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I understand that electrons diffuse from the N to the P region due to the concentration difference. This diffusion of electrons creates an electric field opposing further diffusion.

What I don't understand is why diffused electrons form a layer? Shouldn't they be spread across the whole P-region?

If I assume it's because of electrical stability of the recombined atoms, it still should spread, as neighbouring atoms should also have the same level of stability.

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    $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Commented May 24 at 7:26
  • $\begingroup$ Sorry, typo. Is it correct now? $\endgroup$
    – Abdullah Al Jaber
    Commented May 24 at 7:50
  • $\begingroup$ The moment it goes from the N side to the P side, it will both see an electric field pushing it back towards the N side and also contribute to making that electric field stronger. So it cannot be spread across the whole P region. In fact, at thermal equilibrium, this electric field would be spread throughout the entire depletion region, i.e. before it even gets to the boundary, it would already see this electric field. $\endgroup$
    – naturallyInconsistent
    Commented May 24 at 11:15
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    $\begingroup$ This confusion is one reason why both minority and majority carriers, and generation/recombination need to be taken into account. Those electrons don’t form a layer, they recombine. $\endgroup$
    – Jon Custer
    Commented May 24 at 15:20
  • $\begingroup$ Sorry if I misunderstood. I don't get what you are saying. According to my understanding, if electron build up at depletion layer then the voltage difference between that area and whole P side would cause electron to move across whole P side to equalise voltage. I hope you understand what I am saying. $\endgroup$
    – Abdullah Al Jaber
    Commented May 24 at 18:03

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I found the answer (at least I have a theory). The electrons from N-type (that are now in P-type) are attracted by the positively-charged N-type. This builds up electrons at their barrier (depletion layer), where electrons stay close to N-type due to attractive force. Vice versa, the same thing happens in P-type.

(This is just an idea that felt logical to me. Please do point issues in my theory or provide an better one.)

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