First-principles pseudopotential plane-wave calculations were made of the neutral and negatively charged C impurity on a N site in group-III nitrides. Ultra-soft non-norm-conserving Vanderbilt pseudopotentials permitted the use of extremely large super-cells of up to 2744 atoms. These super-cells attenuated the defect-defect interaction and hence gave an accurate description of the resulting acceptor levels in BN, AlN, GaN and InN. Atomic geometries and energetic positions of the defect levels, Franck-Condon shifts, and formation energies were calculated. The defect stability and the transition of the shallow-deep character were analyzed for the series BN, AlN, GaN and InN. In the case of GaN, a hole activation energy of about 0.2eV was estimated, which corresponded with photoluminescence and temperature-dependent Hall measurements.

Substitutional Carbon in Group-III Nitrides - ab initio Description of Shallow and Deep Levels. L.E.Ramos, J.Furthmüller, L.M.R.Scolfaro, J.R.Leite, F.Bechstedt: Physical Review B, 2002, 66[7], 075209 (9pp)