凯发

Graphene has emerged as a promising material for nanophotonics and optoelectronic applications due to its unique electronic and optical properties. Previous graphene based optoelectronic devices such as ultrafast and broadband photodetectors, optical modulator, and plasmonics, have shown the feasibility of ultrafast signal processing for on-chip optical communications. Among the nanophotonic components, ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. However, monolithic ultrafast light sources with a small footprint remain a challenge. Previously, I demonstrated bright thermal light emission in the visible range from electrically biased suspended graphene which achieves electron temperature up to ~ 2,800 K [1] owing to graphene’s high thermal stability, low heat capacity and ultrafast charge carrier dynamics. After this study, graphene becomes the promising material for nanoscale light source. However, monolithic graphene based ultrafast light source remain challenge due to limited hot electrons cooling pathway bottlenecks in graphene and little is known about the intrinsic thermal modulation rate of graphene under electrical excitation. Here, I will present the demonstration of electrically driven ultrafast thermal light emitters based on hexagonal boron nitride (hBN)-encapsulated graphene that achieve light pulse generation up too 10 GHz bandwidth with a broad spectral range from the visible to near-infrared [2]. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and lattice degree of freedom. Van der Waals heterostructure with ultraclean interface in hBN-graphene provide the strong light-matter interactions and efficient ultrafast direct electronic cooling pathway via near-field coupling by hybrid plasmon-phonon polariton modes, resulting in 460% enhancement of radiation intensity at 720 nm and 92 ps light pulse generation. Furthermore, high stability of encapsulation hBN layers allow the thermal radiation up to 2000 K under ambient condition and life-time above 4 years under vacuum. The high-speed graphene light emitters provide a promising path for on-chip light source for ultrafast optical communications and other optoelectronic applications.

References

[1] Kim, Y. D. et al. Bright visible light emission from graphene. Nat Nano 10, 676 (2015).

[2] Kim, Y. D. et al. Ultrafast Graphene Light Emitters. Nano Letters 18, 934 (2018).