Monte Carlo study of remote Coulomb and remote surface roughness scattering in nanoscale Ge PMOSFETs with ultrathin high-κ dielectrics

In this work we perform full-band Monte Carlo simulations of nanoscale Ge bulk PMOSFETs with ultrathin (<2 nm) effective oxide thickness high-κ dielectrics and investigate the importance of remote Coulomb and remote surface roughness scattering in these devices. In addition to these remote scattering mechanisms, transport is considered in the presence of phonon, ionized impurity, surface roughness scattering and impact ionization. Quantum confinement in the inversion layer is taken into account in the form of a modified potential. We show that the experimentally observed data on the dependence of mobility on the thickness of the high-κ dielectric can be accurately modeled via scattering by remote surface roughness at the gate-dielectric interface and remote Coulomb scattering due to fixed charges in the dielectric. The parameters in the remote scattering mechanisms are fitted by matching Monte Carlo data with those obtained from experiments on the dependence of mobility on the thickness of the dielectric. For a gate overdrive, (Vg − Vt), of 1.0 V, remote scattering mechanisms seem to decrease the saturation current by as much as 15% in these devices. We also show that at the high vertical fields (∼1 MV/cm) in these experimental devices, remote scattering mechanisms can substantially reduce the mobility for oxide thicknesses below 5 nm.