HBT modeling

A simple silicon model called the standard Gummel-Poon (GP) model is modified to work for III-IV heterojunction transistors (HBT) used in power amplifier (PA) applications. In GP model, the mobility and intrinsic concentration are considered constant and the base current is split into two components. The most common approach to measure a change in the transistor temperature is to make some subset of the model parameters functions of temperature. The thinner base used in HBTs combined with the higher electron diffusivity of GaAs results in a low base transmit time. The collector of HBTs for PA applications is long and lightly doped to achieve a low base-collector capacitance and to increase the breakdown voltage, which results in higher gain. The charge model contains a collector transit time formulation that accounts for the electric-field-dependent drift velocity for GaAs and InP collectors.