14 July 2011

Translucent launches GaN-on-Si templates with embedded DBR mirrors

Translucent Inc of Palo Alto, CA, USA (a subsidiary of Australian-listed company Silex Systems Ltd), which provides rare-earth-oxide (REO) engineered silicon substrates for low-cost epitaxy, has developed a proprietary gallium nitride on silicon (GaN-on-Si) wafer template with embedded distributed Bragg reflector (DBR) mirrors for application to low-cost LED growth.

The structure and the process used to grow it is being explained at the International Conference on Nitride Semiconductors (ICNS-9) in Glasgow, Scotland, UK (15 July) in the post-deadline paper ‘Integrated High Reflectivity Silicon Substrates for GaN LEDs’ (Session LN-2).

Translucent is reporting technical details in the development of a 100mm-diameter wafer that exhibits high reflectivity using a lattice-matched rare-earth-oxide material grown onto a silicon substrate. The structure is capped by a GaN layer that can support further nitride epitaxy for the growth of LED structures. The lattice engineering offered by the REO material system, which is grown epitaxially on silicon (111) substrates, can be used to mitigate strain that arises during growth of GaN. REO materials further enable highly reflective mirrors embedded in engineered silicon substrates. The new technology is being offered to prospective customers who are ready to grow LEDs on large-diameter wafers.

Translucent says that its silicon solution mitigates the need to remove the substrate and the use of handle wafers during subsequent processing. As the LED industry migrates to larger wafer sizes, a one-step epitaxial solution is expected to provide the best path to cost-effective scaling, the firm adds.

Translucent says that, using its new embedded silicon solution (‘Mirrored Si’), LEDs can now be grown directly on top of the GaN-on-Si template that includes an embedded DBR mirror, directly lattice matched to the silicon substrate. On top of this DBR mirror is a layer of proprietary patented rare earth oxide, which allows GaN to cap the template and does not require subsequent removal of the substrate.

Translucent’s paper describes how this device-ready GaN template can be supplied to LED makers as-is for LED growth. Calculations are made that show that mirror reflectivity can exceed 98% at the LED-emitted wavelength range of 450nm in ultra-thin layers of lattice-matched REO material.

The material was grown using molecular beam epitaxy (MBE) reactors at Translucent’s facilities. The quality of the growth achieved to date leads to high-quality crystalline interfaces that are scalable to large-diameter silicon wafers, the firm claims.

Translucent is currently preparing to scale its embedded silicon mirror technology for commercial rollout with 150mm and 200mm wafers.

Tags: GaN-on-Si templates LEDs MBE

Visit: www.translucentinc.com/documents/presentation_ICNS9.pdf

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