Electron dynamics in short channel field-effect transistors

The dynamics of electrons between the source and drain of a microwave field-effect transistor (FET) have been studied using a Monte Carlo method. The spatial dependence as well as the time dependence of the average electron velocity is presented. It is shown that in silicon the relaxation time is short enough not to influence the figure of merit of the transistor. However, in direct gap polar semiconductors (e.g., GaAs), the electrons can have a velocity well above their saturation value for an appreciable length of time and, consequently, over a distance nonnegligible compared to the length of the active region of a high frequency FET. This could improve the figure of merit of the FET.