Gate voltage and temperature dependent Ti-graphene junction resistance toward straightforward p-n junction formation

Abstract

High-quality metal-graphene contact is crucial for the fabrication of high-performance graphene transistors. Although Ti has been widely used as metal electrodes in graphene-based devices owing to its excellent adhesive capability, contact resistance (Rc) for Ti/graphene (Ti/Gr) is typically high and varies largely by three orders of magnitude from ∼103 to 106 Ω μm. Here, we have systematically investigated the effects of gate voltage (VG) and temperature (T) on Rc in the Ti/Gr interface. Besides significant VG dependence, Rc in the n branch is always larger than that in the p branch, indicating a Ti induced n-doping in graphene. In addition, Rc exhibits an anomalous temperature dependence and drops significantly as the temperature decreases, reaching ∼234 Ω μm at 20 K. Such Ti/Gr contact can adjust the Fermi energy of up to 0.15 eV and can also directly form a well-defined sharp p-n junction without extra gates or chemical doping. These findings pave the way to develop the next generation of graphene-based electronic and optoelectronic devices.