Radiation hardness after very high neutron irradiation of minimum ionizing particle detectors based on 4H-SiC p+n junctions

In this work we analyzed the radiation hardness of SiC p⁺ n diodes used as minimum ionizing particle (MIP) detectors after very high 1 MeV neutron fluences. The diode structure is based on ion implanted p⁺ emitter in an n-type epilayer with thickness equal to 55 μm and donor doping N_D=2× 10¹⁴cm^-3. The diode breakdown voltages were above 1000 V. At 1000 V the leakage currents are of the order of 1 nA for all the measured diodes. The full depletion voltage is near 220-250 V. The charge collection efficiency to minimum ionizing particle has been investigated by a ⁹⁰Sr β source. At 250 V the collected charge of the unirradiated diodes saturates near 3000 e^-. At bias voltages over 100 V the energy spectrum of the collected charge was found to consist of a signal peak well separated from the noise. At around 250 V the signal saturates, in agreement with CV results. These devices have been irradiated at 6 different fluences, logarithmically distributed in the range 10¹⁴-10¹⁶ (1 MeV) neutrons/cm². The leakage current after irradiation decreases. The collected charges decrease for increasing fluences, remaining very high only until some 10¹⁴ n/cm².