All-Injection Modeling of Collector Current and Transit Time in SiGe Bipolar Transistors

An analytical investigation of the minority-carrier transport properties at arbitrary injection levels is presented. Firstly, it is shown that the minority-carrier transport equation is exactly soluble at high-injection levels, yielding closed-form expressions for the injected current, transit time and sheet resistance. Then, a simple analytical model valid at arbitrary injection levels is proposed. The analysis retains a general dependence of the transport parameters on composition and doping concentration, and is thus applicable to SiGe HBTs.