Potential n-type dopants were investigated by using  ab initio  methods. Well-known distortions around deep-donor N were found to arise from interaction of the N lone pair with a C dangling bond. It was found that P, Li and Na were all shallow dopants, but their solubilities were much too low for doping via in-diffusion. It was noted that Li was a relatively fast diffuser, and that Na was stable up to moderate temperatures. However, P was expected to remain immobile, even at high temperatures. It was concluded that Na, being an interstitial dopant, was particularly suitable for ion implantation since there was no need to displace host atoms.

S.A.Kajihara, A.Antonelli, J.Bernholc, R.Car: Physical Review Letters, 1991, 66[15], 2010-3