News For LED: The Prospects for Gallium Nitride on Silicon

Though some still consider GaN-on-Si a "niche play," new numbers from IHS DisplayBank say the technology will account for 40 percent of LED shipments globally by 2020.

As LED manufacturers compete to reduce their production costs, some are looking at moving from expensive sapphire substrates to the tried-and-true, silicon-based technology perfected in microchip manufacturing. Others see the GaN-on-Si approach as a niche play that will not gain significant traction long-term.

It's no niche, claims IHS / DisplayBank, in a just-published forecast for market penetration of GaN-on-Silicon LEDs. The research points to strong growth, to the tune of a 69 percent CAGR (change in average growth rate), over the time frame to 2020. This silicon-based approach will grow to account for 40 percent of the LED market by the end of the decade, if IHS is correct.

That would be no small accomplishment, and certainly a break-out from the "niche market" forecast by Lux Research, which sees a much different fate for silicon in the LED space.

Silicon bears

Back in July of this year, Lux opined that sapphire will remain the "entrenched wafer technology for solid-state lighting." Lux sees the overall industry growing to some $80 billion and pegs the market for LED epiwafers at $40 billion. But advances in sapphire-based manufacturing, combined with continuing difficulties for GaN-on-Si such as the "physical mismatch between silicon and GaN crystal lattices," will limit the growth of silicon substrates, according to Lux. Researcher Pallavi Madakasira believes that GaN-on-Si will find use only in commercial lighting applications, and will peak at about 10 percent of the overall market by decade's end.

The two research firms do agree on the present global market size. In its yearly formatting document, IHS reported LEDs account for a whopping 90 percent of 1H-2013 demand for LED sapphire substrates, and a December 2013 update from the group said to date, the biggest demand for sapphire ingots and substrates comes from the LED market stating in 2013, 95 percent of GaN LEDs will be manufactured on sapphire wafers, while only 1 percent will be manufactured on silicon wafers. But IHS expects the growth in the manufacturing of GaN-on-Si LEDs between 2013 and 2020 to take market share from both sapphire and silicon carbide wafers, to reach the forecasted 40 percent global market share according to the group.

Silicon bulls

Part of the reason for IHS's optimism is the ease of manufacturing silicon wafers at large sizes. "Manufacturing large ingots made from sapphire is difficult, whereas silicon wafers are available from 8 inches up to 12 inches and are generally cheaper and more abundant," according to IHS researcher Dkins Cho.

Another factor favoring silicon is the existing infrastructure that can readily be converted to LED manufacturing. Cho sees the "large pre-existing industry for silicon-based manufacturing" that can be "leveraged" and that will create the kinds of economies of scale needed to bring LED production costs down. Cho also makes the point that repurposing these facilities should require only "minimal investment." Cho cites the maturity of the CMOS semiconductor industry, with fabs featuring "excellent inspection tools" already in place, which outclass existing LED industry processes.

In its runup to 40 percent global market penetration, IHS sees a gradual buildup over the next two years, with under 20 percent achieved by mid-decade. Penetration will reach 30 percent by 2018 and hit the 40 percent mark by 2020.

By way of contrast, Lux believes the current 4-inch (sapphire) wafer size will continue as the "dominant size," peaking in 2017 with a 62 percent market share (or $2.1 billion in sales.) The group sees larger 6-inch wafers coming into their own by 2020 with a forecast 35 percent share (or $1.4 billion). Lux also cites advances in entrenched sapphire substrate manufacturing, including advances in deposition methods that move away from MOCVD (metal-organic chemical vapor deposition) in favor of hydride vapor phase epitaxy (HVPE). This changeover promises faster and cheaper manufacturing and should help keep sapphire competitive vis-a-vis silicon.

Coin toss

So sapphire continues to make incremental efficacy improvements and equally incremental price decreases. As such, according to Lux research, the long-term bet is still with this entrenched technology. Yields and performance continue to improve even in the face of larger silicon-based wafers and their economies of scale.

IHS still stakes its forecast on silicon, figuring the technology will overcome its serious hurdles, including mismatches with GaN regarding its crystal structural and coefficient of thermal expansion.

My opinion: seven years is a long way off, representing dozens of generations of technology development, by some dedicated and market-leading companies including Philips, Cree, and Osram. So while we don't count out silicon as a long-term manufacturing solution, it's still to early to call which way this race will go.

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