A new InP-InGaAs HBT with a superlattice-collector structure

The dc characteristics of an interesting InP-InGaAs heterojunction bipolar transistor (HBT) with a superlattice (SL) structure incorporated in the base-collector (B-C) junction are demonstrated. In the SL structure, holes injected from the collector collide with holes confined in the SL and impact them out of the SL across the valence-band discontinuities. With a collector-emitter (C-E) voltage V_CE less than the C-E breakdown voltage BV_CE0, the current gain can be increased at base-current inputs because the released holes from the SL inject into the base to cause the emitter-base junction operating under more forward-biased condition. An ac current gain up to 204 is obtained. At base-emitter voltage V_BE inputs, the released holes travel to the base terminal to decrease the base current. The studied HBT exhibits common-emitter current gains exceeding 47 at low current levels and useful gains spreading over seven orders of magnitude of collector current.