Impact of Ni and O vacancies on the electronic properties of NiO: A DFT-based study for optoelectronic applications

We present a comprehensive investigation of the impact of Ni and O vacancies on the properties of NiO by employing density functional theory (DFT) and comparing the theoretical predictions with experimental cathodoluminescence data. While B3LYP, HSE06, or HSEsol functionals yield results within the experimental range, we chose B3LYP due to its reliable accuracy and lower computational cost compared to the more complex Hartree–Fock exchange treatment. Our analysis highlights the effectiveness of the B3LYP hybrid functional in reproducing both the experimental lattice constant and the bandgap, reflecting the importance of strong correlation effects in transition metal oxides. We explore the vacancy defects of NiO, revealing that Ni vacancies introduce distinct intra bandgap states whose energy levels can be modulated through defect concentration. In contrast, O vacancies exhibit donor-like characteristics, enhancing n-type conductivity. These defects significantly alter local magnetic moments, revealing a complex interplay between spin and charge dynamics. These findings provide valuable insights into defect engineering strategies aimed at optimizing NiO for advanced applications in optoelectronics. This study also contributes to the broader understanding of transition metal oxides, showcasing the utility of advanced DFT techniques in accurately modeling their properties.