Hydrogen dynamics in SiO2 triggered by electronic excitations

Ab initio approaches have been used to study microscopic mechanisms of the dielectric degradation of ${\mathrm{SiO}}_2$ induced by electronic excitation. In this article, we focus on the possibility of H dissociation from H-terminated O vacancies in ${\mathrm{SiO}}_2$ induced by Si–H σ→σ^* excitation. To take the finite lifetime of this excitation into account, real-time electron dynamics were treated by solving the time-dependent Schrödinger equation coupled with Newton’s equations for ions. We found that the decay-time constant of the Si–H σ→σ^* excitation is on the order of 10 fs, which is too short to cause direct H dissociation. Therefore, not only the electronic excitation, but also thermal assistance and/or transport of the excited electron from ${\mathrm{SiO}}_2$ to the Si substrate appears responsible for the Si–H bond breaking and subsequent ${\mathrm{SiO}}_2$ degradation.