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 micron and donor doping N-D = 2 X 10^(14) cm^(-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 Sr-90 beta 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 10^(14)-10^(16) (1 MeV) neutrons/cm^(2). The leakage current after irradiation decreases. The collected charges decrease for increasing fluences, remaining very high only until some 10^(14) n/cm^(2).