We investigate the role of two main scattering mechanisms responsible for mobility degradation in ultrashort electron devices like silicon-nanowire FETs. We consider electron-phonon interaction and surface roughness (SR) at the Si/SiO(2) interface as sources of inelastic and elastic scatterings. We address a full-quantum treatment within the nonequilibrium Green's function formalism, which allows us to take quantum confinement, quantum-phase interference, out of equilibrium, and quasi-ballistic transport into account. Our results show that both phonon- and SR-limited mobilities strongly depend on the channel length due to the importance of nonuniform scattering in ultrashort devices and contribute to understand the strong mobility reduction of decananometric devices.
