Role of Surface Processes in Growth of Monolayer MoS2: Implications for Field-Effect Transistors

A predictive approach to grain size control from 10 nm to 100 mu m is demonstrated in chemical vapor deposited MoS2 monolayers. Such control is critical to enabling consistent 2D electronics. Physico-chemical modeling involving adsorption-diffusion- growth-desorption equilibrium has been used to correlate this variation to the change in supersaturation and kinetics on the growth surface. The intentional addition of reaction products to the source chemistry shows that nucleation density (and hence final grain size) is very sensitive to supersaturation in the very initial stage of growth. The steady-state nucleation and edge growth rates are diffusion-controlled by a <1 eV barrier. The different dependencies of the nucleation rate and edge growth rate on surface kinetics and supersaturation have been exploited to reduce nucleation density from 10(7) to 10(3) cm(-2) while simultaneously increasing edge growth rates to as large as 3.3 mu m/s. Rapid coverage, <1 min, over large areas by monolayers with 100 mu m grain sizes is hence obtained. The microstructural improvement is shown to help increase field-effect electronic mobility from 0.1 to 17 cm(2)/V s.