Substitutional carbon in group-III nitrides:: Ab initio description of shallow and deep levels -: art. no. 075209

We present ab initio pseudopotential plane-wave calculations for the neutral and negatively charged carbon impurity on a nitrogen site in group-III nitrides. Ultrasoft non-norm-conserving Vanderbilt pseudopotentials allow the use of extremely large supercells up to 2744 atoms. These supercells attenuate the defect-defect interaction and, hence, give an accurate description of the resulting acceptor levels in BN, AlN, GaN, and InN. We calculate atomic geometries and energetical positions of the defect levels, Franck-Condon shifts, and formation energies. The defect stability and the transition of the shallow-deep character are discussed along the series BN, AlN, GaN, and InN. For GaN we calculate a hole activation energy of about 0.2 eV in correspondence with photoluminescence and temperature-dependent Hall measurements.