Photo-induced reversible change of topological disorder in hydrogenated amorphous silicon

Abstract

The temperature dependence of the optical absorption and photoconductivity spectra of undoped hydrogenated amorphous silicon (a-Si: H) has been measured. We observe for the first time a reversible increase of about 7% of the Urbach edge parameter E ₀ between 115 and 300 K as a result of a 4 h exposure to AM1 light. This suggests that photo-induced changes in a-Si: H involve not only metastable defects near the gap centre but also topological disorder that affects the localized band-tail states.