Schuller "Pushing Photons"

Metasurface design methods can make LED light act more like lasers

photo of LED bulb UC Santa Barbara


In the paper "Unidirectional luminescence from InGaN/GaN quantum-well metasurfaces" published in Nature Photonics, ECE  Prof. Jonathan Schuller and collaborators describe this new approach, which could allow a wide variety of LED devices — from virtual reality headsets to automotive lighting — to become more sophisticated and sleeker at the same time.

“What we showed is a new kind of photonic architecture that not only allows you to extract more photons, but also to direct them where you want,” said Schuller. This improved performance, he explained, is achieved without the external packaging components that are often used to manipulate the light emitted by LEDs.

Light in LEDs is generated in the semiconductor material when excited, negatively charged electrons traveling along the semiconductor’s crystal lattice meet positively-charged holes (an absence of electrons) and transition to a lower state of energy, releasing a photon along the way. Over the course of their measurements, the researchers found that a significant amount of these photons were being generated but were not making it out of the LED.

“We realized that if you looked at the angular distribution of the emitted photon before patterning, it tended to peak at a certain direction that would normally be trapped within the LED structure,” Schuller said. “And so we realized that you could design around that normally trapped light using traditional metasurface concepts.”

The design they settled upon consists of an array of 1.45-micrometer long gallium nitride (GaN) nanorods on a sapphire substrate. Quantum wells of indium gallium nitride (InGaN) are embedded in the nanorods to confine electrons and holes and thus emit light. In addition to allowing more light to leave the semiconductor structure, the design polarizes the light, which co-lead author Prasad Iyer said, “is critical for a lot of applications.”

Read more – Nanoscale Antennae and Right Place, Right Time

The UCSB Current – "Pushing Photons " (full article)