GROWTH AND CHARACTERIZATION OF BETA-SILICON CARBIDE SINGLE CRYSTALS.
Final scientific rept., 16 May 64-15 Jan 67,
STANFORD RESEARCH INST MENLO PARK CALIF
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The process for growing Beta-silicon carbide single crystals from solution in carbon-saturated silicon melts was examined to determine how larger crystals may be obtained. Observed crystal growth effects resulting from increasing the carbon solute transport rate by stirring the solution are described and correlated with boundary layer theory. Both forward growth of platelets into the solution and lateral growth of platelets were accelerated by stirring. However, crystal growth in the forward direction was eventually limited by a boundary layer region, beyond which the solution was no longer supersaturated. Because of the decrease in boundary layer thickness with increasing stirring speed, the terminal lengths of silicon carbide platelets decrease with increasing stirring speed. Agreement between calculated crystal platelet lengths and experimental platelet lengths is good except at very low stirring speeds where free convection fluid motion is greater than the fluid motion caused by stirring. Large single-crystal Beta-silicon carbode platelets were grown in experiments in which convective stirring was reduced by crucible geometry and shielding. Addition of trace amounts of tantalum to the silicon melt improved the surface quality of crystals grown under conditions that normally favor the growth of coarse platelets.