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

Abstract

In this work we analyzed the radiation hardness of SiC p/sup +/ 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/sup +/ emitter in an n-type epilayer with thickness equal to 55 /spl mu/m and donor doping N/sub D/=2/spl times/ 10/sup 14/cm/sup -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 /sup 90/Sr /spl beta/ source. At 250 V the collected charge of the unirradiated diodes saturates near 3000 e/sup -/. 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/sup 14/-10/sup 16/ (1 MeV) neutrons/cm/sup 2/. The leakage current after irradiation decreases. The collected charges decrease for increasing fluences, remaining very high only until some 10/sup 14/ n/cm/sup 2/.