NP2: Hybrid Nanoparticle-Nanoporous nitride materials as a novel precision manufacture route to optoelectronic devices

Augmented reality (AR) has the power to seamlessly integrate the digital world with physical reality. It could provide surgeons with vital medical data as they operate, allow athletes to access training information seamlessly whilst playing sports and offers countless other opportunities in business, leisure and beyond. However, currently AR technologies are let down by the performance of microdisplays. AR devices must operate successfully not only in darkened rooms but also in bright sunlight, and must also be very small and run all day on one charge of a compact battery. Hence, enormous demands are placed on tiny light emitters in microdisplays in terms of brightness and efficiency. For AR to become a mass market technology, any new approach to microdisplays will need to not only meet these demands, but also allow easy manufacturing.

Current light emitting diodes (LEDs) fail to meet these needs, since key materials which work well for larger area light emitters exhibit a drop in efficiency when the device size is shrunk to meet the demands of form factor and resolution imposed by AR. However, in terms of large scale LEDs, devices based on gallium nitride (GaN) have been tremendously successful, transforming the lighting industry. GaN LEDs also show much lower drops in efficiency with reduction in size than other similar materials. Unfortunately, these GaN LEDs are highly efficient only for light emission in the blue region of the spectrum. Green, amber and particularly red devices based on the same materials have much lower efficiencies, but are needed to create full colour microdisplays. In white LED light bulbs, blue light is converted to other colours by phosphor materials, but these phosphors are manufactured as bulky micron sized powders, too coarse to be used in microLEDs.

In this project, we will take a new approach to integrating alternative, nanometre-scale phosphor particles (ca. 100 atoms wide) with nitride LEDs. Our alternative phosphors are highly luminescent colloidal nanoparticles, synthesised straightforwardly in solution using scalable techniques and easily made into nanoparticle inks. These materials are already used in "QLED" display technologies, but display manufacture is complex and the difficulties increase substantially as the device shrinks. Our new concept is to use printing technologies to inject nanoparticles not onto the surface of LEDs, but into nanoscale pores in the GaN itself. The nanoporous GaN materials are a very recent development and unique, scalable methods for their fabrication have been invented in our laboratory. By printing onto these porous scaffolds we will exploit capillary action to suck the nanoparticles into the desired region of the device, preventing spreading of the nanoparticle ink and hence achieving controlled manufacture straightforwardly at the required scale. In so doing, we will create a new optical composite material - a combination of the GaN and the highly luminescent nanoparticles - and by using the structure of the nanopores to align and control the array of nanoparticles, we will enable new and more sophisticated devices, for future display technologies such as AR in three dimensions.