X. Wang, J. Yang, P. Ying, Z. Fan, J. Zhang, H. Sun, Dissimilar thermal transport properties in κ-Ga2O3 and β-Ga2O3 revealed by homogeneous nonequilibrium molecular dynamics simulations using machine-learned potentials. Journal of Applied Physics 135, 065104 (2024).

The lattice thermal conductivity (LTC) of Ga$_2$O$_3$ is an important property due to the challenge in the thermal management of high-power devices. In this work, we develop machine-learned neuroevolution potentials (NEPs) for single-crystalline $\beta$-Ga$_2$O$_3$ and $\kappa$-Ga$_2$O$_3$, and demonstrate their accuracy in modeling thermal transport properties. Combining NEP-driven homogeneous non-equilibrium molecular dynamics (HNEMD) simulations with tensor analysis, we determine the spatial distributions of lattice thermal conductivities (LTCs) for two Ga$_2$O$_3$ crystals, showing dissimilar thermal behaviors. Specifically, $\beta$-Ga$_2$O$_3$ shows isotropic thermal transport properties, with the LTCs along [100], [010], and [001] directions being predicted to be \SI{10.3 \pm 0.2}{\watt\per\meter\per\kelvin}, \SI{19.9 \pm 0.2}{\watt\per\meter\per\kelvin}, and \SI{12.6 \pm 0.2}{\watt\per\meter\per\kelvin}, respectively, consistent with previous experimental measurements. For $\kappa$-Ga$_2$O$_3$, our predictions suggest nearly isotropic thermal transport properties, with the LTCs along [100], [010], and [001] being estimated to be \SI{4.5 \pm 0.1}{\watt\per\meter\per\kelvin}, \SI{3.9 \pm 0.1}{\watt\per\meter\per\kelvin}, and \SI{4.0 \pm 0.1}{\watt\per\meter\per\kelvin}. The reduced LTC of $\kappa$-Ga$_2$O$_3$ versus $\beta$-Ga$_2$O$_3$ stems from its restricted low-frequency phonons up to \SI{5}{\tera\hertz}. Furthermore, we find that the $\beta$ phase exhibits a typical temperature dependence slightly stronger than $\sim T^{-1}$, whereas the $\kappa$ phase shows a weaker temperature dependence, ranging from $\sim T^{-0.5}$ to $\sim T^{-0.7}$.

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