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What is Vacuum level

  1. Mar 15, 2012 #1

    What is vacuum level?
    I browsed internet and came across different definitions like
    1. Threshold energy with which electron leave the atom.
    2. Energy of electron outside the crystal.

    Can you please explain in detail what is vacuum level?

    At the same time, pls clarify why and how the band diagram diagrams bend when an electric field is applied compared to the band diagram under equilibrium.

  2. jcsd
  3. Mar 15, 2012 #2


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    I haven't heard the term (no surprise there, though).
    What was the context in which you read the term? It may be that the author was not being precise and you may need to read his full text to find what he meant. Failing that, email him and demand an explanation!
  4. Mar 15, 2012 #3
    It seems that your definitions are pretty much the same thing. To leave the atom for example in the photoelectric effect it needs a certain minimum energy E. But since energy potentials are only defined up to a number one can either say the electron has potential energy E when free (far away from the atom and not trapped) and when trapped it has energy 0. Or you do it the other way around and say that the free electron has energy 0 and the trapped electron has energy -E which is more common.
  5. Mar 26, 2012 #4
    Vacuum level is the energy level where the energy of an electron becomes zero. It has nothing to do with where the electron is. Electron can be in vacuum level even being inside crystal.

    Any standard textbook in VLSI will explain what you need including effect of electric field on band diagram. eg. Streetman and Banerjee.
  6. Mar 26, 2012 #5
    The vacuum level can be described as the energy at the fermi level plus the work function energy needed to remove an electron from the material.
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