First-principles calculations, based upon density functional theory, were used to determine and understand the driving force of the observed stacking fault expansion in SiC. The suggestion, based upon recent experiments, that the free energy difference between the faulted and perfect structures was responsible for this expansion was verified and it was shown that its origin lay in the large entropy associated with soft vibrational modes of the faulted SiC structure that involved shearing of SiC on a long length scale. As a consequence, the velocity of sound was expected to decrease noticeably in SiC with stacking faults; measurement of which was expected to validate the soft-mode mechanism. Such mode-softening was absent in related group-IV semiconductors, such as Si, Ge, and C.

Soft Modes At the Stacking Faults in SiC Crystals - First-Principles Calculations. T.Thomas, D.Pandey, U.V.Waghmare: Physical Review B, 2008, 77[12], 121203(R) (4pp)