Charge transition levels and stability of Ni- and Ir-doped β-Ga₂O₃: a comprehensive hybrid functional study

In this study, the optimized hybrid functional HSE(0.26,0.0) is employed to investigate the incorporation of nickel (Ni) and iridium (Ir) dopants in β-Ga₂O₃. The formation energies and charge transition levels of Ni and Ir at gallium sites are calculated. The results show that Ni prefers substitution at the octahedral (Ga₂) site, with a formation energy approximately 1 eV lower than at the tetrahedral (Ga₁) site. Ni at the Ga₂ site (Ni_Ga ) exhibits both donor and acceptor behaviors, with charge transition levels at (+1/0) 1.0 eV and (0/-1) 2.24 eV above the VBM, respectively. Ir similarly favors the octahedral site, displaying donor behaviors with charge transition levels at (+2/+1) 1.04 eV and (+1/0) 3.15 eV above the VBM. Our computational findings for the charge transition levels of Ni and Ir ions are in good agreement with recent experimental measurements, and they explain the correlation between Ni³⁺ and Ir⁴⁺ ion concentrations observed in electron paramagnetic resonance studies. Additionally, the calculated vertical transitions at 2.56 eV and 4.25 eV for Ni_Ga , and at 2.91 eV and 4.62 eV for Ir_Ga , below the conduction band minimum, are in good agreement with optical absorption results, confirming the presence of Ni and Ir substitutions at the Ga₂ site in β-Ga₂O₃. These computational results provide a detailed understanding of the behavior of Ni- and Ir-doped β-Ga₂O₃, highlighting the potential applications of Ni- and Ir-doped β-Ga₂O₃ for optoelectronic devices.