MBE grown vertical emitter ballasting resistors to reduce the emitter current crowding effect in heterojunction bipolar transistors

In order to improve thermal stability and extend their safe operation region, epitaxial emitter ballasting resistors have been incorporated into power heterojunction bipolar transistors (HBTs). In this report, we show that this lightly doped layer not only can function as ballasting resistors used in multi-finger power HBT cells, but also can reduce the emitter current crowding effect which is an important limitation in bipolar transistors operating at high emitter current densities. (C) 2001 Elsevier Science B.V. All rights reserved