Study of a 50-nm nMOSFET by ensemble Monte Carlo simulation including a new approach to surface roughness and impurity scattering in the Si inversion layer

A 50-nm nMOSFET has been studied by Ensemble Monte Carlo (EMC) simulation including a novel physical model for the treatment of surface roughness and impurity scattering in the Si inversion layer. In this model, we use a bulk-like phonon and impurity scattering model and surface-roughness scattering in the silicon inversion layer, coupled with the effective/smoothed potential approach to account for space quantization effects. This approach does not require a self-consistent solution of Schrödinger equation. A thorough account of how these scattering mechanisms affect the transport transient response and steady-state regime in a 50-nm gate-length nMOSFET is given in this paper. A set of I_ds-V_ds curves for the transistor is shown. We find that the smoothing of the potential to account for quantum effects has a strong impact on the electron transport properties, both in transient and steady-state regimes. We also show results for the impact that impurity and surface-roughness scattering mechanisms have on the average velocity of the carriers in the channel and the current flowing through the device. It was found that time-scales as short as 0.1-0.2 ps are enough to reach a steady-state channel electron average velocity.