Analytical Model and Current Gain Enhancement of Polysilicon-Emitter Contact Bipolar Transistors

This paper presents an analytical model that simulates the current gain improvement of polysilicon-emitter bipolar transistors based on the effective recombination velocity method. The theoretical framework developed in this paper incorporates the 2-D structure effect of the polysilicon layer with columnar grain boundary, tunneling processes of holes through polysilicon/silicon interface oxide layer, and nonuniform doping concentration and bulk recombination effects in the single-crystal emitter. The study goes on to derive an analytical expression for the base current density from which the analytical expression of the current gain was then derived. The effect of oxide breakup, at the polysilicon/silicon interface, on current gain was also considered. The dependence of the current gain on temperature was analyzed numerically; the results are in good agreement with experimental data. The approach outlined in this paper allows one to avoid many of the unnecessary simplifications inherent in previous works and to clearly assess the relevance of each physical mechanism.