# Valence Band And Conduction Band Pdf

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29.03.2021 at 12:03

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A useful way to visualize the difference between conductors , insulators and semiconductors is to plot the available energies for electrons in the materials. Instead of having discrete energies as in the case of free atoms, the available energy states form bands.

## Valence band

Band Theory was developed with some help from the knowledge gained during the quantum revolution in science. In , Felix Bloch had the idea to take the quantum theory and apply it to solids. In , Walter Heitler and Fritz London discovered bands- very closely spaced orbitals with not much difference in energy. In this image, orbitals are represented by the black horizontal lines, and they are being filled with an increasing number of electrons as their amount increases. Eventually, as more orbitals are added, the space in between them decreases to hardly anything, and as a result, a band is formed where the orbitals have been filled. Sodium's bands are shown with the rectangles.

## Difference Between Valence Band and Conduction Band

The valence band is the band of electron orbitals that electrons can jump out of, moving into the conduction band when excited. The valence band is simply the outermost electron orbital of an atom of any specific material that electrons actually occupy. This is closely related to the idea of the valence electron. The energy difference between the highest occupied energy state of the valence band and the lowest unoccupied state of the conduction band is called the band gap and is indicative of the electrical conductivity of a material. Conversely, when the valence band and conduction band overlap as they do in metals , electrons can readily jump between the two bands see Figure 1 meaning the material is highly conductive. The difference between conductors , insulators , and semiconductors can be shown by how large their band gap is. This property gives them a conductivity between conductors and insulators, which is part of the reason why they are ideal for circuits as they will not cause a short circuit like a conductor.

Energy bands consisting of a large number of closely spaced energy levels exist in crystalline materials. The bands can be thought of as the collection of the individual energy levels of electrons surrounding each atom. The wavefunctions of the individual electrons, however, overlap with those of electrons confined to neighboring atoms. The Pauli exclusion principle does not allow the electron energy levels to be the same so that one obtains a set of closely spaced energy levels, forming an energy band. The energy band model is crucial to any detailed treatment of semiconductor devices.

## Band Theory of Semiconductors

We evaluate magneto-optical absorption spectra of multiple quantum wells with compositions, x , from 0. We analyze the diamagnetic shifts of exciton resonances based on the effective-mass equations taking both conduction- and valence-band nonparabolic dispersion into account. We obtain in-plane electron, hole, and reduced effective masses of excitons and Luttinger-Kohn effective-mass parameters for valence bands as a function of composition.

According to the band theory, semiconductors will actually act as insulators at absolute zero.

### Valence and conduction bands

Conductors are generally substances which have the property to pass different types of energy. In the following, the conductivity of electricity is the value of interest. The conductivity of metals is based on the free electrons so-called Fermi gas due to the metal bonding. Already with low energy electrons become sufficiently detached from the atoms and a conductivity is achieved. The conductivity depends, inter alia, on the temperature. If the temperature rises, the metal atoms swing ever stronger, so that the electrons are constrained in their movements. Consequence, the resistance increases.

A conductor is a material that is able to conduct electricity with minimal impedance to the electrical flow. It is commonly a metal. A conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons. Positive charges may also be mobile, such as the cationic electrolyte s of a battery or the mobile protons of the proton conductor of a fuel cell.

In solid-state physics , the valence band and conduction band are the bands closest to the Fermi level and thus determine the electrical conductivity of the solid. In non-metals, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states. On a graph of the electronic band structure of a material, the valence band is located below the Fermi level, while the conduction band is located above it. The distinction between the valence and conduction bands is meaningless in metals, because conduction occurs in one or more partially filled bands that take on the properties of both the valence and conduction bands.

Valence and Conduction band are the two different energy levels separated by a certain amount of energy. The main difference between the valence band and conduction band is that valence band specifies the energy level of electrons present in the valence shell of an atomic structure. As against a conduction band holds those electrons that are responsible for conduction. It is basically defined as the energy band that comprises of valence electrons present in the outermost shell of an atomic structure.

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