Energy distribution of light-induced gap states in hydrogenated amorphous-silicon alloys

We have studied the effect of prolonged light exposure on the density and energy distribution of gap states in undoped hydrogenated amorphous-silicon alloys. The gap-state distribution in the upper half of the mobility gap has been obtained from measurements of steady-state and transient photoconductivity. The density of states at the Fermi level has been determined from the frequency dependence of capacitance of Schottky diodes. The results suggest that light exposure gives rise to new states in the upper half of the mobility gap.