The Ge-related defects in Ge-doped SiO2 were analyzed by using first-principles density functional techniques. Ge was incorporated at the level of about 1mol% and above. The growth conditions of Ge:SiO2 naturally set up an O deficiency relative to undoped SiO2, with vacancy concentrations increasing by a factor of 105 and O vacancies binding strongly to Ge impurities. All the centers considered exhibited potentially EPR-active states, candidates for identification as the Ge(n) centers. Substitutional Ge produced an apparent gap shrinking via its extrinsic levels.

Stability of Ge-Related Point Defects and Complexes in Ge-Doped SiO2. C.M.Carbonaro, V.Fiorentini, F.Bernardini: Physical Review B, 2002, 66[23], 233201 (4pp)