Contact resistivity of Al/Ti ohmic contacts on p-type ion implanted 4H-and 6H-SiC

Al-Ti alloys with 72 wt% Al were employed for the realisation of ohmic contacts on 4×1019 cm-3 p-type ion implanted 4H- and 6H-SiC samples. Contact resistivity characterisations by TLM measurements were done at wafer level in the temperature range 28-290°C. Analysis of the TLM measurements took into account current crowding at the metal pads. More than half of the evaluated contact resistivity reached the minimum value detectable by the used TLM devices, that was slightly higher than 1×10-6 ?cm2. Above this limit value, contact resistivity decreased for increasing temperature and was spread over a few decades. The maximum contact resistivity at 28°C was 2×10-4 ?cm2, which changed to 5×10-6 ?cm2 at 290°C. The thermal behaviour of these TLM structures featured thermionic-field emission conduction.