Plessey develops native Red InGaN LEDs on silicon

06 Dec 2019

New approach to microLED is attractive because it offers lower manufacturing costs and scalability to larger wafers.

Plessey, an embedded technologies developer of microLED technologies intended for augmented reality and display markets, has developed what it calls The "world’s first GaN (gallium nitride) on silicon-based Red LED.

InGaN-based blue and green LEDs have been commercially available for some time, but red LEDs are typically based on AlInGaP material or color-converted Red. For AR applications, Plessey comments that achieving high efficiency ultra-fine pitch Red pixels (< 5 µm across) remains elusive due to severe edge effects from AlInGaP material and cavity losses from colour conversion processes.

InGaN-based Red is attractive because 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.

Strain-engineered active region

Plessey says it has successfully overcome these challenges by using a proprietary strain engineered active region to create an efficient InGaN Red LED. The new InGaN Red microLEDs offer an output 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 these specifications, Plessey says it now has the capability to manufacture native Blue, Green and Red InGaN material or tune wavelengths from 400nm – 650nm using its GaN-on-silicon platform.

Dr Wei Sin Tan, Director of Epitaxy and Advanced Product Development, at Plessey, commented, “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.”

Other recent achievements from Plessey includes the world’s first wafer-level bonded monolithic 3,000 ppi GaN-on-silicon microLED emissive display hybridised to an active-matrix CMOS backplane; as well as native Blue and Green emission layers on the same wafer. The company is continuing to develop microLED display solutions, including the planned production of full RGB microLED displays in 2020.

Plessey will be exhibiting at CES 2020. Joining forces with Compound Photonics, a developer of compact, high resolution microdisplay technologies, to develop the World’s smallest 1080p microLED based near-eye display solution for AR/MR applications.