P-N junction errors

Discussion in 'Feedback and Suggestions' started by Uzair, Dec 25, 2007.

  1. Uzair

    Thread Starter Guest

    The explanation of the majority and minority charge carriers in the volume III is not enough or simply incomplete.The explanation of the depletion region is not synchronizing with the quantum mechanics which you have explained earlier.
     
  2. Dave

    Retired Moderator

    Nov 17, 2003
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    Relevant Sections:

    PN Junctions - http://www.allaboutcircuits.com/vol_3/chpt_2/6.html

    Quantum Mechanics - http://www.allaboutcircuits.com/vol_3/chpt_2/2.html

    Can you explain what issues you have with the above sections? What is missing? What are the "synchronisation" issues?

    Dave
     
  3. Uzair

    Thread Starter Guest

    In the article, you have not explained why the charges in the depletion region are localized.While all the majority charge carriers namely holes and electrons are present in atoms,where is the explanation about the atoms of crystal lattice.Also explain what has happened to the atoms in the depletion region.
     
  4. Dave

    Retired Moderator

    Nov 17, 2003
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    I will give you a more thorough reply tomorrow; however I will make the point that the e-book sections often have a dependent section previously and as such should not always be read in isolation. As a rule of thumb you should read all sections in a chapter in order to understand all of what is being discussed. Therefore, if you are reading the PN junction section, you should read all sub-chapters of Volume III - Chapter 2.

    Dave
     
  5. uzair

    Active Member

    Dec 26, 2007
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    I have read all the sub-chapters before studying P-N junction and i have not found the respective information given about the topics i mentioned earlier satisfactory.It will be a kind act if you explain it to me because i am wholly relying on this site for my electronics study.
     
  6. Dave

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    Nov 17, 2003
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    Ok, for the purposes of clarity lets deal with one point at a time.

    The two ends of the material are doped with holes or electrons such that they have a net positive (holes) or negative (charge). A process of diffusion occurs across the junction where electrons are attracted into the positive p-doped side and holes are attracted to negative n-doped side. As the electrons (negative) are attracted into the p-side there accumulates a surplus of electrons resulting a net localised negative charge on the p-side. Conversely, as the holes (positive) are attracted into the n-side there accumulates a surplus of holes resulting a net localised positive charge on the n-side. (I have ignored the process of recombination at the junction in order to illustrate the above point).

    Does that explain the idea of localised charges?

    Dave
     
  7. uzair

    Active Member

    Dec 26, 2007
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    Yes but iwant to know the reason that why these charges become localized when they diffuse through the junction into opposite region.
     
  8. Dave

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    By the process of diffusing from one place to another the charge becomes local to the place it diffuses to - local in this sense meaning "in the physical vicinity of".

    Think of it in abstract terms - if a man (charge) moves (diffuses) from town A (the n-side) to town B (the p-side) he becomes local to to town B.

    Clearer?

    Dave
     
  9. Dave

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    Nov 17, 2003
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    I have also tried to clarify my points by pointing out that charge accumulates (i.e. it builds up) to provide the localised charge distribution observed.

    Dave
     
  10. uzair

    Active Member

    Dec 26, 2007
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    Yes it is clear that when a man (charge) moves (diffuse) from town A to town B he becomes local to the town be.In town B,is he able to migrate to town A again?If not,then why?
     
  11. Dave

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    Nov 17, 2003
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    No he is not.

    Why? Because during the process of diffusion when electrons migrate to the p-side and hole migrate to the n-side there is an process of recombination at the junction between the n-side and p-side. The result of this is that a depletion region forms where there is no free charge and an electric-potential across the depletion region width - in order for electrons or holes to return across the depletion region to the n-side (electrons) or p-side (holes) they would need to act against the potential to which they are responsive. In other words an electron (negative) would need to be attracted to a more negative potential and a hole (positive) would need to be attracted to a more positive potential. Whereas in reality we know the opposite would actually happen and hence this is the reason why the "man" cannot migrate back to "town A".

    Clear?

    Dave
     
  12. uzair

    Active Member

    Dec 26, 2007
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    Thanks a lot.This has made the idea very clear.Thanks again
     
  13. Dave

    Retired Moderator

    Nov 17, 2003
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    I think what we have discussed pretty much covers all of your questions:

    Electrons (and holes which are merely the absence of an electron) are the charge carriers, therefore the atomic details of semiconductor lattice are of less importance in understanding how the PN junction works.

    For completeness, can I suggest you look at: Volume I - Chapter 1.1

    There is a process of recombination creating a region where there is no mobile charge and an electric-potential across its width.

    If you have any further questions, feel free to post them up here and I will try and clarify anything you don't understand.

    Dave
     
  14. uzair

    Active Member

    Dec 26, 2007
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    I have no more questions on this topic.If some problem arise i will post it up.Thanks
     
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