Structural and optical characterization of CdS films grown by photochemical deposition

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.