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 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 four 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.