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Physics of semiconductor in light and dark

  1. Oct 21, 2012 #1
    Hi all,
    when we shine light on semiconductor surface with white light, superband gap transition occurs (VB to CB). Also we have surface state (SS) too, so there is probability of transition from VB to SS and SS to CB as well. The time transient of this surface is similar to charging of a capacitor (in light) and discharging of a capacitor (in dark). Could someone explain physics of this process?
    Last edited: Oct 21, 2012
  2. jcsd
  3. Oct 22, 2012 #2
    quantum world,

    Could you define "VB" and "CB" and explain what the superband gap transistion is?"

    What is "SS", and how does it relate to the statement above?

    What surface?

    What process? I doubt if anyone will even try. The question is too broad, ill defined, and not specific enough.

  4. Oct 22, 2012 #3
    VB=valence band CB=conduction band

    when the energy of incident light, hf≥ band gap energy, super band gap illumination takes place.

    The surface between a semiconductor and vacuum or gas is referred as a free surface or just surface.

    The termination of periodic structure of semiconductor at its free surface or the bonds that are free at surface may form surface localized electronic states within semiconductor band gap is called surface state.

    The electrons from ss can move to cb if incident energy hf≥ ( Ecb - Esurface state )

    The electrons from vb can move to ss if incident energy hf≥ ( Esurface state - Evb )
  5. Oct 22, 2012 #4


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    So exactly what is this "physics" that you want an explanation for?

  6. Oct 22, 2012 #5
    Actually the movement of charges from cb to vb or from ss to cb or from vb to ss due to illumination, changes the band bending which is monitored in Surface Photovoltage (SPV) technique. Actually physics is hidden there so I want to be clear about that.
  7. Oct 24, 2012 #6
    Try with Optical Detection of Surface States in Ge Phys. Rev. 144, 749–751 (1966)
  8. Oct 24, 2012 #7


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    The actual "movement" of charges?

    Isn't that like asking the "movement" of an electron when it makes an atomic transition?

    There is no "movement" here. It is a change in the energy state! The conduction band and valence band are not two separate locations.

  9. Oct 24, 2012 #8
    For a general explanation of how orbital electrons can absorb energy
    from light, try reading the first few sections here:

    [note that sometimes electrons just jump energy bands, other times they can actually
    be ejected from the material.]

  10. Oct 24, 2012 #9
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