"Electronic overflow" is the root cause of LED light decay

Researchers at Rensselaer Polytechnic Institute have unveiled the mechanism behind the LED bulb's efficiency droop, which causes up to 20% loss of light efficiency at high LED currents.

Note: Because the ratio of the conduction band to the valence band well is too low, it is impossible to effectively limit the electrons of the conduction band to the quantum well of the active layer to cause electron leakage.

The issue of light decay was first proposed in 1999, and researchers at the University of Virginia believe that the reduction in quantum efficiency at high currents is ultimately due to overflow.

A recent paper in Applied Physics Letters mentioned that researchers have confirmed that overflow is the chief culprit of light decay. The study provides the first comprehensive model to reveal the mechanisms behind light decay and will guide new technologies to solve this problem, said Senior Professor E. Fred Schubert of Rensselaer Polytechnic Institute. “In the past, researchers and lLED manufacturers have made some progress in reducing light decay, but some progress has not been known about the cause of light decay.”

The LED consists of a three-part architecture: a negatively charged n-type crystal, a p-type crystal with positive holes, and a quantum well or active region between the two.

David Meyaard, the first author of the study, explained that electrons are injected from the n-type material into the active region while holes are injected from the p-type material into the active region. Electrons and holes move in opposite directions, and when they meet in the active region, they recombine. During the recombination process, electrons move to lower energy levels, releasing photons. Unfortunately, the researchers cautioned that as the current increases, the LED efficacy will decrease, and as the current increases, the amount of light it emits will decrease accordingly.