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 di-carbon antisite (C_{ 2})_{ Si} (two carbon atoms sharing a silicon site) is an important building block of these clusters.
Categories: cond-mat.mtrl-sci