Tunneling transport in a few monolayer-thick WS2/graphene heterojunction

Yamaguchi, Takeshi; Moriya, Rai; Inoue, Yoshihisa; Morikawa, Sei; Masubuchi, Satoru; Watanabe, Kenji; Taniguchi, Takashi; Machida, Tomoki

doi:10.1063/1.4903190

Cited by 38 publications

(39 citation statements)

References 28 publications

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“…4 (d)) with the tunnel transport model, described in ref. [37]. A plot of temperature-zero-bias conductivity shows the crossover of the two mechanisms around 200 K around the same temperature as reported in the ref.…”

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confidence: 70%

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Graphene- WS2 heterostructures for tunable spin injection and spin transport

Omar

Wees

2017

Phys. Rev. B

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We report the first measurements of spin injection in to graphene through a 20 nm thick tungsten disulphide (WS2) layer, along with a modified spin relaxation time (τs) in graphene in the WS2 environment, via spin-valve and Hanle spin-precession measurements, respectively. First, during the spin-injection into graphene through a WS2-graphene interface, we can tune the interface resistance at different current bias and modify the spin injection efficiency, in a correlation with the conductivity-mismatch theory. Temperature assisted tunneling is identified as a dominant mechanism for the charge transport across the interface. Second, we measure the spin transport in graphene, underneath the WS2 crystal and observe a significant reduction in the τs down to 17 ps in graphene in the WS2 covered region, compared to that in its pristine state. The reduced τs indicates the WS2-proximity induced additional dephasing of the spins in graphene.

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confidence: 70%

“…4(a)) which is clearly is different from the I-V behavior at the WS 2 -AlO 2 -Co interface, and is dominated by the Gr-WS 2 interface. The observed non-linearity can be easily attributed to the presence of a potential energy barrier present only at the Gr-WS 2 interface [26,32,37].…”

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confidence: 99%

Graphene- WS2 heterostructures for tunable spin injection and spin transport

Omar

Wees

2017

Phys. Rev. B

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“…Such materials include graphene, black phosphorous, transition metal dichalcogenides (TMD), and hexagonal boron nitride. Among these materials, heterostructures based on graphene and TMD have been found to exhibit functions that were previously not possible, including those of a vertical field-effect transistor [2][3][4][5], photocurrent generation [6,7], a spin-orbit proximity effect [8], and the ability to fabricate flexible devices [9]. Particularly, vertical field-effect transistors based on graphene/MoS 2 /metal heterostructures have been the subject of considerable attention mainly due to their large current ON-OFF ratio (10 3 to 10 5 ) combined with a large ON current density (>10 3 A/cm 2 ) [3,4].…”

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confidence: 99%

Electric field modulation of Schottky barrier height in graphene/MoSe2 van der Waals heterointerface

Sata

Moriya

Morikawa

et al. 2015

Applied Physics Letters

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We demonstrate a vertical field-effect transistor based on a graphene/MoSe 2 van der Waals (vdW) heterostructure. The vdW interface between the graphene and MoSe 2 exhibits a Schottky barrier with an ideality factor of around 1.3, suggesting a high-quality interface. Owing to the low density of states in graphene, the position of the Fermi level in the graphene can be strongly modulated by an external electric field. Therefore, the Schottky barrier height at the graphene/MoSe 2 vdW interface is also modulated. We demonstrate a large current ON-OFF ratio of 10 5 . These results point to the potential high performance of the graphene/MoSe 2 vdW heterostructure for electronics applications. *E-mail: moriyar@iis.u-tokyo.ac.jp; tmachida@iis.u-tokyo.ac.jp 2 Heterostructures that are held together by the van der Waals (vdW) force between the layered materials have been the subject of considerable interest in the fields of materials science and opto-electronics [1]. To date, several layered materials have been developed and extensively studied. Such materials include graphene, black phosphorous, transition metal dichalcogenides (TMD), and hexagonal boron nitride. Among these materials, heterostructures based on graphene and TMD have been found to exhibit functions that were previously not possible, including those of a vertical field-effect transistor [2][3][4][5], photocurrent generation [6,7], a spin-orbit proximity effect [8], and the ability to fabricate flexible devices [9]. Particularly, vertical field-effect transistors based on graphene/MoS 2 /metal heterostructures have been the subject of considerable attention mainly due to their large current ON-OFF ratio (10 3 to 10 5 ) combined with a large ON current density (>10 3 A/cm 2 ) [3,4]. This level of performance would attract very high demand for electronics applications. Given that the large current ON-OFF ratio is a result of the electric field modulation of the Schottky barrier height at the graphene/MoS 2 interface, the precise tuning of the band alignment at the graphene/TMD interface is crucial in determining the level of performance. To date, such devices have been fabricated using MoS 2 which has an indirect band gap of around 1.3 eV in its bulk form [10]. Changing the chalcogen atom from sulfur to selenium significantly reduces the band gap (the indirect gap of MoSe 2 is around 1.1 eV) [11] and also changes the electron affinity [12,13]. Furthermore, MoSe 2 exhibits better optical properties than MoS 2 [11,14].These results point to MoSe 2 being the better option for opto-electronics applications. In addition, since MoSe 2 has a smaller electron affinity than MoS 2 , under the assumption of Schottky-Mott rule, the Schottky barrier height at graphene/MoSe 2 interface is expected 3 to be larger than that of graphene/MoS 2 . Therefore a comparison of the Schottky barrier property of different TMD materials provides an insight into the vdW interface properties of a graphene/TMD heterostructure. In this study, we fabricated a graphene/MoSe 2 /Ti vertical...

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“…The nearly flat out-of-plane resistivity of ~10 8 ohm·μm 2 [defined as ρ T = 1/( dJ TB / dV ), where J TB is the current density] with decreasing temperature observed in Fig. 3B (MIS-C, blue squares) clearly indicates the tunneling behavior under the overall bias ( 10 , 14 ). Alternatively, GW-B (yellow squares) shows a significant decrease in ρ T by more than four orders of magnitude from 230 to 90 K with semiconducting behavior and from 245 K to room temperature with strong metallic behavior.…”

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confidence: 93%