Fermi level in n-type or p-type semiconductors

  1. Hi, everyone. I'm learning basic theories about semiconductors but can't quite understand the concept of Fermi level. is this just a imaginary energy level or true existence? and why Fermi level is close to the conduction band of n-type semiconductor and valence band of p-type semiconductor? the last question is, if applying a potential on the semiconductor materials, the Fermi level will shift up and down with the increase or decrease of the voltage-why?
    thanks _Cathy:smile:
  2. jcsd
  3. mfb

    Staff: Mentor

    It does not have to be a possible energy level for electrons.
    "imaginary" versus "true" is not physics.

    I think this is easier to see if you imagine an additional energy level in the bandgap. Where would it have to be to be 50% filled?
    For n-type semiconductors, close to the conduction band, as you have additional electrons there.
    For p-type semiconductors, close to the valence band, as you have additional holes there.

    A voltage changes electron energies.
  4. Thanks! that's help :)
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