Gallium nitride on silicon, which opportunities?

GaN on sapphire

While much of the LED industry is now focused on research and development along with mass production of GaN on patterned sapphire substrates, analysts are wondering whether the industry will make a transition to GaN on silicon technology or not.

Advantages of GaN-on-Si compared to GaN-on-sapphire are basically the lower cost of production of silicon substrates when compared to sapphire and the wide availability of CMOS manufacturing equipment for silicon wafers.

However, LEDs fabricated using gallium nitride on silicon still have to reach the efficacy of LEDs made on sapphire, as the LEDs produced using silicon have so far reached efficacies of slightly more than 110 lm/W for production, with Cree claiming an efficacy of 150 lm/W, but still light extraction for LEDs manufactured on silicon remains around one third that of LEDs manufactured on sapphire.

The reason of this lack of light extraction is due to the fact that the silicon crystal structure poorly matches that of gallium nitride and therefore deposition of GaN on silicon creates dislocations and even cracks that impact negatively the efficacy.

The industry is still mainly undecided on the issue, as the current technology with PSS (patterned sapphire substrates) seem to work just fine and cost is going down rapidly, so will the cost differential between the two categories be enough to justify a transition?

While some players like Toshiba in Japan have started to offer GaN on silicon wafers, almost all other major players are still in the R&D phase and it is unclear whether they will move to using silicon substrates.

It is also true that improvements on the GaN-on-Si technology have been made and Toshiba recently announced in partnership with Benelux a new proprietary technology that uses a buffer layer to largely prevent dislocations and cracking on the interface between GaN and the silicon substrate.

However, while research firms like Yole Developpment are skeptic on the future of GaN on silicon for LEDs, claiming that by year 2020 the technology will capture less than 5% of the total LED market, other applications are on the horizon.

Power devices may be the killer application that will propel GaN-on-silicon towards prime time

There are a few reasons for this optimism, the first one being that, differently from the LED market, there is no other GaN-deposition related technology to compete with.

The incumbent technology for microelectronics-related power applications is silicon itself and silicon has already reached its performance peak as for a higher breakdown voltage and other factors that may lead to smaller, more compact devices and cannot improve further.

While it is true that the cost of GaN-deposited power devices is still significantly higher than traditional silicon-based ones, the prices are coming down fast.

Other advantages of GaN-based power devices are high-frequencies and high conversion efficiencies, which would mean cost savings in the long run.

However, GaN-based power devices are not totally exempt from issues.

One of the main ones could be the stark difference in thermal expansion between gallium nitride and silicon which would be a problem during high loads of work and this may require additional layers of material to work as buffer, therefore increasing the cost.

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Further evidence of strong LED production growth in China for the next few years

LED lighting market projected to grow 12-fold by 2023

In a market analysis of last year, research market firm HIS forecast a boom in the LED industry in a report with title “Demand for Key Raw Material Set to Double as LED Market Booms”.

According to the firm, a substantial increase in LED shipments would drive up the request for precursor used in MOCVD to create the appropriate conditions for epitaxial growth of the thin film over the sapphire substrate from 32 tons to 69 tons in just four years.

As written in this blog a few days ago there are other signs that point to a substantial increase in Chinese LED production in the next few years.

Many analysts are questioning whether LED makers, mostly based in China and Taiwan, could sustain such a growth or if, in case of lower growth than expected, whether some Chinese makers may be forced out of business by excess of production capacity and lack of demand.

According to fresh news it now looks that Sanan, which is the largest Chinese LED firm and accounts for some 30% of the whole LED production for the country, seems to be increasing their manufacturing capacity.

In addition to this news, a new Digitimes report suggests that the Chinese Government may have set a new target for LED production to $164 billion for the year 2020, with the lion share of this amount (at about 70%) coming from lightning.

Backlight market in China also grew considerably from 2012 to 2013, with a 74% increase, and there is also hope that the growth will be sustained throughout 2014.

The factors behind this growth are more than one:

  • the rapid urbanization in China, with a forecast for 2020 that 60% of the population will live in urban areas which would drive upwards the demand for urban lighting;
  • the plans for a rapid increase in the country network of railroads and highways, with the high-speed railroads that are expected to create the backbone for the transport infrastructure of China in the 21st century and which would add up to the current expected market for LEDs in the next few years;
  • the trend in decrease in price and increase in efficiency for LEDs which are expected to grow in the future assuming that new technologies such as GaN on silicon wafers instead of sapphire substrates may keep up with the promises.

All the above factors combined together seem to indicate and be conducive to what pointed out to the conclusions highlighted by the market research quoted above.

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