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Boron is most commonly used for the p-type dopant, and phosphorus for the n-type, correct?

Why not aluminum for the p-type and nitrogen for the n-type?

Is it just a matter of cost and/or convenience?

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  • \$\begingroup\$ If you read: en.wikipedia.org/wiki/Doping_(semiconductor) your question will be answered. Realize that defects in the Si-crystal should be avoided as much as possible. \$\endgroup\$ Nov 27, 2021 at 14:04
  • \$\begingroup\$ Aluminum is used as a p-type dopant for silicon carbide devices. \$\endgroup\$
    – Hearth
    Nov 27, 2021 at 14:06
  • \$\begingroup\$ Because N with two shells has higher electron affinity than P, so I doubt how effective donor dopant N can be. Similarly, Aluminum with has lesser electron affinity than Boron with 2 shells. So Boron would be more effective acceptor dopant. \$\endgroup\$
    – Mitu Raj
    Nov 27, 2021 at 19:51

2 Answers 2

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It's a whole series of engineering tradeoffs.

For starters, Nitrogen isn't a dopant at all in crystalline Si.

From an electrical standpoint, Boron is about 50% lower (0.045eV vs 0.067eV for Al) ionization energy than Aluminum in Silicon so makes a better dopant. If you want a better dopant than phosporous from a strictly electrical standpoint, you would choose Antimony(Sb) which is about 10% lower ionization energy.

However, there are lots of considerations. How well does something "dissolve" (solubility) in Silicon (Boron is particularly good for this)? How fast does something diffuse? How do you make diffusion barriers? How well does something anneal and activate? Do things have strange metallurgical properties that interact?

If you really want to dig into this, I recommend that you go find some Semiconductor Device Physics books.

Hope this helps.

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Nitrogen forms molecular species with silicon instead of doping occlusions/lattice defects into crystalline silicon. The molecular silicon nitride is an insulator and was (is?) used as a dielectric material between conductor or semiconductor traces in semiconductors.

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    \$\begingroup\$ Silicon nitride is indeed used as an insulator at times. The oxide is more common, but sometimes a combination of oxide and nitride can be used to produce useful effects--look up the "SONOS transistor". \$\endgroup\$
    – Hearth
    Nov 29, 2021 at 0:38

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