Morphological and Optical Characteristics of ZnO and F: ZnO Thin Films by a Sol-Gel Spin Coating Technique

Abstract

The increase in the application of transparent conducting oxides (TCOs) thin films has led to a continuous demand for improved quality films for solid-state devices. Indium tin oxide (ITO) which is mostly used as TCO is reportedly scarce, thus making it more expensive. This paper investigates physical characteristics and effect of temperature on sol-gel synthesized zinc oxide (ZnO) and fluorine doped zinc oxide (F: ZnO). Samples of ZnO and F: ZnO thin films were prepared by sol-gel spin coating technique using zinc acetate dehydrate as a precursor, methanol as solvent, monoethanolamine as a stabilizer and ammonium fluoride as a dopant at a deposition speed of 4000 r.p.m for 30 seconds and later annealed at temperatures ranged from 100°C to 400°C. The morphological and optical characteristics of prepared thin films were characterized using Scanning Electron Microscopy (SEM) and UV- Visible Spectroscopy respectively. The SEM images of the films showed good homogeneity with distinct grain size ranged from 10.31 to 11.97 nm for ZnO and 7.90 to 17.53 nm for F: ZnO. The average optical transmission in the range (300-1100 nm) for ZnO and F: ZnO thin films were greater than 80% and 70% respectively. The energy band gap increased with temperature ranged from 3.80 to 4.05 eV for ZnO and 3.76 to 3.90 eV for F: ZnO. There is a change in physical characteristics of ZnO and F: ZnO as the temperature varies. The obtained results from this study make ZnO and F: ZnO thin films suitable for solar cell and optoelectronic applications.