Deposition of ZnO Thin Films by Chemical Bath Technique: Physicochemical Conditions and Characterization

Abstract

Zinc oxide (ZnO) was synthesized by chemical bath deposition (CBD) technique at two temperatures (70°C and 90°C). Chemical analysis was carried out on the Zn-NH3-OH zone growth using the species distribution diagrams and the solubility curves in order to determine the parameters to obtain good quality ZnO films. Results show that ZnO films can be obtained when the pH solution is up than 7. Three different pH zones between 7 and 12 were selected for deposition. ZnCl2, NH4NO3, and KOH were the chemical reagents used for the bath. The morphology of the deposited films shows a strong dependence on the pH range of the solution. When the samples are prepared into the Zn(NH3)42+ complexes zone, nano-flowers structures were obtained; whereas, if they are prepared in the zone where the Zn(OH)n2-n ions dominate, nano-flakes were formed. ZnO films deposited at 90°C present highly oriented hexagonal structure (zincite) and a [Zn]/[O]≈1 stoichiometry. While samples deposited at 70°C show degradation in their properties when the pH of the solution increases. By controlling the growth parameters, deposition of the ZnO films and their physical properties can be regulated for determined applications.