Light-Matter Coupling Makes Dark Semiconductor Glow

Researchers from the University of Oldenburg have introduced a light-matter coupling mechanism to make the 2D semiconductor material tungsten diselenide (WSe₂) glow — marking a step toward the control of the properties of matter through light fields. The scientists manipulated the energy levels in an ultrathin sample of the material, which normally possesses a low luminescence yield.

Physicists Hangyong Shan and Christian Schneider led the research. According to the team, the light effect could be used to optimize the optical properties of semiconductors. This level of optimization could then contribute to the development of innovative LEDs, solar cells, optical components, and more.

In particular, the researchers said, the materials solution could enhance the optical properties of organic semiconductors that are used in flexible displays and solar cells, as well as sensors in textiles.

University of Oldenburg physicists directed laser light onto samples of extremely thin semiconductors with various optical components. The experiments could serve to enhance the optical properties of organic semiconductors that are used in flexible displays and solar cells, as well as sensors in textiles. Courtesy of the University of Oldenburg.

The researchers placed a sample of WSe₂ between two specially prepared mirrors and excited the material using a nonresonant continuous-wave laser at 532 nm. The sample consisted of a single crystalline layer of tungsten and selenium atoms with a sandwich-like structure.

The researchers used the method to create a coupling between photons and excited electrons. In a demonstration, they showed that the coupling enabled the structure of electronic transitions to be rearranged such that the dark material — WSe₂ — effectively behaved like a bright one.

Whether a solid can emit light, such as an LED, depends on the energy levels of the electrons in the crystalline lattice of the solid. The researchers also pointed out that quantum 2D materials such as WSe₂ often feature unusual properties because the charge carriers that they contain behave in a manner that is different than those in thicker solids.

According to Schneider, the effect of the experiment is so strong that the lower state of WSe₂ becomes optically active as the experiment takes place.

Additionally, the team showed that its experimental results matched the predictions of a theoretical model to a high degree.

The current study is the result of a multi-institutional collaboration with researchers from institutions in Germany, Iceland, the U.S., and Japan.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-022-30645-5).