Halide chemical vapor deposition of 2D semiconducting atomically-thin crystals: From self-seeded to epitaxial growth

Atomically-thin crystals remain an epicenter of today's ongoing efforts of materials exploration for both fundamental knowledge and technological applications. We show that key modifications in the nucleation and growth steps lead to a controlled self-seeded growth of the monolayer transition metal dichalcogenide (TMDC) crystals and their lateral heterostructures via an halide chemical vapor deposition (HCVD) process which is a proven industrial scale and carbon-free synthesis technique for various material types. We present a general growth model with the limiting conditions on the nucleation density and crystal size of the 2D TMDCs grown in HCVD process. Furthermore, upon reduction of the self-seeded growth by a suitable surface pre-treatment, and by the modification of the nucleation step, epitaxial growth of monolayer TMDCs is also demonstrated using HCVD approach. The steady-state and time-resolved photoluminescence spectroscopic studies revealed the high optical and electronic quality of the as-grown 2D TMDCs semiconducting crystals. Field-effect transistor device characteristics of HCVD grown monolayer MoS₂ using SiO₂ gate dielectric shows an average mobility of 26 ± 7 cm².V⁻¹.s⁻¹ and on-off ratio of ∼10⁷, promising for large-scale device applications.