Current-Driven Terahertz Light Emission from Graphene Plasmonic Oscillations

Graphene is a promising materials system for basic studies and device applications in THz optoelectronics with several key functionalities, including photodetection and optical modulation, already demonstrated in recent years. The use of plasmonic excitations in this context is particularly attractive by virtue of their dynamic gate tunability across the far-infrared spectrum, relatively long lifetimes, and highly subwavelength confinement. Here these favorable properties are exploited for the generation of narrowband tunable THz radiation from current-driven plasmonic oscillations. We employ arrays of graphene nanoribbons, where localized plasmonic resonances are excited by an injected electrical current (through the generation and subsequent energy relaxation of hot carriers) and then radiate into the far field. Pronounced emission peaks are correspondingly measured at tunable frequencies across a wide portion of the THz spectrum (4-8 THz), controlled by design through the ribbon width and actively through the applied gate voltage. These results provide a new path for the study of plasmonic and hot-carrier phenomena in graphene and are technologically relevant for the development of highly miniaturized and broadly tunable THz radiation sources.