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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