A self-consistent model for defect states in a-Si and a-Si:H

Concentrations of electrically active defects in a-Si are three orders of magnitude lower than the density of dangling bonds on internal void surfaces as estimated from the density deficiency of a-Si with respect to crystalline, c-Si. This reduced defect concentration is explained by a chemically controlled self-organization, in which formation of divacancies reduces Si-atom bond-bending constraints on the terminal atoms of the divacancy, as well as their immediate neighbours. This broken constraint relaxation process prevents percolation of local rigidity, thereby explaining defect state reductions. It also identifies an optimized bonded-H concentration in a-Si:H that is enabling for device applications such as solar cells and thin film transistors which require doping.