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How oxidation effects band structure of metals?

  1. Jun 17, 2011 #1

    uLs

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    Hi everyone,

    I'm working on random materials which are coincidencely oxides and showing semiconductor behaviour... Some of these are metals and i suddenly realise MOS (which are practically everywhere). I know them, i know how they work and behave still i can't get to understand the effect of oxygen regarding band structure. I take a quick look to some solid state books in my library but can't come with anything so here i am. Any help will be welcome!
     
  2. jcsd
  3. Jun 17, 2011 #2
    oxygen and metal ions have their own bands and their structures depend on type of metal and lattice. many metal elements have multiple valences and can be replaced with similar metals with ease, allowing an infinite ways to introduce impurity levels. not sure what do you mean by "effect of oxygen".
     
  4. Jun 17, 2011 #3
    He means silicon oxide SiO2, or aluminum oxide Al2O3 for example.
     
  5. Jun 17, 2011 #4

    uLs

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    Apologize if i wasn't clear enough.
    What i try to ask is; metals are conductors obviously however when oxygen introduced a band gap occurs and we get semiconductor behaviour with oxides of metals. It is not just Al2O3 but all of the transition metals for instance from Vanadium oxide(and derivatives) to ZnO... Si is already a semiconductor with a band gap around 1eV... So what does oxygen atoms change so there is always a similar difference in the conductivity and energy levels of the formerly conductive metal structures.
    Hope i can make myself clear this time,
    Regards.
     
  6. Jun 17, 2011 #5
    in oxides, metal atoms are in the forms of cations and oxygen in the form of anions. in other words, oxygen atoms have an empty band(s) lower than metal valence band(s), and some or even all of the metal valence bands are depleted and become conductive band.

    those depleted bands of metal will be significantly shifted up due to the electrostatic field created by surrounding oxygen anions. the other lower metal bands will shift up by a smaller amount. as an over simplification, you can look at it this way: an electron does not interact with itself.

    the degree of this depletion can be manipulated to an extent, and the final band gap is highly dependent on it.
     
  7. Jun 17, 2011 #6

    uLs

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    Thank you for your through explanation. So in metaloxides, highly electronegative oxygen is the owner of the carriers thus behaving as valance band while emptied bands of the metal becomes conduction band for the new structure. From that what i understand is we can assume that as the oxygen ratio to the metal in the crystal increase, the band gap should also increase. I'll check this expectation. It sound so simple now but it explains a lot to me. Thank you once again :)
     
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