  The synergistic effects of neutron and gamma ray radiated PNP transistors are
systematically investigated as functions of the neutron fluence, gamma ray
dose, and dose rate. We find that the damages show a `tick'-like dependence on
the gamma ray dose after the samples are radiated by neutrons. Two negative
synergistic effects are derived, both of which have similar magnitudes as the
ionization damage (ID) itself. The first one depends linearly on the gamma ray
dose, whose slope depends quadratically on the initial displacement damage (DD)
and can be attributed to the healing of neutron-radiation-induced defects in
silicon. The second one has an exponential decay with the gamma ray dose, whose
amplitude shows a rather strong enhanced low-dose-rate sensitivity (ELDRS)
effect and can be attributed to the passivation of neutron-induced defects near
the silica/silicon interface by the gamma-ray-generated protons in silica,
which can penetrate the silica/silicon interface to passivate the
neutron-induced defects in silicon. The simulated results based on the proposed
model match the experimental data very well, but differ from previous model,
which does not assume annihilation or passivation of the displacement defects.
The unraveled defect annealing mechanism is important because it implies that
displacement damages can be repaired by gamma ray radiation or proton
diffusion, which can have important device applications in the space or other
extreme environments.
