CMOS Inverters and P-N Junction Diodes Based on Transition Metal Dichalcogenide Monolayers

The atomically thickness and emerging large bandgap of two dimensional transition metal dichalcogenides (TMDCs) offer a high degree of electrostatic control than those of bulk forms, which provide potential applications to electronics and optoelectronics. Recent progresses of exfoliated-TMDC-based n-type or p-type transistors allow widespread device applications such as circuits, diodes and sensors [1]. However, limited sample size and efficient carrier doping system are still remained, which consequently hamper the practical utility of TMDCs for complementary devices. Towards further advances, establishing scalable preparation techniques of various TMDCs and controlling their electronic properties are highly required. One of the most powerful methods to modulate the carrier density of semiconductors is electrostatic doping by using electrolyte to form electric double layer [2]. The huge specific capacitance of electric double layer transistors (EDLTs) enables the strong depletion of donor carriers and the continuous band filling, resulting in tuning material polarities.

In this study, we fabricated ion-gel-gated EDLTs using large-area TMDC monolayers, MoS₂, MoSe₂ and WSe₂, grown by chemical vapor deposition [3-6]. The Fermi level of TMDCs can be continuously shifted by applying gate voltage, and we can induce both hole and electron transport in these devices. The hole mobility of WSe₂ can be enhanced up to 90 cm²/Vs at high carrier density of 10¹⁴ cm^-2, whereas the MoS₂ showed electron mobility of 60 cm²/Vs. By combining MoS₂ and WSe₂, we demonstrated complementary logic inverters, which yielded extremely high voltage gain of 110 that is the highest value in atomically thin 2D materials. We also introduce unique techniques to form stable pn junctions in ambipolar TMDC EDLTs and investigate its optoelectronic properties.

[1] Q. H. Wang, et al., Nat. Nanotechnol. 7, 699 (2012).  

[2] J. T. Ye, et al., Science. 338, 1193 (2012).

[3] J. Pu, L.-J. Li, T. Takenobu, et al., Nano Lett. 12, 4013 (2012).

[4] J.-K. Huang, T. Takenobu, L.-J. Li, et al., ACS Nano. 8, 923 (2014).

[5] J. Pu, L.-J. Li, T. Takenobu, et al., Appl. Phys. Lett., 103, 23505 (2013).

[6] J. Pu, L.-J. Li and T. Takenobu, Phys. Chem. Chem. Phys., 10.1039/C3CP55270E (2014).