I've done some TCAD modelling of some photodiodes and surrounding areas before to try and reduce interference. I used the genius open source TCAD and the widths, depths from the manual and you can get a rough idea of the doping densities just from the bulk resistivities. But that was strictly a relative effort to say this structure has less interference than this one. I wouldn't attempt to make gain any absolute values without much more process specific info. But it's possible