It is known that the InP Double Heterojunction Bipolar Transistors (DHBTs) may suffer from a current induced conduction band barrier at the base-collector heterojunction. This effect is known to "soften" the knee region of the Ic-Vce characteristics and is called the "soft knee effect". Available approaches to model the soft knee effect are at best approximate. In this project, the student should analyze the physical structure of the composite collector region found in InP DHBTs and develop a better description for the "soft knee effect". The outcome should be a compact model implemented in the commercial software tool "Advanced Design System". The developed compact model should be verified against measurements on large-signal circuits such as frequency multipliers and power amplifiers.