Structural and transport properties in alloyed Ti/Al Ohmic contacts formed on p-type Al-implanted 4H-SiC annealed at high temperature

In this paper, the transport properties of alloyed Ti/Al Ohmic contacts formed on p-type Al-implanted silicon carbide (4H-SiC) were studied. The morphology of p-type implanted 4H-SiC was controlled using a capping layer during post-implantation activation annealing at 1700 degrees C. The different morphological conditions do not affect the macroscopic electrical properties of the implanted SiC (such as the sheet resistance or the mobility). On the other hand, the improved morphology of implanted SiC allows us to achieve a flatter Ti/Al surface and a lower specific contact resistance. The temperature dependence of the specific resistance of the contacts was studied to obtain physical insights into the carrier transport mechanism at the metal/SiC interface. The fit comparing several models shows that thermionic field emission is the dominant transport mechanism through the metal/SiC interface, and that a reduction in the barrier height from 0.51 to 0.46 eV is associated with the improvement of the Ohmic properties. Transmission electron microscopy analysis showed the presence of a laterally inhomogeneous microstructure of the metal/SiC interface. The reduction in the barrier height could be correlated with the different microstructures of the interfacial region.