A Study of Phonon Transport in Si/Ge Superlattice Thin Films Using a Fast MC Solver

We employ a fast Monte Carlo solver, which takes advantage of the geometric symmetry existent in the system to reduce the computational effort, to investigate the phonon transport phenomena in the cross-plane and in-plane directions of Si/Ge superlattice thin films. The simulation results show that the heterogeneous interfaces perpendicular to the heat flow direction create a much stronger thermal resistance than the parallel ones. The cross-plane and in-plane thermal conductivities of a Si/Ge superlattice thin film increase monotonically with the smoothness of the interfaces and the superlattice period. Most of all, a minimum of the in-plane thermal conductivity is observed as the ratio of the layer thicknesses is varied for fixed period. This is due to the effective layer thermal conductivities being determined not only by the phonon intrinsic properties but also by the strong interface scattering. A detailed examination shows that the minimum appears when the effective layer thermal conductivities of the Si and Ge layers are about the same.