The origin of interfacial charging in irradiated silicon nitride capacitors

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Abstract
Many experiments show that when metal‐silicon nitride‐silicon dioxide‐silicon (MNOS) devices are irradiated in short circuit, a large interfacial charge builds up near the nitride‐SiO2‐Si interface. This effect cannot be explained by simple models of radiation‐induced conductivity of the nitride, but it is reported here that inclusion of carrier diffusion and recombination in the photoconductivity equations can predict the observed behavior. Numerical solutions on a computer are required, however, when these complications are added. The simulations account for the magnitude and radiation dose dependence of the results, as well as the occurrence of a steady state during the irradiation. The location of the excess trapped charge near the interface is also predicted, along with the large number of new traps which must be introduced to influence the steady‐state charge distribution.