Annealing Effects on Leakage Current and Epilayer Doping Concentration of p+n Junction 4H-SiC Diodes after Very High Neutron Irradiation

In this work we analyzed the annealing effects on SiC p+n diodes after very high 1 MeV neutron fluence. The diode structure is based on ion implanted p+ emitter in n-type epilayer with thickness equal to 5 µm and donor doping ND = 3×1015 cm-3. These devices were irradiated with 1 MeV neutrons at 4 different fluence values, logarithmically distributed in the range 1014-1016 cm-2. 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 irradiation at the highest fluence value the average leakage current density at 100 V reverse bias decreased from 3 nA/cm2 to values of the order of 100 pA/cm2. After a neutron fluence of 1×1014 cm-2 the epilayer doping concentration decreased to 1.5´1015 cm-3. The samples underwent a sequence of thermal cycles first at 80°C and then at 200°C to verify if a damage recovery occurs in irradiated SiC samples, as in the case of silicon ones. After annealing at 80°C the reverse current further decreased, while the depletion voltage remained almost constant. After thermal cycles at 200°C the current decreased further and the depletion voltage slightly increased, showing a very low recovery of the damage.