18 January 2016

Plessey to fabricate LEDs in cubic GaN on Anvil's 3C-SiC/Si substrates to overcome 'green gap' in efficiency

UK-based Plessey, Anvil Semiconductors Ltd of Coventry, UK and the University of Cambridge have announced that they are working together to fabricate high-efficiency LEDs in cubic GaN grown on Anvil's 3C-SiC/Si (silicon carbide on silicon) substrates.

Anvil was spun off in August 2010 from the University of Warwick's School of Engineering by its technology commercialization subsidiary Warwick Ventures Ltd in order to exploit patented developments in SiC power semiconductor technology. The firm's technology enables the growth of device-quality 3C-SiC epitaxy on 100mm silicon wafers to thicknesses that permit the fabrication of vertical power devices. The proprietary process is said to overcome mismatches in lattice parameter and thermal coefficient of expansion. The material has applications ranging from power devices and LEDs to medical devices and MEMS.

Cubic GaN has the potential to overcome the problems caused in conventional LEDs by the strong internal electric fields that impair carrier recombination and contribute to efficiency droop. This is particularly true for green LEDs, where the internal electric fields are stronger and are believed to cause a rapid reduction in efficiency at green wavelengths (the so-called 'green gap'). The availability of cubic GaN from a readily commercializable process on large-diameter silicon wafers is as a key enabler for increasing the efficiency of green LEDs and reducing the cost of LED lighting, says Plessey.

The collaboration, which is partly funded by Innovate UK under the £14m Energy Catalyst Programme, follows on from work by Anvil and the Cambridge Centre for GaN (part of the University of Cambridge's Department of Materials Science and Metallurgy), where they grew cubic GaN on 3C-SiC on silicon wafers by metal-organic chemical vapor deposition (MOCVD). The underlying 3C-SiC layers were produced by Anvil using its patented stress-relief IP that enables the growth of device-quality silicon carbide on 100mm-diameter silicon wafers. The process can be readily migrated onto 150mm-diameter wafers and potentially beyond without modification and is therefore suitable for large, industrial-scale applications. 

Using IP originally developed at the University of Cambridge, Plessey has started to commercialize LEDs produced in conventional (hexagonal) GaN grown on 150mm silicon wafers – i.e. its gallium nitride on silicon MaGIC (Manufactured on GaN-on-Si I/C) LEDs. Anvil's high-quality 3C-SiC on silicon technology, which is being developed for SiC power devices, is said to provide an effective substrate, to allow single-phase cubic GaN epitaxy growth and provides a process that is compatible with Plessey's GaN on Si device technology.

"The work that has previously been carried out at the University of Cambridge in collaboration with Anvil Semiconductors has demonstrated that high-quality cubic-GaN can be grown on large-area silicon substrates compatible with our manufacturing process," notes Plessey's chief technology officer Keith Strickland. "This has opened up the possibility to develop green LEDs with high efficiency that will allow us to demonstrate a new generation of efficient and controllable lighting products," he adds. 

"The properties of cubic GaN have been explored before, but the challenges of growing this thermodynamically unstable crystal structure have limited its development," says professor Sir Colin Humphreys, director of the Cambridge Centre for GaN. "The high quality of Anvil's cubic SiC on Si substrates and our experience of developing conventional GaN LED structures on large-area wafers have enabled a breakthrough in material quality. This latest project will build on our ongoing collaboration with Plessey to deliver, for the first time, green LED devices with efficiency approaching that in blue and red LEDs," he adds. 

"Our cubic SiC-on-Si has unlocked a route to large-area growth of cubic GaN," comments Anvil's CEO Jill Shaw. "We are delighted to be collaborating on this exciting project that offers the possibility of exploiting our technology in high-efficiency LEDs as well as in our core low-cost, high-efficiency power electronics markets."

See related items:

Plessey gains £30m loan from Deutsche Bank for LED production expansion

UK's Anvil and Cambridge grow cubic GaN-on-Si wafers by MOCVD

Tags: Plessey GaN-on-Si HB-LEDs SiC-on-Si substrates MOCVD The Cambridge Centre for Gallium Nitride

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