Modeling Base-Collector Heterojunction Barrier Effect in InP DHBTs for Improved Large Signal Performance

In this paper, the large-signal model of InP double heterojunction bipolar transistors (DHBTs) is improved by modeling the soft-knee effect. The soft-knee effect in the DHBTs is explained by the quasi-ballistic transport of electrons at the base-collector (BC) junction due to the barrier's influence. The energy barrier experienced by the electrons will decrease as the electrons start acquiring ballistic transport properties over the BC junction. These effects at BC junction are verified by technology computer-aided design (TCAD) simulations and Gummel plot measurements. It is proposed to model these effects by introducing a modified normalized base charge (qb) function in the FBH HBT model. The modified model is in good agreement with the measured I-V and large-signal measurement for 0.5 ×5.6 m
²
(emitter area) transferred-substrate (TS) InP DHBTs at 94 GHz.