Anvil Semiconductors Ltd of Coventry, UK and the Cambridge Centre for GaN (part of University of Cambridge’s Department of Materials Science and Metallurgy) have grown 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 intellectual property (IP) that enables growth of device-quality silicon carbide on 100mm-diameter silicon wafers. The proprietary process is said to overcome mismatches in lattice parameter and thermal coefficient of expansion and can be readily migrated onto 150mm-diameter wafers (and potentially beyond) without modification and is therefore suitable for large industrial-scale applications.
Conducted under a project funded by Innovate UK, the MOCVD growth trials at Cambridge have resulted in single-phase cubic GaN. The layers, characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence and atomic force microscopy (AFM), show promise for LED applications, it is reckoned.
The availability of cubic GaN has the potential to remove the strong internal electric fields which plague conventional green LEDs and which impair electron-hole recombination and make it difficult to improve internal quantum efficiency (IQE). Also, cubic GaN has a narrower bandgap and improved p-type electrical properties compared with the standard hexagonal GaN phase normally used for LEDs and therefore it offers several advantages. The ability to produce cubic GaN from a readily commercializable process on large-diameter silicon wafers is recognised as a key enabler for increasing the efficiency and reducing the cost of LED lighting.
The team intends to continue development to the point of fabricating sample LEDs before looking for an industry partner to help commercialize the technology.
“This is a very promising development and fits well with our current research activities to develop state-of-the-art LEDs,” comments professor Sir Colin Humphreys, director of research in the Department of Materials Science and Metallurgy and head of the Cambridge Centre for GaN. “It has the potential to overcome many of the challenges currently seen for green devices and could contribute significantly to the ongoing solid-state lighting revolution,” he adds.
“This is a very exciting result which potentially opens up the LED market for our 3C-SiC on silicon material,” says Anvil’s CEO Jill Shaw. “We will certainly be looking for partners to help us take this opportunity forward”.
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 material has applications ranging from power devices and LEDs to medical devices and MEMS.
The Cambridge Centre for GaN has been involved in developing GaN growth technologies for over 15 years, supplying epitaxial layers to groups involved in GaN research in both the UK and internationally. It has experience in growing GaN layers on to sapphire, bulk SiC, bulk GaN and large-area silicon substrates. In 2011, the IP developed for GaN growth on silicon was acquired by Plessey Semiconductors, which is using this technology to manufacture LEDs commercially. The centre has a range of EPSRC, EU and industrially funded programs including a grant ‘Lighting the Future’, focused on developing LED structures in GaN and understanding the factors limiting their performance. It also has projects developing GaN for a diverse range of applications, including electronics, lasers and single-photon sources based around its MOCVD growth reactors.
