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Homework Help: Pn junction

  1. Apr 21, 2007 #1
    When an N-type silicon and a P-type silicon are joined together electrons from the n-type diffuse into the p-type. Now the p-type becomes negatively charges and the n-type positively charged.
    With forward biasing electrons are forced from the n region into the p region.
    What is it that makes the electrons move from the holes (which were filled up when the two pieces of silicon were joined together) so that the electrons which are being pushed from the n-type can then fill the holes? Shouldn't the electrons which are filling holes in the p-type repel the electrons since they are the same sign?

    When the current is negatively biased does this mean the + terminal (where electrons are flowing from) is connected to the p-type silicon and when the electrons reach the holes they can't go any further because there's no holes on the other side for them to jump into?

    Also, how can u tell if in a diagram they are using conventional current or electron current?
    In my physics book there is a diagram that shows a wire connected to the negative side of the battery which is connected to the diode and it says the electrons are moving from N to P with N on the right.
    Last edited: Apr 21, 2007
  2. jcsd
  3. Apr 21, 2007 #2


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    The electric field applied across the pn junction motivates the electrons to move from the n-type to the p-type. When the junction is forward biased, there is no depletion region and the electrons flow easily. When the junction is reverse-biased, the depletion region grows and blows the flow of electrons (except for a tiny current called leakage).

    When reverse-biased, the higher voltage is applied to the n-side of the junction.

    Conventional current is used everywhere in electrical engineering, unless otherwise specified.

    - Warren
    Last edited: Apr 21, 2007
  4. Apr 21, 2007 #3
    Last edited: Apr 22, 2007
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