Electronic structure of a nitrogen vacancy in cubic gallium nitride

The electronic structure of a nitrogen vacancy in zinc-blende GaN has been calculated using two different supercells with the plane-wave pseudopotential (PWPP) and the tight-binding linear muffin-tin orbitals (TB-LMTO) methods. The Ga 3d states are included in the valence states. Relaxation near a nitrogen vacancy site was examined with the PWPP method using a 31-atom unit cell. The nearest neighbor Ga atoms were found to move toward the vacancy site by 0.04 A resulting in a relaxation energy of only 0.04 eV. Given the absence of large relaxations, TB-LMTO calculations were then performed for 31- and 63-atom unit cells using an ideal (unrelaxed) geometry. Densities of states and charge density maps show that a nitrogen vacancy can induce a partially filled band, which overlaps with the conduction states, resulting in n-type conductivity. The energy shift of this band under pressure was investigated for volume compressions up to 12% and compared with results from recent high-pressure measurements for GaN.