Optoelectronic properties of graphene-MoS 2 hybrid
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Optoelectronic properties of graphene-MoS2 hybrid Medini Padmanabhan1, Kallol Roy1, Srijit Goswami1, T. Phanindra Sai1, Gopalakrishnan Ramalingam2, Sanjeev Kaushal3, Srinivasan Raghavan2 and Arindam Ghosh1 1
Department of Physics, Indian Institute of Science, Bangalore, India 560012 Materials Research Center, Indian Institute of Science, Bangalore, India 560012 3 Tokyo Electron Ltd., Akasaka Biz Tower, 3-1 Akasaka 5-Chome, Minato-ku, Tokyo, Japan 107-6325 2
ABSTRACT Ultra-thin flakes of layered materials have recently been attracting widespread research interest due to their exotic properties. In this work, we study the optoelectronic response of a hybrid of two such materials – graphene and MoS2. Our devices consist of mechanically exfoliated graphene flakes transferred on top of similarly exfoliated MoS2. The electrical response of the hybrid is studied in the presence of white light. We show that the four-point resistance of graphene is modulated in the presence of light. This effect is observed to be a strong function of gate voltage. We have also extended our studies to CVD (chemical vapor deposition) - grown graphene transferred onto MoS2 which show qualitatively similar features, thereby attesting to the scalability of the device architecture.
INTRODUCTION In the quest for miniaturization, the prospect of using atomically thin materials for device applications is promising. It is in this context that layered materials have recently been attracting much research interest [1]. Ever since the resounding success of graphene [2], researchers have uncovered interesting properties in other layered materials as well. For example, MoS2 with its layer-dependent bandgap [3-5], and BN with its low trap density and favorable dielectric constant [6] are being currently investigated for device applications. Using a hybrid of such layered materials can certainly be expected to open up new doors. For example, it has been shown that graphene devices on BN substrates have higher mobilities compared to the ones on conventional Si/SiO2 substrates [6]. When combined with its superior electrical properties [7], the optical properties of graphene including high absorption coefficient over a wide range of wavelengths [8] and fast recombination lifetimes [9], make it a prominent candidate for optoelectronic device design. Ultra-fast photodetectors [10] have already been demonstrated in graphene. A parallel research direction has been to induce photoconductivity in graphene by combining it with other light absorbing materials such as quantum dots [11] and chromophores [12]. In this article, we demonstrate the optoelectronic properties of a hybrid consisting of graphene transferred on top of an exfoliated MoS2 flake. We show that the resistance of graphene is modulated in the presence of light and that the optical response is a strong function of an externally applied gate voltage. We also do measurements on bare MoS2 samples and analyze the findings to obtain a qualitative understanding of the system.
EXPERIMENTAL METHODS
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