Neutron/gamma induced damage mechanisms and synergistic effects in GaAs MESFETs

Gallium arsenide n-channel MESFETs were irradiated with gamma rays up to 2.4×10⁷ rads and with neutrons from 2.1×10 ¹³ to 2.1×10¹⁵ n/cm², partially annealed, and reirradiated with gamma rays. DC measurements on these devices at every irradiation and postirradiation step were used to analyze the details of the induced damage mechanisms. The overall damage process is shown to consist of two stages: in the low to medium neutron exposure range (up to ~8×10¹⁴ n/cm²), the predominant mechanism is the removal of charge carriers with the overall damage effect being moderate; for larger neutron exposures the predominant mechanism is the reduction of carrier mobility with the damage effect being quite pronounced. It is suggested that a part of the neutron-induced damage may remain latent in the form of displacement defects without trapped charge carriers. Subsequent results on two identical device sets irradiated with the same neutron fluence and gamma dose, except with the neutron/gamma exposure order reversed, exhibit this synergistic effect