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Ankur Goswami1 Ryan McGee1 Soupitak Pal2 Syed Asad Manzoor Bukhari1 Thomas Thundat1

1, University of Alberta, Edmonton, Alberta, Canada
2, University of California Santa Barbara, Santa Barbara, California, United States

Molybdenum disulphide (MoS2) is one of the more promising channel materials for field effect transistor devices and have recently been investigated due to its high current density, excellent electrostatic integrity, large on/off ratio (>108), high carrier mobilities, and good electrical conductivity (~0.03 Ω-1 cm-1) when used as a monolayer (0.65 nm). However, depositing a large uniform area of MoS2 remains challenging, and most of the above properties deteriorate when layer thickness increases more than 2 to 3 layers. Here we show, despite higher thickness (20 nm), uniformly deposited PLD grown MoS2 can show significantly high mobilities as a result of the substrate choice. Boron doped p-type (<100>), phosphorous doped n-type (<100>), polysilicon, sapphire (c-axis oriented), and Si/SiN (polycrystalline) are chosen as model substrates to study the carrier mobilities of MoS2 films influenced by substrate selection. We observe MoS2 grown on all type of silicon substrates show significantly higher mobilities (3 to 7.5×103 cm2/V.s) than grown on the insulating substrates where mobilities are in the range of 5 to 50 cm2/V.s at 300 K. Cross sectional transmission electron microscopy (TEM) reveals that due to the formation of out of plane twin boundary at the MoS2-silicon interface the mobility of MoS2 significantly increases as twin boundaries are the weak scattering centers of the charge carriers. Reduced mobility of MoS2 on insulating substrates (sapphire and Si/SiN) is due to the formation of layer growth morphology where dislocation and stacking faults are prevalent. These defects are the coulomb scattering centers of the carrier pathways which majorly affects the mobility of the carriers1. We believe this important result has a rich implication towards MoS2 based electronic devices for future applications2.

References
Goswami et.al., “Effect of interface on mid-infrared photothermal response of MoS2 thin film grown by pulsed laser deposition” Nano Research, 10 (10) (2017), 3571-3584.

Liu et.al., “Direct-current triboelectricity generation by sliding-Schottky nanocontact on MoS2 multilayers” , Nature Nanotechnology, 2017 (in press)

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