By Debra Vogler, senior technical editor
February 3, 2011 — With GT Solar’s acquisition of Crystal Systems in 2010, the company made a decision to break into large substrates for the LED market. GT Crystal Systems’ COO, Kurt Schmid provides details about the company’s directional solidification process based on the heat exchanger method, in which the seed is at the bottom, thereby forcing impurities away from the solid as the material solidifies (see Figure). Bubbles (and other impurities and dislocations) are forced to move up; the result is a large ingot with low bubble content, high purity levels, and a very uniform crystal structure that lends itself to the deposition of materials such as GaN. According to the company, this process is very controlled and low stress.
Figure. Sapphire growth process. SOURCE: GT Crystal Systems
If the LED market is to continue to thrive, Schmid observes that wafer manufacturers using MOCVD equipment will need to move to traditional semiconductor manufacturing technologies, which are based on 6"-diameter and larger size substrates. Such a move translates to using more automation, which goes hand-in-hand with efforts to lower the price of LEDs. Schmid anticipates additional potential markets will open up as LED prices decrease, and performance improves.