Ammonia gas sensing response of gamma-irradiated CdTe thin films

Abstract

In this work, cadmium telluride (CdTe) thin films of thickness 250 nm are deposited on the glass substrate using the thermal vacuum evaporation (TVE) method. The as-deposited CdTe thin films are then exposed to three different doses of gamma rays (50, 100 and 150 kGy) from 60Co source at Inter University Accelerator Centre, New Delhi, India. The structural, morphological, electrical and gas sensing properties of as-prepared and gamma-irradiated thin films are investigated using grazing incidence X-ray diffraction (G-XRD), Field emission scanning electron microscopy (FESEM) and two-probes set up connected with current-voltage (I–V) source meter, respectively. The assessment of adsorption and desorption rate of pristine and gamma-irradiated films is studied using Brunauer –Emmett-Teller (BET) analysis. After irradiation, the XRD pattern indicates the polycrystalline nature of thin films along with the retention of cubic structure with a minor decrease in the crystallite size at the highest gamma dose. From FESEM, relevant changes in the surface morphology of thermally deposited CdTe thin films have been observed after irradiation. Moreover, the films after irradiation were found to be highly conductive up to the dose of 100 kGy as depicted from electrical studies. The gamma irradiated films are further proposed for gas sensing applications. For the highest concentration of ammonia (36.02 ppm), the maximum sensitivity of the as-deposited film is found to be (14.59%) which is higher than the sensitivity at a maximum gamma dose of 150 kGy (10.28%) for the same concentration of gas which shows that process of gamma irradiation deteriorates the sensing performance of CdTe thin films.