Excitons and magnetic polarons in semimagnetic double quantum wells CdSe/CdMgSe/CdMnSe and CdSe/CdMnSe/CdSe

Abstract

We have studied at high magnetic fields, exciton photoluminescence and reflection spectra of two groups of semimagnetic double quantum wells, CdSe/CdMgSe/CdMnSe and CdSe/CdMnSe/CdSe, with either one of the wells or a coupling barrier being semimagnetic. Owing to strong exchange interaction between band carriers and manganese ions, magnetic tuning of energy levels or the height of the coupling barrier could control the interaction of excitons of the coupled wells and their tunneling. In the first group of structures, we have observed direct and spatially indirect excitons. Photoluminescence intensity of the indirect exciton strongly increased and its half-width decreased with the magnetic field. Dependence of excitons and spin tunneling on the barrier thickness was studied. We also addressed the problem of localized magnetic polarons formation and its peculiarities for indirect and direct excitons. In the second group with a semimagnetic coupling barrier, the energy shifts of the excitons in a magnetic field exceeded significantly the calculated values obtained without account of interface effects. A proper account of both interdiffusion of Mn and Cd ions in the surface layers of the coupling barrier and decrease of antiferromagnetic coupling in these layers, allowed to fit experimental data.