Effect of Gamma irradiation on optical characteristics of Fe-doped CdS thin films prepared using chemical bath deposition

In the present study, the chemical bath deposition technique was used to prepare pure CdS and Fe-doped (0.4, 0.5, and 0.6 mM) CdS nanostructured thin films. The deposition time, bath pH, and bath temperature were adjusted at 2 h, 11, and 80 degrees C, respectively. The prepared thin films were then exposed to gamma irradiation. Different gamma doses (10, 20, and 30 kGy) were irradiated to investigate how they would affect the optical, morphological, and structural characteristics of the samples. The prepared thin films were characterized with various analytical methods including X-ray diffraction (XRD), UV-vis absorption spectroscopy, photoluminescence (PL) emission spectroscopy, energy dispersive X-ray analysis (EDX), and scanning electron microscopy (SEM). The XRD patterns confirmed the two-phase nature of all the pure and Fe-doped CdS samples, which had hexagonal and cubic structures with strong (002) and (111) preferred orientations before and after gamma irradiation, respectively. The investigation of the surface morphology using SEM images showed the nanocrystalline nature of the films. The mean grain sizes were obtained to be 37.92-47.71 nm and 36.60-42.50 nm for the non-irradiated and irradiated pure CdS and Fe-doped CdS films, respectively. The decrease (increase) in the grain sizes of the films were observed with increasing Fe concentration (irradiation dose). The EDX analysis confirmed the presence of Fe atoms in the samples. The optical properties including absorption, band gap, extinction coefficient, and PL were studied. It was observed that all the investigated parameters were affected by Fe doping and gamma irradiation. The variation of E-g is estimated within the ranges 2.47-2.28 eV for the pure, 2.44-2.06 eV for the 0.4-mM Fe-doped, 2.4-2.17 eV for the 0.5-mM Fe-doped, and 2.36-2.16 eV for the 0.6-mM Fe-doped CdS films before and after irradiation at 10, 20, and 30 kGy doses. The direct optical band gap decreased as the gamma dose and Fe concentration increased. It was found that the extinction coefficient values increased with an increase in gamma doses and reduction in Fe concentration. It is found that the broadband emission peak for the pure CdS thin films located in the range of 500-650 nm and centered at 542 nm (green wavelength region) and the Fe doped CdS films have three different emission bands centered at 400, 467, and 530-540 nm. The PL intensity increased with Fe doping and decreased with gamma irradiation.