Structure and optoelectronic properties of CdS thin films for oxygen gas sensor

Thin Films of different thickness of CdS were deposited onto glass substrates at varying substrates temperatures from 50 to 490°C by vacuum evaporation method. The prepared film structure was diagnosed by XRD to elucidate the film crystallinity, nature and size. Both thickness and crystallite size of the CdS decrease as the deposition temperature increase from 340 to 490°C at constant deposition time. The opposite trend was observed when the films were deposited at different deposition time and constant deposition temperature. The interaction of oxygen with surfaces of CdS films with different thickness was studied by x-ray photoelectron spectroscopy (XPS) and thermal deposition mass spectroscopy (TDS) observations combined with the conductivity measurements. For the chemisorbed O - 2 , the Characteristic binding energy of the O's electrons was found to be 531.8 ± 0.2 eV and for the chemisorbed O - , 531,1 ± 0.2 eV The concentration of the chemisorbed oxygen increases when the surface of the investigated sensor was enriched or doped with metal atoms. The optical transmission spectra display a marked blue shift of the absorption band edge, which was attributed quantum size confinement effects. The resistance of the films measured by exposing them to different concentrations films of oxygen to test its use as oxygen sensor. The thinner CdS films show higher sensitivity and shorter response time than the thicker films.