Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > New mechanism of optical gain in two-dimensional material requires only extremely low input power

Trion optical gain mechanism in electrically gated 2D materials: Exciton produced by a pump laser combined to form a trion. A weak probe light bounces off the trion gets amplified by emitting a photon and an electron.

CREDIT
by Zhen Wang†, Hao Sun†, Qiyao Zhang, Jiabin Feng, Jianxing Zhang, Yongzhuo Li, and Cun-Zheng Ning
Trion optical gain mechanism in electrically gated 2D materials: Exciton produced by a pump laser combined to form a trion. A weak probe light bounces off the trion gets amplified by emitting a photon and an electron. CREDIT by Zhen Wang†, Hao Sun†, Qiyao Zhang, Jiabin Feng, Jianxing Zhang, Yongzhuo Li, and Cun-Zheng Ning

Abstract:
In a new paper published in Light Science & Application, researchers from Tsinghua University and Arizona State University report their results on studying the fundamental physics of excitons, trions, and related complexes. Excitons are quasi-particles formed by an electron and a void called hole left when an electron is excited in a semiconductor. Such an exciton can be charged, to form a so called trion when it further binds with another electron or a hole. The team discovered an interesting process that gives optical gain, a prerequisite for signal amplification or lasing in a semiconductor, by exploring the intricate balance and conversion of excitons, electrons, holes, and trions. Interestingly the required level of input power to realize such optical gain is extremely low, 4 to 5 orders of magnitude lower than in a conventional semiconductor such as GaAs or InP, which are the workhorse materials for optoelectronic devices currently.

New mechanism of optical gain in two-dimensional material requires only extremely low input power

Changchun, China | Posted on March 20th, 2020

The distribution of these exciton-related complexes and their dynamical mutual conversion are at the very heart of solid state physics for many decades. There are still unresolved issues as to how these excitons form more complex particles and eventually transform into an ionized conducting phase of charged particles as we introduce more and more of them into a semiconductor. This process is called the Mott transition, after Sir Nevill Francis Mott, the celebrated British Nobel winning physicist. Conventional theory for the occurrence of optical gain says that free excitons cannot produce optical gain before the Mott transition in a semiconductor with freely moving charges. Optical gain occurs after electron density exceeds the so-called Mott density, typically a very high level of density on the orders of trillions of particles per centimeter squared. Such an extremely high density requires a high level of injection of electrical current, or electrical power. Most of our current semiconductor lasers that power our internet, data centers, and many other applications are based on such semiconductors.

Exploring the relationship between occurrence of optical gain and Mott transition, especially searching for new mechanisms of optical gain at low densities before the Mott transition is thus not only an issue of fundamental importance in solid state physics, it is also of importance in device applications in photonics. 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 small amount of driving power. This is obviously of great current interest for energy efficient photonic devices or green photonics. But unfortunately, such issues could not be fully and systematically explored in a conventional semiconductor, because excitons themselves are not very stable and the chance of pursuing higher excitonic complexes is limited.

The recent emergence of atomically thin layered materials made such study possible and more meaningful. These materials comprise of only a few layers of atoms. Because of the thinness of the materials, electrons and holes attract each other 100s times stronger than in conventional semiconductors. Such strong charge interactions make excitons and trions very stable even at room temperature. This was the reason why the authors could explore such intricate balance and carefully control their mutual conversion to achieve optical gain. By creating excitons through optical pumping by a laser, excitons form trions with part of electrons whose number is controlled by a gate voltage. When more electrons are in the trion state than electron state, a condition called population inversion occurs. More photons can be emitted than absorbed, leading to a process called stimulated emission and optical amplification or gain.

"Another motivation for this study was the apparent contradiction between a few high profile experiments in the field in recent years. There have been a few experiments reporting laser demonstrations using 2D materials as gain media. There lasers required very low level of pumping when excitons are dominant light emission mechanism. But the only existing experiment that proved the existence of optical gain in such materials requires much higher level of pumping", said Ning, who leads the research team. Ning noticed the densities in the laser experiments are smaller than the Mott density by 3 to 5 orders of magnitude, while optical gain was only observed after the Mott transition. Since laser operation requires the existence of optical gain, Ning asked "where does optical gain come from in those laser experiments?" or "what is the mechanisms of optical gain at such a lower level of optical pumping? Or more generally, are there any possible new gain mechanisms before Mott transition?" These questions led to their experimental investigation started several years ago.

"We have systematically pursued this issue experimentally for 2-3 years. We bounced a beam of light of a broad spectrum off 2D molybdenum ditelluride and carefully watch if the reflected signal is larger or smaller than the incident beam to look for any sign of light amplification," said Hao Sun, who is a lead author of this paper in charge of optical measurement.

"To be sure, similar trion gain experiment was conducted in 1990s with conventional semiconductors", noticed Ning. "But the excitons and trions were so unstable, both experimental observation and, especially, utilization of this optical gain for real devices are extremely difficult." "Since the excitons and trions are much more stable in the 2D materials, there are new opportunities to make real-world devices out of this observation", pointed out Ning. "For the moment, this result belongs to basic physics research, but as for all the important observations in semiconductors, they could eventually be applied to making real lasers," commented Ning.

####

For more information, please click here

Contacts:
Cun-Zheng Ning

Copyright © Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

Physics

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

2 Dimensional Materials

Closing the gaps — MXene-coating filters can enhance performance and reusability February 28th, 2025

New 2D multifractal tools delve into Pollock's expressionism January 17th, 2025

Chainmail-like material could be the future of armor: First 2D mechanically interlocked polymer exhibits exceptional flexibility and strength January 17th, 2025

FSU researchers develop new methods to generate and improve magnetism of 2D materials December 13th, 2024

Govt.-Legislation/Regulation/Funding/Policy

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Institute for Nanoscience hosts annual proposal planning meeting May 16th, 2025

Rice researchers harness gravity to create low-cost device for rapid cell analysis February 28th, 2025

Possible Futures

Ben-Gurion University of the Negev researchers several steps closer to harnessing patient's own T-cells to fight off cancer June 6th, 2025

Researchers unveil a groundbreaking clay-based solution to capture carbon dioxide and combat climate change June 6th, 2025

Cambridge chemists discover simple way to build bigger molecules – one carbon at a time June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Chip Technology

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Programmable electron-induced color router array May 14th, 2025

Enhancing power factor of p- and n-type single-walled carbon nanotubes April 25th, 2025

Ultrafast plasmon-enhanced magnetic bit switching at the nanoscale April 25th, 2025

Discoveries

Researchers unveil a groundbreaking clay-based solution to capture carbon dioxide and combat climate change June 6th, 2025

Cambridge chemists discover simple way to build bigger molecules – one carbon at a time June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Materials/Metamaterials/Magnetoresistance

Researchers unveil a groundbreaking clay-based solution to capture carbon dioxide and combat climate change June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Institute for Nanoscience hosts annual proposal planning meeting May 16th, 2025

Superconductors: Amazingly orderly disorder: A surprising effect was discovered through a collaborative effort by researchers from TU Wien and institutions in Croatia, France, Poland, Singapore, Switzerland, and the US during the investigation of a special material: the atoms are May 14th, 2025

Announcements

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters

Cambridge chemists discover simple way to build bigger molecules – one carbon at a time June 6th, 2025

Electrifying results shed light on graphene foam as a potential material for lab grown cartilage June 6th, 2025

Quantum computers simulate fundamental physics: shedding light on the building blocks of nature June 6th, 2025

A 1960s idea inspires NBI researchers to study hitherto inaccessible quantum states June 6th, 2025

Grants/Sponsored Research/Awards/Scholarships/Gifts/Contests/Honors/Records

Researchers uncover strong light-matter interactions in quantum spin liquids: Groundbreaking experiment supported by Rice researcher reveals new insights into a mysterious phase of quantum matter December 13th, 2024

New discovery aims to improve the design of microelectronic devices September 13th, 2024

Physicists unlock the secret of elusive quantum negative entanglement entropy using simple classical hardware August 16th, 2024

Atomic force microscopy in 3D July 5th, 2024

Photonics/Optics/Lasers

INRS and ELI deepen strategic partnership to train the next generation in laser science:PhD students will benefit from international mobility and privileged access to cutting-edge infrastructure June 6th, 2025

Institute for Nanoscience hosts annual proposal planning meeting May 16th, 2025

Following the folds – with quantum technology: The connection between a crumpled sheet of paper and quantum technology: A research team at the EPFL in Lausanne (Switzerland) and the University of Konstanz (Germany) uses topology in microwave photonics to make improved systems of May 16th, 2025

Programmable electron-induced color router array May 14th, 2025

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project