PN-junctions: is the voltage measurable? Closed circuit?

[nonequilibrium]

Hello,

If I put a voltmeter over a (pn-junction) diode, do I measure anything?

I would intuitively say "no".

Is the following picture correct?

So let's say the P-region is to the right, N-region to the left. If I were to attach a voltmeter across it, I'd have to attach a metal wire to the P-region. Won't this result into a new PN-junction? Or a P-metal conductor junction? Thermal diffusion would drive the metal conductor electrons into the P-junction, and the holes from the latter into the former, no? This would imply two things, it seems (if true...):
- the voltage difference is not measurable (because the netto effect is made zero by the new pn-junction due to the metal contacts as explained above?)
- when we close a diode with a metal wire, no current will flow, not even temporarily (or only in a selected region), and the netto voltage around the circuit will be zero due to two non-zero voltage differences

Am I way off? Is it impossible for a p-side and metal conductor to form such a junction? I've only had introductory courses on these matters, so I don't pretend to be knowledgeable on these things. I have tried googling a lot, but it's hard to find answers on these questions.

If I'm wrong, what is the right way to see these things? Or can you point me to a good source?

 

[DrDu]

I also asked myself that question. Even if you don't close the circuit, the electric field should be observable, e.g. by accelerating electric charges in the surrounding much like in piezoelectric crystals.