The effect of growth conditions and surface polarity upon the morphology of (00•1) surfaces was studied. The decisive factors which favoured lowest-energy reconstructions were the ionic nature of the Ga-N bond and the strength of the N-N bond. Under Ga-rich conditions, Ga-adatom reconstructions were the most energetically favourable of the 2 x 2 reconstructions to be studied; regardless of the polarity of the surface. Under N-rich conditions, a N-adatom reconstruction was most stable on the Ga-terminated surface. On the N-terminated surface, a N atom spontaneously bonded to a surface N atom so as to create a N molecule and a vacancy substrate. The molecule was weakly bound, and was expected to evaporate at high growth temperatures. Since vacancy reconstruction was unstable over the whole range of chemical potentials, evaporation of N2 molecules was expected to lead to a cascade of reconstructions of the substrate. For both polarities, ¾ of a monolayer of H stabilized the relaxed ideally-cleaved surfaces. These reconstructions had 2 x 2 symmetry. The very small relaxation of surface atoms on N-terminated surfaces, which was below the resolution of low-energy electron diffraction, caused this surface to appear as 1 x 1.

K.Rapcewicz, M.B.Nardelli, J.Bernholc: Physical Review B, 1997, 56[20], R12725-8