2-inch SCAM Crystal Serves as Blue LED Substrate

2014/08/20 17:39
Tadashi Nezu, Nikkei Electronics
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Fukuda Crystal Laboratory Co Ltd succeeded in making ScAlMgO4 (SCAM) crystal with a diameter of 50mm (2 inches).

The company expects that the crystal will be used for the substrates of GaN-based light-emitting devices such as blue LED devices and blue-violet laser diodes.

Compared with sapphire, which is often used as the substrates of blue LED devices, SCAM is suited for the reduction of the crystal defects of GaN-based semiconductors. Therefore, SCAM is expected to improve the brightness of light-emitting devices.

When a research group led by Takashi Matsuoka, professor at the Institute for Materials Research, Tohoku University, formed an LED structure by using the prototyped crystal and stacking GaN-based semiconductor layers, it confirmed the crystal's effect of improving brightness.

The lattice mismatch between SCAM and GaN is as small as 1.8%, and SCAM hardly causes crystal defects called dislocation. Though it has been difficult to make SCAM crystal, Fukuda Crystal Laboratory realized the 2-inch high-quality SCAM crystal by using the Czochralski (CZ) method. It improved crystal quality by changing the conditions for crystal growth and the furnace structure.

When the prototyped SCAM crystal was cleaved and its C surface was examined by X-ray diffraction, its full width at half maximum was 12.9 seconds, which is equivalent to the quality of a silicon (Si) perfect crystal.

Also, Fukuda Crystal Laboratory made a wafer only by cleaving an ingot of SCAM crystal without cutting or polishing it, making it possible to lower the cost of wafers. When a GaN thin film was grown on the cleaved surface of the SCAM crystal by using the metal organic chemical vapor deposition method at a temperature of 1,040°C, a low-dislocation crystal having a mirror surface was formed. The company considers that this is a major achievement.

Fukuda Crystal Laboratory plans to increase the diameter of the SCAM crystal and commercialize it. Specifically, it intends to release a 2-inch SCAM substrate by the spring of 2015.