Fermi Level - clarification needed

In summary: And, when two atoms are close enough, their electrons can't have the same energy and so they split into the different levels.
  • #1
logearav
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Fermi Level -- clarification needed

Homework Statement




Revered Members,
Can i know what is meant by fermi level? I googled this, but i could not understand. One site says Fermi level as top of collection of electron energy levels at absolute zero.

Homework Equations





The Attempt at a Solution



As far as my knowledge I know electron energy levels as K, L,M, N etc with energy values -13.6eV, -3.4eV etc. Top of collection means, is it O eV?
 
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  • #2


logearav said:
As far as my knowledge I know electron energy levels as K, L,M, N etc with energy values -13.6eV, -3.4eV etc. Top of collection means, is it O eV?

Those are the energy levels of a hydrogen atom. Fermi level is defined for crystals -metals, semiconductors.


When two hydrogen atoms are so close that they interact, their electrons can not have the same energy, according to Pauli's Principle. All orbits and their energies split into two: one energy lower, the other higher than that of the individual atom.

In a crystal made of N atoms, the energies split into N different levels. There are very close levels arranged into bands, and there can be only one electron on each level.
At zero temperature (0 K) all the levels are filled up to a certain energy: This is the Fermi energy. Insulators and semiconductors have completely filled bands, the highest called valence band and the next above which is empty at 0 K is the conductance band. There is a "forbidden gap" between the bands.
At higher temperatures, some of the electrons gain enough thermal energy so they can occupy a level in the conductance band, leaving an empty level - a hole - behind in the valence band. The Fermi level means that energy above which there are as many occupied levels as empty levels below it

Read: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html.

ehild
 
  • #3


Thanks ehild. So, Fermi level is the level above valence band,am i right?
 

1. What is the Fermi level?

The Fermi level, also known as the Fermi energy, is a concept in quantum mechanics that refers to the highest occupied energy level in a system at absolute zero temperature. It represents the energy at which electrons in a system have a 50% chance of being occupied.

2. How is the Fermi level related to the electronic band structure?

The Fermi level is an important concept in understanding the electronic band structure of a material. It acts as a reference point, separating the filled energy states from the empty energy states in the material's conduction band. The position of the Fermi level in relation to the band structure determines a material's electrical conductivity and other electronic properties.

3. Can the Fermi level change in a material?

Yes, the Fermi level can change in a material. It is affected by various factors such as temperature, doping, and external electric fields. For example, an increase in temperature can cause the Fermi level to shift towards higher energy states, while doping can shift it towards lower energy states.

4. What is the significance of the Fermi level in semiconductors?

In semiconductors, the position of the Fermi level plays a crucial role in determining the material's electrical properties. At absolute zero temperature, the Fermi level is located exactly in the middle of the band gap, making the material an insulator. However, at room temperature, the Fermi level moves closer to the conduction band, allowing for the flow of electrons and making the material a conductor.

5. How is the Fermi level measured?

The Fermi level can be measured using various experimental techniques, such as photoemission spectroscopy and Hall effect measurements. These techniques involve analyzing the energy and movement of electrons in a material to determine the position of the Fermi level.

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