Depletion to Enhancement Mode Transition and Strongly Suppressed Hysteresis in Surface Engineered Multilayer MoS2 FETs

TL;DR

This study demonstrates that surface modification of multilayer MoS2 FETs with specific organic polymers can convert device operation from depletion to enhancement mode and significantly reduce hysteresis, improving their suitability for CMOS applications.

Contribution

The paper introduces a novel surface engineering approach using PBTTT C14 to achieve mode transition and hysteresis suppression in MoS2 FETs, a first in the field.

Findings

Depletion to enhancement mode transition achieved

Hysteresis reduced by 85%

Interfacial charge transfer confirmed as mechanism

Abstract

Two-dimensional (2D) semiconductors such as molybdenum disulfide (MoS2) have recently attracted extensive research attention due to their promising compatibility with silicon based electronics. However, several key challenges still limit their practical integration. Two of the critical issues are (1) the intrinsic depletion-mode (normally on) operation of MoS2 field-effect transistors (FETs), and (2) the large hysteresis commonly observed in the transfer characteristics of MoS2 FETs due to the inherent sulfur defects. Addressing them is essential for CMOS compatible 2D-transistor technologies. In this work, we report for the first time that surface modification of the exfoliated multilayer MoS2 FETs with PBTTT C14 (poly(2,5 bis(3 tetradecylthiophen-2-yl)thieno[3,2 b]thiophene)), a p type conjugated organic polymer, converts the device from depletion mode to enhancement mode operation while simultaneously and strongly suppressing hysteresis. Specifically, the threshold voltage (Vth) shifts from -9.6 V to +5.9 V (total shift 15.5 V), and the hysteresis window decreases from 8.8 V to 1.3 V (85% reduction). This originates from interfacial charge transfer at the MoS2/PBTTT C14 interface, enabled by favourable band alignment. To further validate this charge transfer driven mechanism, P3HT (poly(3 hexylthiophene 2,5 diyl)) with similar energy levels to PBTTT C14 was employed, and it also showed similar enhancement-mode behaviour and hysteresis suppression.