Compact Si1-xGex/Si heterojunction bipolar transistor model for device and circuit simulation

Abstract

A physical but compact Si1-xGex/Si heterojunction bipolar transistor (HBT) model suited for device design and circuit simulation is presented. The model is based on the de Graaf-Kloosterman formalism for the modelling of the bipolar transistors, but adds important heterostructure device physics as well as physical properties of SiGe material. The model, implemented in the APLAC circuit simulator, shows how currents and charges depend on minority carrier concentrations, which in turn are functions of the heterojunction voltages. In this way, the influence of the built-in electric fields due to Ge concentration and doping density gradients, the bias-dependent transit times and the Early effect can be incorporated naturally. Comparisons between the model prediction and the experimental data for the DC current/voltage characteristics and cutoff frequencies in Si1-xGex/Si HBTs are included to demonstrate the model utility and accuracy.