Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460% enhancement compared to the gray-body thermal radiation for a broad peak centered at 720 nm. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2000 K under ambient conditions as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes under electrical excitation. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.
Bibliographical noteFunding Information:
Y.D.K was partially supported by the Columbia University SEAS Translational Fellow program. At Columbia, device fabrication and electrical testing were supported by the Office of Naval Research, grant no. N00014-13-1-0662; optical spectroscopy was supported by DOE-BES grant no. DEFG02-00ER45799. Ultrafast measurements at MIT were supported in part by the Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences under award no. DESC0001088. M.H.B was supported grants from the National Research Foundation of Korea (grant nos. NRF-2015R1A2A1A10056103 and SRC2016R1A5A1008184) funded by the Korea government. D.S. and H.C. were supported by NRF grant funded by the Korea government (no. 2017R1A2B3011586) and the third Stage of Brain Korea 21 Plus Project. A.N. and T.L were supported by a DARPA grant award no. FA8650-16-2-7640. K.W. and T.T acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, and JSPS KAKENHI, grant no. JP15K21722. The Stanford authors acknowledge support by the National Science Foundation (grant no. DMR-1411107 for Raman measurements) and by the Air Force Office of Scientific Research (grant no. FA9550-12-1-0119 for emission measurements).
- thermal radiation
- ultrafast light emitter
- van der Waals heterostructure