Base current tuning in SiGe HBT's by SiGe in the emitter

Npn-type SiGe heterojunction bipolar transistors (HBT's) have high cut-off frequencies, but low breakdown voltages due to their high current gain. We show that a SiGe layer in the emitter can increase the base current and hence the breakdown voltage while the collector current and cut-off frequency are not reduced. Simulations and first experimental results clearly confirm this effect.