Si/Si0.8Ge0.2 Heterojunction Bipolar Transistors With Ion Implanted Device Contacts

High performance npn Si/SiGe heterojunction bipolar transistors were fabricated with As ad BF2 implanted emitter and base contacts, respectively. Annealing was carried out in a conventional diffusion furnace at 900°C for 2 up to 8 minutes. The DC output characteristcs were clearly improved. A maximum current gain of more than 1000 was achieved and the typical VCE offset was negligible. A serious problem is the SiGe base sheet resistance, which is higher in the outer as compared with the inner base. A 900°C annealing step may reduce the outer base resistance. The first high frequency measurement resulted in a transit frequency of 8.5 GHz at VCE=1V.