90 Degree Dislocation at Ge/Si Interface

(a) What is a core configuration of a 90 degree dislocation at a Ge-Si interface.
(b) Can the formation of misfit dislocations be controlled by manipulating the strain levels in the film?

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Answer

Figure 1

(a) Figure 1 shows the configuration of a coherent Ge film on Si substrate. A semicoherent Ge film includes a 90 degree dislocation edge on. The dislocation is perpendicular to the screen.
Bottom half of the figure is silicon substrate (red atoms) and the top half is a germanium film (green atoms). The core of the dislocation contains a seven atom ring and a five atom ring, whereas the ideal configuration of Si or Ge consists of six atom rings for this orientation.






Figure 2

(b) The starting point of formation of a misfit dislocation was introduction of a vacancy into the top layer of the film. Hence we calculated the activation energy needed for introducing a vacancy into a top layer of a Ge film. The Ge film included three levels of strains: (a) Tensile, (b) Compressive and (c) No strain.

Figure 2 shows a plot of energy changes in the configuration as a vacancy moved into the top layer of the film.
The vacancy was stable in films with compressive strain as well as no strain. The vacancy was however, unstable in a film with tensile strain. Hence it would be energetically unfavorable for a misfit dislocation to nucleate in a film with tensile film.






Questions? Comments? Suggestions?
Send a note to Anjali Nandedkar at CASA Engineering
info@casaengineering.com

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