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terminal transport measurements of MoS2 using a van der Waals heterostructure device platform
Atomically thin two dimensional semiconductors such as MoS2 hold great promise for electrical, van cleef arpels necklace knock off optical and mechanical devices and display novel physical phenomena. However, the electron mobility of mono and few layer MoS2 has so far been substantially below theoretically predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviours. Potential sources of disorder and scattering include defects such as sulphur vacancies in the MoS2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielectrics. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi terminal geometry using gate tunable graphene electrodes. Magneto transport measurements show dramatic improvements in performance, including a record high Hall mobility reaching 34,000cm2V 1s 1 for six layer MoS2 at low temperature, confirming that low temperature performance in previous studies imitation van cleef and arpels vintage alhambra necklace was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also observed Shubnikov de Haas oscillations in high mobility monolayer and few layer MoS2. Modelling of potential scattering sources and quantum lifetime analysis indicate that a combination of short range and long range interfacial scattering limits the low temperature mobility of MoS2.
a, Schematic of the hBN encapsulated MoS2 multi terminal device. The exploded view shows the individual components that constitute the heterostructure stack. Bottom: Zoom in cross sectional schematic of the metal graphene MoS2 contact region. b, Optical microscope image of a fabricated device. Graphene contact regions are outlined by dashed lines. c, Cross sectional STEM image of the fabricated device. The zoom in false colour image clearly shows the ultra sharp interfaces between different layers (graphene, 5L; MoS2, 3L; top hBN, 8nm; bottom hBN, 19nm).
a, Output curves (Ids Vds) of the hBN encapsulated 4L MoS2 device with graphene electrodes at different temperatures. Backgate voltage Vbg was maintained at 80V with a carrier density of 6.851012cm2 in MoS2. The linearity of the output curves confirms that the graphene MoS2 contact is ohmic at all temperatures. b, Resistivity of 4L MoS2 (log scale) as a function of Vbg at different temperatures. The resistivity decreases on cooling, showing metallic behaviour, reaching 130 at 12K. The colour legend is the same as in a (from 300K to 12K). c, Contact resistance RC of the same device (log scale) as a function of Vbg at different temperatures. The colour legend is the same as in a (but from 250K to 12K). Inset: RC as a function of temperature at different Vbg. At high Vbg the contact resistance decreases when decreasing the temperature.
a, Hall mobility of hBN encapsulated MoS2 devices (with different numbers of layers of MoS2) as a function of temperature. To maintain ohmic contact, a finite Vbg was applied. The measured carrier densities obtained from Hall measurements for each device are listed in Supplementary Table1. The solid fitting lines are drawn by the model described in the main text. All fitting parameters are listed in Supplementary Table1. As a visual guide, the dashed line shows the power law phT, and fitted values of for each device are listed in the inset table. b, Impurity limited mobility (imp) as a function of the MoS2 carrier density. For comparison, previously reported values from MoS2 on SiO2 substrates (refs8,46) are plotted. c e, The solid lines show the theoretically calculated long range (LR) impurity limited mobility (c), short range (SR) impurity limited mobility (d) and mobility including both LR and SR based on Matthiessen rule, 1/=1/LR+1/SR, as a function of carrier density for 1L to 6L MoS2 (e). Experimental data from 1L and 6L MoS2 are shown as circles (c e).
a, Longitudinal resistance Rxx (red curve) and Hall resistance Rxy (blue curve) of an hBN encapsulated CVD 1L MoS2 device as a function of magnetic field B measured at 0.3K and with a carrier density of 9.71012cm2. Inset: Oscillation amplitude (black curve) as a function of 1/B after subtraction of the magnetoresistance background. The quantum scattering time extracted from the fitted Dingle plot (red dashed line) is 176fs. b, Rxx (red curve) and Rxy (blue curve) of the hBN encapsulated 4L MoS2 device as a function of B. Hall measurements were conducted at 0.3K and at a carrier density of 4.91012cm2. c, Rxx (red curve) and Rxy (blue curve) of an hBN encapsulated 6L MoS2 device as a function of B. designed the research project and replica van cleef and arpels necklace supervised the experiment. fabricated the devices. performed optical spectroscopy and data analysis. grew and prepared the CVD MoS2 sample. performed theoretical calculations. prepared hBN samples. performed TEM analyses. analysed the data and wrote the manuscript.
Atomically thin two dimensional semiconductors such as MoS2 hold great promise for electrical, van cleef arpels necklace knock off optical and mechanical devices and display novel physical phenomena. However, the electron mobility of mono and few layer MoS2 has so far been substantially below theoretically predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviours. Potential sources of disorder and scattering include defects such as sulphur vacancies in the MoS2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielectrics. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi terminal geometry using gate tunable graphene electrodes. Magneto transport measurements show dramatic improvements in performance, including a record high Hall mobility reaching 34,000cm2V 1s 1 for six layer MoS2 at low temperature, confirming that low temperature performance in previous studies imitation van cleef and arpels vintage alhambra necklace was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also observed Shubnikov de Haas oscillations in high mobility monolayer and few layer MoS2. Modelling of potential scattering sources and quantum lifetime analysis indicate that a combination of short range and long range interfacial scattering limits the low temperature mobility of MoS2.
a, Schematic of the hBN encapsulated MoS2 multi terminal device. The exploded view shows the individual components that constitute the heterostructure stack. Bottom: Zoom in cross sectional schematic of the metal graphene MoS2 contact region. b, Optical microscope image of a fabricated device. Graphene contact regions are outlined by dashed lines. c, Cross sectional STEM image of the fabricated device. The zoom in false colour image clearly shows the ultra sharp interfaces between different layers (graphene, 5L; MoS2, 3L; top hBN, 8nm; bottom hBN, 19nm).
a, Output curves (Ids Vds) of the hBN encapsulated 4L MoS2 device with graphene electrodes at different temperatures. Backgate voltage Vbg was maintained at 80V with a carrier density of 6.851012cm2 in MoS2. The linearity of the output curves confirms that the graphene MoS2 contact is ohmic at all temperatures. b, Resistivity of 4L MoS2 (log scale) as a function of Vbg at different temperatures. The resistivity decreases on cooling, showing metallic behaviour, reaching 130 at 12K. The colour legend is the same as in a (from 300K to 12K). c, Contact resistance RC of the same device (log scale) as a function of Vbg at different temperatures. The colour legend is the same as in a (but from 250K to 12K). Inset: RC as a function of temperature at different Vbg. At high Vbg the contact resistance decreases when decreasing the temperature.
a, Hall mobility of hBN encapsulated MoS2 devices (with different numbers of layers of MoS2) as a function of temperature. To maintain ohmic contact, a finite Vbg was applied. The measured carrier densities obtained from Hall measurements for each device are listed in Supplementary Table1. The solid fitting lines are drawn by the model described in the main text. All fitting parameters are listed in Supplementary Table1. As a visual guide, the dashed line shows the power law phT, and fitted values of for each device are listed in the inset table. b, Impurity limited mobility (imp) as a function of the MoS2 carrier density. For comparison, previously reported values from MoS2 on SiO2 substrates (refs8,46) are plotted. c e, The solid lines show the theoretically calculated long range (LR) impurity limited mobility (c), short range (SR) impurity limited mobility (d) and mobility including both LR and SR based on Matthiessen rule, 1/=1/LR+1/SR, as a function of carrier density for 1L to 6L MoS2 (e). Experimental data from 1L and 6L MoS2 are shown as circles (c e).
a, Longitudinal resistance Rxx (red curve) and Hall resistance Rxy (blue curve) of an hBN encapsulated CVD 1L MoS2 device as a function of magnetic field B measured at 0.3K and with a carrier density of 9.71012cm2. Inset: Oscillation amplitude (black curve) as a function of 1/B after subtraction of the magnetoresistance background. The quantum scattering time extracted from the fitted Dingle plot (red dashed line) is 176fs. b, Rxx (red curve) and Rxy (blue curve) of the hBN encapsulated 4L MoS2 device as a function of B. Hall measurements were conducted at 0.3K and at a carrier density of 4.91012cm2. c, Rxx (red curve) and Rxy (blue curve) of an hBN encapsulated 6L MoS2 device as a function of B. designed the research project and replica van cleef and arpels necklace supervised the experiment. fabricated the devices. performed optical spectroscopy and data analysis. grew and prepared the CVD MoS2 sample. performed theoretical calculations. prepared hBN samples. performed TEM analyses. analysed the data and wrote the manuscript.
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