Lower Limits of Contact Resistance in Phosphorene Nanodevices with Edge Contacts

Edge contacts are promising for improving carrier injection and contact resistance in devices based on two-dimensional (2D) materials, among which monolayer black phosphorus (BP), or phosphorene, is especially attractive for device applications. Cutting BP into phosphorene nanoribbons (PNRs) widens the design space for BP devices and enables high-density device integration. However, little is known about contact resistance (R(C)) in PNRs with edge contacts, although R(C) is the main performance limiter for 2D material devices. Atomistic quantum transport simulations are employed to explore the impact of attaching metal edge contacts (MECs) on the electronic and transport properties and contact resistance of PNRs. We demonstrate that PNR length downscaling increases R(C) to 192 Ω µm in 5.2 nm-long PNRs due to strong metallization effects, while width downscaling decreases the R(C) to 19 Ω µm in 0.5 nm-wide PNRs. These findings illustrate the limitations on PNR downscaling and reveal opportunities in the minimization of R(C) by device sizing. Moreover, we prove the existence of optimum metals for edge contacts in terms of minimum metallization effects that further decrease R(C) by ~30%, resulting in lower intrinsic quantum limits to R(C) of ~90 Ω µm in phosphorene and ~14 Ω µm in ultra-narrow PNRs.