| Summary: | First-principles density functional theory (DFT) is employed to study the electronic structure of oxygen and gallium vacancies in monoclinic bulk β-Ga<sub>2</sub>O<sub>3</sub> crystals. Hybrid exchange–correlation functional B3LYP within the density functional theory and supercell approach were successfully used to simulate isolated point defects in β-Ga<sub>2</sub>O<sub>3</sub>. Based on the results of our calculations, we predict that an oxygen vacancy in β-Ga<sub>2</sub>O<sub>3</sub> is a deep donor defect which cannot be an effective source of electrons and, thus, is not responsible for n-type conductivity in β-Ga<sub>2</sub>O<sub>3</sub>. On the other hand, all types of charge states of gallium vacancies are sufficiently deep acceptors with transition levels more than 1.5 eV above the valence band of the crystal. Due to high formation energy of above 10 eV, they cannot be considered as a source of p-type conductivity in β-Ga<sub>2</sub>O<sub>3</sub>.
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