Synthesis and characterization of binary ZnO–SnO2 (ZTO) thin films by e-beam evaporation technique

Abstract

The binary ZnO–SnO2 (ZTO) thin films with varying SnO2 concentrations (5, 10, 15, and 20 wt%) were grown on glass substrate by e-beam evaporation technique. The prepared ZTO films were annealed at 400 °C in air. These films were then characterized to investigate their structural, optical, and electrical properties as a function of SnO2 concentration. XRD analysis reveals that the crystallinity of the film decreases with the addition of SnO2 and it transforms to an amorphous structure at a composition of 40% SnO2 and 60% ZnO. Morphology of the films was examined by atomic force microscopy which points out that surface roughness of the films decreases with the increasing of SnO2 in the film. Optical properties such as optical transparency, band-gap energy, and optical constants of these films were examined by spectrophotometer and spectroscopic Ellipsometer. It was observed that the average optical transmission of mixed films improves with incorporation of SnO2. In addition, the band-gap energy of the films was determined to be in the range of 3.37–3.7 eV. Furthermore, it was found that the optical constants (n and k) decrease with the addition of SnO2. Similarly, it is observed that the electrical resistivity increases nonlinearly with the increase in SnO2 in ZnO–SnO2 thin films. However, it is noteworthy that the highest figure of merit (FOM) value, i.e., 55.87 × 10−5 Ω−1, is obtained for ZnO–SnO2 (ZTO) thin film with 40 wt% of SnO2 composition. Here, we suggest that ZnO–SnO2 (ZTO) thin film with composition of 60:40 wt% can be used as an efficient TCO film due to the improved transmission, and reduced RMS value and highest FOM value.