## 2 Results
### Production of VO Defect Versus C Concentration
In essence, the T\({}_{\rm ann}\) represents the temperature at which the centers break up. In the case of isovalent dopants it can be reasonably surmised [158] that the effect of their presence on the T\({}_{\rm ann}\) is mainly related to the difference in the strains introduced into the Si lattice by the dopants, due to their different magnitudes. The introduction of larger isovalent dopants is expected to affect the strength of the bonds in the C\({}_{\rm i}\)O\({}_{\rm i}\) and C\({}_{\rm i}\)C\({}_{\rm s}\) structures. The activation energy, E\({}_{\rm a}\), characterizing the energy necessary for the pair to dissociate, can be expressed by the relation E\({}_{\rm a}\) = E\({}_{\rm f}\) + E\({}_{\rm b}\), where E\({}_{\rm f}\) represents the formation energy of the pair, and E\({}_{\rm b}\) its binding energy. It was argued [158] that the binding energy, E\({}_{\rm b}\), is affected by the local strains introduced into the lattice by the isovalent dopants. The structure [161] of C\({}_{\rm i}\)O\({}_{\rm i}\) comprises a C\({}_{\rm i}\) slighted disturbed from its isolated configuration, which pairs with an O\({}_{\rm i}\) atom. On the other hand, C\({}_{\rm i}\)C\({}_{\rm s}\) can exist in two configurations [135; 136], A and B. In heavily electron irradiated Si, the defect is expected to be in the B configuration, where a bond-centered Si atom lies between two C\({}_{\rm s}\) atoms. From the results of Figure 22, it may be concluded that the induced strains from the presence of the isovalent dopants reduce the E\({}_{\rm b}\) of the C\({}_{\rm i}\)O\({}_{\rm i}\) structure, although they increase the E\({}_{\rm b}\) of the C\({}_{\rm i}\)C\({}_{\rm s}\) structure. In other words, the activation energy of C\({}_{\rm i}\)O\({}_{\rm i}\) becomes smaller, although for C\({}_{\rm i}\)C\({}_{\rm s}\) it becomes larger. This is manifested in the observed decrease in T\({}_{\rm ann}\) of C\({}_{\rm i}\)O\({}_{\rm i}\) and the observed increase in T\({}_{\rm ann}\) of C\({}_{\rm i}\)C\({}_{\rm s}\). The production of the C\({}_{\rm i}\)O\({}_{\rm i}\) defect as a function of Ge concentration has been given in previous work (refer to Figure 3 of [141] and/information about the samples from Table 3). In Figure 3, the variation of the C\({}_{\rm i}\)O\({}_{\rm i}\) defect is shown together with the variation of VO, for comparison purposes. For the moderate-doped samples Ge-1, Ge-3, Ge-4 and Ge-7, the two defects showed a similar behavior. Their concentration increased with the increase in Ge concentration. This can [142] be attributed to the tendency of Ge to trap vacancies temporarily in the course of irradiation, preventing their annihilation with self-interstitial atoms. On one hand, these vacancies, when liberated by the dissociation of the GeV pairs, are readily captured by oxygen atoms, thus enhancing the VO production. On the other hand, the self-interstitials are readily captured by C\({}_{\rm s}\) to turn them into C\({}_{\rm i}\). Next, the C\({}_{\rm i}\) atoms combine with oxygen atoms to form C\({}_{\rm i}\)O\({}_{\rm i}\) pairs, thus enhancing the production of the latter defect. For carbon-rich samples Ge-5 and Ge-8, the two defects again showed similar behavior. However, their concentration decreased as Ge concentration increased, showing an opposite trend to the carbon-moderate samples. This behavior occurring at high Ge concentrations could be attributed [145] to the inhomogeneous distributions of Ge atoms in the Si lattice which lead to the formation of Ge clusters. The associated strain fields assist the trapping of vacancies and self-interstitials in their territory, leading, finally, to a decrease in the formation of VO and C\({}_{\rm i}\)O\({}_{\rm i}\) pairs, as observed in our spectra. Figures 23 and 24 show the evolution with T of the C\({}_{\rm i}\)O\({}_{\rm i}\) and C\({}_{\rm i}\)C\({}_{\rm s}\) defects, respectively, as a function of Ge concentration of some characteristic samples such as the Ge-3, Ge-5 and Ge-8 (information about the samples from Table 3).