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Pn junction problem in diode

  1. Mar 5, 2005 #1
    when it comes to pn junction in diode, p and n are doping semiconductors.

    if P and N semiconductor are contacting each other,

    some holes in P and some electron in N are combined. that is, they are recombined.

    this recombination caused the current, very small.

    I was wondering that where did this current flow. did it flow through N? or P?

    Another Question : in depletion layer, when the current due to the free carrier

    diffusion equals the current caused by the electric field, and the pn junction

    reaches equilibrium. I knew that electric field make the current
    when metal like Cu is moving back and forth between electric field.

    but in pn junction, how did electric field make the current?
  2. jcsd
  3. Mar 6, 2005 #2


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    Under equilibrium, there is no current in an unbiased PN junction. The recombination is simply the "annihilation" of free electrons by free holes near the interface, due to diffusion from a difference in chemical potential. You may choose to refer to this recombination process in terms of a transient diffusion current, in which case, a positive transient current would have flowed from the p-type to the n-type SC.

    The process is the same, whether it's a metal or semiconductor. The electric field exerts a force on the free charge carriers in the conduction band. The result of this force (along with phonon/impurity scattering) is a current along the direction of the field.

    The only real differences are in the nature of the majority charge carriers (in pure Cu, these are electrons; in p-type Si, these are holes) and the mechanism by which the conduction band is populated.
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