Valence band, conduction band

In summary, in the conversation, the person asks for help with two questions, one regarding the meaning of "not allowed" in quantum theory for energy gaps and the other about the use of "arches" in energy diagrams. The expert explains that in quantum theory, energy bands have gaps where no energy states exist, and these gaps are caused by the periodic nature of the potential. The expert also clarifies that the "arches" are actually plunging potential due to the arrangement of lattice ions in a solid.
  • #1
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Hi,

Could you please help me with the queries below?

Question 1:
Please have a look on the attachment, conduction_band2, or check the following link for better resolution http://imagizer.imageshack.us/a/img921/4356/vODcjh.jpg

It says, "Figure 1–7 shows energy diagrams for insulators, semiconductors, and conductors. The energy gap or band gap is the difference between two energy levels and is “not allowed” in quantum theory."

What does the part "is not allowed in quantum theory" really mean here? I don't think it means that in quantum theory band gap is not allowed. If it does mean this then why does the gap exist?

Question 2:
Please have a look on the attachment, conduction_band1, or check the following link for better resolution http://imagizer.imageshack.us/a/img924/8813/KsYTN0.jpg

What do these 'arches' mean? Are they really needed? Why would the author use this style?

?temp_hash=eb6bc11b6576c1df5b9341e0e1353b09.jpg


Thank you for the help!
 

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  • #2
PainterGuy said:
Hi,

Could you please help me with the queries below?

Question 1:
Please have a look on the attachment, conduction_band2, or check the following link for better resolution http://imagizer.imageshack.us/a/img921/4356/vODcjh.jpg

It says, "Figure 1–7 shows energy diagrams for insulators, semiconductors, and conductors. The energy gap or band gap is the difference between two energy levels and is “not allowed” in quantum theory."

What does the part "is not allowed in quantum theory" really mean here? I don't think it means that in quantum theory band gap is not allowed. If it does mean this then why does the gap exist?

It means that there are no energy levels in that region. It is similar to the gap between energy levels in an atom where you have discrete energy levels. Here, you have energy BANDS, instead of levels, and there are gaps in the range of energy where no states exist.

It exists because of many reasons, including the periodic nature of the potential.

Question 2:
Please have a look on the attachment, conduction_band1, or check the following link for better resolution http://imagizer.imageshack.us/a/img924/8813/KsYTN0.jpg

What do these 'arches' mean? Are they really needed? Why would the author use this style?

View attachment 236104

Thank you for the help!

Those should not be looked at as "arches", but rather as "plunging potential". Draw the Coulombic potential well, for example. It is -∞ as r→0, and then it approaches 0 as r→∞. This is ONE of those "arches". Now, repeat that when you have many lattice ions at regular intervals. This is the potential that an electron in a solid "sees" due to the regular arrangement of the lattice ions potential as it goes through the solid.

Zz.
 
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Likes PainterGuy

1. What is the Valence Band?

The valence band is the highest energy level in an atom where electrons are located. It is responsible for the chemical properties of an element, as it determines how easily electrons can be gained or lost.

2. What is the Conduction Band?

The conduction band is the energy level in a solid material where electrons are able to move freely and conduct electricity. It is located above the valence band and requires less energy for electrons to enter.

3. What is the difference between the Valence Band and Conduction Band?

The main difference between the valence band and the conduction band is the energy level at which electrons can exist. The valence band is the highest energy level where electrons are bound to the atom, while the conduction band is the energy level where electrons are able to move freely and conduct electricity.

4. How do electrons move from the Valence Band to the Conduction Band?

Electrons can move from the valence band to the conduction band when they receive enough energy, either through heat or an external electric field. Once in the conduction band, electrons can freely move and conduct electricity.

5. What is the role of the Valence Band and Conduction Band in semiconductors?

In semiconductors, the energy gap between the valence band and the conduction band is small, allowing electrons to move between them. This makes semiconductors useful in electronic devices, as they can be easily manipulated to allow or block the flow of electricity.

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