Investigation of light induced degradation in hydrogenated amorphous silicon-germanium alloy thin films using temperature dependent photoconductivity

Abstract

Light induced degradation of undoped hydrogenated amorphous silicon-germanium (a-SiGe:H) alloys with different Ge contents has been investigated using intensity and temperature dependence of photoconductivity between 78K to 300K. The samples were light soaked after annealing, under 5 suns of white light in a high vacuum cryostat without exposing samples to air at 300K. In the annealed state, the magnitude of the sigma(photo) decreases and becomes strongly temperature dependent as the Ge content increases. The exponent gamma shows two distinctly different recombination regions as Ge content increases. In the light-soaked state, a-SiGe: H alloy thin films showed stronger Staebler-Wronski effect than pure a-Si:H, and degradation increases with Ge content. In addition, temperature dependence of the exponent gamma shows substantial changes from its annealed state values and follows similar dependence on temperature as that of pure a-Si: H. These results indicate that the Staebler-Wronski defects created under illumination in Si rich a-SiGe: H alloys and pure a-Si: H are similar in nature and distribution. They dominate the recombination kinetics in the light-soaked state (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim