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pn junction reverse bias working

Discussion in 'General Electronics Discussion' started by subratoc, Jul 15, 2013.

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  1. subratoc


    Jul 15, 2013
    In a reverse biased pn junction the holes are attracted towards the -ve end of the battery and the electrons are attarcted towards the positive end of the battery thereby widening the depletion region. I was wondering why do the electrons not complete the circuit in this case, i.e. why cannot the electrons (which are attracted by the +ve end) come out of the device , enter the wire and reach the p side of the semiconductor through the battery?
    Any help will be greatly apreciated.
  2. BobK


    Jan 5, 2010
    For the same reason they cannot in a capacitor. In fact, a reversed biased diode acts like a capacitor. A small current will flow until it is charged.

  3. john monks

    john monks

    Mar 9, 2012
    When a positive charge is placed on a n doped semiconductor the free electrons near the junction are pushed into the side with the p doped semiconductor region and fills in the holes that are carriers thus making them no carriers causing them to become insulators. Likewise on the n doped side the free electrons are pushed further into the n doped region away from the junction and thus making this portion an insulator. And the greater the voltage the wider this insulated region becomes.

    Interesting note is that this makes a capacitor as Bobk hints at and the greater the voltage applied to this pn junction becomes the lower the capacitance becomes.

    So what happens when the p side is connected to the positive side of the battery and the n side the other? The side with the n doped side has electrons driven away by the negative side right into the p dope side that has holes ready to accept the electrons and you have a complete circuit with current continually moving.

    Semiconductors are doped, that is given impurities, with arsenic or boron or many other types of impurities. Whether the doped material has an extra electron or hole in it has to do with the geometry of the molecule. So when a n type semiconductor is driven with a negative voltage the electron is driven away and the semiconductor becomes an insulator because the molecule just found a stable state and is less willing to pass electrons around to its neighbors.

    The physics of this is somewhat confusing but if you wish I can grind through this further.
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