Berlin 2005 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 63: Ultrakurzzeitph
änomene
HL 63.2: Vortrag
Mittwoch, 9. März 2005, 11:00–11:15, TU P-N201
Ultrafast spin-preserving carrier capture into InGaAs/GaAs quantum dots — •S. Trumm1, M. Wesseli1, A. Laubereau1, M. Betz1, H. J. Krenner2, A. Kress2, D. Schuh2, and J. J. Finley2 — 1Physik-Department E11, TU München, 85748 Garching — 2Walter-Schottky-Institut, TU München, 85748 Garching
The carrier capture and relaxation processes in an ensemble of self assembled InGaAs/GaAs quantum dots (QDs) are studied in a two-color femtosecond transmission experiment. Carriers are injected resonantly into the wetting layer (WL) by a 100 fs pump pulse centered at 1.51 eV. The transmission changes of both the band edge of the WL at 1.45 eV and the excited states of the QDs at 1.38 eV are detected. This nonlinear optical response directly reveals the population of the corresponding states.
For low pump intensities the population of the WL decays with a time constant of 4 ps. In parallel, the occupation of the QD p-shell builds up giving rise to the interpretation of this time scale as carrier capture time. Interestingly, this capture time does not depend on the excitation density as long as it is small as compared to the number of electronic states available in the QDs. Moreover, exploiting the selection rules for circularly polarized excitation and probe pulses, we find a predominantly spin-preserving nature of the capture process. These results suggest a phonon mediated scattering process to govern the capture of carriers into the QDs. This finding may be an important ingredient for the optimization of modern quantum dot lasers.