Critical spacing between emitter and base in InGaP heterojunction bipolar transistors (HBTs)

The influence of the spacing between the emitter and the base on the performance of InGaP heterojunction bipolar transistors (HBT) was experimentally studied. We found that the emitter to base spacing can be reduced to as small as 0.6 μm without causing a significant drop in the current gain. The reduction in emitter-to-base spacing, however, leads to improvement in high-frequency performance and device phase noise. For optimal dc, RF, and low-frequency noise performances, we have determined that a critical spacing of 0.6/spl sim/0.8 μm between the emitter and the base of an InGaP HBT is required.