Don't get the conduction band in solid

In summary,electrons in a valence band can move through a solid, but an electric field can lower the energy of electron in the opposite direction, which provides a net current.
  • #1
luuurey
24
0
I was reading about electronic band structure in wiki and I didn't understand why the conduction bands are necessary for flowing current in a material. If all the atoms in a solid shares valence band and all its eletrons, then these electrons may travel through the solid. I didn't get why the electrons in the valence bands can't freely travel within solid and so make current.

Thanks for explanation!
 
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  • #2
Because the valence band is symmetric in momentum. That is, in a semiconductor with a filled valence band for each electron with momentum +k there is another electron with momentum -k, so there is no net current. Even if one applies an electric field to bias the current in a certain direction, this basic momentum balancing effect is still present.

Once you get some electrons in the conduction band and have a partially filled band, then the application of an electric field can break this symmetry.
 
  • #3
Thank you very much for your help. But there is a thing. Why can't we break this symmetry also in a valence band ? There's no different between them, right? Why can't an electric field break symmetri also in the valence band?
 
  • #4
Because the valence band is full, which means that for every available momentum k, there is an electron with momentum k and -k. That's the definition of a full band. If you apply an electric field, that doesn't change which momenta are available, it just lowers the energies of momenta which point in the opposite direction. But if the band is full then this doesn't change the momenta of any electrons because there are no available states for electrons to shift around.

Now if you remove some electrons from the valence band, then when the E field is electrons will move into the empty states that go opposite the E field, providing a net current. When this happens in the valence band this is referred to as hole current. In the conduction band it is electron current.
 
  • #5
Thanks. Can you please recommend me any material, webside or text where I can read about it more?

Thank you very much.
 
  • #6
Hi,

you might be interested in this series of lectures by keio university



yinx
 
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  • #7
I'm not sure, but he's describing in the video that an electron in valence band cannot move because it's traped. If the electron gets to conduction band then it can flow because it's actually got from the trap.

I'm really not sure of this assertion. I think it's not so simple. I have thought electrons in a valence band can move throught a solid, can't they?
 

What is the conduction band in solid materials?

The conduction band in solid materials refers to the energy level at which electrons are able to move freely and conduct electricity. In a solid, the electrons are usually bound to specific atoms, but in the conduction band, they are able to move between atoms and contribute to the material's conductivity.

Why is it important not to get the conduction band in solid materials?

If the conduction band is reached in a solid material, it means that the electrons have gained enough energy to break free from their bound state and become free electrons. This can lead to the material losing its structural integrity and potentially causing damage or failure.

What factors affect the position of the conduction band in solid materials?

The position of the conduction band in solid materials is affected by various factors, such as the type of material, its atomic structure, and the presence of impurities or defects. The band can also be influenced by external factors like temperature and applied electric or magnetic fields.

How is the conduction band related to the band gap in solid materials?

The conduction band and the band gap are both part of the energy band structure of solid materials. The band gap is the energy level between the valence band (where electrons are bound) and the conduction band. The size of this gap determines the ease with which electrons can move from the valence band to the conduction band and contribute to conductivity.

Can the conduction band in solid materials be manipulated or controlled?

Yes, the conduction band in solid materials can be manipulated or controlled through various methods such as doping, applying external electric or magnetic fields, or changing the material's temperature. These techniques can be used to alter the material's conductivity and create desired electronic properties.

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