Dramatically Enhanced Valley-Polarized Emission by Alloying and Electrical Tuning of Monolayer WTe_2xS_2(1-x) Alloys at Room Temperature with 1T′-WTe₂-Contact

Abstract

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 WTe_2xS_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, we present new strategies to efficiently tailor the valley-polarized PL from semiconducting monolayer WTe_2xS_2(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 WTe_0.12S_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_0.12S_1.88 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/WTe_0.12S_1.88 heterostructures paves new pathways towards harnessing valley excitons in ultrathin valleytronic devices for RT applications.