Dresden 2011 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 9: Topical Session TEM III
MM 9.2: Topical Talk
Montag, 14. März 2011, 16:15–16:45, IFW A
Quantitative STEM: Composition mapping in InGaN — •Andreas Rosenauer1, Thorsten Mehrtens1, Knut Müller1, Katharina Gries1, Marco Schowalter1, Stephanie Bley1, Parlapalli Venkata Satyam1, Christian Tessarek1, Kathrin Sebald1, Moritz Seyfried1, Jürgen Gutowski1, Adrian Avamescu2, Karl Engl2, and Stephan Lutgen2 — 1Universität Bremen, Institut für Festkörperphysik, D-28359 Bremen — 2OSRAM Opto Semiconductors GmbH, D-93055 Regensburg
In this contribution we demonstrate that measurement of In concentration in InGaN layers is possible by scanning transmission electron microscopy Z-contrast imaging as the tendency to form In rich regions due to electron beam irradiation is smaller than for parallel beam illumination. The suggested method is based on comparison of intensity normalized with respect to the incident electron beam with image simulation computed with the STEMsim program. In InGaN, static atomic displacements are caused by the different covalent radii of the metal atoms. These displacements are computed by structure optimization of InGaN supercells using empirical potentials in the Stillinger Weber parameterization. The suggested procedure is validated using an InGaN layer with 7 % homogeneous In concentration by comparison of the STEM results with results obtained by other methods. Despite a high convergence angle of the incident electron beam, simulation of an abrupt interface between InGaN and GaN shows that artificial blurring of the interface is significantly reduced by electron channelling.