The relationship between the structure, H coverage, morphology, and reactivity of plasma deposited hydrogenated amorphous silicon (a-Si:H) film surfaces was investigated using molecular-dynamics simulations. Surfaces of a-Si:H films grown with SiH3 as the sole deposition precursor are found to be remarkably smooth due to a valley-rilling mechanism where mobile precursors, such as SiH3 and Si2H6, diffuse and react with dangling bonds in the valleys on the surface. Surface valleys are reactive due to the increased concentration of dangling bonds and decreased H coverage in these regions. The previously speculated physisorbed configuration, where SiH3 is weakly bound to the surface through a H atom, is highly unlikely to be the mobile precursor state.
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