## 2 Results
### Production of VO Defect Versus C Concentration
Regarding Sn-doped Si, although SnC defects have been reported [53; 156] it has been suggested [100] that the coexistence of Sn and C in the silicon lattice could lead to a suppression of the C\({}_{\rm i}\)O\({}_{\rm i}\) production when the Sn concentration increases. Regarding Ge-doped Si, although theoretical calculations have shown that GeC complexes could be formed [108], it has also been found experimentally [37] that in the case of Ge and C coexistence, the formation of C\({}_{\rm i}\)O\({}_{\rm i}\) pairs tends to increase with the increase in the Ge content of the material. A final note: in the case of C\({}_{\rm H}\), \(\rm\Xi_{\rm H}\) and Pb samples with about similar C concentrations, the formation of C\({}_{\rm i}\)O\({}_{\rm i}\) as seen in Figure 17 was larger in the \(\rm\Xi_{\rm H}\) sample and substantially smaller in the Pb sample, in comparison with the Ge-doped sample. Figure 18 presents the annealing behavior of C\({}_{\rm i}\)O\({}_{\rm i}\) for various isovalent dopants, together with the evolution of a band at 1048 cm\({}^{-1}\) arising in the spectra upon the annealing out of the C\({}_{\rm i}\)O\({}_{\rm i}\). The latter band has been attributed [157] to a C\({}_{\rm s}\)O\({}_{\rm 2i}\) structure. The C\({}_{\rm i}\)O\({}_{\rm i}\) defect anneals out [16; 132; 155; 157] either by destruction (C\({}_{\rm i}\)O\({}_{\rm i}\)\(\rightarrow\)C\({}_{\rm i}\)  
Figure 8:1 The production of C\({}_{\rm i}\)O\({}_{\rm i}\) defect as a function of isovalent dopant covalent radius. Reproduced with permission from [155]. American Institute of Physics, 2013.  
with another defect, as, for instance, in our case, the VO defect. In the former case, the produced C\({}_{i}\) reaction with VO\({}_{2}\) defects leads [155] to the formation of the C\({}_{s}\)O\({}_{2i}\) structure (C\({}_{i}\) + VO\({}_{2}\)\(\sim\)C\({}_{s}\)O\({}_{2i}\)). In the latter case, VO and C\({}_{i}\)O\({}_{1}\) pairs react to form [155; 157] C\({}_{s}\)O\({}_{2i}\). Figure 19 presents the conversion ratio of the C\({}_{i}\)O\({}_{i}\) to C\({}_{s}\)O\({}_{2i}\) defect for various isovalent dopants (data from Table 5). Given the different C concentrations of the samples it is not prudent to reach a final conclusion. A comment could be made possibly only in the case of Sn\({}_{\rm H}\) and Pb doped Si samples, with about the same C content [158]. It seems that the conversion ratio is larger in the Pb-doped sample than in the Sn\({}_{\rm H}\)-doped sample. Possibly, the amount of C that binds with Sn is different than that which binds with Pb, and some of the reactions in which C participates, in the course of anneals, are also different between the two materials. This is reflected in the corresponding conversion rates of C\({}_{i}\)O\({}_{i}\) to C\({}_{s}\)O\({}_{2i}\). More experimental data are necessary to clarify the picture. Figure 20 presents the evolution with temperature of the C\({}_{i}\)O\({}_{i}\) defect in Si for various isovalent dopants (data from Table 6). In this figure, spectra of pairs of samples such as (Ge\({}_{\rm L}\), Ge\({}_{\rm H}\)) (Sn\({}_{\rm L}\), Sn\({}_{\rm H}\)), as well as (Pb, SnPb), are compared. The C\({}_{i}\)O\({}_{i}\) for a Cz-Si sample is also given. Figure 8:2 The annealing behavior of C\({}_{i}\)O\({}_{i}\) and C\({}_{s}\)O\({}_{2i}\) defects for various isovalent dopants. Reproduced with permission from [155]. American Institute of Physics, 2013. Figure 21 shows the respective evolutions of the C\({}_{\text{i}}\)C\({}_{\text{s}}\) defect for the same pairs of isovalent doped samples (data from Table 6) as Figure 8:3 Prior to comparing the annealing characteristics of C\({}_{\text{i}}\)O\({}_{\text{i}}\) and C\({}_{\text{i}}\)C\({}_{\text{s}}\) centers, a comment for the latter is needed. The C\({}_{\text{i}}\)C\({}_{\text{s}}\) anneals out at around 350 \({}^{\circ}\)C. No signal arises in the IR spectra upon the disappearance of the C\({}_{\text{i}}\)C\({}_{\text{s}}\) defect.