Uncovering the Effects of Metal Contacts on Monolayer MoS.

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 grown by chemical vapor deposition. We evaporate thin metal films onto MoS 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 type (>2 × 10 cm) without degrading its mobility, (2) Ag, Au, and Ni deposition causes varying levels of damage to MoS (e.g. broadening Raman E' peak from <3 to >6 cm), and (3) Ti, Sc, and Y react with MoS. Reactive metals must be avoided in contacts to monolayer MoS, 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, as confirmed by X-ray diffraction. These are important findings for metal contacts to MoS and broadly applicable to many other 2D semiconductors.