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Converting an indirect gap material to direct one

  1. Jun 18, 2014 #1
    For which reason some of materials have direct gap and the other have indirect gap?
    In other words, what we have to do to convert a direct gap material to indirect one?
  2. jcsd
  3. Jun 18, 2014 #2


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    This is a question of the electronic structure. In direct band gap materials, the valence and the conduction band have a maximum and minimum at k=0, respectively. In the semiconductors Si or Ge, both the valence and the conduction bands are made up of p orbitals (this is exact at k=0, at other values of k, other orbitals like s, will contribute, too), which leads to a direct band gap. In other materials, the valence band may be s but the conduction band p type, which leads to a different picture. Also polar bonding as in III-V semiconductors may lead to a shift of band maxima and minima.
  4. Jul 7, 2014 #3
    They can change indirect band gap silicon (single crystal and polycrystalline) into direct bandgap by making it amorphous
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