Impeded thermal transport in composition graded SiGe nanowires

Abstract

Composition graded nanowires (NWs) have attracted increasing research interest in the application of optoelectronic devices, due to their graded bandgaps caused by the changing composition. However, the thermal transport property of composition graded NWs is not clear, which is critical for their potential applications in electronics and thermoelectrics. In this Letter taking SiGe NW as an example, we explore the thermal transport property of composition graded NWs. Molecular dynamics simulations reveal that the thermal conductivities (κ) of the composition graded SiGe NWs can be reduced up to 57% compared with that of the corresponding SiGe NW with abrupt interfaces. The κ reduction stems from the shortening of phonon mean free paths due to the inhomogeneous composition distributions. The phonon wave packet propagation analysis reveals that the composition gradient can reflect more than 70% of the wave packet energy, and phonon localization is observed in the composition graded region. Our findings suggest a promising prospect of composition graded NWs in the use of thermoelectrics and high temperature coatings, where low thermal conductivity is expected.