Growth of undoped ZnO thin films by spray pyrolysis: effect of precursor concentration

Undoped zinc oxide (ZnO) thin films have been deposited by the low-cost spray pyrolysis technique. The effect of precursor concentration on film's structural and optoelectronic properties is investigated. A set of ZnO samples were prepared with different concentration solution varied from 0.1 to 0.25 M on heated glass substrates at 400 degrees C. The synthetized films structural, optical and electrical properties were studied by mean of X-ray diffraction (XRD), UV visible transmittance and dark conductivity measurements at ambient temperature. We found that the film thickness increases with the starting solution concentration. The XRD results reveal that the films have hexagonal wurtzite structure with preferential orientation of (002). The crystallite sizes increase, and the structural defects decrease with increasing molarity. The optical characterizations revealed that the films exhibit high optical transmittance (80-90%) in the visible range with large optical band gap varied from 3.2 to 3.31 eV. The dark conductivity is enhanced with the variation of Zn concentration due to the improvement in the structural quality of the films.