Determination of the indices of refraction of molecular-beam-epitaxy-grown ZnSe/ZnCdSe multiple-quantum-well structures

We have fabricated a series of ZnSe/ZnCdSe multiple-quantum-well (MQW) structures in order to test the dependence of the resultant index of refraction $n$ of the composite system on the $n$ values of the constituents. The ZnSe/ZnCdSe MQWs were grown by molecular-beam epitaxy on GaAs substrates. We used photoluminescence and x-ray diffraction experiments to initially characterize the specimens. Using a prism coupler system—which measures $n$ with high precision—we obtained $n$ at three discrete laser wavelengths. We find that the effective values of $n$ of these MQWs differ from their “Vegard-law-like” values; that is, the $n$ of the composite structure is not a linear function of the $n$ values of the constituents. This departure results from the energy-level structure of the MQW system associated with confinement of electrons and holes in the well layers.