Exciton magnetic polarons in (100)- and (120)-oriented semimagnetic digital alloys (Cd,Mn)Te

Abstract

We report on optical studies of exciton magnetic polarons in artificial crystals of digital alloys of diluted magnetic (semimagnetic) semiconductors built of alternating CdTe and ${\mathrm{Cd}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ layers, each only a few monolayers thick. Specially designed quantum well structures with the digital magnetic alloy in the quantum well region were grown and studied experimentally by magneto-optical methods. Precise comparative studies of the structures grown simultaneously either on (120)- or (100)-oriented substrates were performed by photoluminescence excitation spectroscopy and photoluminescence under selective excitation. While no difference in magnetic properties, as measured by the giant Zeeman splitting of excitonic states, was observed between (120)- and (100)-oriented diluted magnetic structures, the exciton magnetic polaron energy was found to be by $10--40%$ larger in (120)-oriented structures than in (100)-oriented counterparts. This increase is explained by the effect of the heavy-hole effective mass anisotropy: greater hole mass in [120] direction causes an enhancement of an initial exciton localization which, in turn, gives rise to an increase of the magnetic polaron energy. Results of model calculations are in good agreement with experimental data.