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Bulk GaN: Too Little, Too Late?

Development may be in full swing, but the market is still waiting for much cheaper bulk GaN, reports Compound Semiconductor.

While nitride-based devices more than challenge the performance of silicon- and sapphire-based counterparts, LED and power electronics industries are still waiting for bulk GaN costs to come down. Your average six inch silicon wafer costs a mere $12, a two inch sapphire substrate will set you back only $8 to $10, but the cost of a two inch GaN substrate could run to $2000 at least.

"We have ran simulations of LED price structures and we think for the moment that GaN substrates are just too expensive," saysHong Lin, market and technology analyst of compound semiconductors, at Yole Développement.

While the performance of a GaN-on-GaN LED beats that of the GaN-on-sapphire equivalent, the manufacturing costs of the die are so much higher that this performance just can't compensate. "The [substrate] price must reduce by at least two to three times to significantly increase adoption," adds Lin.

The analyst outlines a similar scenario in power electronics applications. While many companies worldwide manufacture GaN-based devices, very few are using a GaN substrate. "We see Hitachi Metals and Sumitomo Electric showing products of GaN on GaN power devices," she says. "But in general not many manufacturers are developing power GaN, instead they are working on GaN on silicon."

Indeed, Lin reckons bulk GaN simply won't penetrate power electronics segments unless four inch wafer costs drop to around $1500 by 2020. This, says Lin, is possible, but will take a lot of work.

But while LED and power electronics manufacturers wait for GaN substrates to compete on price with silicon and sapphire alternatives, laser diodes have provided a lucrative market for bulk GaN. Blu-ray applications currently represent the largest market for blue laser diodes, significantly bolstering demand for GaN substrates; but will this last?

"The new generation of playstations is coming, which include blue laser diodes but Blu-ray will not grow forever," she says. "In two to three years, we will still have Blu-ray technologies, but consumers are now using the Internet [for gaming and watching DVDs] instead, so Blu-ray technology growth will not persist."

And while many await laser diode lighting to take off, Lin reckons performance issues are holding back progress. "We've seen a lot of work on the use of laser diodes for white light coming out of the University of California, Santa Barbara, but efficiency is still an issue," she says. "BMW has been working on using laser diode-based white lighting in its car lights but we haven't actually seen any [products] since the first announcement [in 2011]."

Ramping up development

But amid sluggish markets, bulk GaN development is still rife. Today, Japan-based companies produce the majority of commercial GaN wafers - some 85% - using hydride vapour phase epitaxy, while the remaining market comprises US- and China-based players honing HVPE techniques and developing ammonothermal methods.

Key Japan-based companies Sumitomo Electric, Hitachi Metals and Mitsubishi Chemical all manufacture two inch wafers and according to Lin, these and other Japan-based companies have also showcased four and even six inch wafers. Larger wafer sizes have yet to move beyond demonstrations, but according to Lin, the established Japan-based conglomerates definitely have an edge over the rest of the market.

"Japanese companies have been [growing crystals] for a long time with much of their demand coming from Japan. Many devices, especially laser diodes, are all produced in Japan," she highlights. "We also hear suspicions still exist over the quality of substrates [from outside of Japan]. When manufacturers go into production, they want constant substrate quality, so prefer to buy from Japan-based companies."

However, US-based businesses are making headway. Both Soraa, Kyma and other crystal growers have bagged millions of dollars in US Department of Energy funding to develop bulk GaN for LEDs and power electronics.

For example, Soraa is honing its ammonothermal bulk gallium nitride (GaN) substrates. Having produced two inch wafers, the business reckons it will soon deliver four inch versions. Meanwhile Kyma is focusing on HVPE to ramp up production of high quality low cost GaN substrates.

Still, the delivery of competitive, commercial products may take time. As Lin points out: "Thesecompanies can't yet challenge the Japanese businesses and I don't see it happening for the next three to five years."

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