Dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots of CdSe coupled with a diluted magnetic semiconductor layer of Zn0.80 Mn0.20 Se
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 19, 195308- p.Article in journal (Refereed) Published
We study the dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of Zn0.80 Mn0.20 Se, where spin-polarized excitons can be injected from the DMS into the QDs. The degree of circular polarization P of excitonic photoluminescence (PL) at 5 T in the coupled QDs exhibits a rapid increase with increasing delay time, up to +0.3 at 25 ps after the pulse excitation of the DMS by a linearly polarized light. This development of a positive P value directly reflects the spin-injection dynamics from the DMS, since the intrinsic polarization of the QD excitons due to Zeeman splitting is P∼-0.1 when only the QDs are selectively excited. The P value gradually decays with time after reaching its maximum, as a result of the exciton-spin relaxation with a time constant of 800 ps in the QDs. Time-resolved circularly polarized PL spectra immediately after the pulse excitation directly show the exciton-energy dependence of the spin-injection dynamics in the QD ensemble, where two-dimensional-like QDs with higher exciton energies show higher receptivity to the spin-polarized excitons than three-dimensional-like dots with lower exciton energies. A rate equation analysis reveals all time constants responsible for the spin-injection dynamics. We deduce a time constant of 10 ps for the spin injection. The spin-injection efficiency of 0.94 is also obtained, which corresponds to the ratio between the number of the spin-polarized excitons responsible for the rise of the positive P value in the QD emission and the total number of the excitons injected from the DMS. Moreover, we observe that interdot exciton transfer significantly affects the P value within the QD emission band after the fast spin injection, in addition to the spin relaxation within the QDs. © 2007 The American Physical Society.
Place, publisher, year, edition, pages
2007. Vol. 75, no 19, 195308- p.
National CategoryNatural Sciences Condensed Matter Physics
IdentifiersURN: urn:nbn:se:liu:diva-38834DOI: 10.1103/PhysRevB.75.195308Local ID: 45827OAI: oai:DiVA.org:liu-38834DiVA: diva2:259683