Long-range Coulomb interactions in small Si devices. Part II. Effective electron mobility in thin-oxide structures

In metal–oxide–semiconductor structures with polycrystalline Si gates, electrons in the inverted channel of the substrate scatter with electrons in the gate via long-range Coulomb interactions. For thin oxides, these interactions can cause a significant transfer of momentum from the channel to the gate, thus reducing the effective mobility of the two-dimensional electron gas in the substrate. We present calculations of the dispersion of the interface plasmons in poly-Si/SiO2/Si structures, comparing the results obtained in the long-wavelength limit to those obtained using the random-phase approximation. Employing the former model, we compute the effect of plasmon scattering on the effective electron mobility in Si inversion layers. We find a significant reduction of the mobility for oxides thinner than about 3 nm.