What does temperature do to Germanium transistors specifically?

[GhostofJohnToad]

So I know that an increased temperature affects germanium somehow but I do not know what  that is specifically.  Is it just a high temperature in general or is it a rapid change in temperature?  Do low temps affect it as well?  And what is the affect?  more leakage, noise, volume drop, etc?  Just trying to increase my knowledge here.