A violet laser, which has a shorter wavelength than a red laser, is used in such equipment.A violet laser utilizes 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 density to become extremely high; cleavage grows to an unsatisfactory level which reduces the output power and lifetime of the laser. As a result, there has been strong demand for high-quality (low-dislocation), large-diameter GaN substrate. Although there is an active development effort for GaN substrate throughout the world, fabrication of GaN substrate was said to be extremely difficult because nitrogen's decomposition pressure is large.
Using its experience in crystal growth and the processing of other compound semiconductors (GaAs and InP), SEI has developed a GaN substrate that has following features:
(1) Large diameter (2 inches)
(2) Low dislocation density (in the order of 100,000 or less per square centimeter)
(3) Better cleavage, which is vital to a high-performance laser.
SEI has extensive experience in the development and manufacture of GaAs and InP. GaAs is used in near infrared semiconductor lasers for CD players and in red semiconductor lasers for DVD players. InP is used in infrared semiconductor lasers for optical communication equipment. SEI is the world's leading manufacturer of GaAs and InP, supplying its compound semiconductor products to more than 100 companies in Japan, Europe, the U.S., and Asia.
Using its experience in the development and production of GaAs and InP, SEI started developing GaN substrate in 1995, and succeeded in developing 2-in GaN substrate in 2000. SEI gained proficiency in the production of 2-in GaN substrate through sample shipment to major Japanese laser device manufacturers, and initiated mass-production and sales this month.