Effects of Very High Neutron Fluence Irradiation on p+n Junction 4H-SiC Diodes
In this work we analyzed the radiation hardness of SiC p+n diodes after very high 1 MeV neutron fluence. The diode structure is based on a p+ emitter ion implanted in n-type epilayer with thickness equal to 5 %m and donor doping ND = 3×1015 cm-3. Before irradiation, the average leakage current density at 100 V reverse bias was of the order of 3 nA/cm2. These devices were irradiated at four different fluence values, logarithmically distributed in the range 1014-1016 (1 MeV) neutrons/cm2. After irradiation the epilayer material became more resistive, as indicated by the reduction of the forward and reverse current density at a given voltage. In particular, after a neutron fluence of 1×1014 n/cm2 the epilayer active doping concentration decreased to 1.5×1015 cm-3. After irradiation at 1016 n/cm2, i.e. the highest fluence value, the average leakage current density at 100 V reverse bias decreased to values of the order of 0.1 nA/cm2. This very low noise even after very high fluence is very important to obtain a high signal to noise ratio even at room temperature.
N. Wright, C.M. Johnson, K. Vassilevski, I. Nikitina and A. Horsfall
F. Moscatelli et al., "Effects of Very High Neutron Fluence Irradiation on p+n Junction 4H-SiC Diodes", Materials Science Forum, Vols. 556-557, pp. 917-920, 2007