Formation of electron traps in amorphous silica

Abstract

The capture of an electron by a silicon atom in a defect-free bulk of amorphous silica $(a\text{\ensuremath{-}}{\mathrm{SiO}}_{2})$ has been investigated. Ab initio constrained dynamics has been applied to evaluate the energy barrier. The computed energy barrier involved in the mechanism was found to be $0.23\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The electron trapping is accompanied by a strong local distortion of the tetrahedron of $\mathrm{Si}$ and $\mathrm{O}$ involved in the process. Hydrogen, which is an electronically active impurity of silicon dioxide, bonds to the oxygen of the $\mathrm{Si}\text{\ensuremath{-}}\mathrm{O}$ silica bond on which the electron is localized. Upon restoring the neutrality of the system a paramagnetic configuration is found. The eigenvalues of the hyperfine tensor have been evaluated.