Band Gap in a Square Quantum Well

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Discussion Overview

The discussion revolves around the variation of the direct band gap in square quantum wells, particularly in relation to well width and the determination of conduction and valence bands in semiconducting materials. It touches on theoretical aspects and computational methods relevant to quantum mechanics and semiconductor physics.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about how the direct band gap in GaAs varies with well width.
  • Another participant suggests that the band gap typically shrinks with increasing well width, relating it to examples from elementary quantum mechanics.
  • A different participant questions how to determine the valence band, proposing that it might involve different effective mass considerations.
  • Another reply challenges the understanding of the initial question, indicating that band structure calculations for semiconductors are not trivial and should yield both valence and conduction bands.
  • This participant also notes the importance of computational methods and the coordination number of elements in producing band structures.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the determination of band structures and the relationship between well width and band gap, with no consensus reached on the specifics of these topics.

Contextual Notes

There are limitations regarding the assumptions made about the relationship between well width and band gap, as well as the methods for determining valence and conduction bands, which remain unresolved.

John.Blair571
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How does a direct band gap (like that in GaAs) vary with its well width?
 
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Different semiconducting material have different band gaps, that is the
reason why electrons and holes can be trapped into the wells.
I think your problem is the same as the examples from the elementary
quantum mechanics: square well or infinite well problems
Usually, the gap (the energy difference between the first bound state level for
the electron and the first bound state level for
the hole) will shrink with the increase of the well width.
 
It has been easy to find literature for the calculation of the conduction band, but how does one determine the valence band? Is it by the same means, only with a different effective mass?
 
Not sure if I've understood your question here. Aren't you really looking for the band structure calculations for a straightforward band semiconductor (as opposed to the more exotic Mott insulators, for example)? If you are, then (i) it really isn't this trivial and (ii) it should give you both the valence and conduction bands. So I'm not sure how you are able to find literature on the conduction band, but not on the valence band. I would imagine various computational methods once one knows the coordination number of various elements within the unit cell would be able to produce such band structures.

Zz.
 

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