Emitter and base transit time of polycrystalline silicon emitter contact bipolar transistors

The author formulates transit time in the neutral emitter region, tau /sub E/, and in the neutral base region tau /sub B/, of polycrystalline silicon emitter contact bipolar transistors. An analytical theory derived for tau /sub E/ of polysilicon emitter contact bipolar transistors and its dependence on the emitter junction depth, the polysilicon thickness, and the base width are presented. The influence of bandgap narrowing on tau /sub E/ and tau /sub B/ is analyzed. Bandgap narrowing increases tau /sub E/, but tau /sub B/ is insensitive to it. tau /sub E/ is proportional to base width W/sub B/ and tau /sub B/ to W/sup 2//sub B/. tau /sub E/ is not negligible compared to tau /sub B/ when W/sub B/ is less than 100 nm. Reducing emitter junction depth and polysilicon thickness is indispensable to developing shallow base bipolar transistors.<
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