Performance comparison analysis of GeSi and Si bipolar transistors

Performance improvements of Si/Ge/sub x/Si/sub 1-x//Si heterojunction bipolar transistors with linearly graded Ge profile in the epitaxial base layer are compared with Si transistors without Ge by using a combined DC and low-frequency (1 kHz) small-signal AC measurements. Quantitative analysis of the minority-carrier transport parameters in the GeSi base layer, and of the current gain and recombination current components, for both GeSi and Si transistors are reported for the first time. The two fold improvement of the base transit time in GeSi transistors is due to the built-in electric field from Ge grading, rather than to improved diffusivity.