A comparison between Monte Carlo and extended drift-diffusion models for abrupt InP/InGaAs HBTs

In this paper, a comparison between the simulation results of abrupt InP/InGaAs n-p-n heterojunction bipolar transistors (HBTs) obtained from both an extended drift-diffusion (EDD) model and from a Monte Carlo (MC) HBT simulator is carried out. The EDD approach is based on Grinberg´s model for the electron current through the interfacial emitter-base spike-like potential barrier. The MC procedure includes the effects of quantum transmission/reflection through the abrupt heterojunction. The transmission coefficient is obtained from a numerical solution of Schrodinger´s equation (self-consistently embedded in the general MC procedure) that takes into account the nonparabolicity of the bands and the spatial change in the effective mass. The differences between both models and their physical causes are also analyzed in this paper. It Is shown that, for the HBT under consideration, the collector current is determined by the transmission of electrons through the spike, while the numerical values of the parameters associated with the transport mechanisms in the base region have a very small influence on the collector current. An alternative equation to the conventional diffusion current equation in the neutral base region has also been developed, which includes the hot electron effects