Conductivity of SiC during neutron and proton irradiation

The radiation-induced conductivity (RIC) of single crystalline 6H-SiC has been measured in a pulsed fission reactor (BARS-6: the pulse-width is 80 μs, dose rate <1.5×105 Gy/s) and under 17 MeV proton irradiation (dose rate <5×103 Gy/s). The magnitude of RIC has been compared by normalizing the ionizing dose rates. The RIC efficiency of the pulsed reactor irradiation is four times lower than the proton irradiation. To explain the lower RIC efficiency, we point out importance of cascade effects induced by pulsed neutrons, though the RIC consists of synergistic processes. Spatial distribution of energy loss of pulsed neutrons is more irregular than that of protons, due to the different distribution and parameters of cascades. The carrier production rate is not constant in the microscopic region of the material but abruptly changes by several orders of magnitude. During the reactor irradiation, intense charge carrier production (at least 103 times faster) occurs in the microscopic regions (size up to ∼1000 nm) occupying a small part (lower than 10−3) of the bulk SiC. The localized ionization is due to dense tracks of primary recoil ions and atomic collision cascades. Sharp spikes of charge carrier production may considerably contribute to the mean carrier-production rate, but, due to non-additive contributions, their effect on overall conductivity is not dominant.