Berkeley Lab researchers have found evidence for excitonic dark states in monolayers of tungsten disulfide that could explain the unusual optoelectronic properties of single atomic layers of transition metal dichalcogenide (TMDC) materials.
A team of Berkeley Lab researchers believes it has uncovered the secret behind the unusual optoelectronic properties of single atomic layers of transition metal dichalcogenide (TMDC) materials, the two-dimensional semiconductors that hold great promise for nanoelectronic and photonic applications. Using two-photon excitation spectroscopy, the researchers probed monolayers of tungsten disulfide, one of the most promising of 2D materials, and found evidence for the existence of excitonic dark states - energy states in which single photons can be neither absorbed nor emitted. These excitons were predicted from ab initio calculations by members of the research team to have an unusual energy sequence, plus excitonic binding energy and bandgaps that are far larger than was previously suspected for 2D TMDC materials. "Discovery of very large excitonic binding energy and bandgaps and its nonhygrogenic nature in 2D semiconductor materials is important not only for understanding the unprecedented light-matter interaction arising from strong many-body effect, but also for electronic and optoelectronic applications, such as ultra-compact LEDs, sensors and transistors," says Xiang Zhang, director of Berkeley Lab's Materials Sciences Division and the leader of this study. "Such a large binding energy - 0.7eV - could also potentially make room-temperature excitons stable for future quantum computing efforts. Zhang holds the Ernest S. Kuh Endowed Chair Professor at the University of California (UC) Berkeley, directs the National Science Foundation's Nano-scale Science and Engineering Center, and is a member of the Kavli Energy NanoSciences Institute at Berkeley.
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