Regensburg 2010 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 49: Optical Properties
HL 49.10: Vortrag
Donnerstag, 25. März 2010, 12:00–12:15, H14
Longitudinal-transverse splitting of individual excitonic
polaritons in ZnO derived from ellipsometry — •Munise Cobet1, Christoph Cobet2, Markus R. Wagner1, Norbert Esser2, and Axel Hoffmann1 — 1Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin — 2ISAS- Institute for Analytical Sciences, 12489 Berlin
The complex dielectric tensor of ZnO in the regime of the excitonic transitions is determined with ellipsometry and analyzed concerning the quantization of the electromagnetic field in terms of coupled polariton-eigenmodes. Negative sections in the real part indicate the significant formation of polaritons for the dipole-allowed excitons of the three upper valence-bands Γ7,Γ9,Γ7. The transverse-longitudinal splittings which separate the upper polariton branch from the lower branch are deduced precisely for each subband and for different strain levels. Mainly for E∥c, additional absorption peaks are observed at the longitudinal B-exciton and closely above. One is considered to be a mixed-mode and the other is seen as a consequence of interference effects in an exciton free surface layer which is also visible in Reflectance Anisotropy Spectroscopy (RAS). Furthermore, the effect of d-level-hybridization on valence-band-symmetries is evaluated by the effective number of electrons neff in high energy data between 3 and 32 eV. CdS polaritonic spectra were also measured as a reference and further support the inversed ordering of valence bands (negative spin-orbit splitting) in ZnO.