Effect of Composition and Annealing on Structural and Optical Properties of (ZnO)_1-X (TiO_2)_X Thin Films Prepared by Sol-Gel Method

The study describes effect of composition parameter, x, and annealing-temperature, Ta , on structural, and optical properties of (ZnO)_1-x(TiO_2)_x thin-films prepared by sol-gel method. Experimental results are explained and theoretical equations are suggested for optical energy-gap, Eg, and Urbach-energy, Eu in terms of their variation with (x) and (Ta). With increased x and Ta, Eg decreases whereas Eu increases. The behavior of Eg was explained by evoking that increasing x will randomize the crystal periodicity, and that annealing temperature (400, 500, and 600) ⁰C relaxes the structure more towards better crystalline forms. The increase of Eu with increased x was attributed to the lower mass of Ti ions as compared to that of Zn ions. Generally, making composites destroys the crystalinity observed in pure ZnO and pure TiO_2 films but annealing does improve the quality of the film in terms of its degree of crystal structure.