Minority-carrier injection into polysilicon emitters

The hole transport equation is solved for a polysilicon emitter of a bipolar transistor. The recombination at the grain boundaries as well as at the poly-monosilicon interface is considered. An effective surface recombination velocity is defined and calculated as a function of surface state density and number of grain boundaries. A comparison between the injected hole current into the diffused region of both an Al contact and a polysilicon-silicon emitter is given as a function of surface state density for different numbers of grain boundaries. Also the injected current is calculated for different values of junction depth and surface concentration.