Structural and optical characterization of polycrystalline CdSexTe1-x thin films

Solid solutions of CdSexTe1-x (0.7 less than or equal to x less than or equal to 1) were synthesized by vacuum fusion of stoichiometric amounts of CdSe and CdTe constituents in a silica tube. X-ray and electron microscope diffractometry techniques revealed that the CdSexTe1-x thin films were polycrystalline with a hexagonal structure. The variation of lattice constants with composition was found to obey Vegard's law. The compositional dependence of the optical constants, the refractive index n and the absorption index k, of the films was determined in the spectral range of 400-2000 nm. The dispersion of the refractive index of the films could be described using the Wemple-DiDomenico single oscillator model. Changes of the dispersion parameters were also studied as a function of the mole fraction x. A plot representing alpha(2) = f(hv) showed that the CdSexTe1-x thin films of different compositions have two direct transitions corresponding to the energy gaps E-g and E-g + Delta. The variation in either E-g or E-g + Delta with x indicates that this system belongs to the amalgamation type. The variation follows a quadratic dependence and the bowing parameters were found to be 0.4 and 0.5 eV, respectively.