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Researchers Successfully Make Dark Semiconductors Glow

The energy levels of the electrons in a solid’s crystalline lattice determine whether it can generate light or not, for example as a light-emitting diode (LED).

In their experiments, the Oldenburg physicists directed laser light onto samples of extremely thin semiconductors with various optical components. Image Credit: University of Oldenburg

An international team of scientists led by University of Oldenburg physicists Dr. Hangyong Shan and Professor Dr. Christian Schneider successfully fabricated this material, which typically has a low luminescence yield, so that it is able to shine — successfully changing the energy levels in an ultra-thin sample of the semiconductor tungsten diselenide.

The team has published a paper on its research in the scientific journal Nature Communications.

The researchers claim that their findings represent a first step in manipulating the physical characteristics of matter using light fields.

The idea has been discussed for years, but had not yet been convincingly implemented.

Dr. Christian Schneider, Physicist, University of Oldenburg

The light effect has the potential to enhance the optical capabilities of semiconductors and will thus help to create cutting-edge LEDs, solar cells, optical parts, and other applications.

This could improve the optical qualities of organic semiconductors, plastics with semiconducting properties used in versatile screens, solar cells, or as sensors in textiles.

The uncommon class of semiconductors made up of a transition metal plus one of the three elements—sulfur, selenium, or tellurium—includes tungsten diselenide. The scientists employed a sample made of a single crystalline layer of sandwich-shaped tungsten and selenium atoms for their studies.

These few atom-thick materials are also referred to as two-dimensional (2D) materials in physics. They are also referred to as “quantum materials,” since they frequently have peculiar features because the charge carriers they carry behave entirely differently from those in thicker solids.

The tungsten diselenide sample was placed between two specially crafted mirrors by the researchers, which were directed by Shan and Schneider, and excited with a laser. They were able to couple energized electrons and light particles (photons) using this technique.

In our study, we demonstrate that via this coupling the structure of the electronic transitions can be rearranged such that a dark material effectively behaves like a bright one,” Schneider described. “The effect in our experiment is so strong that the lower state of tungsten diselenide becomes optically active.”

The researchers were also able to demonstrate that the experimental outcomes accurately reflected a theoretical model to a high degree.

The results are a result of a collaboration between scientists at the Carl von Ossietzky University of Oldenburg (Germany) and colleagues from Reykjavik University (Iceland), the University of Würzburg (Germany), Friedrich Schiller University (Germany), Arizona State University (USA) and the National Institute for Materials Science in Tsukuba (Japan). Parts of the theory were developed by colleagues at ITMO University in St. Petersburg (Russia) before the universities terminated their collaboration.

Journal Reference:

Shan, H., et al. (2022) Brightening of a dark monolayer semiconductor via strong light-matter coupling in a cavity. Nature Communications.

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