Engineering the physical properties of CdS thin films through incorporation of Fe dopant for photodetector applications

Abstract

Pure CdS and 1, 2, 3, 4, and 5 wt% Fe-doped CdS thin films have been fabricated on glass substrates at a coating temperature of 450 °C by a simple and economical spray-pyrolysis technique. The prepared samples have been characterized by various analytical techniques to assess their crystalline, morphological, optical, and photo-sensing properties. X-ray diffraction (XRD) analysis has revealed the presence of the hexagonal wurtzite phase of CdS, with (002) as the predominant plane. With the incorporation of the Fe dopant into CdS, the peak of the predominant plane (002) increases, suggesting an increase in the crystallinity of the samples. The CdS:Fe4% sample showed the largest crystallite size of 49 nm. The morphologies of the prepared thin films reveal uniform clusters of very fine nanoparticles, with the incorporation of Fe ions in CdS improving the particle size and porosity, which is beneficial for light harvesting. UV/Vis studies have indicated an improvement in the optical absorption of the CdS:Fe4% sample, with a reduction in the band gap to 2.29 eV. Photoluminescence (PL) spectra feature broad emission peaks at around 460, 535, and 640 nm, the intensities of which increase with the incorporation of the Fe dopant, suggesting improved radiative recombination of excitons and defect sites, such as S vacancies and Cd vacancies. Photo-sensing studies of the fabricated devices showed the highest photocurrent (28 μA), responsivity (5.59 × 10−1 AW−1), detectivity (9.05 × 1010 Jones), and external quantum efficiency (180%), as well as the shortest response time (0.1 s) and recovery time (0.2 s), for the CdS:Fe4% photodetector, suggesting that this sample is best suited for commercial application in photodetectors.