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Homework Help: Solid State Physics Help Please (Instrinsic->Extrinsic)

  1. Apr 21, 2012 #1
    Solid State Physics Help Please!!! (Instrinsic->Extrinsic)

    1. The problem statement, all variables and given/known data

    3 samples of silicon with donor densities of:

    1st sample: 10^18 cm^-3
    2nd sample: 10^16 cm^-3
    3rd sample: 10^14 cm^-3

    for each, find out at what temp the sample transitions from intrinsic to extrinsic behavior

    2. Relevant equations

    this is what i need help with.. I read the section of intrinsic->extrinsic behavior but I can't find any equations that relate donor densities with temperature..

    the equations i know/see from the section:

    for instrinsic:

    n = p (concentration of electron in conduction band = concentration of holes in valence band )

    r_i = g_i (regeneration rate of EHP (electron hole pairs) = recombination rate of EHP)

    from those 2 and equilibrium we can get :

    r_i = alpha_r n_0 p_0 = alpha_r (n_i)^2 = g_i (at any temperature we can predict that the rate of recombination of electrons and holes r _i is proportional to the equalibrium concentration of electrons n_0 and the concentration of holes p_0)

    for extrinsic materials, it just talks about what it is (when a crystal is doped s uch that the equilibrium carrier concentrationns n_0 and p_0 are different from the intrinsic carrier concentration n_i )

    After this section it goes on and tals about Fermi energy and levels..

    So I'm not quite sure how I can apply the equations I have to solve this problem..

    Please advise.
    Thank you
  2. jcsd
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