Furry LEDs in the making

Furry LEDs in the making

Technology News |
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.
By Julien Happich


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 eeNews 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.

Indeed, in prior research, Geelhaar demonstrated clusters of NW-LEDs about 0.2mm2 in area, and estimated that the actual density of NW-LEDs that could potentially be designed (each NW being roughly about 100nm in diameter) could be of the same order of magnitude as the total density of NWs orderly grown on a substrate, measured in billions per square centimetre.

Since (In,Ga)N/GaN nanowire ensembles could be designed with bandgaps ranging from the UV to the infrared, this research not only opens the path to flexible high density LED arrays, but could also lead to very high density, bright and bendable full colour LED displays.

“At PDI, we like to describe our research as “device-inspiring”, and we definitely aim at fabricating a demonstrator LED on a flexible foil. However, taking this to the level of actual applications will be beyond our scope of expertise. We believe that the fabrication of LEDs that are inherently flexible will be an important achievement and hope that our work will inspire other groups to build up on that”, Geelhaar concluded.

Visit the Paul-Drude-Institut für Festkörperelektronik (PDI) at https://www.pdi-berlin.de

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