Alternative channel materials for future ultra-scaled electronic devices have been intensively pursued nowadays since the feature size of silicon-based transistors has been scaled down to their physical limit. Atomically-thin semiconducting transitional metal dichalcogenides (TMDCs) including WS₂, MoS₂, WSe₂, MoSe₂, e. have shown a lot of unique properties compared to their bulk crystals, such as indirect-to-direct bandgap transitions, strong spin-orbit coupling and valley polarization. In particular, monolayer WS₂ has shown the highest theoretical room temperature electron mobility among other semiconducting TMDCs as a result of its low effective mass. Combined with the large exciton/trion binding energy with high photoluminescence quantum yield, monolayer WS₂ is a strong candidate as a potential channel material for high-efficiency optoelectronic applications.

However, it is still challenging to grow wafer-sized, highly uniform and strictly monolayer TMDCs continuous film through the conventional chemical vapor deposition (CVD) due to the uncontrollable growth kinetics. The evaporation rates and amounts of the heated precursors are uncontrollable because the saturation vapor pressure of the precursor is exponentially dependent on the temperature inside the furnace. The sulfurized film is thus consisted of a mixture of monolayer, bilayer and multiple layers of TMDCs. The film with such unreproducible quality is not applicable for real industrial applications.

In this work, we provide a self-limiting growth strategy based on modified CVD process to prepare the wafer-sized monolayer TMDCs. Theoretical simulations were performed to understand the fundamental thermodynamically mechanism of the strictly monolayer growth. The property-variation in TMDCs due to difference in electronic structure between different layers of TMDCs can be significantly reduced based on this new approach. The following figure indicates that the PL spectra detected from different spots (spot 1 to 5) of the WS₂ film. All spectra measured from the 4'' wafer-sized sample show characteristics unique to monolayer WS₂. This poses a reliable route for the growth of large-area monolayer TMDCs, which is essential for their reliable and robust applications in nanoelectronic devices.