Controllable Growth of Monolayer and Bilayer WSe by Liquid-Phase Precursor via Chemical Vapor Deposition for Photodetection.

Two-dimensional WSe nanosheets have received increasing attention due to their excellent optoelectronic properties. Solid precursors, such as WO and Se powders, have been extensively employed to grow WSe nanosheets by the chemical vapor deposition (CVD) method. However, the high melting point of WO results in heterogeneous nucleation sites and nonuniform growth of the WSe nanosheet. By dissolving WO powder in a NaOH solution, we report a facile and uniform growth of monolayer and bilayer WSe nanosheets on a SiO/Si substrate at a large scale using liquid precursor by the CVD method. The size and thickness of the WSe nanosheets were controlled by modulating the precursor concentration and growth temperature. The as-prepared monolayer and bilayer WSe nanosheets were well characterized by optical microscopy, atomic force microscopy, and Raman and photoluminescence spectroscopy. With the increase in precursor concentration, the size of the monolayer WSe increased up to 120 μm. Bilayer WSe nanosheets were grown at higher temperatures. The photosensitivity of the bilayer WSe was one order of magnitude higher than that of the monolayer WSe. The carrier mobility, specific detectivity, photoresponsivity, and external quantum efficiency of the bilayer WSe were about two orders of magnitude higher than those of the monolayer WSe. Our method opens up a new avenue to grow monolayer and bilayer WSe for optoelectronic applications.