Germanium Power Diodes
A couple reasons
Silicon is much more plentiful then germanium, so much less expensive.
Silicon is much easier to process.
Silicon has a much higher peak inverse voltage rating (breakdown).
Silicon is much more tolerant of high temperatures then Germanium... Especially important in a power diode.  A germanium diode is easily destroyed by moderately high temperatures, typically less then half of what silicon can handle.
Silicon junctions have a much lower leakage than germanium.

As compared to schottky diodes, germanium diodes have a much softer knee as they begin to conduct.  The shottky diode switches pretty much instantly from blocking to conduction, but the germanium one will follow a curve.
Silicon schottky's also have lower leakage and greater current capacities (as above) then germanium, and share the same plentiful element base and ease of manufacturing.