Understanding thermal transport at the nanoscale is crucial for developing nanostructured thermoelectric materials and managing heat in nanoelectronic devices. This dissertation focuses on thermal transport in SiGe-based superlattices. Initially, we studied the cross-plane thermal conductivity of SiGe superlattices by varying the thickness of Si(Ge) spacers. The additive nature of thermal resistance in SiGe nanodot/planar layers enables us to engineer thermal conductivity by adjusting the interface distance to approximately 1.5 nm. Ge surface segregation leads to Si-Ge intermixing, which is essential for achieving highly diffusive phonon scattering at the interfaces. By comparing the thermal conductivity of nanodot Ge/Si superlattices with different nanodot densities to those with only wetting layers, we found that the impact of nanodots is similar to that of planar wetting layers. This similarity arises from the shallow morphology and flattening of SiGe nanodots during Si overgrowth. Furthermore, experiments indicate that the interface effect on phonon transport can be diminished or eliminated by reducing interface distance or enhancing Si-Ge intermixing through post-growth annealing. The findings in this dissertation are expected to inform applications that require optimized thermal transport for effective heat management and the development of thermoelectric materials and devices utilizing superlattice structures.
