Synthesis of nanocrystalline ZnS thin films by chemical bath deposition: Influence of hydrazine hydrate concentration

Nanocrystalline Zinc Sulphide (ZnS) thin films were deposited via Chemical Bath Deposition (CBD) method using varying concentrations of Hydrazine Hydrate (H.H., 0-2.0 M) as a complexing agent. The earlier studies have typically examined only selected properties, limited concentration ranges, or a single thermal state (as deposited or annealed); in comparison, the present work systematically investigated the effects of H.H. concentration and post-deposition annealing on structural, optical, photoluminescence, morphological, and compositional properties. X-ray Diffraction (XRD) of the precipitated powder confirmed the formation of cubic-phase ZnS with average crystallite sizes of 4-5 nm. The optical absorption measurements showed that the direct band gap of as-deposited films increased with H.H. concentration, consistent with a decrease in particle size due to enhanced nucleation. Annealing reduced the band gap owing to particle growth and coalescence. Photoluminescence spectra (excitation at 345 nm) exhibited band-edge emission near 358-360 nm together with defect-related emissions associated with sulfur and zinc vacancies. Scanning Electron Microscopy (SEM) revealed that H.H. improves film uniformity and compactness and reduces particle size, while annealing produces a more compact granular morphology. Energy Dispersive X-Ray Analysis (EDAX) showed that the concentration of H.H. and annealing have a strong influence on the atomic ratio of Zn and S. The results show that the concentration of hydrazine hydrate is a good parameter to adjust the nanocrystalline properties of ZnS thin films with direct relevance to Cd-free buffer layers for optoelectronic applications