CHEMICAL-EQUILIBRIUM DESCRIPTION OF STABLE AND METASTABLE DEFECT STRUCTURES IN A-SI-H

A model for the equilibrium and metastable defect structure in a-Si:H is presented. Allowing chemical equilibration between dangling bonds and weak bonds with a broadened band of available defect energy levels, and requiring electronic occupancy according to occupation statistics during the chemical equilibration process, an expression for the steady-state defect structure under general nonequilibrium conditions is derived. A single reaction involving e-h pair recombination is found to account for the vast majority of experimental data, such as the dependence of equilibrated and saturated defect densities on temperature, generation rate, and band gap. The model predicts an excess of charged defects in as-grown undoped a-Si:H and a change in the energetic distribution of defect states by light soaking with an associated decrease of the ratio of charged-to-neutral defects, in agreement with measurements.