A theoretical study of light induced defect creation, annealing and photoconductivitydegradation in a-Si:H

Abstract

This work is a theoretical study of the defect creation and annealing, and of thephotoconductivity degradation of an intrinsic a-Si:H film under continuous illumination. Anew model is developed for the Staebler–Wronski effect (SWE). In this model, we considerthat a defect of the SiHD type is locally created by a non-radiative recombinationat a weak bond close to a SiHHSi configuration. Also, it is considered that thelight induced defect (LID) annealing requires a hydrogen diffusion motion. Usingthe fact that the areas of defect Gaussians increase with illumination time whiletheir positions and widths remain unchanged, we present the evolution of thegap state defect density, calculated by the defect pool model, with illuminationtime. This density of states, which varies during illumination, is introduced in thesimulation of the photoconductivity to obtain its degradation. In addition, thevalidity of the proportionality of the photoconductivity to the illumination intensityG and to the inverse dangling bond density is assessed. Our investigations show amonomolecular behaviour of the photoconductivity for moderate intensity. They also show an illumination intensity dependency onGα,with α varying between 0.5 and 1, in agreement with a large number of similar investigations.