Hydrogen dynamics in SiO2 triggered by electronic excitations

Ab initio approaches have been used to study microscopic mechanisms of the dielectric degradation of SiO2 induced by electronic excitation. In this article, we focus on the possibility of H dissociation from H-terminated O vacancies in SiO2 induced by Si-H sigma -->sigma* excitation. To take the finite lifetime of this excitation into account, real-time electron dynamics were treated by solving the time-dependent Schrodinger equation coupled with Newton's equations for ions. We found that the decay-time constant of the Si-H sigma -->sigma* 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 SiO2 to the Si substrate appears responsible for the Si-H bond breaking and subsequent SiO2 degradation. (C) 2000 American Institute of Physics. [S0021-8979(00)09619-5].