Does direct/indirect band gap occur in solids other than semiconductors?

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qnach
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TL;DR
Is direct and indirect band gap also occurs in other solids?
I learnt direct and indirect band gap in semi-conductor books. Is direct and indirect band gap also occurs in other solids?
 
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qnach said:
this page as well as other books all mentioned only direct and indirect band gap in semi-conductor
Note that while the article does focus on semiconductors, the first example it gives of a band gap, in the figure at the top of the page, is in diamond, which is not a semiconductor but an insulator.
 
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qnach said:
We all know how to google and look at wiki. There is really no need to give a wiki link.
Please note, this page as well as other books all mentioned only direct and indirect band gap in semi-conductor without discussing what I asked!!!
Please calm down. The reply by @Baluncore was meant to be helpful without outright giving you the answer to your question. It is ironic that you say that you know how to look this up on wiki/Google, since that will give you the answer directly. Your original thread title was pretty terse, so I added to it to make it more descriptive about the same time that Baluncore replied. If you do a Google search on the better thread title, you will see your direct answer.

Unfortunately, Google uses AI for its initial answer, so you cannot trust it. I post the AI answer below, along with one of the first real hits that helps with the answer you were seeking.

This thread is reopened provisionally in case you have questions about the answer you can get by doing the Google search that I did.

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https://www.rp-photonics.com/band_gap.html
 
qnach said:
We all know how to google and look at wiki. There is really no need to give a wiki link.
Please note, this page as well as other books all mentioned only direct and indirect band gap in semi-conductor without discussing what I asked!!!
One could have searched on "direct/indirect band gaps in metals, insulators, dielectrics, . . . . " When I searched on "direct/indirect band gaps in insulators", I found the artlcle berkeman cited, "Band Gap" in the
RP Photonics Encyclopedia, which mentions other forms of matter besides semiconductors.

There are many studies on band gaps in a variety of materials other than semiconductors.
For example, "Band Gap in Magnetic Insulators from a Charge Transition Level Approach"
https://pubs.acs.org/doi/10.1021/acs.jctc.0c00134

Elucidating the high-k insulator α-Al2O3 direct/indirect energy band gap type through density functional theory computations
https://www.sciencedirect.com/science/article/abs/pii/S0009261415005916

Pick any transitional metal oxide and one will find studies on its band gap. I'm interested in the behavior of n-type and p-type oxides, which have implications in a protective oxide (insulator and corrosion resistance layer (passivation of metal substrates)) and conductive oxide (catalysts, photochemical reactors, photoconductors). Note, like semicconductors, there are no pure oxides, and the 'doping', or presence of other elements, affects the chemical-electronic properties of the metal oxide.
 
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