First-principles quantum-chemical calculations were applied to clusters of atoms which represented a divalent Ge defect in Ge-doped SiO2 glasses. It was found that the divalent Ge defect interacted with a nearby GeO4 tetrahedron; thus forming complex structural units that were responsible for an observed photo-absorption band at about 5eV. It was noted that these structural units could transform into 2 equivalent Ge E’ centers, via the positively charged defect centre.

Structure and Formation Mechanism of Ge E’ Center from Divalent Defects in Ge-Doped SiO2 Glass. T.Uchino, M.Takahashi, T.Yoko: Physical Review Letters, 2000, 84[7], 1475-8