Effects of potassium incorporation on the structural, optical, vibrational and electrical properties of NiO sprayed thin films for p-type optical windows

Nickel oxide thin films were deposited on glass substrates by a simple mini spray technique at 460 degrees C. Alternatively, some of the obtained films were doped with potassium at the molar rates of: 1, 2 and 3% (K). In addition to the classical structural investigations including XRD, the opto-thermal studies, Raman spectroscopy and photoluminescence measurements were investigated. First, structural study by means of X-ray diffraction shows that all K-doped NiO thin films crystallized in cubic space group with some noticeable changes in terms of [K]/[Ni] ratio. In the same line, Raman spectroscopy reveals the principal NiO vibration's mode with the shift related to K incorporation in NiO matrix. Second, some optical parameters, such as optical band gap, Urbach energy, refractive indices extinction coefficients and dielectric constant were studied in terms of K doping level. For all NiO:K prepared thin films, PL measurements show three large bands located at 405, 420, 485 and 529 nm. Furthermore, electrical properties were performed using impedance spectroscopy technique in the frequency range 5 Hz-13 MHz at various temperatures. DC conductivity is thermally activated showing a semiconductor behavior of NiO:K sprayed thin films. This study shows that the electrical conductivity is thermally activated. The calculated values of the activation energy show semiconductor behavior of such films. On the other hand AC conductivity is investigated through Jonscher law. The imaginary part of the complex impedance has a maximum whose relaxation frequency increases with temperature according to Arrhenius law. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.