Quantum confinement effect in multilayer structure of alternate CdSe and SiOx insulator matrix thinfilms

Abstract

Multilayer (ML) structure of layer-by-layer deposited CdSe/SiOx thin films and their monolayers were prepared using sequential thermal evaporation technique. X-ray diffraction study confirmed the (002) plane of CdSe with wurtzite structure. It is noticed that the microstrain, developed in ML thin films, increased with decreasing particle size. Experimentally measured band gap energies confirmed the splitting of valence band energy levels which rise due to hole confinement in CdSe. Crystallite sizes (5–7nm) were calculated using the effective mass approximation model (i.e., Brus model) which shows that the diameter of crystallites was smaller than the Bohr exciton diameter (11.2nm) of CdSe. The main band in the emission spectra of ML samples gradually shifted to longer wavelength side when particle size was increased from 5 to 7nm. This is characteristic of quantum size effect. It is inferred that disorderliness in CdSe/SiOx ML thin films would increase when the thickness of CdSe sublayer is greater than that of SiOx matrix layer.