The electrical activity of threading dislocations (TDs), occurring in a thin SiGe Strain Relaxed Buffer (SRB) layer has been investigated by a number of techniques and its impact on the reverse current of p-n junction diodes has been evaluated. It is shown that besides the density of TD, there are at least two other parameters playing an important role. The distance with respect to the metallurgical junction of the 5 nm C-rich layer, used for the strain relaxation and the dopant type in the well region also affect the leakage current. This complex behaviour is further reflected in the Emission Microscopy (EMMI) images, showing different breakdown sites for p+/n or n+/p junctions. Results will be presented whereby one of these parameters is varied, while the others are kept constant, in order to arrive at some idea of the relative importance of the different factors.