Enhanced luminescence and visible-light photodetection performance of novel Bi, Sm, and Bi:Sm co-doped CdS nanostructured thin films developed via nebulizer spray pyrolysis technique

Our novel research presented the development of CdS thin films for photodetectors with significantly enhanced photosensing performances. This was achieved using Bi and Sm dopants. For the first time, we successfully developed pure CdS, Bismuth-doped CdS (CdS:Bi), samarium-doped CdS (CdS:Sm), and Bi and Sm co-doped CdS (CdS:Bi:Sm) films using facile nebulizer spray pyrolysis (NSP) route. The structural analysis by X-ray diffraction (XRD) confirmed the hexagonal phase of CdS, with a polycrystalline nature. The crystallite size was 56, 63, 68, and 59 nm for the CdS, CdS:Bi2%, CdS:Sm2%, and CdS:Bi2%:Sm2% films. The elemental composition and presence of every element in the developed films were confirmed by energy-dispersive X-ray spectroscopy (EDX) analysis. The field emission scanning electron microscopy (FESEM) study revealed distinct changes in the surface morphology. Photoluminescence (PL) study showed the enhancement of emission intensity with doping, and the highest intensity was noticed for CdS:Sm2% films, and intense green and red emission peaks at ~521 ± 2 nm and 681 ± 3 nm were observed in all films. The optical absorption spectra revealed that there was a shift in absorption edge due to doping, which led to a change in the energy gap of CdS films, and the values of the energy gap were found to be reduced from 2.39 eV to 2.29 eV (ΔE = 0.1 eV). Furthermore, the grown films were used to develop photodetectors and investigate their key photosensing parameters. The photodetector developed with CdS:Sm2% film showed the maximum responsivity (R), detectivity (D*), quantum efficiency (EQE), and rise and fall time compared to all other photodetectors. The values of R, EQE, D*, were found to be 0.3  AW^-1, 70%, and 1.59 × 10¹⁰Jones, for CdS:Sm2% films-based photodetector, which was ~5 times higher than pure CdS films-based photodetector. The rise and fall times of the developed CdS:Sm2% devices were found to be 0.94 s and 0.32 s, which were very quick compared to pure. These outcomes signified that the developed photodetectors based on CdS:Sm2% films possessed significantly enhanced values compared to others. However, the photodetector performance improved for each dopant and co-dopant compared to pure. Hence, the developed photodetectors based on Bi and Sm dopants were more suitable for photosensing applications with enhanced performances.

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