Elastic Strain Relaxation inSi1-xGexLayers Epitaxially Grown on Si Substrates

I. Berbezier, B. Gallas () and J. Derrien
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I. Berbezier: Centre de Recherche sur les Mécanismes de Croissance Cristalline, CNRS, Campus de Luminy, Case 913, Laboratoire associé aux universités Aix Marseille II et III, 13288 Marseille CEDEX 9, France
B. Gallas: Centre de Recherche sur les Mécanismes de Croissance Cristalline, CNRS, Campus de Luminy, Case 913, Laboratoire associé aux universités Aix Marseille II et III, 13288 Marseille CEDEX 9, France
J. Derrien: Centre de Recherche sur les Mécanismes de Croissance Cristalline, CNRS, Campus de Luminy, Case 913, Laboratoire associé aux universités Aix Marseille II et III, 13288 Marseille CEDEX 9, France

Surface Review and Letters (SRL), 1998, vol. 05, issue 01, 133-138

Abstract: We have investigated the elastic strain relaxation inSi1-xGexlayers grown by the molecular beam epitaxy (MBE) technique andin situcontrolled with RHEED. Up to ≈0.8% critical lattice mismatch (about 20% Ge) uniform strained and flat layers were grown both on (111) and on (001) Si substrates. Calculations of the elastic constants evidenced a tetragonal distortion about 50% higher on (001) than on (111) in the same experimental conditions. At higher misfits (and/or thicknesses) a growth instability was evidenced only on (001) Si substrates.Si1-xGexlayers there displayed a surface layer undulation. On the contrary,Si1-xGexlayers grown on (111) Si substrates remained smooth throughout the growth up to the plastic relaxation of the layers. To determine stress fields in theSi1-xGexlayers, a high spatial resolution convergent beam electron diffraction (CBED) experiment was performed with a field effect analytical microscope. The CBED technique was applied to two typical cases: totally strained layer and undulated dislocation-free layer. In the latter case, CBED patterns recorded on nanometer scale areas of an undulation crest (cross-section sample) showed a gradual elastic relaxation mainly directed along the growth axis(z). Moreover a triclinic distortion of the unit cell was pointed out. These results were confirmed on a plane view sample. In conclusion, our results show that the driving force for the undulation is not the in-plane elastic relaxation since CBED experiments proved an important elastic relaxation of the (001)Si1-xGexlayers along thezaxis. This was in agreement with the calculations of the elastic constants. We think that this could be at the origin of the undulation.

Date: 1998
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DOI: 10.1142/S0218625X98000268

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