US Patent 11145725 Heterojunction bipolar transistor

The present disclosure relates to semiconductor structures and, more particularly, to a heterojunction bipolar transistor and methods of manufacture. The structure includes: a sub-collector region; a collector region in electrical connection to the sub-collector region; an emitter located adjacent to the collector region and comprising emitter material, recessed sidewalls on the emitter material and an extension region extending at an upper portion of the emitter material above the recessed sidewalls; and an extrinsic base separated from the emitter by the recessed sidewalls.