Method to fabricate SiGe HBTs with controlled current gain and improved breakdown voltage characteristics

The present invention relates to heterojunction bipolar transistors (HBTs), and more particularly to a method of fabricating SiGe HBTs which exhibit controlled current gain and improved breakdown voltage. The present invention is also directed to a SiGe HBT structure which includes a bilayer of in-situ phosphorus (P)-doped amorphous silicon (a:Si) and in-situ P-doped polysilicon as the emitter. A method of fabricating a SiGe heterojunction bipolar transistor (HBT) is provided which results in a SiGe HBT that has a controllable current gain and improved breakdown voltage. The SiGe HBT having these characteristics is fabricated by forming an in-situ P-doped emitter layer atop a patterned SiGe base structure. The in-situ P-doped emitter layer is a bilayer of in-situ P-doped a:Si and in-situ P-doped polysilicon. The SiGe HBT structure including the above mentioned bilayer emitter is also described herein.