Van der Waals β-Ga₂O₃ thin films on polycrystalline diamond substrates

The self-heating effect in wide bandgap semiconductor devices makes epitaxial Ga₂O₃ on diamond substrates crucial for thermal management. However, the lack of wafer-scale single-crystal diamond and severe lattice mismatch limit its industrial application. This study presents van der Waals β-Ga₂O₃ (VdW-β-Ga₂O₃) grown on high-thermal-conductivity polycrystalline diamond. VdW forces modify the coupling state between the single-crystal thin film and polycrystalline substrate. Tunable growth of ( $\overline{2}01$ ) VdW-β-Ga₂O₃ is achieved by leveraging the mismatch between graphene and the oxygen surface densities of varying crystal orientations and their oxygen-partial-pressure dependence. The 350 nm thick, high-crystallinity films exhibit a smallest rocking curve FWHM value of 0.18° and a root mean square roughness of 6.71 nm. Graphene alleviated interfacial thermal expansion stress; β-Ga₂O₃/diamond interface exhibits an ultralow thermal boundary resistance of 2.82 m²·K/GW. Photodetectors exhibit a photo-to-dark current ratio of 10⁶ and a responsivity of 210 A/W, confirming the strategy's practicality and technological significance.