Light-induced, reversible, above-gap, optical changes in hydrogenated amorphous silicon films

Abstract The purpose of this work is to determine if there are reversible, light-induced changes in the hydrogenated amorphous silicon optical properties in the higher than band gap photon energy region. For that purpose, we propose a new technique in which spectroscopic ellipsometry (SE) measurement is made through a transparent substrate to avoid effects related to changes in surface oxidation or contamination. Decrease in the imaginary part of the pseudo-dielectric function 〈 e 2 〉 was observed in the higher than band gap photon-energy range after the sample was illuminated with visible light. The change was reversible by thermal annealing at 220°C for one hour. Optical simulations show that the origin of the observed change may be localized to a region within a few nanometers of the interface with the transparent substrate.