Thermal boundary conductance across epitaxial ZnO/GaN interfaces: Assessment of phonon gas models and atomistic Green's function approaches for predicting interfacial phonon transport

TL;DR

This study measures the thermal boundary conductance of epitaxial ZnO/GaN interfaces from 77 to 500 K and critically assesses the accuracy of phonon gas models and atomistic Green's function methods in predicting interfacial phonon transport.

Contribution

It provides experimental data across a wide temperature range and evaluates the assumptions of existing theoretical models against these measurements.

Findings

TBC influenced by long wavelength, zone center modes at high temperatures

Discrepancies between models and experiments suggest inelastic scattering effects

Experimental TBC at room temperature is approximately 490 MW/m²K

Abstract

We present experimental measurements of the thermal boundary conductance (TBC) from $77 - 500$ K across isolated heteroepitaxially grown ZnO films on GaN substrates. These data provide an assessment of the assumptions that drive the phonon gas model-based diffuse mismatch models (DMM) and atomistic Green's function (AGF) formalisms for predicting TBC. Our measurements, when compared to previous experimental data, suggest that the TBC can be influenced by long wavelength, zone center modes in a material on one side of the interface as opposed to the "vibrational mismatch" concept assumed in the DMM; this disagreement is pronounced at high temperatures. At room temperature, we measure the ZnO/GaN TBC as $490\lbrack +150, -110\rbrack$ MW m$^{-2}$ K$^{-1}$. The disagreement among the DMM and AGF and the experimental data these elevated temperatures suggests a non-negligible contribution from additional modes contributing to TBC that not accounted for in the fundamental assumptions of these harmonic formalisms, such as inelastic scattering. Given the high quality of these ZnO/GaN interface, these results provide an invaluable critical and quantitive assessment of the accuracy of assumptions in the current state of the art of computational approaches for predicting the phonon TBC across interfaces.