A comprehensive semi-analytical model of the polysilicon emitter contact in bipolar transistors

This paper aims to develop a comprehensive physical model for a bipolar transistor's polysilicon-contacted emitter. Poisson's equation is solved numerically in the emitter-base space charge region to specify the boundary conditions and the excess minority carriers injected from base to emitter. The continuity and current transport equations are also solved numerically to obtain the minority carrier current in the emitter region. The polysilicon along with the interface layers is modeled by using an effective value for the lifetime. In this model, all the technological parameters of different emitter regions are taken into consideration. Also, the heavy doping effects and the built-in electric field in the shallow non-homogeneous doped single crystalline layer are also included. Such a systematic model does not exist in the literature. The results of the analytical model are numerically evaluated using MATLAB. The trends provided by the model are validated against published experimental results whenever possible and found to be in good agreement with them.