A study of nucleation at initial growth stage of SiC single crystal by physical vapor transport

The nucleations of SiC at the initial growth stage of SiC single crystal via physical vapor transport (PVT) technique were studied using the classical nucleation theory. Four possible nucleation sites including single and composite substrates involving SiC seed edges and graphite crucible walls are considered. Our results show that the mostly preferred nucleation site is on the corners between seed edge and graphite crucible wall. There exists a narrow and low supersaturation range for radial seed expansion instead of forming polycrystalline regions around the seed, which is beneficial to enlarge the ingot size of SiC single crystal. Beyond this range, nucleations will occur around the corners and polycrystalline regions develop. Further increasing supersaturation will lead to nucleations on all other three sites in the initial stage of crystal growth. Our results also provide a common theory for the nucleation on composite substrates.