Soft Modes at the Stacking Faults in SiC Crystals

We use first-principles calculations based on density functional theory to determine and understand the driving force of the observed stacking fault expansion in SiC. We verify the suggestion based on recent experiments that the free energy difference between the faulted and the perfect structures is responsible for this expansion, and show that its origin lies in a large entropy associated with soft vibrational modes of the faulted SiC structure. These soft modes involve shearing of SiC on a long length-scale and are absent in related group IV semiconductors, such as Si, Ge and C.