Two-Step Growth of Uniform Monolayer MoS₂ Nanosheets by\nMetal–Organic Chemical Vapor Deposition

Abstract

To achieve large\narea growth of transition metal dichalcogenides\nof uniform monolayer thickness, we demonstrate metal–organic\nchemical vapor deposition (MOCVD) growth under low pressure followed\nby a high-temperature sulfurization process under atmospheric pressure\n(AP). Following sulfurization, the MOCVD-grown continuous MoS₂ film transforms into compact triangular crystals of uniform\nmonolayer thickness as confirmed from the sharp distinct photoluminescence\npeak at 1.8 eV. Raman and X-ray photoelectron spectroscopies confirm\nthat the structural disorders and chalcogen vacancies inherent to\nthe as-grown MOCVD film are substantially healed and carbon/oxygen\ncontaminations are heavily suppressed. The as-grown MOCVD film has\na Mo/S ratio of 1:1.6 and an average defect length of ∼1.56\nnm, which improve to 1:1.97 and ∼21 nm, respectively, upon\nsulfurization. The effect of temperature and duration of the sulfurization\nprocess on the morphology and stoichiometry of the grown film is investigated\nin detail. Compared to the APCVD growth, this two-step growth process\nshows more homogenous distribution of the triangular monolayer MoS₂ domains across the entire substrate, while demonstrating\ncomparable electrical performance.