Strain-relief mechanism in surfactant-grown epitaxial germanium films on Si(111)
We have studied the strain-relief mechanism in Ge thin films grown on Si(111) with and without a surfactant. Films grown on bare Si tend to form islands, which results in dislocations being nucleated at numerous sites at the edges of the islands. Since the dislocations glide as Shockley partial dislocations in this system, this process generates stacking faults that thread through the film and, eventually, to the surface when the islands coalesce. When Ge is grown on an antimony-terminated Si(111) surface, the growth mode changes to a layer-by-layer mode. This forces the dislocations to nucleate at the surface. Again, Shockley partial dislocations are formed, so that, initially, a threading stacking fault extends from the surface to the interface, and then along the interface. The intersection between the surface and the threading part of the stacking fault then acts as a nucleation site for the second partial dislocation, which results in the ‘‘self-annihilation’’ of the threading defects. We describe relaxed Ge films on Si(111) grown by this method, as well as relaxed multilayers of the Si/Ge/Si(111) type.
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