Preparation and Characterization of Single Crystals and Epitaxial Layers of Silicon Carbide by Molten Salt Electrolysis.
Annual technical rept. 15 Jul 78-14 Jul 79,
STANFORD UNIV CALIF CENTER FOR MATERIALS RESEARCH
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The synthesis of silicon carbide by electrolysis of molten salts has been achieved for the first time. Two systems have been investigated, one involving K2SiF6 and Li2CO3 dissolved in a KFLiF eutectic, the other being a combination of Na2CO3 and SiO2 with NaBO3 and LiF. The latter system has given much more reproducible results. In both cases, electrolysis has proceeded at about 750 C which is very low in comparison with the melting point of silicon carbide. Synthesis of SiC at temperatures below 1000 C does not appear to have been previously reported. Possibly because of the low deposition temperature, it has been found necessary to use deposition potentials which are appreciably highter than the minimum value. This use of relatively high deposition potentials and corresponding current densities leads to irregular growth morphology and to deposition of metastable 2H and 33R polytypes rather than the stable 6H or 15R. The SiC is co-deposited with an excess of amorphous carbon. Changes in melt composition to reduce the carbonate to silicate ratio are necessary to eliminate this excess. Initial deposits are relatively impure, the major contaminants being constituents of the inconel furnace lining.
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