Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Penn Researchers Break Light-Matter Coupling Strength Limit in Nanoscale Semiconductors

16.06.2011
New 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”

This research was supported by the Netherlands Organization for Scientific Research Rubicon Programme, the U.S. Army Research Office, the National Science Foundation, Penn’s Nano/Bio Interface Center and the National Institutes of Health.

Evan Lerner | EurekAlert!
Further information:
http://www.upenn.edu

More articles from Physics and Astronomy:

nachricht NASA detects solar flare pulses at Sun and Earth
17.11.2017 | NASA/Goddard Space Flight Center

nachricht Pluto's hydrocarbon haze keeps dwarf planet colder than expected
16.11.2017 | University of California - Santa Cruz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>