Comprehensive ab initio study of properties of monovacancies and antisitesin 4H-SiC

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 me thod based on density-functional theory and the local spin-density approxim ation. Formation energies, ionization levels, and local geometries of the r elaxed structures are reported for defects at all possible cubic and hexago nal lattice sites. To correct for the electrostatic interaction between cha rged supercells, we use a Madelung-type correction for the formation energi es, leading to good agreement with experimentally observed ionization level s. Our calculations indicate no negative-U behaviour for carbon vacancies. Hence, the singly positive charge state of the carbon vacancy V-C(+) is sta ble, as recently found in experiments. The silicon antisite Si-C(+) is foun d to be stable at low values of electron chemical potential-again in agreem ent with experiment.