Significant phonon localization and suppressed transport in silicon-doped gallium oxide: A study using a unified neural network interatomic potential

Monoclinic gallium oxide (β-Ga₂O₃) is a fourth-generation semiconductor with great application potential in high-power microelectronics. Recent studies indicate that the electrical conductivity of β-Ga₂O₃ can be substantially enhanced through silicon (Si) doping. However, the effects on thermal transport, especially by considering the practical nanostructures within the crystal, have not yet been explored. To address this gap, we have developed a unified neural network potential for investigating the unexplored phonon transport of the β-(Si_xGa_1–x)₂O₃ with varying doping levels. Our atomistic simulations showed that compared to intrinsic β-Ga₂O₃, the room-temperature thermal conductivities respectively decreased by 36.5%, 33.5%, and 38.8% along the a, b, and c axes in β-SiGa₅₁₁O₇₆₈, and by 79.6%, 74.9%, and 77.8% in β-SiGa₇O₁₂. The significant degradation in phonon transport is attributed to increased lattice anharmonicity, reduced sound velocity, and most importantly, induced phonon localization due to Si substitutions. A quantitative analysis reveals that the localization primarily occurs in phonons with frequencies exceeding 2.5 THz. The vibration is confined to a region around the Si atom, extending only to its second-nearest neighbors.