Whilst InGaN-based blue and green LEDs are commercially available, red LEDs are typically based on AlInGaP material or colour converted red. For 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 attractive as it offers lower manufacturing costs, scalability to larger 200 mm or 300 mm 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.
The company’s InGaN red microLEDs have a wavelength of 630 nm at 10 A/cm2, full width at half maximum of 50 nm, 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 - 650nm using its GaN on Silicon platform.