The energetics and structure of a laterally contracted Ga bilayer model for the Ga-rich pseudo-(1 x 1) phase of the (00•1) surface were considered. First-principles total-energy calculations revealed that a laterally contracted overlayer of Ga atoms, bonded to a 1 x 1 Ga adlayer, was energetically favourable in the Ga-rich limit. Calculations also showed that the energy of this surface structure was very insensitive to the lateral position of the contracted layer with respect to the underlying Ga layer. The flatness of the energy surface suggested the presence of rapidly moving domain boundaries which separated regions of the surface which had differing registries. Such motion was suggested to lead to the 1 x 1 corrugations which were observed in scanning tunnelling microscopic images.

Structure of GaN(0001) - the Laterally Contracted Ga Bilayer Model J.E.Northrup, J.Neugebauer, R.M.Feenstra, A.R.Smith: Physical Review B, 2000, 61[15], 9932-5