Navigation Links
Penn researchers break light-matter coupling strength limit in nanoscale semiconductors

PHILADELPHIANew engineering research at the University of Pennsylvania demonstrates that polaritons have increased coupling strength when confined to nanoscale semiconductors. This represents a promising advance in the field of photonics: smaller and faster circuits that use light rather than electricity.

The research was conducted by assistant professor Ritesh Agarwal, postdoctoral fellow Lambert van Vugt and graduate student Brian Piccione of the Department of Materials Science and Engineering in Penn's School of Engineering and Applied Science. Chang-Hee Cho and Pavan Nukala, also of the Materials Science department, contributed to the study.

Their work was published in the journal Proceedings of the National Academy of Sciences.

Polaritons are quasiparticles, combinations of physical particles and the energy they contribute to a system that can be measured and tracked as a single unit. Polaritons are combinations of photons and another quasiparticle, excitons. Together, they have qualities of both light and electric charge, without being fully either.

"An exciton is a combination of a an electron, which has negative charge and an electron hole, which has a positive charge. Light is an oscillating electro-magnetic field, so it can couple with the excitons," Agarwal said. "When their frequencies match, they can talk to one another; both of their oscillations become more pronounced."

High light-matter coupling strength is a key factor in designing photonic devices, which would use light instead of electricity and thus be faster and use less power than comparable electronic devices. However, the coupling strength exhibited within bulk semiconductors had always been thought of as a fixed property of the material they were made of.

Agarwal's team proved that, with the proper fabrication and finishing techniques, this limit can be broken.

"When you go from bulk sizes to one micron, the light-matter coupling strength is pretty constant," Agarwal said. "But, if you try to go below 500 nanometers or so, what we have shown is that this coupling strength increases dramatically."

The difference is a function of one of nanotechnology's principle phenomena: the traits of a bulk material are different than structures of the same material on the nanoscale.

"When you're working at bigger sizes, the surface is not as important. The surface to volume ratio the number of atoms on the surface divided by the number of atoms in the whole material is a very small number," Agarwal said. "But when you make a very small structure, say 100 nanometers, this number is dramatically increased. Then what is happening on the surface critically determines the device's properties."

Other researchers have tried to make polariton cavities on this small a scale, but the chemical etching method used to fabricate the devices damages the semiconductor surface. The defects on the surface trap the excitons and render them useless.

"Our cadmium sulfide nanowires are self-assembled; we don't etch them. But the surface quality was still a limiting factor, so we developed techniques of surface passivation. We grew a silicon oxide shell on the surface of the wires and greatly improved their optical properties," Agarwal said.

The oxide shell fills the electrical gaps in the nanowire surface, preventing the excitons from getting trapped.

"We also developed tools and techniques for measuring this light-matter coupling strength," Piccione said. "We've quantified the light-matter coupling strength, so we can show that it's enhanced in the smaller structures,"

Being able to quantify this increased coupling strength opens the door for designing nanophotonic circuit elements and devices.

"The stronger you can make light-matter coupling, the better you can make photonic switches," Agarwal said. "Electrical transistors work because electrons care what other electrons are doing, but, on their own, photons do not interact with each other. You need to combine optical properties with material properties to make it work."


Contact: Evan Lerner
University of Pennsylvania

Related biology technology :

1. Understanding the science of solar-based energy: more researchers are better than one
2. Researchers decode viral process that prepares cells for HIV infection
3. Dartmouth researchers advance cellulosic ethanol production
4. Researchers develop new model for cystic fibrosis
5. Use it or lose it? Researchers investigate the dispensability of our DNA
6. Sigma-Aldrich and the University of Illinois Offer New Boronic Acid Surrogates to Researchers Worldwide Through Licensing Agreement
7. Researchers write protein nanoarrays using a fountain pen and electric fields
8. Researchers show how to stamp nanodevices with rubber molds
9. The Lancets New Online Medical Journal Helps Clinicians and Medical Researchers Find Practice-Changing Evidence Quickly and Easily
10. Ultrafast lasers give CU-Boulder researchers a snapshot of electrons in action
11. VAP(R) Cholesterol Test Helps Researchers Identify Treatment Effects of Combination Therapy
Post Your Comments:
(Date:10/13/2015)... Hills, MI (PRWEB) , ... October 13, 2015 ... ... Michigan-based manufacturer and distributor of automation systems, material handling solutions and components, is ... Located off I-94 near State Street, the facility is Exotic’s second major expansion ...
(Date:10/13/2015)... New Jersey (PRWEB) , ... October 13, 2015 ... ... to enhance the educational opportunities for school age children in the areas of ... essential for all sectors of the national economy, and the program aims to ...
(Date:10/12/2015)... Oct.12, 2015  MiMedx Group, Inc. (NASDAQ: MDXG ... tissue and patent-protected processes to develop and market advanced ... Spine, Sports Medicine, Ophthalmic, and the Dental sectors of ... been filed against the Company has been dismissed by ... Chairman and CEO, stated, "As we suspected, this case ...
(Date:10/12/2015)... , 12 de octubre de 2015 ... (D-CA) llegó a un récord en el congreso con ... anual de la International Plasma Awareness Week (IPAW), que ... IPAW está patrocinada por la Plasma Protein Therapeutics ... para: , Aumentar la concienciación mundial ...
Breaking Biology Technology:
(Date:10/12/2015)... 9, 2015 Research and Markets ( ... new report "Biometrics: Market Shares, Strategies, and Forecasts, ... --> --> The study is ... market segment. Research represents a selection from the mountains ... market materials, with selections made by the most senior ...
(Date:10/8/2015)... Calif. , Oct. 8, 2015 ... of human interface solutions, announced today that it ... of fiscal 2016 on Thursday, October 22, 2015, ... host a corresponding conference call for analysts and ... during which management may discuss forward-looking information.    ...
(Date:10/6/2015)... , Oct. 6, 2015 Track Group, Inc. ... that it has signed a contract with the Virginia ... the full range of sentences under the Department,s oversight. ... the Americas. "This contract with the Virginia DOC will ... US and advances our position as a trusted leader ...
Breaking Biology News(10 mins):