ENERGETICS OF THE AS VACANCY IN GAAS - THE STABILITY OF THE 3-STATE( CHARGE)

Total-energy calculations predict that the As vacancy in GaAs adopts a 3+ charge state under p-type conditions, and that the formation energ y of V-As(3+) is competitive with that of the gallium intrstitial Ga-i (3+). After a breathing-mode relaxation, which reduces the energy by m ore than 1.5 eV, the nearest-neighbor Ga atoms exhibit a nearly sp(2) bonding configuration. On the basis of our results we propose that cha rged anion vacancies with sp(2)-bonded cation neighbors should be exam ined as possible mechanisms for the compensation of p-type doping in I II-V and II-VI semiconductors, and as possible facilitators of accepto r diffusion and anion selfdiffusion in these materials.