Growth and characterization of undoped and aluminium doped zinc oxide thin films for SO₂ gas sensing below threshold value limit

The present work explores the capability of undoped and aluminium doped zinc oxide thin films for the detection of low concentration of Sulphur dioxide gas (SO₂). Highly transparent undoped and aluminium-doped ZnO thin films were successfully deposited using sol-gel spin coating technique. The influence of various concentrations of aluminium (Al) doping on structural, morphological, optical and electrical properties has been studied. The Al doping affected the crystallinity of the films as evident from the X-ray diffraction (XRD) studies. The Atomic force microscope (AFM) and the Field emission scanning electron microscope (FESEM) studies depict the wrinkled structure of the thin films. The transparency of the deposited films was revealed by the UV–Visible characterization. Electrical characterization showed a variation in the conductivity with varying aluminium concentration which influences the gas sensing performance of the thin films. The 2 at.% aluminium doped ZnO thin films exhibited a higher sensitivity of 70% for 3 ppm of SO₂ gas which is below the threshold value limit. For comparison, NH₃ gas sensing of the grown films was also studied.