SiGe-base heterojunction bipolar transistors: Physics and design issues

It has been shown that SiGe technology has the capability to extend the performance of Si bipolar transistors at both high and low current levels. The ability to tailor the bandgap, independently of the doping profile design, provides considerable flexibility for optimizing cutoff frequency, intrinsic base resistance, and junction capacitances for a given application. It is concluded that, when combined with a self-aligned process, SiGe can significantly improve the speed of Si bipolar circuits.