Photo-thermionic effect in vertical graphene heterostructures

• Published in: Nature communications Vol. 7; no. 1; pp. 12174 - 7
• Main Authors: Massicotte, M., Schmidt, P., Vialla, F., Watanabe, K., Taniguchi, T., Tielrooij, K. J., Koppens, F. H. L.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14.07.2016; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/357/918; 639/624/1075/401; 639/624/399/918/1052; 639/925; Condensed Matter; Electrons; Graphene; Humanities and Social Sciences; Lasers; multidisciplinary; Physics; Science; Science (multidisciplinary); Temperature; Thermal energy; Spain
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms12174

Finding alternative optoelectronic mechanisms that overcome the limitations of conventional semiconductor devices is paramount for detecting and harvesting low-energy photons. A highly promising approach is to drive a current from the thermal energy added to the free-electron bath as a result of light absorption. Successful implementation of this strategy requires a broadband absorber where carriers interact among themselves more strongly than with phonons, as well as energy-selective contacts to extract the excess electronic heat. Here we show that graphene-WSe 2 -graphene heterostructure devices offer this possibility through the photo-thermionic effect: the absorbed photon energy in graphene is efficiently transferred to the electron bath leading to a thermalized hot carrier distribution. Carriers with energy higher than the Schottky barrier between graphene and WSe 2 can be emitted over the barrier, thus creating photocurrent. We experimentally demonstrate that the photo-thermionic effect enables detection of sub-bandgap photons, while being size-scalable, electrically tunable, broadband and ultrafast. The detection of low-energy photons may be enabled by devices that make use of the excess thermal energy from photoexcited carriers as a result of light absorption. Here the authors demonstrate a vertical graphene-WSe 2 -graphene heterostructure that takes advantage of the photo-thermionic effect.