Before I explain my problem I'd like to mention I'm still green and about 2 weeks into these topics. I learned most of it from youtube videos, wikipedia and other science sites, so I'll be explaining the smallest details in order to confirm I didn't mess anything up.

I have several questions regarding the P-N junction; the forming of a depletion region - the nature of ions created during the diffusion of carriers to be specific.

So here's what I've figured out so far (please correct any inaccuracies):

  • We dope the n region of the semiconductor with an element that has more electrons in it's valence shell than the semiconductor atoms. The added element "wants to behave" like the rest of the atoms in the crystal due to the rules of covalent bonds and gives away it's excess electrons. In doing so it becomes a positively charged ion, because it has less electrons than protons. Now there are a lot of free electrons in the conduction band of the n region which increases conductivity.
  • We dope the p region of the semiconductor with an element that has less electrons in it's valence shell. The rules are the same except this time it wants to accept missing electrons to fit in the structure, so it becomes a negatively charged ion. Now there are a lot of electrons missing in the valence band of the p region which increases it's conductivity.
  • a depletion region forms because the excess electrons in the n part are attracted to the holes in the p part. In doing so, the ions on both sides of the p-n border become neutral/complete again and they refuse to accept electrons at this point, so they create a barrier.

My questions are:

  1. Am I right in thinking the depletion region forms because the dope ions have regained the balance between the amount of protons and electrons, so they repel electrons which are the only real charge carriers (By real I mean holes are just empty spaces for electrons, not some magical positive charge carriers that can move in a way that electrons do.) ?
  2. How come the depletion region even exists, shouldn't the depletion region atoms still share their electrons/holes with the rest of the structure?
  3. This one might be offtopic, but do atoms with 8 electrons in their valence shell accept or give away electrons? Is the octet rule a key concept to understand all of this fully, or maybe it has nothing to do with it?

Also, if you could recommend some good literature that can explain these topics thoroughly I'd be grateful.


1 Answer 1


Protons are not the positive carriers, holes are. In a P-N junction, you have donor impurities on the n-side and acceptor impurities on the p-side. Acceptor impurities will produce holes, since they will capture electrons, making the p-side "more positive" while the opposite occurs on the n-side. When there's separation of charges, you get a electrical field, so a current appears, and electrons will start flowing from the n-side, but they'll start leaving holes behind, positively charging it. The equilibrium of those two currents, thermal and diffusion, is what creates the depletion region. That's why if you apply a electric field that makes the depletion region shorter, you'll favor the thermal current.


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