Surface Diffusion-Limited Growth of Large and High-Quality Monolayer Transition Metal Dichalcogenides in Confined Space of Microreactor

Hiroo Suzuki; Ryoki Hashimoto; Masaaki Misawa; Yijun Liu; Misaki Kishibuchi; Kentaro Ishimura; Kenji Tsuruta; Yasumitsu Miyata; Yasuhiko Hayashi

doi:10.1021/acsnano.2c05076

Surface Diffusion-Limited Growth of Large and High-Quality Monolayer Transition Metal Dichalcogenides in Confined Space of Microreactor

ACS Nano. 2022 Jul 26;16(7):11360-11373. doi: 10.1021/acsnano.2c05076. Epub 2022 Jul 6.

Authors

Hiroo Suzuki^{1

2}, Ryoki Hashimoto¹, Masaaki Misawa^{1

2}, Yijun Liu¹, Misaki Kishibuchi¹, Kentaro Ishimura¹, Kenji Tsuruta^{1

2}, Yasumitsu Miyata³, Yasuhiko Hayashi^{1

2}

Affiliations

¹ Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
² Faculty of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
³ Department of Physics, Tokyo Metropolitan University, Hachioji 192-0397, Japan.

PMID: 35793540
DOI: 10.1021/acsnano.2c05076

Abstract

Transition metal dichalcogenides (TMDCs), including MoS₂ and WS₂, are potential candidates for next-generation semiconducting materials owing to their atomically thin structure and strong optoelectrical responses, which allow for flexible optoelectronic applications. Monolayer TMDCs have been grown utilizing chemical vapor deposition (CVD) techniques. Enhancing the domain size with high crystallinity and forming heterostructures are important topics for practical applications. In this study, the size of monolayer WS₂ increased via the vapor-liquid-solid growth-based CVD technique utilizing the confined space of the substrate-stacked microreactor. The use of spin-coated metal salts (Na₂WO₄ and Na₂MoO₄) and organosulfur vapor allowed us to precisely control the source supply and investigate the growth in a systematic manner. We obtained a relatively low activation energy for growth (1.02 eV), which is consistent with the surface diffusion-limited growth regime observed in the confined space. Through systematic photoluminescence (PL) analysis, we determined that a growth temperature of ∼820 °C is optimal for producing high-quality WS₂ with a narrow PL peak width (∼35 meV). By controlling the source balance of W and S, we obtained large-sized fully monolayered WS₂ (∼560 μm) and monolayer WS₂ with bilayer spots (∼1100 μm). Combining two distinct sources of transition metals, WS₂/MoS₂ lateral heterostructures were successfully created. In electrical transport measurements, the monolayer WS₂ grown under optimal conditions has a high on-current (∼70 μA/μm), on/off ratio (∼5 × 10⁸), and a field-effect mobility of ∼7 cm²/(V s). The field-effect transistor displayed an intrinsic photoresponse with wavelength selectivity that originated from the photoexcited carriers.

Keywords: chemical vapor deposition; field-effect transistor; heterostructures; microreactor; surface diffusion-limited growth; transition metal dichalcogenide.