Browsing by Author "Chou, W-C."

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Coherent Aharonov-Bohm oscillations in type-II (Zn,Mn)Te/ZnSe quantum dots
(2008-06-01)
Sellers, I. R.
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Whiteside, V. R.
;
Govorov, A. O.
;
Fan, W. C.
;
Chou, W-C.
The magneto-photoluminescence of type-II (Zn,Mn)Te quantum dots is presented. As a result of the type-II band alignment, Aharonov-Bohm (AB) oscillations in the photoluminescence intensity are evident. In addition, an interesting interplay between the AB effect and the spin polarization in these diluted magnetic semiconductor quantum dots is observed. The intensity of the AB oscillations increases with both magnetic field and the degree of optical polarization, indicating that the suppression of spin fluctuations improves the coherence of the system.
Coulomb induced recombination dynamics in magnetically doped type-IIb quantum dots
(2019-01-01)
Tarasek, S.
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Chou, W-C.
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Fan, W. C.
;
Cartwright, A. N.
;
Thomay, T.
We observe that the wavefunction overlap of the carriers in type-IIb quantum dots can be controlled by magnetic doping and strongly depends on the excitation power density. We study epitaxially grown ZnTe/ZnSe and magnetically doped (Zn,Mn)Te/ZnSe quantum dots that show a fast and slow recombination channel at two different energies. The emission shift of the slow recombination is independent of excitation power density (P-ex), whereas the fast recombination channel exhibits a larger emission shift with increasing P-ex. This blue shift saturates for high P-ex, however at a lower P-ex and smaller maximum shift in the magnetic system compared to the nonmagnetic system. The emission wavelength immediately after pulsed excitation typically changes as a function of charge carrier density due to the spatially indirect nature of type-IIb quantum dots. As carriers increase, the confinement potential of the system is altered due to a Coulomb interaction. The magnetic system exhibits a limited change in the wavefunction overlap of the carriers for high excitation power densities which we attribute to magnetic interactions to the hole wavefunction inside the dot. This would allow for an external manipulation of the magnetic polaron binding energy through varying the excitation power density P-ex in quantum dots.
Robust Coherent Magneto-optical Properties of Columnar Type-II Quantum Dots in ZnTe/ZnSe and ZnMnTe/ZnSe Systems
(2011-01-01)
Whiteside, V. R.
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Sellers, I. R.
;
Eginligil, M.
;
Oszwaldowski, R.
;
Petrou, A.
We present recent experimental results that show strong optical AB effects in the magneto-photoluminescence of columnar II-VI quantum dots (QDs). The AB effects manifest themselves as oscillations in the photoluminescence energy and intensity with magnetic field. It will be shown that this coherent behavior is remarkably robust, persisting at 180K. We, also, present results for a magnetic system, ZnMnTe QDs. These magnetic type-II systems also display evidence of robust magnetic ordering. This behavior is attributed to the formation of magnetic polarons caused by the exchange interaction between strongly localized holes and Mn ions within the QDs. Time-resolved PL measurements display evidence of magnetic polarons up to 200K with a binding energy of approximately 40 meV.
Time-resolved magnetophotoluminescence studies of magnetic polaron dynamics in type-II quantum dots
(2015-07-24)
Barman, B.
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Oszwaldowski, R.
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Schweidenback, L.
;
Russ, A. H.
;
Pientka, J. M.
We used continuous wave photoluminescence (cw-PL) and time-resolved photoluminescence (TR-PL) spectroscopy to compare the properties of magnetic polarons (MP) in two related spatially indirect II-VI epitaxially grown quantum dot systems. In the ZnTe/(Zn, Mn)Se system the holes are confined in the nonmagnetic ZnTe quantum dots (QDs), and the electrons reside in the magnetic (Zn, Mn)Se matrix. On the other hand, in the (Zn, Mn)Te/ZnSe system, the holes are confined in the magnetic (Zn, Mn)Te QDs, while the electrons remain in the surrounding nonmagnetic ZnSe matrix. The magnetic polaron formation energies E-MP in both systems were measured from the temporal redshift of the band-edge emission. The magnetic polaron exhibits distinct characteristics depending on the location of the Mn ions. In the ZnTe/(Zn, Mn)Se system the magnetic polaron shows conventional behavior with E-MP decreasing with increasing temperature T and increasing magnetic field B. In contrast, E-MP in the (Zn, Mn)Te/ZnSe system has unconventional dependence on temperature T and magnetic field B; E-MP is weakly dependent on T as well as on B. We discuss a possible origin for such a striking difference in the MP properties in two closely related QD systems.