Optical properties of molecular beam epitaxy-grown ZnSe_xTe_1−x II–VI semiconductor alloys

Abstract

A series of ZnSe_xTe_1−x alloys with varying compositions that cover the entire range between the two binaries ZnSe and ZnTe were grown to determine the index of refraction, n, as a function of both wavelength and the alloy concentration. The ZnSe_xTe_1−x alloys were all grown directly on GaAs (100) substrates using molecular beam epitaxy. X-ray diffraction experiments were performed to determine the quality and the compositions of each of the ZnSe_xTe_1−x specimens. The n was then measured with an accuracy of at least 0.1% at four discrete wavelengths using a prism coupler method. Since these data points are inadequate to ascertain, an accurate dispersion of the index of refraction, we next performed reflectivity measurements on each of the samples to complement the prism coupler data. The reflectivity and the prism coupler data allow us to arrive at the dispersion relations of the indices of refraction of ZnSe_xTe_1−x ternary alloys very accurately. We also find that, unlike most semiconductors, the values of n of ZnSe_xTe_1−x alloys do not follow an inverse relationship with the energy gap.