MBE-grown Si/SiGe HBTs with high beta , f/sub T/, and f/sub max/

Si/SiGe heterojunction bipolar transistors (HBTs) were fabricated by growing the complete layer structure with molecular beam epitaxy (MBE). The typical base doping of 2*10/sup 19/ cm/sup -3/ largely exceeded the emitter impurity level and led to sheet resistances of about 1 k Omega / Square Operator . The devices exhibited a 500-V Early voltage and a maximum room-temperature current gain of 550, rising to 13000 at 77 K. Devices built on buried-layer substrates had an f/sub max/ of 40 GHz. The transit frequency reached 42 GHz.>