IOSR Journal of Applied Physics (IOSR-JAP) e-ISSN: 2278-4861. Volume 6, Issue 1 Ver. II (Feb. 2014), PP 47-51 www.iosrjournals.org www.iosrjournals.org 47 | Page The Optical Study of ZnO Thin Films at Different Times of Annealing and Varying Temperatures Prepared by Chemical Bath Deposition. J.I.Onwuemeka, O.K. Nwofor, N.C. Nwulu, I.E. Nwosu, F.M. Ezike and C.G. Obizo Department of Physics/Industrial Physics, Imo State University, Owerri Nigeria. Abstract: A research on the Deposition and Characterization of ZnO Thin Films by Chemical Bath Deposition Technique using Ammonia (NH 3 ) as a complexing agent. Thin films of ZnO are deposited onto glass substrates at room temperature for 5hours. The optical properties of the films were measured using Double Beam UV- Spectrophotometer with serial number UV061514, Rutherford Back Scattering Spectroscopy (RBS) analysis revealed that the thin filmshave percentage ratios of the elements of Zn/O, 47/53 as annealed for 3hours at the temperature of 250⁰C and Zn/O, 48.8/51.2as annealed for 1hour at the temperature of 150⁰C. The thicknesses are 80nm for 3hours and 150nm for 1hour asannealed samples at 250⁰C and 150⁰C respectively. It was found that ZnO thin films exhibits n-type conduction. Optical band gap values of the twosamples are 3.1±0.05eV as annealed for 3hours and 3.3±0.05eV as annealed for 1hour with an average of 3.2±0.05eV. Other optical properties calculated from transmittance using appropriate equations are absorbance, reflectance, band gap , absorption coefficient, optical conductivity, refractive index and extinction coefficient. Keywords: Annealing, absorption coefficient, extinction coefficient, absorbance, band gap substrates. I. Introduction Advances in the area of alternative energy technology will ensure a stable electricity which will lead to smooth transition away from fossil fuels and nuclear energy, that comprise about 93% of the world’s energy budget with a negligible contribution from solar energy. ZnO thin films have valued properties such as high optical transparency in the visible and near-infrared region of electromagnetic spectrum [1], chemical stability in hydrogen plasma [2], high refractive index [3], and wide band gap semiconductor [4]. The thin films of the metallic oxide have wide range of applications such as antireflection coating [5], surface acoustic wave devices [6], band pass filter [7], laser deflectors using piezoelectric and piezo-optic properties [8]. ZnO thin films can be produced by different methods such as pulse laser deposition[9], spray pyrolysis[10], sol-gel technique[11],chemical bath deposition[12]. The films in this study are grown by chemical bath deposition (CBD) which creates a thin film on a solid substrate via a reaction in a liquid solution. The CBD method is inexpensive, easy to prepare and its necessary vessels can be found in an ordinary chemistry laboratory [13]. In this work, we report the study of the optical properties of ZnO thin films at varying annealing times and temperatures prepared by chemical bath deposition on glass substrates. Experiments ZnO thin films were deposited on glass substrates by chemical bath deposition based on the reaction between ZnCl 2(aq) ,NaOH (aq) and with NH 3(aq) as complexing agent according to the equation; ZnCl 2 + 4NH 3 + H 2 O [Zn(NH 3 ) 4 ] 2+ + H 2 O + 2Cl - [Zn(NH 3 ) 4 ] 2+ + 2NaOH ZnO + 4NH 3 + 2Na - + OH - An excess aqueous ammonium was added to 20ml of 0.5M solution of ZnCl 2 to form a white (Zn[NH 3 ] 4 2+ ) which dissolved completely on stirring to form a clear solution. 10ml of 1M solution of NaOH was finally added for complete formation of ZnO thin films in an alkaline medium. The pH of the final solution was measured to be 9.3 and was done at room temperature. Glass substrates were then immersed vertically into the final solution which were made in 50ml beaker and optimum depositions were obtained after five hours