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Phys. Rev. B 59, 4973 - 4979 (1999)

Dynamics of exciton localization in CdS/HgS quantum-dot quantum wells
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Alvin T. Yeh
Department of Chemistry, University of California, Berkeley, California 94720
Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 2-300, Berkeley, California 94720

Giulio Cerullo *
Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 2-300, Berkeley, California 94720

Uri Banin † and Alf Mews ‡
Department of Chemistry, University of California, Berkeley, California 94720

A. Paul Alivisatos and Charles V. Shank
Department of Chemistry, University of California, Berkeley, California 94720
Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 2-300, Berkeley, California 94720

Received 17 August 1998

Localization of carrier wave functions to the quantum-well portion of the CdS/HgS quantum-dot quantum well (QDQW) is investigated. Nanosecond hole-burning (HB) spectra measure the photoinduced exciton coupling to a 250-cm-1 HgS phonon mode indicative of localization. Femtosecond pump-probe spectroscopy of these QDQW, however, show the photoinduced exciton couples to coherent 300-cm-1 CdS longitudinal optical-phonon modes, which is indicative of delocalization throughout the QDQW.  Femtosecond HB and three pulse pump-dump experiments reveal these results are dependent on the time scale of the experiment. These experiments indicate that the initially photoexcited electron and hole wave functions are weakly confined to the HgS monolayer. Only after long times (∼400 fs) will the exciton localize to the HgS well. These results indicate that the primary optical interaction excites electrons from a delocalized QDQW ground state and not from a localized HgS well state.


©1999 The American Physical Society

URL: http://link.aps.org/abstract/PRB/v59/p4973
DOI: 10.1103/PhysRevB.59.4973
PACS: 73.20.Dx, 73.20.Fz

* Present address: Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy.
† Present address: Department of Physical Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
‡ Present address: Institut fuer Physikalische Chemie, Universitaet Mainz, Welderweg 11, D-55099 Mainz, Germany.

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