The GaN wafers developed by NGK feature low defect density across the entire 2-inch diameter of the wafer surface and have a colorless transparency. NGK achieved this through proprietary improvements to liquid phase epitaxial technology for single crystal growth.
In joint research carried out with Nagoya University, green LED chips formed on the NGK GaN wafers showed a 60% internal quantum efficiency*1 (injection current density of approximately 200 amperes per square centimeter). This figure is roughly double that of the green LED chips currently on the market. The results were jointly announced at the International Workshop on Nitride Semiconductors 2012 (IWN 2012) held in Sapporo, Hokkaido (Japan) from October 14-19, 2012.
In previous LED chips using sapphire wafers as substrates, defects of light emission layer were common, especially for green LEDs. These defects prevented a large operation current, which in turn prevented the LEDs from achieving sufficient brightness. This issue can be addressed by the use of the low-defect GaN wafers produced by NGK as substrates that enable dramatically improved light emission layer quality. The reduction in current loss that results allows for a large current, making high brightness green LED elements a reality. When these elements are used to make up green LED light sources, the result is an improvement in brightness of more than 20 times*2 compared to previous models. Light sources can also be made more compact thanks to the simplified heat dissipation structure made possible by less heat generated from current loss. This control of heat-related degradation also enables longer product life.
The realization of high brightness green LED light sources means that high brightness LED light sources are now available for the primary colors of light (red, green and blue). We can thus expect to see advancements in the development of new applications for LEDs, specifically for use in projectors and other imaging applications.
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