  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 MoS2 grown by chemical
vapor deposition. We evaporate thin metal films onto MoS2 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 MoS2 n-type (> 2x10^12 1/cm^2)
without degrading its mobility, 2) Ag, Au, and Ni deposition causes varying
levels of damage to MoS2 (broadening Raman E' peak from <3 1/cm to >6 1/cm),
and 3) Ti, Sc, and Y react with MoS2. Reactive metals must be avoided in
contacts to monolayer MoS2, 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 MoS2, as confirmed by X-ray diffraction.
These are important findings for metal contacts to MoS2, and broadly applicable
to many other 2D semiconductors.
