# Unifying first principle theoretical predictions and experimental measurements of size effects on thermal transport in SiGe alloys

## TL;DR

This study combines first principles calculations and experimental measurements to accurately predict size effects on thermal conductivity in SiGe alloys, demonstrating a reliable framework for thermal transport analysis.

## Contribution

It introduces a unified approach linking DFT-based phonon properties with experimental TTG measurements to predict size effects in SiGe alloys.

## Key findings

- Theoretical predictions match experimental data within 25% reduction in thermal conductivity.
- The variational solution to the phonon BTE accurately models size effects.
- Agreement validated against Monte Carlo simulations.

## Abstract

In this work, we demonstrate the correspondence between first principle calculations and experimental measurements of size effects on thermal transport in SiGe alloys. Transient thermal grating (TTG) is used to measure the effective thermal conductivity. The virtual crystal approximation under the density functional theory (DFT) framework combined with impurity scattering is used to determine the phonon properties for the exact alloy composition of the measured samples. With these properties, classical size effects are calculated for the experimental geometry of reflection mode TTG using the recently-developed variational solution to the phonon Boltzmann transport equation (BTE), which is verified against established Monte Carlo simulations. We find agreement between theoretical predictions and experimental measurements in the reduction of thermal conductivity (as much as $\sim$ 25\% of the bulk value) across grating periods spanning one order of magnitude. This work provides a framework for the tabletop study of size effects on thermal transport.