Lattice matching periodic interfacial dislocation network in surfactant-mediated growth of Ge on Si(111)
The use of Sb as surfactant allows to grow continuous and smooth Ge films free of defects and of arbitrary thickness on Si(111)-substrates. The lattice mismatch of 4.2% is adjusted by a periodic network of dislocations in the interface plane. The strain fields of the dislocations give rise to an elastic deformation of the surface of less than 0.1 nm, which results in a spot splitting in low energy electron diffraction. The exact shape of the deformation and thus the arrangement of the dislocations at the interface are deduced from the intensity variation of the satellite spots with electron energy. The dislocations do not intersect in one point but form an extended node with a size of 1.8 nm. From the shape of the satellite spot profiles the distance variations of the dislocation network are derived. Therefore the lateral lattice constant fluctuates about ±1%, although the Ge film shows on average the Ge bulk lattice constant. With increasing film thickness the strain fields of the dislocations interact more and more resulting in a higher regularity of the dislocation spacings. The lattice constant of the Ge film is well defined only for thicknesses exceeding about 10 nm.
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