Optical single dot studies in wide-band gap diluted magnetic CdSe/ZnMnSe quantum dots have been performed. Due to the sample design, the photoluminescence energy of the quantum dot signal is energetically below the internal Mn2+ transition, resulting in high quantum efficiencies comparable to nonmagnetic CdSe/ZnSe quantum dots. Magnetic-field- and temperature-dependent measurements on individual dots clearly demonstrate the exchange interaction between single excitons and individual Mn2+ ions, resulting in a giant Zeeman effect and a formation of quasi-zero-dimensional magnetic polarons.

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The effect of spin coupling on the spin polarization of exciton was investigated in double quantum dot (QD) structures, one layer consisting of self-assembled nonmagnetic CdZnSe quantum QDs, and the other of CdMnSe diluted magnetic semiconductor QDs, both layers embedded in ZnSe. The magneto-photoluminescence (PL) studies on this double-layer structure were carried by detecting a single circular polarization in order to investigate the polarization dependence of the PL intensity. We have observed two well separated PL peaks in double QDs, corresponding to emissions from the CdZnSe and CdMnSe QD layers, respectively. It appears that the degree of the PL polarization emitted by the CdZnSe QDs in this double-layer structure is much larger than that observed in a single layer of nonmagnetic CdZnSe QDs. We discussed this enhancement of polarization in terms of antiparallel spin interaction between excitons localized in the nonmagnetic QDs and in the magnetic QDs.

We investigated time-resolved differential reflection in GaMnAs by pump-probe method at various wavelengths. The signals in GaMnAs were found to be more influenced by the compensating nature of the samples, rather than by the Mn concentrations. The time-resolved reflectivity of highly compensated samples exhibited stronger negative ∆R component at photon energies higher than the bandgap energy. This behaviour was similar to that of As + -ion implanted GaAs. Our results suggest that arsenic antisites (As Ga ) act as deep donors as in low-temperature grown GaAs and play an important role in compensating holes in GaMnAs.

Nearly complete spin polarization (SP) of carriers was observed in photoluminescence (PL) experiments on CdSe self-assembled quantum dots (QDs) embedded in ZnMnSe at 5 K in magnetic fields above 1 T. The redshift of the PL from CdSe QDs in the presence of the magnetic field was less than that of ZnMnSe, but still sufficiently large to account for the high SP. At low fields, however, the SP of carriers in CdSe QDs is observed to be smaller than in the surrounding ZnMnSe. This, along with time-resolved PL data, suggests that the SP in CdSe QDs is mainly due, not to the injection of SP carriers from ZnMnSe, but rather due to the Zeeman splitting of internal QD states.