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Homework Help: Homework in Solid state material

  1. Sep 2, 2011 #1
    Here is the problem:

    The electron concentration in a region of silicon depends linearly on depth with concentration of 5x10^15 cm^-3 at surface (x=0) and 10^15 cm^-3 at depth of x=500nm. If the vertical electron current density in this region is constant at Jn=100 A/cm^2, calculate the electric field near x=500nm. assume that the mobility is constant at 1250cm^2/Vs.

    If anyone can at least explain the meaning of each value written in the problem and the formula that can be used to solve this problem ..

    Thank you...
  2. jcsd
  3. Sep 5, 2011 #2
    No one know???
  4. Sep 5, 2011 #3


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    Science Advisor

    The equation that you need is for the total electron current density (drift plus diffusion).

    [tex]J_n = q D_n \frac{dn}{dx} + q \mu_n E [/tex]

    q = 1.6E-19

    D_n = (kT/q) u_n which is approx 0.026 u_n at room temperature.

    Since you know J_n and dn/dx then E is the only unknown.
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