Structure and vibrational spectra of carbon clusters in SiC

TL;DR

This study uses ab initio methods to analyze the structure, vibrational spectra, and potential origins of carbon-related defects in SiC, linking specific defect complexes to observed photoluminescence centers.

Contribution

It provides detailed vibrational mode analysis of carbon clusters in SiC and proposes defect identities for certain photoluminescence centers based on computational results.

Findings

Localized vibrational modes above bulk phonon spectrum identified

High-frequency LVMs up to 250 meV in antisite clusters

Dicarbon antisite linked to D_{II} center, carbon split-interstitial to P-U centers

Abstract

The electronic, structural and vibrational properties of small carbon interstitial and antisite clusters are investigated by ab initio methods in 3C and 4H-SiC. The defects possess sizable dissociation energies and may be formed via condensation of carbon interstitials, e.g. generated in the course of ion implantation. All considered defect complexes possess localized vibrational modes (LVM's) well above the SiC bulk phonon spectrum. In particular, the compact antisite clusters exhibit high-frequency LVM's up to 250meV. The isotope shifts resulting from a_{13}C enrichment are analyzed. In the light of these results, the photoluminescence centers D_{II} and P-U are discussed. The dicarbon antisite is identified as a plausible key ingredient of the D_{II}-center, whereas the carbon split-interstitial is a likely origin of the P-T centers. The comparison of the calculated and observed high-frequency modes suggests that the U-center is also a carbon-antisite based defect.