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 silicon carbide (SiC) p+n diodes after very high 1MeV neutron fluence. The diode structure is based on ion-implanted p+ emitter in n-type epilayer with thickness equal to 5 mm and donor doping ND ¼ 3x10^15 cm^3. These devices were irradiated with 1MeV neutrons at four different fluence values, logarithmically distributed in the range 10^14-10^16 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 100V reverse bias decreased from 3 nA/cm^2 to values of the order of 100 pA/cm^2. After a neutron fluence of 1x10^14 cm^2, the epilayer doping concentration decreased to 1.5x10^15 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.