Physics and implications of minority carrier injection induced dopant deionization in bipolar transistor

We examine here the physics and implications of minority carrier injection induced dopant deionization in bipolar transistors. At low temperatures, the rate of such deionization with increasing bias is significant in the neutral base of SiGe HBTs doped at a level near Mott transition, and charge control based transit time equations need to be modified properly. The total charges associated with conduction band, integral of q(n - N⁺_d), and the total charges associated with valence band, integral of q(p - N^-_a), replace the total electron and hole charges in transit time equations. Another consequence is that considerably less hole charge is induced by the injected electron charge in the neutral base, which has implications on both device analysis and compact modeling.