Why Conduction Band? Understanding Its Significance

In summary, insulators have a conduction band, which is normally empty, and a valence band. When an electron is displaced across the band gap, it becomes delocalized and conductive. However, it can also lose energy rapidly and become immobile and nonconducting if trapped in the band gap. Both immovable electron and hole defects exist in the band gap, with electrons occupying states close to the conduction band edge and holes occupying states close to the valence band edge.
  • #1
snorkack
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Why are insulators supposed to possesses a "conduction band", even if usually empty?

If you do take the energy to cross the "band gap" and displace an electron, just why should it become delocalized/conductive? Couldn´t it just lose energy rapidly by exciting phonons until it gets trapped somewhere as an electron or anion defect, completely immobile and nonconducting in a weak field?
 
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  • #2
If you do take the energy to cross the "band gap" and displace an electron, just why should it become delocalized/conductive?
As a simplified model: it has so much energy that it is not bound to individual atoms.

Couldn´t it just lose energy rapidly by exciting phonons until it gets trapped somewhere as an electron or anion defect, completely immobile and nonconducting in a weak field?
Yes, but then it leaves the conduction band (and it needs an empty place with lower energy to do that).
 
  • #3
snorkack said:
Why are insulators supposed to possesses a "conduction band", even if usually empty?

All solids contain a valence and conduction band. Whether it is normal empty or normally occupied is by definition the difference between an insulator and a conductor. It gives a unified treatment of all solids.

snorkack said:
If you do take the energy to cross the "band gap" and displace an electron, just why should it become delocalized/conductive? Couldn´t it just lose energy rapidly by exciting phonons until it gets trapped somewhere as an electron or anion defect, completely immobile and nonconducting in a weak field?

To add a bit to mfb's explanation, the "somewhere" you mentioned is typically a state located in the bandgap. The bandgap is only free of energy states when the solid is defect free.
 
  • #4
So the occupied states for immovable electron defects are in the bandgap - as are the unoccupied states for immovable electron defects that might exist but do not.

Where are immovable hole defects, compared to the mobile charge carrier holes? Are both in the valence band?
 
  • #5
snorkack said:
So the occupied states for immovable electron defects are in the bandgap - as are the unoccupied states for immovable electron defects that might exist but do not.

Where are immovable hole defects, compared to the mobile charge carrier holes? Are both in the valence band?

The hole defects are also in the bandgap. Typically holes occupy states close to the valence band edge and electrons occupy states close to the conduction band edge.
 

1. What is the conduction band?

The conduction band is the energy level in a material where electrons can move freely and conduct electricity. It is the highest energy level in the valence band, and electrons must be excited to this level in order for a material to conduct electricity.

2. How does the conduction band differ from the valence band?

The valence band is the energy level in a material where electrons are tightly bound to atoms and cannot move freely. The conduction band is higher in energy and allows for the movement of electrons, making it responsible for the electrical conductivity of a material.

3. Why is the conduction band significant?

The conduction band is significant because it allows for the flow of electric current in materials. This is essential for many electronic devices, as well as for the functioning of biological systems that rely on electrical signals.

4. How is the conduction band related to the band gap?

The band gap is the energy difference between the valence band and the conduction band. If the band gap is small, electrons can easily be excited from the valence band to the conduction band, resulting in a material with good electrical conductivity. If the band gap is large, the material will be an insulator, as there is a significant energy barrier that prevents electrons from moving to the conduction band.

5. Can the conduction band be manipulated?

Yes, the conduction band can be manipulated by altering the material's structure or composition. This can be done through processes such as doping, where impurities are intentionally introduced to the material to change its electrical properties. Additionally, external factors such as temperature and electric fields can also affect the conduction band and its significance in a material.

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