Comparative study of ZnO thin film samples prepared by two different chemical bath methods

Abstract

Chemical bath deposition (CBD) is considered to be one of the simplest, low cost and effective chemical methods in thin film preparation. Over these years much advancement were introduced in CBD like Successive Ion Layer Adsorption and Reaction (SILAR) and other methods. Here an attempt has been carried out in order to study and optimize the methodology by comparing ZnO thin film samples prepared by SILAR method and a modified CBD method. Precursor medium of 0.025M were prepared using Zinc ammoniac solution and samples were synthesized by both SILAR and modified CBD methods. SILAR cycles were carried out for 50 dip cycles maintaining an optimum temperature of 80°C. Modified CBD was performed as making the sample to undergo a 50dip cycle of SILAR first and then keeping it in the chemical bath for two days. Prepared samples were annealed at 450°C for 2 hours. Thus obtained ZnO thin films were marked as S1(SILAR sample) and S2( Modified CBD sample) respectively and were investigated using UV-Visible spectrometer, X ray diffraction spectrometer (XRD) and Scanning electron microscope (SEM). The optical behavior of the samples revealed by UV-Visible data were plotted as transmittance and absorbance spectrum. Transmittance of S1 was found to be greater than that of S2 on the other hand absorbance of S2 was greater than that of S1. The optical data giving information regarding the increment of crystallinity occurred for the sample S2 in the chemical bath. For both the samples the average and peak values of transmittance and absorbance were recorded. Idea regarding the applications of these samples in transparent optical components could be obtained from their optical studies. The obtained XRD data were plotted for intensity of diffraction. The characteristic peaks of ZnO in the XRD spectrum were identified and from it h,k,l values were determined. Thus calculated lattice parameter confirms hexagonal structures of ZnO. The purity of the samples was revealed from the XRD spectrum, which also shows the enhancement of intensity peaks in sample S2 which was identified as due to the increment in crystallinity of S2. Using Scherer formula crystallite size for each samples were calculated and found that it is greater for S2 than that of S1. The morphological analyses of the samples were presented by SEM images. The image of sample S1 shows a uniform distribution of grains over the surface, whereas S2 sample surface was found as rough and non-uniform. S1 sample shows the formation of rod like structures which is very useful in aspect of its applications in sensors. The surface to volume ratio of S1 was found to be greater than S2 due to rod like structure formation, which is a valuable property in synthesizing thin film. The grain size identified from SEM images also reveals the Nano size of ZnO grains in S1 sample. Hence it could be concluded from the investigation that the sample S1 is found to be useful compared to S2 in its applications in optoelectronic and sensor applications.