IMPACT IONIZATION IN INALAS/INGAAS HFETS

The presence of an energy barrier to the transfer of holes from the channel to the gate electrode of InAlAs/InGaAs HFET's prevents the gate current from being a reliable indicator of impact ionization. Consequently, we have used a specially designed sidegate structure to demonstrate that due to the narrow bandgap of InGaAs, impact ionization takes place in the channel of these devices under normal operating conditions. The ionization coefficient was found to follow a classic exponential dependence on the inverse electric field at the drain end of the gate, for over three orders of magnitude.