So which method works better for random number generation(in terms of flatter frequency spectrum): transistor breakdown or Zener noise? I want to know whether to use a Zener diode or a Transistor when building a white noise generator. And FTR I intend to use Germanium because of its higher electron mobility and lower barrier potential. But what about covered photodiode dark saturation current? Has that even been tested as a white noise source(Germanium photodiodes are much noisier than Silicon photodiodes).