Effect of optical gap energy on the Urbach energy in the undoped ZnO thin films

The ZnO thin films were prepared with different precursor molarities by ultrasonic spray and spray pyrolysis techniques on glass substrate at 350 °C. The thin films were deposited at different substrate temperatures ranging between 0.02 and 0.125 M. In this paper we focused our attention on the present a new approach to correlate the Urbach energy, this correlation based on experimental data were published previously. The measurement of the Urbach energy of undoped ZnO thin films were realized at different model proposals; these measurements shows that the Urbach energy of the films can be estimated by varying the optical gap energy and the concentration of ZnO solution. The best estimated results are measured by Eqs. (2) and (3) with minimum relative error value was limited to 20%. Thus results indicate that the ZnO thin films are chemically purer and have many fewer defects and less disorder owing to an almost complete chemical decomposition.