Oxygen vacancy-driven interfacial alloying and mixing for enhanced heat transfer in gallium oxide

β-Gallium oxide (β-Ga₂O₃) is a superior material for power electronic applications due to ultra-wide bandgap and high critical field strength. The bottlenecking issue for its application lies in promoting heat dissipation and robust interfacial contact. Opposite to the common notion that a clean interface leads to high thermal conductivity, here we demonstrate an opposite strategy with alloying the interface for a significantly promoted heat conduction. Through sophisticated machine learning-powered molecular dynamics simulations coupled with comprehensive density functional theory analyses, we demonstrate that oxygen vacancies (V_O) serve as key facilitators of phonon coupling between β-Ga₂O₃ and Au layers. The phonon density of states and spectral heat current analyses unveil a remarkable mechanism: V_O catalyzes interfacial mixing due to inverted interfacial built-in electric field, generating an alloy-like transition region that effectively bridges the phonon mismatch and enables more efficient phonon transmission. Intermediate scattering function analysis reveals that while V_O maintains long-range structural integrity (at q = 0.51 Å⁻¹), it significantly modifies local atomic dynamics at shorter length scales. Our findings open new avenues for developing advanced heat dissipation strategies, offering crucial insights into the development of next-generation high-performance electronic systems.