How ionization energy can be lower than band gap?

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Discussion Overview

The discussion revolves around the relationship between ionization energy and band gap energy in semiconductors, specifically focusing on silicon. Participants explore the conditions under which ionization energy can be lower than the band gap energy, addressing both theoretical and practical implications.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the concept of ionization energy being lower than the band gap, seeking clarification on whether this refers to the ionization energy of an electron in the conduction band.
  • Another participant suggests that there is no inherent problem with having an ionization energy lower than the band gap, indicating a possible misunderstanding by the original poster.
  • A participant acknowledges that the clarification provided makes sense, although the original source did not explicitly state this relationship.
  • Concerns are raised about the context of the discussion, with one participant mentioning that the phenomenon might only occur near the surface of materials treated with special coatings, such as cerium on gallium arsenide, and questioning whether this is a bulk effect.
  • Another participant confirms that the clarification about ionization energy is correct, indicating that their earlier confusion has been resolved.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints, with some participants agreeing on the possibility of ionization energy being lower than the band gap, while others express uncertainty about the conditions under which this occurs, particularly regarding surface effects versus bulk properties.

Contextual Notes

Participants reference historical aspects of semiconductor research, suggesting that the understanding of these concepts may have evolved over time, and there may be limitations in the current literature regarding explicit explanations.

newuser
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I am reading about the ionization energy in semiconductors and came across this thing that for Silicon, the ionization energy is lower than its band gap energy. I don't understand how can this be?
 
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Is this for the ionization energy of an electron in the conduction band? It seems to me that there should be no problem having an ionization energy lower than the band gap. Why do you find it problematic?
 
Well that makes sense. The book does not says it explicitly so I guess what you say is the case.
 
I thought that was only the near the surface and when treated with a special coating. E.g. Ce on GaAs. I didn't think it was a bulk effect too. Are you reading a paper from before 1985? The history of semiconductors has a lot of back and forth.
 
@ rigetFrog: I was reading the book. The answer given by matterwave is correct. I has a silly confusion which is clear now.
 

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