At the International Nanotechnology Exhibition & Conference (nano tech 2009), Toshiba Corp showcased a near-ultraviolet LED that is being developed for use in next-generation LED lighting. The company says the LED features a high external quantum efficiency of 36% and an emission wavelength of 380nm band.
Toshiba Showcases Near-ultraviolet LED
In order to enhance the luminous efficiency, the company increased the flatness by minimizing the GaN crystal defects. Specifically, Toshiba improved the AlN buffer layer provided between the sapphire substrate and the GaN crystals to absorb the difference in lattice constant. It employed the "two-step growth process" in which AlN single crystals on the scale of microns are formed by a high-temperature process at 1,300°C or higher after a thin AlN layer is formed on the sapphire substrate.
The company says this process reduced the defects of GaN crystals grown on the AlN layer. On the other hand, when the thickness of the AlN layer increases, the substrate tends to break more easily due to the difference in thermal expansion coefficient between the sapphire substrate and the AlN layer. But Toshiba avoided this problem using a proprietary technique.
In addition, the company notes that the new near-ultraviolet LED has a color temperature of 2,800K and a general color rendering index (Ra) of 90 or higher by using a combination of red (R), green (G) and blue (B) phosphors, which are almost equivalent to those of fluorescent lamps.
