GaN(0001) surface structures studied using scanning tunneling microscopy and first-principles total energy calculations

Surface reconstructions occurring on the (0001) surface of wurtzite GaN are studied using scanning tunneling microscopy, electron diffraction, and Aug er electron spectroscopy. The family of reconstructions found on this face includes 2 x 2, 5 x 5, 6 x 4, and '1 x 1', in order of increasing surface G a/N ratio. Detailed experimental results are presented for each of these re constructions. First-principles total energy calculations are employed to i dentify possible model structures. An adatom model, with N-adatoms occupyin g H3 sites, is proposed for the 2 x 2 reconstruction. A model composed of N adatoms, Ga adatoms, and Ga vacancies is proposed for the 5 x 5 reconstruc tion. (C) 1999 Elsevier Science B.V. All rights reserved.