Generalized diffusion, mobility, and the velocity autocorrelation function for high-field transport in semiconductors

A general study of the velocity autocorrelation function for high electric field transport in Si is presented. Calculations have been carried out using a Monte Carlo technique for calculating the transport parameters. Additionally, a generalized model for defining diffusion and mobility in terms of a transport equation is presented. A detailed Shockley model is used to evaluate these equations for the velocity autocorrelation function. It is found that f′(t) initially relaxes exponentially, due to momentum relaxation, goes negative and displays a local minimum, then relaxes to zero at a slower rate due to energy relaxation.