Electronic structures of substitutional C and O impurities in wurtzite GaN

The electronic structures of the substitutional O on N site and C on Ga site in wurtzite GaN have been studied by employing ab initio 'mixed-basis + norm conserving non-local pseudo-potential' method and a 32-atom wurtzite supercell with and without lattice relaxations. Present calculations indicate that the host Ga atoms bonding to O impurity relax outward slightly while one of them draws along the c-axis toward another. The charge density distribution appears distinctly lower with lattice relaxations near the host Ga atoms bonding to the O impurity. These results suggest that the substitutional O with cation-cation-bond configuration is likely to act as the DX center in wurtzite GaN with heavy O dopants. On the other hand, the host N atoms bonding to the substitutional C relax inward largely which is accompanied by one of them turning toward another. The charge density distributions around the substitutional C are distinctly higher with lattice relaxations. The results of the energy band structure suggest that the substitutional C acts as a deep electron trap that is expected to offer electrons under light excitation. (C) 2003 Elsevier Science B.V. All rights reserved.