Synthesis of 2D MoS_2(1-Se₂ semiconductor alloy by chemical vapor deposition

Alloying/doping in two-dimensional (2D) materials is emerging as an increasingly important strategy due to the wide-range bandgap tunability and versatility of these materials. Monolayer 2D transition metal dichalcogenide (TMD) alloy has been investigated both theoretically and experimentally in recent years. Here, we synthesized a bilayer MoS_2(1-Se₂ semiconductor alloy via the chemical-vapor deposition technique. The as-grown triangular MoS_2(1-Se₂ flakes with size of roughly 10 μm were observed by optical microscope and scanning electron microscope (SEM). The 1.4-1.9 nm thickness of the samples, as measured by AFM, means that bilayer MoS_2(1-Se₂ alloys were grown. The characteristic Raman modes related to Mo-S and Mo-Se vibrations were observed in the Raman spectrum. Two emission peaks were respectively found, corresponding to the A and B excitons in the photoluminescence (PL) spectrum. XPS measurements confirmed the Se doping of the alloy. The first-principles calculation results show a contraction of the band gap value with the increase of Se doping in the MoS₂ lattice. Compared with monolayer MoS_2(1-Se₂ alloy, the band bending effect is more obvious, and the bilayer MoS_2(1-Se₂ alloy still shows the direct band gap luminescence characteristic, which has certain guiding significance for the growth of two-dimensional materials and for device preparation.