DC and AC performances in selectively grown SiGe-base HBTs

A selectively grown Si1-xGex base heterojunction bipolar transistor (HBT) w as fabricated, and effects of Ge and B pro files on the device performance were investigated. Since no obvious leakage current was observed, it is sho wn that good crystallinity of Si1-xGex was achieved by using a UHV/CVD syst em with high-pressure H-2 pre-cleaning of the substrate. Very high current gain of 29,000 was obtained in an HBT with a uniform Ge profile by both inc reasing electron injection from the emitter to the base and reducing band g ap energy in the base. Since the Early voltage is affected by the grading o f Ge content in the: base, the HBT with the graded Ge profile provides very high Early voltage. However, the breakdown voltage is degraded by increasi ng-Fe content because of reducing bandgap energy and changing dopant profil e. To increase the cutoff frequency, dopant diffusion must be suppressed, a nd carrier acceleration by the internal drift field with the graded Ge prof ile has an additional effect. By doing them, an extremely high cutoff frequ ency of 130 GHz was obtained in HBT with graded Ge profiles.