Optoelectronic Properties of Few-Layer MoS2 FET Gated by

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Optoelectronic Properties of Few-layer MoS FET Gated by Ferroelectric Relaxor Polymer Yan Chen, Xudong Wang, Peng Wang, Hai Huang, Guangjian Wu, Bobo Tian, Zhenchen Hong, Yutao Wang, Shuo Sun, Hong Sheng, Jianlu Wang, Weida Hu, Jinglan Sun, Xiangjian Meng, and Junhao Chu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b10206 • Publication Date (Web): 01 Nov 2016 Downloaded from http://pubs.acs.org on November 1, 2016

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ACS Applied Materials & Interfaces

Optoelectronic Properties of Few-layer MoS2 FET Gated by Ferroelectric Relaxor Polymer

Yan Chen

1,2

, Xudong Wang1, Peng Wang1, Hai Huang1,2, Guangjian Wu1, Bobo

Tian,1,2 Zhenchen Hong3, Yutao Wang3, Shuo Sun1, Hong Sheng1, Jianlu Wang1*, Weida Hu1*, Jinglan Sun1, Xiangjian Meng1*, Junhao Chu1 1

National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics,

Chinese Academy of Sciences, 500Yu Tian Road, Shanghai 200083, China, 2

University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China.

3

Department of physics, University of Science and Technology of China, Hefei 230000,

China

*

Corresponding authors:

J. W. (email: [email protected]), W. H. (email: [email protected]), X. M. (email: [email protected])

ACS Paragon Plus Environment


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Abstract: Recently, new devices combining two-dimensional (2D) materials with ferroelectrics, have been a new hotspot for promising applications in electronics and optoelectronics. Here, we design a new type of FET using the 2D MoS2 and poly(vinylidene

fluoride-trifluoroethylene-chlorofloroethylene)

terpolymer

ferroelectric relaxor. The device exhibit excellent performance including a large on/off ratio) and an insignificant leakage current. Moreover, the hysteresis characteristics are effectively modulated for its ferroelectric properties at low temperature. Additionally, a broad range photoresponse (visible to 1.55 µm) and a high sensitivity (>300 A/W, λ=450 nm) are achieved. These results indicate that ferroelectric relaxor can be applied into the high-performance 2D optoelectronic devices.

Key words: MoS2, Ferroelectric relaxor, P(VDF-TrFE-CFE), high-κ, photodetectors


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The emergency of graphene, transition metal dichalcogenides (TMDs), black phosphorus and other high performance two demensional (2D) materials, have been predicated to deeply impact future electronic and optoelectronic applications.1-4 These layered 2D materials be exfoliated by the micromechanical cleavage technique since the neighboring layers are bound by Van der Waals interactions.1,4,5 Moreover, these 2D materials can be grown by many technologies, chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) for example.6-10 MoS2 is a typical TMD with a layered structure and the indirect bandgap of 1.2 eV gradually shifts to a direct bandgap of 1.8 eV as the bulk material is extracted down to a monolayer.4,11 MoS2 thin layers demonstrate many excellent properties, such as high room temperature mobility, the absence of dangling bonds, resistance to oxidation, and so on.1, 4-8 All of these unique characteristics make ultra-thin MoS2 a good candidate for application to various electronic devices and optoelectronics. Mobility, an essential parameter, determines the speed of a carrier moves through a semiconductor. Mobility depends on many factors such as material thickness, temperature, contact quality, interface surroundings, measurement environment and so on.5,12 Many research groups are devoting their efforts to improving the mobility of 2D materials.13-14 The mobility for a material can be measured by Hall geometry or field-effect transistor characteristics. The mobility measurement based on the Hall geometry can remove the effect of contact resistance to achieve more accurate mobility. Meanwhile, the field-effect mobility can be acquired from the transfer characteristic curve at the turning point where the gate capacitance is a crucial factor.15 A MoS2 field effect transistor (FET) covered with high dielectric constant materials has shown enhancements of mobility at room temperature.5,14-16 The strongly damped scattering from coulomb impurities observed in the FET device may result from screening by high-dielectric environment or modification of phonon distribution in monolayer MoS2.1 A significant increase of mobility by depositing a top-gate dielectric was also observed in multilayer samples.5 At temperatures around 200-300 K, mobility exhibits a temperature dependency and can be up to 410 cm2·V-1·s-1 at room temperature according to theoretical calculations.17 The mobility of single-layer/few-layer MoS2 ranging from 0.1 to 100 cm2·V-1·s-1 has been reported by several research groups.14 The deposition of a top-gate dielectric is assumed to quench the homopolar phonon mode and make the mobility coefficient reduce to



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1.52.13 Traditionally, MoS2 FETs have been fabricated with different gate dielectrics, such as SiO2, HfO2 and Al2O3.1,5 These studies indicated that the dielectric constant of gate material can influence the mobility of the MoS2 channel effectively. 2D materials combined with ferroelectrics show a better performance of devices. 18,19 Recently, we have fabricated a phototransistor based on triple-layer MoS2 where ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] acts as a gate dielectric.20 Compared with traditional MoS2 photodetectors, our detector shows an enhanced detectivity in the region from visible to near-infrared (0.85µm) as the band gap of MoS2 ranges from 1.2 eV to 1.8 eV. The improved performance is due to the notable suppression of the dark current attributed to the local electric field provided by the ferroelectric polarization. More interestingly, the photodetector shows response to light of wavelengths to 1.55 µm, suggesting that the bandgap of the few-layer MoS2 becomes narrower. Such bandgap-modified effect has been discovered in other 2D materials and nanowire devices.21,22 However, the mechanisms of the ferroelectric polarization on few-layer MoS2 FET are still not clear. Furthermore, the mobility of few-layer MoS2 device with a P(VDF-TrFE) gate is approximately a factor of 10 higher than a device with a SiO2 gate.18,20 When the P(VDF-TrFE) is doped with chlorofloroethylene(CFE), a type of ferroelectric relaxor terpolymer, poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) [P(VDF-TrFE-CFE)] will be achieved. This terpolymer is a typical relaxor ferroelectric with a very small polarization but a higher dielectric constant than that of P(VDF-TrFE) copolymer at room temperature. The room temperature dielectric constant of P(VDF-TrFE-CFE) is up to 50, which is much higher than HfO2 and Al2O3.24-26 The higher the dielectric constant is, the stronger ability to screen the coulomb scattering supposed to be. Furthermore, a transition from relaxor to ferroelectric phase is observed for the P(VDF-TrFE-CFE) at low temperature.25 This characteristic is closely connected to the semi-crystalline structures of polar sequences for switching their conformation in response to the external electric field or the environmental temperature.26 These unique properties make P(VDF-TrFE-CFE) a potential application in flexible electronic devices. For instance, the terpolymer can be used in a multilayer capacitor, optoelectronic device, memory device, etc.24,27 In the present work, the few-layer MoS2 FET with relaxor ferroelectric polymer


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P(VDF-TrFE-CFE) gate dielectric material is fabricated, and the electrical and photoelectric properties have been systematically investigated. We expect to observe enhanced mobility of the MoS2 channel with the high dielectric constant of the P(VDF-TrFE-CFE) terpolymer. Additionally, we can tune the temperature to make the terpolymer transform from relaxor to a normal ferroelectric phase, which will create a strong local electric field. Our work aims to investigate the effect of local electric field on the electronic structure and optoelectrical properties of MoS2. Figure 1a shows the schematic diagrams for the structure of MoS2 sheets and the molecular chain conformation of the P(VDF-TrFE-CFE) terpolymer. The molecular chain conformations, suggesting the crystallinity of the polar /nonpolar regions, play a decisive role in determining the properties of relaxor terpolymers. MoS2 flakes exfoliated by Scotch tape were peeled off and applied to an n-doped silicon substrate covered with 285 nm thick silicon dioxide. Four-layer MoS2 is employed in the device. The thickness of the MoS2 layer is confirmed by the Raman spectrum and shown in Figure 1b from an optical microscope image. The Raman spectrum shows that the 1

peaks at 383.295 cm-1 and 407.179 cm-1 represent an in-plane vibration mode ( E 2 g ) and an out-of-plane vibration mode (A1g) respectively. The difference between the two peaks is 23.884 cm-1, representing the fact that the MoS2 is four-layer according to the previously reported results.2 The 3D schematic view of the MoS2 transistor device structure driven by ferroelectric relaxor film gating is shown in Figure 1c. And the optical image of the device is shown in Figure 1d. As previously mentioned, the gate dielectric environment is a crucial factor for the transistor. The dielectric properties of P(VDF-TrFE-CFE) film have been investigated. Figure 2a shows the temperature dependence of dielectric permittivity (ɛ) and dielectric loss (tan δ) versus frequency. Both ɛ and tan δ display a broad peak around temperature Tm, which shifts to higher temperature with increasing frequency. In the P(VDF-TrFE-CFE) film, the mixture of nonpolar trans-gauche TGTG and TG3TG3 (paraelectric phase) is the predominant molecular chain conformation when temperature is higher than 340 K. In the temperature range of ~260 K to ~340 K, the T3GT3G molecular chain conformations (ferroelectric relaxor phase with polar nanoregion) are superior to others. The T>3G molecular chain conformations occur when environmental temperature is lower than ~260 K. The T>3G conformation



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shows the typical ferroelectric properties.24 The polarization versus electric field (P-E) loops for relaxor P(VDF-TrFE-CFE) terpolymer at a series of temperatures is shown in Figure 2b. Note that normal P-E loops are observed at temperatures below ~260K, which indicates the formation of a normal ferroelectric state of the P(VDF-TrFE-CFE) films. The transfer properties of the P(VDF-TrFE-CFE) top-gate few-layer MoS2 FeFET, compared with the SiO2 back-gate device at room temperature, is shown in Figure 2c. The on/off ratio of the FeFET with P(VDF-TrFE-CFE) gating can reach 3.27×106. The field effect differential mobility was calculated to be 51.94 cm2/(V·s) and 3.5 cm2/(V·s) of MoS2 with P(VDF-TrFE-CFE) top gate and SiO2 back gate respectively, using the following equation: L d dI µ= × × sd , W ε 0ε rVsd dVg where L and W are the length and width of the channel, d is the thickness of the gate materials , εr is the and dielectric constant of SiO2 or P(VDF-TrFE-CFE) film, and dIds/dVg is the differential of Ids-Vg characteristics slope taken from the linear region.1,28 The superior performance can be observed in MoS2 with a P(VDF-TrFE-CFE) top gate rather than with a SiO2 back gate. These enhanced transfer properties can be attributed to the effective coulomb scattering screening on the interface by the high-κ P(VDF-TrFE-CFE). The output characteristic curves of the device under different temperatures are shown in Figure 2d. It can be seen that the current

increases

in

the

cooling

process,

which

is

opposite

to

the

temperature-dependency of the resistance properties of the semiconductor channels. This unusual phenomenon should be associated with a remnant polarization of the terpolymer at low temperature. The measurements were performed after a positive voltage had been applied to the P(VDF-TrFE-CFE), which causes the MoS2 channel to operate in the accumulation state. With decreasing temperature, P(VDF-TrFE-CFE) tends to transform to normal ferroelectric from the relaxor state. Remnant polarization occurs and increases. In this case, the remnant polarization acts as an additional positive gate voltage to accumulate carriers in the MoS2 channel. Such a gating effect in our FeFET becomes more obvious at lower temperatures, resulting in higher carrier concentrations of the channel, which is an opposite tendency to the intrinsic temperature dependence of traditional MOSFET. However, the effect of remnant polarization is more pronounced than the direct effect of temperature on carrier


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concentration. As a result, the output current of our device is not consistent with the general temperature-dependent rule of semiconductors, showing a negative correlation between resistivity and temperature. To further investigate the effect of this special gate dielectric P(VDF-TrFE-CFE), transfer characters of MoS2 FeFET with P(VDF-TrFE-CFE) top gate were measured at various temperatures. In Figure 3a, with the temperature ranging from room temperature to 200 K, the transfer curves are clockwise. The hysteresis windows of the curves are derived from the P-E loops of P(VDF-TrFE-CFE) as shown in Figure 2b. Similarly, this phenomenon was observed in graphene transistors and the hysteresis originates from charge injection into the trap sites or transport from adsorbates on the dielectric substrate.29 With increasing temperature, the higher ratio of P(VDF-TrFE-CFE) tends to become T3GT3G conformations. The combination of the impurities and polar nanoregions causes the window to become narrow with decreasing temperature and these effects achieve a balance at 220 K. Below 200 K, the long-range order structure molecular chain conformations of T>3G (ferroelectric phase) play a dominant role. In Figure 3b, the transfer curves show ferroelectric hysteresis and the windows become broader with the decreasing temperature. In other words, the relaxor/ferroelectric properties of P(VDF-TrFE-CFE) can be successfully reproduced when it serves as a gate in MoS2 FeFET. The ferroelectricity of the P(VDF-TrFE-CFE) at lower temperature can be corroborated by confirming three states of the terploymer: P(VDF-TrFE-CFE) without polarization (fresh state), polarization up (Pup) and polarization down (Pdown) state. The polarization state can be achieved even when the applied voltage，which is larger than the coercive voltage, is removed immediately. Here we applied a top gate voltage of ±10 V (referring to the hysteresis of P(VDF-TrFE-CFE) in Figure 2b) to accumulate (Pdown state) and deplete (Pup state) the carriers in the MoS2 channel. The output characteristics of the three states at 200 K are shown in Figure 3c, demonstrating that the terpolymer was transformed to ferroelectrics at lower temperature. In addition to thickness dependence, contact metals and scattering mechanisms, temperature (T) is a crucial factor affecting carrier mobility in the channel. Furthermore, we can tune temperature to determine its effect on the number and type of phonons taking part in carrier scattering. Figure 3d depicts the



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temperature dependence of mobility for the FeFET based on P(VDF-TrFE-CFE). The result corresponds with the theoretical study that the relationship between mobility and temperature follows a power-law of µ ∝ T γ with γ being a parameter dependent on phonon type in carrier-phonon scattering. The fitting of our experimental data shows that the value of γ is approximately 2.9. In bulk MoS2 , the exponent γ is predicted to be ~2.6, ~1.6, and ~1 correspond to homopolar optical, polar optical and acoustic phonons.12 For monolayer MoS2, the exponent γ was calculated to be ~ 1.69 near room temperature and 1 below 100 K.18 Experimentally, high values of 1.9 for monolayer and 2.5 for double layer MoS2 were reported by Hone et al.30 As a semiconductor, the main scattering mechanisms in MoS2 are coulomb impurities, remote interfacial phonons, lattice phonons which present different dependence on temperature. The value of γ ~2.9 demonstrates that the primary scattering centers are optical phonons in the channel of our device and the small deviation from the calculated value is caused by the charged impurities in the interface generating much coulomb scattering. The quality of the MoS2 samples is not the only factor in this result. High contact resistance and the presence of remote phonons from SiO2 substrate should be taken into consideration also. Graphene and other 2D materials, of alternative bandgap and high responsivity, have been demonstrated to be promising and comprehensive materials of photodetectors. Previous work by our group has proposed that an ultra-high electrostatic field created by polarization of P(VDF-TrFE) can narrow the bandgap to detect a wider spectrum range in the infrared region. This provides an unique and innovative way of energy band engineering.20 In this work, we confirmed that conclusion by carrying out the photoresponse detection through the whole temperature range of 160-300 K. As we recognized, changing the temperature can alter the ferroelectric/relaxor properties of P(VDF-TrFE-CFE). The Isd-Vsd curves at 200 K for dark and under the illumination of short wavelength infrared 1550 nm laser light are shown in Figure 4a. The current responsivity of the device can be calculated by the formula R= (Iillum-Idark) /P, where P is the incident light intensity on the channel. The responsivity turns out to be 46.31 A/W under the illumination power of 20 nW. Figure 4b shows that light of 1550 nm can be detected until the temperature decreases to 220 K where the terploymer transforms its properties to a ferroelectrics/relaxor. Therefore, we can reach the firm conclusion that the bandgap of


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MoS2 can be altered by ferroelectrics. Also, we have test the device respond to the laser of 2000 nm and no signal have been found. This is another proof that can exclude the thermal effect and confirm the respond to light of 1550 nm is the interband optical transition. As a detector, the characteristics of photo-electric response under different wavelengths were also tested. Figure 4c shows the photo-switching behavior (with zero gate bias) of MoS2 flakes with a P(VDF-TrFE-CFE) top gate under 450 nm and 1060 nm incident laser illumination at 200 K. The responsivity is calculated to be 346.24 A/W and 247.03 A/W under 20 nW illumination of 450 nm and 1060 nm laser respectively. In summary, the relaxor ferroelectric polymer P(VDF-TrFE-CFE) as a gate material for 2D semiconductor FET has been studied. The electronic characteristics of this structure have been investigated and explained. The screening coulomb impurities associated with the dielectric environment of the P(VDF-TrFE-CFE) polymer which enhance the mobility of MoS2 have been confirmed. The P(VDF-TrFE-CFE) polymer can transform from relaxor to normal ferroelectrics with temperature change. The typical FeFET effect is achieved at low temperatures and some unique properties, such as high sensitivity photodetection, and bandgap modification, have been studied. Although the results above have been obtained on non-fully optimized devices and the mechanism of the interaction of ferroelectrics and 2D materials should be studied in future research, they sketch a proof of novel concept for electronic and optoelectronic devices based on a ferroelectric polymer relaxor.



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Backgate MoS2 device fabrication: The MoS2 nanosheets were extracted by mechanical exfoliation of a 2H-MoS2 bulk crystal (purchased from HQ graphene) and then transferred to a heavily doped p-type silicon substrate covered with a 285-nm-thick silicon oxide. An optical microscope was used to identify flakes suitable for electrical characterization and accurate number of layers was inspected by Raman spectrum. The electrodes of the device were made by standard ultraviolet lithography technology, followed by thermal evaporation of a Ni/Au film (5/50 nm thick). The devices were then annealed at 200 ℃ in vacuum with 100 sccm Argon atmosphere for 2 hours to release the adsorbate and decrease contact resistance. Topgate MoS2 FET device fabrication: Once the back-gate FET device was fabricated and annealed, the P(VDF-TrFE-CFE) (56.2/36.3/7.5 mol%) organic ferroelectric polymer solution (dissolved in the diethyl carbonate with 2.5 % wt) was spin coated on top of the MoS2 with the thickness of 300 nm approximately. Then the P(VDF-TrFE-CFE) film was annealed at 118 ℃ in an oven for four hours. Finally, 9-nm-thick aluminum was deposited on the top of the P(VDF-TrFE) film by electron beam evaporation and patterned by photolithography as the top-gate semitransparent electrode. Measurement: The electric and opto-electric measurements were performed by an Agilent B2902A semiconductor parameter analyzer in vacuum. The system was cooled by vaporizing liquid nitrogen and a temperature controller to maintain the temperature set point. Measurements were not performed until the temperature remained at the set point for 5 minutes. The few layer MoS2 Raman spectroscopy were carried out by a Lab Ram HR800. Acknowledgements This work is supported by the Major State Basic Research Development Program (Grant Nos. 2013CB922302 and 2016YFA0203900), the Natural Science Foundation of China (Grant Nos. 11374320, 61404147，61574151, 11322441 and 61574152), Natural Science Foundation of Shanghai (13JC1406000; 14JC1406400), Key Research Project of Frontier Sciences of CAS (Grant Nos. QYZDB-SSW-JSC016 and QYZDB-SSW-JSC031) Reference：： 1. Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, V.; Kis, A. Single-layer


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MoS2 Transistors. Nat. Nanotechnol. 2011, 6, 147-150. 2. Lee, C.; Yan, H.; Brus, L. E.; Heinz, T. F.; Hone, J.; Ryu, S. Anomalous Lattice Vibrations of Single- and Few-Layer MoS2. ACS Nano 2010, 4, 2695-2700. 3. Xia, F.; Mueller, T.; Lin, Y.-m.; Valdes-Garcia, A.; Avouris, P. Ultrafast Graphene Photodetector. Nat. Nanotechnol. 2009, 4, 839-843. 4. Splendiani, A.; Sun, L.; Zhang, Y. B.; Li, T. S.; Kim, J.; Chim, C. Y.; Galli, G.; Wang, F. Emerging Photoluminescence in Monolayer MoS2. Nano Lett. 2010, 10, 1271-1275. 5. Zou, X.; Wang, J.; Chiu, C.-H.; Wu, Y.; Xiao, X.; Jiang, C.; Wu, W.-W.; Mai, L.; Chen, T.; Li, J.; Ho, J. C.; Liao, L. Interface Engineering for High-Performance Top-Gated MoS2 Field-Effect Transistors. Adv. Mater. 2014, 26, 6255-6261. 6. Eda, G.; Yamaguchi, H.; Voiry, D.; Fujita, T.; Chen, M. W.; Chhowalla, M. Photoluminescence from Chemically Exfoliated MoS2. Nano Lett. 2011, 11, 5111-5116. 7. Lee, Y. H.; Zhang, X. Q.; Zhang, W. J.; Chang, M. T.; Lin, C. T.; Chang, K. D.; Yu, Y. C.; Wang, J. T. W.; Chang, C. S.; Li, L. J.; Lin, T. W. Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition. Adv. Mater. 2012, 24, 2320-2325. 8. Liu, K. K.; Zhang, W. J.; Lee, Y. H.; Lin, Y. C.; Chang, M. T.; Su, C.; Chang, C. S.; Li, H.; Shi, Y. M.; Zhang, H.; Lai, C. S.; Li, L. J. Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates. Nano Lett. 2012, 12, 1538-1544. 9. Wang, F.; Wang, Z. X.; Xu, K., Wang, F. M.; Wang, Q. S.; Huang, Y.; Yin, L.; He, J. Tunable GaTe-MoS2 van der Waals p–n Junctions with Novel Optoelectronic Performance. Nano Lett. 2015, 15, 7558-7566. 10. Xu, K.; Wang, Z. X.; Wang, F.; Huang, Y.; Wang, F. M.; Yin, L., Jiang, C.; He, J. Ultrasensitive Phototransistors Based on Few-Layered HfS2. Adv. Mater. 2015, 27, 7881–7887. 11. Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105,136805. 12. Fivaz, R.; Mooser, E. Mobility of Charge Carriers in Semiconducting Layer Structures. Phys. Rev. 1967, 163, 743. 13. Radisavljevic, B.; Kis, A. Mobility Engineering and a Metal-insulator Transition in Monolayer MoS2. Nat. Mater. 2013, 12, 815-820. 14. Wang, J.; Li, S.; Zou, X.; Ho, J.; Liao, L.; Xiao, X.; Jiang, C.; Hu, W.; Wang, J.; Li, J. Integration of High-k Oxide on MoS2 by Using Ozone Pretreatment for High-Performance MoS2 Top-Gated Transistor with Thickness-Dependent Carrier Scattering Investigation. Small. 2015, 11, 5932-5938. 15. Lee, E.; Ko, J.; Lim, K. H.; Kim, K.; Park, S. Y.; Myoung, J. M.; Kim, Y. S. Gate Capacitance-Dependent Field-Effect Mobility in Solution-Processed Oxide Semiconductor Thin-Film Transistors. Adv. Funct. Mater. 2014, 24, 4689-4697. 16. Koppens, F. H. L.; Mueller, T.; Avouris, P.; Ferrari, A. C.; Vitiello, M. S.; Polini, M. Photodetectors Based on Graphene, Other Two-dimensional Materials and Hybrid Systems. Nat. Nanotechnol. 2014, 9, 780-793.



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17. Kaasbjerg, K.; Thygesen, K. S.; Jacobsen, K. W. Mobility Engineering and a Metal-insulator Transition in Monolayer MoS2. Phys. Rev. B 2012, 85,115317. 18. Kobayashi, T.; Hori, N.; Nakajima, T.; Kawae, T. Electrical Characteristics of MoS2 Field-effect Transistor with Ferroelectric Vinylidene Fluoride-trifluoroethylene Copolymer Gate Structure. Appl. Phys. Lett. 2016, 108, 132903. 19. Lee, Y. T.; Hwang, D. K.; Im, S. High-performance a MoS2 Nanosheet-based Nonvolatile Memory Transistor with a Ferroelectric Polymer and Graphene Source-drain Electrode. J. Korean Phys. Soc. 2015, 67，1499-1503. 20. Wang, X. D.; Wang, P.; Wang, J. L.; Hu, W. D.; Zhou, X. H.; Guo, N.; Huang, H.; Sun, S.; Shen, H.; Lin, T.; Tang, M.; Liao, L.; Jiang, A. Q; Sun, J. L.; Meng, X. J.; Chen, X. S.; Lu, W.; Chu, J. H. Ultrasensitive and Broadband MoS2 Photodetector Driven by Ferroelectrics. Adv. Mater. 2015, 27, 6575-6581. 21. Zheng, D. S.; Wang, J. L.; Hu, W. D.; Liao, L.; Fang, H. H.; Guo, N.; Wang, P.; Gong, F.; Wang, X. D.; Fan, Z. Y.; Wu, X.; Meng, X. J.; Chen, X. S.; Lu, W. When Nanowires Meet Ultrahigh Ferroelectric Field–High-Performance Full-Depleted Nanowire Photodetectors. Nano Lett. 2016, 16, 2548-2555. 22. Wu, G. J.; Wang, X. D.; Wang, P.; Huang, H.; Chen, Y.; Sun, S.; Shen, H.; Lin, T.; Wang, J. L.; Zhang S. T.; Bian, L. F.; Sun, J. L.; Meng, X. J.; Chu, J. H. Visible to Short Wavelength Infrared In2Se3-nanoflake Photodetector Gated by a Ferroelectric polymer. Nanotechnology 2016, 27，364002. 23. Hee Sung, L.; Sung-Wook, M.; Min Kyu, P.; Young Tack, L.; Pyo Jin, J.; Jae Hoon, K.; Sunmin, R.; Seongil, I. MoS2 Nanosheets for Top-gate Nonvolatile Memory Transistor Channel. Small 2012, 8, 3111-3115. 24. Wang, J. L.; Meng, X. J.; Yuan, S. Z.; Yang, J.; Sun, J. L.; Xu, H. S.; Chu, J. H. High Electric Tunability of Relaxor Ferroelectric Langmuir-Blodgett Terpolymer Films. Appl. Phys. Lett. 2008, 93, 192905. 25. Tian, B. B.; Zhao, X. L.; Liu, B. L.; Wang, J. L.; Han, L.; Sun, J. L.; Meng, X. J.; Chu, J. H., Abnormal Polarization Switching of Relaxor Terpolymer Films at Low Temperatures. Appl. Phys. Lett. 2013, 102, 072906. 26. Meng, X. J.; Wang, J. L.; Xu, H. S.; Sun, J. L.; Chu, J. H. The Effect of a Field Amplitude on the Relaxor Behaviors in Langmuir-Blodgett Terpolymer Films. J. Appl. Phys. 2009, 106, 114106. 27. Zhao, X. L.; Wang, J. L.; Tian, B. B.; Liu, B. L.; Zou, Y. H.; Wang, X. D.; Sun, S.; Sun, J. L.; Meng, X. J.; Chu, J. H. Temperature Dependence of Electronic Transport Property in Ferroelectric Polymer Films. Appl. Surf. Sci. 2014, 316, 497-500. 28. Lopez-Sanchez, O.; Lembke, D.; Kayci, M.; Radenovic, A.; Kis, A. Ultrasensitive Photodetectors Based on Monolayer MoS2. Nat. Nanotechnol. 2013, 8, 497-501. 29. Wang, H. M.; Wu, Y. H.; Ni, Z. H.; Shen, Z. X. Electronic Transport and Layer Engineering in Multilayer Graphene Structures. Appl. Phys. Lett. 2008, 92, 053504. 30. Cui, X.; Lee, G.-H.; Kim, Y. D.; Arefe, G.; Huang, P. Y.; Lee, C. H.; Chenet, D. A.; Zhang, X.; Wang, L.; Ye, F.; Pizzocchero, F.; Jessen, B. S.; Watanabe, K.; Taniguchi, T.; Muller, D. A.; Low, T.; Kim, P.; Hone, J. Multi-terminal Transport Measurements of MoS2 Using a Van der Waals Heterostructure Device Platform. Nat. Nanotechnol. 2015, 10, 534-540.


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Figures and captions

Figure 1. Fabrication and structure of few layer MoS2 FeFET. (a) Schematic structure of triple-layer MoS2 and P(VDF-TrFE-CFE). (b) Raman spectra of four-layer MoS2 and optical microscopic image insert, scale bar, 5 µm. (c) 3D schematic view of the few layer MoS2 FeFET. (d) Optical microscopic image of the MoS2 FeFET. The scale bar stands for 20 µm.



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Figure

2.

Temperature

related

electric

properties

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of

the

P(VDF-TrFE-CFE)/MoS2 structures. (a) Dielectric constant and loss tangent of P(VDF-TrFE-CFE) at 0.3-600 kHz frequency between 150-350 K. (b) The ferroelectric hysteresis loop of 300 nm P(VDF-TrFE-CFE) film capacitor at different temperatures. It is measured using Sawyer-Tower circuit at 1 Hz frequency. (c) The transfer characteristics of four-layer MoS2 channel with P(VDF-TrFE-CFE) ferroelectric polymer top gate and SiO2 back gate at room temperature when Vsd = 1 V. (d) The output characteristics without gate voltage at different temperatures.


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Figure 3. Ferroelectricity related electric properties of the device. (a) The transfer characteristics over Tc (in this case, relaxor ferroelectrics start to be ferroelectrics below this temperature). (b) The transfer characteristics below Tc. (c) The output characteristics (Vg=0 V) with three states of ferroelectric layer at 200K. The three states are fresh state (ferroelectric layer without polarization), Pup state (Vtg= -10 V) and Pdown state (Vtg=10 V). (d) Temperature dependence of carrier mobility µ.



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Figure 4. Ferroelectricity related optical properties of the device. (a) The output characteristics (Vg=0 V) with/without incident light (1550 nm) at 200 K. (b) Time resolved photoresponse for 1550 nm wavelength light with Vg=0 V and Vsd=0.1 V. (c) Photoswitching behavior of MoS2 flakes with P(VDF-TrFE-CFE) top gate under 450 nm and 1060 nm laser incidents at 200 K and Vsd=0.1 V.



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Table of Contents Graphic


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Optoelectronic Properties of Few-Layer MoS2 FET Gated by

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