Vertical cubic GaN LEDs on 150mm 3C-SiC substrates

Our research is based on gallium nitride and its alloys, an amazing family of materials which can emit light over a wide range of colours - from the infra-red (IR) to the ultra-violet (UV). Already these materials are widely used in light emitting devices that are part of our everyday lives, perhaps most commonly in blue light emitting diodes (LEDs) and laser diodes (LDs). The LDs are at the heart of the blu-ray HD-DVD player, whilst the blue LEDs are combined with phosphors that emit other colours of light to produce white light. Such white LEDs are now very common in bicycle lights, torches and backlighting for displays on portable electronic devices from mobile phones to tablet computers.

However, the efficiency of green LEDs is much lower than that of blue LEDs: this is called the green-gap problem. If we could make green LEDs more efficient we could produce low-cost high quality white light by mixing red, green and blue LEDs, eliminating the need for phosphors. This would make LED lighting even more efficient than it is now and also improve the quality of the light. A key reason green LEDs are less efficient than blue is because there is a much stronger internal electric field inside the green LEDs. However, if we can grow the gallium nitride in a different form, cubic, from the standard form, hexagonal, we can eliminate this internal electric field across the LED, which should greatly increase its efficiency. We have found an exciting new way to do this, by growing the gallium nitride LEDs on a special form of a material called silicon carbide, developed by a small company called Anvil Semiconductors.

Together Cambridge, Anvil and Plessey have just completed an innovate UK funded project that has demonstrated many of the key steps to deliver high efficiency, low cost GaN based green LEDs based on cubic GaN, i.e. the growth and processing of cubic-GaN on 150mm diameter SiC on Si substrates. This offers a route to the large scale, low cost manufacture of green LEDs along side Plessey's existing (hexagonal) GaN on Si technology for blue LEDs. This new project will enable the cubic GaN technology to be taken to the next level, allowing the production of the 150mm SiC/Si substrates to be scaled up (Anvil), the quality of the cubic-GaN to be further improved (Cambridge), the cubic-GaN growth process to be transferred to industrial growth machines and a commercial device process to be developed (Plessey). This will bring efficient, low cost green LEDs one step closer, advancing the replacement of incandescent lights and CFLs with solid state lighting. It would also reduce electricity usage, save carbon emissions and generate new manufacturing jobs in UK industry.

This project will have an impact on society and the economy:

*Society*: Under the terms of the 2015 Paris Agreement on climate change, the UK is committed to achieving net zero emissions of greenhouse gases by the end of the century. This requires a rate of reduction in fossil fuel usage even greater than that which is embodied in the 2008 Climate Change Act. Lighting uses some 19% of the world's electricity. Since LED lights are up to 65% more efficient than traditional lighting, according to the Earth Policy Institute, replacing incandescent bulbs with LEDs could reduce this by more than half. In the UK, using the 19% figure, the total energy used for lighting is approximately 58 TWhrs annually. Moving to LEDs would save 37 TWhrs and 20 million tonnes (mt) of CO2 per year. More broadly, the US DoE estimates, in the US, a switch to LED lighting would alleviate the need for 133 new 1000 MW power stations, saving 255 million metric tons of CO2 and $115 billion per annum. However, the current generation of LED bulbs are expensive and the colour of the light they emit can make them unattractive to consumers. By switching to red-green-blue (RGB) LED bulbs, costs can be reduced by eliminating expensive rare-earth doped phosphors, and the colour of the light will become user tunable, so that the new bulbs will satisfy user preferences whilst realising large energy savings. Using the DoE price sensitivity figures the uptake of LEDs could increase by some 23% over baseline for RGB LED bulbs: a potential saving of 4.6mt CO2 per year if efficient green LEDs could be realised to allow improved quality of LED bulbs. Colour tunable light can also be used to promote health (for example mitigating seasonal affective disorder, jet-lag and some types of insomnia), also helping to improve alertness and performance in the workplace. It is also possible to utilise energy efficient RGB lighting to perform additional functions, such as wireless data transfer via optical communication technologies ("LiFi"), mitigating the growing problem of insufficient bandwidth for WiFi traffic. Green LEDs also have additional high impact applications in displays, signage, medical research and surgical lighting.

*The Economy*: The introduction of LEDs using GaN-on-3C-SiC-on-Si substrates would result in lower cost, more efficient LEDs than forecasters anticipate, so speeding up the replacement of incandescents and CFLs with LEDs. The US DoE predicts that introduction of this technology is likely to speed up the acceptance of LEDs by 5 years, based on a 50% lower cost than the baseline, which is approximately what this technology could bring. Success in this project is likely to lead to £300m pa revenue increase for Plessey for LEDs and £20m licence revenue for Anvil by 2022, with the associated benefits to UK plc of tax revenue and exports (most likely 75% given the location of much of the world's LED production). If Anvil licensed the epitaxial deposition of SiC on Si to a UK company, which is very likely, this could result in an income to that company of some £400 m, again mainly from export. The introduction of LEDs within households and commercial premises would significantly reduce electricity bills. With the introduction of LEDs, total household electricity bills could be reduced by 10%. The DOE study indicates that these benefits would be brought forward 5 years by the introduction of the technology in this proposal. Many local authorities have looked at the case for replacing street lights, which account for 30% of their energy bills, by LEDs, but few have done so to date. Our proposed technology would reduce the outlay for doing so significantly, enhancing the business case and bring forward implementation to reduce annual bills by up to £200 m. If successful, this technology would create up to 100 jobs in Plessey in the UK and if the 3C-SiC wafer production was licensed to a UK manufacturer up to 100 jobs there.