Doping mechanisms in graphene-MoS2 hybrids

Abstract

We present a joint theoretical and experimental investigation of charge doping and electronic potential landscapes in hybrid structures composed of graphene and semiconducting single layer MoS2. From first-principles simulations we find electron doping of graphene due to the presence of rhenium impurities in MoS2. Furthermore, we show that MoS2 edges give rise to charge reordering and a potential shift in graphene, which can be controlled through external gate voltages. The interplay of edge and impurity effects allows the use of the graphene-MoS2 hybrid as a photodetector. Spatially resolved photocurrent signals can be used to resolve potential gradients and local doping levels in the sample.Being a truly two-dimensional material [1], graphene can be integrated into hybrid structures with other 2D crystals such as boron nitride (BN), tungsten disulfide (WS 2 ) or molybdenum disulfide (MoS 2 ) [2-6]. The ability to build 'on demand' complex heterostructures via layer-by-layer integration establishes a whole family of new materials with widely varying characteristics and exciting possibilities for novel 2D nanodevices [7][8][9]. A prerequisite for future electronic applications lies in the understanding of interface effects when different building blocks come together. In particular, the electronic properties of realistic interfaces of graphene and two-dimensional materials present an open problem.In this work, we investigate heterostructures made of graphene and the semiconducting transition metal dichalcogenide MoS 2 , a system that has already been utilized for vertical field-effect transistors [3]. We study how different charge transfer mechanisms control relative Fermi level positions, built-in electric fields and charge reordering at realistic graphene-MoS2 interfaces. The simulated charge and potential landscapes are compared to photovoltaic measurements.In order to investigate the graphene-MoS 2 hybrid structures theoretically, we performed first-principles density functional theory (DFT) simulations [10]. As the lattice constant of isolated graphene is about 23% smaller than the one of isolated MoS 2 , we constructed a supercell consisting of a 5x5 layer graphene (50 C atoms) coated with a 4x4 layer MoS 2 (16 Mo atoms and 32 S atoms) with a stacking as shown in Fig. 1b to account for this lattice mismatch. The remaining lattice mismatch of about 3-4% is reasonably small and compensated by a slight strain of graphene to the MoS 2 lattice constant.The graphene-MoS 2 structure was then fully relaxed, which leads to an equilibrium graphene-MoS 2 distance of 3.35 A in good agreement with Ref.[11] and indicates a weak interlayer bonding of van der Waals-type. Based on this setup, we simulated realistic edge and impurity effects on the electronic properties of graphene-MoS 2 hybrids.We first address the role of impurity effects. To this end, we consider the fully MoS 2 -covered graphene as in Fig. 1b without impurities and compare it to the case with impurities in the MoS 2 . The band diagram of the pristine sy...

Graphene Oxide as a Promising Hole Injection Layer for MoS2-Based Electronic Devices

“…Another arrangement, where a C atom sits above a S atom, has been shown to be energetically and electronically equivalent to that of the TM configuration. 34,35 Once the graphene/MoS 2 supercell is constructed, oxygen functional groups are randomly attached above and below the graphene plane. 38,39 GO structures are obtained by relaxing the supercell without the MoS 2 monolayer first, and then the MoS 2 monolayer is introduced with an initial distance between the C plane of GO and the Mo plane of MoS 2 of 4.85 Å, which is the van der Waals distance obtained for the MoS 2 /graphene case.…”

Graphite edge controlled registration of monolayer MoS2 crystal orientation

“…14 Hence, the study of the interfaces between MoS 2 and graphene (or graphite) is critically important and may provide useful hints for various applications. 6,15 Shi et al have recently reported the formation of MoS 2 flakes on the graphene surface via thermal decomposition of ammonium thiomolybdate. 16 Although there is a large lattice mismatch between the MoS 2 and the graphene structure, graphene can serve as an epitaxial substrate for MoS 2 .…”

“…Recently, many proposed novel devices are based on heterostructures of MoS 2 and graphene. [5][6][7][8][9] Such heterostructures offer the possibility to create devices with new functionalities or better performance in electronic logic and memory devices, [9][10][11] and also offer great potential in the hydrogen evolution reaction. 12 Graphene/MoS 2 heterostructures have also been adopted to demonstrate an extremely high photosensitivity and gain 13 as well as the ultrasensitive detection of DNA hybridization.…”

Pressure-induced semiconducting to metallic transition in multilayered molybdenum disulphide

“…Previously, several approaches have been undertaken to alter the solid-state properties of MoS 2 , including chemical doping 3,[10][11][12] , intercalation 13,14 , surface functionalization 15 and defect engineering 11,16,17 . Furthermore, previous theoretical studies have suggested that an iso-structural semiconducting to metallic (S-M) transition in multilayered MoS 2 can be induced by pressure or strain [18][19][20] .…”