Can electron stay between donor energy level and valence band?

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Discussion Overview

The discussion revolves around the behavior of electrons in n-type semiconductors, specifically regarding the relationship between donor energy levels, the Fermi level, and the conduction and valence bands. Participants explore concepts related to energy levels, occupancy probabilities, and the implications for intrinsic and extrinsic semiconductors.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the donor energy level in n-type semiconductors refers to the Fermi level.
  • Another participant clarifies that the donor energy level is distinct from the Fermi level, which varies after equilibrium is reached, while the donor level is fixed relative to other energy levels.
  • It is noted that electrons can only occupy donor or acceptor levels if they are between the conduction and valence bands, assuming defect states are ignored.
  • Participants discuss that the Fermi level serves as a reference line for electron occupancy but does not represent an energy level where electrons can reside.
  • There is a question regarding the probability of occupancy at the Fermi level and whether electrons in intrinsic semiconductors can exist in the energy gap.
  • Clarifications are made that the Fermi level cannot hold electrons and that no electrons can be present in the energy gap of intrinsic semiconductors.
  • Participants confirm that in intrinsic semiconductors, the relevant energy levels are the conduction and valence bands.

Areas of Agreement / Disagreement

Participants generally agree on the distinction between donor energy levels and the Fermi level, as well as the behavior of electrons in intrinsic semiconductors. However, there is some ambiguity regarding the implications of the Fermi level and its role in electron occupancy, indicating that the discussion remains somewhat unresolved.

Contextual Notes

Participants express uncertainty about the definitions and roles of energy levels and occupancy probabilities, particularly concerning the Fermi level and its relationship to electron presence in energy gaps.

Outrageous
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In n-type semiconductor, Can electron stay between donor energy level and valence band?
Can I say that the donor energy level here refer to the Fermi level?

Thank you
 
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No, donor energy level is different than fermi level. Donor energy level is fixed w.r.t other energy levels (like 0.01 eV below conduction band). But fermi level varies after equilibrium is reached (like after dopant insertion and equilibrium fermi level will rise up).

Everything b/w conduction and valence band is forbidden except donor and acceptor levels. So, electrons can only stay in donor or acceptor levels if b/w conduction and valence bands. (if defect/surface/recombination states are ignored)
 
Thank you
Then in n-type semiconductor , there will be conductn band ,valence band , donor energy level and Fermi level at the same time?
 
Yeah, four of them will be there. But, remember the fermi level, itself, does not designate any energy level(slot) where electrons can reside. Its just a reference line which determines how electrons will be populated.
 
Kholdstare said:
Its just a reference line which determines how electrons will be populated.

You make this statement because Fermi level is a level that has a probability of 50% to be occupied by electrons at any given temperature?

And one more: electrons of intrinsic semiconductor can't stay at energy gap except Fermi level ?
 
Outrageous said:
You make this statement because Fermi level is a level that has a probability of 50% to be occupied by electrons at any given temperature?

And one more: electrons of intrinsic semiconductor can't stay at energy gap except Fermi level ?

You're confusing fermi level with energy level. Fermi level is not an energy level as it cannot hold any electron. Its a reference line which determines electron occupancy. Occupancy means probability of presence of electron IF there is an energy level ALREADY present. So even if fermi level is lying inside forbidden energy gap, no electron will be present in it.

electrons of intrinsic semiconductor can't stay anywhere inside the energy gap.
 
Kholdstare said:
Its a reference line which determines electron occupancy. Occupancy means probability of presence of electron IF there is an energy level ALREADY present. So even if fermi level is lying inside forbidden energy gap, no electron will be present in it..

In intrinsic semiconductor, the energy level ALREADY present refers to the conduction and valence band ,right?
 
Outrageous said:
In intrinsic semiconductor, the energy level ALREADY present refers to the conduction and valence band ,right?

Yeah. That's right.
 
Thanks a lot.
 

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