Whilst InGaN-based Blue and Green LEDs are commercially available, Red LEDs are typically based on AlInGaP material or colour converted Red. For augmented reality (AR), achieving high efficiency ultra-fine pitch Red pixels (< 5 µm) remains elusive due to severe edge effects from AlInGaP material and cavity losses from colour conversion processes.
InGaN-based Red is seen as an attractive solution as it offers lower manufacturing costs, scalability to larger 200mm or 300mm wafers and better hot/cold factor over incumbent AlInGaP-based Red. However, achieving red spectral emission with InGaN material is challenging due to the high indium content inducing significant strain in the active region, subsequently reducing crystal quality and creating numerous defects. Plessey has successfully overcome these challenges by using a proprietary strain engineered active region to create an efficient InGaN Red LED.
Plessey’s InGaN Red microLEDs have a wavelength of 630 nm at 10 A/cm2, full width at half maximum of 50nm, hot cold factor over 90% and higher efficiencies over conventional AlInGaP and colour converted Red at ultra-fine pixel pitches. With this result, Plessey now has the capability to manufacture native Blue, Green and Red InGaN material or tune wavelengths from 400 - 650 nm using its GaN on Silicon platform.
Commenting Dr Wei Sin Tan, Director of Epitaxy and Advanced Product Development, at Plessey, said: “This is an exciting result as it creates a path towards low cost manufacturing of ultra-fine pitch and efficient Red InGaN pixels, which will accelerate the adoption of microLEDs in both AR microdisplays and mobile/large display applications. Our innovative solutions have once again proven Plessey’s position as the world leader in microLED technology.”