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5 October 2007


Sandia demos high-quality GaN growth on Aonex’s A-GaN substrates

The USA’s Sandia National Laboratories has demonstrated the growth of high-quality gallium nitride on the A-GaN substrates of Aonex Technologies Inc, a subsidiary of Arrowhead Research Corp of Pasadena, CA, USA.

Aonex says that its A-GaN substrates provide a way to reduce the cost of GaN-based devices while also improving performance. According to recent studies by Strategies Unlimited, the market for such advanced substrates for GaN devices is expected to grow to more than $440m by 2010. This growth will be driven strongly by the blue laser diode market, which Strategy Analytics expects to grow at a compounded average annual growth rate (CAAGR) of 103% to over $1bn by 2011. Strategy Analytics also forecasts the LED market to grow from $5.2bn currently to $8.9bn by 2011.

The A-GaN substrates are intended to offer a low-cost replacement for bulk GaN substrates in blue laser manufacturing, and could enable improved design flexibility, leading to smaller devices and further cost savings. The firm claims that the substrates could also offer benefits for manufacturing blue LEDs (currently fabricated on sapphire and silicon carbide substrates, which give lower-than-desired device quality and yield). Using bulk GaN substrates instead can produce superior devices, but the substrate cost is prohibitively high. Aonex reckons that its A-GaN substrates could help break this trade-off between cost and performance by enabling the growth of high-performance device structures on reasonably priced substrates while simplifying the manufacture of high-efficiency, vertical devices.

The firm describes its A-GaN wafers as effectively veneers of bulk GaN wafers, offering high material quality at a lower price than bulk GaN. Each substrate consists of a thin, single-crystal layer of GaN (about 500nm thick) bonded to a low-cost polycrystalline aluminum nitride support wafer. The thin GaN layer provides the high-quality surface for device fabrication, while the AlN support material is chosen for its low cost, fracture resistance, process compatibility, and ease of removal following device growth.

The substrates are fabricated using a proprietary process to transfer thin layers of GaN directly from bulk GaN substrates and onto the support material. These layers enable the growth of GaN with quality comparable to that of the original bulk GaN donor, the firm claims. Also, because multiple layers can be transferred from each bulk GaN donor wafer and used to form multiple substrates, the cost of A-GaN wafers could be substantially lower than that of bulk GaN. Aonex has already demonstrated the transfer of 10 layers from a single substrate and expects to reach 20 layers or more in production.

A-GaN also offers a coefficient of thermal expansion that is nearly identical to GaN and increased physical robustness relative to bulk GaN wafers, reducing breakage-related yield loss. In addition, the support material that makes up most of the substrate is readily removable via a simple chemical etch, which could simplify the fabrication of high-performance devices such as vertical LEDs and open up new design possibilities, the firm reckons.

In the collaboration, Sandia grew GaN on A-GaN and sapphire reference substrates. The GaN was then characterized using analytical techniques including transmission electron microscopy (TEM) to measure the material quality, particularly the density of defects (dislocations). Data analysis indicates that GaN grown on A-GaN was as good as the bulk GaN donor wafer that was used to fabricate the substrate (about 4 x 10^6cm-²). Aonex says that it is currently in discussions with device manufacturers to fabricate devices on A-GaN substrates.

See related items:

Aonex and Kyma collaborate to cut blue laser and LED substrate costs

Sandia demonstrates reduced-bowing GaN growth on Aonex's sapphire-on-AlN substrates

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