Characterisation of MoS₂ FET Devices Gated Via Novel Ionic Liquids

Ionic liquids (IL), molten salts at room temperature with mobile cations and anions, have demonstrated the ability to electrostatically dope MoS2 and MoSe2 top gated field effect transistors to increase charge density, carrier mobility and even induce superconductivity [1]. Furthermore, ionic liquid gating has been demonstrated to be able to induce changes in the polymorphs of MoS2 and MoTe2 from the semiconducting 2H phase to the semi-metallic 1T’ and the metallic 1T phase [2]. When a gate voltage is applied to the ionic liquid, an electric double layer (EDL) is formed on the surface of the MoS2/MoSe2 sample as a layer of cations or anions accumulate at the sample/IL interface to create a high capacitance, highly doping the surface.

Here, the use of a novel ionic liquid N1114-TFSI as a gating dielectric on MoS2 FET devices will be discussed. N1114-TFSI has a much smaller cation compared to conventionally used DEME-TFSI and EMIM-TFSI, affecting the packing and layering of the anions and cations at the interface which could increase the amount of electrostatic doping of the MoS2 channel. Furthermore, the ability of small cations to intercalate between the layers of the MoS2 channel and the effect it has on the transport characteristics of the device will be explored.

[1] Shi, W., Ye, J., Zhang, Y., Suzuki, R., Yoshida, M., Miyazaki, J., Inoue, N., Saito, Y. and Iwasa, Y., 2015. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating. Scientific Reports, 5(1).

[2] Zakhidov, D., Rehn, D., Reed, E. and Salleo, A., 2020. Reversible Electrochemical Phase Change in Monolayer to Bulk-like MoTe2 by Ionic Liquid Gating. ACS Nano, 14(3), pp.2894-2903.