Monte Carlo simulation of non-equilibrium transport in ultra-thin base Si bipolar transistors

Abstract
Ultrathin base (<or=50-nm) Si n-p-n and p-n-p bipolar transistors are simulated by a two-dimensional, self-consistent Monte Carlo program with both electron and hole transport models. The results reveal that two nonequilibrium carrier transport effects, velocity overshoot at the base-collector junction and quasi-ballistic transport through the neutral base region, play important roles in shaping the electrical characteristics of these scaled bipolar devices. For such thin base devices, the collector transit time, instead of the base transit time, becomes the major limitation on the device performance. Furthermore, the base transit time of these devices is predicted to be linearly dependent on the neutral base thickness. It is suggested that Fermi-Dirac statistics and long-range Coulomb correlation effects are very important for bipolar simulations using the Monte Carlo technique.