Effect of optical gap energy on the Urbach energy in the undoped ZnOthin films

Abstract

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