Silicon heterojunction bipolar transistors with amorphous and microcrystalline emitters

Abstract

The emitter Gummel number of bipolar transistors with an amorphous silicon emitter-base heterojunction is shown to be very large. The temperature dependence of the common-emitter current gain of such heterojunction bipolar transistors is much smaller than that of conventional homojunction transistors. With the actual technology the applicability of amorphous silicon emitters is limited by the emitter series resistance which is too high for VLSI applications. Microcrystalline silicon is a promising emitter material as it combines the high emitter efficiency of amorphous silicon emitters with a much lower resistivity, yielding lower emitter resistances.