Nanowire LEDs fill the gap between green and yellow in white light

Researchers at the King Abdullah University of Science and Technology in Saudi Arabia and the Old King Technology City have proposed a novel approach that can fill the "green-yellow" common in multi-phosphor-based white LED applications due to poor conversion efficiency.

In the research paper published in the journal ACS Photonics, "True Yellow Light-Emitting Diodesas Phosphor for Tunable Color-Rendering Index Laser-Based White Light", a nanowire LED (NWLED) emitting at 588 nm is described. Can be grown on low cost titanium (Ti) thin film/silicon (Si) substrate platforms compatible with CMOS processes. Its compact nanowire layer can grow to a surface density of 9x109 cm^2 with a fill factor of 88%.

Each nanowire pi-nLED structure is embedded in an active region of a stack of 5 layers of 3 nm thick InGaN quantum discs (Qdisks) separated by 10 nm quantum barrier layers.

When operating the yellow-light nanowire LED alone, the researchers observed a peak emission of 588 nm and a low on-voltage of about 2.5 V at 29.5 A/cm^2 (about 75 mA on a 0.5x0.5mm^2 component), internal The quantum efficiency is about 39%, and the "efficiency reduction" does not occur until the implantation density of 29.5 A/cm^2 is reached.

20161101 LED NT01P3 SEM image of component structure using two temperature step growth method

Next, the researchers showed the benefits of mixing this yellow light with red, green, and blue laser diodes. In the actual setup, the RGB beam is used to illuminate the yellow nanowire LED, just like a phosphor, and a light scattering layer is used in the reflective configuration to add its yellow light emission to the white light mixture.

LEDNT01P2 component structure shows multiple nanowires growing side by side

The result is a correlated color temperature of approximately 6000K and a color rendering index of 87.7.

LED NT01P1 yellow light nanowire LED

Boon S. Ooi, director of the KACST Solid State Lighting Technology Innovation Center and professor of electrical engineering, said the goal of this approach is to reduce the intensity of blue light in white light, creating a warm white light that is more friendly to the human eye, while also being based on lasers. Solid-state lighting (SSL) provides a new way to tune color temperature. “At the moment, we have patented this technology,” and this also hints at some future business opportunities.