Question about Doping/electrons & holes

Discussion in 'Physics' started by EGY5, Sep 22, 2008.

  1. EGY5

    Thread Starter New Member

    Sep 22, 2008
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    If I understand this all correctly, semiconductors have a small bandgap which their electrons can overcome thru thermal excitations. When an electron jumps the gap, it creates two carriers, an electron and a hole.

    Doping increases the carrier concentration by replacing an Si atom with B or P, which has either 3 or 5 electrons for P or N type doping.

    If this is correct, then my question is why are the donor atoms treated as Si atoms within the lattice? In the case of B it has one less electron, but it also has one less proton, so shouldn't that yeild a different internal potential/orbitals and hence different interactions with the surrounding Si atoms? And if that takes place, wouldn't the surrounding Si atoms have their behavior change due to the decreased charge within the lattice?

    Hopefully this question makes sense :confused:
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. scubasteve_911

    Senior Member

    Dec 27, 2007
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    If this is correct, then my question is why are the donor atoms treated as Si atoms within the lattice?

    How are they treated as Si atoms? Usually, the dopant is treated as a concentration within the Si lattice. Check out how the molecular structure is represented.

    http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c2

    Semiconductor physics is very difficult to understand, it will take many years of research to get a good grasp. I took a course last semester and was completely baffled, it's a strange world :( Although I did manage a 72 in the class, I am still pretty clueless..

    Steve
     
  4. EGY5

    Thread Starter New Member

    Sep 22, 2008
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    I meant more locally than macroscopic concentrations. I guess a better way to phrase my question was:

    If you are literally replacing a Si atom with a B or P atom, then why are the electrons of the surrounding Si atoms bonding with the B or P atom in the same manner as a Si atom (leaving the holes or electrons) when they are subject to a different potential?
     
  5. scubasteve_911

    Senior Member

    Dec 27, 2007
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    Sorry, your question is pretty confusing.

    Okay, a B or P atom gets added to some silicon. The impurity atom is now within the lattice structure.

    You are asking, why the Si atoms are bonding with the impurity atoms in the same 'manner' as an Si atom when they are subject to a different potential.

    Some undefined parts of your question are. What do you mean by 'manner' in this case? Secondly, what leads you to believe that they are bonding in the same way at different potentials?

    Steve

    I'm assuming you understand the type of bond occuring on the molecular level, is that correct? Much of the understanding of semiconductor has to do with quantum mechanics; thus, much probabilities and energy states.
     
  6. EGY5

    Thread Starter New Member

    Sep 22, 2008
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    I apologize if my question was confusing. Your questions about my question (confusing right) straightened me out I think. I assumed that different orbitals would lead to different bonding, but I guess the bonds between Si and B or Si and P atoms are still sigma bonds, which would make the whole thing make sense.

    Thanks
     
  7. scubasteve_911

    Senior Member

    Dec 27, 2007
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    Well, that's a first! Question a question and get an answer :p

    I kind of decided that understanding semiconductors is a lost cause for me, since I am more of an applied science kind of guy. It was an interesting course though.

    Steve
     
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