Furry LEDs in the making

June 06, 2016 // By Julien Happich
As a first step to designing densely packed arrays of nanowire-sized LEDs, a team of researchers from Berlin-based Paul-Drude-Institut für Festkörperelektronik (PDI) have used a titanium foil as a flexible substrate to grow impeccably detached and vertically aligned GaN nanowires.

Grown through plasma–assisted molecular beam epitaxy, the nanowires they obtained exhibited a similar crystalline perfection, a lower degree of coalescence, a higher concentration of stacking faults, and a reduced density of inversion domain boundaries than those prepared on Si substrates, they reported.

At the same time, bending the Ti foil substrate even to a radius of 4mm didn't affect the nanowires' structure, showing their very good adhesion.

"The next step will be to grow NWs with doped segments and an active region on Ti foils, and then we will adapt our established LED processing procedure to the new type of substrate. We believe that in particular the spinning of an insulating material that fills the space between the NWs will require optimization. The subsequent deposition of a top electrode will be very similar to the processing on Si", explained Dr. Lutz Geelhaar, Head of the Epitaxy Department, pointing EETimes Europe to his team's previous work on the characterization of (In,Ga)N/GaN nanowires-based LEDs.


(a) Flexing the Ti foil, invisibly covered in nanowires. (b) Scanning electron micrographs of the GaN nanowire ensemble grown on the Ti foil.

So would this yield clusters of LED-forming NWs or would the researchers aim at individually addressing nano-sized LEDs from this high density carpet of LEDs?
"By patterning the top electrode, LEDs can be fabricated that can be individually addressed even though they share the same conductive substrate" Geelhaar answered.