Remotely screened electron-impurity scattering model for nanoscale MOSFETs

The ionized impurities within the channel of nanoscale MOSFETs are shown to be strongly remotely screened by the close proximity of the highly doped, degenerate source and drain regions due to polarization charge effects. The position of the ionized impurity within the channel region controls the strength of the remote screening due to polarization charges induced in the source and drain, which increase heavily as the channel screening length exceeds the channel length. A remotely screened ionized impurity scattering potential is calculated based on an exact solution to Poisson's equation for a model system. This scattering potential includes the polarization charge effects from the source and the drain which may contribute separately or in combination depending on the position of the ionized impurity and the channel screening length. A scattering model is developed based on a simplified form of this scattering potential that is suitable for use in Monte Carlo simulations. The resulting scattering model is analysed and is shown to increase the ionized impurity mobility in the channel by a noticeable amount.