Low resistance TiAl ohmic contacts with multi-layered structure for p-type 4H-SiC

The effect of the Al concentration and layer structure on the electrical and microstructural properties of TiAl Ohmic contacts for p-type 4H-SiC were investigated. The Al concentration was found to effect strongly on these contact properties, and the specific contact resistance of 1 x 10(-5) Omega-cm(2) was obtained for the TiAl contacts with the Al concentration higher. than 77 at% after annealing at 1000degreesC. However, agglomeration of Al was observed after annealing, which caused the rough surface morphology. On the other hand, the TiAl contacts with the Al concentration lower than 75 at% showed non-Ohmic behavior and had smooth surface morphology after annealing at 1000degreesC. It was found from X-ray diffraction analysis that the interface structures were strongly influenced by the Al concentrations of the TiAl contacts. For the TiAl contact with high Al concentration, formation of Al3Ti, Ti3SiC2, and Al4C3 was observed, and for the TiAl contact with low Al concentration, formation of Al3Ti, Ti3SiC2, and Ti5Si3 was observed. It was concluded that the electrical property of the TiAl contact was not affected by the number of TiAl layers and was very sensitive to the Al concentration in the TiAl contacts.