Comparative Optical study of ZnO thin films prepared by SILAR Method

ZnO thin films find verity of applications in scientific and electronic world. Due to specific features of ZnO thin films like wide band gap energy, transparency in visible region, photoluminescence etc it is considered as a favorable material in optoelectronic and solar cell devices. Thus optical studies play an important role in selectivity of of ZnO thin films in different fields. The present work is carried out in a way to compare and to study the optical properties of ZnO thin films prepared with out annealing and annealed at 350 degrees C. The method of preparation adopted was Successive Ion Layer Adsorption and Reaction (SILAR). Here precursor medium of 0.1M Zn salt was prepared and SILAR of 50 dip cycles were executed. Thus obtained first film was not annealed and the second film annealed for 350 degrees for two hours. Thus obtained respective samples S1 and S2 were investigated with UV-Visible spectrometer and absorbance and transmittance values were obtained. About 350-400nm wave length the absorbance of S1 was found greater than that of S2. Around 400 nm a spike was observed for S2, which could be due to absorption corresponding to band gap. Form absorption spectrum maximum value of each samples were noted. From the transmission spectrum it was observed that between 350-400nm transmittance of S2 was greater than S1. The maximum values of transmittance were compared and reported. Thus calculated values of extinction coefficient and reflectance were plotted against wave length and it was observed that, extinction coefficient variation as similar to absorption, S1 is greater than S2 in the above mentioned range of wave lengths and reflectance were comparable for both samples for entire range of wave lengths. The variation of extinction coefficient and reflectance of respective samples were studied and minimum value of extinction coefficient was reported. Photon energy Vs (alpha hv)(2) plot were prepared for the samples and variations were recorded. It is observed from the study that absorption and extinction coefficient of S1 increases where as transmittance decreases between 350-400nm wave lengths. On the other hand reflectance and energy curves are comparable for both the samples. Hence SILAR was found to be an effective preparatory method for ZnO thin films.