Ultrasmall MOSFETs: the importance of the full Coulomb interaction on device characteristics

A novel scheme that accounts for the short-range Coulomb forces and prevents the double-counting of the long-range interaction is described in the context of three-dimensional (3-D) ensemble Monte Carlo particle-based simulations. It is shown that the inclusion of full Coulomb interactions strongly affects both the threshold voltage, the carrier dynamics and the resulting device characteristics. The proper treatment of the short-range Coulomb forces significantly reduces the distances over which thermalization of the carriers occurs in the drain region and leads to about a factor of two smaller on-state drain currents. The proposed scheme was successfully used to describe fluctuations in various device parameters due to the random dopant fluctuations. Correlation of device threshold voltage to the number of dopant atoms at a given depth showed that most dopant atoms have an impact on the threshold voltage, while only those in the top 8-10 nm affect the device velocity.