Impact ionization in silicon

The electron dynamics for electron energies up to 5 eV has been studied by soft x-ray photoemission spectroscopy. Monte Carlo simulations have been performed to derive the energy dependence of the pair-production rate using these results in combination with published data on the ionization coefficient and on the quantum yield for pair production. The obtained ionization rate shows a very soft threshold at 1.2 eV, approaching the results by Kane [Phys. Rev. 159, 624 (1967)] at higher energies. Several published models have been found to be inconsistent with the full set of experimental data we have considered.