Influence of Ar ion beam on WSe2 and resulting contact interfaces in 2D field-effect transistors

Semiconducting two-dimensional materials, such as the transition metal dichalcogenides (TMDs), are atomically thin with desirable bandgaps that make them highly applicable for aggressively scaled transistors. However, it has proven challenging to achieve reproducible, high-quality metal-semiconductor contact interfaces to TMDs. Past work has employed intentional TMD crystal damage prior to contact metallization to improve the metal-semiconductor interface, but such an approach has not been studied for tungsten-based TMDs (W-TMDs), which are resistant to most standard etching techniques. In this study, we use an Ar ion beam to parametrically investigate the etching effect of ion energy and exposure time on mechanically exfoliated WSe2. Results indicate that 300 eV Ar ion bombardment provides sufficient energy to modify WSe2 without complete destruction of the crystal lattice, supported by atomic force microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. This Ar ion beam exposure is then applied to modify the contact region of WSe2 field-effect transistors via exposure immediately prior to in situ metal deposition. Compared to the unexposed devices, the devices with contact regions exposed to the ion beam demonstrate a minor reduction in device on-current; however, a 3 s ion beam exposure reveals a surprising improvement in standard deviation of on-current across a set of devices from 5.42 down to 0.77 μA/μm. This study provides a basis for future W-TMD processing and a potential route for improving TMD field-effect transistor variability through contact region modifications.