Dresden 2009 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 13: Optical properties

HL 13.7: Vortrag

Dienstag, 24. März 2009, 11:00–11:15, BEY 118

Temperature dependent dielectric function of nonpolar ZnO — •Philipp Kühne, Rüdiger Schmidt-Grund, Chris Sturm, Matthias Brandt, and Marius Grundmann — Universität Leipzig Institut für Experimentelle Physik II Halbleiterphysik Linnéstraße 5 04103 Leipzig Germany

ZnO is a direct semiconductor which crystallizes in the wurtzite structure. Due to its wide band gap of 3.4 eV and a high exciton binding energy of 60 meV, ZnO is a promising material for optoelectronic devices. Non-polar surfaces like m-plane (1-100) are of special interest since they avoid electric fields at interfaces, which can negatively influence the performance of optoelectronic devices grown on these surfaces.In this work we study the temperature dependence of the tensor of the dielectric function of nonpolar m-plane bulk ZnO single crystals by means of spectroscopic ellipsometry in the spectral range 1 eV−4.5 eV and for temperatures 5 K−470 K. The independent components parallel є_|| and perpendicular є_⊥ to the crystal axis were found by layer stack model analysis, using parameterised model dielectric functions.

Ellipsometry is very sensitive to surface morphology and surface contamination. We gave emphasis to the sample preparation. After an annealing process the sample exhibits atomic steps at the surface. To avoid the growth of films by resublimation of residual gases at low temperatures, we are working in an UHV system at p<10⁻⁹ mbar. For this pressure the growth rate is reduced to maximal one mono-layer per hour. Finally we derive the near band gap band-to-band transition energies, exciton binding energies and broadening parameters.