Energy Bands and its Classifications

Electronic band structure (or simply band structure) in solid-state physics refers to the range of energy levels that electrons can have in a solid and the range of energies that they may not have. The quantum-mechanical wave functions permitted for electrons in a vast systematic lattice of an atom or molecule are examined using band theory to determine these bands and band gaps. Several manual features of solids have been satisfactorily explained using the band theory model. Become familiar with electrical resistance, light absorption, and solid state devices as a foundation for further study.

What are energy bands?

In the explanation of energy wheels, the arrangement of molecules is not close, i.e. they have slowly clogged away from each other. The molecular arrangement in the liquid is moderate, i.e. the molecule is slightly separated. When it becomes solid, the molecule is closely placed so that the electron (subatomic particles having charge load) tends to move towards the orbit of the adjacent atom. As a result, the electronic agency overlaps as the atoms gather. Instead of individual energy levels, mixing atoms in solid-state substances results in the  formation of energy bands. A group of densely or tightly packed energy levels is what we call an energy band.

Formation of energy bands

In an isolated atom, an electron has specific energy in each orbit. However, in the case of solids, the energy levels of the outermost orbital electrons are affected by adjacent atoms. When two isolated charges approach each other, the electrons in the outermost orbits are attracted by the closest or adjacent nuclei. Therefore, the energy of the electron is not the same level, and the energy level of the electron is changed to a value higher or lower than  the original energy level of the electron. Electrons present in the same orbit have different energy levels. The manner in which the different energy levels are grouped is called the energy band. However, the energy of internal orbital electrons is not significantly affected by the presence of adjacent atoms.

Classification of energy bands

Valence band

The band of electron orbits where electrons can jump and move to the conduction band when excited is the valence band. The valence band is the outermost electron orbital of an atom of a particular material that the electron actually occupies. This is closely related to the idea of ​​valence electrons.

Conduction band

The valence electrons are not absolutely held in the nucleus. Few of the valence electrons may skip the band and are free even at room temperature. Known as free electrons as they seem to push themselves closer to the adjacent atoms. Free electrons are called conduction electrons because they conduct an electric current through a conductor. This band contains conduction electrons and the level of occupied energy is the lowest.

Forbidden energy gap

The gap between the valence band and the conduction band is the forbidden energy gap. As the name implies, there is no energy in this energy gap and no electrons remain in that energy band. During the transition towards the conduction band, valence electrons make themselves pass through the forbidden energy gap. When the forbidden energy gap is large, the electrons in the valence band are tightly bonded to each other or bonded to the nucleus. Pushing an electron away from the valence band requires a certain amount of external energy which is equal to the energy of the forbidden gap.

Conductors

Conductors are substances which transmit electricity by passing an electric current through it. When the conduction band and the valence band converge and overlap, the energy gap prohibited in the conductor disappears. Copper, gold, and silver are some examples of conductors.

Semiconductors

A semiconductor is a substance or material that has a conductivity between a conductor and an insulator. In semiconductors, the prohibited energy gap is small, and current conduction occurs only when external energy is applied. Germanium and silicon are some examples of semiconductors.

Insulators

These are substances or materials that do not conduct electricity because they do not carry current. The insulator’s restricted energy gap is vast so no current conduction occurs. Rubber and wood are some examples of insulators.

Conclusion

In order to understand the behaviour of solids, energy bands, and its classification are important to understand. Bohr’s theory states that each shell of an atom contains discrete amounts of energy at various levels. The interaction of electrons between the outermost and innermost shells is explained by the theory. Based on energy band theory, there are three different energy bands,  Valence band, Forbidden energy gap, and  Conduction band.