Another easy way to look at it is, it's the small amount of voltage needed to turn on the switch. The Si, Ge, GaAs...whatever type, is just the material used during the fabrication process which has different electrical properties.
I have been researching on the net and books for some time now. I have a few tables and equations but was wondering if anyone has the one I am looking for?
I'm looking for a table that lists Wavelength(nm), Extinction Coefficient(k), Absorption Coefficeint(a) and Density(d) values from ~300nm...