Plasma-hydrogenation effects on conductivity and electron spin resonance in undoped polycrystalline silicon

Abstract

The effect of plasma‐hydrogenation on the electrical properties and electron spin resonance (ESR) are investigated for undoped polycrystalline silicon films produced by annealing from chemical vapor deposited amorphous silicon. The conduction type for all samples used is p‐type. Under a constant plasma annealing temperature, a maximum of the dark conductivity and a minimum of its activation energy are observed at a certain annealing time. This result suggests the presence of two stages in the process of hydrogenation, which is not explained by the models proposed up to now. The ESR spin density decreases and the photoconductivity increases with plasma annealing time, and both are saturated at the first stage. A model for the carrier transport mechanism is proposed in which crystallites with surface bandbending and a damaged layer between the crystallites are included, and the variations of the dark conductivity and photoconductivity are attributed to surface conduction of crystallites and limitation at the damaged layer, respectively, depending on the density of localized states. The temperature dependence of the dark conductivity is also discussed based on this model.