Current transport in narrow-base transistors

Abstract

The transport of carriers across the base and the collector space-charge region of a silicon, narrow-base, bipolar transistor, is investigated by means of a Monte Carlo simulation of the transport process. The resulting carrier concentration within the base region turns out to be larger than that determined from the usual drift-diffusion equation, and the carrier transit-time is correspondingly increased. At the beginning of the collector space-charge region, where the field is suddenly increasing to a very large value, an anomalously high carrier mean velocity is observed. The latter than decays to the saturation velocity, with a time constant related to the field and the various kinetic relaxation times. This phenomenon is a non-equilibrium effect which cannot be accounted for by the drift-diffusion equation, but is of a limited influence on the collector transit-time.