Ambipolar transport in MoS 2 based electric double layer transistors
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Ambipolar transport in MoS2 based electric double layer transistors Jianting Ye1, Yijin Zhang1, and Yoshihiro Iwasa1 1 Quantum Phase electronics center and department of Applied Physics, The University of Tokyo, Tokyo, Japan ABSTRACT Making field effect transistors (FETs) on thin flake of single crystal isolated from layered materials was pioneered by the success of graphene. To overcome the difficulties of the zero band gap in graphene electronics, we report the fabrication of an electric double layer (EDL) transistor, a variant of FET, based on another layered material, MoS2. Using strong carrier tunability found in EDL coupled by ion movement, MoS2 transistor displayed an unambiguously ambipolar operation in addition to its commonly observed n-type transport. A high on/off ratio >104, large “ON” state conductivity of ~mS, and a high reachable n2D ~ 1×1014 cm-2 confirmed the high performance transistor operation being important for application. The high-density carriers of both holes and electrons can drive the MoS2 channel to metallic states indicating that new electronic phases could be accessed using the protocol established in making EDL gated transistors on layered materials. INTRODUCTION Layered materials led by graphene are now attracting great interests by the success of the Scotch-tape method, which offers a simple and effective process for field effect transistor (FET) device fabrication based on thin flakes isolated from their bulk layered crystals [1,2]. Although graphene-FETs exhibit high performance such as high mobility up to ~ 104 Vs/cm2 and ambipolar operation [1], the gapless nature in its Dirac band structure prevents device application in real world. To overcome the difficulty in graphene-FETs to realize “OFF” state in device operation, semiconducting transition-metal dichalcogenides, represented by molybdenum disulfide MoS2, are regarded as promising candidates for FET device with its gapped nature for creating “OFF” state [3]. The first demonstration of MoS2-FET with SiO2 as the gate dielectrics following the same manner as graphene only showed a poor modulation in conductivity [2], while the later attempt with HfO2, one of the high-k materials, as the gate dielectrics realized a clear switching operation with ON/OFF ratio up to 108 [4]. The straight forward interpretation of this improvement may be the enhancement of charge accumulation capability with improved gate efficiency from SiO2 to HfO2. Although a practical FET device can be realized using HfO2 dielectrics, a significant nature of ambipolarity with highly symmetric operation as demonstrated in graphene-FET is still absent [1]. A further improvement of the gate efficiency is necessary to reach such a ambipolar operation in MoS2. We demonstrated an ambipolar FET operation in MoS2 by enhancing the gate efficiency using electric double layer transistor (EDLT) with ionic liquid as the gate dielectrics. EDLT is a proved device structure for significant enhancement of transport [5].
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EXPERIMENT MoS2 single crystal was grown using chem
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