We report a systematic study of magneto-optical properties in CdZnSe/ZnSe semiconductor quantum dots ͑QDs͒ subjected to postgrowth thermal annealing. The theoretical and experimental characterizations are combined in order to understand the evolution of Zeeman splitting and the blueshift as well as redshift of the magnetic subcomponents with magnetic field strength of excitons confined in annealed QDs as a function of different annealing times. A combination of a multiband model as well as parameter interpolation supported by ab initio calculations is presented and points toward an inversion of the light-hole-heavy-hole states due to annealing. The band mixing of exciton states explains besides the variation in the Zeeman splitting for differently annealed QD excitons, the evolution of the diamagnetic blueshift into a paramagnetic redshift of the magnetic subcomponents. A discussion of the effects associated to the Coulomb interaction on the polarized excitonic recombinations modulated by magnetic field is given.

A negative magnetic dispersion of the degree of circular polarization is reported for the photoluminescence of self-assembled ZnCdSe quantum dots ͑QDs͒ after a postgrowth thermal annealing ͑TA͒ treatment. Multiband calculations in the framework of the k · p model reveal that the phenomenon is explicable considering, apart from the changes in the confinement and composition of the QDs due to TA-induced Zn-Cd interdiffusion, the presence of extra charges of one kind within the structure. Magneto-optical properties of self-assembled semiconductor quantum dots ͑QDs͒ have emerged in the recent years as a widely pursued field of research, 1,2 triggered by the possibility of using the spin degree of freedom of a threedimensionally confined exciton to realize the basic building blocks of quantum information processing. 3,4 The magnetooptical response of an individual QD and an ensemble of QDs yields much fundamental information, imperative to achieving this goal, i.e., the spin splitting of the exciton ground state 5-10 and the spin lifetime of the electron and the hole comprising the exciton. 11,12 The polarization behavior of photoluminescence ͑PL͒, emitting from QDs in the presence of a magnetic field, serves as an excellent tool to probe the exciton spin dynamics in QDs.In this work, the evolution of the degree of circular polarization ͑DCP͒ has been studied for the magneto-PL of epitaxially self-assembled ZnCdSe QDs before and after a postgrowth rapid thermal annealing ͑TA͒ treatment. While for the as-grown ͑not-annealed͒ QDs the DCP undergoes a reversal from positive to negative sign beyond a magnetic field strength of B = 3 T, we demonstrate here that the DCP corresponding to the annealed QDs exhibits a negative magnetic dispersion in the entire range of B =0-5 T. A multiband calculation in the framework of the k · p theory reveals that apart from changes in the composition and configuration of the QDs due to TA-induced interdiffusion of Zn and Cd, the presence of extra charges of one kind needs to be taken into account. Albeit spin splitting and DCP of magneto-PL have been studied for quantum wells of a few systems, 10,13 such studies for three-dimensionally confined excitons, especially their evolution with changing composition and confinement of QDs, to the best of our knowledge, has not been pursued so far.The samples under investigation were grown by molecular beam epitaxy on top of homoepitaxially grown undoped GaAs buffers on GaAs:Si ͑100͒ substrates. The CdSe QD layer was embedded between a 50 nm thick ZnSe buffer layer, grown atop a GaAs pseudosubstrate, and a 25 nm thick ZnSe cap layer. In this manner, two different samples were realized with the CdSe layer either nominally 2 or 1 ML thick. In CdSe/ ZnSe heteroepitaxy, QDs ensue due to fluctuations in Cd concentration in an alloyed Zn 1−x Cd x Se quantum-well ͑QW͒-like structure.Postgrowth rapid thermal annealing of the samples was performed in a N 2 environment at T A = 500°C. Thermal annealing induces a pronounced blueshift of the PL spectra as demonst...

The photoluminescence of annealed Cd x Zn 1−x Se quantum dots (QDs) under the influence of an external magnetic field has been studied in this paper. Post-growth annealing was performed for different annealing times. Above a critical annealing time, the QD luminescence shows a pronounced red-shift of the Zeeman split magnetic subcomponents. This observation is in contrast to the blue-shift caused by the diamagnetic behavior that is usually observed in non-magnetic QDs. We attribute our finding to the paramagnetism caused by the mixing of heavy and light hole states. Hence, post-growth thermal annealing treatment might be employed to render undoped epitaxial 7

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