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Homework Help: Finding Free Electrons and Hole Concentration

  1. Sep 8, 2007 #1
    1. The problem statement, all variables and given/known data
    Silicon is doped with an Aluminum Concentration of 2 X 10^16 cm^-3

    What are the free electron and hole concentrations at room temperature?

    What are the electron and hole mobilities at 300K?

    What is the majority carrier? What is the minority carrier?

    2. Relevant equations
    n_0 * p_0 = (n_i)^2 [[(Concentration of Electrons) * ( Hole Concentration) = (Intrinsic Carrier Concentration)^2]]

    n_i = 1.5 X 10^10 cm^-3 [[For Silicon]]

    3. The attempt at a solution

    This is actually for my electronics class, but this is more of a chemistry type question so I posted here.

    I've missed few lectures and I'm already lost. Can anyone just start me off, provide me some hints and equations I should use to find the mobility?

    As for the majority/minority carrier part, I understand that if the semiconductor is n-type, electrons are the majority carrier and holes are the minority carriers and the opposite for the p-type. How do you tell which type of material this is?
    Last edited: Sep 8, 2007
  2. jcsd
  3. Sep 9, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Please try not to miss class. Presumably one's textbook contains the necessary information.

    For semiconductor like Si, if one adds trivalent atoms (Group 13 (IIIA) e.g. B, Al, Ga) to the Si lattice, the trivalent atoms will tend to accept loosely bound valence electrons from the Si atoms. This will produce a p-type semiconductor. Similarly, if adds pentavalent atoms (Group 15 (VA), e.g. N, P, As, Sb) to the Si lattice, the pentavalent atoms will donate an electron to the lattice, and this produces an n-type material.

    See this - http://hyperphysics.phy-astr.gsu.edu/hbase/solids/semcn.html

    and http://ece-www.colorado.edu/~bart/book/book/chapter2/ch2_6.htm

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