New 3-D photonic crystals have both electronic optical properties

New 3-D photonic crystals have both electronic and optical properties

5:11 PM, 26th July 2011
New 3-D photonic crystals have both electronic and optical properties
Researchers at Illnois, led by Paul Braun, a professor of materials science and engineering and of chemistry, have demonstrated the first optoelectronically active 3-D photonic crystal.

CHAMPAIGN, US: In an advance that could open new avenues for solar cells, lasers, metamaterials and more, researchers at the University of Illinois have demonstrated the first optoelectronically active 3-D photonic crystal.

“We’ve discovered a way to change the three-dimensional structure of a well-established semiconductor material to enable new optical properties while maintaining its very attractive electrical properties,” said Paul Braun, Professor of materials science and engineering and chemistry who led the research effort.

The team published its advance in the journal Nature Materials.

Photonic crystals can induce unusual phenomena and affect photon behaviour in ways that traditional optical materials and devices can’t. They are popular materials of study for applications in lasers, solar energy, LEDs, metamaterials and more.

However, previous attempts at making 3-D photonic crystals have resulted in devices that are only optically active - that is, they can direct light - but not electronically active, so they can’t turn electricity to light or vice versa.

The Illinois team’s photonic crystal has both properties.

“With our approach to fabricating photonic crystals, there’s a lot of potential to optimize electronic and optical properties simultaneously,” said Erik Nelson, a former Graduate Student in Braun’s lab who now is a Postdoctoral Researcher at Harvard University.

To create a 3-D photonic crystal that is both electronically and optically active, the researchers started with a template of tiny spheres packed together. Then, they deposit gallium arsenide (GaAs), a widely used semiconductor, through the template, filling in the gaps between the spheres.

The GaAs grows as a single crystal from the bottom up, a process called epitaxy. “The key discovery here was that we grew single-crystal semiconductor through this complex template,” said Braun, who also is affiliated with the Beckman Institute for Advanced Science and Technology and with the Frederick Seitz Materials Research Laboratory at Illinois.

The epitaxial approach eliminates many of the defects introduced by top-down fabrication methods, a popular pathway for creating 3-D photonic structures.

To test their technique, the group built a 3-D photonic crystal LED - the first such working device.

Now, Braun’s group is working to optimize the structure for specific applications. “From this point on, it’s a matter of changing the device geometry to achieve whatever properties you want,” said Nelson. “It really opens up a whole new area of research into extremely efficient or novel energy devices.”

The US Department of Energy and the Army Research Office supported this work. Other Illinois faculty involved in the project are electrical and computer engineering Professors James Coleman and Xiuling Li, and materials science and engineering Professor John Rogers.

(C) University Of Illinois News




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