Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Doping of semiconductors and fermi energy.

  1. Apr 8, 2007 #1


    User Avatar

    I understand the principle behind p and n type doping, but I don't understand how such a small amount, 1ppm, can cause such a massive change in the fermi energy.


    as I understand it:

    for the intrinsic case the number of electrons exactly matches the number of holes and the fermi energy is equal to the mid-gap energy.

    When a very small amount of atoms are added which have an extra electron/hole then electrons/holes are added to system which adds extra levels (as in diagram).

    But how can such a small addition of electrons/holes have such a large change in the fermi energy?
  2. jcsd
  3. Apr 8, 2007 #2


    User Avatar
    Science Advisor
    Gold Member

    It's because it introduces a lot of excess charge carriers over that of the intrinsic material. Silicon at 300K has about 10^10 carriers per cc, while 1ppm of dopant donates or accepts about 10^-6 x 10^22 = 10^16 electrons per cc so it significantly changes the Fermi level (chemical potential).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook