
352 Gallium Nitride (GaN): Physics, Devices, and Technology
approaches the breakdown. A more abrupt variation in drain current is obtained
when avalanche processes are taken into account. Recent works [116,117] proposed
that at high drain voltages also impact ionization can play a signicant role, and
induce a signicant increase in breakdown current. Impact ionization is usually
simulated by considering that the carrier generation rate (due to impact ionization)
is given by
nn
G
q
=
α+α
(10.7)
where J
n
and J
P
are the electron and hole current densities, respectively, α
n
and α
P
are the ionization rates for electrons and holes, and q is the electron ...