$ifimpact ion

$ifimpact_ion is a function to turn on the impact ionization. It is a field and current dependent function which will rely on the electric field in the simulation program.

The impact ionization generation rate is decided by

$G_impact = \frac{|Jn|}{e} \times \alpha_n +\frac{|Jp|}{e} \times \alpha_p$
$\alpha_{n} = a_{n}*exp\left( - \left| \left(\frac{b_{n}*|Jn|}{\vec{E}\cdot \vec{Jn}}\right)^{c_{n}} \right|\right)$
$\alpha_{n} = a_{p}*exp\left( - \left| \left(\frac{b_{p}*|Jp|}{\vec{E}\cdot \vec{Jp}}\right)^{c_{p}} \right|\right)$

           Gimpact=-absjn/ELCHG*impactratelayer(1,indEl)*&
               exp(-abs( ((impactratelayer(2,indEl)*absjn)/productEJ(1))**impactratelayer(3,indEl)))