Theoretical and experimental investigations of the effect of cobalt doping on the structural, optical and electrical properties of sputtered NiO films for optoelectronic applications

Abstract

Nickel oxide material is considered an interesting class of p-transparent-conductive oxides for various fields of application. Improving the conductivity of these materials while retaining a high level of optical transmittance is considered a real challenge for their functional use. In the present work, a detailed study of the effect of cobalt incorporation on NiO thin films is reported. The films were deposited onto the glass substrates using radio frequency (RF) sputtering without annealing or post-annealing process. Various techniques of characterization were used. The X-ray diffraction (XRD) analyses show one clear peak of (200) plane, typical of the cubic structure of NiO, with an expansion of the lattice parameter and a decrease of the crystallinity as the substitution of Ni by Co increases. Raman spectroscopy confirms the result by the presence of the strong peak at 551 cm−1. The high transmittance and optical gap of NiO were retained and have not affected by Co-doping. The refractive index (n) calculated from various models shows a slight increase in n values with increasing Co/Ni ratio. The electrical measurements show an enhancement of the conductivity by Co-doping. The obtained results were compared and enriched with the theoretical calculation (DFT) using the GGA + U approximation.