Gallium adsorption onto (1120) gallium nitride surfaces

We report on a systematic study of transients in reflection high energy electron diffraction specular intensities due to adsorption and subsequent desorption of gallium onto (112̄0) GaN surfaces both during the gallium adsorption by itself or during the growth of GaN by plasma-assisted molecular beam epitaxy. We determined the boundaries between N-rich growth, Ga-rich growth with only a two-dimensional phase of adsorbed Ga, and Ga-rich growth with droplets of liquid Ga. The thermal dependence of the boundary between the Ga-rich regimes with and without droplets was found to be approximately 3.2 eV for both the cases of gallium adsorption and GaN growth. This temperature dependence is explained in terms of a quasiequilibrium model for the interaction between the surface phases. Evidence is presented indicating that the two-dimensional phase saturates at submonolayer coverage for temperatures below 700 °C.