CdS thin films are grown by photochemical deposition from an aqueous solution and characterized by x-ray diffraction (XRD), Raman spectroscopy, photoluminescence measurement, and optical transmission spectroscopy. The films are deposited at room temperature and annealed at temperatures up to 500 °C. The as-deposited film is dominantly zinc blende cubic. The cubic phase remains dominant until the annealing temperature becomes higher than 400 °C. By the annealing at 450 °C, the XRD pattern turns to that of hexagonal phase. Moreover, its peak width decreases and the near-band-edge luminescence begins to be observed. The band gap is decreased by annealing below 400 °C and then abruptly increased by the annealing at 450 °C. This annealing behavior of the band gap is interpreted considering the quantum size effects, the band tail due to disorder, and the cubic-hexagonal transition.

CdS films were successfully formed on a glass substrate in an aqueous solution containing S₂O₃ ^2- and Cd²⁺ ions by photochemical reaction. S₂O₃ ^2- ions in the growth solution absorb ultra-violet light of wavelengths shorter than about 300 nm, and the excited S₂O₃ ^2- ions supply sulfur atoms and electrons to the metal ions such as Cd²⁺. Thus, the formation reaction of the sulfide semiconductor occurs in the only illuminated region. Photochemically deposited CdS thin films were polycrystalline of hexagonal structure. The composition of the films became stoichiometric by the annealing at temperatures higher than 300° C.