Structural and optical studies on sol–gel derived ZnO thin films by excimer laser annealing

Abstract

High-quality polycrystalline ZnO thin films were deposited onto alkali-free glasses at a temperature of 300°C in air ambience by combining sol–gel spin coating and KrF excimer laser annealing. The effects of laser irradiation energy density on the crystallization, microstructure, surface morphology, and optical transmittance of as-prepared ZnO thin films were investigated and compared to the results of thermally annealed ZnO thin films. The crystallinity level and average crystallite size of laser annealed ZnO thin films increased as laser energy density increased. The crystallinity levels and average crystallite size of excimer laser annealed (ELA) thin films were greater than those of the thermally annealed (TA) thin films. However, laser annealed thin films had abnormal grain growth when irradiation energy density was 175mJ/cm2. Experimental results indicated that the optimum irradiation energy density for excimer laser annealing of ZnO sol–gel films was 150mJ/cm2. The ELA 150 thin films had a dense microstructure, an RMS roughness value of 5.30nm, and an optical band gap of 3.38eV, close to the band gap of a ZnO crystal (3.4eV).