The electronic, structural, and vibrational properties of small C interstitial and antisite clusters were investigated by ab initio methods in 3C- and 4H-SiC. The defects possess sizable dissociation energies and may be formed via condensation of C interstitials, e.g., generated in the course of ion implantation. All considered defect complexes possess localized vibrational modes well above the SiC bulk phonon spectrum. In particular, the compact antisite clusters exhibit high-frequency localized vibrational modes up to 250meV. The isotope shifts resulting from a 13C enrichment were analyzed. In the light of these results, the photoluminescence centers DII and P–U were analyzed. The di-carbon antisite was identified as a plausible key ingredient of the DII center, whereas the C split interstitial was a likely origin of the P–T centers. The comparison of the calculated and observed high-frequency modes suggested that the U center was also a carbon-antisite-based defect.

Structure and Vibrational Spectra of Carbon Clusters in SiC. A.Mattausch, M.Bockstedte, O.Pankratov: Physical Review B, 2004, 70[23], 235211 (15pp)