LEDs ♦ news digest
the source. These results are claimed to advance the fundamental understanding of LED technology and open up new research pathways.
Fig. 2: 405 nm reflectance (left) of InGaN/GaN MQW stacks and the corresponding STEM image of the MQWs (right).
According to Tripathy‘s team, LayTec in-situ metrology is a key element for identifying the epitaxial process spotentials. In comparison to the time consuming, destructive ex-situ cross section transmission electron microscopy analysis, the in-situ tool provides real time information on growth thickness and homogeneity already during growth.
LayTec says its system has reduced significantly IMRE‘s R & D cycles for epitaxial growth optimisation and enables faster industrialisation of the GaN-on-Silicon technology.
Electron Microscopy solves key puzzle of LED efficiency
Scientists have used electron microscopy imaging techniques on indium gallium nitride (InGaN) LEDs to settle the controversy of indium clustering and raise new experimental possibilities
From the high-resolution glow of flat screen televisions to light bulbs that last for years, LEDs continue to transform technology.
The celebrated efficiency and versatility of LEDs, and other solid-state technologies including laser diodes and solar photovoltaics, make them increasingly popular. Their full potential, however, remains untapped, in part because the semiconductor alloys that make these devices work continue to puzzle scientists.
A contentious controversy surrounds the high intensity of one leading LED semiconductor, InGaN, with experts split on whether or not indium-rich clusters within the material provide the LED’s remarkable efficiency.
Now, researchers from the Massachusetts Institute of Technology (MIT) and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory say they have demonstrated definitively that clustering is not
“This discovery helps solve a significant mystery in the field of LED research and demonstrates breakthrough experimental techniques that can advance other sensitive and cutting-edge electronics,” says MIT professor, Silvija Gradečak. “The work brings us closer to truly mastering solid-state technologies that could supply light and energy with unprecedented efficiency.”
These images of the InGaN samples, produced by CFN’s low-voltage scanning transmission electron microscope, reveal a lack of structural changes over time. After 16 minutes of scanning, no damage or decomposition is visible, and the higher magnification (c) exhibits none of the clustering previously thought to be central to LED efficiency
Building a Better Bulb
Incandescent lights, the classic bulbs that use glowing wires of tungsten or other metals, convert only about five percent of their energy into visible light, with the rest lost as heat. Fluorescent lights push that efficiency up to about 20 percent, still wasting 80 percent of the electricity needed to keep homes and businesses bright. In both of these instances, light is only the by-product of heat-generating reactions rather than the principal effect, making the technology inherently inefficient.
“Solid-state lights convert electric current directly into photons,” explains Eric Stach, leader of the Electron Microscopy Group at Brookhaven Lab’s Centre for Functional Nanomaterials (CFN). “LED bulbs use semiconductors to generate light in a process called electroluminescence. The efficiency of this process could, in theory, be nearly perfect, but the experimental realisation has not reached those levels. That disconnect helped motivate this study.”
For this study, the scientists looked at the LED compound InGaN, which is particularly promising for practical applications. InGaN alloys contain dislocations, structural imperfections that could inhibit electricity flow and light production, but somehow the alloy performs exceptionally well. To understand the light-emitting reactions, physicists needed to understand what was happening on the atomic scale. After researchers started to investigate, however, not everyone reached the same
June 2013
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