Transition between the 1 x 1 and (√3 x 2√3)R30° surface structures of GaN in the vapor-phase environment

Out-of-plane structures of the GaN(0001) surface in the metal-organic chemical vapor deposition (MOCVD) environment have been determined using in situ grazing-incidence X-ray scattering. We measured 11 (2) over bar l crystal truncation rod intensities at a variety of temperatures and ammonia partial pressures on both sides of the 1 x 1 to (root 3 x 2 root 3)R30 degrees surface phase transition. The out-of-plane structure of the (root 3 x 2 root 3)R30 degrees phase appears to be nearly independent of temperature below the transition, while the structure of the 1 x 1 phase changes increasingly rapidly as the phase transition is approached from above. A model for the structure of the 1 x 1 phase with a partially occupied top Ga layer agrees well with the data. The observed temperature dependence is consistent with a simple model of the equilibrium between the vapor phase and the surface coverage of Ga and N. In addition, we present results on the kinetics of reconstruction domain coarsening following a "quench" into the (root 3 x 2 root 3)R30 degrees phase held. (C) 2000 Elsevier Science B.V. All rights reserved.