Thermal conductivity in Si/Ge and Si/SiGe superlattices

Silicon-germanium and silicon-germanium alloy-based superlattices show promise for application as efficient thermoelectrics because of their low thermal conductivity, below that of bulk Si_1-xGe_x alloys. In this paper, we demonstrate the sensitivity of the lattice thermal conductivity in Si/Ge and Si_1-xGe_x/Si_1-yGe_y superlattices to the interface properties, based on solving the phonon Boltzmann transport equation with partially diffusive scattering at the interfaces, captured by a momentum and direction-dependent interface specularity parameter. We demonstrate that scattering from the atomically imperfect interfaces that separate the layers of the superlattice plays a strong role in the lattice thermal conductivity, and that a competition exists between scattering from the partially diffuse interfaces and the internal scattering mechanisms, especially in alloy-based superlattices. Therefore, interface properties, such as roughness, orientation, and composition, are expected to play a significant role in thermal transport and they offer additional degrees of freedom to control the thermal conductivity in semiconductor nanostructures based on superlattices.