DISSOCIATION OF MISFIT DISLOCATION NODES IN (111) GESI/SI INTERFACES

The accommodation of lattice mismatch is studied in Ge0.15Si0.85 layers grown epitaxially on (111)-oriented Si substrates. Weak-beam dark-field transmission electron microscopy (TEM) reveals a regular misfit dislocation network, which resembles the honeycomb network of edge-type dislocations expected by the O-lattice theory. In contrast to the theory, however, the misfit dislocations dissociate into misfit partials. Triangular planar faults, bounded by misfit partials, are observed where the O-lattice theory expects dislocation nodes. High-resolution TEM identifies the planar faults as intrinsic and extrinsic stacking faults, respectively. The regular pattern of these faults results in a total of three different atomistic interface structures. The central conclusion from the experimental observations is that the formation of interfacial stacking faults by dissociation of misfit dislocation nodes minimizes the energy of the (111) GeSi/Si interface. The measured extensions of the fault triangles agree with the extensions expected in mechanical equilibrium. The model describing the dissociated misfit dislocation network can be extended to explain also the dislocation configuration observed in highly mismatched(lll) GeSi/Si interfaces. Possible nucleation mechanisms for the misfit dislocations are discussed.