1. |
- Dagnelund, Daniel, et al.
(author)
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Carrier and Spin Injection from ZnMnSe to CdSe Quantum Dots
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Other publication (other academic/artistic)abstract
- Optical carrier/exction and spin injection processes from a ZnMnSe dilute magnetic semiconductor (DMS) to CdSe quantum dots (QD’s) are studied in detail by means of spinpolarized magneto- photoluminescence (PL) and PL excitation spectroscopies. Efficiency of carrier/exciton transfer is found to be practically independent of width (Lb) of a ZnSe barrier layer inserted between the DMS and QD’s. This is tentatively explained in terms of photonexchange energy transfer. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with large Lb, pointing towards increasing spin loss.
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2. |
- Dagnelund, Daniel, 1980-, et al.
(author)
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Carrier and spin injection from ZnMnSe to CdSe quantum dots
- 2008
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Conference paper (other academic/artistic)abstract
- Optical carrier/exction and spin injection processes from a ZnMnSe dilute magnetic semiconductor (DMS) to CdSe quantum dots (QD’s) are studied in detail by means of spinpolarized magneto- photoluminescence (PL) and PL excitation spectroscopies. Efficiency of carrier/exciton transfer is found to be practically independent of width (Lb) of a ZnSe barrier layer inserted between the DMS and QD’s. This is tentatively explained in terms of photonexchange energy transfer. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with large Lb, pointing towards increasing spin loss.
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3. |
- Dagnelund, Daniel, 1980-, et al.
(author)
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Efficiency of optical spin injection and spin loss from a diluted magnetic semiconductor ZnMnSe to CdSe nonmagnetic quantum dots
- 2008
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 77:3, s. 035437-
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Journal article (peer-reviewed)abstract
- Magneto-optical spectroscopy in combination with tunable laser spectroscopy is employed to study optical spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe into nonmagnetic CdSe quantum dots (QDs). Observation of a DMS feature in the excitation spectra of the QD photoluminescence polarization provides clear evidence for optical spin-injection from the DMS to the QDs. By means of a rate equation analysis, the injected spin polarization is deduced to be about 32% at 5 T, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process including crossing the heterointerfaces and energy relaxation within the QDs. © 2008 The American Physical Society.
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4. |
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5. |
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6. |
- Dagnelund, Daniel, et al.
(author)
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Magneto-optical and tunable laser excitation spectroscopy of spin-injection and spin loss from Zn(Cd)MnSe diluted magnetic quantum well to CdSe non-magnetic quantum dots
- 2008
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Conference paper (peer-reviewed)abstract
- Magneto-optical spectroscopy in combination with tunable laser spectroscopy is employed to study the effect of sample design on optical spin-injection efficiency from a Zn(Cd)MnSe diluted magnetic semiconductor (DMS) into non-magnetic CdSe quantum dots (QDs). Two samples with inverted growth sequence of the DMS and QD layers were grown for this purpose. Despite observation of clear evidence for exciton/carrier-injection from the DMS to the QDs in both structures, their spin-injection efficiency is markedly different. The structure grown with the QD layer topmost exhibits rather efficient spin-injection, while the structure grown with the DMS layer topmost does not show any sign of spin-injection. Even in the former case, the spin-polarization of the injected excitons/carriers is deduced to be about 32%, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin-injection across the heterointerfaces. © 2007 Elsevier B.V. All rights reserved.
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7. |
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8. |
- Dagnelund, Daniel, et al.
(author)
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Spin injection in a coupled system of a diluted magnetic semiconductor Zn0.80Mn0.20Se and self-assembled quantum dots of CdSe
- 2008
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In: Proceedings of the 7th International Conference on Physics of Light-Matter Coupling in Nanostructures. - : Elsevier BV. ; , s. 615-619
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Conference paper (peer-reviewed)abstract
- Spin injection processes from a Zn0.80Mn0.20Se diluted magnetic semiconductor (DMS) to adjacent self-assembled CdSe quantum dots (QDs) were investigated by cw and time-resolved magneto-optical spectroscopy in combination with tunable laser excitation. Direct experimental evidence for the spin injection was provided from the generation of the spin polarization in the QDs, which was opposite to their expected intrinsic polarization, by resonantly generating the spins in the DMS. The observed limited spin polarization generated by the spin injection, together with the sensitivity of the spin injection efficiency on structure design, indicates severe spin loss during the process and calls for further investigations to optimize spin injection efficiency in quantum structures. © 2007 Elsevier Ltd. All rights reserved.
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9. |
- Furuta, T., et al.
(author)
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Spin-injection dynamics and effects of spin relaxation in self-assembled quantum dots of CdSe
- 2008
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In: Journal of the Korean Physical Society. - 0374-4884 .- 1976-8524. ; 53, s. 163-166
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Journal article (peer-reviewed)abstract
- We study the spin injection dynamics and the effects of spin relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin-polarized excitons can be injected from the DMS into the QDs because of the potential difference. The degree of circular polarization, $P$, of excitonic photoluminescence (PL) at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulse excitation, indicating the spin-injection dynamics. The $P$ value tends to decay gradually because of the exciton-spin relaxation in the QDs after the spin injection. The spin-polarized excitons in the QD ensemble migrate simultaneously from QDs with higher exciton energies to those with lower exciton energies. This inter-dot transfer of excitons also affects the $P$ value in the lower energy region of the QD-emission band because the excitons lose their spin polarizations due to the spin relaxation in the dots during the migration. The detailed analysis for the exciton-spin transfer is presented in a coupled QD system after spin injection.
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10. |
- Murayama, A., et al.
(author)
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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
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:19, s. 195308-
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Journal article (peer-reviewed)abstract
- 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.
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11. |
- Murayama, A., et al.
(author)
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Propagation dynamics of exciton spins in a high-density semiconductor quantum dot system
- 2009
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In: physica status solidi c. - : phys. stat. sol. c. - 1862-6351 .- 1610-1642.
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Conference paper (peer-reviewed)abstract
- We study propagation dynamics of exciton spins in a system composed of high-density self-assembled quantum dots (QDs) of CdSe and a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin-polarized excitons are generated in the DMS layer and are subsequently injected into the QDs. The degree of circular polarization, P, of excitonic photoluminescence at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulsed excitation, indicating the exciton-spin injection from the ZnMnSe to CdSe-QDs. The P value tends to decay gradually because of the exciton-spin relaxation in the QDs after the injection. The spin-polarized excitons in the QD ensemble migrate simultaneously from the QDs with higher exciton energies to those with lower exciton energies, where the exciton-spins relax inside each dot during the migration. Therefore, the observed P values in the QD emission band are affected by this feeding of the relaxed spins.
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12. |
- Murayama, A, et al.
(author)
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Transfer dynamics of spin-polarized excitons into semiconductor quantum dots
- 2009
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In: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 129, s. 1927-1930
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Journal article (peer-reviewed)abstract
- We study on the transfer dynamics of spin-polarized excitons into self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ZnMnSe through a ZnSe barrier layer. A variation in the degree of circular polarization P of excitonic photoluminescence in the coupled QDs was observed between samples with different thicknesses (LB) of the non-magnetic barrier. Relatively high values of P (0.3) were obtained in the samples with LB=1 or 2 nm, and the time dependences of the P value indicate the spin-transfer dynamics. From the LB dependence of the spin-transfer time, the spin-transfer mechanism is discussed, namely spin-conserving energy transfer.
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13. |
- Park, J. H., et al.
(author)
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Transfer dynamics of spin-polarized excitons in ZnCdMnSe/ZnCdSe double quantum wells
- 2008
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In: Journal of the Korean Physical Society. - 0374-4884 .- 1976-8524. ; 53, s. 167-170
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Journal article (peer-reviewed)abstract
- We study the transfer dynamics of spin-polarized excitons in diluted magnetic semiconductor (DMS) double quantum wells (QWs) of ZnCdMnSe/ZnCdSe, where the spin-polarized excitons tunnel from the non-magnetic ZnCdSe to DMS-ZnCdMnSe wells and subsequently relax to the ground state in the DMS well with phonon emissions. The exciton-transfer time decreases when the exciton-energy difference between both the wells is equal to the one-LO-phonon energy, indicating the LO-phonon-assisted acceleration of the spin transfer. Moreover, the exciton transfer alters into the separate transfer of the electron and the heavy hole when the electron potential difference becomes larger than the LO-phonon energy. This observation demonstrates the importance of energy-relaxation dynamics in the spatial transport of spins in semiconductor quantum structures.
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