Energy Dependence of Displacement Effects in Semiconductors

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Abstract
In a semiconductor, the formation of a space-charge region is a logical consequence of the creation of a defect cluster. The dependence of cluster size and defect density on neutron energy can be derived directly from neutron-scattering data and recoil range-energy relationships. The effect of clusters on macroscopic semiconductor properties (e.g., recombination rate, carrier removal) is more uncertain, but the shape of the dependence on cluster size is not strongly dependent on the constants used in the calculation. The relative effectiveness of 14- and l-MeV neutrons before annealing is predicted to be significantly larger for recombination rate (factor of 2.7) than for carrier removal (factor of 1.7). The annealing process can decrease this difference. Moreover, it is possible that the time scale on which annealing proceeds can be different for the larger clusters produced by 14-MeV collisions. In establishing relative damage factors between different energy neutrons, it is important to note that the relative damage curve can be a function of the property measured. In comparing the damage produced by reactor neutrons and 14-MeV neutrons, it is important to take into account the very large energy recoils (>300 keV) produced by inelastic interactions of 14-MeV neutrons. These are responsible for intense ionization as well as displacement production. If the contribution from these recoils can be shown to be negligible or to be equivalent to a number of lower-energy recoils not producing as much ionization, the effects of 14-MeV and reactor neutrons can be correlated.