Reducing graphene-metal contact resistance via laser nano-welding

Performance of the graphene-based devices is usually limited by the large electrical contact resistance at the graphenemetal junctions. In this work, a laser nano-welding method has been developed in order to reduce the graphene-metal contact resistances by improving the carrier injection at the junctions. Laser-induced breakdown of C-C bonds was performed at the edges of graphene-metal contact areas, to facilitate the bonding between the metallic atoms and graphene after the annealing process and, therefore, maximize the carrier transport. It is experimentally proved that the structural defects and open-ended C atoms are formed as a result of the laser irradiation performed at λ=514 nm and optical power of 20 mW. The edge-contacted junctions were then realized by an annealing step that followed the laser irradiation step. After this two-step treatment, contact resistance (£C) as low as 2.57 ω.μm² is achieved, which is less than 6% of its pristine value and close to the 2015 International Technology Roadmap for Semiconductors (ITRS 2015; £C = 2.57 ω.μm²). Moreover, the site-selective nature of the proposed laser nano-welding method prevents degradation of the superior electrical properties of the graphene channel which is considered a common limitation in most of approaches proposed for achieving a reproducible low graphene-metal contact resistance.