Synthesis and Characterization of Cadmium Sulphide (CdS) and Cobalt Sulphide (CoS) Heterostructure Using the Chemical Bath Deposition Method

In this study, cadmium Sulphide (CdS), a group II–VI semiconductor known for its wide applications in optoelectronics, piezoelectric devices, and other semiconductor technologies, and cobalt Sulphide (CoS), notable for its roles in solar-selective coatings, infrared sensing, and photo electrochemical energy storage, were investigated. Thin films of CdS, CoS, and their heterostructure (CdS/CoS and CoS/CdS) were synthesized via the chemical bath deposition (CBD) method at 80°C for 1.5 hours, using cadmium acetate, cobalt acetate, thioacetamide, and EDTA as precursor materials. The films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and optical absorption spectroscopy. Optical measurements revealed that pure CdS and CoS films exhibited direct band gaps of 2.4 eV and 1.6 eV, respectively, at deposition pH values of 2.5 and 6. The heterostructure films showed dual band gaps of 2.4 eV (CdS) and 1.65 eV (CoS) for CdS/CoS, and 1.45 eV (CoS) and 2.5 eV (CdS) for CoS/CdS. SEM analyses indicated that CoS films were compact with uniformly distributed grains, while CdS films displayed smooth, spherical grains free of pinholes. The CdS/CoS layers appeared denser with occasional surface defects. XRD analysis confirmed that CdS and CoS/CdS films crystallized in a cubic structure with a preferred (111) orientation, CoS exhibited a hexagonal phase, and CdS/CoS composites displayed a mixed cubic–hexagonal structure. EDX results showed a near-stoichiometric Cd/S ratio (48:52) in CdS and validated the presence of Cd, Co, and S in all prepared samples.