Collection efficiency of <i>a</i>-Si:H Schottky barriers: A computer study of the sensitivity to material and device parameters

Abstract

A comprehensive numerical calculation of the spectral response, or equivalently, collection efficiency behavior of a-Si:H Schottky barrier detector and solar cell structures is presented. This allows, for the first time, for a thorough assessment of the impact of materials property variations as well as of device parameter variations on spectral response. In the case of material parameters, the analysis shows that the spectral response measurement for a-Si:H type materials is not sensitive to the tail-state density or tail-state capture cross sections for the band whose carriers are repelled at the barrier. However, it is sensitive to these quantities for the band tail of the carriers collected at the barrier and it is sensitive, in general, to the midgap states. It is sensitive to the carrier mobilities but again the sensitivity depends on the role of the carrier in barrier formation. This sensitivity does not follow a simple mobility-lifetime product model. Spectral response is also sensitive to the device length and front surface barrier parameters. All of this spectral response behavior is shown to be due to the interplay of three loss mechanisms with certain general features.