LEDs in cubic GaN to overcome “green gap”

January 18, 2016 // By Graham Prophet
Plessey Semiconductors (Plymouth, UK), Anvil Semiconductors 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-on-Si substrates, as part of a drive for more efficient LED light sources.

Cubic GaN has the potential to overcome the problems caused in conventional LEDs by the strong internal electric fields which 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 known as "the green gap". The availability of cubic GaN from a readily commercialisable 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.

The collaboration, which is partly funded by Innovate UK under the £14m Energy Catalyst Programme, follows on from work by Anvil Semiconductors and the Cambridge Centre for GaN at the University of Cambridge where they successfully grew cubic GaN on 3C-SiC (cubic silicon carbide) on silicon wafers by MOCVD (metal oxide chemical vapour-phase deposition). The underlying 3C-SiC layers were produced by Anvil using its patented stress relief IP that enables growth of device quality silicon carbide on 100 mm diameter silicon wafers. The process is readily migrated onto 150 mm diameter wafers and potentially beyond without modification and is therefore suitable for large, industrial-scale applications. Plessey has started to commercialise LEDs produced in conventional (Hexagonal) GaN grown 150 mm silicon wafers using IP originally developed at The University of Cambridge. Anvil’s high quality 3C-SiC on Silicon technology, which is being developed for SiC power devices, provides an effective substrate, to allow single phase cubic GaN epitaxy growth and provides a process which is compatible with Plessey's GaN on Si device technology.

Keith Strickland, the CTO of Plessey commented: "At Plessey we are constantly striving to find novel technology that can enhance our LED products. 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