title: Time-resolved ultrafast photocurrents and terahertz generation in freely suspended graphene.
abstract: Graphene, a two-dimensional layer of carbon atoms, is a promising building block for a wide range of optoelectronic devices owing to its extraordinary electrical and optical properties, including the ability to absorb ~2% of incident light over a broad wavelength range. While the RC-limited bandwidth of graphene-based photodetectors can be estimated to be as large as 640 GHz, conventional electronic measurement techniques lack for analysing photocurrents at such frequencies. Here we report on time-resolved picosecond photocurrents in freely suspended graphene contacted by metal electrodes. At the graphene-metal interface, we demonstrate that built-in electric fields give rise to a photocurrent with a full-width-half-maximum of ~4 ps and that a photothermoelectric effect generates a current with a decay time of ~130 ps. Furthermore, we show that, in optically pumped graphene, electromagnetic radiation up to 1 THz is generated. Our results may prove essential to build graphene-based ultrafast photodetectors, photovoltaic cells and terahertz sources.
authors.affiliation: Walter Schottky Institut and Physik-Department, Technische Universität München, Am Coulombwall 4a, 85748 Garching, Germany.
authors.forename: Leonhard
authors.initials: L
authors.lastname: Prechtel
authors.forename: Li
authors.initials: L
authors.lastname: Song
authors.forename: Dieter
authors.initials: D
authors.lastname: Schuh
authors.forename: Pulickel
authors.initials: P
authors.lastname: Ajayan
authors.forename: Werner
authors.initials: W
authors.lastname: Wegscheider
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Holleitner
mesh_terms: D002244:Carbon / Q000737:chemistry; D004566:Electrodes; D060733:Electromagnetic Radiation; D020342:Finite Element Analysis; D006108:Graphite / Q000737:chemistry*; D007834:Lasers; D008027:Light; D008670:Metals / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods; D055095:Optics and Photonics / Q000379:methods; D009991:Oscillometry / Q000379:methods; D010777:Photochemistry / Q000379:methods; D013696:Temperature; D055068:Terahertz Spectroscopy / Q000379:methods; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D008670:Metals; D002244:Carbon; D006108:Graphite