The effects of Ti concentration on the structure, optical, and electrical properties of Al and Ti co-doped ZnO thin films

Nano-structured Al and Ti co-doped ZnO (ATZO) thin films were synthesized with different concentrations of Ti (0.1–0.5 at.%) by sol–gel method. The X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) methods were used to investigate the structure, morphology, and surface roughness of the thin films. The optical properties were investigated by spectroscopic ellipsometry (SE) and UV–vis spectrophotometry methods. The XRD results revealed the wurtzite structure for all the samples. Increase in the Ti content resulted in reduction of the crystal size from 23 to 15 nm, along with decrease in the surface roughness of the samples from 8.2 to 3.4 nm. The optical measurement demonstrates that the band gap energy (Eg) increases from 3.26 to 3.31 eV. It was observed that the resistivity increase with the increase in the Ti content, meanwhile, the transmittance decrease with the increase in the Ti content.