| A conceptual illustration shows a defect in a GaN-based LED's crystal lattice contributing to nonradiative recombination of electrons and holes in the LED. (Photo Credit: Peter Allen illustration) |
Researchers at the University of California, Santa Barbara (UCSB) have identified a specific type of defect in the atomic structure of gallium nitride (GaN) based LEDs that results in less efficient performance.1 The characterization of these point defects could lead to fabrication of more-efficient, longer-lasting LED lighting.
Vacancies in gallium form complexes with oxygen and/or hydrogen; what the USCB group discovered was that these complexes cause nonradiative recombination of holes and electrons, called Shockley-Read-Hall (SRH) recombination. Whenever an SRH recombination occurs, a photon that should have been produced isn't.
Even modest concentrations of these vacances of around 1016/cm3 can significantly reduce the internal quantum efficiency of GaN-based LEDs (the LEDs that form the basis of most LED lighting).
The method lends itself to future work identifying other defects and mechanisms by which SRH recombination occurs, says researcher Chris Van de Walle.
"These gallium vacancy complexes are surely not the only defects that are detrimental," he says. "Now that we have the methodology in place, we are actively investigating other potential defects to assess their impact on nonradiative recombination."
Source: http://www.news.ucsb.edu/2016/016653/becoming-crystal-clear
REFERENCE:
1. Cyrus E. Dreyer et al., Applied Physics Letters (2016); http://dx.doi.org/10.1063/1.4942674