Uncovering the Effects of Metal Contacts on Monolayer MoS₂

Abstract

Metal contacts are a key limiter to the electronic performance of two-dimensional (2D) semiconductor devices. Here we present a comprehensive study of contact interfaces between seven metals (Y, Sc, Ag, Al, Ti, Au, Ni, with work functions from 3.1 to 5.2 eV) and monolayer MoS 2 grown by chemical vapor deposition. We evaporate thin metal films onto MoS 2 and study the interfaces by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and electrical characterization. We uncover that, 1) ultrathin oxidized Al dopes MoS 2 ntype (>2×10 12 cm -2 ) without degrading its mobility, 2) Ag, Au, and Ni deposition causes varying levels of damage to MoS 2 (broadening Raman E' peak from <3 cm -1 to >6 cm -1 ), and 3) Ti, Sc, and Y react with MoS 2 . Reactive metals must be avoided in contacts to monolayer MoS 2 , but control studies reveal the reaction is mostly limited to the top layer of multilayer films. Finally, we find that 4) thin metals do not significantly strain MoS 2 , as confirmed by X-ray diffraction. These are important findings for metal contacts to MoS 2 , and broadly applicable to many other 2D semiconductors.

High-specific-power flexible transition metal dichalcogenide solar cells

“…We find that replacing Au with lower work function metals such as Ti and Al leads to a lower performance, most probably due to their reactive nature therefore forming poor interfaces with WSe 2 (Supplementary Fig. 2 ) 52 . On the other hand, layered materials Gr and WSe 2 experience no Fermi-level pinning at their vdW interface 32 – 34 .…”

Structurally Driven Environmental Degradation of Friction in MoS2 Films

“…Traditional X-ray diffraction (XRD) as well as the more surface sensitive grazing incidence techniques have been used to measure lamellae size in MoS 2 powder samples and thin films, but are not suited to the assessment of lateral dimensions of MoS 2 flakes, since calculated lamellae sizes are more representative of the thickness of the lamellar structure [66][67][68]. Raman spectroscopy has been used recently to assess defect density as well as lamellae size in MoS 2 [68][69][70], but again with limited depth-resolution.…”

Extremely anisotropic van der Waals thermal conductors

“…2b (solid lines) to determine κ ⊥ of r-MoS 2 alone, regardless of the quality and chemical nature of the top and bottom interfaces (see Methods and Extended Data Fig. 3d), which can potentially be altered by metal deposition 24,25 . We measure κ ⊥ = 57 ± 3 mW m −1 K −1 for r-MoS 2 and κ ⊥ = 41 ± 3 mW m −1 K −1 for r-WS 2 , which are similar to the lowest value ever observed in a fully dense solid 15 and comparable to the thermal conductivity of ambient air (~26 mW m −1 K −1 ).…”