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Fermi Level - clarification needed

  1. Nov 18, 2011 #1
    Fermi Level -- clarification needed

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


    Revered Members,
    Can i know what is meant by fermi level? I googled this, but i could not understand. One site says Fermi level as top of collection of electron energy levels at absolute zero.
    2. Relevant equations



    3. The attempt at a solution

    As far as my knowledge I know electron energy levels as K, L,M, N etc with energy values -13.6eV, -3.4eV etc. Top of collection means, is it O eV?
     
  2. jcsd
  3. Nov 19, 2011 #2

    ehild

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    Re: Fermi Level -- clarification needed

    Those are the energy levels of a hydrogen atom. Fermi level is defined for crystals -metals, semiconductors.


    When two hydrogen atoms are so close that they interact, their electrons can not have the same energy, according to Pauli's Principle. All orbits and their energies split into two: one energy lower, the other higher than that of the individual atom.

    In a crystal made of N atoms, the energies split into N different levels. There are very close levels arranged into bands, and there can be only one electron on each level.
    At zero temperature (0 K) all the levels are filled up to a certain energy: This is the Fermi energy. Insulators and semiconductors have completely filled bands, the highest called valence band and the next above which is empty at 0 K is the conductance band. There is a "forbidden gap" between the bands.
    At higher temperatures, some of the electrons gain enough thermal energy so they can occupy a level in the conductance band, leaving an empty level - a hole - behind in the valence band. The Fermi level means that energy above which there are as many occupied levels as empty levels below it

    Read: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html.

    ehild
     
  4. Nov 19, 2011 #3
    Re: Fermi Level -- clarification needed

    Thanks ehild. So, Fermi level is the level above valence band,am i right?
     
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