Perspective: Mitigation of structural defects during the growth of two-dimensional van der Waals chalcogenides by molecular beam epitaxy

The growth of wafer-scale van der Waals (vdW) thin films and heterostructures by molecular beam epitaxy (MBE) is important for future applications in quantum technologies, next generation optoelectronic devices, and fundamental physics investigations. When grown using co-deposition methods that are typically used for compound semiconductor MBE, vdW materials typically show a high density of structural defects including twin or antiphase domains, spiral growth, and pyramidal growth. These defects are caused by the relatively weak film/substrate interaction and/or the poor wettability of typical substrates by many vdW materials. These difficulties can be mitigated using a multi-step growth procedure in which growth stages including nucleation and coalescence can be rigorously controlled, resulting in high-quality deposition of vdW thin films. This article will describe a general recipe for the growth of highly-crystalline wafer-scale vdW thin films by MBE.