Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 13: Poster 1
HL 13.18: Poster
Montag, 26. März 2007, 15:00–17:30, Poster A
Anisotropic optical properties and excitonic structure of ZnO between 2.5 and 32eV — •Christoph Cobet1, Munise Rakel1,2, Christoph Werner1, Wolfgang Richter2,3, and Norbert Esser1,2 — 1ISAS - Institute for Analytical Sciences, Department Berlin, Albert-Einstein-Str. 9, D-12489 Berlin — 2Institut für Festkörperphysik, TU-Berlin, Hardenbergstr. 36, D-10623 Berlin — 3Dipartimento di Fisica, C139 Roma II (Tor Vergata), Via della Ricerca Scientifica 1, I-00133 Rome
The dielectric response functions of bulk ZnO for polarisations parallel and perpendicular to the c-axis are obtained in the spectral range from 2.5 to 32 eV by analysis of ellipsometric data. The optical absorption of ZnO in the direct band gap region is highly complex and cannot be explained only in terms of interband or pure excitonic absorption. The main peaks can be divided into two classes, which also differ in their temperature dependence: The dominant exciton absorptions and the so called exciton-phonon complexes. It is shown that the ordering of valence band maxima at k=0 is Γ9−Γ7−Γ7 analog to the most wurtzite compounds. At higher energies electronic transitions involving Zn-3d and O-2s bands are detected. Although the O2s-levels are core-like, they show a residual anisotropy. Finally, the plasmon frequency was recorded to be ℏωp=18.95 eV for E⊥ c and 18.12 eV for E∥ c, respectively.