Atomistic modeling of anharmonic phonon-phonon scattering in nanowires

Abstract

Phonon transport is simulated in ultrascaled nanowires in the presence of anharmonic phonon-phonon scattering. A modified valence-force-field model containing four types of bond deformation is employed to describe the phonon band structure. The inclusion of five additional bond deformation potentials allows us to account for anharmonic effects. Phonon-phonon interactions are introduced through inelastic scattering self-energies solved in the self-consistent Born approximation in the nonequilibrium Green's function formalism. After calibrating the model with experimental data, the thermal current, resistance, and conductivity of $\ensuremath{\langle}100\ensuremath{\rangle}$-, $\ensuremath{\langle}110\ensuremath{\rangle}$-, and $\ensuremath{\langle}111\ensuremath{\rangle}$-oriented Si nanowires with different lengths and temperatures are investigated in the presence of anharmonic phonon-phonon scattering and compared to their ballistic limit. It is found that all the simulated thermal currents exhibit a peak at temperatures around 200 K if phonon scattering is turned on while they monotonically increase when this effect is neglected. Finally, phonon transport through Si-Ge-Si nanowires is considered.