Unraveling the role of oxygen vacancies in the electronic and optical properties of κ-Ga2O3

Oxygen vacancies are regarded as crucial defects greatly affecting the electronic and optical properties of oxide films and devices, yet systematic studies on k-Ga2O3 are still lacking. Herein, we investigate the thermodynamic, electronic, and optical properties of oxygen vacancies in k-Ga2O3 using density functional theory calculations with the hybrid functional. The electronic structure reveals that oxygen vacancies create a deep donor defect in the bandgap, with defect levels and transition energies influenced by Ga atom displacement and localized electron dynamics. This correlation links the stability of oxygen vacancies at specific sites and the contribution of oxygen orbitals to charge density at the valence band maximum with the microscopic origins of experimental defect levels in oxygen vacancy states. Oxygen defects give rise to additional peaks in the lower energy ultraviolet regions of the absorption and electron energy loss spectra, consistent with earlier experimental studies. Our results elucidate the nature of oxygen vacancies, and offering a foundation for tuning and optimizing the electrical and optical properties of κ-Ga2O3 films and improving device performance through defect engineering.