A technique to reduce the contact resistance to 4H-silicon carbide using germanium implantation

The effects of implanted Ge on the resistance of nickel-metal contacts to n-type and p-type 4H-SiC are reported. The Ge was implanted with an energy of 346 kev and a dose of 1.7 x 10 super(16) cm super(-2), and the wafer was annealed up to 1700 degree C for 30 min. Contact resistance measurements using the transfer length method (TLM) were performed on etched mesas of n-type and p-type 4H-SiC, with and without the Ge. For the annealed-Ni metal contacts, the Ge lowered the specific contact resistivity from 5.3 x 10 super(-4) Omega cm super(2) to 6.0 x 10 super(-5) Omega cm super(2) for n-type SiC and from 1.2 x 10 super(-3) Omega cm super(2) to 8.3 x 10 super(-5) Omega cm super(2) for p-type SiC. For the as-deposited (unannealed) Ni, the Ge produced ohmic contacts, whereas the contacts without Ge were rectifying. These results suggest that the addition of Ge can be an important process step to reduce the contact resistance for SiC-device applications.