Photo-induced changes in the coefficient of the temperature dependence of the Fermi level in discharge-produced amorphous silicon

Abstract

New data on photo-induced changes in the photoconductivity σp and dark conductivity σD (Staebler-Wronski effect) of a-Si : H are described. Some films are shown to be much less sensitive to light exposure than others : the change in the activation energy ΔEσ of σD between the annealed state A and the fully-irradiated state B is small and in some cases ΔEσ ≃ 0. The results are interpreted in terms of minimum metallic conductivity theory and the change in the coefficient of the temperature dependence of the Fermi level (βA - β B) between states A and B is calculated. Upper and lower bounds of β A and βB are deduced. It is found that for films exhibiting large photo-induced effects β B > βA. The coefficient βB is positive and typically ∼ 4-10 x 10-4 eV K-1. In contrast for most films exhibiting small changes upon illumination both β A and βB are negative and the change when passing from state A to state B is small