Nanowire LED fills the green-yellow gap in white light

October 28, 2016 // By Julien Happich
Nanowire LED fills the green-yellow gap in white light
An international team of researchers from King Abdullah University of Science and Technology (KAUST) and King Abdulaziz City for Science and Technology (KACST) have come up with a novel way to fill the “green-yellow gap” typically seen in white-LED implementations based on multiple phosphors.
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 9x109 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 0.5x0.5mm2 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.

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