Neutron and proton irradiation of shallow channel GaAs direct-coupled field-effect-transistor logic devices and circuits

Abstract

Neutron and proton irradiations have been performed on self-aligned GaAs metal-semiconductor field-effect transistors (MESFETs) and resistors utilizing shallow ion-implanted channels. FET threshold voltage shifts during irradiation were lower than reported elsewhere (less than 115 mV for a −0.85 V threshold FET irradiated by 4.3×1014 neutron cm−2). This is shown to be explained by the shallow active layers used. A neutron carrier removal rate between 20 and 25 cm−1 is necessary to fit the FET data. Carrier removal rates derived from resistor damage were 150 cm−1 for peak doping levels of 4×1017 cm−3, greatly in excess of those derived from epitaxial or bulk GaAs resistors, and inconsistent with values obtained from threshold shifts of FETs with identical active layers. Resistor and FET threshold voltage changes for 52 MeV proton irradiation were nearly an order of magnitude greater than for an equivalent dose of 1 MeV (Si) neutrons. The extrapolated worst-case failure dose of direct-coupled FET logic inverters was better than 1.8×1015 neutron cm−2 despite the limited noise margins of this logic scheme.