Considering a PN junction with a difference in fermi level between the P and N type regions given by eV0. Does this V0 correspond to the potential at which the diode "switches on"? My intuition tells me that they probably are as when you apply an external potential of V0 across the junction the fermi levels are the same and at this point the electrons/holes can easily pass across the junction. I have been unable to find sources that either confirm or deny this so links to any papers or textbooks would be greatly appreciated.
(See the first diagram on this page for reference http://www.electronics-tutorials.ws/diode/diode_3.html)