This is a continuation of the research program at the University of Massachusetts on the computer modeling of advanced semiconductor devices. A specific objective is to extend the state-of-the-art of the numerical modeling of heterojunction semiconductor devices for high speed and/or high frequency applications. Over the past twelve years, we have modeled semiconductor devices ranging from large VMOS power transistors to submicron permeable base transistors (PBT) in our laboratory. In view of recent interest in high speed heterojunction transistors such as HEMT (high electron mobility transistors) and HBT (heterojunction bipolar transistors), it is natural to extend our research to the modeling of semiconductor devices involving heterojunctions. Focus will be placed on the AlGaAs/GaAs system but the InGaP/GaAs heterojunction and the InGaAs/GaAs strained-layer heterojunction may be included as well, time permitting. The basic heterojunction GaAs structures to be modeled are vertical devices such as HBTs. Hot carrier transport in the graded base region of these devices will be investigated. Both transient and small-signal ac drift-diffusion analysis will be performed to accurately determine the unit-current gain cutoff frequency.
