Indices of refraction and their dispersion characteristics of ZnMgCdSe thin films grown by molecular beam epitaxy

We have measured the dependence of the indices of refraction $n$ on alloy composition of $Zn1−x−yMgxCdySe$ films grown by molecular beam epitaxy on InP substrates for a series of alloy compositions $x$ and $y.$ The compositions of the $Zn1−x−yMgxCdySe$ thin films were determined by photoluminescence and x-ray diffraction experiments. A prism coupler technique, capable of measuring $n$ with an accuracy of at least 0.1% at discrete wavelengths, was then used to measure $n$ of each of the thin films. In all of the samples, at least three guided modes were observed in the spectrum obtained by the prism coupler method. The accurate values of $n$ obtained by this method show an inverse relationship with respect to their band gaps. In addition, by comparing the $n$ values obtained for the quaternary $Zn1−x−yMgxCdySe$ alloys with the previously obtained values for the ternary $Zn1−xCdxSe$ and $Zn1−xMgxSe$ alloys, it is concluded that $n$ of the quaternary system is almost completely dictated by the content of Mg.