Dimensional dependence of magneto-optical properties of ZnMnSe MBE layers

A set of samples have been grown consisting of ZnMnSe MBE layers with x(Mn) = 0.12 and various layer thicknesses between 500 nm and 3 monolayers. Luminescence, excitation and reflection spectroscopy were performed in a magnetic field up to 7.5 T. Whereas for thick ZnMnSe layers of 500 and 50 nm direct excitons are to be seen, in the case of thin layers d < 10 nm only spatially indirect excitons are observable in luminescence with holes localized mainly in the ZnMnSe layers and the electrons localized in the adjacent ZnSe layers. These interface localized spatially indirect excitons exhibit a reduced Zeeman splitting compared to the direct excitons observable in the thick layers, due to the reduced number of Mn ions inside of the exciton volume. The corresponding ZnMnSe gap energy shift shows, however, a strong increase with decreasing layer thickness, The enhancement of paramagnetic response is only partly due to the interface. We suggest a strong increase of the exchange integrals for the dimensional crossover.