D1 type in 20v generator

[xba0bab]

Hello all!

I was looking for a scheme of "really random number" generator for my own purposes, and I've found it in OneRNG (scheme part with avalanche diode). I try to built it, but I couldn't find type of D1 in generator. All other types of elements are clear from drawing except this one.
Could anyone help me to get information about this diode type?
I'd prefer to reproduce scheme which really works (I'm not so familiar to the electronics in practice, that is why I prefer existing and well-tested scheme like OneRNG).