Reduce thermal conductivity by forming a nano-phononic crystal on a Si slab

Abstract

Due to the strong interaction with phonons, nano-phononic crystals (NPC) have attracted much consideration in the study of novel thermoelectric materials. Using a long wavelength approximation, we demonstrate that the dispersions of phonons in NPC can be extracted from the corresponding elastic wave dispersion. A modified plane-wave expansion method is utilized to calculate the dispersion of phonons in Si-based NPC with mesoscopic holes for nearly the entire spectrum. In addition, the Callaway-Holland model is used to analyze the thermal transportation properties of such Si-based NPC. We show more than fifty times reduction of thermal conductivity in NPCs compared with that in bulk silicon, which results in a considerable improvement in the thermoelectrical efficiency. We attribute the remarkable reduction in thermal conductivity to the participation of both coherent and incoherent scatterings of phonons.