Ab Initio Identification of the Nitrogen Diffusion Mechanism in Silicon

In this Letter, we present ab initio results identifying a new diffusion path for the nitrogen pair complex in silicon, resulting in an effective diffusivity of $67\exp (-2.38\mathrm{eV}/\mathrm{k}T){\mathrm{cm}}^2/\mathrm{s}$. This nudged elastic band result is compared with other nitrogen diffusion paths and mechanisms, and is determined to have unmatched agreement with experimental results. It is also shown that careful consideration of total energy corrections and use of a fully temperature-dependent diffusion prefactor have modest but important effects on the calculation of diffusivity for paired and for interstitial nitrogen.

Figure 1

Experimental data for the nitrogen diffusion constant in silicon with best fit line and new theoretical diffusion profile. The darker points are FTIR data specific to nitrogen pair diffusion. A theoretical curve is also presented using the activation energy from Sawada et al. [24], together with a diffusion prefactor from Itoh and Abe [13].

Figure 2

Low activation barrier diffusion series for a nitrogen pair (in purple) moving through the silicon lattice (gray) in (100) projection. The first and last configurations are equivalent, and the energetics are provided in Fig. 3. Both atoms move, making their jumps at different times. In the highest energy configuration, (C), the Si atoms marked with a ($*$) have only three bonds, and the N-N separation is at its maximum. The upper purple atom is N(1).

Figure 3

Energy profile for the ${\mathrm{N}}_2$ diffusion path. The migration barrier energy is 2.36 eV.