title: Broad-range modulation of light emission in two-dimensional semiconductors by molecular physisorption gating.
abstract: In the monolayer limit, transition metal dichalcogenides become direct-bandgap, light-emitting semiconductors. The quantum yield of light emission is low and extremely sensitive to the substrate used, while the underlying physics remains elusive. In this work, we report over 100 times modulation of light emission efficiency of these two-dimensional semiconductors by physical adsorption of O2 and/or H2O molecules, while inert gases do not cause such effect. The O2 and/or H2O pressure acts quantitatively as an instantaneously reversible "molecular gating" force, providing orders of magnitude broader control of carrier density and light emission than conventional electric field gating. Physi-sorbed O2 and/or H2O molecules electronically deplete n-type materials such as MoS2 and MoSe2, which weakens electrostatic screening that would otherwise destabilize excitons, leading to the drastic enhancement in photoluminescence. In p-type materials such as WSe2, the molecular physisorption results in the opposite effect. Unique and universal in two-dimensional semiconductors, the effect offers a new mechanism for modulating electronic interactions and implementing optical devices.
authors.affiliation: Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA.
authors.forename: Sefaattin
authors.initials: S
authors.lastname: Tongay
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.forename: Can
authors.initials: C
authors.lastname: Ataca
authors.forename: Jonathan
authors.initials: J
authors.lastname: Liu
authors.forename: Jeong Seuk
authors.initials: JS
authors.lastname: Kang
authors.forename: Tyler S
authors.initials: TS
authors.lastname: Matthews
authors.forename: Long
authors.initials: L
authors.lastname: You
authors.forename: Jingbo
authors.initials: J
authors.lastname: Li
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Grossman
authors.forename: Junqiao
authors.initials: J
authors.lastname: Wu