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Resistivity and Mobility

  1. Feb 7, 2010 #1
    1. The problem statement, all variables and given/known data
    Assume the mobility ratio u_n/u_p = b in Si is a constant independent of impurity concentration. Find the maximum resistivity [tex]\rho_m[/tex] in terms of the intrinsic resistivity [tex]\rho_i[/tex]. If b = 3 and the hole mobility of intrinsic Si is 450 cm^2/Vs calculate [tex]\rho_i[/tex] and [tex]\rho_m[/tex]

    2. Relevant equations

    3. The attempt at a solution

    Well I know that conductivity is [tex]\sigma[/tex] = q(u_n * n + u_p * p)
    For the intrinsic conductivity [tex]\sigma_i[/tex] = q(u_p *b * n_i + u_p * n_i) = q u_p n_i (b + 1).

    Now I'm having a bit of trouble expressing [tex]\sigma_m[/tex] where this is a minimum conductivity (or maximum resistivity)...
    [tex]\sigma_m[/tex] = q ( b * u_p * n + u_p * p)
    To get a minimum conductivity I would think that n should be extremely low but I fail to see how I can express this in terms of the intrinsic conductivity. I know that n_i at 300 K is 10^10/cm^3. Does anyone have any hints?
  2. jcsd
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