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Conduction Band

Last Updated : 11 Jan, 2024
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Conduction Band is an electron band where electrons are arranged after jumping from the valence band when they are excited. The presence of electrons in the conduction band allows the matter to allow the flow of electricity through them. This explains why metals are good conductors of electricity as their conduction band bs are partially filled with electrons. This special band inside solid-state materials (like metals or semiconductors) is like a little express highway for electrons to travel on.

In this article, we will learn what is Conduction Band, Band Theory of Electrons, Difference between Conduction Band and Valence Band, and related terminologies.

What is Conduction Band?

Conduction Band is an important concept in solid-state physics, the conduction band describes a range of energy levels within a material where electrons are free to move and conduct electricity. In solid materials like metals and semiconductors, electrons usually exist in certain energy levels called Bands. The conduction band is the highest energy portion of a material where electrons are mobile.

The conduction band is of key importance in defining the electrical properties of materials, whether they are conductive or non-conductors, and how well they serve as electronic devices like transistors, diodes, and conductors.

Conduction band is the highest energy band in which there are some electrons with enough kinetic energy to migrate within a piece of material and thus make it electrically conductive.

Conduction Band Definition

Conduction Band is a Electron Band where electrons reach when then jump from valence band after they are excited.

Conduction Band is Energy level in a material where electrons are fairly free to move, thus capable of carrying an electric current.

Valence Band and Conduction Band

Valence band is the highest level of energy band where electrons are arranged at absolute zero temperature. It is the region where most of the electrons are located when they are in ground state. Let’s see difference between Conduction Band and Valence Band.

Difference between valence Band and Conduction Band

Conduction Band and Valence Bands are two energy bands in a solid state material where electrons are present. The amount of electrons present in this regions along with other factors determine the electrical conductivity of a material. The difference between Valence Band and Conduction Band is Tabulated below:

Valence Band vs Conduction Band

Characteristic

Valence Band

Conduction Band

Energy Level

Lower energy levels

Higher energy levels

Electron Location

Atoms have a hold on electrons

Electrons freely move in the material

Electrical Conductivity

Poor conductor of electricity

Good conductor of electricity

Electron Mobility

Low electron mobility

High electron mobility

Role in Conduction

Electrons from the valence band participate in chemical bonding and are not that mobile

Experts say this kind of electronegativity will disappear completely if there is too much electricity.

Band Gap

Minimal or zero band gap

There is a large energy gap between the valence and conduction bands

Conduction Band – Important Terminologies

Following are some important terms related to conduction band which need to be learnt

  • Fermi Level
  • Conduction Electron
  • Conductivity
  • Band Gap
  • Electron Mobility

Fermi Level

Fermi level refers to an energy level at which there is zero probability of occupation. Fermi level represents the splitting of occupied and unoccupied electron states at absolute zero temperature. The Fermi level is of great importance in understanding the electronic properties of materials, and especially helps one decide whether a material will act as conductor or insulator.

Conduction Electron

Conduction Electrons are the electrons in conduction band of a material responsible for conductivity of the material. These electrons are free, have enough energy to travel anywhere and assist in electrical conductivity. In metals the conduction band partially overlaps with valence band, so electrons can move freely across energy bands within a small range and metals conduct electric Current well.

Conductivity

Conductivity is the ability of a material to conduct electric current. A material is conducting or not depends on the existence of free electrons in the conduction band. High conductivity materials such as metals permit electrons to move freely; insulators prevent electron flow. Performance of electronic devices depends on one important property conductivity. Conductivity is inverse of resistivity. Hence, conductivity is given as

σ = 1/ρ

where,

  • σ is Conductivity
  • ρ is Resistivity

Band Gap

Band gap is the energy difference between the valence and conduction bands. It determines a material’s electrical properties. The larger the gap, an insulator; and a small or zero gap is typical of conductors. Between insulators and conductors, semiconductors have a moderate band gap that provides for electronic conductivity limited by conditions.

Electron Mobility

Electron mobility is a measure of how easily electrons can pass through in response to an electric field. The electrons in the conduction band are mobile, so that electrical conductivity is efficient. The concept is important in the design of electronic components and understanding the operation of semiconductor devices. The formula of Electron Mobility is given as

μn = eτ/m*n

where,

  • μn is Mobility of Electron
  • e is Charge of Electron
  • τ is Relaxation Time
  • m*n is Mass of Electron

Band Theory of Electrons

Band Theory is a fundamental concept to understand electronic properties of materials, especially the solids. The theory categorizes the electron movement patterns into bands, and describes it as it happens in a crystalline structure.

  • Electrical Conductivity: The valence band which has electrons at low energy that are closely bonded to atoms and the conduction band which has high energy levels in which free moving of electrons occurs.
  • Semiconductor Devices: Semiconductor devices is extremely important to understand band theory when designing.
  • Optical Properties: There is also band theory which describes how materials behave optically. Interaction of these materials with light depends on the energy difference between bands.
  • ​Magnetic Properties: Band theory aids in the elucidation of magnetic properties of materials.
  • Thermal Properties: Thermal properties understanding is another essential thing it does. Heat conduction/insulation capacity of a material is dependent on behavior of electrons in energy bands.

Also, Read

Conduction Band – Numerical

Numerical 1: Given a semiconductor with an electron mobility of 0.15 m2/V s and a charge carrier concentration of 8 × 1015m-3, calculate its conductivity.

Solution:

Formula for conductivity (σ) is:

σ = n e μ

n = Charge carrier concentration (8 × 1015m-3)

e = Charge of an electron (1.6 × 10-19 C)

μ = Electron mobility (0.15 m2/ V s)

Substituting Values:

σ = (8 × 1015) × (1.6 × 10-19) × (0.15)

σ = 1.92 × 107 S/M

Therefore, the conductivity of the semiconductor is 1.92 × 107 S/M

Numerical 2: In a semiconductor with an electron mobility of 0.25 m2/V s and a charge carrier concentration of 6 × 1015m-3, calculate its conductivity.

Solution:

Formula for conductivity (σ) is:

σ = n e μ

n = Charge carrier concentration (8 × 1015m-3)

e = Charge of an electron (1.6 × 10-19 C)

μ = Electron mobility (0.15 m2/ V s)

Substituting Values:

σ = (6 × 1015) × (1.6 × 10-19) × (0.25)

σ = 2.4 × 107 S/M

Therefore, the conductivity of the semiconductor is 2.4 × 107 S/M

Conduction Band – Practice Questions

Q1. Take a semiconductor with the bandgap of 0.7 eV, for example. Would this semiconductor behave more like a conductor or an insulator at absolute zero temperature? Explain your answer in terms of the band theory.

Q2. Why does the valence band and conduction band overlap for a metal? Explain. And how does this overlap produce the high electrical conductivity found in metals?

Q3. In a p-type semiconductor, which way is the Fermi level closer to–the valence band or the conduction band? Give a simple explanation of the Fermi level position in p-type semiconductors.

Q4. Explain the relationship between conduction band and electron mobility in a semiconductor. What impact does the presence of impurities have on electron mobility in the conduction band?

Q5. How do band theory concepts apply to the operation of a P-N junction diode? describing the function of the depletion region, flow of charge carriers and band structure in diode operation.

Conduction Band – Frequently Asked Questions

What is Band Theory?

Band theory is concerned with how electrons arrange into energy bands in solids. Based on their band structures, it classifies materials as conductors, insulators or semiconductors.

Why is Band Theory Important?

Band Theory plays an important role in designing energy materials and electronics, as well as in predicting new material properties.

What is the Fermi Level?

Fermi level is the which represents the energy where the probability of finding an electron is 0.5 at zero absolute temperature.

What are Conduction Electrons?

Conduction Electrons are unconfined electrons (in the conduction band) allow materials to conduct electricity because they are free to move in response to electric fields.

What is Electron Mobility?

Increasing electron mobility means facilitating electrons ‘mobility in a material when it is in an electric field. This affects the conductivity of the material and the performance of electronic devices.

What is Forbidden Band?

The Energy gap between Conduction Band and Valence Band is called Forbidden Band.

How Does Band Theory Explain Material Behavior?

Band theory explains how electrons migrate through materials; it also underlies their ability to conduct electricity and helps us understand material characteristics.



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