Structural and Optical Properties of Zinc Oxide Thin Films Prepared by Sol-Gel Spin Coating

Abstract

ABSTRACT Zinc oxide is a wide-bandgap semiconductor of great interest for transparent electronics, ultraviolet optoelectronics, and solar cells, and the sol-gel spin coating route offers a simple, low-cost way to prepare it as a thin film. The structural and optical quality of such films depends strongly on the annealing temperature. This paper reports the structural and optical properties of zinc oxide thin films prepared by sol-gel spin coating and studies how annealing affects them. Films were deposited on glass substrates and annealed at different temperatures, then characterised by X-ray diffraction for crystal structure, scanning electron microscopy for morphology, and ultraviolet-visible spectroscopy for optical transmittance and bandgap. The films were polycrystalline with the hexagonal wurtzite structure, and annealing improved their crystallinity, increasing the crystallite size and the optical transmittance while slightly narrowing the bandgap. The film annealed at the highest temperature combined the best crystallinity with over ninety percent transmittance in the visible region. The results show that sol-gel spin coating with suitable annealing produces high-quality transparent zinc oxide films suitable for optoelectronic applications.

KEYWORDS: zinc oxide, thin films, sol-gel, optical bandgap, X-ray diffraction, transparent semiconductor