Single event induced charge transport modeling of GaAs MESFETs

Two-dimensional computer simulations of charge collection phenomena in GaAs MESFETs have been performed for alpha and laser ionization. In both cases, more charge is collected than is created by the ionizing event. The simulations indicate that a bipolar transport mechanism (t<60 ps) and a channel modulation mechanism (t>40 ps) are responsible for this enhanced charge collection. The first mechanism is a bipolar type effect that injects charge into the bulk of the device and is collected at the drain due to the electric field. The second is a back channel turn-on mechanism that is associated with a positive hole density located beneath the channel and exists on a much longer time scale. These results show that electrons supplied by the source implant are responsible for charge collected at the drain in excess of any collected deposited charge