Unusually efficient photocurrent extraction in monolayer van der Waals heterostructure by tunnelling through discretized barriers.

Woo Jong Yu,Hyunyong Choi,Munseok Jeong,A H Castro Neto,Xiangfeng Duan,Joo-Youn Kim,Soonyoung Cha,Young Hee Lee,Hong Gi Nam,Alexandra Carvalho,Hailong Zhou,Quoc An Vu,Hyemin Oh

doi:10.1038/ncomms13278

Abstract

Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device.

Highlights

Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties
In contrast to typical diode characteristics observed in graphene/ML-MoS2/metal van der Waals heterostructures (vdWHs) due to asymmetric contact between top and bottom junction[7,12], a linear transport curve is observed in the graphene/1L-MoS2/graphene heterostructure device, which can be attributed to direct tunnelling (IDT)
We introduce a tunnelling transport model to describe the photocarrier tunnelling through electrostatic potential barriers formed at the atomically thin vdW heterojunctions

Summary

Introduction

Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. We report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. The broad possibility to combine different materials in van der Waals heterostructures (vdWHs) can create a new paradigm in materials science with unprecedented flexibility to integrate highly disparate materials and enable unique functions, as exemplified by the recent demonstration of vertical tunnelling transistors and vertical field-effect transistors for ultra-thin and flexible devices[6,7,8,9,10,11,12,13] Graphene/multi-layer (ML)-TMD/graphene stack has been shown to function as a unique photodiode for photocurrent generation or photodetection[7,12]. We report a layer-number-dependent photocurrent generation in graphene/MoS2/graphene vdWHs by creating a device with two distinct regions containing one-layer (1L) and seven-layer (7L)-MoS2 to exclude extrinsic device factors. The discretized electrostatic potential barriers were introduced to interpret the photocarrier tunneLling and extracting in ultrathin vdWHs

Methods

Results

Conclusion