Surface structure of GaN(0001) in the chemical vapor deposition environment

We report the first observation of the atomic-scale structure of the GaN(00 01) surface in the metalorganic chemical vapor deposition environment. Meas urements were performed using in situ grazing-incidence x-ray scattering. W e determined the surface equilibrium phase diagram as a function of tempera ture and ammonia partial pressure, which contains two phases with 1 X 1 and (root 3 X 2 root 3)R30 degrees symmetries. The (root 5 X 2 root 5)R30 degr ees phase is found to have a novel "missing row" structure with 1/3 of the surface Ga atoms absent.