Coupled Monte Carlo-drift diffusion analysis of hot-electron effects in MOSFETs

A general method of calculating the substrate current for n-MOSFETs, using a two-dimensional conventional device simulator coupled with a full-band-structure Monte Carlo simulation, has been enhanced through the use of efficient estimators and statistical weighting of the high-energy electrons. The detailed physics of hot-electron effects in MOSFETs is explained on the basis of the energy distribution as a function of the spatial variables. Monte Carlo results show that the distribution function in the region of the device that makes the largest contribution to the substrate current does not fit a Maxwell-Boltzmann function. The effective cooling of the distribution, due in part to energy loss to impact ionization, is shown clearly. The results of the Monte Carlo calculation are used to evaluate the validity of the assumption of a constant mean path for inelastic scattering used in various analytic treatments. The calculated values of substrate current are compared to experimental results.>