Regensburg 2002 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 23: II-VI Halbleiter

HL 23.2: Vortrag

Dienstag, 12. März 2002, 15:30–15:45, H17

Exciton Transport in Quantum Wells: Coherent and Hot Exciton Regimes — •H. Zhao, S. Moehl, B. Dal Don, and H. Kalt — Institut für Angewandte Physik, Universität Karlsruhe, D-76128 Karlsruhe, Germany

We investigate the in-plane transport of excitons in ZnSe quantum wells by solid immersion lens (SIL)-enhanced micro-photoluminescence with a spatial resolution of 200 nm (HWHM of the Airy pattern). The collection efficiency of the system is improved by more than 4 times by introducing the SIL. We study the spatial evolution of the coherent exciton luminescence, and determine the coherent length of the excitons to be 300∼ 400 nm, about 25∼ 30 times of the exciton de Broglie wavelength. The coherent length decreases slowly with increasing the exciton energy, consistent with the fact that the coherent transport process is terminated by acoustic phonon scattering. The hot exciton relaxation during the transport is studied directly by monitoring the spatial evolution of the LO-phonon sideband, thus the exciton energy distribution function. The average energy of the excitons drops by less than 20% after a transport of 1.5 µm. Together with a strong periodic dependence of the transport length on the laser excess energy with a period of LO-phonon energy, we conclude that the transport on the length scale of several µm is dominated by hot excitons if the excitons are generated energetically. In the case of cold-exciton injection, we identify the phonon wind driven transport process from the excitation intensity dependence of the transport behavior.