Role of Hydrogen in Suppressing Secondary Nucleation in Chemical Vapor-Deposited MoS2

We investigate the ability of different carrier gases to control defects and secondary nucleation in atmospheric pressure chemical vapor deposition (APCVD) growth of MoS2 on Si/SiO2 substrates. We observe that a reducing environment using H2 gas is more favorable for achieving uniform two-dimensional (2D) growth. Compared to the growth in an inert environment, secondary nucleation on primary MoS2 domains grown using H2 as the carrier gas (H-MoS2) is drastically reduced. We employ a phase-field model to understand the role of enhanced surface diffusion in H-MoS2, due to passivation of defects and dangling bonds, promoting compact secondary domain formation as opposed to dendritic secondary domains under an inert environment. Using X-ray photoelectron spectroscopy, we show that the Mo(VI) oxidation state (corresponding to MoO3), which is prominent for MoS2 grown under an inert atmosphere, is highly suppressed in H-MoS2, leading to more pristine MoS2. This explains the superior electrical performance of H-MoS2 compared to those grown with other carrier gases. Our results offer a facile route to explore different growth environments to realize large-area true 2D films.