Lower Limits of Contact Resistance in Phosphorene Nanodevices with Edge Contacts.

Mirko Poljak,Mislav Matić,Tin Župančić,Ante Zeljko

doi:10.3390/nano12040656

Abstract

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 (RC) in PNRs with edge contacts, although RC 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 RC to 192 Ω µm in 5.2 nm-long PNRs due to strong metallization effects, while width downscaling decreases the RC 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 RC by device sizing. Moreover, we prove the existence of optimum metals for edge contacts in terms of minimum metallization effects that further decrease RC by ~30%, resulting in lower intrinsic quantum limits to RC of ~90 Ω µm in phosphorene and ~14 Ω µm in ultra-narrow PNRs.

Highlights

Two-dimensional (2D) materials are considered to be feasible candidates for future post-silicon electron devices due to their atomic thickness and exceptional mechanical, electronic, and carrier transport properties [1,2,3,4,5]
Among monoelemental 2D materials, monolayer black phosphorus (BP) or phosphorene is frequently identified as promising for future nanoscale field-effect transistors (FETs) due to its acceptable bandgap and carrier mobility that should enable appropriate switching and current-driving performance of phosphorene-based electron devices [6,7]
Atomistic nonequilibrium Green’s function (NEGF) calculations are employed to investigate the electronic and transport properties of ultra-scaled phosphorene nanoribbons (PNRs), and to calculate contact resistance that emerges in PNRs after attaching metal edge contacts (MECs)

Summary

Introduction

Two-dimensional (2D) materials are considered to be feasible candidates for future post-silicon electron devices due to their atomic thickness and exceptional mechanical, electronic, and carrier transport properties [1,2,3,4,5]. While 2D materials and their nanostructures seem promising for nanodevices, they suffer from high contact resistance (RC ), which limits their performance and conceals their exceptional transport properties. Almost all theoretical research on 2D material or nanoribbon-based FETs assumes ideal contacts, which only provides upper limits to device performance since the parasitic contact resistance is completely ignored [4,10,11]. Optimum electrode material for PNRs is a more strongly-interacting metal in the case of longer devices, whereas ultra-short nanoribbons with lengths under ~6 nm demand contacts with a weaker interaction strength. Our results give an encouraging perspective on the suitability of phosphorene and PNR FETs for future nanoscale electron devices and contribute towards theoretical understanding and practical minimization of contact resistance in nanodevices with edge contacts

Methods

Discussion

61 Ω μm that for the optimum and thenparameter increases to 247 leading

4.4.Conclusions