Fundamental limitation of van der Waals homoepitaxy by stacking fault formation in WSe2 (original) (raw)

As interest in layered van der Waals (vdW) materials keeps increasing, fundamental knowledge about their synthesis is gaining more and more value. The defect-free heteroepitaxial integration of vdW materials on large-area substrates is currently thoroughly being researched since it might encompass a successful transition of these materials to industrial applications. To date, Transition Metal Dichalcogenides (TMDs) are considered as one of the most promising vdW materials within the field of nanoelectronics. Nevertheless, the electrical characterization of heteroepitaxially grown TMDs still shows inferior performance as compared to exfoliated TMD flakes. This is mainly attributed to the high density of defects resulting from their challenging vdW heteroepitaxial synthesis. In this work, we have investigated in depth the vdW homoepitaxial synthesis of the WSe2 TMD compound. We have demonstrated that even for homoepitaxy, the simplest type of crystal growth, challenges such as the formation of 60 o twins need to be addressed. We evidenced the presence of 60 o twins during vdW homoepitaxy which is assigned to stacking faults. The formation of these stacking faults is associated with their very similar binding energy as revealed by Density Functional Theory (DFT) calculations. Therefore, stacking faults are identified in this work to be the fundamental limitation of lowly-defective TMD vdW epitaxy. Furthermore, a generalized model is developed that determines the lower limit of the defect density based on the degree of control on the bilayer stacking phase and the nucleation density of the TMD compound. This model therefore assesses and quantifies for the first time the ultimate defect density level that can be achieved with vdW epitaxially grown 2D materials.