Surface impact ionization in silicon devices

In the past, carrier ionization rates in the silicon bulk have been measured and reported extensively. We present experiments and accurate electric field calculations for deriving the surface impact ionization rate of electrons. It is given by
\alpha_{n}(surface) = 2.45 \cdot 10^{6} \cdot \exp(-1.92.10^{6}/E)
[cm
^-1
] Due to the lower mean free path at the surface, this ionization rate is much smaller then the well known bulk values and falls-off more steeply for low electric fields. The consequences for the simulation of MOS substrate currents will be shown.