GaAs fieldhyphen;effect transistors (FETs) exposed to 40 agr;/sec for about 60 sec in the gate region revealed burnout from under the gate to both the drain and source. To explain this result, we show by using a 2D numerical FET simulation that a single event, particularly normal to the gate, has all the harmful electrical and thermal transients as that of a reverse gatehyphen;voltage pulse or positive drainhyphen;voltage pulse. The latter two are well known to initiate burnout failure mechanisms in GaAs FETs, depending on duty cycle and peak power applied. The onset of burnout due to a succeeding single event may be further aided by the ionizationhyphen;enhanced outdiffusion of deephyphen;level traps to the active channel during a series of single events. The experimental data, principally from SEM analysis and degradation ofIhyphen;Vcharacteristics, seem to support the thermal runaway burnout mechanism proposed in this paper. Other mechanisms previously suggested are either ruled out or deemed inadequate. A highhyphen;fluence radiationhyphen;hardened structural FET design is suggested.
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