Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Beyond the Energy Band Calculations.

Hongxia Zhong,Junjie Shi,Meng Ye,Yangyang Wang,Li Yang,Zhigang Song,Ruge Quhe,Jing Lu,Zeyuan Ni,Ming Lei,Yuanyuan Pan,Jinbo Yang

doi:10.1038/srep21786

Abstract

Although many prototype devices based on two-dimensional (2D) MoS2 have been fabricated and wafer scale growth of 2D MoS2 has been realized, the fundamental nature of 2D MoS2-metal contacts has not been well understood yet. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS2 due to a charge transfer. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS2-Sc interface. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. BL MoS2-metal contacts generally have a reduced SBH than ML MoS2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency.

Highlights

Owing to their excellent properties, two-dimensional (2D) molybdenum disulfide MoS2 has attracted much recent attention [1,2,3,4,5,6]
Inversion symmetric BL MoS2 is not a valley Hall insulator (VHI), but it can be transformed into a VHI with a tunable valley magnetic moment by a vertical electric field, which destroys the inversion symmetry [5]. (3) Zeeman-like spin splitting is nearly intact by a vertical electric field in ML MoS2 but it becomes tunable in BL MoS2 because top and bottom MoS2 feel different electric potentials [16]
We find that the energy band calculation is unable to reproduce the observed Schottky barrier height (SBH) in 2D MoS2-Sc and -Pt interfaces. This failure prompts us to perform direct an ab initio quantum transport device simulation, and we find the SBHs in 2D MoS2-Sc and -Pt interfaces can be better reproduced in latter calculation

Summary

Introduction

Owing to their excellent properties, two-dimensional (2D) molybdenum disulfide MoS2 has attracted much recent attention [1,2,3,4,5,6]. Among 2D MoS2, monolayer (ML) and bilayer (BL) MoS2 attract the most attention [2,3,5,6,7,8,9,10,11,12,13,14,15,16,17,18] They show quite interesting differences and make up a pair of complementary materials: (1) ML MoS2 has a larger direct band gap, while BL MoS2 possesses a smaller indirect band gap due to the strong interlay coupling. Inversion symmetric BL MoS2 is not a VHI, but it can be transformed into a VHI with a tunable valley magnetic moment by a vertical electric field, which destroys the inversion symmetry [5]. The SBH of a 2D MoS2-metal contact depends on the work function of metal and the layer number of MoS2. Lower work function metal and more MoS2 layer number favor a smaller SBH. There are several energy band calculations based on single particle density functional theory (DFT) to examine ML MoS2-metal interfaces [22,23,25,27,28], a comprehensive energy band calculation for BL

Methods

Results

Conclusion