Nucleation and growth of WSe ₂ : enabling large grain transition metal dichalcogenides

Abstract

The limited grain size (<200 nm) for transition metal dichalcogenides (TMDs) grown by molecular beam epitaxy (MBE) reported in the literature thus far is unsuitable for high-performance device applications. In this work, the fundamental nucleation and growth behavior of WSe 2 is investigated through a detailed experimental design combined with on-lattice, diffusion-based first principles kinetic modeling to enable large area TMD growth. A three-stage adsorption-diffusion-attachment mechanism is identified and the adatom stage is revealed to play a significant role in the nucleation behavior. To limit the nucleation density and promote 2D layered growth, it is necessary to have a low metal flux in conjunction with an elevated substrate temperature. At the same time, providing a Serich environment further limits the formation of W-rich nuclei which suppresses vertical growth and promotes 2D growth. The fundamental understanding gained through this investigation has enabled an increase of over one order of magnitude in grain size for WSe 2 thus far, and provides valuable insight into improving the growth of other TMD compounds by MBE and other growth techniques such as chemical vapor deposition (CVD).

A roadmap for electronic grade 2D materials

“…MBE utilizes ultra-pure sources which are heated in effusion cells, resulting in "beams" of atoms or molecules, which are then deposited on a heated substrate (Figure 3c). 87 The lower temperature growths in MBE also help in minimizing chalcogen vacancies and intermixing of layers during the growth of vertical heterostructures, which are common problems associated with high temperature growths in P-CVD and gas source CVD. MBE growth of transition metal dichalcogenides was investigated prolifically by Koma beginning in the 1980s.…”

Multiscale computational understanding and growth of 2D materials: a review

“…It was found that the fast kink nucleation and propagation, rather than edge attachment and diffusion, could lead to ultrafast growth of monolayer WSe 2 168 . KMC simulations also guided CVD growth of large-scale WSe 2 grains by controlling the three-stage adsorption-diffusion-attachment mechanisms 169 . KMC model is also a key component in a more generalized mechanistic model for growth morphology predictions of 2D materials 47 .…”

Magneto-spectroscopy of exciton Rydberg states in a CVD grown WSe2 monolayer

“…Best specimens of S-TMD monolayers are usually obtained by the mechanical exfoliation of bulk (natural or synthetic) crystals which leads to micrometer sized flakes, suitable for scientific investigations or for demonstrating a) Electronic mail: clement.faugeras@lncmi.cnrs.fr prototype devices, but preventing their use in realistic applications produced at an industrial scale. Growth techniques, mainly chemical vapor deposition (CVD) 17 and molecular beam epitaxy (MBE) 18,19 , have been developed to produce large scale monolayers of S-TMD suitable for electronics and optoelectronics applications, or to elaborate vertical/horizontal heterostructures 20,21 . In this letter, we demonstrate CVD grown S-TMD monolayers with optical quality comparable to state of the art exfoliated flakes.…”