Theory ofGaN(101¯0)and (112¯0) surfaces

The surface energies and atomic structures for two nonpolar surfaces of GaN have been calculated within the local-density approximation. For the ($10\overline{1}0$) surface, which has Ga-N dimers in the surface layer, the calculated surface energy is 118 meV/${\mathrm{\AA }}^2$, and for the ($11\overline{2}0$) surface, which has Ga-N chains in the topmost layer, the energy is 123 meV/${\mathrm{\AA }}^2$. The relaxation mechanisms on both surfaces are a Ga-N bond contraction and a ∼7° buckling rehybridization in the surface layer. For the ($10\overline{1}0$) surface we find that under Ga-rich conditions a nonstoichiometric surface having Ga-Ga dimers is stable with respect to the ideal Ga-N dimer-terminated surface.