The dependence of the electron mobility on the longitudinal electric field in MOSFETs

The dependence of the electron mobility on the longitudinal electric field in MOSFETs has been studied in detail. To do so, a Monte Carlo simulation of the electron dynamics in the channel, coupled with a solution of the two-dimensional Poisson equation including inversion-layer quantization and drift-diffusion equations, has been developed. A simplified description of the silicon band structure in the effective-mass approximation including non-parabolicity has been considered. Different-channel-length MOSFETs and different biases have been taken into account. It has been shown that in order to accurately describe electron-mobility behaviour in short-channel MOSFETs it is necessary to take into account the electron-velocity overshoot. An analytical expression, easy to include in device simulators, is provided to account for the dependence of the electron mobility on the high values of the longitudinal electric field and of its gradient found in state-of-the-art MOSFETs.