Neutron Damage Equivalence for Silicon, Silicon Dioxide, and Gallium Arsenide

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Abstract
Displacement- and ionization-energy transfers to Si, SiO2, and GaAs as functions of incident neutron energy were calculated using new cross section data and fine group structure in the NJOY code system. Neutron spectra determinations for several reactor neutron environments were made using new activation cross sections and a new technique with the SAND II code. Measurements of carrier removal rates in GaAs and of Si transistor gain degradation were made in representative neutron environments. Experimental results are compared to damage ratios predicted with the new spectra and NJOY displacement functions. For fission-like spectra, calculated Si damage ratios are in good agreement with those determined with ASTM E722-85 and with measured transistor damage ratios. Significant differences are found between Si NJOY and ASTM E722-85 for 14-MeV-to-reactor neutron damage ratios where NJOY gives better agreement with experimental data reported in the literature. In GaAs 14-MeV-to-reactor experimental damage ratios are smaller than predicted by calculated displacement ratios. This suggests that a more complex model of damage for majority carrier removal in GaAs is required. The use of incorrect damage functions is shown to adversely affect simulation fidelity in some representative neutron environments.