November 12, 2012 - Wide bandgap semiconductor materials such as gallium nitride can significantly outperform traditional silicon-based devices in power electronics and light-emitting diodes (LEDs). On the other hand, they're also vastly more expensive ($1900 for a 2-in. bulk GaN substrate, vs. $25-$50 for a 6-in. Si substrate), and silicon has the advantage of being easily integrated into volume manufacturing. So where's the midpoint where GaN's capabilities and extra costs align to make it the technology of choice, and for which application?

"The future of bulk GaN is going to come down to how it faces off against silicon substrates," stated Pallavi Madakasira, Lux Research analyst and the lead author of a new report which breaks down the manufacturing costs for ammonothermal and hydride vapor phase epitaxy (HVPE) processes for making bulk GaN, as well as for GaN epitaxy on both silicon and GaN substrates, and determined where the price/performance trade-off will land. "Bulk GaN wins in laser diodes and it can become relevant in LEDs and power electronics by boosting yield and performance."

Among the report's findings:

-- HVPE is the cheaper alternative. Costs for ammonothermal substrates (2-in.) will fall by more than 60% to $730/substrate in 2020. That's a steeper curve and to half the anticipated cost of 4-in. HVPE substrates, which are seen falling 40% to $1340/substrate -- but HVPE's larger size from which more chips can be yielded makes it the more economical choice, Lux says. (It's a mantra that has always driven, and continues to drive, cost reduction efforts in semiconductor manufacturing.)

-- Performance boost is key. Bulk GaN can overcome high cost by boosting performance -- lumen (lm) output in LEDs, or volt-amp (V-A) capacity in power electronics -- by allowing the use of smaller dies and providing higher yields. In LEDs, GaN can match silicon with a 380% relative performance -- an ambitious but realistic goal. For power electronics, performance at 360% of devices on silicon makes bulk GaN a winner.

-- New materials are on the horizon. Emerging materials such as aluminum nitride (AlN) are ideally suited to very low wavelength, ultraviolet LED, green laser diode, and high-switching-frequency power electronics applications, and can be an effective alternative to bulk GaN.

GaN-on-silicon as a substrate will continue to proliferate as the low-cost option for wafers. Bulk GaN (GaN-on-GaN), while costing more, can be competitive at the device level under certain conditions, such as laser diodes. In other applications such as LEDs and power electronics, though, "it must race to become relevant" by proving it can make devices cost-competitive through higher yields and performance.

Substrate and epitaxy cost breakdownfor GaN-on-silicon and GaN-on-bulk GaN. (Source: Lux Research)