Ellipsometric Investigation of Optical Parameters and Characterization of Spray Pyrolysis-Derived ZnO Films

The pH value of solution is an important parameter in thin film production. In this work, ZnO films were successfully produced for various pH values (6.9 ≥ pH ≥ 3.2) by spray pyrolysis. The effects of the pH value on the optical parameters such as thickness, refractive index and extinction coefficient, structural, surface, and electrical properties were investigated by spectroscopic ellipsometry and other characterization technique. Thickness, refractive index, and extinction coefficient values were defined by spectroscopic ellipsometry technique using Cauchy–Urbach model. The thickness values of ZnO films were found to be in the range of 345 to 376 nm. The crystalline structure, orientation, and lattice parameters of the films were determined using XRD patterns. X-ray diffraction revealed that the crystallization level increased prominently with decreasing of the pH value and the best crystallization was found for pH 3.5 value. The average optical transmittance of the films was improved with changing of the pH values. Atomic force microscopic image was shown that the surface morphology improved and roughness value decreased with decrease of pH values. Electrical resistivity values of ZnO films decreased as the pH value decreased and the lowest resistivity value was found 1.1 × 10⁻³ Ω cm for pH 3.5 deposited films. As a result, the low pH values have a strong effect on the mentioned properties of spray pyrolysis-derived ZnO films.