PN junction: electrostatics

Discussion in 'Physics' started by Wikkez, Jan 26, 2013.

  1. Wikkez

    Thread Starter New Member

    Jan 26, 2013
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    Hi,
    First post here, I'm learning semiconductor physics&electronics on my own, but I'm a bit lost.
    In the depletion regio,The total charge in the n-regio equals the total charge in the p-regio, so why is there actually an E-field.
    Since u can calculate the strength of E-fields with Gauss' Law with the charge density and the charge density is the same but opposite in charge, why doesn't it cancel?
    Why is there a field, if there's not net charge(p and n regio combined)?
    ρp = ρn
    [​IMG]

    Hopefully someone can sort this out for me :)
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    What is the basis for saying that the total charge in the N region is the same as the total charge in the P region?
     
  3. Wikkez

    Thread Starter New Member

    Jan 26, 2013
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    What do you mean with that question?

    Charge neutrality?
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    So is the total charge on one plate of a charged capacitor the same as the total charge on the other? If so, then how do you explain the presence of an electric field in between the plates?
     
  5. Wikkez

    Thread Starter New Member

    Jan 26, 2013
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    0
    I reviewed some electromagnetics and I understand it now, guess I was mistaking electric field for electric flux and charge density for charge.
    My excuses.
    But I have another question that's probably stupid:
    One of the boundary conditions for solving the electric field on the pn-junction with poisson equation, is stating that @ x=0 the electric field must be continuous.
    Well, if the field is not continuous, it means that there is a presence of charge just @ your junction right since field lines always end on a charge.
    So why exactly is this impossible?
    Also: why does the electric field reaches a maximum value @ x=0, what is the physical meaning of this.

    Thanks in advance.
     
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