UK group plans to develop LEDs on 6-inch silicon wafers

A UK collaboration is participating in a £3 million program with government funding to develop a low-cost route to LEDs.

A consortium of UK organizations - Filtronic, Forge Europa, QinetiQ, Thomas Swan and Cambridge University - has won a three-year contract under the DTI (Department of Trade & Industry) Technology Programme, worth just under £3 million, to develop a route to low-cost LEDs for solid-state lighting. The DTI and the industrial partners will each fund 50% of the total contract cost.

The project goal is to demonstrate high-quality LEDs grown on 150mm silicon substrates to enable large-scale production of LED lamps for solid-state white lighting.

Gallium nitride (GaN) based blue LED chips, which are used to make white LEDs, are manufactured by depositing multiple layers of GaN-based materials onto sapphire or silicon carbide wafers. These are limited to small wafer diameters, with 2 inches the norm in production. Larger wafer diameters should result in less wastage, higher yields and lower-cost production.

Silicon is not the ideal material on which to deposit GaN-based LED layers, due to the mismatch between the two materials. However, says Steve Clements, Optical Business Manager at Filtronic Compound Semiconductors, silicon wafers provide an extremely high quality surface for growth, which should prove beneficial in the material deposition (epitaxy) process. However, a range of growth issues will need to be solved, and this will be the initial focus of the project.

Once good quality LED layers on silicon wafers are available, Filtronic will be able to develop device fabrication processes using its 6-inch wafer line. The company manufactures gallium arsenide (GaAs) based RF devices on 6-inch wafers, and Clements says they have also fabricated optical modulators. He explains that there are very substantial reproducibility benefits in using tools developed for the silicon semiconductor industry and successfully utliized in Filtronic's GaAs fab.

The DTI is motivated by energy-efficiency and environmental concerns. Replacement of conventional lighting by solid-state lamps has the potential to offer major savings in electricity use with a reduced environmental impact. The key to adoption of the technology is cost, and this project addresses the development of low-cost solutions by exploiting large diameter substrates and the consistency of mature proven volume production in the UK.

The project combines proven expertise in high-volume compound semiconductor manufacturing with some of the foremost capabilities within the UK for GaN growth, together with fundamental science and expertise in packaging and LED marketing.

The collaborators expect that the project will not only achieve significant progress on the solid-state lighting roadmap, but also provide a route for the UK to enter this major future market.

About the partners:

Filtronic is a leading global designer and manufacturer of customised microwave electronic subsystems and compound semiconductor components for the wireless telecommunications and defence industries. It operates the largest compound semiconductor plant in Europe, and manufactures gallium arsenide (GaAs) based ICs on 6-inch wafers for mobile phone handsets and the wireless infrastructure.

QinetiQ is a leading international defence and security technology company that was formed in July 2001 from the UK Government's Defence Evaluation & Research Agency (DERA). QinetiQ's Optronics Centre in Malvern, Worcestershire has an international reputation for the growth of GaN-based structures for microwave transmitters.

Based in Cambridge, Thomas Swan Scientific Equipment Ltd.is a wholly owned subsidiary of Aixtron AG and designs and manufactures of metal-organic chemical vapour deposition (MOCVD) systems for the growth of LED layer structures and other devices.

Forge Europa is an independent SME specialising in the design and development of high-performance LED displays, assemblies and light sources.

Cambridge University has a renowned position in the understanding and development of GaN-based devices under the leadership of Prof Colin Humphreys.

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