Excitation Power Dependent Coulomb Induced Recombination Dynamics In Magnetically Doped Type-Ii Quantum Dots

We observe that the wavefunction overlap of the carriers in type-II quantum dots (QDs) can be controlled by magnetic doping and strongly depends on the excitation power density. We study two different II-VI magnetic systems; ZnTe/(Zn, Mn)Se QDs with magnetic dopants in the matrix surrounding the dots, and (Zn, Mn)Te/ZnSe QDs doped in the dot core. Both magnetic systems, regardless of the location of the dopant magnetic ions, show a stark contrast in their emission with high excitation power densities (P-ex) when compared to nonmagnetic ZnTe/ZnSe QDs. Using time-resolved photoluminescence (TRPL), we observe a saturation in the blue shift for the magnetic systems at a lower P-ex, while additionally exhibiting a limited lifetime shortening over the entire range of P-ex, when compared to the nonmagnetic QDs. The results for the two magnetic systems are very similar, showing no dependence on the location of the magnetic impurities. This suggests that the behavior observed is an effect of the magnetic polaron on the band bending in the high P-ex regime. The ability to use magnetic ions to quickly saturate the charge concentration and control band bending in QDs could potentially aid in optimizing optoelectronic devices which are sensitive to high charge variations.