Bright visible light emission from graphene

Abstract: Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible, and transparent optoelectronics. In particular, the strong light-matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators, and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. 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; 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. 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 technique by realizing arrays of chemical-vapour-deposited graphene bright visible-light emitters. These results pave the way towards the realisation of commercially viable large-scale, atomically-thin, flexible and transparent light emitters and displays with low-operation voltage, and graphene-based, on-chip ultrafast optical communications.

• The paper demonstrates a 1000-fold enhancement in thermal radiation by using suspended graphene, which enables clear visible light emission.
• It employs spatial localization of hot electrons (up to 2800 K) and tunable interference via engineered trench depth to precisely control the emission spectrum.
• Scalable device arrays fabricated through CVD methods pave the way for practical applications in ultrafast optical communications and flexible display technologies.

Analysis of Bright Visible Light Emission from Graphene

The paper presents a detailed investigation into the bright visible light emission from electrically biased suspended graphene. The study underscores a novel approach that leverages the unique thermal and optical properties of graphene, achieving a significant enhancement in thermal radiation efficiency. This enhancement is primarily attributed to the spatial localization of hot electrons in suspended graphene structures, minimized heat dissipation, and tunable optical interference.

Key Findings

1. Enhanced Thermal Radiation: The research shows a remarkable increase in thermal radiation efficiency, approximately 1000-fold, when transitioning from substrate-supported to suspended graphene devices. In the latter, heat dissipation is significantly minimized, allowing hot electrons with temperatures up to 2800 K to localize effectively at the center of the graphene layer.
2. Visible-Light Emission: Traditionally challenging for graphene due to its gapless nature, the visible-light emission is achieved by exploiting the superior thermal stability of graphene and the strong light-matter interaction enabled by its suspension. The paper reports that the emitted visible light is intense enough to be observed with the naked eye.
3. Interference Effects for Spectrum Tuning: The study demonstrates that the emission spectrum can be precisely manipulated through interference effects between the emitted light from suspended graphene and the reflected light off the substrate. By engineering the trench depth over which graphene is suspended, the researchers could tailor specific emission peaks.
4. Scalability and Fabrication: The scalability of producing these graphene light emitters is validated by fabricating arrays of devices using chemical vapor deposition (CVD) methods. These arrays show consistent visible-light emission, paving the way for potential integration into large-scale applications.
5. Threshold Electrical Fields: For visible-light emission, the study identifies a critical electric field point (~0.4 V/µm) in the suspended graphene, beyond which there is a rapid increase in light-emission intensity. This insight is crucial for device optimization in practical applications.

Theoretical and Practical Implications

Theoretically, this research enhances the understanding of electronic transport and optical processes in graphene. It offers insights into how the unique structural properties of graphene, when manipulated, can alter its thermal and optical behavior profoundly. This could inform future studies on other 2D materials and their potential applications in photonics.

Practically, the potential applications of graphene-based light emitters are significant. These include ultrafast optical communications and development of flexible, transparent displays that operate at low voltages. The approach described could lead to commercially viable graphene-based optoelectronic devices, addressing critical industry challenges such as miniaturization and integration with existing silicon technologies.

Future Directions

Future research may focus on further optimization of the trench depth and other structural parameters to improve emission efficiency and spectral characteristics. Exploring other substrate materials or configurations could provide additional degrees of tunability. Moreover, integrating such graphene-based devices with existing semiconductor technologies could be a vital step in transitioning from laboratory demonstrations to industrial applications.

In conclusion, this study exemplifies a significant advance in the exploration of graphene's application in optoelectronics, demonstrating both the unique properties of suspended graphene and its potential role in advancing photonic technologies.