Considerations in Establishing a Standard for Neutron Displacement Energy Effects in Semiconductors

Over the past several years a number of semiempirical or theoretical curves have been generated to represent the neutron-induced displacement effects in silicon as a function of neutron energy. Since the mode of failure for most silicon semiconductor devices is a loss of gain and this is, in turn, proportional to the reduction in carrier lifetime the same curves are used to express both the neutron energy damage effectiveness for devices as well as the degradation of lifetime. A useful feature of such a curve is that the damage produced in a semiconductor by a neutron fluence of a given energy spectrum may be predicted by folding the spectral information together with the damage curve. Once this is done, the damage may be expressed as that resulting from an equivalent monoenergetic neutron source (the monoenergetic equivalent). This procedure enables the results of an exposure to a source of one spectrum to be used to predict the effects of a different one. In order for this technique to be useful as a means of communication there must be some standardization of the damage curve, the neutron energy to which the damage is referred and the description of the spectrum. Recent interest, throughout the radiation effects community, in establishing such a standard has prompted several proposals each of which contains some shortcomings. This paper compares the various deficiencies and merits and arrives at what constitutes a minimum set of requirements for standardization at this time.