Controllable Growth of Monolayer and Bilayer WSe2 by Liquid-Phase Precursor via Chemical Vapor Deposition for Photodetection

Two-dimensional WSe2 nanosheets have received increasing attention due to their excellent optoelectronic properties. Solid precursors, such as WO3 and Se powders, have been extensively employed to grow WSe2 nanosheets by the chemical vapor deposition (CVD) method. However, the high melting point of WO3 results in heterogeneous nucleation sites and nonuniform growth of the WSe2 nanosheet. By dissolving WO3 powder in a NaOH solution, we report a facile and uniform growth of monolayer and bilayer WSe2 nanosheets on a SiO2/Si substrate at a large scale using liquid precursor by the CVD method. The size and thickness of the WSe2 nanosheets were controlled by modulating the precursor concentration and growth temperature. The as-prepared monolayer and bilayer WSe2 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 WSe2 increased up to 120 μm. Bilayer WSe2 nanosheets were grown at higher temperatures. The photosensitivity of the bilayer WSe2 was one order of magnitude higher than that of the monolayer WSe2. The carrier mobility, specific detectivity, photoresponsivity, and external quantum efficiency of the bilayer WSe2 were about two orders of magnitude higher than those of the monolayer WSe2. Our method opens up a new avenue to grow monolayer and bilayer WSe2 for optoelectronic applications.