Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 51: Poster IV
HL 51.48: Poster
Donnerstag, 28. Februar 2008, 16:30–19:00, Poster D
Polarisation dependence of the free discrete exciton luminescence in ZnO microwires — •Rüdiger Schmidt-Grund, Helena Hilmer, Christian Czekalla, Bingqjang Cao, Chris Sturm, and Marius Grundmann — Universität Leipzig, Fakultät für Physik und Geowissenschaften, Inst. für Exp. Physik II, Linnéstr. 5, 04103 Leipzig
We report on the polarisation dependence of the free discrete exciton luminescence recorded from unstrained single-crystal ZnO microwires at temperatures between 10 K and room temperature. The threefold split topmost valence band in ZnO gives rise to the formation of three excitons (labeled A, B, C for increasing energy) with different energies and different selection rules for the coupling to light polarised parallel (pc) or perpendicular (sc) to the ZnO optical axis, specified by the symmetry of the valence bands. The sign of the spin-orbit and crystal field interaction and therefore the symmetry order of the three valence bands for ZnO is still a subject under debate. For our samples, at temperatures larger than 180 K, the emission from the A- and B-excitons was found to dominate the photoluminescence spectra for polarisation sc, while the C-exciton is more pronounced in the spectra for polarisation pc. This finding is concordant with predictions made for a valence band order Γ7-Γ9-Γ7. At very low temperatures, no luminescence of the C-exciton for any polarisation could be detected, but the luminescence from the A- and B-excitons is suppressed for the polarisation pc. As the intensity of the C-exciton luminescence increases with increasing temperature, we attribute this finding to be caused in the temperature dependence of the occupation function of the exciton states.