Ultrafast Growth of Large Single Crystals of Monolayer WS2 and WSe2
Zhengwei Zhang, Peng Chen, Xiangdong Yang, Yuan Liu, Huifang Ma, Jia Li, Bei Zhao, Jun Luo, Xidong Duan, Xiangfeng Duan
Natl. Sci. Rev. 7, 737-744 (2020)
Monolayer transition metal dichalcogenides (TMDs) have attracted considerable attention as atomically thin semiconductors for the ultimate transistor scaling. For practical applications in integrated electronics, large monolayer single crystals are essential for ensuring consistent electronic properties and high device yield. The TMDs available today are generally obtained by mechanical exfoliation or chemical vapor deposition (CVD) growth, and often plagued with a mixed layer thickness, a limited single crystal domain size or a very slow growth rate. Scalable and rapid growth of large single crystals of monolayer TMDs requires maximizing lateral growth rate while completely suppressing the vertical growth, which represents a fundamental synthetic challenge and has motivated considerable efforts. Herein we report a modified CVD approach with a controllable reverse flow for the rapid growth of large domain single crystals of monolayer TMDs. With the reverse flow to precisely control the chemical vapor supply in thermal CVD process, we can effectively prevent the undesired nucleation before reaching optimum growth temperature and enable rapid nucleation and growth of monolayer TMD single crystals at a high temperature that is difficult to access in a typical thermal CVD process. We show monolayer single crystals with 450 μm lateral size can be prepared in 10 s, with a highest lateral growth rate up to 45 μm/s. Electronic characterizations show the resulting monolayer WSe2 material exhibit excellent electronic properties with the carrier mobility up to 90 cm2V-1s-1, comparable to that of the best exfoliated monolayers. Our study provides a robust pathway for rapid growth of high-quality TMD single-crystals.