Revised analysis of the mobility and ION degradation in high-k gate stacks: surface optical phonons vs. remote Coulomb scattering

We use Multi-Subband Monte Carlo simulations to understand which mechanism is mainly responsible for the mobility degradation observed in nMOSFETs featuring high-k dielectrics. Direct comparison with the experimental data of Cassé et al. points out that for realistic interfacial layer thicknesses the effect of surface optical phonons on the mobility is very modest, and that the measured mobility reduction can be attributed to remote Coulomb scattering of charge in the gate-stack with concentrations in the order of 10^14 cm-2. We found that the drain current reduction in short channel devices is, instead, not as strong as the mobility reduction.