ФТТ, 2006, том 48, выпуск 10

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Enhancement of the photoluminescence intensity of a single InAs/GaAs quantum dot by separate generation of electrons and holes

V.Donchev\kern1pt*,**, E.S.Moskalenko\kern1pt*,***, K.F.Karlsson\kern1pt*, P.O.Holtz\kern1pt*, B.Monemar\kern1pt*,
W.V.Schoenfeld\kern1pt****, J.M.Garcia\kern1pt*****, P.M.Petroff\kern1pt****

* Department of Physics and Measurement Technology, Linkoping University,
S-58183 Linkoping, Sweden
** Faculty of Physics, Sofia University,
1164 Sofia, Bulgaria
*** A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences,
194021 St. Petersburg, Russia
**** Materials Department, University of California,
Santa Barbara, California 93106 USA
***** Instituto de Microelectronica de Madrid, CNM-CSIC Isaak Newton 8, PTM,
28760 Tres Cantos, Madrid, Spain
E-mail: evgenii.moskalenko@mail.ioffe.ru

(Received January 24, 2006)

It is demonstrated that the micro-photoluminescence (muPL) spectrum of a single InAs/GaAs self-assembled quantum dot (QD) undergoes considerable changes when the primary laser excitation is complemented with an additional infrared laser. The primary laser, tuned slightly below the GaAs band gap, provides electron-hole pairs in the wetting layer (WL), as well as excess free electrons from ionized shallow acceptors in the GaAs barriers. An additional IR laser with a fixed energy, well below the QD ground state transition, generates excess free holes from deep levels in GaAs. The excess electron and hole will separately experience a diffusion, due to the time separation between the two events of their generation, to eventually become captured into the QD. Although the generation rates of excess carries are much lower than that of the electron-hole pairs generation in the WL, they influence considerably the QD emission at low temperatures. The integrated PL intensity increases by several times compared to single laser excitation and the QD exciton spectrum is redistributed in favor of a more neutral charge configuration. The dependence of the observed phenomenon on the powers of the two lasers and the temperature has been studied and is in consistence with the model proposed. The concept of dual excitation could be successfully applied to different low-dimensional semiconductor structures in order to manipulate their charge state and emission intensity.

This work was supported by grants from the Swedish Foundation for Strategic Research (SSR) and Swedish Research Council (VR). Financial support from the Wenner-Gren Foundation and the program \glqq Low-Dimensional Quantum Structures\grqq of the Russian Academy of Sciences is achnowledged by E.S.M. V.D. is thankful for financial support from the Swedish Foundation for International Cooperation in Research and Higher Education (STINT) and from the Bulgarian National Science Fund.

PACS: 78.67.Hc, 71.55.Eq, 73.50.Gr

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