$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

$G_{i}mpact=\frac{|Jn|}{e}\times {\alpha }_n+\frac{|Jp|}{e}\times {\alpha }_p$
${\alpha }_n=a_n*exp(-\left|{\left(\frac{b_n*|Jn|}{\overrightarrow{E}\cdot \overrightarrow{Jn}}\right)}^{c_n}\right|)$
${\alpha }_n=a_p*exp(-\left|{\left(\frac{b_p*|Jp|}{\overrightarrow{E}\cdot \overrightarrow{Jp}}\right)}^{c_p}\right|)$

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