Induced base transit time of an epitaxial n +pn −n + bipolar transistor in saturation

Abstract

Minority carrier recombination, drift and diffusion currents are considered in determining induced base transit time of an epitaxial n +pn −n + bipolar transistor operated in quasi-saturation and hard-saturation. The dependence of transit time upon the characteristics of the epitaxial–substrate interface is also studied for the transistor driven into hard saturation. The study shows that transit time in the induced base is significant when the transistor is driven into hard saturation and the interface is highly reflecting. The induced base transit time calculated analytically is compared with numerically obtained results in order to demonstrate the validity of the assumptions made in deriving analytical expressions. The closed form expressions for collector current density and transit time offer a physical insight into device operations at various bias conditions and are a useful tool in device design and optimization.