Gap states density in a-Si:H deduced from subgap optical absorption measurement on Schottky solar cells

Abstract

The density of states in amorphous hydrogenated silicon is obtained by deconvolution of the optical absorption coefficient a in the full sub band-gap region. The spectral dependence of the optical absorption coefficient is measured by a constant photocurrent method (CPM) on forward-biased Schottky diodes. The spectral dependence of reflection on the semitransparent Pt electrode is determined. All assumptions used in the deconvolution of a are discussed. The difference in measured value of a (by CPM) in the region below approximately 0.9 eV compared to the measurement of α by photothermal deflection spectroscopy (PDS) is explained by an absorption process seen in PDS and not seen in CPM. This absorption is supposed to be a transition from a deep localized state to a deep localized gap state (two different charge states of the same defect). [Russian Text Ignored]