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.