Difference between Valence band and Conduction band

Valence band and conduction band are two different types of energy levels that are separated by some amount of energy. The basic difference between conduction band and valence band is that in the conduction band the electrons which take part in the process of conduction exists while in the valence band the electrons are present in the outermost shell or the valence electrons are present. In this article, we will see the actual difference between valence band and conduction band.

Difference between Valence band and Conduction band in tabular form

Let’s look at the differences between the valence band and conduction with the help of a table.

Valence band Conduction band
The valence band consists of the electrons that lie in the outermost shell or valence shell of the atom. The conduction band consists of the free electrons that take part in the process of conduction.
The valence band lies below the Fermi level. The conduction band lies above the Fermi level.
When external energy is given to the electrons in the valence they leave the valence band. When external energy is given to the electrons they leave the valence band and reach the conduction band.
There is no flow of current due to the electrons present in the valence band. The free electrons present in the conduction band are free to move anywhere within the volume of the solid, therefore current flows due to these electrons.
Due to the presence of electrons valence band is partially or completely filled. The conduction band is either empty or partially filled.

What is valence band?

It is the energy band that consists of electrons that are present in the outermost shell or valence shell of the atom. When external energy is supplied to the valence band electrons, after getting a sufficient amount of energy the electrons become free and they move from the valence band into the conduction band thereby causing conductivity.

The valence band is denoted by VB and lies at the lower energy level than the conduction band in the energy diagram. There lies a difference in the energies of the valence band and the conduction band, this difference of energy is known as the forbidden energy gap.

This forbidden energy gap depends on the type of material used i.e, conductor, semiconductor, or insulator.

The valence band lies below Fermi level. The nucleus exerts a great amount of force on this band since the electrons in this band are closer to the nucleus. Since electrons are present in this band, this band is completely or partially filled.

What is conduction band?

It is the energy band that consists of the free electrons which are responsible for conduction. Electrons in the valence band after getting a sufficient amount of energy move to the conduction band and contribute to the conductivity.

The conduction band lies above the fermi energy level which means this band has higher energy than the Fermi energy level. Since this band has higher energy a large amount of energy is needed for the electrons to move into this band and giving rise to current. The conduction band is denoted by CB and electrons can move freely in this band.

We have seen above that the forbidden energy gap is different types of materials, i.e. for conductors, semiconductors and insulators. For the conductors the valence band and conduction band both overlap with each other therefore electrons can easily pass into the conduction band from the valence band. It is due to this reason that current can easily flow in conductors or they are good conductors of electricity.

There is some difference in energies of the conduction band and valence band for the semiconductors. The value of the forbidden energy gap for semiconductors lies in between the conductors and insulators. Therefore a little amount of energy is required for the electrons to pass into the conduction band from the valence band.

The band gap between the conduction band and valence band is very large for the insulators. A large amount of energy is needed for the electrons to move into the conduction band, therefore insulators cannot conduct electric current.

Conclusion

From the above discussion, we have concluded that there are various factors that differentiate between the valence band and conduction band, one major difference being the position of these bands with respect to Fermi level. The valence band has lower energy hence it lies below the fermi level and the conduction band has higher energy than the fermi energy level hence it lies above the Fermi energy level.

The materials like conductors, semiconductors and insulators are also differentiated on the basis of difference in energies between the valence band and conduction band.

Author
Deepak Yadav
Aligarh Muslim University, Aligarh

References

1. https://www.theengineeringknowledge.com/difference-between-valence-band-and-conduction-band
2. https://byjus.com/jee/conduction-band

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