Phenomenological model for equilibrium and metastable defects in undoped hydrogenated amorphous silicon

Abstract

The thermal equilibrium and metastable defects in undoped hydrogenated amorphous silicon (a-Si:H) are considered. A simple model is proposed in which the time rate of change of defect density N(T, t) is given by (t/θ) β-1 [c d(T) n(T, t) p(T, t) - λ(T) N(T, t) c(T, t)], n(T, t) and p(T, t) being the carrier densities, c(T, t) being equal to n(T, t) or p(T, t), and c d(T) and λ(T) two parameters depending on temperature T. β≤1 and θ characterize the dispersive nature of the process. This model is shown to render account of a variety of experimental results obtained in the dark or under cw or pulsed illumination. It is suggested that the annealing mechanism is likely driven by holes and that the parameter λ(T) is one of the key factors in order to characterize the stability of undoped a-Si:H.