Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 36: Heterostructures
HL 36.6: Vortrag
Donnerstag, 29. März 2007, 11:15–11:30, H14
Intersubband-dephasing in an undoped multi-quantum well — •Martin Wagner1, Dominik Stehr1, Harald Schneider1, Stefan Winnerl1, Manfred Helm1, Max Andrews2, Tomas Roch2, and Gottfried Strasser2 — 1Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, Postfach 510119, 01314 Dresden — 2Institut für Festkörperelektronik, TU Wien, Floragasse 7, 1040 Wien, Österreich
We have investigated the dephasing time associated with intersubband transitions of photocarriers in an undoped GaAs/AlGaAs multi quantum-well heterostructure. Our measurements were performed directly in the time-domain. After optical generation of electron-hole pairs across the band-gap, a resonant THz-pulse excited the electrons to the second subband and generated a coherent polarization involving the ground and the first excited subbands. The re-radiation from this polarization was detected by a cross-correlation technique with a second THz-pulse. The polarization was observed to decay with short decay-times between 50 fs and approx. 200 fs. They depend on the carrier concentration which was adjusted by the optical excitation power. These time constants determine directly the linewidth of this intersubband transition. At low temperatures, the dephasing signals show a pronounced beating at all optical excitation powers which we attribute to excitonic effects such that more than two energy levels are involved in the interaction with the THz-pulse.
By varying the excitation power, we also found a strong depolarization shift of the absorption line.