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Fermi level pinning in doped semiconductors

  1. Feb 11, 2008 #1
    I am reading 'Mesoscopic electronics in Solid State Nanostructures', second edition, by Thomas Heinzel. And I find it a bit too difficult from time to time. Especielly on the concept of Fermi level pinning in doped semiconductors.

    Does anyone know where to find a good explanation for this concept? Or do you know one yourself?

  2. jcsd
  3. Feb 14, 2008 #2
    Fermi Level Pinning expresses the fact that the metal workfunction changes in magnitude when you replace SiO2 by HfSiO4 in a metal/SiO2/SC-stack, irrespective of the metal itself (material,etc). This problem disturbs the basic MOSFET-operation because of several reasons

    Check out : http://academic.brooklyn.cuny.edu/physics/tung/Schottky/index.htm

    The above website will teach you that in case of an interfacial region between two materials in a stack, there does not have to be charge transfer from one material to the other. This means that the Fermi Level is fixed or pinned !

    This is the case when there is an insulator between the two materials like the metal/SiO2/SC stack. In that case, the Fermilevels will still align for the same reason. The potential difference over the interface equals the surface charge at the SC-surface and its image charge at the metal surface. The big question is what system generates this surface charge ? You have several models like the Metal induced Gap states where the metal wavefunctions penetrate through the interface (SiO2 layer) and they generate a certain amount of energylevels in the SC-bandgap. These energylevels (and hence the electrons occupying them) can be seen as a metal of which the Fermi level is called the charge neutrality level. Depending on the position of the SC-Fermilevel with respect to the charge neutrality level (the SC-surface-Fermi Level) the SC surface acquires the required net-charge. "required" means corresponding to lowest potential energy of the material-stack. This is just one of the several models that are out there (look at Tung's website for this). The biggest problem with this model is the fact that it does not depend on the interfacial chemistry and Tung corrected this in his socalled Bond-Polarization-model..

  4. Feb 14, 2008 #3
    This is great! Thank you so much. My professor couldn't answer the question! You are great! :)

    The page is exactly on my level!
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