Growth of a Large, Single-Crystalline WS2 Monolayer for High-Performance Photodetectors by Chemical Vapor Deposition

2D WS₂ is a promising candidate for the next generation nanoelectronics, spintronics, valleytronics, and optoelectronics. However, the uncontrollably large-area growth of WS₂ nanosheets and their unsatisfactory performance of the photodetectors based on WS₂ hindered its applications. Here, we proposed a CVD method using tungstic acid as the precursors to grow WS₂ flakes. After being characterized by AFM, Raman, PL, and TEM, we found the as-grown WS₂ flakes were high-quality structures. Then the photodetectors based on the as-grown WS₂ were fabricated, which exhibited high responsivity (7.3 A W⁻¹), a fast response rate (a response time of 5 ms and a recovery time of 7 ms), prefect external quantum efficiency (EQE) (1814%), and remarkable detectivity (D*) (3.4 × 10¹² Jones). Our works provided a new CVD method to grow some high-quality WS₂ nanosheets.