Monolayer ternary
tellurides based on alloying different two-dimensional (2D) transition
metal
dichalcogenides (TMDs) can result in new 2D materials ranging
from semiconductors
to metals and superconductors with tunable optical and electrical
properties. Semiconducting
WTe2xS2(1-x)
monolayer possesses two inequivalent valleys in the Brillouin zone,
each valley
coupling selectively with circularly polarized light (CPL). The degree
of
valley polarization (DVP) under the excitation of CPL represents the
purity of
valley polarized photoluminescence (PL), a critical parameter for
opto-valleytronic
applications. Here, we present
new strategies to efficiently tailor the valley-polarized PL from
semiconducting
monolayer WTe2xS2(1-x) at room temperature (RT) through alloying
and back-gating.
The DVP at RT is found to increase drastically from < 5% in WS2
to
40% in WTe0.12S1.88 by Te-alloying to enhance the spin-orbit coupling.
Further
enhancement and control of the DVP from 40% up to 75% is demonstrated
by
electrostatically doping the monolayer WTe0.12S1.88
via metallic 1T′-WTe2
electrodes, where the use of 1T′-WTe2 substantially lowers
the Schottky barrier height (SBH)
and
weakens the Fermi-level pinning of the electrical contacts. Our demonstration of drastically
enhanced DVP and electrical tunability in the valley-polarized emission
from 1T′-WTe2/WTe0.12S1.88
heterostructures paves new pathways towards harnessing valley
excitons
in ultrathin valleytronic devices for RT applications.