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

In summary, this article discusses the idea of shallow and deep levels within a semiconductor material, and how they contribute to its electronic behavior.
  • #1
chopper13
6
0
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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  • #2
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.
 
  • #3
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.
 
  • #4
  • #5
Any help would be greatly appreciated.
 
  • #6
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.
 
  • #7
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.
 

1. What are "donor" and "acceptor" energy levels?

"Donor" and "acceptor" energy levels refer to the energy levels of atoms or molecules that are involved in a process of donating or accepting electrons. In donor-acceptor interactions, the donor molecule has an excess of electrons and transfers them to the acceptor molecule, which has a deficit of electrons.

2. How do donor and acceptor energy levels affect chemical reactions?

The energy difference between donor and acceptor energy levels determines whether a chemical reaction will occur. If the energy difference is favorable, the electrons will transfer from the donor to the acceptor, resulting in a chemical reaction. If the energy difference is not favorable, the reaction will not occur.

3. How are donor and acceptor energy levels measured?

The energy levels of atoms and molecules are typically measured using spectroscopy techniques, such as UV-Vis spectroscopy or fluorescence spectroscopy. These techniques involve shining light on the sample and measuring the amount of energy absorbed or emitted by the molecules, which can then be used to determine the energy levels.

4. Can donor and acceptor energy levels be manipulated?

Yes, donor and acceptor energy levels can be manipulated by changing the chemical structure of the molecules. Introducing electron-donating or electron-withdrawing groups can alter the energy levels of a molecule, making it a more favorable donor or acceptor in a chemical reaction.

5. How do donor and acceptor energy levels play a role in organic solar cells?

In organic solar cells, donor and acceptor molecules are used in the active layer to generate electricity from sunlight. The energy levels of the donor and acceptor molecules must be properly aligned to allow for efficient electron transfer and energy conversion. If the energy levels are not aligned, the solar cell will not function effectively.

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