Abstract
Monolayer ternary tellurides based on alloying different transition metal dichalcogenides (TMDs) can result in new two-dimensional (2D) materials ranging from semiconductors to metals and superconductors with tunable optical and electrical properties. Semiconducting WTe(2) (x) S(2(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, new strategies to efficiently tailor the valley-polarized PL from semiconducting monolayer WTe(2) (x) S(2(1-) (x) ()) at room temperature (RT) through alloying and back-gating are presented. The DVP at RT is found to increase drastically from < 5% in WS(2) to 40% in WTe(0.12) S(1.88) 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 WTe(0.12) S(1.88) via metallic 1T'-WTe(2) electrodes, where the use of 1T'-WTe(2) substantially lowers the Schottky barrier height (SBH) and weakens the Fermi-level pinning of the electrical contacts. The demonstration of drastically enhanced DVP and electrical tunability in the valley-polarized emission from 1T'-WTe(2) /WTe(0.12) S(1.88) heterostructures paves new pathways towards harnessing valley excitons in ultrathin valleytronic devices for RT applications.