Effects of stabilizer ratio on structural, morphological, optical and waveguide properties of ZnO nano-structured thin films by a sol–gel process

Abstract

We report an experimental study on the synthesis and characterization of sol–gel zinc oxide (ZnO) nano-structured thin films. The effect of different monoethanolamine (MEA) to zinc acetate (ZnAc) molar ratios on the microstructure, surface morphology and optical transmittance were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM), atomic force microscopy (AFM) and UV–Vis–NIR spectrophotometry. Waveguide properties such as propagating modes and optical losses were also measured at 632.8nm wavelength by M-lines spectroscopy (MLS). XRD spectra have shown that all the thin films are polycrystalline wurtzite hexagonal structure and exhibit higher c-axis preferred orientation (002) as stabilizer molar ratio increases. SEM micrographs and AFM images have revealed that morphology and surface roughness are affected by the stabilizer molar ratio. The UV–Vis–NIR spectroscopy analyses have shown that all the thin films were transparent in the visible region with an average transmittance ranging from 70% to 90%, while in the infrared one, it exceeds 80%. The obtained results from MLS measurements have also shown that all ZnO thin film optical waveguides are single mode and the ones deposited at stabilizer molar ratio of 1.50 have demonstrated for the first time optical loss of less than 1.0dB/cm.