Dissociative chemisorption of NH3 molecules on GaN(0001) surfaces

We performed ab initio calculations to study the structure and the relative stability of hydrogenated GaN(0001) surfaces which may form during the growth of gallium nitride using an NH3 nitrogen source. The surfaces that we have studied contain H ad-atoms and NH2 ad-complexes adsorbed on GaN(0001). We find that adsorption of H, alone or accompanied by other species, stabilizes the surface of GaN and is able to catalyze the formation of an ideal-like geometry. We give an interpretation of this effect in terms of the electron band structure. Our results suggest, on microscopic grounds. that rough surfaces are formed by metal organic chemical vapor deposition under N-rich conditions. Ga-rich and H-rich conditions are suggested for the attainment of high quality films.