Phase transformation and quantum confinement effect in CdSe/Se multilayer thin films prepared by physical vapour deposition

Abstract

CdSe/Se multilayer (ML) thin films with different thickness ratios of Se and CdSe sublayers were prepared by using a thermal evaporation method. Prepared samples were annealed at temperature 300 K. From X-ray diffraction (XRD) studies, samples prepared at room temperature showed a (100) plane of CdSe with wurtzite structure, whereas the annealed samples confirmed the cubic structure. Stress created in ML systems was calculated from XRD data and found that it increases with decreasing particle size. The energy band gap value of a CdSe/Se ML thin film is shifted to a value higher than that of the bulk CdSe (1.74 eV) semiconductor. This is due to decrease in the crystallite size smaller than the Bohr exciton diameter of CdSe (11.2 nm). Crystallite sizes (≈5 nm) were calculated from UV–VIS data with the predictions of an effective mass approximation model. The photoluminescence peak of the ML samples is split into two bands having nearest values due to the emissions from spin–orbit split-up of the excited energy state.