Role of entropy in silicon carbide polytype competition

Abstract

Polytype control has long been a critical issue in silicon carbide single crystal growth. Empirically, the competition among different polytypes can be manipulated through temperature, carbon-to-silicon ratio, doping control, etc. However, the underlying physics remains largely elusive. Herein, we reveal that entropy difference, particularly that of the vibrational entropy and configurational entropy, is the thermodynamic origin of these polytype regulation methods. The bulk vibrational entropy difference suppresses the 3C–SiC and favors hexagonal polytypes at a higher temperature. Furthermore, the defect vibrational and configurational entropy difference arising from inequivalent carbon sites further stabilizes n-type 6H–SiC over 4H–SiC in the presence of carbon vacancies and nitrogen substitutions at elevated temperatures. These defects are reduced with high carbon chemical potentials, explaining the preference of 4H–SiC at high C/Si ratios. These entropy analyses suggest that a moderate temperature and C-rich condition are beneficial to the growth of 4H–SiC and provide physical perspectives into the thermodynamic role of phonons and defects in single crystal growth.