Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots

Abstract

We used continuous wave photoluminescence (cw-PL) and time-resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the $\mathrm{ZnTe}/(\mathrm{Zn},\mathrm{Mn})\mathrm{Se}$ system the holes are confined in the nonmagnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn,Mn)Se matrix. On the other hand, in the $(\mathrm{Zn},\mathrm{Mn})\mathrm{Te}/\mathrm{ZnSe}$ system, the holes are confined in the magnetic (Zn,Mn)Te QDs, while the electrons remain in the surrounding nonmagnetic ZnSe matrix. The magnetic polaron formation energies ${E}_{\mathrm{MP}}$ in both systems were measured from the temporal redshift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the $\mathrm{ZnTe}/(\mathrm{Zn},\mathrm{Mn})\mathrm{Se}$ system the magnetic polaron shows conventional behavior with ${E}_{\mathrm{MP}}$ decreasing with increasing temperature $T$ and increasing magnetic field $B$. In contrast, ${E}_{\mathrm{MP}}$ in the $(\mathrm{Zn},\mathrm{Mn})\mathrm{Te}/\mathrm{ZnSe}$ system has unconventional dependence on temperature $T$ and magnetic field $B$; ${E}_{\mathrm{MP}}$ is weakly dependent on $T$ as well as on $B$. We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.