Influence of molar concentration on the physical properties of nebulizer-sprayed ZnO thin films for ammonia gas sensor

Zinc oxide (ZnO) thin films were deposited by nebulizer spray pyrolysis technique with different molar concentrations of 0.05 M, 0.10 M and 0.15 M. The films were characterized by structural, morphological, electrical and optical properties. X-ray diffraction confirms that the all films are polycrystalline in nature with hexagonal crystal structure having preferential orientation along (002) plane and the maximum crystallite size is found to be ∼77 nm. The band gap energy increases with molar concentration and reaches a maximum value of 3.2 eV at 0.15 M. Room temperature photoluminescence measurements were performed and band to band emission energies of ZnO films were determined. High resolution scanning electron microscopy shows the uniform distribution, densely packed grains with a plate like structure of ∼55 nm (0.05 M).