D–T Neutron and 60Co-Gamma Irradiation Effects on HPSI 4H-SiC Photoconductors

Abstract

The 14.1-MeV neutron irradiation- and 60Co-gamma irradiation-produced traps in high-purity semi-insulating (HPSI) 4H-SiC photoconductors (PCs) are reported, and the irradiation-induced changes in substrate resistivity, dark current, and UV response of the 4H-SiC PCs are analyzed. From the zero-bias thermally stimulated current measurements, six new traps at the energy levels $E_{v} \,+\, 0.58$ eV, $E_{v} \,+\, 0.68$ eV, $E_{v}\,+\, (0.7-0.9)$ eV, $E_{c} \, - \,0.64$ eV, $E_{c}\, -\, 0.91$ eV, and $E_{c} \, - \,1.04$ eV are identified in the 14.1-MeV neutron-irradiated PCs at the fluence of 1011 n/cm2, along the defects already detected before neutron irradiation. The thermal activation energy range (1–1.3 eV) for HPSI 4H-SiC is unaffected, and no considerable changes in the UV response of the PCs are noticed after the 14.1-MeV neutron irradiation. On the other hand, in addition to the traps determined prior to the irradiation, one new deep hole trap at $E_{v} + 1.31$ eV and significant changes in the activation energies (1.1–1.35 eV) are observed in the gamma-irradiated PCs at the dose of 100 Mrad, which suggest that the HPSI 4H-SiC substrate resistivity is increased due to the gamma irradiation-produced traps. Moreover, the signal-to-dark current ratio of the PCs is reduced after the gamma irradiation, as inferred from the UV response of the PCs.