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Nanowire LED fills the green-yellow gap in white light

Technology News |
By Rich Pell


SEM image of the device structure based
on a two temperature-step growth method
(inset, TEM of Qdisks embedded in a nanowire).

Published in the ACS Photonics journal, their paper “True Yellow Light-Emitting Diodes as Phosphor for Tunable Color-Rendering Index Laser-Based White Light” describes a nanowire-based LED emitting at 588nm, grown on a low-cost, CMOS-foundry-compatible Ti-thin-film/Si substrate platform. A dense layer of nanowires is grown, reaching a surface density of 9×109 cm2, with a fill factor of 88%.

Device structure showing multiple nanowires
grown side-by-side.

And each nanowire p-i-n LED structure embeds an active region made of five stacks of 3nm thick InGaN quantum disks (Qdisk) separated by a 10nm quantum barrier.

Operating the yellow NW LED alone, they observed a peak emission of 588nm at 29.5 A/cm2 (75mA in a 0.5×0.5mm2 device) and a low turn-on voltage of about 2.5V, with an internal quantum efficiency of 39%, without “efficiency droop” up to an injection current density of 29.5A/cm2.


Then they demonstrated the benefit of mixing such a yellow light with the light of red, green, and blue laser diodes. In their setup, the yellow NW LED was illuminated by RGB beams, like a phosphor, and used as a light-scattering plane in a reflective configuration, adding its own yellow emission to the white mix.

The result was a correlated color temperature circa 6000 K and a color-rendering index of 87.7.

Visualization of the fabricated yellow NW LED.

Corresponding author Boon S. Ooi, Professor of Electrical Engineering and Director of the KACST Technology Innovation Center for Solid State Lighting wrote us that the objective of this method is to reduce the blue-intensity of white lights, creating an eye-friendly warmer white, while offering a new way to tune the color temperature for laser-based SSL. “We have submitted a US provisional patent on this technology”, he added, hinting at some commercial opportunities.

Visit KAUST at https://photonics.kaust.edu.sa

Related articles:
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Less expensive, sustainable white LED unveiled


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