Preparation and Investigation of the Structural, Morphological, and Optical Properties of ZnO Thin Films by Chemical Spray Pyrolysis

Abstract

Zinc oxide (ZnO) thin films prepared previously on borosilicate glass substrates by means of a method called chemical-thermal spray. Zinc chloride () aqueous solution was used at 0.1 M, and the film was deposited at a base temperature of 350°C with a total amount of 13 spray cycles (15 seconds each separated by a pause of 10 minutes). According to the results of X-ray diffraction analysis, formation of Wurtzite-type hexagonal ZnO with a preferred crystal growth mainly along (002) plane pattern. The average crystallite size and microstrain were about 51.58 nm and 0.264% respectively. The scanning electron microscopy (SEM) images showed the polygonal compact grains with average size of about 299.06nm and on surfaces of some grains were micro nano clumps. The average thickness of the film was ~753.9 nm When analyzed by atomic force microscopy (AFM), surface demonstrated an organized topography with mean roughness (Sa) and root mean roughness (Sq) of approximately 43.113 and 53.945 nm respectively. The film showed intense UV absorption as the maximum value was around 2.05 and, the maximum absorbance coefficient was around 6.3 × 104  Transmittance increased steadily with increasing wavelength which had about 60% at 1100 nm. The direct optical band gap of the film was ∼3.15 eV by Tauc analysis as well. In conclusion, these results show that conditions for applying an intermittent sprayed process have promoted the growth of a crystalline film with a sharp surface morphology and high UV absorption.