We present results of ab initio calculations for the electronic and atomic structures of monovacancies and antisite defects in 4H-SiC in all possible charge states. The calculations make use of a plane-wave pseudopotential method based on density-functional theory and the local spin-density approximation. Formation energies, ionization levels, and local geometries of the relaxed structures are reported for defects at all possible cubic and hexagonal lattice sites. To correct for the electrostatic interaction between charged supercells, we use a Madelung-type correction for the formation energies, leading to good agreement with experimentally observed ionization levels. Our calculations indicate no negative-U behaviour for carbon vacancies. Hence, the singly positive charge state of the carbon vacancy VC+ is stable, as recently found in experiments. The silicon antisite SiC+ is found to be stable at low values of electron chemical potential—again in agreement with experiment.

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Abstract. 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 totalenergy 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 rangingbesides higher metastable ones -from 6.3 to 6.7 eV in stoichiometric SiC. In 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 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.