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What makes a semiconducting material a semiconductor?

  1. Jun 14, 2010 #1
    what really makes a semiconductor? Is it just the presence of a band gap but then insulators and metals also have band gaps or carrier concentration? Or we need to perform Hall measurements and also need to study I-V characteristics? Or do we need all of these parameters to establish a material as semiconductor?
  2. jcsd
  3. Jun 15, 2010 #2
    In metals you have half-filled bands, so that the fermi level is within the band. In semiconductors and insulators the fermi level is in the band gap, so at 0 K the bands are either completely filled (valence band) or completely empty (conduction band).
    I think that the difference between semiconductor and insulator is that in insulators the gap is much larger than in semiconductors.
  4. Jun 15, 2010 #3
    Thanks! So what sort of experimental measurements we should make in order establish a material as a semiconductor, metal or insulator? Apparently having a band gap is not enough.
  5. Jun 15, 2010 #4
    One indicator is to measure how resistance changes with temperature.With intrinsic(pure) semiconductors resistance reduces with temperature.
  6. Jun 15, 2010 #5


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    Do a resistivity versus temperature measurement. Metals will have a decreasing resistivity with decreasing temperature, whereas a semiconductor/insulator will have an increasing resistivity with decreasing temperature.

  7. Jun 15, 2010 #6
    Last edited by a moderator: May 4, 2017
  8. Jun 15, 2010 #7
    The way I understand it is.

    Perfect Insulator: No energy band is partially filled. Relatively large amount of energy required for a particle to reach the next energy level.

    Conductor: Partially filled energy band, very little energy required to move to the next highest energy level.

    Semi: Highest energy band is mostly empty, band before that is almost but not full. Some particles start to gain energy and quickly reach a gap, others are free as if they were in a conductor.
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