Controllable CVD Growth of Monolayered WS2 From Triangular Flakes toward Wafer-Scale Thin Film by Precise Design of Growth Environment

Here, a large-area monolayered WS₂ thin film is synthesized via near atmospheric pressure chemical vapor deposition, and the effects of different parameter adjustments on the growth of the monolayered WS₂ thin films are discussed. Unlike previous studies, which focused on the growth of WS₂ flakes, the current study investigated the effect of two experimental configurations, face-up and face-down, on the growth of the WS₂ from triangular flakes into large-area and high-coverage wafer-scale thin films. A series of Ar/H₂ gas ratio parameters for the monolayered WS₂ growth and the effect of H₂ addition are discussed when the configuration is face-up. The following face-down method is the key strategy for the large-area growth of monolayered WS₂ films. A large-area monolayered WS₂ synthesis is successfully realized on half of a two-inch sapphire substrate by adjusting parameters such as temperature, pressure, carrier gas, and gas flow rate. Finally, a large-area monolayered WS₂ film is used as the channel material to fabricate back-gate field-effect transistor arrays, with which I_on/I_off ratios of 10⁵ to 10⁶ and the highest carrier mobility of 0.84 cm²V⁻¹S⁻¹ can be achieved.