Abstract:

The relief of strain during hetero-epitaxial growth of non-lattice matching materials is an important and unavoidable process, which includes the formation of strain relieving defects such as dislocations. Spot profile analysing low energy electron diffraction (SPA-LEED) has been used to observe for the first time the dynamics of the formation of those dislocations in situ during the growth process. Using Sb as surfactant in the growth of Ge on Si(111) confines all strain relieving defects into a periodic network of dislocations at the interface. The dislocations at the interface give rise to an elastic deformation of the film up to the surface, which, due to its regularity, is seen as a spot splitting in LEED. The exact form of the deformation and thus the arrangement of the dislocations is deduced from the intensity variation of the satellite spots with energy. The data are in excellent agreement with elasticity theory. The dislocations of the three sets do not intersect in one point but form an extended node with a size of 18 Å. The first dislocations are generated at a Ge coverage of 8 monolayers, the final dislocation network is completed just after 10 additional monolayers of coverage. The network is detectable at the surface up to 60 monolayer thickness of the film.