Adsorption of dissociated NH3 molecules on the GaN(0001) surface: implications for growth.

We present the results of ab initio calculations performed to investigate the structure and relative stability of hydrogenated GaN(0001) surfaces which may play a relevant role in the microscopic mechanisms of GaN growth using NH₃ as nitrogen source. The surfaces that we have studied contain adsorbed H ad-atoms and NH₂ ad-complexes. Our results show 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 suggest, on microscopic grounds, that for the attainment of high quality films, by metal organic chemical vapor deposition, Ga-rich and H-rich conditions are favourable; under N-rich growth conditions, rough surfaces are obtained. Part of the work was done in the frame of INFM Project PRA-1MESS.