Reducing the metal-graphene contact resistance through laser-induced defects
Abstract
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 (RC), ranges from a few tens of μm up to a few k 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 RC in nickel-contacted devices. A laser with a wavelength of λ = 532 nm is used to induce defects at the contact regions, which are monitored in-situ using micro-Raman spectroscopy. Physical damage is observed using ex-situ atomic force and scanning electron microscopy. The transfer line method (TLM) is used to extract RC from back-gated graphene devices with and without laser treatment under ambient and vacuum conditions. A significant reduction in RC is observed in devices where the contacts are laser irradiated, which scales with the laser power. The lowest RC of about 250 μm is obtained for the devices irradiated with a laser power of 20 mW, compared to 900 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 RC reduction in graphene and potentially other two-dimensional materials.