Impact Ionization In Silicon: A Microscopic View

A microscopic, single-particle view of impact ionization in silicon is obtained from a modified full-band Monte Carlo simulation. For each ionization event, the balance between the energies supplied by the electric field and lost to the lattice is plotted as a function of time before ionization. It is shown that two separate mechanisms can be identified. The lucky-electron model describes well impact ionization at very low electric fields. At higher fields, a different form of "lucky scattering" becomes the preferred ionization mechanism, where ionizing electrons suffer a sequence of scattering events with a final velocity directed along the electric field. This process is the microscopic equivalent of the energy-transport theories describing the ensemble dynamics at high fields. (C) 1998 American Institute of Physics.