First principles study of oxygen-deficient centers in pure and Ge-doped silica

Abstract

Using ab initio calculations on 108 atoms pure- and Ge-doped (2.8 mol%) silica-based supercells, we performed a statistical study on the electronic structure and energetic contribution of neutral oxygen vacancies, also named Oxygen Deficient Centers (ODCs). All the 72 oxygen sites in the amorphous silica ( a-SiO 2) cell were considered as possible candidates for the formation of the vacancies leading to study 72 different Si-ODCs ( Si Si bond) and 144 Ge-ODCs ( Ge Si bond). The distributions of structural parameters and formation energies of the ODCs were evaluated through Density Functional Theory calculations. The obtained parameters showed a wide distribution that can be mainly associated with the differences in the local environments surrounding the point defects. We show that the formation energies of Si and Ge-ODCs generated from the same oxygen site of our supercell are correlated. Moreover, the local asymmetry around the Si Ge or Ge Si bond can also affect their formation energies, providing a strong evidence for the influence of short-range environment on the ODC generation efficiency.