Structural, optical, electrical and humudity sensing properties of (Y/Al) co-doped ZnO thin films

Abstract

Undoped ZnO and Zn0.995-x Al0.005Y (x) O (x = 0.0 (AZO), 0.005, 0.01, and 0.02) solutions were prepared by sol-gel method and grown on soda-lime glass substrates by using dip coating method. In this study, the effects of dopant concentration on the morphology, crystal structure, electrical and optical properties of Al/Y co-doped ZnO (AZOY) thin films were investigated. Structural characterization of produced thin films were examined using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Diffractometer (XRD), respectively. SEM images indicated that the nanoparticles are formed on the thin films surface and the particle sizes of nanostructures decrease with increasing Yttrium (Y) doping concentration. XRD results revealed that undoped ZnO and Y/Al co-doped ZnO nanostructures have single phase hexagonal (wurtzite) structure with (002) orientation. Optical properties of thin films were investigated by Varian UV-Vis. Spectrophotometer in 350-800 nm range and the band gaps of nanoparticles were calculated from the transmission data using Tauc equation. We found that the optical transmittance of AZOY samples increases up to 95% and the band gaps (Eg) of samples decrease from 3.272 to 3.242 eV with increasing the Y doping concentration. The resistance measurements were employed to understand the DC electrical performance by Y amount of each Zn995-x Al0.005Y (x) O thin film in the 50-300 K temperature range in the voltage interval -10 to 10 V using four point method. This measurement showed the resistivity increases with increasing Y concentration and different types of conductivity mechanisms were observed for high and low temperature regions. Finally, humidity sensing properties of AZOY films were investigated at room temperature. It was observed that the humidity sensing properties increase with increasing Y doping ion in AZOY samples.