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-halfmaximum 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.

Ultrafast electronic readout of diamond nitrogen–vacancy centres coupled to graphene

“…So far, the energy of the transferred electronic excitations has been considered to be lost within the electron bath of the graphene. Here we demonstrate that the transferred excitations can be read out by detecting corresponding currents with a picosecond time resolution 7,8 . We detect electronically the spin of nitrogen-vacancy centres in diamond and control the non-radiative transfer to graphene by electron spin resonance.…”

“…2a). At this position, the electric field is dominated by the built-in potential at the graphene-gold interface 8,14,15,33 . The longlived transient currents (blue-shaded region in Fig.…”

“…To this end, we can take advantage of the excellent optical and electronic properties of graphene 9 , which include good photodetection capabilities 8,[10][11][12][13][14][15] , efficient energy absorption 3 and strong light-matter interactions at the nanoscale 16,17 . In particular, it has been reported recently that, because of graphene's specific properties, the near-field interaction between light emitters and graphene is greatly enhanced as compared to that of conventional metals [2][3][4][5][6] .…”

“…On optical excitation of the NV centre, the relaxation process occurs via NRET into the graphene, which generates an electron-hole pair. We detect the corresponding electronic excitations that originate from the NRET process by utilizing an Auston switch 7,8 that enables an on-chip ultrafast electronic readout with picosecond resolution ( Fig. 1b inset and Methods).…”

Imaging Ultrafast Carrier Transport in Nanoscale Field-Effect Transistors

“…Only recently, ultrafast pump-probe photocurrent techniques have been demonstrated for studying carrier dynamics in carbon nanotube devices by using a collinear pump and probe beams, focused at the same position 20,21 . In addition, ultrafast phenomena in graphene and GaAs NWs have been investigated by measuring terahertz radiation that results from the ultrafast photocurrent in spatially designed circuit structures 22,23 . However, the carrier dynamics have not been directly visualized, in particular, with respect to various working conditions.…”