Experimental Determination of the Impact Ionization Coefficients in Irradiated Silicon

We present new results on the influence of radiation-induced damage on the electron Impact Ionization (I.I.) coefficient
$\alpha$
, suggesting a small but distinct reduction of
$\alpha$
at high fluence with respect to unirradiated silicon. Experiments on thick (1.5
$\mu$
m) and thin (1
$\mu$
m) epitaxial silicon samples confirm that such a reduction of
$\alpha$
is expected even in cases where impact ionization is not simply a field driven process because of strongly non local transport conditions.