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 pse udopotential (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 me thod using a 31-atom unit cell. The nearest neighbor Ga atoms were fou nd to move toward the vacancy site by 0.04 Angstrom resulting in a rel axation energy of only 0.04 eV. Given the absence of large relaxations , TB-LMTO calculations were then performed for 31- and 63-atom unit ce lls using an ideal (unrelaxed) geometry. Densities of states and charg e density maps show that a nitrogen vacancy can induce a partially fil led band, which overlaps with the conduction states, resulting in n-ty pe conductivity The energy shift of this band under pressure was inves tigated for volume compressions up to 12% and compared with results fr om recent high-pressure measurements for GaN.