Morphological evolution in nanocrystalline CdS thin films from flowers to salt rock like structures

Surface morphological evolution is observed in thermally activated nanocrystalline CdS (nc-CdS) thin films. The chemical bath deposited nc-CdS thin films show flower like structures on micro-crack background. Thermal annealing of nc-CdS thin films at different temperatures viz. 300, 350, 400 and 450 °C for 3 h in Ar ambient developed surface morphology towards salt rock like structures with clear particle boundaries at higher temperatures. Besides, structural phase transition from zincblende to wurtzite is observed, at 350 °C in nc-CdS thin films. It is observed that on increasing the annealing temperature longitudinal optical phonon Raman mode shifts toward higher frequency side in either of the crystal structure and bandgap reduces. Photoluminescence study illustrates thermally activated enhancement in green emission and disappearance of yellow and red emission in both the structures. The variation in emission intensity is described on the bases of morphology and structural changes occur due to thermal activation.