Low-temperature refractive indices of Cd1−xMnxTe and Cd1−yMgyTe

The refractive indices of ${\mathrm{Cd}}_{\text{1−x}}{\mathrm{Mn}}_x\mathrm{Te}$ and ${\mathrm{Cd}}_{\text{1−y}}{\mathrm{Mg}}_y\mathrm{Te}$ ($\text{0<x<0.28}$ and $\text{0<y<0.70}$ ) were determined by analyzing interference fringes in reflectivity spectra of thin films grown by molecular beam epitaxy. It is shown that their dispersions in the transparent region at 4 K are well described by a Sellmeier relation. These results have been applied to grow CdMnTe/CdMgTe Bragg mirrors incorporated in a II–VI microcavity operating in the strong exciton-photon coupling regime.