Structural and optical properties of CdTe/CdSe heterostructure multilayer thin films prepared by physical vapor deposition technique

CdTe/CdSe heterostructure multilayer thin films and single layers of CdSe and CdTe thin films were prepared. Sequential thermal evaporation technique is made possible to adjust the layer thickness precisely. XRD studies were used to calculate average size of the crystallites and confirmed the (111) and (100) planes of CdTe and CdSe, respectively. Bulk CdTe has band gap energy of 1.54 eV that can be shifted to larger values by reducing the crystallite size to dimensions smaller than the Bohr radius of the exciton. Experimentally measured energy levels show the spin-orbit split of valance band of CdTe. Crystallite sizes (7-12 nm) were calculated with the predictions of effective mass approximation model (i.e., Brus model) which shows that the diameter of crystallites were much smaller than the Bohr exciton diameter (14 nm) of CdTe. It is found that the emission peaks of the prepared CdTe/CdSe ML samples were shifted from the peaks of CdSe and CdTe single layers toward red region as a characteristic of type II band alignment.