Reducing the Metal-Graphene Contact Resistance through Laser-Induced Defects.

Graphene has been extensively studied for a variety of electronic and optoelectronic applications. The reported contact resistance between metal and graphene, or rather its specific contact resistance ( ), ranges from a few tens of Ω μm up to a few kΩ μm. Manufacturable solutions for defining ohmic contacts to graphene remain a subject of research. Here, we report a scalable method based on laser irradiation of graphene to reduce the in nickel-contacted devices. A laser with a wavelength of = 532 nm is used to induce defects at the contact regions, which are monitored using micro-Raman spectroscopy. Physical damage is observed using atomic force and scanning electron microscopy. The transfer length method (TLM) is used to extract from back-gated graphene devices with and without laser treatment under ambient and vacuum conditions. A significant reduction in is observed in devices where the contacts are laser irradiated, which scales with the laser power. The lowest of about 250 Ω μm is obtained for the devices irradiated with a laser power of 20 mW, compared to 900 Ω μm for the untreated devices. The reduction is attributed to an increase in defect density, which leads to the formation of crystallite edges and in-plane dangling bonds that enhance the injection of charge carriers from the metal into the graphene. Our work suggests laser irradiation as a scalable technology for reduction in graphene and potentially other two-dimensional materials.