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Burgers Vector Analysis of Vertical Dislocations in Ge Crystals by Large-Angle Convergent Beam Electron Diffraction

Published online by Cambridge University Press:  05 May 2015

Heiko Groiss*
Affiliation:
Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz, Austria
Martin Glaser
Affiliation:
Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz, Austria
Anna Marzegalli
Affiliation:
L-NESS and Department of Materials Science, Università degli Studi di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy
Fabio Isa
Affiliation:
L-NESS and Department of Physics, Politecnico di Milano, via Anzani 42, 22100 Como, Italy
Giovanni Isella
Affiliation:
L-NESS and Department of Physics, Politecnico di Milano, via Anzani 42, 22100 Como, Italy
Leo Miglio
Affiliation:
L-NESS and Department of Materials Science, Università degli Studi di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy
Friedrich Schäffler
Affiliation:
Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstr. 69, 4040 Linz, Austria
*
*Corresponding author. heiko.groiss@jku.at
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Abstract

By transmission electron microscopy with extended Burgers vector analyses, we demonstrate the edge and screw character of vertical dislocations (VDs) in novel SiGe heterostructures. The investigated pillar-shaped Ge epilayers on prepatterned Si(001) substrates are an attempt to avoid the high defect densities of lattice mismatched heteroepitaxy. The Ge pillars are almost completely strain-relaxed and essentially defect-free, except for the rather unexpected VDs. We investigated both pillar-shaped and unstructured Ge epilayers grown either by molecular beam epitaxy or by chemical vapor deposition to derive a general picture of the underlying dislocation mechanisms. For the Burgers vector analysis we used a combination of dark field imaging and large-angle convergent beam electron diffraction (LACBED). With LACBED simulations we identify ideally suited zeroth and second order Laue zone Bragg lines for an unambiguous determination of the three-dimensional Burgers vectors. By analyzing dislocation reactions we confirm the origin of the observed types of VDs, which can be efficiently distinguished by LACBED. The screw type VDs are formed by a reaction of perfect 60° dislocations, whereas the edge types are sessile dislocations that can be formed by cross-slips and climbing processes. The understanding of these origins allows us to suggest strategies to avoid VDs.

Type
Materials Applications
Copyright
© Microscopy Society of America 2015 

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