The contention of LED substrate material: the difficulty of catching GaN on silicon base is bigger?

On the use of GaN on silicon substrate of LED, although the LED sapphire substrate and its performance and now occupy the market, but there are still some problems in the production. Moreover, the sapphire substrate prices continue to fall, the performance of the LED formed on the sapphire substrate is also gradually improved. For example, the recent PSS (patterned sapphire substrate) is a large-scale application, a substantial increase in the brightness of sapphire substrate LED. Therefore, it is more and more difficult to pursue the sapphire substrate on silicon substrate GaN.

The LED formed on the Si substrate should be much cheaper than the sapphire substrate LED. Silicon wafer prices have been lower than Sapphire Wafers, the situation will continue in the future, so the use of silicon based GaN substrate cost reduction effect can be immediately displayed. The most effective way to cut costs is in the high degree of automation, has completed the depreciation of the Si-CMOS plant processing Lei Jingjing circle. LED manufacturing process is fully compatible with the CMOS production line, without additional investment is also very important.

But the cost reduction effect may also be the problems in the production of offset, the problem is that the Si and GaN of the thermal expansion coefficient and different lattice constants, existence of lattice mismatch and thermal mismatch between the two, will cause the LED epitaxial wafer bending or cracking. The Si substrate usually sets the dislocation control layer, but it is very difficult to control the dislocation in mass production. Therefore, it is difficult to establish a reproducible production process with high yield.

Silicon based GaN substrate production companies are trying to get rid of monopoly

Market oriented production of silicon based GaN substrate LED companies only one of China's crystal optoelectronics. In the entire LED market, the technology share of less than 1%. Germany OSRAM Opto Semiconductors (Osram Opto Semiconductors) is expected to become the largest new enterprise. The company is now using 150mm wafer (6 inches) of the pilot line, performance of silicon GaN substrate is gradually approaching the sapphire substrate, using 200mm (8 inches) production line production estimates need about 2 years time.

On the other hand, the United States Bridgelux (BridgELux) announced in 2011, will put all the products from the sapphire substrate was changed to Si substrate, and released a variety of high performance LED, but performance than the sapphire substrate products to the poor. At that time, the company used 1 200mm wafers can produce about 1000 chips, and the commercial attractiveness of the production of about 20 thousand, but if the current output close to this figure will have a certain advantage. 200mm is preparing to cooperate with Toshiba, starting in 2013 to produce silicon wafers in japan. The United States also enjoy PHILPS lumens of major LED companies of the US Department of energy subsidies to develop the Si substrate, the company published about 75mm (3 inches) wafer results become the focus of attention, now the research object is the 150mm wafer. In addition, South Korea SamSung also uses 200mm silicon wafer fabrication of the device was verified. Low prices continue to give birth to new technologies

Through the use of new technologies, 200mm sapphire wafer is expected to be put into use, and Si wafer competition. Moreover, sapphire wafer prices also fell sharply, the 150mm wafer prices in 1 years ago for $450, now down to 220 to 270 dollars, to 2012 low will probably fall below $200 mark, then there may soon fell to $150. Even so, the price of sapphire wafers is still close to 2 times the Si wafer, but it is still called a new business led to a major price competition.

The push for a new round of price decline, will be a large supplier of sapphire crystal manufacturing equipment, sapphire substrate made by cutting sapphire crystal. 2 years ago, the weight of the crystal is from 25 to 35kg, and now it has reached the range of 80 to 100kg. Some companies can even produce more than 100kg crystals.

Other new crystal growth techniques may be able to make the yield more than 2 times the previous. But now, these techniques can only be applied to less than 50kg crystals. Generally, the sapphire crystal grows along the A surface, and the orientation of the substrate is parallel to the C plane. Its purpose is to control the lattice mismatch with GaN at a minimum. When the substrate is manufactured, the wafer is removed from the crystal along the direction perpendicular to the axis. Therefore, the yield of raw material is less than 30%. And now, the crystal has been able to grow along the C axis on the surface, you can cut the crystal like bread, raw material yield increased to 85%. However, due to the slow extraction of wafers from the crystal, the cycle time will increase. It can be seen that both the growth of the crystal on the axis of the technology, or the development of larger crystal block technology, can significantly reduce the cost. Moreover, there may be other technology debut. For example, ribbon growth (EFG) is a difficult to master technology, but for more than 150mm of the wafer, the technology is expected to improve the cost efficiency.

The sapphire substrate LED, silicon substrate using GaN LED to overcome the increasingly high performance cost, is facing a big problem, GaN on silicon substrate LED may even never reach the "future" hat, without the light of day. Silicon based GaN substrate LED can capture some of the market, or completely replace the sapphire substrate it? For now, Si LED is still a strong competitor. Contributing author: Jean-Christophe Eloy, President and CEO of Yole Developpement