Carbon antisite clusters in SiC: A possible pathway to the D-II center

The photoluminescence center D-II is a persistent intrinsic defect which is common in all SiC polytypes. Its fingerprints are the characteristic phonon replicas in luminescence spectra. We perform ab initio calculations of vibrational spectra for various defect complexes and find that carbon antisite clusters exhibit vibrational modes in the frequency range of the D-II spectrum. The clusters possess very high binding energies which guarantee their thermal stability-a known feature of the D-II center. The dicarbon antisite (C-2)(Si) (two carbon atoms sharing a silicon site) is an important building block of these clusters.