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Homework Help: Solid State Electronic Devices - Valence Electrons Question

  1. Feb 2, 2012 #1
    1. The problem statement, all variables and given/known data
    2. Determine the concentration of valence electrons in doped
    (a) Si (a = 0.543 nm)
    (b) GaAs (a = 0.565 nm)

    2. Relevant equations

    3. The attempt at a solution
    This is the problem, I don't really know what they're looking for. I know what valence electrons are, but doesn't it matter what it's doped with? Why are they giving me the crystal lattice constant? I can't find anything that quite relates these things in the chapters we have gone through, nor in the lecture notes. I'm really stumped, I just have no idea where to start. The TA sent out an email, but here is what it said,

    "Many of you have some problems with the problem 2 of HW2, here are some hints:

    1) The dopants (too small concentration) don't influence the number of valence electrons.
    2) Refer to Figure 3-3 for "valence electrons" definition."

    The definition I know, but how does 1 help me at all?

    The only thing I can think of is that when the relative spacing of atoms reaches a certain small point (when the band begins to emerge) there are 4N (N being the number of atoms) electrons in the valence band. However, wouldn't this change when they are doped? Wouldn't that change depending on what it was doped with?

    Any help would be greatly appreciated. Thank you.
  2. jcsd
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