by diffusion, while at lower pressures the heterogeneous surface processes influence the kinetics of growth.

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 question of the interrelation of synthesis conditions with the energy distribution in photoluminescence spectra is studied for SiC epitaxial layers of 4H and 6H polytypes grown in the presence of rare-earth metals Tb and Sc. Marked differences in the energy distribution in the observed spectra indicate that in the process of growth from gas and liquid phases different emission centres are formed. It is found that the position of the maxima of the high temperature photoluminescence bands for 6H-SiC epilayers grown from the gas phase in the presence of Tb coincides with that for 6H-SiC layers in which boron is introduced by diffusion. [Russian text Ignored]

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]

Recombination centres in luminescent crystals n-SiC(6H) doped with nitrogen and compensated with boron during the diffusion process are investigated by photocapacitance method. Boron diffusion results in appearance of a deep centre which is able to capture holes effectively. The ionization energy of this centre ET = (0.4 ± 0.02) eV coincides with the boron ionization energy in p-SiC(6H): B crystals and the spectral dependence of photoionization cross-section qp is similar to the spectral dependence of absorption near the long-wave edge of the absorption band of these crystals. But such centre is not observed in n-SiC(6H): B original samples in spite of the large quantity of boron in them. Based on these facts the conclusion can be made that boron with respect to the capture of the holes may be either in active or in bound states depending on the method of doping. This results in different efficiency of photoluminescence of crystals doped with boron in the growth and diffusion processes. [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.

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.