Comprehensive study of β-Ga₂O₃ epitaxial growth using a variable closed-coupled showerhead MOCVD reactor

β-Ga₂O₃ is a highly promising ultrawide bandgap semiconductor material that is poised to transform the high-power electronics field. The manufacturability of device quality β-Ga₂O₃ epitaxial films at scale is urgently needed. Using a production-ready closed-coupled showerhead MOCVD reactor with in situ reflectance monitoring, this study presents a detailed investigation of the impact of growth parameters on the epitaxial growth of β-Ga₂O₃ on both (010) and (001) oriented native substrates, as well as on c-plane sapphire substrates with 0°-8° off-axis orientations. By tuning the showerhead-susceptor gap and mapping the other growth parameters, including annealing, nucleation, growth temperature, reactor pressure, and substrate orientation, we achieved state-of-the-art crystal quality, extraordinary wafer-level thickness uniformity of <1% variation for both 2-in. and 4-in. substrates for growth rates as high as 7.2 μm/h. All growth was performed using TMGa and pure O₂ as the precursors and N₂ as the carrier gas instead of the more widely used argon; no detectable nitrogen and carbon incorporation was observed by secondary ion mass spectrometry. For the homoepitaxy of Si-doped β-Ga₂O₃ films on (010) substrates, a room temperature Hall mobility of 148 cm²/V s was achieved at a carrier concentration of 1.26 × 10¹⁷ cm⁻³, with a growth rate of 2.6 μm/h. For the heteroepitaxy on sapphire, off-axis substrates exhibited enhanced crystallinity, as shown by the continued reduction of x-ray diffraction rocking curve full width at half maximum from 2834 to 1300 arcsec for 0° and 8° offcut sapphire substrates, respectively. The results demonstrate the scalability and potential advantages of this reactor design for manufacturing-scale β-Ga₂O₃ growth and offer new insights into the controllability of uniform high-quality films for power electronics applications.