Reconstructions of the (00•¯1) surface were studied for the first time. Four primary structures, 1 x 1, 3 x 3, 6 x 6, and c(6 x 12) were observed by using scanning tunnelling microscopy and reflection high-energy electron diffraction. On the basis of first-principles calculations, the 1 x 1 structure was shown to consist of a Ga monolayer that was bonded to a N-terminated GaN bilayer. By combining experimental data, and theory, it was argued that the 3 x 3 structure was an adatom-on-adlayer structure with one additional Ga atom per 3 x 3 unit cell.

A.R.Smith, R.M.Feenstra, D.W.Greve, J.Neugebauer, J.E.Northrup: Physical Review Letters, 1997, 79[20], 3934-7