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I know that direct band gap semiconductors are very attractive for optical emission, and even though indirect band gap are used as well, I keep wondering: is there any technology that specifically makes use of an indirect bandgap semiconductor? In other words, is there any piece of hardware that simply wouldn't work (or it would, but very poorly) if the material it was based on, wasn't an indirect bandgap semiconductor?

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    \$\begingroup\$ I guess, this fits better into physics. \$\endgroup\$
    – tobalt
    Apr 2, 2021 at 15:00
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    \$\begingroup\$ Are you aware that silicon is indirect bandgap? Are you asking about applications that make use of the indirect gap specifically? Or any application that uses an indirect gap material whether or not it cares about direct vs indirect gap? Silicon has some material processing advantages that you wouldnt get if you switched to any direct gap material, although the reason isnt the indirect gap. Is this what you are looking for? \$\endgroup\$
    – Matt
    Apr 2, 2021 at 15:53
  • \$\begingroup\$ The first option. I'm looking for applications that make specific use of the indirect gap. I know that Si is indirect but I believe that's not the reason it's so widely used. Am I wrong? \$\endgroup\$
    – Bidon
    Apr 2, 2021 at 15:55
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    \$\begingroup\$ @Bidon Si is widely used because it is readily available, is relatively easy to make very high quality large single crystals, and has a very nice oxide. So you are correct, it isnt the indirect bandgap. \$\endgroup\$
    – Matt
    Apr 2, 2021 at 16:04

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In compound semiconductors, the use of compounds with indirect bandgap is ok, as long as they are not in part of laser / LED which need to generate light (usually quantum well region). Indirect bandgap layers are used as optical confinment to shape up refractive index of laser devices. AlAs is example of indirect semiconductor used in III-V lasers, as binary or ternary AlGaAs, which has transition to indirect at Al fraction above 45%.

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