Surfons and the Electron Mobility in Silicon Inversion Layers

Abstract

Surfons are acoustic phonons in a body with surfaces, having both bulk and surface modes. To account for the electron mobility µ in Si inversion layers in the range of surface electron density Ns=(0.5∼5)×1012 cm-2 and temperature T=200∼300 K, scattering due to the surfon deformation potential is calculated. Qualitative features of the calculated mobility µcalc such as its dependence upon Ns and T, its variation with the surface orientation and its anisotropy agree with experiments. Quantitatively, however, µcalc is about three times as large as the values measured so far, when the estimated scattering by optical phonons is taken into account. The effect of the phonon reflection on the surface is about 15%. The theory uses the deformation potential constants and all the other parameters from bulk measurements. Some of these values could perhaps be different in the surface region, or the value of the mobility may become bigger as sample preparation techniques improve further so that the discrepancy may be less pronounced.