Self-interstitials in 3C-SiC

We report results from density-functional plane-wave pseudopotential calculations for carbon and silicon self-interstitials in cubic silicon carbide (3C-SiC). Several initial ionic configurations are used in the search for the global total-energy minimum including tetragonal, split [100] and split [110] geometries. Neutral carbon interstitials are found to have several nearly degenerate total-energy minima configurations in split-interstitial geometries, with formation energies ranging-besides higher metastable ones-from 6.3 to 6.7 eV in stoichiometric SiC. By contrast, the neutral silicon interstitials have a clear single minimum total-energy configuration at the tetrahedral configuration with carbon nearest neighbours, exhibiting a formation energy of 6.0 eV. The split interstitial in the [110] direction at the silicon site and the tetrahedral configuration with silicon nearest neighbours are metastable and have significantly higher formation energies. The present calculations indicate that the carbon interstitial introduces deep levels in the band gap while the silicon interstitial at the tetrahedral site behaves like a shallow donor.