Spatially composition-graded monolayer tungsten selenium telluride

Heterogeneous materials with spatially modulated bandgaps have many unique applications, such as super-broadband nanolasers, color engineered displays, hyperspectral detectors, and full spectrum solar cells. In this work, spatially composition-graded WSe2 - 2xTe2x flakes are synthesized through an in situ chemical vapor deposition method. Furthermore, a monolayer flake topography is confirmed by atomic force microscopy. Photoluminescence and Raman line-scanning characterization indicate the bandgap changes continuously from center (1.46 eV) to edge (∼1.61 eV) within a monolayer flake. Electronic devices based on this spatially composition-graded material exhibit tunable transfer curves. First principal calculation reveals that the electron affinity increases, while the bandgap decreases based on tellurium composition. This is consistent with experimentally observed non-monotonic dependence of the hole current on tellurium composition. This work provides the experimental groundwork for synthesis of the composition-graded transition metal dichalcogenide materials and offers a route toward tailoring their electrical properties by bandgap engineering in the future.