Grain boundary passivation and crystallographic reorientation in Ni and Ni–N co-doped CuCrO2 thin films: Enhancing electrical properties and NIR transparency via process–structure control

This work investigates the impact of synthesis parameters and nitrogen co-doping on the structural, optical, and electrical properties of Ni-doped CuCrO${}_2$ thin films, a promising p-type transparent conducting oxide. Ni-doped films were fabricated under varying sputtering conditions, followed by nitrogen annealing and co-doping to assess the role of nitrogen in tailoring film characteristics. Structural studies revealed that film orientation and crystallinity are strongly governed by sputtering power and gas pressure, while nitrogen annealing caused lattice expansion without phase change. Importantly, nitrogen co-doping induced preferential growth along a new crystallographic plane, attributed to altered adatom kinetics and selective surface passivation. EDX confirmed variable Ni diffusivity under nitrogen atmospheres. Electrical analysis showed that nitrogen annealing drastically reduced grain boundary potential barrier height (from 10.5 to 1.23 meV), boosting mobility to 11.12 cm${}^2$V⁻¹s⁻¹ at 300 K. In contrast, nitrogen co-doping preserved mobility but significantly increased carrier concentration, yielding the highest electrical conductivity of 9159 S/m among all samples. Optical studies revealed that transmittance in the near-infrared region was highly sensitive to sputtering conditions, with a maximum of 84.4% at 2000 nm. Nitrogen annealing slightly reduced transmittance without altering the band gap, whereas Ni–N co-doping triggered a Burstein–Moss shift, widening the band gap via carrier density enhancement. These results demonstrate the synergistic role of process tuning.