Surface analysis of CdS_1-xSe_x films grown by chemical bath deposition through AFM and Raman spectroscopy mapping

CdS_1-xSe_x films are deposited by chemical bath (CBD) onto corning glass, varying the composition x from 0 to 1, at 50 ℃, 75 ℃, and 90 ℃ for deposition times going from 5 to 180 min. Concentrations and ratios of precursors are modified to obtain the respective nominal film composition. Analysis through atomic force microscopy (AFM) and Raman scattering show that the roughness, topography, phonon intensity, and frequency are composition-dependent. Moreover, the roughness and cluster size increase with temperature, selenium content, and deposition time. Raman spectroscopy mapping allowed to analyze the evolution of crystallinity, homogeneity, and bond length of the films. CdS and CdSe films exhibit each a single Raman active phonon mode at frequencies that vary from 296 cm⁻¹ to 298 cm⁻¹ and from 201 cm⁻¹ to 204 cm⁻¹, respectively. This variation results of residual strain and small particle size; x=0 and x=1, show lower perturbation of crystallinity, whereas the intermediate composition x=0.5 has a local minimum. The dependence of phonon frequency on nanoparticle size in binary compounds is well established. In the case of the ternary compounds in this manuscript, both respective LO-phonon modes are observed and their frequencies depend on the stoichiometry via the evolution of the lattice parameter with progressive substitution of anions with different radii. The evolution of the respective mode frequency is anticorrelated, reflecting the corresponding substitution of anions. An anomaly for x=0.25 was detected trough the corresponding phonon frequency. The intensity ratio CdS/CdSe decreases with the content and optical properties of Se.