In his latest line of research, Cun-Zheng Ning, a professor of electrical engineering in the Ira A. Fulton Schools of Engineering at Arizona State University, and his peers explored the intricate balance of physics that governs how electrons, holes, excitons and trions coexist and mutually convert into each other to produce optical gain. Their results, led by Tsinghua University Associate Professor Hao Sun, were recently published in the Nature publication Light: Science & Applications.
"While studying the fundamental optical processes of how a trion can emit a photon [a particle of light] or absorb a photon, we discovered that optical gain can exist when we have sufficient trion population," Ning says. "Furthermore, the threshold value for the existence of such optical gain can be arbitrarily small, only limited by our measurement system."
In Ning's experiment, the team measured optical gain at density levels four to five orders of magnitude—10,000 to 100,000 times—smaller than those in conventional semiconductors that power optoelectronic devices, like barcode scanners and lasers used in telecommunications tools.
Ning has been driven to make such a discovery by his interest in a phenomenon called the Mott transition, an unresolved mystery in physics about how excitons form trions and conduct electricity in semiconductor materials to the point that they reach the Mott density (the point at which a semiconductor changes from an insulator to a conductor and optical gain first occurs).
But the electrical power needed to achieve Mott transition and density is far more than what is desirable for the future of efficient computing. Without new low-power nanolaser capabilities like the ones he is researching, Ning says it would take a small power station to operate one supercomputer.
"If optical gain can be achieved with excitonic complexes below the Mott transition, at low levels of power input, future amplifiers and lasers could be made that would require a small amount of driving power," Ning says.
This development could be game-changing for energy-efficient photonics, or light-based devices, and provide an alternative to conventional semiconductors, which are limited in their ability to create and maintain enough excitons.
文章信息：More information: Zhen Wang et al, Excitonic complexes and optical gain in two-dimensional molybdenum ditelluride well below the Mott transition, Light: Science & Applications (2020). DOI: 10.1038/s41377-020-0278-z
文章链接：https://www.nature.com/articles/s41377-020-0278-z
