Si0.84Ge0.16/Siheterostructures with variable finite lateral dimensions (10–300 &mgr;m) and different layer thicknesses grown by selective low pressure chemical vapor deposition epitaxy at a temperature of 700 °C were investigated with regard to relaxation by formation of misfit dislocations. While in small structures only nucleation and propagation occur, the dislocation–dislocation interaction (mainly multiplication) becomes more and more important in larger structures. Therefore it was possible to separate the three different mechanisms which play a role in relaxation, i.e., nucleation, propagation, and multiplication, and to study them independently. From the analysis of the misfit dislocations at the initial stage of relaxation it was possible to determine the nucleation site density and an activation energy of 2.8 eV for the heterogeneous nucleation of misfit dislocations. ©1997 American Institute of Physics.