Stoichiometry-driven tuning of hole conductivity in MOCVD-grown β-Ga2O3 on r-sapphire substrates
Résumé
β-Ga2O3 is a promising ultra-wide bandgap semiconductor for next-generation power and optoelectronic devices, but achieving stable p-type conductivity remains a major challenge with limited understanding of native point defects engineering. In this work, we report a systematic study on the influence of Ga and O flow rate 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 fixed Ga content, and (ii) varying gallium content at 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 O/Ga flow ratio improves grain alignment, 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 6.0×10 13 to 1.7×10 15 cm -3 at 800 K. Interestingly, the improvement in hole mobility correlates with the increasing in Ga content (up to 18.5 cm 2 /V•s) at higher growth rate and improved grain alignment. These results demonstrate that reproducible control of stoichiometry and microstructure of β-Ga2O3 thin films grown by MOCVD provides a possibility to tune native-defect concentrations, thus electrical properties of material.
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