The Stranski-Krastanow growth mode, which leads; to the self-assembled formation of dots, allows one to exceed the critical thickness without introducing dislocations. We report the coverage limits for the dislocation-free dot regime in dependence of the Ge content, and also the composition dependent thickness of the two-dimensional wetting layer. To reduce the size inhomogeneity of the self-assembled dots, we investigated ordering effects in Si/Ge-dot multilayers. The experiments do not only reveal a strong vertical ordering of the dots, but also a lateral correlation and a significantly increased size homogeneity is observed. Results on first device structures, a npn-infrared detector and a silicon based tunneling structure, both with embedded layers of self-assembled Ge dots, are presented.