MBE-GROWN SI SIGE HBTS WITH HIGH-BETA, FT, AND FMAX/

Si/SiGe heterojunction bipolar transistors (HBT's) have been fabricate d by growing the complete layer structure with MBE. The typical base d oping of 2 . 10(19) cm-3 largely exceeded the emitter impurity level a nd led to sheet resistances of about 1 k OMEGA/open-square-box. The de vices exhibited 500-V Early voltage, and a maximum room-temperature cu rrent gain of 550 rising to 13000 at 77 K. Devices built on buried-lay er substrates had an f(max) of 40 GHz, the highest value reported for Si/SiGe HBT's. The transit frequency reached 42 GHz, a record for MBE- grown transistors of this kind.