title: Influence of stoichiometry on the optical and electrical properties of chemical vapor deposition derived MoS2.
abstract: Ultrathin transition metal dichalcogenides (TMDCs) of Mo and W show great potential for digital electronics and optoelectronic applications. Whereas early studies were limited to mechanically exfoliated flakes, the large-area synthesis of 2D TMDCs has now been realized by chemical vapor deposition (CVD) based on a sulfurization reaction. The optoelectronic properties of CVD grown monolayer MoS2 have been intensively investigated, but the influence of stoichiometry on the electrical and optical properties has been largely overlooked. Here we systematically vary the stoichiometry of monolayer MoS2 during CVD via controlled sulfurization and investigate the associated changes in photoluminescence and electrical properties. X-ray photoelectron spectroscopy is employed to measure relative variations in stoichiometry and the persistence of MoOx species. As MoS2-δ is reduced (increasing δ), the field-effect mobility of monolayer transistors increases while the photoluminescence yield becomes nonuniform. Devices fabricated from monolayers with the lowest sulfur content have negligible hysteresis and a threshold voltage of ∼ 0 V. We conclude that the electrical and optical properties of monolayer MoS2 crystals can be tuned via stoichiometry engineering to meet the requirements of various applications.
authors.affiliation: Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: In Soo
authors.initials: IS
authors.lastname: Kim
authors.forename: Vinod K
authors.initials: VK
authors.lastname: Sangwan
authors.forename: Deep
authors.initials: D
authors.lastname: Jariwala
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Wood
authors.forename: Spencer
authors.initials: S
authors.lastname: Park
authors.forename: Kan-Sheng
authors.initials: KS
authors.lastname: Chen
authors.forename: Fengyuan
authors.initials: F
authors.lastname: Shi
authors.forename: Francisco
authors.initials: F
authors.lastname: Ruiz-Zepeda
authors.forename: Arturo
authors.initials: A
authors.lastname: Ponce
authors.forename: Miguel
authors.initials: M
authors.lastname: Jose-Yacaman
authors.forename: Vinayak P
authors.initials: VP
authors.lastname: Dravid
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hersam
authors.forename: Lincoln J
authors.initials: LJ
authors.lastname: Lauhon
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D008982:Molybdenum / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D013059:Spectrum Analysis, Raman
chemical_list: D004220:Disulfides; D008982:Molybdenum; C082964:molybdenum disulfide
keywords: X-ray photoelectron spectroscopy; chemical vapor deposition; field-effect mobility; molybdenum disulfide; photoluminescence; stoichiometry; transition metal dichalcogenides