Optical properties of ternary ZnS x Se1−x polycrystalline thin films
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Ternary ZnSxSe1−x polycrystalline thin films were prepared by evaporation in vacuum of 10−5 Torr. The molecular fractionx varied in the region o≦x≦1. The optical constants (the refractive indexn, the absorption indexk, and the absorption coefficientα) were determined in the wavelength range 300–1600nm. A plot representingα2=f(hv) shows that the ZnSxSe1−x polycrystalline thin films of different compositions have two direct transitions corresponding to the energy gapsE andE+Δ. The variation in eitherE orE+Δ withx indicates that this system belongs to the amalgamation type. Such variation follows a quadratic equation. The bowing parameter was found to be 0.456 eV, roughly equal to the calculated value 0.60 eV using the empirical pseudopotential method based on the virtual-crystal approximation, in which the disorder effect has not been taken into account.
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