One-step growth of structured ZnO thin films by chemical bath deposition in aqueous ammonia solution

Abstract

Structured ZnO films have been fabricated on soda-lime glass slides at a low temperature (80–85 °C) by a chemical bath deposition method in one step without seed layers. Mixed aqueous solutions of zinc sulfate, ammonia and thiourea were used at alkaline conditions. The influence of the ammonia concentration in the initial solution on the property of the deposited film was investigated systematically. The morphology, structural and optical properties of the deposited films were examined and characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy x-ray diffraction (EDX), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectroscopy. Structural analyses with XRD, EDX and SEM revealed that the formed films exhibit a wurtzite hexagonal phase. The deposited film was more preferentially oriented in the (0 0 2) direction with an increase in the ammonia concentration from 0.75 to 2 mol l−1. The optical-phonon E2 mode at 437 cm−1 in the Raman spectrum, together with the XRD and EDX analyses, showed that flower-like and columnar crystalline ZnO films were formed in two ammonia concentration ranges, 0.75–1.4 mol l−1 and 1.6–2.0 mol l−1, respectively. Furthermore, PL spectra showed strong and high intensity peaks of UV emission with suppressed green emission for these deposited ZnO films. ZnS films were formed with a high ammonia concentration of 3.0 M. The formation mechanisms of ZnO, Zn(OH)2 and ZnS phases were discussed.