Plessey has successfully manufactured native Green microLEDs using the development of their proprietary 2D planar gallium nitride on silicon (GaN-on-Si) process to emit Green light without the need for colour conversion techniques for micro-displays. This will enable the next generation of consumer electronics, globally.

Plessey’s LEDs are made from GaN-on-Si, instead of the usual sapphire. This enables the creation of monolithic microLEDs – with multiple emitters on a single chip. This unique approach brings several key advantages and solves the issues that have held back microLEDs from the mass market until now, which in turn holds back the development of next-generation of consumer electronics.

The silicon substrates’ thermal conductivity means heat can be dissipated from the system much more quickly compared to the widely used sapphire substrate. As a result, GaN-on-Si LEDs are more reliable and reduce both the cost of heatsinking and the space this takes up.
Better thermal conductivity will also allow the devices to operate at lower temperatures for a given output level, helping improve lifetime, or they can run at even higher brightness levels. Very high brightness is especially critical for daytime use in AR and HUD applications.

This also results in greater lumen output, increased energy efficiency, higher resolution and better contrast. It’s also more cost-effective to produce than competing LED technologies. Plessey processes 150mm and 200mm wafers but the technique can easily be scaled to 300mm and larger, improving cost and yield. GaN-on-sapphire currently uses 50mm and 100mm wafers.

Displays require microLEDs to interface to a backplane, and while bonding individual LEDs to a backplane has been shown to be technically viable, it is questionable whether using a pick-and-place method is commercially viable, to scale it down to smaller displays. By contrast, Plessey’s monolithic solution enables all the microLEDs to be bonded to an active matrix backplane in a single process and is largely independent of wafer size.

To create a bright enough full-colour microLED display for a variety of applications, Plessey needed a native Green as colour converted Blue to Green had a lot of losses and we knew quality could be dramatically improved. As we already had our proprietary native Blue GaN-on-Si material we just needed to manipulate the process to be able to emit Green light.

To produce Green light, LED manufacturers typically apply phosphors or quantum dot conversion materials to native Blue LEDs. These materials then convert short wavelength, typically 450nm, Blue light to Red or Green wavelengths with typically 10% to 30% efficiency.

Plessey’s native Green light has been achieved by using its proprietary GaN-on-Si technology that already generates Blue and extended this by engineering certain early layers that generate the transitions with silicon to gallium nitride. This then alters the natural emission from 450 nanometres, which is Blue, to 530 nanometres, which is Green.

Plessey’s native Green LEDs are formed inherently using its proprietary GaN-on-Si epitaxial growth process like the native Blue LEDs with the principal difference coming in the amount of indium that is incorporated in the quantum well structures of the LED.

With no colour conversion losses, the native Green emission is orders of magnitude times brighter than the colour converted process for microLEDs. With a dominant Green wavelength of 530nm and a full width half maximum wavelength (FWHMW) of 31nm, the native Green is well suited for colour displays; compared to over 40nm for QD converted green colour converted Green. Additionally, the Green emission exhibits outstanding wavelength stability versus current density.

Plessey’s Green native GaN delivers higher luminance than the standard Blue device with Green colour conversion techniques. Green has better efficiency at low current densities, and reduced efficiency droop with decreasing emitter size when compared with blue microLEDs. Native Green generates several million nits per 3.5 µm emitter at 30 Acm-2.
The market objectives for this upgrade was to enable the production of an overall brighter microLED display without the use of colour conversion techniques, which prior to this breakthrough was cadmium-free quantum dots. As previously mentioned, colour conversion creates losses which then, in turn, affects the brightness and performance of the LEDs.

Green displays are also essential to the military market so our new native Green microLEDs will enable better quality Head-Up and Head-Mounted Displays (HUDs/HMDs). Green is the colour the eye is most sensitive to, so a typical emitter can be driven at a less powerful current and still be seen. microLEDs emit even more brightness at lower powers so with the use of native Green microLEDs, military applications could be enhanced further.
MicroLEDs are still a developing technology, however, we have many public partners including WaveOptics and Vuzix, one of the world’s leading developers of smart glasses and video wearable devices, announced in June 2018 it will be using Plessey’s microLED technology in the development of its next-generation AR glasses.
In fact, the market opportunity for microLEDs is nothing short of staggering. MicroLED forecasting report by n-tech Research projects the overall market opportunities for MicroLED technology to grow from $0.5B to $22. 4B by 2024.
In 2020, we will continue our commitment to provide ‘world firsts’ and ‘technology breakthroughs’ for the microLED display market and for the wider display industry. In October 2019, we announced the ground-breaking ability to grow native Blue and Green on the same silicon wafer, so now we are looking to create a fully-integrated native RGB display on the same wafer, after also recently developing a native Red InGaN material. This proves our capability to tune wavelengths from 400 – 650 nm using our GaN-on-Silicon platform. Achieving a full RGB display will have a huge impact on the market, increasing demand for microLED displays in next-generation consumer technologies.

To support these achievements, Plessey has formed an influential advisory board including former VP of Macintosh Hardware Systems Engineering at Apple, Dr Edward H. Frank. It is also essential to note that, Plessey has many active R&D partnerships which are confidential but do include some key players within the consumer electronics industry.

Native Green MicroLEDs PDF