Channel and Substrate Currents in GaAs FETS Due to Ionizing Radiation

Measurements of photocurrents due to pulsed ionizing radiation are reported and analyzed for planar, ion implanted GaAs junction field-effect transistors fabricated on semi-insulating GaAs substrates. With the help of various device geometries and contact arrangements, it will be shown that the primary photocurrent of the pn-junction gate of the JFET is much smaller than the additional photocurrent originating in the semi-insulating substrate by electron hole pair generation. For a 3 μm contact separation the substrate photocurrent in amperes is empirically given by Ips = 6 × 10-11 VAWγ, where VA is the applied voltage in volts, W the width of the contacts in cm and γ the dose rate in rad(GaAs)/s. The relation for Ips has also been theoretically assessed in good agreement with the experimental results. Since the primary photocurrent Ipp, is much smaller than Ips, the prediction of logic upset due to ionizing radiation dose rate has to be expanded to include this induced substrate photocurrent.