Evolution of structural, optical properties and electrical transport of NiOX films annealed in different environment

Abstract

The influence of the annealing medium of thin films of nickel oxide (NiO_x) on structural, optical and electrical transport properties is studied in this paper. NiO_x films were synthesized by sol-gel method and annealed at a temperature of 300 °C in air, inert nitrogen (N₂), oxygen (O₂) gases and vacuum. The values of the films thickness were determined from the transverse cleavage of the SEM image. The films thickness depends on the annealing medium. Measurements of the EDX spectra of NiO_x films were carried out. Analysis of the quantitative O/Ni ratio showed that the film annealed in an air atmosphere is close to the stoichiometric parameters of NiO. Measurements of the EDX spectra of NiO_x films were carried out. According to the Raman spectra, an increase in peak intensities is observed indicating an increase in the density of defects in the film by Ni vacancies depending on the annealing medium. Absorption spectra and Tauc plots of NiO_х films were obtained. The optical density of the films depends on the annealing conditions of the films. Data analysis shows that the band gap width depends on the annealing medium and varies from Eg = 3.12 eV to Eg = 3.45 eV. The analysis of the impedance spectra allowed us to estimate the values of the resistances R₁ and R₂. It is shown that an increase in the resistance of R₁ is associated with a decrease in the density of defects in the NiO_x film, decrease in the recombination resistance of R₂, and an increase in recombination processes at the interface.