Synthesis of Wafer-Scale Monolayer WS Crystals toward the Application in Integrated Electronic Devices.

Two-dimensional transition-metal dichalcogenides (TMDCs) possess unique electronic and optical properties, which open up a new opportunity for atomically thin optoelectronic devices. Synthesizing large-scale monolayer TMDCs on the SiO/Si substrate is crucial for practical applications, however, it remains a big challenge. In this work, a method which combines chemical vapor deposition (CVD) and thermal evaporation was employed to grow monolayer tungsten disulfide (WS) crystals. Through controlling the density and the distribution of W precursors, a wafer-scale continuous uniform WS film was achieved, with the structural and spectral characterizations confirming a monolayer configuration and a high crystalline quality. Wafer-scale field-effect transistor arrays based on the monolayer WS were fabricated. The devices show superior electrical performances, and the maximal mobility is almost 1 order of magnitude higher than those of CVD-grown large-scale TMDC devices reported so far.