MOLECULAR-DYNAMICS SIMULATIONS OF DEFECT FORMATION IN HYDROGENATED AMORPHOUS-SILICON

We have performed molecular-dynamics simulations to understand the Staebler-Wronski effect and defect formation in a-Si:H. The calculations are based on a-Si:H networks containing (1) only monohydride species and (2) both monohydride and dihydride species. A two- and three-body potential for Si-H interactions has been developed and used in conjunction with previous interatomic-potential models for Si-Si interactions. A localized excitation is used to model the nonradiative energy transfer of a photoexcited electron-hole pair to the lattice. Defect formation and annealing are discussed, together with their dependences on the positions of localized excitations, hydrogenation of Si, and the amount of excitation energy. The a-Si:H model with monohydride species only is stable to bond-breaking excitations. The a-Si:H model with both monohydride and dihydride species is less stable and does exhibit higher-energy dangling-bond states that can, however, be easily annealed away.