Nano-LEDs emit full visible spectrum of light

Jun 17, 2011 by Lisa Zyga feature
(Left) A single nanodisk-nanorod LED viewed with a field-emission scanning electron microscope. (Right) Some colors of light emissions from nanodisk-nanorod LEDs - violet, blue, cyan, green, and yellow - viewed with an optical microscope. Image credit: Lu, et al. ©2011 American Institute of Physics

(PhysOrg.com) -- Physicists from Taiwan have designed and fabricated nano-sized light-emitting diodes (LEDs) that emit light spanning the entire visible spectrum. Although the tiny full-color LEDs aren't intended for commercial lighting applications, they should be useful in high-resolution microscopy and subwavelength photolithography.

The researchers, Yu-Jung Lu, et al., from National Tsing-Hua University in Hsinchu, Taiwan, have published their study on the nano-LEDs in a recent issue of Applied Physics Letters.

The new nano-LEDs have a unique structure that consists of 40-nm-thick nanodisks sandwiched between two layers of nanorods, resulting in a nanodisk-in-nanorod . The nanodisks are made of gallium nitride (InGaN), a that is widely used in LEDs and , while the nanorods are made of (GaN). However, InGaN LEDs capable of emitting light of the entire have not been achieved until now.

“The InGaN/GaN nanodisk/nanorod structure is similar to a well-known quantum well structure, but in a reduced dimensionality (reduction in lateral sizes),” coauthor Shangjr Gwo, a physics professor at National Tsing-Hua University, told PhysOrg.com. “The InGaN nanodisks sandwiched between the p- and n-GaN regions act as the full-color visible-light emitters when electrons and holes are injected across the p-n junction at a forward bias voltage. The electroluminescent light comes from the electron-hole recombination within the InGaN nanodisks.”

As the researchers explained, the key to achieving full-color LEDs was overcoming large lattice strains, which degrade long-wavelength emissions. The InGaN/GaN system resolves this issue due to the strain relaxation in the nanostructured geometry.

The researchers hope that these full-color nano-LEDs can be used in high-resolution imaging techniques that can resolve ultrasmall subwavelength features of objects. To do this, these techniques must overcome the diffraction limit, which is a fundamental limit on imaging resolution caused by the spreading out – or “diffraction” – of waves. Imaging techniques can get around this limit by using evanescent waves, which reveal information on objects’ subwavelength features, but also decay exponentially away from the object. Due to the short range of the evanescent waves, imaging techniques that detect them are based on near-field optics.

One of these techniques is scanning near-field optical microscopy (SNOM), which uses a tiny probe to generate and retrieve . One of the biggest challenges in SNOM is getting a light source that is small and versatile enough to work on this probe, and that’s where the new nano-LEDs come in. While previous research has demonstrated the advantages of using nano-LEDs on the probes, this is the first time that a nano-LED with a full-color range has been available.

“For microscopy, we can use the nano-LED as a localized excitation light source at a chosen wavelength to selectively excite specific fluorescent molecules,” Lu said.

In their study, the researchers experimentally demonstrated using the nanodisk-in-nanorod for subwavelength photolithography, in which light is used to create a pattern on a light-sensitive material. They predict that, by fabricating the nano-LEDs onto the SNOM probe tips, they could achieve better spatial control for future subwavelength photolithography.

“For the applications of photolithography, the freedom of using nano-LEDs at any wavelength broadens the choice of photoresist and allows for the control of their photo-response,” Lu said.

Explore further: In-situ nanoindentation study of phase transformation in magnetic shape memory alloys

More information: Yu-Jung Lu, et al. “Single InGaN nanodisk light emitting diodes as full-color subwavelength light sources.” Applied Physics Letters. DOI: 10.1063/1.3597211

4.9 /5 (18 votes)

Related Stories

Zeroing in on the elusive green LED

Apr 25, 2011

Researchers at Rensselaer Polytechnic Institute have developed a new method for manufacturing green-colored LEDs with greatly enhanced light output.

Gold nanoparticles that make leaves glow in the dark

Oct 25, 2010

(PhysOrg.com) -- Researchers in Taiwan think they may eventually be able to replace street lamps with trees laced with gold nanoparticles that turn their leaves into bio-light-emitting diodes.

Recommended for you

'Exotic' material is like a switch when super thin

Apr 18, 2014

(Phys.org) —Ever-shrinking electronic devices could get down to atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all: superconductivity, magnetoresistance ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

that_guy
not rated yet Jun 17, 2011
even if this doesn't directly lead to a commercial breakthrough, it is definitely a great step to making leds more efficient and versatile!
Eikka
5 / 5 (1) Jun 18, 2011
Does it emit the colors at the same time, or is it simply tunable?

More news stories

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.