Bright visible light emission from graphene

Abstract

2Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible, and transparent optoelectronics 1,2 . In particular, the strong light-matter interaction in graphene 3 has allowed for the development of state-of-the-art photodetectors 4,5 , optical modulators 6 , and plasmonic devices 7 .In addition, electrically biased graphene on SiO 2 substrates can be used as a low-efficiency emitter in the mid-infrared range 8,9 . However, emission in the visible range has remained elusive. Here we report the observation of bright visible-light emission from electrically biased suspended graphenes. In these devices, heat transport is greatly minimised 10 ; thus hot electrons (~ 2800 K) become spatially localised at the centre of graphene layer, resulting in a 1000-fold enhancement in the thermal radiation efficiency 8,9 . Moreover, strong optical interference between the suspended graphene and substrate can be utilized to tune the emission spectrum. We also demonstrate the scalability of this For the realisation of graphene-based bright and broadband light-emitters, a radiative electron-hole recombination process in gapless graphene is not efficient because of the rapid energy relaxation that occurs through electron-electron and electron-phonon interactions [11][12][13] .Alternatively, graphene's superior strength 14 and high-temperature stability may enable efficient thermal light emission. However, the thermal radiation from electrically biased graphene supported on a substrate 8,9,[15][16][17] has been found to be limited to the infrared range and 3 to be inefficient as an extremely small fraction of the applied energy (~ 10 -6 ) 8,9 is converted into light radiation. Such limitations are the direct result of heat dissipation through the underlying substrate 18 and significant hot electron relaxation from dominant extrinsic scattering effects such as charged impurities 19 and surface polar optical phonon interaction 20 , limiting the maximum operating temperatures.On the other hand, a freely suspended graphene is mostly immune to such undesirable vertical heat dissipation 10 and extrinsic scattering effects 21,22 , promising much more efficient and brighter radiation in the infrared-to-visible range. Fortuitously, due to the strong Umklapp phonon-phonon scattering 23 , we find that the thermal conductivity of graphene at high lattice temperatures (1800 ± 300 K) is greatly reduced (~ 65 Wm -1 K -1 ), which additionally suppresses lateral heat dissipation; therefore, hot electrons (~ 2800 K) become spatially localised at the centre of the suspended graphene under modest electric fields (~ 0.4 V/µm), greatly increasing the efficiency and brightness of the light emission. The bright visible thermally emitted light interacts with the reflected light from the separated substrate surface, allowing interference effects that can be utilized to tune the wavelength of the emitted light.We fabricate the freely suspended graphene devices with mechanically exfoliated graphene flakes, and for d...

Mid-infrared integrated photonics on silicon: a perspective

“…The function is plotted in Figure 8 for several emitter temperatures. We see that even at an extremely high emitter temperature of 3000 K (close to hot electron temperature in a graphene emitter [131]), the PSD of thermal radiation is still merely of the order of 0.1 nW/nm in the mid-IR, far smaller than the attainable PSD of other types of light sources discussed here. In the category of extrinsic emitters relying on luminescent dopants, Cr-or Fe-doped ZnSe/ZnS (for emission Table 4 compares the mid-IR light source technologies discussed above.…”

An introduction to polymer nanocomposites

“…This is produced by Graphene Lighting, a company formed by the University of Manchester and the UK's National Graphene Institute. Almost simultaneously, researchers based in South Korea and the USA published reported bright visible light emission from single-monolayer-thick graphene devices suspended between electrodes (Kim et al 2015, Wogan 2015 -effectively these are graphene light-emitting diodes. The authors also created arrays of graphene light emitters by chemical-vapour-deposition, which may provide a starting point to develop graphene-based on-chip optical communications.…”

Stability of suspended monolayer graphene membranes in alkaline environment

“…Previous studies on KOH interaction with graphene were limited to its role as an electrolyte [30][31][32] as well as an agent for chemical modification of graphene [33] for supercapacitive applications, or as a processing step to remove graphene from SiO 2 [34,35]. However a comprehensive study on the interaction of KOH processing on the structural and electrical properties of micronsized single layer flakes is missing.…”