Density-dependent dynamics of exciton magnetic polarons in ZnMnSe/ZnSSe type-Ⅱ quantum wells

摘要

We report on time-resolved photoluminescence studies of exciton dynamics in a ZnMnSe/ZnSSe type-Ⅱ quantum well. Strong separation of the electrons, confined to the nonmagnetic semiconductor ZnSSe, and holes, confined to the diluted magnetic semiconductor ZnMnSe, results in an exciton lifetime exceeding 3 ns. Two excitonic emission lines are observed in this structure at low temperatures. The lower-energy line was associated with the formation of an exciton magnetic polaron (EMP), whereas the higher-energy line was attributed to the emission of nonmagnetically localized excitons. The intensity of the EMP line was found to saturate at a relatively low density of photoexcited carriers well below the exciton Mott density. This behavior evidences a limited density of sites where the hole localization radius is small enough to ensure the fast formation of EMP's with a noticeable binding energy.