2-D simulation of interface properties of a polysilicon-contacted BJT: is there a residual potential barrier after the oxide is broken?

Two dimensional simulations were performed on a poly-contacted bipolar, studying the effects of changing the size of broken sections of the “oxide” on the base current. Previous simulations (Egley et al. 1991) used sections which were ~250 Å in length, while the simulations presented here use ~50 Å sections, closer to what was observed from TEM by Wolstenholme et al. (1987). The smaller gaps provide a substantially more rapid increase in base current with percentage oxide broken than found with the 250 Å sections. This extremely rapid rise in base current with the percentage oxide broken is not observed experimentally. It is proposed that a residual barrier remains after a section of the oxide is removed. This potential energy barrier would arise from the grain boundary itself and from the possible presence of electrically active As there