Regensburg 2007 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 38: ZnO I

HL 38.4: Talk

Thursday, March 29, 2007, 10:45–11:00, H17

The anisotropy of the dielectric function of ZnO films. — •Chris Sturm, Rüdiger Schmidt-Grund, Tsvetan Chavdarov, Bernd Rheinländer, Holger Hochmuth, Michael Lorenz, and Marius Grundmann — Universität Leipzig, Institut für Experimentelle Physik II, Linnéstr. 5, 04103 Leipzig

In the last years, the tensor of the optical dielectric function (DF) of ZnO has been of much interest. Many properties of this tensor are still unknown. We report on the influence of the film thickness and film crystallographic orientation on this dielectric tensor. The a-plane and m-plane ZnO films were deposited on r-plane and m-plane sapphire, respectively, by Pulsed Laser Deposition. The m-plane and a-plane orientation of the ZnO films permits the determination of the two independent components of the dielectric tensor (ε_⊥ and ε_∥). The thicknesses of the ZnO films in the different samples vary in a range (30−600) nm. The samples were studied by Generalized Spectroscopic Ellipsometry in the energy range (1,0−4,5) eV. The DF was obtained with help of a layer stack model and model dielectric function analysis. The DF in the band-gap region is dominated by free excitons. Comparing the DF of m-plane and a-plane ZnO films with each other, a blue shift of the exciton peak energy was found for the a-plane ZnO films. A blue shift and an increasing line broadening of the exciton peaks with decreasing film thickness were found for both film orientations. This behavior is attributed mainly to strain effects since thickness non-uniformity, free charge carrier and surface over-layer effects can be excluded as responsible for the blue shift and the line broadening.