Analysis of the effect of copper concentration on the structural, spectroscopic, and electrical properties of Cu:ZnO thin films

A detailed report on the investigation of structural, spectroscopic, and electrical properties of copper doped zinc oxide (CZO) thin films on the glass substrate is presented here. The spray pyrolysis technique was employed to prepare optimized ZnO thin films and copper (Cu) was added as the dopant with different concentrations. Structural properties of all samples were studied by analyzing the x-ray diffractogram (XRD) that showed a crystallite size around 40 nm. Zinc oxide (ZnO) films deposited at various Cu concentrations possess hexagonal crystal structure with (002) preferential orientation. At high copper concentrations, impurity peaks corresponding to copper were observed. Scanning electron micrographs (SEM) revealed good connectivity between the grains, along with the dense and uniform texturing on the surface. Absorbance spectra showed a red shift in absorption edge. A second band gap was observed at higher copper concentrations corresponding to the copper oxide (CuO) phase. Raman analysis with spatial imaging, x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) studies were carried out for all the samples, that showed the presence of copper secondary phase at high copper concentration. CZO films showed higher resistivity than pristine ZnO. However, resistivity decreased at a higher Cu level. Photosensitivity measurements showed a sensitivity of about 32.64 for 5 at% Cu doped ZnO films under white light. Photosensitivity of the material is attributed to the copper-related defect levels. (c) 2021 Elsevier B.V. All rights reserved.