title: Ultrafast charge transfer in atomically thin MoS₂/WS₂ heterostructures.
abstract: Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two-dimensional layers, including graphene, hexagonal-boron nitride and transition-metal dichalcogenides (MX2), give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because two-dimensional MX2 monolayers can have an optical bandgap in the near-infrared to visible spectral range and exhibit extremely strong light-matter interactions. Theory predicts that many stacked MX2 heterostructures form type II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. Here, we report the first experimental observation of ultrafast charge transfer in photoexcited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond pump-probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50 fs after optical excitation, a remarkable rate for van der Waals coupled two-dimensional layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel two-dimensional devices for optoelectronics and light harvesting.
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2].
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Hong
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2].
authors.forename: Jonghwan
authors.initials: J
authors.lastname: Kim
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [3].
authors.forename: Su-Fei
authors.initials: SF
authors.lastname: Shi
authors.affiliation: Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Chenhao
authors.initials: C
authors.lastname: Jin
authors.affiliation: Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Yinghui
authors.initials: Y
authors.lastname: Sun
authors.affiliation: 1] Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] Department of Materials Science and Engineering, University of California, Berkeley, California 94720-1760, USA [3] School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: Sefaattin
authors.initials: S
authors.lastname: Tongay
authors.affiliation: 1] Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] Department of Materials Science and Engineering, University of California, Berkeley, California 94720-1760, USA.
authors.forename: Junqiao
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China.
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: 1] Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA [2] Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [3] Kavli Energy NanoSciences Institute at the University of California, Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang