Thermal degradation of Ni-based Schottky contacts on 6H–SiC

We prepared Ni and Ni2Si Schottky contacts on lightly doped (5.5 × 1015 cm−3) n-type 6H–SiC and evaluated their thermal degradation after annealing in the temperature range of 750–1150 °C. Ni contacts had Schottky behavior after annealing at 750 and 850 °C; they gradually degraded at 960 and 1065 °C, and achieved ohmic behavior at 1150 °C. Ni2Si contacts had higher values of saturation current density and lower Schottky barrier heights than Ni contacts after annealing at 750 and 850 °C, and an abrupt transition from Schottky behavior at 850 °C to ohmic behavior at 960 °C. We assume that the abrupt transition from Schottky to ohmic behavior in the case of Ni2Si metallization is caused by its low reactivity with silicon carbide, which was verified by XPS depth profiling. The results indicate that the discrepancy in the behavior of Ni contacts on lightly doped SiC reported in the literature might have been caused by non-equal processing or by inaccurate determination of the annealing temperature.