Effect of substrate temperature on the physical properties of spray pyrolysed CdO thin films for gas sensing application

Abstract

Cadmium oxide (CdO) thin films were deposited on glass substrates at different temperatures (250, 350, 400 and 500°C) using spray pyrolysis technique. Structural, morphological, optical and electrical characterization studies were performed on the films. The thicknesses of the films prepared on different substrate temperatures vary from 497 to 465 nm. X-ray diffraction studies revealed that the films are polycrystalline in nature having cubic structure with a lattice constant, 4.655Å. SEM images show that the thin film morphology exhibits spherical shaped grains and the size becomes uniform with increase in substrate temperature. EDAX analysis gives the atomic percentage of cadmium and oxygen as 49 and 51% respectively exhibiting good stoichiometry. From the transmission spectra, optical energy band gaps of CdO films were found to be in the range 2.34 to 2.44 eV prepared at various substrate temperatures. Photoluminescence spectra depict the characteristic emission peaks of CdO. Electrical properties were studied using Hall measurement and I-V study of gas sensing action was carried out for CdO film prepared at 400°C which showed better (~78%) response for nitrogen gas for a flow rate of 1LMP. Based on the above studies, the film prepared at 400°C is recommended for gas sensing applications as it shows high electrical conductivity and sensitivity to detect gas flow.