Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 62: Nitrides: Advanced Characterization Techniques
HL 62.3: Talk
Wednesday, March 16, 2011, 15:45–16:00, POT 51
A (S)TEM and Atom Probe Tomography Study of InGaN — •Thorsten Mehrtens1, Stephanie Bley1, Marco Schowalter1, Kathrin Sebald1, Moritz Seyfried1, Jürgen Gutowski1, Stephan S.A. Gerstl2, Pyuck-Pa Choi2, Dierk Raabe2, Adrian Avramescu3, and Andreas Rosenauer1 — 1Institut für Festkörperphysik, Universität Bremen, Bremen — 2Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf — 3OSRAM Opto Semiconductors GmbH, Regensburg
InGaN is a well suited material for opto-electronic devices such as LEDs and laser-diodes in spite of its high dislocation density. The reason for this is still under discussion, but small fluctuations of the indium concentration or layer thickness are assumed to be the origin.
We have investigated an InGaN/GaN multi quantum well structure via quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and atom probe tomography (APT). For the (S)TEM study the preparation process was optimized by low-energy milling in order to reduce amorphous surface layers. The indium concentration of the quantum wells were deduced by comparing HAADF-STEM images, where measured intensities strongly depend on the nuclear charges of the scattering atoms (Z-contrast), with multislice simulations. An indium concentration of around 16% was obtained. This value is in good agreement with the concentrations obtained with APT and energy-dispersive X-ray analysis (EDX).
Existence of short and long-range fluctuations in these layers will be discussed in comparison to µ-photoluminescence measurements.