May 8, 2017: Paris-Sud University, CNRS Orsay (France) and Grenoble’s CEA (French Alternative Energies and Atomic Energy Commission), have jointly fabricated flexible inorganic LEDs based on gallium-nitride semiconductor nanowires.
The researchers have discovered a novel fabrication procedure that is used to produce flexible devices like inorganic semiconductor nanowires. These flexible devices can compete with organic devices in terms of brightness.
Nitride LEDs are likely to replace other light sources in general lighting, displays and life-science applications. While inorganic semiconductor devices are rigid and cannot be used in applications that require mechanical flexibility, flexible LEDs have a upper hand, are being a topic of research as they can be used in many applications like foldable displays, wearable optoelectronics, bendable light sources, and biomedical devices. Currently, flexible devices are fabricated from organic materials, for example, OLEDs—being commercially used in curved TV and smartphone screens. But, OLEDs have bad temporal stability and lower luminescence than nitride semiconductor LEDs. As a result, efforts are being made to fabricate flexible inorganic LEDs.
Flexible inorganic LEDs are fabricated in a number of steps—layer lift-off, microstructuring, and transfer to plastic supports. If one wants to avoid the microstructuring step and facilitate the lift-off, it is possible to shrink the active element dimensions and use bottom-up nanostructures like nanowires, NWs. These NWs, that is, elongated nanocrystals have good mechanical and optoelectronic properties. NWs can also withstand deformation without suffering plastic relaxation.
The researchers found that the devices had the properties of nitride NW LEDs, with a turn-on voltage of 3V. These can be bent to a curvature radius of 3mm without any degradation of electrical or luminescent properties. Unlike OLEDs, these devices can be stored for several months without degradation.
Since a NW-LED array can be connected as a single LED sheet, several such sheets can be stacked, embedding NW-LEDs with different compositions. The researchers, thus created a flexible bi-colour LED sheet made of transparent flexible blue LED on top of a green LED, and each can produce either blue or green light, or a mix of both.