At 0k, why is fermi level halfway in bandgap?

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Discussion Overview

The discussion revolves around the position of the Fermi level at absolute zero (0K) in relation to the bandgap in semiconductors. Participants explore the implications of the Fermi level's definition and its relationship to electron states within the bandgap, questioning why it appears to be positioned halfway in the bandgap despite the absence of available states for electrons there.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant states that the Fermi level is defined as the maximum energy an electron possesses at 0K, which is said to be midway in the bandgap, raising questions about the existence of electrons at that energy.
  • Another participant emphasizes that electrons cannot physically exist in the bandgap due to the lack of available states, suggesting that the Fermi level merely indicates the maximum possible energy of electrons.
  • A subsequent reply proposes that while electrons in the valence band can have energy that is midway in the bandgap, they do not occupy states within the bandgap itself.
  • Another participant introduces the idea of defect states existing below the Fermi level but above the top of the valence band, where electrons could potentially be found.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the Fermi level's position and its implications regarding electron states. There is no consensus on whether the Fermi level's position indicates the presence of electrons in the bandgap.

Contextual Notes

The discussion highlights the complexities of defining electron states in relation to the Fermi level and the bandgap, with assumptions about the nature of defect states and their influence on electron energy levels remaining unresolved.

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At 0k, why is fermi level halfway in bandgap??

Fermi Level is defined as the maximum energy an electron posesses at 0k, which appears to be midway in the bandgap. I learned that in the bandgap, there are no available states (i.e. no wavefunctions of electrons) hence, no electrons can possibly EXIST at the bandgap, so why is it that at 0k, some electrons have energy halfway between the band gap?? Does it mean that there are electrons halfway in the bandgap??

Shouldnt the fermi level be at the TOP of the valence band instead?
 
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physically, u cannot find the electrons between the band gap since there is no avaliable states within the bandgap. as u said the "Fermi Level is defined as the maximum energy an electron posesses at 0k". it just said that is the maximum possible energy that the electrons might have.
 


so, its just the ENERGY possessed by the electrons, which means the electrons in the valence band can have energy MID-WAY of the band gap but not be physically at the bandgap?
 


yes. this is what i think. u can imagine if there are some defected states below the fermi level but above the top of the valence band. electrons can be found there.
 

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