Polariton effects in the dielectric function of ZnO excitons obtained by ellipsometry

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 pol...

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Bibliographic Details
Published in:Applied physics letters 2010-01, Vol.96 (3)
Main Authors: Cobet, Munise, Cobet, Christoph, Wagner, Markus R., Esser, Norbert, Thomsen, Christian, Hoffmann, Axel
Format: Article
Language:English
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Summary: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, corresponding to the k-vector of the used light, are deduced precisely for each subband. 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.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.3284656