An investigation was made of the structure of the anion- and cation-terminated (00•1) surfaces of wurtzite-phase GaN and AlN, using  ab initio  local-orbital calculations that were based upon the local-density approximation and the pseudopotential method. All of the stable surface configurations which were studied differed, in atomic composition and periodicity, from the ideal bulk-like termination. The calculated total energies were compared for various p(2 x 2) geometries of GaN and AlN (00•1). Vacancy structures were found to be the most stable configurations for the anion- and cation-terminated surfaces. Under metal-rich growth conditions, the predictions favoured the adsorption of metal atoms at the cation-terminated surface. Anion- and cation-derived dangling-bond states appeared in the bulk band-gap as a result of the formation of vacancies or the adsorption of group-III atoms. Flat surfaces of both types were found to be stabilized by ¾ of a monolayer of adsorbed H.

J.Fritsch, O.F.Sankey, K.E.Schmidt, J.B.Page: Physical Review B, 1998, 57[24], 15360-71