Vapor-Liquid-Solid Growth of Morphology-Tailorable WS toward P-Type Monolayer Field-Effect Transistors.

Although substantial efforts have been made, controllable synthesis of p-type WS remains a challenge. In this work, we employ NaCl as a seeding promoter to realize vapor-liquid-solid (VLS) growth of p-type WS. Morphological evolution, including a one-dimensional (1D) nanowire to two-dimensional (2D) planar domain and 2D shape transition of WS domains, can be well-controlled by the growth temperature and sulfur introduction time. A high growth temperature is required to enable planar growth of 2D WS, and a sulfur-rich environment is found to facilitate the growth of high-quality WS. Raman and photoluminescence (PL) mappings demonstrate uniform crystallinity and high quantum efficiency of VLS-grown WS. Moreover, monolayer WS-based field-effect transistors (FETs) are fabricated, showing p-type conducting behavior, which is different from previous reported n-type FETs from WS grown by other methods. First-principles calculations show that the p-type behavior originates from the substitution of Na at the W site, which will form an additional acceptor level above the valence band maximum (VBM). This facile VLS growth method opens the avenue to realize the p-n WS homojunctions and p/n-WS-based heterojunctions for monolayer wearable electronic, photonic, optoelectronic, and biosensing devices and should also be a great benefit to the development of 2D complementary metal-oxide-semiconductor (CMOS) circuit applications.