Optical and electrical properties of Ni-doped CdO thin films by ultrasonic spray pyrolysis

Transparent conducting oxides like ZnO, CuO and CdO have applications in photovoltaic solar cells and optoelectronic devices. Recently, much thin film work has investigated the characteristic properties of CdO films. In this work, Ni-doped CdO films in different concentration ratio were successfully deposited on soda lime glass (SLG) substrate using ultrasonic spray pyrolysis (USP) technique. The influence of 1, 2, 3, and 5% Ni concentrations in the films on the structural (orientations, D, ε_str), morphological (roughness value), optical (transmittance, energy band gap) and electrical properties (electrical conductivity, carrier concentration, Hall mobility) of the deposited CdO thin films was studied, respectively. X-ray diffraction (XRD) studies indicated that the obtained CdO films had good crystallinity and cubic phases with (111), (200), (220), (311), and (222) orientations with increasing Ni concentrations in the thin film. The optical energy band gap, E_g, was changed from 2.35 to 2.51 eV for wavelengths of 300–1100 nm for soda lime glass substrate. Atomic force microscopy showed the effect of the substrate temperature on the surface morphology and roughness of the obtained films. The roughness value of the obtained films decreased related to increasing of the Ni doped CdO films. Scanning electron microscopy showed nanostructure particles homogeneously distributed on the film surfaces. In addition, the electrical conductivity of the obtained films changed with various Ni concentrations like 0, 1, 2, 3 and 5 at.% in solution for increasing free carrier concentration.