Optical dispersion of ternary II–VI semiconductor alloys

The wavelength dependence of the refractive indices n of a series of II–VI ternary alloys grown by molecular beam epitaxy on (100) GaAs substrates over a wide range of compositions were measured at frequencies below their respective energy gaps using the combined techniques of optical reflectivity and the prism coupler method. A modified single-effective-oscillator (SEO) model was used to fit the wavelength dependence of n, and a set of semiempirical parameters was established for selected ternary II–VI-based alloys. The availability of these parameters makes it possible to calculate the index of refraction of any given II–VI ternary alloy for any composition and at any wavelength. Furthermore, these parameters provide valuable physical insights, such as the relationship between the covalency (or ionicity) of the material and its refractive index. In addition to its fundamental usefulness, this approach can also be used for obtaining the dispersion properties of ‘hypothetical’’ zinc blende compounds that do not form under equilibrium crystal growth conditions, such as MnTe, MnSe, or BeSe.