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New Relaxation Mechanism in Short Period Si/Ge Strained-Layer Superlattices

Published online by Cambridge University Press:  21 February 2011

Werner Wegscheider ,
Karl Eberl ,
Gerhard Abstreiter ,
Hans Cerva  and
Helmut Oppolzer
Werner Wegscheider
Affiliation:
Walter Schottky Institut, Technische Universität München, Am Coulombwall, D-8046 Garching, Federal Republic of Germany
Karl Eberl
Affiliation:
Walter Schottky Institut, Technische Universität München, Am Coulombwall, D-8046 Garching, Federal Republic of Germany
Gerhard Abstreiter
Affiliation:
Walter Schottky Institut, Technische Universität München, Am Coulombwall, D-8046 Garching, Federal Republic of Germany
Hans Cerva
Affiliation:
Siemens AG, Research Laboratories, Otto Hahn Ring 6, D-8000 München 83, Federal Republic of Germany
Helmut Oppolzer
Affiliation:
Siemens AG, Research Laboratories, Otto Hahn Ring 6, D-8000 München 83, Federal Republic of Germany
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Abstract

High quality Si/Ge strained-layer superlattices composed of a sequence of alternating 3 monolayers pure Si and 9 monolayers pure Ge have been grown by molecular beam epitaxy at 310°C on Ge(001) substrates. In order to investigate the transition from coherent to incoherent growth in these tensily strained structures a set of samples with varying number of superlattice periods has been studied by transmission electron microscopy. It is found that superlattices as thick as 33 nm at least show perfect and defect-free layer growth whereas for thicker superlattices strain accommodation occurs. For this strained heteroepitaxial system we observed, to our knowledge, for the first time the formation of microtwins as the only relaxation mechanism. High-resolution lattice imaging reveals that the twin lamellae result from successive glide of 90° (a/6)<112> Shockley partial dislocations on adjacent {111} planes from the surface towards the bulk. The activation barrier which has to be overcome in the case of 90° partial dislocations is compared with the energies required for the nucleation of 60° perfect and 30° partial misfit dislocation half-loops.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 183: Symposium E – High Resolution Electron Microscopy of Defects in Materials , 1990 , 155
Copyright
Copyright © Materials Research Society 1990

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