Structure and Stability of Microvoids in a-Si:H

Microvoids have been observed in a-Si:H as demonstrated by small angle X-ray scattering. We have studied the structural properties of these microvoids with molecular dynamics simulations. Using molecular dynamics simulations with classical potentials, we have created microvoids by removing Si and H atoms from a computer generated a-Si:H network. The internal surfaces of the microvoids were passivated with additional H atoms and the microvoids were fully relaxed. Microvoids over a limited range of sizes (5–90 missing atoms) were examined. We obtained a relaxed microvoid structure with no dangling bonds for a microvoid with 17 missing atoms, whereas other sizes examined produced less relaxed models with short H-H distances at the microvoid surface. The strains near the microvoid surface are described. The microvoid model was stable to local excitations on weak bonds in the vicinity of the microvoid.