Epitaxial Growth of Stacking Faults-Free Bilayer MoS₂

Atomically thin and dangling bond-free 2D transition metal dichalcogenides (TMDs) have emerged as promising post-silicon channel materials. Notably, the bilayer MoS₂ exhibits narrower band gaps and enhanced carrier mobility compared to the monolayer, attributed to a higher carrier concentration. However, the minimal formation energy differences between the 2H and 3R stacking configurations in bilayers result in non-uniform phases of bilayer MoS₂. Such non-uniform phases can introduce carrier scattering at grain boundaries and alter band structure conjugation, which consequently reduces mobility and decreases the on/off ratio. In this study, Our team report the synthesis of a centimeter-scale uniform 2H-stacked bilayer MoS₂ film by controlling the grain edge configuration of the second layer. Unlike the conventional triangular shape, we successfully achieved the growth of a hexagonal-shaped second layer with repeated S-zigzag and Mo-zigzag edge constructs, where a double bond S-passivated Mo edge configuration simultaneously appears in both the first and second layers an observation not previously documented. This unique edge interaction between the first and second layers supports a more stable growth model, thereby promoting the 2H stacking order during the layer-by-layer epitaxial growth process. previously known 3R phase single-crystal films consist of mixed AB and BA stacking orders, with each exhibiting opposing out-of-plane polarities. Due to the low activation energy for phase transition between the AB and BA stacking modes, switching can occur at the boundary when a gate voltage is applied, leading to hysteresis. However, the uniform 2H-stacked bilayer MoS₂ minimizes hysteresis due to the absence of polarization within the film, thus enabling the fabrication of high-performance field-effect transistor (FET) devices. Optical and TEM analyses confirm that the synthesized film exclusively comprises the 2H stacking phase, devoid of stacking faults. This approach offers a promising strategy for controlling the stacking order of other TMD materials.