Stability of hydrogenated amorphous silicon prepared by reactive evaporation

Abstract

Hydrogenated amorphous silicon (a-Si:H) was prepared by evaporating Si in a controlled ambient of reactive gases. Contamination of the samples by exposure to air affects both the dark conductivity and the photoconductivity. Some of the contamination effects can be removed by annealing, but some changes are not reversible. The irreversible changes are mainly due to the chemisorption of oxygen obtained from water vapour when the samples are stored in air. The Staebler–Wronski effect is observed in all samples whose photoconductivity is at least an order of magnitude higher than the dark conductivity. The photoconductivity versus time curve displays at t−1/3 dependence, typical of the Staebler–Wronski effect, but the degradation is much slower than that reported for glow discharge a-Si:H. The activation energy for the effect is 0.12 eV, which is larger than the 0.04 eV expected for the bond-switching model.