Electrical characterization of back-gated bi-layer MoS2 field-effect transistors and the effect of ambient on their performances
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(Color online) (a) Optical image of a bi-layer MoS2 exfoliated on Si/SiO2 substrate. (b) AFM image of a bi-layer MoS2. (Inset) Cross-sectional profile along the white line showing the height of ∼1.4 nm. (c) Ids-Vbg curve for a back-gated bi-layer MoS2 FET (Vds = 100 mV). (Inset) AFM image of the device. (d) From bottom to top, Ids-Vds characteristics of the same device in (c) for Vbg = 0–40 V in steps of 10 V. (c) and (d) are measured at room temperature after vacuum annealing.
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(Color online) (a) Double sweep Ids-Vbg characteristics of the bi-layer MoS2 FET in Fig. 1, probed in air (square), in vacuum (circle), and after 350 K vacuum annealing for 24 h (350 K VA) (triangle). Vds = 100 mV for all cases. (Inset) Ids-Vds characteristics for the three cases at Vbg = 40 V. (b) The XPS of MoS2 in the O 1 s region after exposure in air and after 350 K vacuum annealing for 24 h (symbols). The solid lines are Lorentzian fittings with peak values at 531.7 eV and 532.2 eV, respectively. Inset shows typical Mo 3 d doublet in MoS2. There is no obvious difference in Mo 3 d peaks for the two samples. (c) Ids-Vbg characteristics of the bi-layer MoS2 FET under O2 pressure of 1 Torr (circle), 10 Torr (triangles pointing up), and 150 Torr (triangles pointing down) and after 350 K vacuum annealing (square). Vds = 100 mV for all cases. (Inset) From left to right, on-state current at Vds = 100 mV and Vbg = 40 V after vacuum annealing, under O2 pressure of 1 Torr, 10 Torr, 150 Torr and after vacuum annealing following exposure in O2, showing that the conductance can be recovered after exposure to oxygen. (d) On-state current (solid triangle, left axis) at Vds = 100 mV and Vbg = 40 V and extrinsic field-effect mobility (open triangle, right axis) versus O2 pressure for the bi-layer MoS2 FET. The red dashed line shows extrinsic mobility of the same device in air.
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(Color online) (a) From bottom to top, Ids-Vbg characteristics of the bi-layer MoS2 device taken at Vds = 1 V at 30 K, 120 K, 210 K, and 300 K. (b) From bottom to top, Ids-Vds curves taken at Vbg = 40 V at 30 K, 120 K, 210 K, and 300 K. The low bias region becomes non-linear at low temperatures, indicating a positive Schottky barrier. (c) A set of Arrhenius plots for electron transport at Vbg = 40 V under different Vds. Thesolid lines at high temperatures are exponential fittings to extract the Schottky barrier. (d) Plot of the Schottky barrier height for electron as the function of the square root of Vds. The barrier height in the absence of thefield is extrapolated to be 65 meV.
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