Investigation on the Thickness Effect on the Structural and Optical Properties of ZnO Thin Films Prepared by Thermal Evaporation Technique

The films of conductive transparent oxides (TCO) is one of the most important semiconductor
consisting of metal combined with oxygen such as ZnO, SnO2 and In2O3. Using the thermal
evaporation technique we prepared Zinc Oxide thin films (ZnO) with different thicknesses. Crystallinity
and optical characterization of the films were studied by XRD and UV-VIS techniques, respectively.
The (Zn) powder material was evaporated on the unheated laboratory glass slides then thermal
oxidation was performed at temperature 400°C for 1 h. The effect of film thickness on the structural
and optical properties of the ZnO films has been done. All the films had a well-defined crystal
structure with hexagonal wurtize and the preferred orientation along (002) plane. Optical properties
such as transmission, absorption and optical band gap were measured and calculated. The results
showed that the ZnO films have a direct band gap and the value of energy band gap (Eopt.) decreased
with the increasing of film thickness. Finally, due to an increase in crystallite size we showed that the
refractive index (n) increases with increasing of film thickness.