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Nano-Etching Makes LEDs 7X Brighter

Photonics.com
Jul 2006
GAITHERSBURG, Md., July 24, 2006 -- Researchers at the National Institute of Standards and Technology (NIST) have made semiconductor LEDs more than seven times brighter by etching nanoscale grooves in a surrounding cavity to guide scattered light in one direction. The novel nanostructure may have applications in areas where LED brightness is crucial, such as in biomedical imaging, the scientists said.

Semiconductor LEDs are used increasingly in displays and many other applications, in part because they can efficiently produce light across a broad spectrum, from near-infrared to the ultraviolet. However, they typically emit only about two percent of the light in the desired direction: perpendicular to the diode surface. Far more light skims uselessly below the surface of the LED, because of the extreme mismatch in refraction between air and the semiconductor. nanoetchedLED.jpg
Etched nanostructured rings around an LED can make it more than seven times brighter. The novel technique developed at the National Institute of Standards and Technology may have applications in areas such as in biomedical imaging. (Image: NIST)


The NIST nanostructured cavity boosts useful LED emission to about 41 percent and may be cheaper and more effective for some applications than conventional post-processing LED shaping and packaging methods that attempt to redirect light, its creators said. Their work is described in the July 17 issue of Applied Physics Letters.

The NIST team fabricated their own infrared LEDs consisting of gallium arsenide packed with "quantum dots" of assorted sizes made of indium gallium arsenide. Quantum dots are nanoscale semiconductor particles that efficiently emit light at a color determined by the exact size of the particle. The LEDs were backed with an alumina mirror to reflect the light emitted backwards. The periphery of each LED was turned into a cavity etched with circular grooves, in which the light reflects and interferes with itself in an optimal geometry.

The researchers experimented with different numbers and dimensions of grooves. The brightest output was attained with 10 grooves, each about 240 nanometers (nm) wide and 150 nm deep, and spaced 40 nm apart. The team spent several years developing the design principles and perfecting the manufacturing technique. The principles of the method are transferable to other LED materials and emission wavelengths, as well as other processing techniques, such as commercial photolithography, according to lead author Mark Su.

For more information, visit: www.nist.gov

GLOSSARY
diode
A two-electrode device with an anode and a cathode that passes current in only one direction. It may be designed as an electron tube or as a semiconductor device.
indium
Metal used in components of the crystalline semiconductor alloys indium gallium arsenide (InGaAs), indium gallium arsenide phosphide (InGaAsP), and the binary semiconductor indium phosphide (InP). The first two are lattice-matched to InP as the light-emitting medium for lasers or light-emitting diodes in the 1.06- to 1.7-µm range, and the last are used as a substrate and cladding layer.
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.
Consumerdiodeemissiongallium arsenidegeometrygroovesindiumindustrialinfraredlightmanufacturingnano-etchingNews & FeaturesNISTquantum dotssemiconductorLEDs

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