Difficulty understanding "donor" and "acceptor" energy levels.

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Discussion Overview

The discussion centers on the concepts of donor and acceptor energy levels in semiconductors, particularly in the context of doping group IV materials with group III and V atoms. Participants explore the implications of defects in the silicon lattice and the classification of energy levels as donor-like or acceptor-like, as well as the distinction between shallow and deep levels.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes the basic understanding of doping, noting that donor atoms introduce shallow energy levels just below the conduction band edge, while acceptor atoms introduce levels just above the valence band edge.
  • Another participant emphasizes the need for citations when referencing external sources, highlighting the importance of clarity in discussions.
  • A reference is provided to a paper that discusses vacancy states above the valence band edge, labeled as donor states, which raises questions about the classification of energy levels.
  • Additional references are shared that discuss donor-like and acceptor-like levels in the context of the band gap, indicating that these classifications may not align with traditional definitions.
  • A participant introduces the concept of deep levels, noting that they typically do not contribute to electronic conductivity, contrasting them with shallow levels that do.
  • Another participant expresses confusion about the terminology of deep and shallow levels, suggesting that the definitions may be misleading based on the context of defect potentials.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding donor and acceptor energy levels, with some confusion about the classification of deep and shallow levels. There is no consensus on the implications of defects in the silicon lattice or the definitions of energy levels.

Contextual Notes

Participants note that the terms "deep" and "shallow" can be misleading, as they refer to different aspects of defect potentials rather than strict energy level positions relative to the band edges.

chopper13
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Hi all,

I think I understand the concept of doping a group IV semiconductor material with a group V atom which has one extra valence electron to "donate" to the conduction band, or doping with a group III atom with one too few electrons which will "accept" an electron from the lattice and leave behind a hole.

As I understood it, donor atoms introduce shallow energy levels just below the conduction band edge, and acceptor atoms introduce levels just above the valence band edge.

However I have been reading about defects within the silicon lattice and have seen several references to "donor-like" energy levels just above the valence band edge, and "acceptor-like" defect levels close to the conduction band edge. Is there something simple that I am missing here?

I would appreciate any help to shed some light on this.
 
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chopper13 said:
However I have been reading about...

It is the policy of this forum that whenever there is a phrase similar to this, you must cite what you read, i.e. give us the full citation. While there may be instances where what is being referred to might be obvious, in many cases they aren't! Therefore, in general, all referrals to external sources must be cited in full.

Zz.
 
ZapperZ said:
It is the policy of this forum that whenever there is a phrase similar to this, you must cite what you read...

Apologies for this.
For example, the paper "Negative-U Properties for Point Defects in Silicon" by Watkins (Phys. Rev Letters, Vol. 44, no.9) shows in its first figure vacancy states just above the valence band edge which are labelled donor states.
 
Any help would be greatly appreciated.
 
chopper13,
These are called deep levels. Usually they do not contribute to inducing electronic conductivity in the semiconductors.
A big part of research in semiconductors (especially in compound semiconductors such as ZnO) focuses on determining whether certain defect or dopant would introduce shallow or deep levels. Shallow levels (close to band edges) contribute to electronic conductivity, while deep levels do not.
 
Ah ok that's great, I figured it might have something to do with shallow and deep levels but was a little confused by the fact that some of the "deep" levels were actually close to band edges. It was only on further reading that I discovered the words deep and shallow can be a little misleading as they actually refer to which component of the defect potential is responsible for the particular level. Thanks a lot for the response.
 

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