# Nitrogen-Related Defects in Crystalline Silicon
## 2 Background Information of N-Related Defects in Si
### The N\({}_{\mathrm{s}}\)V Defect  
A N\({}_{\mathrm{s}}\) impurity can be readily associated with a vacancy to form the N\({}_{\mathrm{s}}\)V complex. In this structure, N\({}_{\mathrm{s}}\) is at a nearest neighbor site, with respect to V in the Si lattice [50; 51; 53; 63; 68; 69]. The calculations of [50] predict that N\({}_{\mathrm{s}}\)V possesses two deep levels, one single acceptor at E\({}_{\mathrm{c}}\)\(-\)0.7 eV, and one double acceptor at E\({}_{\mathrm{c}}\)\(-\)0.5 eV. Also, an LVM band at 663 cm\({}^{-1}\) was calculated [50] in association with the N\({}_{\mathrm{s}}\)V complex and in agreement with the experimental results [40]. The possibility was considered [63] that the defect is linked with the SL6 EPR signal [36].  
In the study by [PERSON] et al. [54], DFT calculations were employed to study N\({}_{\mathrm{s}}\)V defects in Si, with the lowest energy structure schematically represented in Figure 4a. This study confirms the formation of the N\({}_{\mathrm{s}}\)V defects as it is calculated that N\({}_{\mathrm{s}}\) and V are associate with a binding energy of \(-\)2.1 eV [54]. In the N\({}_{\mathrm{s}}\)V defect, the nitrogen atom effectively forms a trigonal planar structure that is distorted but has identical N-Si bond  
Figure 2: A schematic representation of the defects with a single nitrogen atom. (**a**) The Si lattice, (**b**) the C\({}_{\mathrm{1h}}\) <001> nitrogen split-interstitial site, (**c**) the N\({}_{\mathrm{i}}\) puckered bond-centered structure, and (**d**) the N\({}_{\mathrm{s}}\)V defect. Black and gray circles represent the N and Si atoms, whereas the vacancy is indicated with a dashed circle [50].  
lengths (1.84 A) and bond angles (117.8\({}^{\circ}\)) (refer to Figure 4) [54]. This structure forms because of a nearest neighbor Si vacancy that alters the Si-N bond distances (\(\sim\)0.20 A) as compared to the case of N\({}_{\text{s}}\)[54]. The reason for this can be traced to the strong bonding between N and Si atoms as realized using the DFT-derived positive Bader charge analysis which shows a gain of nearly three electrons by the N atom [54]. In Figure 4c, the charge density distribution around the N and the vacancy is shown, whereas Figure 4d reveals the band-decomposed charge density [54]. Finally, the total DOS indicates that it is an n-type doped material, with the states appearing within the bandgap that is predominately associated with the nitrogen s and p electrons (refer to Figure 4e,f).  
Figure 4: (**a**) The N\({}_{\text{s}}\)V in the Si lattice, (**b**) tetrahedral units comparing Bader charges, bond distances and angles, (**c**) charge density, (**d**) band-decomposed charge density plot for the N\({}_{\text{s}}\), (**e**) total DOS, and (**f**) atomic DOS plot of N [54].  
Figure 3: A schematic representation of the defects of two nitrogen atoms. (**a**) The Si lattice, (**b**) the C\({}_{\text{2h}}\) N\({}_{\text{i}}\)N\({}_{\text{i}}\) defect, (**c**) the D\({}_{\text{2d}}\) split-interstitial N\({}_{\text{i}}\)N\({}_{\text{s}}\) defect, (**d**) the N\({}_{\text{s}}\)–bond-centered N\({}_{\text{i}}\) defect, (**e**) the N\({}_{\text{s}}\)N\({}_{\text{s}}\) defect, and (**f**) the N\({}_{\text{s}}\)N\({}_{\text{s}}\)V defect. Black and gray circles represent the N and Si atoms, whereas the vacancy is indicated by a dashed circle [50].