A minority-carrier transport model for polysilicon contacts to silicon bipolar devices, including solar cells

Abstract

A physical, analytic model for heavily doped polysilicon contacts to silicon bipolar devices is developed. The model defines an effective surface recombination velocity S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</inf> for minority carriers at the polysilicon-silicon interface in terms of the physical properties of the polysilicon. It thus allows the carrier transport problem in the adjacent silicon region, e.g., the emitter, to be solved and the efficacy of the device, e.g., a transistor or a solar cell, to be characterized, and hence can be an effective design aid. The model is shown to compare well with published experimental data indicating the benefits of polysilicon contacts to bipolar transistors. Such benefits, which result because of the relatively low values of S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</inf> , might also occur when polysilicon contacts are used on silicon solar cells.