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Homework Help: Doped semiconductor-to find the resistance?

  1. Jan 18, 2012 #1
    1. The problem statement, all variables and given/known data
    An extrinsic semiconductor sample of cross section A and length L is doped in such a way that the doping concentration varies as Nd=N0 Exp(-x/L)
    Assume that mobility μ of the majority carriers remain constant.What is the resistance of the sample?

    2. Relevant equations

    3. The attempt at a solution
    In the eqn n is the free electron concentration.
    I thought this will be eqal to doping concentration.
    then,R = L/(AμeNoExp(-x/L))
    But this is not the right answer.

    Can this resistance be varrying with x since doping concentration depend on x?

  2. jcsd
  3. Jan 18, 2012 #2


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    Staff Emeritus
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    The resistance, dR, for a very short length, dx, of semi-conductor is [itex]\displaystyle dR=\frac{dx}{A\mu N_0 e^{-x/L}}[/itex]

    Integrate that .
  4. Jan 25, 2012 #3
    That was really helpful.Thank you.
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