Wafer‐scale single‐crystalline MoSe₂ and WSe₂ monolayers grown by molecular‐beam epitaxy at low‐temperature — the role of island‐substrate interaction and surface steps

Abstract

Ultrathin two-dimensional transition-metal dichalcogenides (TMDs) have been pursued extensively in recent years for interesting physics and application potentials. For the latter, it is essential to synthesize crystalline TMD monolayers at wafer-scale. Here, we report growth of single-crystalline MSe 2 (M = Mo, W) monolayers at wafer-scale by molecular-beam epitaxy at low temperatures (200-400 • C) on nominally flat Au(1 1 1) substrates. The epifilms have low intrinsic defect densities of low 10 12 cm −2 . The grown films have then been exfoliated and transferred onto SiO 2 /Si by a wet chemical process, on which some optical measurements are performed, revealing high spatial uniformity of the samples. We also establish that MSe 2 grows on Au via the van der Waals epitaxy mechanism, where a continuous film extends across the whole surface, overhangs atomic-layer steps on substrate. We identify that the growth of highly crystalline MSe 2 is promoted by an enhanced interaction between Au substrate and MSe 2 islands rather than by the guidance of surface steps on substrate. The latter only arrests MSe 2 lateral growth if they are multilayer high. Key points• MBE growth of wafer-scale highly crystalline TMD monolayers at low-temperature is achieved.• Island-substrate interaction is found to play a critical role in vdW epitaxy of singlecrystalline TMDs on on-axis substates.• The TMD monolayers are of high uniformity and low intrinsic defect density.

Comparative coherence between layered and traditional semiconductors: unique opportunities for heterogeneous integration

“…Xia et al reported the growth of wafer-scale single-crystalline MSe 2 (M = Mo, W) monolayers by MBE at low temperatures (200 • C-400 • C) on nominally flat Au (111) substrates. The low temperature of MBE process was conducive to alignment of MSe 2 nucleation with Au surface, and brought advantages for epitaxial growth of single crystal TMD [137].…”

Growth of Wafer‐Scale Single‐Crystal 2D Semiconducting Transition Metal Dichalcogenide Monolayers

“…Therefore, only single‐crystal Au (111) thin film offers an excellent opportunity to grow 2D TMD monolayers with suppressed grain boundaries for various applications. [ 41 , 42 ] Eliminating the twin/grain boundaries of metal structures is also beneficial for electronic and optoelectronic devices. There are few works reported on the growth of 2D TMDs monolayer on a single crystal Au (111) thin films deposited on c ‐plane sapphire by using the CVD technique.…”

Tuning the atomic and electronic structures of mirror twin boundaries in molecular beam epitaxy grown MoSe2 monolayers via rhenium doping

“…Monolayer (ML) transition metal dichalcogenides (TMDs) MX 2 (M for transition metals, X for chalcogens), as an important family of two-dimensional (2D) materials, hold promise for potential applications in nanoelectronics [1], optoelectronics [2], and catalysis [3]. Given that defects play a more prominent role in 2D materials compared to their bulk counterparts, the investigation of defects in 2D TMDs has garnered increasing attention, resulting in a considerable body of research [4][5][6][7].…”