Graphene layers build quantum LEDs

Article By : Carolyn Mathas

Graphene Flagship researchers have created an all-electrical quantum LED with single-photon emission.

I love LED research and it looks like Graphene Flagship is hitting its research out of the proverbial park. They’ve created an all-electrical quantum LED with single-photon emission. The LEDs are atomically thin and have potential as on-chip photon sources that can be used in quantum information apps.

__Figure 1:__ *This composite image shows an isolated bright spot that corresponds to a quantum emitter generating a stream of single photons. (Source: Mete Atatüre)*

Graphene Flagship researchers used layers that included transition metal dichalcogenides (TMDs), graphene and boron nitride to build the thin LEDs that can be used in quantum communications and network applications. The research was reported in Nature Communications, and was led by the University of Cambridge, UK.

According to the paper, “The diverse materials are layered forming a heterostructure. As electrical current is injected into the device, tunnelling from single-layer graphene, through few-layer boron nitride acting as a tunnel barrier, and into the mono- or bi-layer TMD material, such as tungsten diselenide (WSe2), where electrons recombine with holes to emit single photons. At high currents, this recombination occurs across the whole surface of the device, while at low currents, the quantum behaviour is apparent and the recombination is concentrated in highly localised quantum emitters.”

While quantum communication is still a way off, the research brings it closer. According to Professor Mete Atatüre at the Cavendish Laboratory at the Univesity of Cambridge, co-author of the paper, "Ultimately, in a scalable circuit, we need fully integrated devices that we can control by electrical impulses, instead of a laser that focuses on different segments of an integrated circuit. For quantum communication with single photons, and quantum networks between different nodes—for example, to couple qubits—we want to be able to just drive current, and get light out. There are many emitters that are optically excitable, but only a handful are electrically driven."

The research complements other recent research, for example, quantum dots were discovered to exist in layered TMDs in 2015. Stable quantum emitters at the edges of WSe2 monolayers that showed highly localised photoluminescence with single-photon emission characteristics were also discovered. Quantum emitters may possibly supplant research into the more traditional quantum dot counterparts because of the benefits of the ultra-thin devices of layered structures.

According to the researchers, this is just the beginning regarding possible applications that will come out of the combination of graphene and other insulating, semiconducting, superconducting, or metallic layered materials. Expect more in the near future on the subject from a variety of researchers tackling the challenge.

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