Band Theory of Conductors

The conductor is usually a substance that has the property of passing various types of energy. Let us understand the band theory and the electrical conductivity in conductors.

Band theory of Conductors, Semiconductors and Insulators

Band Theory of Conductors

A conductor is a substance that carries electrical charges that may move. 

Electrons are the moveable charged particles in metallic conductors like copper or aluminium. Positive charges can also be mobile; examples include the cationic electrolyte(s) in a battery or the mobile protons in a fuel cell’s proton conductor. 

Insulation materials are non-conducting materials having a small number of moveable charges that convey only a few electric currents.

The band theory of conductors involves conductors that employ mobile electrons to carry electricity. According to the theory, a conductor is essentially a substance with its conduction bands and valence bands overlapping, permitting electrons to flow through it with little applied voltage.

Band Theory of Semiconductors

The band theory states that semiconductors will operate as insulators at absolute zero. The metal would act as a semiconductor above this temperature, while remaining below the solid’s melting point. 

The completely occupied valence band and the unoccupied conduction band classify semiconductors. Due to the tiny band gap between these two bands, it takes a lot of energy to excite the electrons from the valence to the conduction band.

Although the semiconductor is an insulator at absolute zero temperature, it conducts electrical charges with temperature changes. When thermal agitation is applied, the charge carriers start moving from one band to another. The energy band gap of nearly 1eV separates both bands.

Band Theory of Insulators

The band gap energy between the conduction band and the valence band, the prohibited energy gap, is relatively large. It is for this reason that such compounds have no conductivity.

In the case of an insulating material, a significant forbidden difference exists between the valence band and the conduction band. As a result, such materials are called insulators since they cannot carry electricity.

The forbidden energy gap between the conduction and valence bands in insulators is large enough, roughly 7eV. The diamond is an insulator with a forbidden energy gap of approximately 6eV. These materials may only conduct at extremely high temperatures or when exposed to a high voltage.

Insulation breakdown, sometimes known as “insulator breakdown,” is an uncommon kind of conduction. Wood, glass, paper, mica, and other insulating materials are available.

Energy band theory terms

Bohr’s theory states that each atom’s shell and subshell contains a defined quantity of energy. The energy levels of an atom vary. Electrons in the topmost shell interact when atoms are closer to each other. Interatomic interactions are the forces that bind electrons together.

The valence band

There are multiple energy ranges present in the solid at absolute zero temperature, and the band produced by the highest range of energy is known as the valence band. 

The valence electrons are abundant in this band, which is beneath the Fermi level. The valence band electrons have less energy than the conduction band electrons. The capacity to transport electrons from one band to the other determines a solid’s electrical conductivity.

When atoms are pushed closer together to create a solid, quantum mechanical force disrupt discrete energy levels. Many electrons in the group of the particular atom occupy a band of levels in the solid. The band refers to this range of values. The electrons in the outermost shell create this band.

The forbidden band 

The Fermi energy level is another name for the forbidden energy gap. Due to the quantisation of energy, no electron state exists in this electrical energy range. The forbidden energy band, also known as the forbidden gap, is formed by separating the conduction and valence bands.

The electrons in solids do not dwell in the forbidden gap since it has no energy state. Using the forbidden gap, we may calculate the primary factor, i.e., the material’s electrical conductivity.

The conduction band 

The conduction band is the energy band created by the energy levels of free electrons. The conduction band is either empty or partially full, but electrons in the valence band jump to the conduction band and become free electrons by applying an external field to them.

The energy of electrons in the conduction band is greater than that of electrons in the valence band. Electrons are not bound to the atom’s nucleus in the conduction band. 

Conduction bands are also known as empty states, extended into various levels. This band is set higher than the Fermi level. It is the lowest level of electronic vacancy.

Conclusion

The article provides in-depth information about the band theory of conductors, semiconductors, and insulators. It also covers the terminology in the band theory, viz., valence band, forbidden band, and the conduction band.