Atomic-Scale Investigations Solve Key Puzzle of LED Efficiency
MIT and Brookhaven Lab scientists use electron microscopy imaging techniques to settle a solid-state controversy and raise new experimental possibilities
May 22, 2013
For this study, the scientists looked at the LED compound InGaN (pronounced in-gan), 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 conclusions.
scanning transmission electron microscope
This scanning transmission electron microscope's non-destructive imaging of specific InGaN samples clarified a decade of research, demonstrating conclusively that indium-rich clustering does not drive the efficient light emission.
"Years ago, a team of researchers used electron microscopes to examine InGaN samples, and they identified a surprising phenomenon—the material appeared to be spontaneously decomposing and forming these isolated indium-rich clusters," Stach said. "This behavior could explain the efficient light emission, as the clusters might help electrons avoid the structural problems in the InGaN. But then things became really interesting when another group proposed that the electron microscope itself caused that clustering decomposition. We had a real divide in the semiconductor field."