Composition evaluation by lattice fringe analysis (CELFA)
Transmission electron microscopy is the most valuable technique to access composition and morphology of semiconductor heterostructures. Nanostructures containing ternary layers (e.g. InxGa1-xAs and AlxGa1-xAs) are subject of intensive research because of their application in novel optoelectronic devices. The CELFA technique aims to provide a well applicable tool for near atomic scale spatial resolution composition determination in ternary semiconductor nanostructures, giving insight into kinetic growth effects such as segregation and migration.
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The image shows the local In concentration in a Stranski-Krastanow InGaAs quantum dot structure, that was grown by molecular beam epitaxy. It was taken on a Philips CM200 FEG microscope and evaluated with the CELFA method. The red region corresponds to a quantum dot embedded in a wetting layer with smaller In-concentration. The CELFA method uses a 2 beam interference of the undiffracted (000) beam with the chemically sensitive (002) beam. The simplicity of this condition provides for a simple thickness dependence of the (002) beam amplitude.
The local (002) Fourier component of the image intensity is evaluated from the resulting lattice fringe image. The composition x is obtained by a comparison with Bloch-wave calculations, carried out with the EMS program package.
Publikationen:
[1] A. Rosenauer, U. Fischer, D. Gerthsen, A. Förster, Composition evaluation by lattice fringe analysis, Ultramicroscopy 72, 121-133 (1998)
[2] A. Rosenauer, D. Gerthsen, Composition evaluation by lattice fringe analysis using defocus series, Ultramicroscopy 76, 49 (1999)
[3] A. Rosenauer, D. Gerthsen, Atomic scale strain and composition evaluation from high-resolution transmission electron microscopy images, Advances in Imaging and Electron Physics 107, 121-230 (1999)
[4] S. Kret, A. Rosenauer, D. Gerthsen, P. Ruterana, Extracting quantitative information from high resolution electron microscopy, Phys. stat. sol.(b) 227, 247 (2001)
[5] D. Litvinov, D. Gerthsen, A. Rosenauer, A. Grau, M. Hetterich, Ph. Gilet, L. Grenouillet, Determination of the nitrogen distribution in InGaNAs/GaAs quantum wells by transmission electron microscopy, Appl. Phys. Lett. 85, 3743 (2004)
[6] H. Blank, D. Litvinov, R. Schneider, D. Gerthsen, T. Passow, K. Scheerschmidt, Quantification of the In-distribution in embedded InGaAs quantum dots by transmission electron microscopy, Cryst. Res. Technol. 44, 1083 (2009)