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Si and light

  1. Jan 25, 2006 #1
    Hi i was reading yesterday in a semiconductor lessons that the Si is not suitable for creating light.. Do u know why is this happening?
  2. jcsd
  3. Jan 27, 2006 #2


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    "Not suitable" is correct in a simplistic sense, because crystalline Silicon is not a direct band-gap material. However, over these last two years, researchers have shown that you can make Silicon based photonic devices, using the Raman effect.

  4. Jan 28, 2006 #3
    To speak more of this, there are semiconductors with Direct band gaps and Indirect band gaps.
    In direct band gap materials optical transitions are more probable eg:- GaAs. Here valance band maximum and conduction band minimum lie at same K-value.
    Where as in indirect band gap materials optical processes are not dominant eg:-Si, Ge .Here VB maximum and CB minimum are at different K-values.So the incoming photon has to be excited first to a virtual state and then to the conduction minimum.
  5. Jan 30, 2006 #4
    Thx a lot but how can u explain me that optical transitions in Si are not propable to occur? How the indirects bands affect these transitions
  6. Jan 30, 2006 #5


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    This is clearly explained in the article I linked. An indirect bandgap is one when the VB maximum and CB minimum have different crystal momenta. For an electron to go from the first to the second, it needs a considerable change in momentum. A photon does not have enough momentum to make this change possible; so a photon can not facilitate this transition.
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