RheoMan: a five-year, ERC-funded (Advanced Grant), project to model the rheology of the Earth's mantle

Oct 23, 2012 Francesca Boioli in Lille General

Francesca Boioli, PhD student in Materials Science at the University of Milano Bicocca in italy will visit us and give a seminar on dislocations modeling in nanostructures.

Dislocation modeling in Si(1-x)Gex micro and nanostructures
F. Boioli1, R. Gatti2, B. Devincre2 , F. Montalenti1 , and Leo Miglio1
1 L-NESS and Department of Material Science, University of Milano-Bicocca Italy
2 LEM, CNRS / ONERA, Châtillon Cedex, FRANCE


For the epitaxial integration of different materials on Si(001), it would be highly desirable to obtain pre-determined regions free of detrimental threading dislocations (TD), as wide as few hundred nanometers at minimum. However, during the hetero-epitaxial growth of thin films on planar Si(001) substrates, a network of dislocations is formed, because of heterogeneous nucleation of dislocation loops at existing defects on the surface of the growing film, preventing any meaningful control of TD position [1]. To this aim, a turning point is the introduction of preferential dislocation nucleation sites by a suitable nano-patterning of the Si substrates. In this work, we show with the help of finite element method calculations and dislocation dynamics simulations, that the stress heterogeneities in the epitaxial film, induced by patterning the Si substrate with a periodic array of 111 trenches or pits, allow to select dislocation sources position. Such structures produce an ordered network of misfit dislocations trapped along the trench or pit lines, and provides large areas free of detrimental TD, suitable for device integration.
The plastic relaxation process is often an unavoidable strain-relief mechanism also in the fabrication of strained three dimensional islands and nanowires. Our work is also aimed to establish the coherency limits for growing such hetero-structures and obtain at least qualitative insight into the relevant dislocation nucleation and propagation mechanisms.


[1] Y. Shiraki, A. “Sakai Fabrication technology of SiGe hetero-structures and their properties”, Surf. Sci. Rep. 59, 153 (2005)

 

October 23rd, 2012 - 14:00 - C6 building, room 202