Calculations of SiH3 diffusion and growth processes on a-Si:H surfaces

Surface diffusion of a growth species is needed to give the observed smooth surface of hydrogenated amorphous silicon (a-Si:H). But what diffuses, the weakly bound SiH3 radical on the hydrogenated surface, or the bound SiH3 at a growth site. Diffusion is complicated by the change in the surface termination of a-Si:H as temperature rises. We use total energy pseudopotential calculations on a variety of periodic Si:H surface configurations to show that it is the weakly bound SiH3 that diffuses. We provide an overall energy scheme of the bound states and transport levels of SiH3 on a-Si:H surfaces.