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nickhobbs
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I was wondering what the difference was between the valence band and fermi level? How do we distinguish between the two?
Thanks in advance.
Thanks in advance.
Thanks for your response.phyzguy said:They are very different things. The valence band is the energy below which there are available states for electrons to occupy. Similarly the conduction band is the energy above which there are available states. Between these two is the energy gap, where there are no (or very few) available states. The Fermi level is the energy at which the probability of a state being occupied is 1/2. In the diagram below, for example, [itex] E_V[/itex] is the valence band, [itex] E_C[/itex] is the conduction band, and [itex] E_F[/itex] is the Fermi level.
View attachment 224005
That makes sense. Thanks very much.phyzguy said:At zero temperature all of the states below Ef will be filled and all the states above Ef will be empty. So in a metal for example, where Ef lies within a region where there are states to occupy, what your instructor said would be true. But typically Ef in a semiconductor lies within the band gap where there are no available states. So I don't think it is true to say it represents the topmost filled state. At non-zero temperature, I think the best definition is what I said. It is the energy at which the probability of a state being occupied is 1/2.
The valence band is the highest energy band in a material that is fully occupied by electrons at absolute zero temperature. The Fermi level is the energy level at which there is a 50% probability of finding an electron at absolute zero temperature.
The difference between the valence band and Fermi level is known as the band gap, and it determines a material's electrical conductivity and other properties. A larger band gap means the material is an insulator, while a smaller band gap allows for more electron movement and makes the material a semiconductor or conductor.
Yes, the valence band and Fermi level difference can be altered by introducing impurities or doping the material with different atoms. This can change the band gap and thus the material's properties.
At higher temperatures, electrons in the valence band can gain enough energy to move to the conduction band, reducing the band gap and increasing the material's conductivity. The Fermi level also shifts with temperature, but the valence band remains at its highest occupied energy state.
The valence band and Fermi level difference is crucial in determining the behavior of electronic devices. It affects how easily electrons can move through a material and thus the device's overall performance and efficiency. Understanding and controlling this difference is essential in designing and optimizing electronic devices.