Exploring mechanism of defect engineering and metal-insulator transition in MoS2 field effect transistors
Hao Wei Tu1*, Jian-Jhong Lai1, Ji-Chang Luo1, Chin-Lung Lin1, Geng-Li Lin1, Wen-Bin Jian1
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
* Presenter:Hao Wei Tu, email:tuhw0.ep05g@g2.nctu.edu.tw
The graphene devices1 of fabrication technology is widely employed in emergent two-dimensional (2D) semiconducting materials to make field effect transistors (FETs). According to neoteric reports, graphene is not suitable for making FET devices cause it doesn’t possess any band gaps. In comparison, the single-layer MoS2 exhibits a direct band gap of ~1.9 eV and an on/off ratio of up to 106 in recent reports, indicating a potential candidate for applications on optical or logical electronic devices in the future2.
In our research, we employ mechanical exfoliation to transfer few-layer thick MoS2 flakes on SiO2/Si substrates. The Au electrode is followed by a standard electron-beam patterning and thermal evaporation on MoS2. The as-made MoS2 FETs show an on/off ratio in the range between 106 and 108 and the highest current density of ~10 μA/μm at room temperature of the electrical characteristic. The mobility shows the range from 20 to 60 cm2V-1s-1 at temperatures ranging from 80 to 300 K. It is interesting that the MoS2 FET devices can be categorized into two distinct groups. One group of MoS2 FET devices exhibit a high mobility at room temperature, accompanied with an increased mobility with decreased temperature and the other group of MoS2 FET devices exhibit a low mobility at room temperature accompanying with a decreasing mobility with a decrease of temperature.
The two different temperature behaviors of mobility indicate different disorder characteristic in low- and high-mobility MoS2 FET devices3. The difference between this two group shows the metal-insulator transition in low disorder group. In the low disorder MoS2 FET devices, the phonon scattering dominates while, in the high disorder devices, the impurity scattering dominates in electron transport and the defects of devices which can identify by HRTEM. On the other hand, The Mott’s 2D variable range hopping transport can well-described temperature behaviors of conductance4. We can successes estimate the disorder parameter T0 of all devices and find that the room-temperature mobility of MoS2 FET devices decrease with increasing T0 parameter by a fitting curve. It indicates a strong dependency between the mobility and the disorder effect in MoS2.


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2. Desai, S. B.; Madhvapathy, S. R.; Sachid, A. B.; Llinas, J. P.; Wang, Q.; Ahn, G. H.; Pitner, G.; Kim, M. J.; Bokor, J.; Hu, C., MoS2 transistors with 1-nanometer gate lengths. Science 2016, 354 (6308), 99-102.
3. Radisavljevic, B.; Radenovic, A.; Brivio, J.; Giacometti, i. V.; Kis, A., Single-layer MoS 2 transistors. Nature Nanotechnology 2011, 6 (3), 147.
4. Mott, N., Metal-insulator transition. Reviews of Modern Physics 1968, 40 (4), 677.

Keywords: MoS2, 2D material, MIT, high mobility, low disorder