GaN Substrates In Mass Production
GaN substrates are needed for stable manufacture of the high-power, high-quality violet lasers to be used in next generation high-capacity optical disc equipment such as for the Blu-ray and Advanced Optical Disc (AOD) formats. Conventional DVD players typically use red lasers, which depend on gallium arsenide (GaAs) as their light source for reading and writing data from and to optical discs.
A violet laser uses a laser emission from the GaN epitaxial layer. In the epitaxial growth of GaN, sapphire substrates are commonly used. Since the physical properties of sapphire substrates and GaN are different, sapphire substrates cause dislocation densities to become high. Cleavage grows to an unsatisfactory level, reducing the output power and lifetime of the laser. As a result, there has been strong demand for high-quality (low-dislocation), large-diameter GaN substrates. Fabrication of GaN substrates is also made difficult because of a large nitrogen decomposition pressure.
SEI's 50mm GaN substrate has a low dislocation density of the order of 100,000/cm2 or less.
SEI started developing a GaN substrate in 1995, and succeeded in developing 2mm GaN substrates in 2000. SEI gained proficiency in GaN substrate production through sample shipments to major Japanese laser device manufacturers.
