Effects of Al ion implantation to 4H-SiC on the specific contact resistance of TiAl-based contact materials

To realize high-performance silicon carbide (SiC) power devices, low-resistance ohmic contacts to p-type SiC must be developed. To reduce the ohmic contact resistance, reduction of the barrier height at metal/SiC interfaces or increase in the doping concentration in the SiC substrates is needed. Since the reduction of barrier height is extremely difficult, the increase in the Al doping concentration in 4H-SiC by an ion-implantation technique was challenged. The Ti/Al and Ni/Ti/Al metals (where a slash “/” sign indicates the deposition sequence) were deposited on the Al ion-implanted SiC substrates. By comparing the experimental and theoretical contact resistances, the current transport mechanism through the metal/SiC interfaces was concluded to be thermionic field emission and the barrier height was determined to be ∼0.4 eV. Although the hole concentration increased with increasing the Al doping concentration in 4H-SiC, the barrier height at metal/SiC interfaces increased due to high density of dislocation loops observed in the implanted SiC layers by transmission electron microscopy. The present experiments suggested that the low-resistance ohmic contacts would be formed when a technique to eliminate the crystal defects formed in the 4H-SiC substrates after ion implantation was developed.