Plessey of Plymouth, England, Anvil Semiconductors and the University of Cambridge reported that they are collaborating on fabricating high-efficiency LEDs in cubic GaN grown on Anvil’s 3C-SiC / Si substrates.
Plessey contends that cubic GaN has the potential to overcome the problems from the strong internal electric fields in LEDs, which impair carrier recombination and contribute to efficiency droop.
Plessey points out that efficiency droop is particularly an issue with green LEDs in which the internal electric fields are stronger and are thought to reduce efficiency rapidly at green wavelengths known as “the green gap”.
According to Plessey, the availability of cubic GaN from a readily commercialized process on large diameter silicon wafers is as a key for increasing the efficiency of green LEDs and reducing the cost of LED lighting.
The collaboration, which Innovate UK partly funds under the £14m Energy Catalyst Programme, follows on from the work by Anvil Semiconductors and the Cambridge Centre for GaN at the University of Cambridge. The Cambridge Centre for GaN and Anvil Semiconductors employed MOCVD to grow cubic GaN on 3C-SiC on silicon wafers.
Avil fabricated the underlying 3C-SiC layers using its patented stress relief technology that enables growth of high-quality silicon carbide on 100mm diameter silicon wafers.
Avil says that the process can readily transfer onto 150mm diameter wafers and potentially beyond without modification, and the process is therefore suitable for large, industrial-scale applications.
Plessey has begun to commercialize LEDs produced in conventional (Hexagonal) GaN grown 150mm silicon wafers using IP originally developed at the University of Cambridge. Anvil’s high-quality 3C-SiC on Silicon technology, which is also being developed for SiC power devices, provides an effective substrate that allows single phase cubic GaN epitaxy growth and offers a compatible process for Plessey’s GaN on Si device technology.
Keith Strickland, the CTO of Plessey commented, “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 Si substrates compatible with our manufacturing process. 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.”
Professor Sir Colin Humphreys, Director of the Cambridge Centre for GaN, added, “The properties of Cubic GaN have been explored before, but the challenges of growing this thermodynamically unstable crystal structure have limited its development. 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.”
Jill Shaw, CEO of Anvil, added, “Our cubic SiC on Si has unlocked a route to large area growth of cubic GaN. 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.”