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So I know that silicon is the most common semiconductor out there by far. But I also know that there are countless other options; silicon carbide, germanium, SiGe alloy, gallium arsenide, aluminum gallium phosphide, the terrifying-sounding mercury cadmium telluride...

So, what properties would make a device designer choose one over the others? I understand that for LEDs and laser diodes matching the bandgap to give the right photon energy would be one reason, but are there others?

Germanium used to be the semiconductor of choice, but it was booted out by silicon fairly early on, and now it's near impossible to find germanium components. Why is that? Likewise, no one uses selenium rectifiers anymore (though they have more obvious disadvantages, like the ridiculously low reverse breakdown voltage and their physical size).

There's a lot of question marks in this question; I do hope that's not too many. While I am curious about this myself, I'd like to also make it a resource for others to use, so I tried to cover as much ground as possible without straying too far from the topic.

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  • \$\begingroup\$ I think it would be better to keep the question more focused by removing the part about dopants. It only costs you twice as much to ask a second question to cover that part. \$\endgroup\$ – The Photon Apr 30 '17 at 4:15
  • \$\begingroup\$ Yeah, I was considering that. Think I probably will, if someone else has the same thought. \$\endgroup\$ – Hearth Apr 30 '17 at 4:16
  • \$\begingroup\$ Related: Why don't we use GaN transistors everywhere? and What is silicon germanium (SiGe)? \$\endgroup\$ – The Photon Apr 30 '17 at 4:20
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Silicon has many advantages that have made it the dominant semiconductor material:

  • A native oxide. This is key to the development of the MOSFET.
  • Relatively good physical robustness. Some other competing materials are more fragile, leading to losses in production simply due to mechanical breakage of wafers.
  • Abundance in nature. Silicon is the 2nd most abundant element in the Earth's crust, making it easy to mine, though refining it to the purity needed for electronics is still a significant effort.

Further, since silicon is so widely used, economies of scale make it much cheaper to produce chips or devices in silicon than in other semiconductors.

So, if silicon will do the job, we will almost always choose silicon to achieve low cost.

We might choose other materials if we need

  • A direct-gap material, typically for optical sources like LEDs.
  • A specific bandgap. For example for photodiodes for detecting 1550 nm wavelength, a bandgap less than about 0.8 eV is needed.
  • High carrier mobility, which allows higher frequency devices. For this you'll see materials like SiGe, GaAs, GaN, or InP used.
  • A specific lattice constant, for growing one material epitaxially on a substrate of another material. The ability to engineer both lattice constant and bandgap is why you see ternary and quaternary compounds like GaAlAsP used.

I'll leave aside the question of how dopants are chosen because 1) I know almost nothing about it, and 2) the choice of dopants is likely different for each semiconductor material.

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  • \$\begingroup\$ I've moved the bit about dopants to a different question anyway! \$\endgroup\$ – Hearth Apr 30 '17 at 4:36
  • \$\begingroup\$ (+1) excellent answer. I'd clarify the point about the native oxide. That oxide, SiO2, is an excellent insulator, compared to other oxides (the various kinds of glass are amorphous SiO2 with some "dopant" materials, after all!). Fused silica (SiO2) is at the end of the scale of most "insulator vs. conductor" materials table. \$\endgroup\$ – Lorenzo Donati Apr 30 '17 at 11:27
  • \$\begingroup\$ @LorenzoDonati, yes. Also, other semiconductors have native oxides, but they're problematic in other ways. Germanium's is water soluble, for example. \$\endgroup\$ – The Photon Apr 30 '17 at 15:04

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