Contact Resistance Reduction of MoS₂-Based Field Effect Transistor Using Semimetallic TiS₂ Contact Layer Deposited By Atomic Layer Deposition

Abstract

Recently, two-dimensional transition metal dichalcogenides (2D TMDCs) have been researched as promising channel materials for filed effect transistors (FETs) owing to their high mobility at atomic-level thickness. As miniaturization and high performance of the electronic devices are required, however, high contact resistance at the interface between the metal electrode and 2D TMDC channel has become a major challenge. 1 The high contact resistance at the metal-semiconductor interface originates from the uncontrollable high Schottky barrier height (SBH). Due to Fermi-level pinning induced by metal-induced gap state (MIGS) and defect-induced gap state (DIGS), the barrier height cannot be controlled by conventional Schottky-Mott rule, regardless of metal work function. Since MIGS occurs due to perturbation of metal wave function into the semiconductor, inserting semimetallic material as contact layer can be a solution to suppress the MIGS and further reduce the contact resistance. 2 In this study, ALD TiS 2 was used as semimetallic contact layer between the MoS 2 channel and Ti/Au electrode for MoS 2 -based TFT. With the TiS 2 contact layer, we could observe improvements in overall device performances, which is attributed to the semimetallic nature of TiS 2 . In addition, low temperature ALD TiS 2 process contributed to the clean interface with vdW bonding between MoS 2 and TiS 2 , resulting in suppression of DIGS, as well as MIGS. Owing to the ALD TiS 2 contact, we could mitigate FLP and achieve metal-semiconductor interface with low Schottky barrier height, resulting in low contact resistance. References 1 K. Schauble et al. , “Uncovering the effects of metal contacts on monolayer MoS2,” ACS Nano , vol. 14, no. 11, pp. 14798–14808, 2020, doi: 10.1021/acsnano.0c03515. 2 P. C. Shen et al. , “Ultralow contact resistance between semimetal and monolayer semiconductors,” Nature , vol. 593, no. 7858, pp. 211–217, 2021, doi: 10.1038/s41586-021-03472-9.