Photo-induced magnetic polarons in low-dimensional dilute magnetic semiconductors

The temperature dependence of exciton magnetic polaron energies was determined from the pico-second time-resolved photoluminescence (PL) spectra, and have shown characteristic dynamical behavior of exciton localization process in bulk-Cd1−xMnxTe (x=0.1–0.2). The overall behavior appears different from that reported previously for the bound- or localized-exciton magnetic polarons (EMP) in the same material. In symmetric diluted magnetic semiconductor (DMS) quantum wells (QWs), CdTe/Cd1−xMnxTe, studied here by steady-state and transient-PL, it is plausible that the exciton magnetic polaron formation occurs after localization by the nonmagnetic disorders. Temperature and magnetic-field dependencies (up to 15 T) of PL have been studied in Cd1−xMnxTe−CdTe–Cd1−yMgyTe asymmetric single QWs. These show the phenomena similar to those expected in the exciton ‘bifurcation’ effect due to magnetic polaron formation on one side of the diluted magnetic barrier. The doublet PL lines observed are attributed to symmetric and asymmetric exciton states. Biexcitons are observed in DMS-QWs, and confirmed by the polarized two-pulse degenerate four-wave-mixing (DFWM) experiment.