Influence of Deposition and Annealing Times on Structural, Optical, and Electrical Properties of ZnS Nano Rods Structured Thin Films

Zinc sulfide thin films were synthesized using the chemical bath deposition method with deposition durations ranging from 1 to 7 hours to examine the influence of deposition time and post-deposition annealing (60 °C to 100 °C) on their structural, optical, and electrical properties. X-ray diffraction confirmed the formation of the cubic zinc blende phase, with enhanced crystallinity and increased grain size at longer deposition times. Ultraviolet-visible spectroscopy revealed a tunable optical bandgap between ~3.5 and 3.8 eV, depending on deposition duration. Surface morphology and elemental composition were analyzed using scanning electron microscopy and energy-dispersive X-ray analysis. Energy-dispersive X-ray analysis results indicated that the 3-hour annealed film had a near-stoichiometric Zn:S ratio (41.1% Zn and 58.9% S), while the 1-hour annealed film exhibited a high oxygen content (70.31%) due to oxidation. Films annealed for 5 and 7 hours showed sulfur loss, resulting in zinc-rich compositions. Fourier-transform infrared spectroscopy confirmed improved Zn–S bonding over time, with sharper vibrational peaks in the 600–700 cm⁻¹ range and a marked reduction in organic and hydroxyl impurities. Among all samples, the 5-hour film showed the most favorable combination of crystallinity, purity, and low contamination, indicating its potential for optoelectronic applications. Electrical properties, evaluated using the two-probe method, demonstrated thermally activated conductivity in the 1-hour film annealed at 100°C, with an activation energy of 0.2857 eV, suggesting semiconducting behavior and applicability in thermoelectric and biosensing devices. However, electrical measurements for films deposited for 3, 5, and 7 hours were unfeasible due to extremely high resistivity and limited charge transport.