Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 57: ZnO: Optical Properties
HL 57.3: Talk
Wednesday, March 16, 2011, 15:00–15:15, POT 151
Low-temperature dielectric tensor of MgZnO thin films and ZnO single crystals — •David Schumacher, Rüdiger Schmidt-Grund, Helena Hilmer, Chirs Sturm, Holger Hochmuth, Michael Lorenz, and Marius Grundmann — Universität Leipzig, Institut für Experimentelle Physik II, Linnestr. 5, Leipzig, Germany
We determined the temperature evolution of the spin-orbit interaction and crystal field splitting energies in a-plane MgxZn1−xO (x < 0.1) thin films and m-plane ZnO single crystals. In so doing we obtained hints on the ZnO valence band (VB) ordering, which is still under debate.
The temperature dependent dielectric tensor has been obtained by means of spectroscopic ellipsometry in the near band-gap spectral range (1 - 4.5) eV and temperatures (10 - 470) K. We derived the near bandgap band-to-band transition energies, amplitudes and broadening parameters. In order to get insight in the VB ordering of wurtzite ZnO our model dielectric function were constrained to satisfy the quasi cubic model, which gives expressions for the energy differences of the split-off bands due to spin-orbit interaction and crystal field splitting. We discuss the evolution of these quasi-cubic parameters, Δso and Δcf, as a function of temperature and Mg-content under the assumption of positive as well as negative spin-orbit-coupling.
We would like to stress that during the analysis our model had to be expanded by an additional ZnO surface-near-region layer in order to describe the data adequately. We ascribe this finding to the influence of electronic surface states and to mechanical damages of the surface.