Appl. Phys. Lett. 97, 073101 (2010)

White LEDs are a promising technology for next-generation lighting, but cannot emit efficiently over the whole visible spectrum. For example, indium gallium nitride, commonly used in LEDs because it emits efficiently in the blue, can be tuned towards the red by increasing indium content. However, this tuning also causes defects and strain owing to the large lattice mismatch between indium nitride and gallium nitride, and efficiency drops quickly. Now, Shangjr Gwo and colleagues at National Tsing-Hua University in Taiwan have demonstrated efficient indium gallium nitride electroluminescence across the entire visible spectrum.

The key to this accomplishment was relaxing the strain that usually accompanies high indium content. Gwo and colleagues began by self-assembling onto a silicon substrate vertical gallium nitride nanorods that contained a junction between hole- and electron-doped regions. They then grew disks of indium gallium nitride into these junction areas. The nanorod growth template allowed the disks to have relatively low strain, increasing their emissive efficiency. Although each disk emitted a slightly different colour, the total emission summed to a white light. The technique is expected to allow a variety of new designs and to scale well to larger areas.