The anisotropic thermal conductivity and the phonon mean free path (mfp) in monoclinic β-Ga2O3 single crystals and homoepitaxial films of several μm were determined using the 3ω-method in the temperature range from 10K-300 K. The measured effective thermal conductivity of both, single crystal and homoepitaxial films are in the order of 20 W/(mK) at room temperature, below 30 K it increases with a maximum of 1000 to 2000 W/(mK) and decreases with T3 below 25 K. Analysis of the phonon mfp shows a dominance of phonon-phonon-Umklapp scattering above 80 K, below which the influence of point-defect scattering is observed. Below 30 K the phonon mfp increases until it is limited by the total β-Ga2O3 sample size. A crossover from resistive to ballistic phonon transport is observed below 20 K and boundary effects of the total sample size become dominant. This reveals that the homoepitaxial film-substrate interface is highly phonon-transparent. The resistive and ballistic phonon transport regimes in β-Ga2O3 are discussed corresponding to the models of Callaway and Majumdar, respectively.
@article{arxiv.2403.11341,
title = {Resistive and ballistic phonon transport in $\beta$-Ga$_2$O$_3$},
author = {R. Ahrling and R. Mitdank and A. Popp and J. Rehm and A. Akhtar and Z. Galazka and S. F. Fischer},
journal= {arXiv preprint arXiv:2403.11341},
year = {2025}
}