Paper accepted in Physical Review B

Our paper, “Controlling thermal conductance through quantum dot roughening at interfaces,” was just accepted into Physical Review B.  In this work, we control thermal transport across an Al/Si interface by patterning quantum dots on the Si surface to control the RMS roughness.  This work was done in collaboration with Jerry Floro’s group at U.Va.

Abstract

We examine the fundamental phonon mechanisms affecting the interfacial thermal conductance across a single layer of quantum dots (QDs) on a planar substrate. We synthesize a series of Ge_xSi_1-x QDs by heteroepitaxial self-assembly on Si surfaces and modify the growth conditions to provide QD layers with different RMS roughness levels in order to quantify the effects of roughness on thermal transport. We measure the thermal boundary conductance (h_K) with time-domain thermoreflectance. The trends in thermal boundary conductance show that the effect of the QDs on h_K are more apparent at elevated temperatures, where at low temperatures, the QD patterning does not drastically affect h_K. The functional dependence of h_K with RMS surface roughness reveals a trend that suggests that both vibrational mismatch and localized phonon scattering near the interface contribute to the reduction in h_K. We find that QD structures with RMS roughness greater than 4 nm decreases h_K at Si interfaces by a factor of 1.6. We develop an analytical model for phonon transport at rough interfaces based on a diffusive scattering assumption and phonon attenuation that describes the measured trends in h_K. This indicates that the observed reduction in thermal conductivity in SiGe quantum dot superlattices is primarily due to the increased physical roughness at the interfaces, which creates additional phonon resistive processes beyond the interfacial vibrational mismatch.