Dose rate and total dose dependence of low frequency noise performance, I-V curves and sidegating for GaAs MESFETs

Total dose and dose rate performance of GaAs MESFET devices of various geometries and sidegating structures at various distances and orientations are presented. Parameters measured include low frequency noise, I-V curves and sidegating. The GaAs MESFET devices tested are shown to be useful to a total dose greater than 500 Mrad(GaAs). The observed reduction in drain current for a given bias point versus total dose is believed to be due to the sinking gate effect. The post irradiation degradation of 1/f noise performance shows a Lorentzian component which grows continuously with total dose to 1 Grad(GaAs). The during irradiation noise performance exhibits a dose rate dependent Lorentzian component. This component has been named selfgating dose rate noise. The sidegating effect exhibits a dose rate dependent degradation which decreases with increasing distance at low dose rates and saturates at a dose rate of approximately 150 krad(GaAs)/hour. The dose rate dependent sidegating effect is reduced with accumulated total dose.