Stoichiometry-Driven Tuning of Hole Conductivity in MOCVD-Grown β <i>-</i> Ga ₂ O ₃ on <i>r-</i> Sapphire Substrates

β-Ga2O3 is a promising ultrawide-band-gap semiconductor for next-generation power and optoelectronic devices, but achieving stable p-type conductivity remains a major challenge with the limited understanding of native point defects engineering. In this work, we report a systematic study on the influence of Ga and O flow rates during MOCVD growth on the structural and electrical properties of undoped β-Ga2O3 epilayers. Two sets of samples were grown: (i) varying oxygen content to span O/Ga ≈ 180–2700 at a fixed Ga content and (ii) varying gallium content at a fixed O/Ga = 1600. Structural characterization using out-of-plane and in-plane high-resolution X-ray diffraction, Raman spectroscopy, and scanning electron microscopy revealed a strong correlation between growth conditions and film microstructure. Increasing the O/Ga flow ratio improves grain alignment and reduces lattice disorder. Hall effect measurements show the semi-insulating p-type conductivity in all samples, with enhancement of native p-type conductivity in oxygen-rich conditions, increasing the hole concentration from 6.0 × 1013 to 1.7 × 1015 cm–3 at 800 K. Interestingly, the improvement in hole mobility correlates with the increase in Ga content (up to 18.5 cm2/V·s) at higher growth rate and improved grain alignment. These results demonstrate that the reproducible control of stoichiometry and microstructure of β-Ga2O3 thin films grown by MOCVD provides a possibility to tune native-defect concentrations and thus electrical properties of a material.