Regensburg 2010 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 38: ZnO and Related Semiconductors
HL 38.1: Talk
Wednesday, March 24, 2010, 09:30–09:45, H17
Surface structure and excitonic transitions of ZnO single crystals for homoepitaxy — •Daniel Fritsch1, Olga Roshupkina2, Jörg Grenzer2, and Heidemarie Schmidt2 — 1School of Physics, Trinity College Dublin, Ireland — 2FZD, Institute of ion beam physics and materials research, Germany
The surface quality and mosaicity of as received ZnO single crystals strongly depends on the applied crystal growth and subsequent surface polishing techniques. As a result single crystallite ZnO substrates are very often build up as a complex of single crystallite columnar structures. This microcrystalline substrate structure strongly influences the preparation of high-quality homoepitaxial ZnO films [1].
The columnar vs. mosaicity structure of as received Zn- and O-polar polished surfaces and unpolished backsides of (0001) ZnO substrates has been evidenced from high-resolution x-ray diffraction of the (0004) and (1124) reflections and from atomic force microscopy analyses. It was shown that there is a weak increase of the c-lattice parameter due to the polishing. The strain, induced by polishing, is evaluated from the probed c-and a-lattice parameter and used as an input parameter for emipirical pseudopotential (EPM) [2] calculations including excitonic effects near the direct bandgap. The calculated strain-dependent optical absorption near the direct band gap of ZnO has been related with the optical properties of the polished surfaces of ZnO single crystals probed in the spectral region from 1 to 4 eV using a VASE spectral ellipsometer. [1] H. von Wenckstern et al., phys. stat. sol. (RRL) 1, 129-131 (2007). [2] D. Fritsch, PhD thesis, Engelsdorfer Verlag, 2007.