Friday, July 3, 2020

New Breakthrough: Stable Nanolasers using 2D Semiconductors

We might be one step closer to realizing the dream of making laser technology on a silicon

Professor Cun-Zheng Ning from the Ira A. Fulton Schools of Engineering at Arizona State University and collaborators from the Tsinghua University in China discovered a phenomenon of physics that enables the production of low-powered nanolasers in 2D semiconductors. Their research, led by Associate Professor Hao Sun, was recently published in the Nature publication Light: Science & Applications.

A phenomenon called Mott Transition was the driving factor for their study. In physics, a Mott Transition is a change in a material’s behavior from an insulator to a conductor due to various factors. In Excitonic insulators, excitons form trions and conduct electricity to the point that they reach the Mott density. Mott density is the point at which Mott Transition and first optical gain occur. 

Ning’s Experiment

In Ning’s experiment, a single layer of 2D material was placed on a carefully designed silicon substrate with gold as a back-gate to control the number of electrons. A laser source pumps the 2D material to create excitons; some of these excitons form trions with the pre-existing electrons. The team measured optical gain at densities four to five orders of magnitude; 10,000 to 100,000 times smaller than those in conventional semiconductors that power optoelectronic devices.  

Credit: Cun-Zheng Ning

A condition called population inversion occurs when more electrons are in the trion state than their original electron state. Optical amplification or gain occurs when more photons are emitted than absorbed. 

In similar experiments conducted in the 1990s with conventional semiconductors, the excitons and trions were so unstable, making both experimental observation and practical utilization of this optical gain mechanism extremely difficult. However, in Ning’s experiment, because of the thinness of the materials, electrons, and holes attract each other hundreds of times stronger than conventional semiconductors, making excitons and trions very stable even at room temperatures.

According to Ning, there is more study required to determine how this new mechanism of optical gain works at different temperatures, and to design lasers that can operate using the new optical gain mechanism.

Significance of this discovery

The discovery uncovered a new mechanism using which researchers can create low-powered 2D semiconductor nanolasers. These nanolasers can be game-changing for optoelectronics and can provide an alternative to the conventional semiconductors. 

One day, this research could pave the way for supercomputers on a chip by combining photonics and electronics in a single integrated platform.

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Source: Phys.org

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