The impact of In doping on the parameters of ZnO films has been studied. Film structure, emission, and evolution of O- and In-related defects versus In contents have been investigated using Raman scattering, photoluminescence (PL), x-ray diffraction, and high-resolution x-ray photoelectron spectroscopy (HR-XPS). Three stages of the variation of optical and structural parameters of ZnO films at In doping were detected. The formation of In-related point defects is connected with the first two stages, which is accompanied by improving the ZnO crystal structure, the insignificant changes of Raman scattering spectra, and the intensity increases of high energy emission bands. At the third stage of In doping, the intensities of Raman peaks and PL bands decrease owing to the formation of In-related nanoclusters and O-related defects. To analyze the In-related defects, HR-XPS was monitored for the lines (i) In 3d3/2 and In3d5/2, and (ii) In4d3/2 and In4d5/2 in In-doped ZnO thin films. The trend in the change of the In ion charges versus In contents has been revealed and discussed.

The study of wide-bandgap nanomaterials has gained considerable attention in recent years, especially in the case of semiconductor oxides that exhibit full or partial optical transparency in fundamental research and technological applications. These include optoelectronic devices, gas sensors and photovoltaic cells, among others. The activation or adjustment of optical and structural properties, especially the bandgap and the parameters of unit cell lattice, can be achieved by varying the dopant concentration during the synthesis of semiconductor thin films in these applications. In this context, copper oxide has emerged as a valuable material, owing to its thoroughly analyzed structural behavior and its broad potential across multiple technological fields. The present work focuses on the synthesis of zinc-doped copper oxide (Zn_xCu_1−xO) thin films on silicon and quartz substrates through ultrasonic spray pyrolysis. The effects of varying the zinc doping concentration (0.0, 5.0, 10.0 and 20.0 at. %) on the morphological, structural, and optical characteristics of the Zn_xCu_1−xO films were analyzed. Scanning electron microscopy (SEM) analysis indicated a gradual increase in nanoparticle size, rising from 221 nm for CuO to approximately 322 nm for the Zn_0.2Cu_0.8O samples as the zinc content increased. Structural characterization via X-ray diffraction (XRD) confirmed a monoclinic crystal arrangement belonging to the $C_{2h}^6$ (c2/c) space group. As the percentage of zinc increased, the XRD peaks shifted to lower angles, consequently increasing the volume and crystal lattice parameters of the Zn_xCu_1−xO structure; this finding was additionally supported by a redshift observed in the Raman analysis. The transmittance spectra of the films showed low transmittance between 40 and 44%. The optical bandgap of the Zn_xCu_1−xO thin films was estimated from the transmittance data by applying the Tauc plot method. A decrease in the band gap was observed at higher doping concentrations. It can be confirmed that no secondary phases are observed at a doping level of 20.0 at. % of zinc, indicating good solubility of zinc in CuO. The analysis and discussion of these findings are included throughout this work to elucidate the controversies noted in the literature.