Cooling-mediated One-step Synthesis of Monolayer WSe₂/WSe_2xTe_2-2x Lateral Heterostructures for High-Performance Spectral Photodetectors

Tellurium (Te) based transition metal dichalcogenides (TMDCs), especially tungsten ditelluride (WTe₂), have attracted intensively owing to their unique electrical and optical properties. However, the ternary alloy tungsten selenium telluride (WSe_2xTe_2-2x) and its lateral hetero-structure with other TMDCs remains largely unexplored due to the considerable challenge in synthesizing these materials, since WTe₂ has very weak bonding and tends to decompose at high reaction temperature. Here, we demonstrate a successful one-step synthesis of monolayer WSe₂/WSe_2xTe_2-2x lateral hetero-structures via cooling-mediated chemical vapor deposition. We find that the cooling rate and flow ratio between argon and hydrogen gas are crucial factors for the morphology. The Te incorporation in the alloy is studied by aberration-corrected scanning transmission electron microscopy. The correlation between Te composition and the bandgap of the alloy is simulated by density functional theory. Furthermore, through the study of the optical and electrical properties, we demonstrate the possibility of high-performance spectral photodetectors with spatially graded bandgap.