Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Forward biased diode

  1. Feb 11, 2009 #1
    There are a lot of resources out there which mention that when a diode is forward biased the majority carriers at the n-type material will move to the p-type material "through" the holes therefore the holes will move from the p-type region to the n-type region.

    However, this doesn't make any sense to me at all...

    As the majority carriers in the n-type region are at an excited state they are free to move about the material. Therefore when the diode is forward biased (assuming that external voltage is higher than barrier potential) the majority carriers (electrons) in the n-type region would move along the p-type material without recombining with the holes.
    However, the holes would still move in opposite direction not due to the n-type's majority carriers but due to the neighbour valence electrons (which aren't in an excited state) being pushed due to the external voltage.

    This explanation makes much more sense to me than the first one although I'm not sure whether that's what real happens.

    I'd like to "hear" your suggestions/thoughts...

    Edit:

    http://img21.imageshack.us/img21/9639/84077772ht7.jpg" [Broken] illustrates what I'm talking about; Notice the hole in the middle moving to the right plus the free electron at the top moving in opposite direction.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 11, 2009 #2
    Ok, I'll make the question in this way...

    Would there be conduction if I joined a n-type material (extrinsic) with an intrinsic silicon material and connected an external voltage across both ends (neglecting e-h pair generation)?
     
  4. Feb 16, 2009 #3

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    In a forward-biased p-n junction, electrons from the depletion region are pushed further into the p material where they quickly recombine with holes.

    As I understand it, this creates a deficit of holes, the majority carrier, in the p material. Additional holes are available and abundant in the p material, and move in to "fill in" the deficit. Additional holes keep moving in from the wire contact (actually, the wire keeps removing electrons to create additional holes in the p material.)

    The net flow of holes in most of the p material, and the flow of electrons from the depletion region into a short distance of the p material, maintain the same net current throughout the material.

    An analogous process occurs in the n material.

    Hope that is clear enough. I have always struggled to understand this on a microscopic scale, and have pretty much resigned myself to accepting the v-i curve for what it is.

    Hmmm, don't know if this is done in practice. I know that sometimes a thin intrinsic-material layer is used between the p and n regions, I think to lower capacitance in for example p-i-n photodiodes.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook