A physical approach to the current and charge relations in SiGe-base HBT modeling for circuit simulation and device design

The current and charge relations for SiGe-base heterojunction bipolar transistor (HBT) are derived from the differential equations for carriers in the base. A universal description for all injection levels is obtained, which is suitable for circuit simulation. Based on these relations, the invalidity of the concept of effective doping used previously in high injection is identified and explained physically. The base profile design for applications at both room and liquid nitrogen temperature is also discussed.