Beta-phase gallium oxide (β-Ga2O3), the most thermally stable phase of Ga2O3, has stimulated great interest in power electronics due to its ultra-wide bandgap (∼4.9 eV) and high breakdown electric field. The relatively low thermal conductivity of β-Ga2O3, however, limits the device performance due to excessive temperature driven by self-heating. Recently, integrating β-Ga2O3 thin films on substrates with high thermal conductivities has been proposed to improve heat rejection and device reliability. In this work, we prepare high-quality single-crystal β-Ga2O3 thin films by mechanical exfoliation of bulk crystals and study their thermal transport properties. Both the anisotropic thermal conductivity of β-Ga2O3 bulk crystals and the thickness-dependent thermal conductivity of β-Ga2O3 thin films are measured using the time-domain thermoreflectance technique. The reduction in the thin-film thermal conductivity, compared to the bulk value, can be well explained by the size effect resulting from the enhanced phonon-boundary scattering when the film thickness decreases. This work not only provides fundamental insight into the thermal transport mechanisms for high-quality β-Ga2O3 thin films but also facilitates the design and optimization of β-Ga2O3-based electronic devices.

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