Effect of Post Air Annealing on the Characteristics of Spray Deposited ZnO Thin Films and Their use as MOS Ethanol Gas Sensor

Spray Pyrolysis (SP), a low-cost chemical procedure was employed to deposit ZnO thin films under optimum conditions at 350 °C using a predetermined precursor concentration of 0.1 M. This study investigates how post-air annealing affects the structural, compositional, morphological, optical, and electrical properties of ZnO thin films. The deposited films were heated by air at 400, 450 and 500 °C for 1 h. X-ray diffraction, scanning electron microscope, x-ray dispersive spectroscopy, Raman spectroscopy, Fourier Transform Infrared Spectroscopy, optical spectroscopy, and Hall effect studies were conducted to investigate how post-air annealing alters the properties of the as-deposited film. XRD measurements show that annealing resulted in the growth of polycrystalline hexagonal wurtzite without the formation of any other phases in ZnO films. When heated to 500 °C, the estimated crystallite size of the as-deposited film increased from 6.22 nm to 6.57 nm. The SEM show the creation of compact and tightly packed films, as well as the visible network of large grains during annealing. Raman and FTIR studies have validated the chemical structure, molecular interactions, and formation of chemical bonds in ZnO thin films. Optical studies show that the energy band gap widens during annealing. Optical profilometer studies verified the uniformity of the deposited film surface. According to Hall effect analysis, conversion of p to n type occurs at an annealing temperature of 450 °C. A ZnO-based MOS gas sensor was found to have better selectivity towards C2H5OH than other test gases such as NH3, NO2, and H2S. At room temperature, the sensor response and recovery time is shorter for NH3 than for C2H5OH test gas. In environmental monitoring, the present gas sensor can detect ethanol.