Wachstum von dreidimensionalen Germaniuminseln auf unverspannten und verspannten Silizium(001)-Oberflächen

This thesis is dedicated to the scanning tunneling microscopical investigation of the influence of strain and relaxation on the epitaxial growth of germanium on conventional silicon substrates, as well as on silicon-germanium substrates covered by a strained silicon layer. With respect to a possible application e.g. as quantum dots, it is desirable to achieve a high density of spatially ordered, small islands, with uniform shape and orientation. This requirements could be met by suitable choice of the epitxial parameter during growth of germanium on conventional silicon (001)-substrates, except for the spatial ordering. The lattice misfit has a fundamental influence on the nucleation of germanium on silicon surfaces. Therefore it has been investigated, if it is possible to achieve a spatial arrangement of islands due to the variation of the surface lattice constant. Silicon-germanium substrates have an adjustable spatial variation of the lattice constant and dislocation density. Each dislocation is connected with a strain field that results in a variation of the lattice constant and a slip step at the surface. Up to now it was in question where the nucleation of germanium islands takes place. Does the nucleation take place at the slip-steps due to the dislocations or at the positions where the silicon cap layer is strained due to the underlying dislocation network? It could be proved that the only reason for the spatial ordering of the islands is the variation of the strain in the growth area. The islands nucleate at the positions, where the lattice constant of the strained silicon cap layer is similar to the natural lattice constant of germanium. An influence of dislocation slip-steps could be excluded. To find out which processes dominate growth process and ripening, temper experiments have been used, to investigate how shape, size and spatial ordering develop in dependence to the duration of the temper process. In summary it might be said, that the selforganized growth of germanium islands is a suitable process to achieve spatially ordered nanostructures, with well defined size, shape and adjustable distances and density