Measurements and Numerical Calculations of Thermal Conductivity to Evaluate the Quality of \beta-Gallium Oxide Thin Films Grown on Sapphire and Silicon Carbide by Molecular Beam Epitaxy

TL;DR

This study combines experimental measurements and numerical modeling to evaluate and understand the thermal conductivity of eta-Ga2O3 thin films grown by MBE, highlighting the impact of defects on thermal performance.

Contribution

It introduces a comprehensive approach using TDTR, DFT, and Boltzmann transport calculations to analyze defect effects on thermal conductivity in eta-Ga2O3 thin films.

Findings

Experimental thermal conductivity is about one-third of perfect crystal predictions.

Defects like vacancies and stacking faults significantly reduce thermal conductivity.

Matching defect densities in models aligns calculations with experimental results.

Abstract

We report a method to obtain insights into lower thermal conductivity of \beta-Ga2O3 thin films grown by molecular beam epitaxy (MBE) on c-plane sapphire and 4H-SiC substrates. We compare experimental values against the numerical predictions to decipher the effect of boundary scattering and defects in thin-films. We used time domain thermoreflectance (TDTR) to perform the experiments, density functional theory and the Boltzmann transport equation for thermal conductivity calculations, and the diffuse mismatch model for TBC predictions. The experimental thermal conductivities were approximately 3 times smaller than those calculated for perfect Ga2O3 crystals of similar size. When considering the presence of grain boundaries, gallium and oxygen vacancies, and stacking faults in the calculations, the crystals that present around 1% of gallium vacancies and a density of stacking faults of 106 faults/cm were the ones whose thermal conductivities were closer to the experimental results. Our analysis suggests the level of different types of defects present in the Ga2O3 crystal that could be used to improve the quality of MBE-grown samples by reducing these defects and thereby produce materials with higher thermal conductivities.