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Making white LED from three-tiered GaN nano-rods

Posted: 04 Feb 2016 ?? ?Print Version ?Bookmark and Share

Keywords:National Taiwan University? white LED? nano-rod? GaN? ITO?

The current method in creating white light emitting diode (LED) entails that engineers must either use a white phosphor coated package illuminated by a single colour LED or mix red, green and blue LEDs together. But if researchers at National Taiwan University (NTU) are successful, they will be able to produce white light from a single tiered-column LED producing white light at a single pixel.

The work at NTU is being headed by professor Chih-Chung Yang at the Institute of Photonics and Optoelectronics. It is based on the idea of embedding quantum wells inside gallium nitride (GaN) and indium gallium nitride (InGaN) nano-rods grown very close to one another from the same substrate. These LED arrays are constructed using metal-organic chemical vapour deposition (MOCVD) pulsed growth resulting in superior emission performance than can be achieved with traditional methods, according to Yang.

GaN LED

Scanning electron microscopy (SEM) images reveal a single uniform diameter column pixel will emit a single colour (left) but by narrowing it at the top tier (right) two different colours can be emitted by the same pixel, and by adding a third even narrower tier a third colour can be emitted, permitting a single pixel to emit red, green and blue (RGB) resulting in white light from a single pixel. (Source: NTU)

"We can grow multi-section nano-rods of different cross-sectional sizes, and demonstrate a broader mission spectrum compared to single-section nano-rods," Yang said. "Our development of these multi-section nano-rod LEDs targets the implementation of phosphor-free white-light emission," he added.

The sidewall emission also is much more efficient because there is much more surface area, he said. By extending a pyramid of different diameters vertically, even more light can be emitted from inside each column. With a properly balanced red-green-blue (RGB) light source, the technique should be able to produce a variety of cold and warm hues of white light.

GaN LED

Using oppositely doped gallium nitride (+GaN top and -GaN bottom) and a sandwiched quantum well, researchers at NTU show the principles by which a GaN LED works. (Source: NTU)

"We can also use gallium zinc oxide [GaZnO] instead of ITO [indium tin oxide] for transparent interconnections which a very highly conductive," said Yang.

His group is also working on enhancing light emission with surface plasmons, providing efficiency and avoiding the droop effect as well as increasing the modulate on bandwidth by swapping out the carriers, allowing high-speed communications using visible light because of the very fast decay of surface plasmons coupled to gallium tin oxide.

- R. Colin Johnson
??EE Times





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