Graphene Thermal Emitter with Enhanced Joule Heating and Localized Light Emission in Air

Controlling thermal radiation in nanoscale is critical for verifying the Planck's law in subwavelength limit, and is the key for a range of innovative technologies including energy, display and security. Benefit from the superior electronic, thermal, and mechanical properties, electrically biased graphene has been recently demonstrated as promising thermal emitter with only one-atom thickness. Here, we show an enhancement of Joule heating effect in graphene by confining the current flow through narrow constrictions. The lattice temperature distribution of graphene shows a well localized "hot spot" at the middle of the constriction. Hexagonal boron nitride encapsulated graphene devices can sustain high lattice temperature up to similar to 1600 K, enabling localized light emission from the constriction in air. The spectrum of graphene emitter is drastically modified to visible range by the photonic cavity composed of SiO2 and hBN dielectrics. The intensity of emission can be tuned by changing the applied bias voltage. A 4 X 4 graphene emitters array is realized using chemical vapor deposited graphene and atomic layer deposited Al2O3 capping layer to demonstrate the scalability and compatibility to Si platform of this technique. The results explore one potential "killer application" of graphene-based devices as electrically driven thermal emitters, paving the way for future nano-optoelectronics.