Gap States in a-SiGe:H Examined by the Constant Photocurrent Method

Abstract

Gap states in a-SiGe:H alloys were examined by the deconvolution analysis of subgap absorption spectra obtained by the constant photocurrent method. A broad distribution of defect states was found in a-SiGe:H alloys by the analysis postulating a Gaussian distribution of defect states. Analysis postulating two Gaussian peaks suggested that defects in a-SiGe:H can be divided into Si- related and Ge-related types. The energy positions of two defect peaks relative to the conduction band edge were almost constant irrespective of the optical gap of alloy films, and the position of one peak agreed with the defect peak in a-Si:H. The other peak which locates around 0.75 eV below the conduction band edge appeared when Ge was introduced into a-Si:H. The ratio of these two peaks exhibited a fairly good correlation to the Ge/Si ratio of alloys.