Electrical characterization of titanium-based ohmic contacts to 4h-silicon carbide for high-power and high-temperature operation

We report on titanium-based ohmic contacts (titanium carbide, titanium tungsten, and titanium) on both highly doped epilayers (n⁺ and p⁺) and Al-ion-implanted layers. The TiC contact layer was epitaxially grown on epilayers as well as an Al-ion-implanted layers of 4H-SiC by co-evaporation Ti and C₆₀ under an ultra-high vacuum condition at low temperature (<500 °C). For comparison and long-term stability test, we also deposited TiW (weight ratio 30: 70) ohmic contacts to p- And n-type epilayers of 4H-SiC. The specific contact resistances (ρ_c) were found to be as low as 5 × 10^-6, 2 × 10^-5, 2 × 10^-5, 3 × 10^-4, 4 × 10^-5 and 1 × 10^-4 Ωcm² for TiC contacts to n⁺ epilayers, p⁺ epilayers, and Al-ion-implanted layers, Ti contacts to p⁺ epilayers, and TiW contacts to p⁺ and to n⁺ epilayers, respectively, by using linear transmission line method (TLM) measurements. During the long-term reliability tests in a vacuum chamber, we found that evaporated Au capping layers helped to keep the contacts from degrading.