Mechanisms of Controllable Growth and Ohmic Contact of Two-Dimensional Molybdenum Disulfide: Insight from Atomistic Simulations

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), in particular molybdenum disulfide (MoS₂), have recently attracted huge interest due to their proper bandgap, high mobility at 2D limit, and easy-to-integrate planar structure, which are very promising for extending Moore’s law in postsilicon electronics technology. Great effort has been devoted toward such a goal since the demonstration of protype MoS₂ devices with high room-temperature on/off current ratios, ultralow standby power consumption, and atomic level scaling capacity down to sub-1-nm technology node. However, there are still several key challenges that need to be addressed prior to the real application of MoS₂-based electronics technology. The controllable growth of wafer-scale single-crystal MoS₂ on industry-compatible insulating substrates is the prerequisite of application while the currently synthesized MoS₂ films mostly are polycrystalline with limited sizes of single-crystal domains and may involve metal substrates. The precise layer-control is also very important for MoS₂ growth since its electronic properties are layer-dependent, whereas the layer-by-layer growth of multilayer MoS₂ dominated by the van der Waals (vdW) epitaxy leads to poor thickness uniformity and noncontinuously distributed domains. High density up to 10¹³ cm^–2 of sulfur vacancies (SVs) in grown MoS₂ can cause unfavorable carrier scatting and electronic properties variations and will inevitably disturb the device performance. The dangling-bond-free surface of MoS₂ gives rise to an inherent vdW gap at metal–semiconductor (M–S) contact, which leads to high electrical resistance and poor current-delivery capability at the contact interface and thereby substantially limits the performances of MoS₂ devices.