Dresden 2009 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 9: Poster 1
HL 9.57: Poster
Monday, March 23, 2009, 14:30–17:00, P2
Anisotropy of the dielectric function of ZnO including exciton-polariton formation obtained from ellipsometry — •Munise Cobet1, Ronny Kirste1, Markus Wagner1, Axel Hoffmann1, Christoph Werner2, Christoph Cobet2, Norbert Esser2, and Christian Thomsen1 — 1Institut für Festkörperphysik, TU Berlin, 10623 Berlin — 2ISAS- Institute for Analytical Sciences, 12489 Berlin
The complex dielectric tensor of ZnO is obtained by analysis of ellipsometric data for photon energies of 2.5-32 eV. The comparison to ab-initio calculations performed including many-body effects shows a good agreement for both independent components. A strong anisotropy mainly above 10 eV could be verified by our results. At the band gap ZnO shows free exciton absorptions containing a significant formation of polaritons and the related exciton-phonon-complexes. The scattering near k=0 with the longitudinal optical phonon shows up in a replication of the three-peak structure every 72meV but might be mixed with higher excitations (n=2,3,.). A possible reversal in the two upper valence bands due to a negative spin-orbit-splitting is considered as a consequence of the near resonance between the Zn3d-level and the O2p-orbital (p-d-repulsion). Vice versa, strain as a structural treatment could affect the d-level or lead to changes in the crystal-field interaction. Raman and XRD revealed even in homoepitaxial grown samples the existence of strain. At energies 9.5-16 eV transitions including the 3d-level and at higher energies O2s-core-level occur. The loss function shows prominent peaks at the plasmon frequencies ℏωp.