Impact of copper doping in NiO thin films deposited by spray pyrolysis on their physical properties

In this study, pure Cu-doped NiO thin films were deposited on glass substrates of soda lime by chemical spray pyrolysis. The effects of Cu-doping on the structural, optical, and electrical properties of the thin films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy with energy dispersive X-ray analyzer (FE-SEM–EDX), atomic force microscopy (AFM), ultraviolet–visible spectroscopy, and electrical resistance; van der Pauw techniques were also used to measure the Hall effect. Studies on X-ray diffraction showed that the films contained only one nickel oxide phase and were polycrystalline in a cubic crystal structure with preferred orientations along (111). Other orientations were along the (200) and (220) planes. In general, the FE-SEM and AFM images also showed that as Cu-doping increased, the grain size and surface roughness of the thin films decreased. The expected elemental compositions were confirmed by EDX. In the Raman spectra of the thin films, there were two peaks at 530 cm−1 and 1100 cm−1 that confirmed the presence of NiO on the films. The optical bandgap of the thin films decreased from 3.09 to 2.21 eV as Cu-dopant increased. As the Cu-doping concentration increased from 0 to 0.16 (at.%), the electrical resistance, carrier mobility, and activation energy decreased from 1.88 × 103 to 430 Ω.cm, 18.1 to 4.9 cm2/v.s, and 0.245 to 0.203 eV, respectively; conversely, the carrier concentration increased from 1.84 × 1014 to 29.64 × 1014. Hall effect studies showed that the films exhibited p-type conductivity.