ALD-grown semimetallic TiSx for hole injection into monolayer WSe2

Abstract

Semimetal contacts have recently emerged as promising due to the remarkably low contact resistance of Bi and Sb to n-channel field effect transistors (FETs) prepared from two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductors. However, hole injection in 2D semiconductors remains a bottleneck, hindering application of 2D devices in advanced logic nodes. In this study, we investigate the use of atomic layer deposition (ALD) to fabricate high work function semimetallic TiS_x interlayers for efficient hole injection into WSe₂, a 2D semiconductor of considerable interest due to its potential for next-generation scaled electronics. By employing ALD-grown semimetallic TiS_x combined with capping the device with MoO_x, we achieved a hole current of ∼64 µA µm⁻¹ at V_D = −1 V, a contact resistance of 10 ± 3 kΩ µm, and an I_ON/I_OFF ratio exceeding 10⁶ at room temperature. Hole injection may be favored because of a high work function and low density of states at the Fermi level of TiS_x, promoting a low Schottky barrier to the valence band of WSe₂, and by the van der Waals nature of the contacts. Performance is further aided by channel doping by MoO_x.