Device properties following MeV heavy ion, electron and neutron irradiations

Abstract

The irradiation effects of 45 MeV lithium. 65 MeV boron and 70 MeV oxygen ions on silicon diodes have been compared with those of 6 MeV electrons and 14 MeV neutrons. The trade-off between the turn-off time and the forward voltage is found to be superior for the heavy ion irradiated diodes as compared to the diodes irradiated with 6 MeV electrons and 14 MeV neutrons. These variations in the switching characteristics are attributed to the mechanisms by which energetic heavy ions, electrons and neutrons deposit energy in silicon. The characteristics of power thyristors in which the gold diffusion process was replaced by 6 MeV electron irradiation are briefly reported. A new technique of electron irradiation has been developed to induce a layer of defects of thickness varying from 80 to 200 μm at a desired depth in the thyristor or in the diode. This enables one to achieve an appreciable reduction in the reverse recovery charge, but with only a marginal increase in the forward voltage drop. In the diodes and MOSFETs irradiated with 14 MeV neutrons or with Cf-252 neutrons upto a fluence ∼1011 n/cm2, no appreciable change in the characteristics has been observed.