Is it possible to shift the fermi level?

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Discussion Overview

The discussion centers around the possibility of shifting the Fermi level in materials, particularly semiconductors, without altering the positions of the valence and conduction bands. Participants explore various methods of shifting the Fermi level, including doping and applying pressure, while seeking clarification on the underlying mechanisms involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that doping with pentavalent or trivalent elements can shift the Fermi level, but question whether this can occur without changing the positions of the valence and conduction bands.
  • One participant raises a concern about the vagueness of the question regarding the reference point for the positions of the bands and suggests that shifting the Fermi level may be similar to shifting the bands under the rigid band assumption.
  • Another participant mentions that the chemical potential can be shifted, which is equivalent to the Fermi energy at absolute zero but differs at higher temperatures.
  • Some participants express confusion about how methods like doping and applying pressure affect the Fermi level and seek further explanation on these processes.
  • Questions are raised about the definition of the Fermi level and the implications of adding electrons to a metal versus a semiconductor, particularly regarding the band gap under the rigid-band assumption.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the Fermi level can be shifted without altering the band positions, and there are multiple competing views regarding the mechanisms and definitions involved in shifting the Fermi level.

Contextual Notes

Participants note the importance of defining terms like "Fermi level" and the reference points for band positions, indicating that these definitions may influence the discussion. There is also mention of the rigid-band assumption, which may affect interpretations of the relationship between the Fermi level and band structure.

Anoop MD
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I know we can shift the fermi level by doping the material with other elements. In case of semiconductors doping with the pentavalent or trivalent will change the fermi level. But my question is ''can we shift the fermi level, without altering the position of valence band and conduction band?" Thank you.
 
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Anoop MD said:
I know we can shift the fermi level by doping the material with other elements. In case of semiconductors doping with the pentavalent or trivalent will change the fermi level. But my question is ''can we shift the fermi level, without altering the position of valence band and conduction band?" Thank you.

This is rather vague. The location of the valence and conduction band are often indicated with respect to the Fermi energy, i.e. in many instances, the Fermi energy is referenced to be "zero". Even if it isn't, when you talk about position of the valence and conduction band, what would be your reference point? Are you talking about simply shifting them simultaneously up and down, keeping their positions relative to each other constant (i.e. keeping the gap the same)? Isn't this similar to just shifting the Fermi level under the rigid band assumption?

Zz.
 
thank you for your explanation, I think my question is incomplete. I ll get back soon with clear question.
 
You can shift the chemical potential which is the same as the Fermi energy at T=0 but differs at T>0.
 
There are methods which I read to change the fermi level, one is doping another is applying pressure but I can't understand how these things change the fermi level. Please explain. Thank you
 
Anoop MD said:
There are methods which I read to change the fermi level, one is doping another is applying pressure but I can't understand how these things change the fermi level. Please explain. Thank you

1. Figure out the EXACT definition of "Fermi level".

2. Take a bunch of electrons, and force it into a metal.

3. What just happened to the those electrons? Where did they go as far as the energy level that they occupy in the metal is concerned?

4. What just happened to the Fermi level?

5. How is this different if the metal is replaced by a semiconductor? Will it change the band gap, within the rigid-band assumption?

Zz.
 

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