title: Multiple hot-carrier collection in photo-excited graphene Moiré superlattices.
abstract: In conventional light-harvesting devices, the absorption of a single photon only excites one electron, which sets the standard limit of power-conversion efficiency, such as the Shockley-Queisser limit. In principle, generating and harnessing multiple carriers per absorbed photon can improve efficiency and possibly overcome this limit. We report the observation of multiple hot-carrier collection in graphene/boron-nitride Moiré superlattice structures. A record-high zero-bias photoresponsivity of 0.3 A/W (equivalently, an external quantum efficiency exceeding 50%) is achieved using graphene's photo-Nernst effect, which demonstrates a collection of at least five carriers per absorbed photon. We reveal that this effect arises from the enhanced Nernst coefficient through Lifshtiz transition at low-energy Van Hove singularities, which is an emergent phenomenon due to the formation of Moiré minibands. Our observation points to a new means for extremely efficient and flexible optoelectronics based on van der Waals heterostructures.
authors.affiliation: Department of Physics, University of Washington, Seattle, WA 98195, USA.
authors.forename: Sanfeng
authors.identifier: 0000-0002-6227-6286
authors.initials: S
authors.lastname: Wu
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.; Department of Electrical Engineering, Columbia University, New York, NY 10027, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA.
authors.forename: You
authors.identifier: 0000-0003-0478-8547
authors.initials: Y
authors.lastname: Lai
authors.affiliation: Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
authors.forename: Wen-Yu
authors.identifier: 0000-0001-7765-0982
authors.initials: WY
authors.lastname: Shan
authors.affiliation: Department of Physics, University of Washington, Seattle, WA 98195, USA.
authors.forename: Grant
authors.initials: G
authors.lastname: Aivazian
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
authors.forename: Xian
authors.initials: X
authors.lastname: Zhang
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Kenji
authors.identifier: 0000-0003-3701-8119
authors.initials: K
authors.lastname: Watanabe
authors.affiliation: Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
authors.forename: Di
authors.initials: D
authors.lastname: Xiao
authors.affiliation: Department of Physics, Columbia University, New York, NY 10027, USA.
authors.forename: Cory
authors.identifier: 0000-0003-2967-5960
authors.initials: C
authors.lastname: Dean
authors.affiliation: Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hone
authors.affiliation: National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA.
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Physics, University of Washington, Seattle, WA 98195, USA.; Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Xu
mesh_terms: D004583:Electrons; D006108:Graphite / Q000737:chemistry*; D008962:Models, Theoretical; D017785:Photons
chemical_list: D006108:Graphite
keywords: Graphene; Shockley-Queisser limit; Van Hove singularities; carrier multiplication; hot carriers; optoelectronics; superlattice; van der Waals heterostructures