Theory of GaN(10(1)over-bar-0) and (11(2)over-bar-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(1)over bar 0>) surface, which has Ga-N dimers in the surface layer, the calculated surface energy is 118 meV/Angstrom(2), and for the (<11(2)over bar 0>) surface, which has Ga-N chains in the topmost layer, the energy is 123 meV/Angstrom(2). The relaxation mechanisms on both surfaces are a Ga-N bond contraction and a similar to 7 degrees buckling rehybridization in the surface layer. For the (<10(1)over bar 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.