ABINITIO MOLECULAR-DYNAMICS SIMULATIONS OF AMORPHOUS-SILICON

With a view to elucidating the microscopic mechanisms of the Staebler-Wronski effect in a-Si:H, we study the fundamental electronic and atomic processes by means of ab-initio molecular dynamics simulations originally proposed by Car and Parrinello. Our conclusions include: (1) Weak Si-Si bonds tend to be weakened further by illumination of light or by hole injection. (2) When a Si-Si bond is weak enough, there exists a metastable site for a hydrogen atom between these two Si atoms, at which the total energy becomes local minimum. The metastable site is either "on" or "off" Si-Si bond depending on the length of the Si-Si bond. (3) It requires much less energy to move H from a typical Si-H bond into an "off-bond" metastable site in the vicinity than into some interstitial site.