# Dresden 2009 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 22: Focused Session: Semi- and nonpolar group III nitrides II

### HL 22.1: Topical Talk

### Dienstag, 24. März 2009, 14:00–14:30, BEY 118

**Optical anisotropy of nitride semiconductors** — •Rüdiger Goldhahn — Institut für Physik, Technische Universität Ilmenau

The ordinary and extraordinary dielectric functions (DF) describe the optical response of a semiconductor to an electromagnetic wave with electric field polarization perpendicular and parallel to the optic axis (c-axis), respectively. The spectral dependence is closely related to the valence band ordering at the center of the Brillouin zone as well as to the transition energies and transition probabilities in the vicinity of the high-energy van Hove singularities. We have applied ellipsometry in the photon energy range from 0.7 to 9.5 eV in order to determine the DFs of binary and ternary nitrides with wurtzite structure. Results for both polarization directions will be presented and discussed. The experimental results are compared to the results of theoretical calculations. Density functional theory in the local density approximation leads to independent-particle DFs which emphasize the observed optical anisotropy, but the peaks are found at higher energies with respect to the experimental data. If instead the electron-hole Hamiltonian (exciton effects) is employed for the calculations the overall agreement is strongly improved, i.e. the comparison of both calculated DFs yields the size of the peak shift for the high-energy CPs caused by the final state interaction.