# Nitrogen-Related Defects in Crystalline Silicon
## 2 Background Information of N-Related Defects in Si
### The CN and CNO Defects  
The so-called \"impurity engineering\" technique is a very promising strategy to improve the quality of a material through the introduction of harmless impurities in the crystal lattice [14]. N and C are electrically neutral impurities in Si, and their presence in the lattice can improve the intrinsic gettering ability of Si; they can eliminate void defects; enhance the mechanical strength of the material; significantly affect the oxygen precipitation process; as well as reduce the size of microdefects and control their growth [14; 102; 103; 104]. It deserves to be noted that optical absorption and electron spin resonance (ESR) measurements have concluded that C suppresses the formation of N-O complexes [105]. Apparently, the interaction between N and C is important in this framework, since the formation of corresponding complexes may affect the electrical and optical properties of Si. Therefore, for technological purposes any relative information about N and C-related defects is necessary for controlling Si wafers containing these impurities. Regarding the N-C pairs, systematical studies have been reported, employing the photoluminescence (PL) spectroscopy by [PERSON] et al. [106; 107; 108; 109]. A number of Pl no-phonon transitions in the spectra of C and N implanted Si have been reported: N\({}_{1}\) = 745.6 meV, N\({}_{2}\) = 758.0 meV, N\({}_{3}\) = 761.5 meV, N\({}_{4}\) = 757.4 meV, and N\({}_{5}\) = 772.4 meV, each one with different formation temperatures. The model concluded that the N-C center involves a N atom distorted out of the substitutional lattice site along the \(<\)111\(>\) axis in an almost planar Si\({}_{3}\)N configuration and a C\({}_{i}\) atom, which is inserted into the N-Si bond along the \(<\)111\(>\) axis, popped out from the bond-centered position in one of the three equivalent \(<\)100\(>\) planes [106; 107; 108; 109]. Regarding the C-N-O defect, the so-far-reported experimental results are poor. Two IR lines labeled N\({}_{1}\) and N\({}_{2}\) have been reported [90]. An IR line at 588 cm\({}^{-1}\) labelled as  
Figure 8: A schematic representation of the N\({}_{2}\)V\({}_{2}\)O\({}_{1}\) defect [56]. the X line of the CO complex supports the conclusion that the \(\rm{NX_{1}}\) and \(\rm{NX_{2}}\) bands may be due to a CO complex which is disturbed by a N atom in the vicinity. However, further experimental and theoretical verification is necessary. The structures N-C and N-C-O have been recently investigated using DFT calculations [57]. The DFT results by [PERSON] et al. [57] showed that in the relaxed structure of the \(\rm{C_{i}N}\) defect, nitrogen is in a distorted trigonal planar configuration with the nearest neighbor silicon atoms (refer to Figure 9a). The Si-N bond distances are 1.74-1.80 A and are shorter as compared to the Si-Si bond distance (2.37 A) in the undoped Si lattice [57]. The key is the higher electronegativity of N as compared to Si, which also impacts the Bader charges [57]. In particular, N has accumulated a high negative Bader charge (-3.21) with the nearest neighbor Si atoms having a positive Bader charge (refer to Figure 9b) [57]. Considering the \(\rm{C_{i}}\) is tetrahedrally coordinated and has four nearest neighbor Si atoms [57]. The shorter Si-C bond distances (1.92-2.02 A) as compared to the Si-Si bond distance and the negative Bader charge on the C atom reflect the electronegativity difference between the C and Si atoms (refer to Figure 9c) [57]. The \(\rm{C_{i}N}\)\(\rm{O_{i}}\) defect can form by adding an \(\rm{O_{i}}\) in the \(\rm{C_{i}N}\) defect in Si (refer to Figure 10a) [57]. The introduction of \(\rm{O_{i}}\) induces relatively small changes in the Bader charges, bond distances, and angles (refer to Figure 10b,c) [57]. As oxygen is more electronegative, it accumulates a Bader charge of -2.09 [57]. To aid the reader, Table 1 summarizes the properties of the most important nitrogen-containing defects in Si.