## 2 Results
### Production of VO Defect Versus C Concentration
For example, in previous work [123] the optimized structures for the GeVO, SnVO, PbVO, GeV, SnV, and PbV defects in Si were given (refer to Figure 14). These studies indicated that the oversized isovalent dopants (Sn or Pb) preferentially occupy the space between two semi-vacant lattice sites (i.e., the split-vacancy configuration) [123]. Nevertheless, when an O\({}_{\mathrm{i}}\) is present in the defect, it effectively prevents the Sn (or Pb) to shift towards the vacant site [123]. DFT calculations can be used to provide complementary information on the thermal evolution of defects. The thermal evolution of defects and their relative concentration is important to understand the defects that are bound to form in different conditions. Experimental work is key in that respect, but DFT studies can be used to provide complementary information on whether specific defects will form and their exact configurations. For example, the different defect configurations are given at the top of Figure 15, whereas the FTIR experimental results indicate their thermal evolution [93]. Figure 11: Deconvolution of the VO defect spectral region of the IR bands into Lorentzian profiles for the samples (C\({}_{\rm L}\)) (**a**), (Ge) (**b**), (Sn) (**c**), and (Pb) (**d**). Reproduced with permission from [143]. American Institute of Physics, 2012. Figure 12: (**a**) The amplitudes of the V\({}_{2}\)O defect as a function of the isovalent dopant covalent radius of the Si sample, and (**b**) the amplitudes of the V\({}_{3}\)O defect as a function of the isovalent dopant covalent radius of the Si. Reproduced with permission from [143]. American Institute of Physics, 2012. Figure 13: An illustration of the minimum energy structure of (**a**) the VO (A-center), (**b**) the nearest neighbor \(D\)VO, (**c**) the next nearest neighbor \(D\)VO, (**d**) the nearest neighbor \(D\)OV, and (**e**) the next nearest neighbor \(D\)OV defects. Yellow and gray spheres indicate the Si and \(D\) atoms, respectively, whereas \(\mathsf{O}_{\text{i}}\) are represented by the red spheres, and the vacant site by the black sticks. Reprinted with permission from [148]. American Institute of Physics, 2010. In the following part we will consider carbon-related defects. Figure 14: The isovalent dopant—VO interactions along the (10-1) direction: (**a**) GeVO, (**b**) SnVO, (**c**) PbVO, (**d**) GeV, (**e**) SnV, and (**f**) PbV. Larger spheres represent the isovalent dopant, blue spheres the Si atoms, and red spheres the O atoms. All the distances are in Å. Reprinted with permission from the PCCP Owner Societies, [123]. Figure 15: The thermal evolution of the A-center, VO\({}_{2}\), and SnVO defects for samples with Sn-poor content and Sn-rich content. The constituent defects are sketched using red circles for the oxygen atoms, blue and green circles for the D and Si atoms, respectively. The square and dotted square represent the V and semi-vacancies. The thermal evolutions of the Oi for Sn-poor and Sn-rich concentrations are given at the bottom of the figure Reprinted with permission from [93]. American Institute of Physics, 2011. Carbon is the second most important impurity, besides oxygen, unintentionally added into the Si lattice during growth. Its presence in the monocrystalline Si originates mainly from polycrystalline material during processing [153] with various chemicals such as ethylchlorosilanes. The mechanisms of C incorporation into Si and its distribution in the lattice has been studied in detail in previous studies [41; 43; 153]. Carbon as an isovalent impurity is substitutionally dissolved in the Si lattice, C\({}_{\text{s}}\), and interacts with oxygen, forming various C\({}_{\text{s}}\)O\({}_{\text{i}}\) complexes during growth. Carbon has a covalent radius smaller than Si and the tensile strains introduced into the lattice by its presence is relieved with the capture of self-interstitials.