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Homework Help: ACTUAL Variation of Potential inside a diode.

  1. Oct 25, 2015 #1
    1. The problem statement, all variables and given/known data
    The figures showing the potential variation inside a PN junction normally shows the potential to be constant in the neutral P and N regions

    2. Relevant equations

    3. The attempt at a solution
    Since the potential due to the positive and negative charges should also exist in the neutral P and N region( since their electric field will definitly extend to those regions and electric field and potential are directly related); i have come up with a new figure showing how the actual variation of potential in the neutral N and P regions will take place. I have attached the figure with this thread.
    Figure showing the variation in potential from my textbook is also attached.

    Attached Files:

  2. jcsd
  3. Oct 25, 2015 #2


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    Homework Helper

    The electric field does not extend over the space charge region in case of an unbiased diode. In the neutral parts of the P and N regions, the electric field is zero, the potential is constant.
    Think of a planar capacitor. There is charge on both plates ( equal and of opposite signs) but the electric field is non-zero only between the plates.
    If the diode is biased, and current flows through it, there should be some electric field outside the pn junction that drives that current, as the semiconductor material has got some resistance. In this case, the potential changes even in the neutral region.
    Last edited: Oct 25, 2015
  4. Nov 1, 2015 #3
    It is said in the book 'Solid State Electronic Devices' by Ben G Streetman (page no.172) to ASSUME that there is NO electric field in the neutral regions.
    Also since V=Q/4ΠΣr the potential should be present both inside the junction and in the Neutral region since 'r' can be taken in either directions.
    My point was since v∝1/r the potential should NOT be constant and it should decrease in a parabolic manner.
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