Role of local structure in the optical and electronic properties of oxygen vacancies in different crystal phases of Ga2O3

Abstract

We investigate the structural, electronic, and optical properties of oxygen vacancies (${\mathrm{V}}_{\mathrm{O}}$) in crystalline $\alpha , \beta$, and $\epsilon \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ using density functional theory (DFT) calculations with the PBE0-TC-LRC functional. Our results reveal that the charge transition levels (CTLs) associated with ${\mathrm{V}}_{\mathrm{O}}$ exhibit significant variations depending on the crystal phase and the coordination environment of surrounding atoms. In particular, ${\mathrm{V}}_{\mathrm{O}}\mathrm{s}$ surrounded by tetrahedral Ga atoms ($T\text{-Ga}$) exhibit deeper CTLs compared to those surrounded by octahedral Ga atoms ($O\text{-Ga}$). We also observe distinct atomic relaxations, with larger displacements of $T\text{-Ga}$ atoms compared to $O\text{-Ga}$ atoms in the vicinity of ${\mathrm{V}}_{\mathrm{O}}\mathrm{s}$. Using linear-response time-dependent DFT, we investigate the optical transitions of ${\mathrm{V}}_{\mathrm{O}}$ and identify two distinct types of transitions: defect state to conduction band state and valence band to defect state. These results can be used to better understand the optical properties of ${\mathrm{V}}_{\mathrm{O}}$ defects in ${\mathrm{Ga}}_2{\mathrm{O}}_3$ films.