A comprehensive defect model for amorphous silicon

The density and distribution of dangling-bond defects in a given sample of hydrogenated amorphous silicon (a-Si:H) depends on thermal history and on electron and hole densities. As a consequence, the defect density of a-Si:H devices changes during their operation. Optoelectronic device modeling therefore must be coupled with the modeling of the density and distribution of dangling-bond defects. In this paper such a defect model is presented. The model accounts for the effects of the temperature of film growth, the rate of film growth, the film thickness, light-soaking intensity, time, and temperature, and the temperature and duration of thermal annealing. The model is based on the assumption of a limited pool of defects with a Gaussian distribution of thermal annealing energies. This is the most simple model that agrees reasonably well with a variety of experimental data. The applicability of the model is demonstrated on many examples drawn from measurements of dark and photoconductivity, transmission spectroscopy, and subgap optical absorption.