Reaction processes occurring in physical vapour transport (PVT) method for silicon carbide (SiC) single crystals are described in the light of thermodynamics. A possible mechanism for SiC single crystal growth phenomena in PVT is reviewed briefly based upon the pressure-dependent Si-C equilibrium phase diagram we proposed, and the description is then applied to the case of surface graphitization of growing crystals, demonstrating that accurate thermodynamic understanding of the growth phenomena in PVT is quite important for the realization of larger diameter SiC single crystals with markedly reduced defect densities such as the micropipe defect or other various dislocations. Further, the effect of source mixture compositions on the thermal decomposition process of the mixtures is also discussed using the phase diagrams by examining the thermal decomposition processes of two exemplified cases of source powder mixtures with compositions of SiC(s)+C(s) and SiC(s)+Si(s) where SiC(s), C(s) and Si(s) represent solid SiC, solid graphite and solid silicon, respectively. It is suggested from the examination that, in the former SiC(s)+C(s) system, C(s) shows negligible evaporations unless the mutual mass exchange of carbon with the vapours is taken into account, whereas, for the latter SiC(s)+Si(s) system, an ordinary SiC single crystal growth can occur if such source mixtures are adopted in PVT growths, but it strongly depends on the whole composition of the source mixture as well as the temperature gradient between the seed and the source.
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