Here are some insights into the basic physics within a Silicon Germanium rectifier. In the left-hand picture, you can see the cross-section of a Schottky rectifier where the interface between the Schottky metal and the Silicon epitaxial layer forms the Schottky junction with a certain electrical barrier depending on the choice of metal. The right-hand picture shows a cross-section of a Silicon Germanium rectifier where the junction, covered by a contact metal, is formed between the Silicon epitaxial layer and a Silicon Germanium layer. In both cases, the thickness and doping of the Silicon epitaxial layer determine the breakdown voltage of the device. Now, the major differences are that the Silicon Germanium rectifier junction is not a Schottky junction and, in effect, does not suffer from high leakage currents. On the other hand, Silicon Germanium has a smaller band gap than Silicon leading to the injection of minority charge carriers at a lower threshold voltage and eventually to lower conduction losses at high current densities.