Kirk effect mechanism in type-II InP∕GaAsSb double heterojunction bipolar transistors

Abstract

The Kirk effect mechanism is studied in type-II InP∕GaAsSb∕InP NpN double heterojunction bipolar transistors (DHBTs) both experimentally and through two-dimensional hydrodynamic numerical simulations. We show that the large valence band discontinuity ΔEV at the GaAsSb–InP base∕collector heterojunction does not allow hole injection into the InP collector as is the case in homojunction collectors. Instead, a blocking barrier is electrostatically induced in the base layer at high collector current densities: this barrier increases base recombination and decreases the current gain. We show that tunneling transport must be considered at the base∕collector heterojunction and that the induced barrier depends on the base layer doping level—effectively, InP∕GaAsSb DHBTs display high-current limitations that are also controlled to some extent by the base doping level.