A microscopic model was presented for metastable Si dangling-bond defect creation in hydrogenated amorphous Si. It was applicable to both light-induced defect creation in solar cells (Staebler-Wronski effect) and bias-stress-induced defect creation in thin-film transistors. Light or gate bias caused electron-hole pairs or electrons, respectively, to be localized on short, weak Si-Si bonds, which then break. An H atom, from a neighboring, doubly hydrogenated weak Si-Si bond (SiHHSi) moves to the Td site of the broken Si-Si bond. The other H atom from the SiHHSi was also located in the energetically favorable Td site. Overall, the reaction produces two SiHD defects. Each SiHD defect was an intimate Si dangling bond and Si-H bond, where the H atom was in the Td site, not the BC site. The distance between the dangling bond and the H atom in the Td site was in the range of 0.4 to 0.5nm; in agreement with electron spin resonance data. The majority of Si dangling bonds, both metastable and stable, exist as SiHD, with the H atom in the Td site. The microscopic process for defect creation was fairly well localized, requiring only short-range H motion, which proceeds via bond switching between neighboring Td sites. In contrast, the microscopic process for defect removal during thermal annealing involves re-equilibration of H in the a-Si:H network and was a global process involving a large fraction of H atoms. The rate-limiting step for this process was Si-H bond breaking from SiHHSi sites, which accounts for the maximum activation energy of 1.5eV. A revised H density of states diagram was presented which was in line with this process.

Microscopic Mechanisms for Creation and Removal of Metastable Dangling Bonds in Hydrogenated Amorphous Silicon. M.J.Powell, S.C.Deane, R.B.Wehrspohn: Physical Review B, 2002, 66[15], 155212 (11pp)