Nucleation and Movement of Dislocations during Relaxation of He Implanted Si_xGe_1-x/Si_x Heterostructures

Abstract

The fabrication of strain relaxed SixGe1-xbuffer layers is technologically of great importance, because biaxial, tensile strain can be achieved within a thin Si layer grown onto these SixGe1-x virtual substrates. Strain relaxation of the SixGe1-x layer can be accomplished by He implantation and subsequent annealing. In this paper we address the nucleation and movement of dislocations in He implanted SixGe1-x/Si heterostructures. By in-situ transmission electron microscopy we find clear evidence, that He precipitates formed during annealing act as internal dislocation sources and therefore promote the relaxation. This can be understood in view of the results of quantitative evaluation of the shear stress around He filled precipitates. Clearly, for some of the precipitates, the critical resolved shear stress for dislocation formation is exceeded at the edge of the platelets.