Regensburg 2000 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 20: Ultrakurzzeitdynamik I
HL 20.9: Vortrag
Dienstag, 28. März 2000, 17:00–17:15, H17
Directional Secondary Emission of a Semiconductor Microcavity — •Wolfgang Langbein1, Jacob R. Jensen2, and Jørn M. Hvam2 — 1Lehrstuhl für Experimentelle Physik EIIb, Universität Dortmund, 44227 Dortmund — 2Research Center COM, DTU Bldg. 349, 2800 Lyngby, Denmark
We investigate the time-resolved secondary emission of a homogeneously broadened microcavity after resonant excitation. The sample consists of a 25 nm GaAs single quantum well (QW) in the center of a wedged λ cavity with AlAs/AlGaAs Bragg reflectors, grown by molecular beam epitaxy. At zero detuning between the cavity and the heavy-hole exciton, equal lorentzian linewidths of 180 µeV are observed for the three polariton modes in the reflectivity, which are created from the cavity, heavy-hole exciton, and light-hole exciton resonances. When resonantly exciting the lower polariton mode, the secondary emission shows a strong directional dependence due to its large in-plane dispersion. Four different components of the emission can be distinguished. (i) strong coherent emission scattered in the directions [110], [110] by nonresonant scattering of the Bragg-mirrors. (ii) coherent emission scattered on a ring with nearly constant in-plane momentum ℏ|k||→| by random disorder of the QW or the mirrors. (iii) an incoherent emission on a similar ring, possibly by photoluminescence of impurities. (iv) an incoherent emission over a wide emission angle range, by photoluminescence of QW excitons. The emission dynamics are time-resolved with picosecond resolution, and the dependencies on the excitation conditions and the lattice temperature are presented and used to identify the origin of the different components.