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6 March 2007


Panasonic launching first white LED using GaN substrate

Japanese consumer electronics company Panasonic (Matsushita Electric Industrial Co Ltd) has developed what it claims is the first commercial blue LED chip using a gallium nitride substrate. Volume production of white LEDs incorporating the InGaN-based chip is due to start in mid-March. The company also claims the highest power output for white LEDs.

Compared to conventional, low-cost sapphire substrates, use of a GaN substrate reduces the defect density in the light-emitting layer by 100-fold or more and improves the performance at high drive currents, boosting LED output. The GaN substrate also has a thermal conductivity about five times higher, plus higher electrical conductivity, suppressing the usual reduction in efficiency when the drive current is increased.

The GaN substrate also has a similar refractive index to that of the InGaN light-emitting layer, suppressing reflection at the interface and boosting light extraction efficiency to over 1.5 times that of the company’s sapphire-based LED. The wavelength of the light emitted from the chip is 460nm. The chip is flip-chip mounted on a submount (via an Au bump), so light is extracted from the substrate side of the chip. Panasonic has also added irregularities on the backside of the substrate so that reflection can be prevented completely. The total radiation flux is 355mW, driven at a forward current of 350mA. External quantum efficiency is 38%.

Finally, the fluorescent layer (for converting the chip’s blue light to white light) has uniform thickness, yielding minimal variation in color (unlike the conventional process for applying the fluorescent layer, which generates unevenness in color, the firm says).

Compared to sapphire, the expense of GaN - about ¥1m ($8600) for a 2-inch diameter substrate - has been a bottleneck to commercialization. The company decided to use the substrate because it can set a reasonable price for a high-output LED product. Samples are ¥500 ($4.30) per unit.

The white LED comes in three types: LNJ090W3GRA (with power output of 3W) for automotive and lighting applications, LNJ0H0V8KRA (with a reflector design) for camera flash applications, and LNJ0Y0F9KRA (a point source) for compact lighting applications. Luminous fluxes are 100, 80 and 90lm, respectively, when driven at 1A. Brightnesses are 35, 60 and 35lx, respectively, when the distance between the light source and the measurement device is set to 1m. Package sizes are 7.7mm x 4.2mm x 1.5 mm, 4mm x 4mm x 1.4mm, and 2.04mm x 1.64mm x 0.7mm, respectively.