Structural, electrical and optical properties of thin ZnO films prepared by chemical precipitation

A chemical method for the production of thin ZnO films by using a chemical precipitation technique is presented in this paper. The method consists in obtaining the thin ZnO films (300–500 nm) by thermal decomposition of zinc hydroxide formed by the precipitating of zinc acetate from alkaline solution, in the presence of ethylenediamine on a solid support i.e. glass. The use of this method implies investment economies, and the simplicity of the work technique, together with the production of good quality thin ZnO films. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) were used to characterize the surface morphology and crystallinity of the obtained ZnO films. The optical transmission through the films was measured spectrophotometrically in the wavelength range 300–1000 nm; the optical energy gap was estimated by extrapolating the square of the absorption coefficient versus the wavelength energy. The electrical parameters were obtained by the van der Pauw method. The SEM micrographs of the ZnO samples reveal the existence of regular-shaped crystals while the XRD analysis points out the reflection characteristics of ZnO and indicates that the crystallites are preferentially oriented along the cc-axis, [002] direction of the hexagonal crystal structure. The obtained ZnO thin films are transparent (about 80%–90% optical transmittance) in the near-UV, VIS and near-IR ranges and have a band gap of 3.20–3.25 eV. The resistivities of the films were about 10−2Ωcm.