Copper-induced features in rocksalt NiO using ab initio calculations

Nickel oxide (NiO) is a transparent conducting oxide which has become an active area of research due to potential to be used in the next generation of Resistive RAM (RRAM) and Solar Cell devices. Doping N i1−xO with Cux has been shown to improve transparency and conductivity. The optical bandgap was experimentally found to decrease with increasing Cu concentration (from 3.2 to 2.96 eV, for x = 0% − 10%)[1]. Density Functional Theory (DFT) together with the VASP-PAW method based ab initio calculations to study the effects of substitutional Cu dopants into rocksalt NiO. Exchange-correlation effects included in the calculations within the generalized gradient approximation (GGA). To better describe d-orbitals of Ni and Cu a Hubbard potential U contribution was added (GGA+U). Results also considering a hybrid functional (HSE06) to treat exchange correlation are shown for pristine and Cu-doped systems. Doped NiO systems were studied using supercells grown along [111] direction of 32 and 108 atoms to simulate anti-ferromagnetic configurations. Concentrations of Cu of 1.85%, 3.70%, 6.25%, and 12.5% were investigated. Cu-induced trends in the stability and energetics of NiO are analyzed as a function of doping concentration.