Predictable arrays of plasmonic nano-particles can be grown on the surface of LEDs to improve photon emission by localised surface plasmon resonances, according to the University of Michigan.

“The idea of adding nano-particles to increase LED efficiency is not new, but previous efforts to incorporate them have been impractical for large-scale manufacturing,” said the university. “They focused on pricey metals like silver, gold and platinum. Furthermore, there was no cost-effective way to incorporate particles below the surface.”

The researchers worked with gallium arsenide (GaAs), irradiating its surface with a focused beam of gallium ions.

Researcher Sunyeol Jun prepares MBE apparatus

Picture credit: Joseph Xu Michigan Engineering

Gallium particles

Self-assembling arrays of similar sized gallium particles grew, with, among other things, the beam angle with respect to the substrate controlling the eventual particle size and population density.

The surface, including its particles, was then buried under another layer of GaAs using molecular beam epitaxy – which, in this case, grew poly-crystalline GaAs.

Various combinations of particle size and burial layer thickness were tried, with the emissive characteristics measured by photo-luminescene.

It became apparent that the high quality underlying single crystal GaAs emitted better than any polycrystalline surface that was deposited on top without nano-particles, but certain combinations of particle size and deposited polycrystalline layer depth were best of all.

For example, 40nm particles covered by 40nm of polycrystalline GaAs was a winning combination. A deeper top layer then reduced emission.

“If you carefully tailor the size and spacing of nano-particles and how deeply they’re embedded, you can find a sweet spot that enhances light emissions,” said researcher Myungkoo Kang.

The work is published as ‘Formation of embedded plasmonic Ga nano-particle arrays and their influence on GaAs photoluminescence’ in the Journal of Applied Physics.