[Paper Review] Ultrafast Graphene Light Emitter

Young Duck Kim, Yuanda Gao+18 more|arXiv (Cornell University)|Oct 24, 2017

Thermal Radiation and Cooling Technologies4 citations

TL;DR

This paper demonstrates electrically driven ultrafast graphene light emitters with up to 10 GHz modulation bandwidth across the visible to near-infrared spectrum, enabled by ultrafast carrier dynamics and weak electron-phonon coupling. Encapsulation with hexagonal boron nitride (hBN) enhances emission by up to 460% by modifying the local density of optical states, enabling stable, bright visible radiation at 2,000 K under ambient conditions.

ABSTRACT

Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth, across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge carrier dynamics in graphene, and weak electron-acoustic phonon-mediated coupling between the electronic and lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460 % enhancement compared to the grey-body thermal radiation for a broad peak centered at 720 nm. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2,000 K under ambient conditions, as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.

Motivation & Objective

• To develop compact, electrically driven nanoscale light sources for on-chip photonic integration.
• To overcome the limitations of compound semiconductors in achieving monolithic, ultrafast, and small-footprint light emitters.
• To exploit graphene's ultrafast carrier dynamics for high-bandwidth optical emission.
• To engineer emission spectra using hexagonal boron nitride (hBN) encapsulation to enhance light extraction and stability.

Proposed method

• Electrically driven graphene photonic devices are fabricated using exfoliated graphene on hBN substrates.
• Ultrafast carrier dynamics in graphene are leveraged to achieve sub-picosecond response times and high modulation bandwidth.
• hBN encapsulation modifies the local optical density of states, enhancing emission through photonic engineering.
• Near-field coupling to hybrid polaritonic modes enables efficient electronic cooling and thermal stability.
• Spectral emission is measured across the visible to near-infrared range using broadband spectroscopy.
• Electronic temperatures up to 2,000 K are achieved and maintained under ambient conditions via controlled electrical injection.

Experimental results

Research questions

• RQ1 Can graphene-based light emitters achieve ultrafast modulation bandwidth suitable for high-speed optical communications?
• RQ2 How does hBN encapsulation influence the emission spectrum and efficiency of graphene light emitters?
• RQ3 To what extent can graphene sustain high electronic temperatures without degradation under ambient conditions?
• RQ4 Can near-field coupling to polaritonic modes enable efficient cooling and enhance emission intensity?
• RQ5 What is the maximum achievable emission enhancement in graphene via photonic engineering with hBN?

Key findings

• The graphene light emitter achieves a modulation bandwidth of up to 10 GHz, enabling ultrafast optical signaling.
• Emission spans the visible to near-infrared spectrum, covering 400–1000 nm.
• hBN encapsulation increases emission intensity by up to 460% compared to grey-body thermal radiation.
• A broad emission peak centered at 720 nm is observed due to modified local optical density of states.
• Stable and bright visible thermal radiation is maintained at electronic temperatures up to 2,000 K in ambient conditions.
• Near-field coupling to hybrid polaritonic modes enables efficient electronic cooling, enhancing device stability and performance.