Role of phonon scattering and bonding in resolving lattice thermal conductivity ambiguities of β-Ga2O3

Abstract

Understanding the lattice thermal conductivity (κ_l) of β-Ga₂O₃ is very intriguing owing to its advantages in high-voltage and high-temperature applications. Despite several attempts, the underlying mechanism and causes of the notable discrepancies found in the κ_l values of β-Ga₂O₃ along [100] and [001] directions calculated using first principles remained unresolved. We demonstrate that the understanding of the nature of chemical bonding is crucial to overcome the inconsistency in theoretically reported κ_l values. In low-symmetry structures such as β-Ga₂O₃, the nature of the interactions is primarily long-range; therefore, a sufficiently large supercell inclusive of various bonding characteristics is required to capture relevant phonon wavelengths. Bonding nature-aware structure modeling allows precise estimation of acoustic and optical mode contributions towards κ_l. Additionally, phonon mean free path analysis confirms that considering only third-order interaction terms is adequate to determine the κ_l of β-Ga₂O₃. The calculated κ_l values are in excellent agreement with experimentally reported values in all three directions. Our results establish that the bonding nature and its influence on phonon scattering are essential to consider in calculating κ_l accurately.