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O: Fachverband Oberflächenphysik

O 65: Density functional theory and beyond for real materials III

O 65.1: Vortrag

Donnerstag, 25. März 2010, 10:30–10:45, H34

Mott transition and Mahan exciton in MgO and ZnO from first principles — •André Schleife, Claudia Rödl, Frank Fuchs, Karsten Hannewald, and Friedhelm Bechstedt — Institut für Festkörpertheorie und -optik, Jena, Germany

Under the name “Transparent Electronics” a field is emerging, which already attracted interest, mainly due to the demand for transparent conducting materials for solar cells. Driven by the next generation of optoelectronic devices it is expected to grow even further.
Especially important in this context are the transparent conducting oxides. To combine transparence and conductivity, free carriers have to be present in the conduction bands of these semiconducting materials, which in turn affects the optical properties.

We approach this topic from the theoretical point of view: the solution of the Bethe-Salpeter equation is perfectly suited to describe the optical properties of a system. With this method we gain insight into the optical properties of a system from first-principles and obtain a quantitative understanding of the interplay of additional free carriers and many-body effects.

After introducing our approach along with necessary approximations and technical tweaks, we present results for MgO and ZnO taking into account the influence of an additional free electron gas by including Thomas-Fermi screening and Pauli-Blocking. We relate the resulting effects in the absorption spectrum to the Fermi-edge singularity or Mahan excitons. The comparison with experimental spectra is excellent, but the Mott transition of the excitons is difficult to observe.