The Science
While you might think of new light-emitting diode (LED) lights when replacing a burnt-out bulb, not all LEDs are alike. The technology works in a diverse array of applications, including water purification and search and rescue efforts. When an electric current is applied to a LED, pairs of electrons and holes (missing electrons in the orbitals around an atom) are created. Ideally, these electron-hole pairs recombine to generate light. In real systems, however, 100% efficiency is not realized. Using computational modeling, scientists determined the microscopic mechanism behind the LED’s inefficiency. This mechanism centers on a few missing gallium atoms that cause the electrons and holes to recombine without giving off light.
The Impact
Researchers have discovered a new mechanism based on atomic-level defects that reduces the efficiency of LEDs. If the defects can be removed, the efficiency of the LEDs could be dramatically improved resulting in a significant improvement in this technology.
Summary
The presence of defects in semiconductor materials, such as the missing gallium atoms in the image, were known to drastically decrease the light emission from these materials. However, the atomic-level details of why this happens remained unknown, because of the limited experimental information available. Understanding the microscopic origin of various physical pathways that lead to those losses is crucial for the improvement of future devices. Researchers at the University of California-Santa Barbara carried out cutting-edge theoretical and computational studies to explore a variety of recombination mechanisms and candidate atomic-level defects. This research has identified point defects due to missing gallium atoms as a prime culprit impacting the efficiency of LEDs. This theoretical understanding should allow for the development of devices with significantly higher efficiencies.
Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. A.A. was supported by Marie Skłodowska-Curie Action of the European Union. Computational resources were provided by the National Energy Research Scientific Computing Center, a DOE Office of Science user facility.
Publications
C.E. Dreyer, A. Alkauskas, J.L. Lyons, J.S. Speck, and C.G. Van de Walle, “Gallium vacancy complexes as a cause of Shockley-Read-Hall recombination in III-nitride light emitters.” Applied Physics Letters 108, 141101 (2016). [DOI: 10.1063/1.4942674]
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