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

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.