Sol-gel synthesis of Si-ZnO, Ti-ZnO and Si-Ti-ZnO thin films: Impact of Si and Ti content on structural and optical properties

In this study, Ti and Si doped ZnO thin films were fabricated on glass substrates using the sol-gel spin coating method. The structural and optical properties of Si-ZnO, Ti-ZnO, and Si-Ti-ZnO thin films were investigated using XRD, SEM, UV-Vis, Photoluminescence (PL), FTIR, and Raman spectroscopy. SEM microstructure examinations showed that the surface morphology of all thin-film samples consisted of ZnO fiber structures, and the thickness of the thin films on the glass substrate increased with Ti content. XRD patterns of thin films showed that Ti and Si did not disturb the hexagonal wurtzite crystal structure of ZnO thin films. But the crystallinity of the films decreased. Raman spectroscopy results showed that when thin films were excited with He-Ne laser at 732 nm, the structure was a hexagonal wurtzite crystal, and in this lattice structure Silicon and Titanium metals in the structure of TEOS (Tetraethyl orthosilicate, SiC8H20O4) and TBOT (Titanium (IV) butoxide, C16H36O4Ti) were bonded with oxygen atoms. All films were found to have an optical transmittance greater than 95%. It led to an increment in the crystal grain size values. The increase in this crystal size was observed as a band edge redshift in the UV spectrum. In the photoluminescence spectra of the films, the peak intensity diminished and shifted to a slightly higher wavelength (redshift) with increasing Si concentration.