Wavelength dependence of the indices of refraction of molecular beam epitaxy-grown ZnMgSe and ZnCdSe thin films measured by two complementary techniques

We have measured the wavelength dependence of the indices of refraction n of epitaxial Zn_1-xMg_xSe and Zn_1-xCd_xSe films for a series of alloy compositions x, at wavelengths below the energy gaps of these semiconductor alloys. The measurements were performed using a combination of the prism coupler method and reflectivity. The prism coupler technique was capable of measuring n with an accuracy of at least 0.1% at four discrete wavelengths, and simultaneously to determine the thickness of the layers with an uncertainty of less than 0.5%. Using these discrete, highly precise values of n, the Fabry-Perot oscillations of the reflectivity spectra were then analyzed to obtain the continuous variation of the indices of refraction as a function of wavelength in the transparency region of the alloys.