Molecular dynamics (MD) simulations have been performed to examine enhanced surface diffusion of Si adatoms during silane(SiH4)-based plasma enhanced chemical vapor deposition (PECVD) processes. Such high surface diffusion, if it actually takes place, has been known to account for the growth of microcrystalline silicon(mu c-Si) in the PECVD process. Focused in the present study is the motion of a silicon (Si) adatom on a hydrogenated Si surface and the surface diffusion coefficient of Si adatoms on the fully hydrogenated (111) Si surface at 600 K was evaluated from MD simulations. The obtained diffusion coefficient is much larger than those of typical clean Si surfaces known in the literature. The interatomic potential functions for Si-H systems used for the simulations, which we have developed for this study based on ab initio calculations of the interatomic energies, are also presented. (C) 2007 Elsevier B.V. All rights reserved.