Study of annealing-induced changes in CdS thin films using X-ray diffraction and Raman spectroscopy

Abstract

We have investigated as grown and annealed (300 °C, 400 °C and 500 °C) thin films of CdS grown on GaAs (001) by chemical bath deposition. X-ray diffraction (XRD) shows that the as grown CdS film is polycrystalline and predominantly cubic. A residual compressive stress of the order of 1.45% in the as grown film relaxes on annealing the film at 300 °C. Furthermore, CdS film undergoes a structural phase transition from the metastable cubic phase to the stable hexagonal phase, when, annealed at 500 °C. This is accompanied by significant improvement in crystalline quality of the film. Line shape analysis of the asymmetry of the longitudinal optical phonon shows a disorder-activated mode, which correlates well with the crystalline quality estimated from XRD and photoluminescence measurements. The additional features observed in the Raman spectra ∼ 254 cm − 1 and 309 cm − 1 are investigated using temperature dependent Raman spectroscopy and identified as superposition of transverse optical: E 1 (TO) and E 2 phonons at q = 0 and combination mode (two zone-edge E 2 phonons) respectively.