Density Functional Theory (DFT) Analysis of the Nitrogen Hyperdoping Ability to Induce Intermediate Band (IB) in Silicon*

DFT has been used to evaluate the effectiveness of N hyperdoping in creating intermediate (IB) in silicon. The exchange and correlation functional MGGA, Pseudo-Dojo pseudopotential, a moderately accurate basis set, and 7x7x7 k-points for sampling the Brillouin zone have been used. Large Si supercell (3x3x3 Si unit cells, 216 atoms) was chosen to reduce defect perturbations. This size matches N concentration in hyperdoped silicon. The symmetry reduced the k-points, for instance, to 172 in the case of the substitutional nitrogen (Ns). We focus on VxNyO complexes (x=0,1 and y=0,1,2) in Si.

By occupying tetravalent vacancy sites, N forms negatively charged (Ns-) complex. The band structure has shown a higher density of bands due to degeneracy removal by the perturbation caused by Ns-. Complexes with odd numbers of N are negatively charged and appear to drastically effect and even control the silicon band structure and the IB formation. These complexes have been discussed as deep levels by Voronkov et al. We show that added O atoms do not essentially change the energy band structure and the O does neither hinder the hyperdoping of silicon with N nor the formation of an IB in silicon. We propose that the little influence of O on the IB is due to the well relaxed Si-O-Si bridging bonds.