Coherent dynamics in InGaAs quantum dots and quantum dot molecules |
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Authors: | W Langbein P Borri U Woggon M Schwab M Bayer S Fafard Z Wasilewski P Hawrylak V Stavarache D Reuter AD Wieck |
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Institution: | aExperimentelle Physik II, Universität Dortmund, Otto-Hahn Str. 4, 44227 Dortmund, Germany;bInstitute for Microstructural Science, National Research Council, Ottawa, Canada, K1A 0R6;cAngewandte Festkörperphysik, Ruhr-Universität Bochum, 44780 Bochum, Germany |
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Abstract: | We measure the dephasing time of the exciton ground state transition in InGaAs quantum dots (QD) and quantum dot molecules (QDM) using a sensitive four-wave mixing technique. In the QDs we find experimental evidence that the dephasing time is given only by the radiative lifetime at low temperatures. We demonstrate the tunability of the radiatively limited dephasing time from 400 ps up to 2 ns in a series of annealed QDs with increasing energy separation of 69–330 meV from the wetting layer continuum. Furthermore, the distribution of the fine-structure splitting δ1 and of the biexciton binding energy δB is measured. δ1 decreases from 96 to with increasing annealing temperature, indicating an improving circular symmetry of the in-plane confinement potential. The biexciton binding energy shows only a weak dependence on the confinement energy, which we attribute to a compensation between decreasing confinement and decreasing separation of electron and hole. In the QDM we measured the exciton dephasing as function of interdot barrier thickness in the temperature range from 5 to 60 K. At 5 K dephasing times of several hundred picoseconds are found. Moreover, a systematic dependence of the dephasing dynamics on the barrier thickness is observed, showing how the quantum mechanical coupling in the molecules affects the exciton lifetime and acoustic-phonon interaction. |
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Keywords: | Quantum dots Dephasing Four-wave mixing Coupled quantum dots Exciton fine-structure Biexcitons |
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