Electrical properties and microstructure of ternary Ge ∕ Ti ∕ Al ohmic contacts to p -type 4H-SiC Improved Ni based composite Ohmic contact to n-SiC for high temperature and high power device applications Using cross-sectional transmission electron microscopy ͑TEM͒, microstructural changes in Ni contacts on n-type 4H-SiC as a function of annealing temperature were investigated. From these results, the correlation between the microstructural change and electrical properties was interpreted. After annealing at 800°C, which yielded rectifying behavior, the silicide phases were formed, composed of Ni 2 Si and Ni 31 Si 12 . From the results shown in microbeam diffraction patterns, Ni 31 Si 12 remains at the surface and Ni 2 Si is dominant in the contact, indicating that Ni 2 Si started to grow at the interface through the outdiffusion of Si atoms. When the sample was annealed at 950°C, ohmic behavior was shown, and the layer structure was changed to a C-rich layer/Ni 2 Si/NiSi/n-type SiC. The NiSi phase was observed. These results imply that the composition of Si in nickel silicide at the interface with SiC increased with the increase of annealing temperature. The observation of the graphite phase at the surface indicates that the C atoms diffused out to the surface at 950°C. This leads to the formation of carbon vacancies, acting as donors for electrons. These suggest that the production of carbon vacancies plays a major role in the formation of ohmic contact through the reduction of the effective Schottky barrier height for the transport of electrons.

Interfhcial reactions, surface morphology, and current-voltage (I-V) characteristics of Ti/AI/4H-SiC and TiN/AI/4H-SiC were studied befbre and after hightemperature annealing. It was observed that surfhce smoothness of the samples was not significantly aftbcted by the heat treatment at up to 900°C, in contrast to the case of Al/SiC. Transmission electron microscopy (TEM) observation of the Ti(TiN)/AI/SiC interfhce showed that A1 layer reacted with the SiC substrate at 900°C and Ibrmed an AI-Si-(Ti)-C compound at the metal/SiC interfhce, which is similar to the case of the Al/SiC interfhce. The I-V measurement showed reasonable ohmic properties for the Ti/A1 films, indicating that the films can be used to stabilize the Al/SiC contact by protecting the A1 layer from the potential oxidation and evaporation problem, while maintaining proper contact properties.