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Forward biased PN junction help needed

  1. Oct 27, 2011 #1
    1. The problem statement, all variables and given/known data

    Assume silicon, at room temperature (300k) and complete ionization.
    An abrupt n+-p junction with Nd=10^20 cm^-3 and Na=10^17 cm^-3 is forward biased at 0.5V



    2. Relevant equations

    a)Draw the band diagram, label n and p regions, show direction of the current flow. Also what is the current type (electrons or holes, drift or diffusion) in the p-type region just outside the depletion region?
    b)Calculate the depletion charge capacitance per unit area.

    3. The attempt at a solution
    I have managed to draw the band diagram but I'd appreciate it if there was a way I could check my answers. Also I get confused with the wording for the 2nd portion of part A. I understand that the current in a forward biased pn junction is due to diffusion would this be considered the same for p-type region?

    For part B would it be correct if I use the equation

    C'=[(eεsNaNd)/(2(Vbi-Vr)(Na+Nd))]^1/2

    But I get stuck since C=AC' but I can't seem to figure out the value for A, would I be able to use A=10^-4cm^2?
     
  2. jcsd
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