Phonon-hopping thermal conduction in quantum dot superlattices

We investigated the thermal conductivity in Ge∕Si quantum dot superlattices both theoretically and experimentally. It is proposed that thermal conduction through the quantum dot superlattices can be described by the phonon-hopping model with the interface transparency obtained from the experiment. Thermal conductivity has been measured as a function of temperature T from 10K to 400K. We have observed an order of magnitude decrease in thermal conductivity value compared to bulk and shift of its peak position to higher temperatures. The thermal conductivity manifests T0.7-T0.9 dependence for T⩽200K. The phonon-hopping model describes the measured thermal conductivity surprisingly well over the wide range of T from ∼40Kto400K. The model allows one to include the specifics of thermal conduction in quantum dot superlattices, such as the dot size, disorder, and interface quality. Our results suggest that the examined quantum dot superlattices are closer to the disordered or polycrystalline materials in terms of thermal transport.