Nonequilibrium electron transport in HBTs

Nonequilibrium electron transport in heterojunction bipolar transistors (HBTs) becomes clearly observable as their vertical dimensions are reduced, This is the reason for the superior tradeoff relationships between the device parameters and the resultant high-speed performance of HBTs fabricated with III-V semiconductor materials. This paper reviews the hot carrier effect in the base and the velocity overshoot effect in the collector and discusses the roles these effects play in reducing carrier traveling times and improving device performance.