Arrowhead Subsidiary, Aonex, Demonstrates High Quality Gan Growth On Its Proprietary A-Gan Substrates Which Target The Gan Laser Diode And LED Device Markets
Pasadena, CA - Arrowhead Research Corporation announced recently that its majority-owned subsidiary, Aonex Technologies, Inc. and partner Sandia National Laboratories have successfully demonstrated the growth of high-quality gallium nitride on Aonex's proprietary A-GaN substrates. Gallium nitride (GaN) and its alloys with indium nitride and aluminum nitride form the building blocks of devices such as blue, green, and white light emitting diodes (LEDs) and blue laser diodes. Aonex's A-GaN substrates provide a pathway for reducing the cost of GaN-based devices while also improving performance. According to recent studies by Strategies Unlimited, the market for advanced substrates like A-GaN for gallium nitride devices is expected to grow to more than $440 million by 2010. Much of this growth will be driven by the blue laser diode market which Strategy Analytics expects to grow to over $1B by 2011, a compounded average annual growth rate of 103% over the next four years. Strategy Analytics forecasts the market for LEDs to grow from its current value of $5.2B to $8.9B by 2011.
Laser diodes are manufactured by depositing (or ‘growing') GaN-based device structures on expensive bulk GaN substrates. Aonex's A-GaN substrates are intended to offer a low-cost replacement for bulk GaN and could enable improved design flexibility that could lead to smaller devices and further cost savings. A-GaN™ substrates may also offer substantial benefits to LED manufacturers. Blue LEDs are currently fabricated by depositing GaN-based device structures on sapphire and silicon carbide substrates. Because of the challenges of growing GaN layers on these materials, the resulting device quality and yield is lower than desired. While superior devices can be produced using bulk GaN substrates, the cost of such substrates is prohibitively high. Aonex's 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.
Aonex's A-GaN wafers are, in effect, veneers of expensive bulk GaN wafers, offering high material quality at a lower price than bulk GaN. Each A-GaN substrate consists of a thin, single crystal layer of GaN (~500 nm) that is bonded to a low-cost polycrystalline aluminum nitride support wafer. The thin GaN layer provides the high quality surface for device fabrication while the support material is selected for its low cost, fracture resistance, process compatibility, and ease of removal following device growth. A-GaN substrates are fabricated using a proprietary process to transfer thin layers of GaN directly from bulk GaN substrates and onto the support material. These transferred GaN layers enable the growth of GaN of a quality that is comparable to that of the original bulk GaN donor. In addition, because multiple layers can be transferred from each bulk GaN donor wafer and used to form multiple A-GaN 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.
Beyond its growth-related benefits, A-GaN offers a coefficient of thermal expansion that is nearly identical to GaN and increased physical robustness relative to bulk GaN wafers, which reduces breakage-related yield loss. In addition, the support material that makes up most of the A-GaN substrate is also readily removable via a simple chemical etch, which could simplify the fabrication of high performance devices, such as vertical LEDs, and open up a wide range of new design possibilities.
In the collaboration, Sandia National Laboratories grew GaN on A-GaN and sapphire reference substrates. The gallium nitride was then characterized using a variety of analytical techniques including transmission electron microscopy (TEM) to measure the material quality, particularly the number of dislocations in a given area, commonly referred to as defect density. Defect density is strongly correlated with GaN material quality, and reduction of the defect density results in better performing GaN-based devices. Analysis of the data indicates that GaN grown on A-GaNTM was as good as the bulk GaN donor wafer that was used to fabricate the substrate, approximately 4 x 10-6 cm-2.
Aonex is currently in discussions with device manufacturers to fabricate devices on A-GaN™ substrates. Interested parties should contact samples@aonextech.com.
SOURCE: Arrowhead Research Corporation