15th group elements like As, Sb, P can be used for doping whereas N and Bi cannot be used for doping even though they too belong belong to 15th group. Why ?


For good doping you need two things: (1) get enough dopant in to be useful in changing carrier concentrations, and (2) having an energy level close to a band edge to generate electrons (holes) in the band, rather than making a mid-level recombination center. The below is assuming you are trying to dope Silicon. Data is generally from Sze's excellent 'Physics of Semiconductor Devices' text.

Bismuth certainly has a donor level not much lower than As, satisfying (2). However, the solid solubility of Bi is roughly 3 orders of magnitude less than As, peaking at below $10^{18}/cm^3$. This limits the utility of Bi in current device technology - you just can't get enough in.

Nitrogen has very low solubility in silicon. I cannot find quickly any info on energy levels in the gap, but oxygen has several levels, all pretty much near gap. I'd say nitrogen loses out on both (1) and (2).

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  • $\begingroup$ Just curious... do you know if the solubility problem still exists for ion implantation? After all, getting these atoms into the lattice is not a problem, the only problem would be, how long it would take for them to migrate out of the material or to aggregate during annealing, which may or may not be "long enough" for a useful industrial process. $\endgroup$ – CuriousOne Aug 26 '14 at 18:08
  • $\begingroup$ @CuriousOne - if you are above the solubility limit, you won't get them all on to lattice sites. The solubility limits of B, P, and As are high enough that they are pretty close together (~ 5 at.%). Added to that, the lattice damage from the implant leads to enhanced diffusivity from all the excess point defects floating around until they anneal out. $\endgroup$ – Jon Custer Aug 26 '14 at 18:18

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