ZnO thin films prepared by a single step sol–gel process

Abstract

ZnO thin films were prepared on fused silica from a single spin-coating deposition of a sol–gel prepared with anhydrous zinc acetate [Zn(C2H3O2)2], monoethanolamine [H2NC2H4OH ] and isopropanol. Crystallization annealing was performed over the range 500 to 650 °C. X-ray analysis showed that thin films were preferentially orientated along the [002] c-axis direction of the crystal. The films had a transparency of greater than 85% in the visible region for sol–gels with a zinc content of up to 0.7 M and exhibited absorption edges at ∼378 nm. The optical band-gap energy was evaluated to be 3.298–3.306 eV. Photoluminescence showed a strong emission centered at ca. 380 nm along with a broad yellow-orange emission centered at ca. 610 nm. Single step sol–gel thin film deposition in the film thickness range from 80 nm to 350 nm was demonstrated. The effect of sol–gel zinc concentration, film thickness and crystallization temperature on film microstructure, morphology and optical transparency is detailed. A process window for single spin coating deposition of c-axis oriented ZnO discussed.