Improved Carrier Mobility in Few-Layer MoS2 Field-Effect Transistors with Ionic-Liquid Gating

TL;DR

This paper demonstrates that ionic liquid gating significantly enhances electron mobility in few-layer MoS2 FETs, achieving high ON/OFF ratios and near-ideal sub-threshold swings, due to reduced Schottky barriers and phonon limitations.

Contribution

The study introduces ionic liquid gating as a method to improve carrier mobility and device performance in few-layer MoS2 transistors, surpassing traditional back-gated devices.

Findings

Electron mobility exceeds 60 cm2V-1s-1 at 250 K in IL-gated devices.

Mobility increases from 100 to 220 cm2V-1s-1 as temperature decreases from 180 K to 77 K.

Devices exhibit high ON/OFF ratios (>10^7) and near-ideal sub-threshold swing (~50 mV/dec).

Abstract

We report the fabrication of ionic liquid (IL) gated field-effect transistors (FETs) consisting of bilayer and few-layer MoS2. Our transport measurements indicate that the electron mobility about 60 cm2V-1s-1 at 250 K in ionic liquid gated devices exceeds significantly that of comparable back-gated devices. IL-FETs display a mobility increase from about 100 cm2V-1s-1 at 180 K to about 220 cm2V-1s-1 at 77 K in good agreement with the true channel mobility determined from four-terminal measurements, ambipolar behavior with a high ON/OFF ratio >107 (104) for electrons (holes), and a near ideal sub-threshold swing of about 50 mV/dec at 250 K. We attribute the observed performance enhancement, specifically the increased carrier mobility that is limited by phonons, to the reduction of the Schottky barrier at the source and drain electrode by band bending caused by the ultrathin ionic-liquid dielectric layer.