It was recalled that an increase in the metastable defect density of hydrogenated amorphous films, under high-intensity illumination, was usually described by an empirical 2-parameter stretched-exponential time dependence. A clearly different, 1-parameter, analytical function was derived here from a microscopic model that was based upon the formation and trapping of metastable H atoms. In this model, which was deduced from experimental observations and assumed that metastable H atoms were the only mobile species, only 3 basic reactions were significant. That is, metastable H atoms were produced from doubly hydrogenated configurations and were trapped either at broken bonds or Si-H bonds. This corresponded to light-induced annealing, and light-induced creation of defects, respectively. Competition between trapping sites resulted in the saturation of the defect density at a steady-state value. An implicit analytical function was obtained for the continuous-wave illumination time-dependence of the metastable defect density. A 1-parameter fit of this analytical function, to experimental data, was generally good; thus indicating that the use of a statistical distribution of trap energies was not necessary.

C.Godet: Philosophical Magazine B, 1998, 77[3], 765-77