Research ArticleAPPLIED OPTICS

Multiple hot-carrier collection in photo-excited graphene Moiré superlattices

Science Advances  13 May 2016:
Vol. 2, no. 5, e1600002
DOI: 10.1126/sciadv.1600002

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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.

Keywords
  • Graphene
  • van der Waals heterostructures
  • optoelectronics
  • Van Hove singularities
  • carrier multiplication
  • hot carriers
  • Shockley-Queisser limit
  • superlattice

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