Electron transport and breakdown in SiO₂

The transport of electrons at high electric fields in SiO₂ has been calculated using an iterative solution of the path-variable formulation of the Boltzmann transport equation. Scattering due to the polar-optical modes and acoustic modes of the lattice are included. It is found that both the 0.153- and 0.063-eV polar-optical modes are important for scattering electrons. The electron velocity "saturates" near 1.9×10⁷ V/cm for fields below 5×10⁶ V/cm. The calculated curves are in excellent agreement with experimental data and indicate a best estimate of the polaron-corrected conductivity mass of 1.3m₀. Above 5×10 ⁶ V/cm, the electric field induced modifications of the carrier scattering rates cause the velocity to rise sharply. Time-resolved polar runaway is observed with an absolute threshold in the field range of (7-8) ×10⁶ V/cm, with the runaway field increasing for short times, as may be appropriate for transport through thin oxides. Impact ionization is governed by the polar runaway, and carrier generation is observed at fields corresponding to the threshold for polar runaway.