The study found: Auger recombination is the culprit LED efficiency decline

University of California-Santa Barbara (UCSB) research team claimed by the first principle calculation found for potassium nitride (GaN) based light emitting diode (LED), Auger recombination (Auger recombination) is a decline in the efficiency of (LED droop) and green (green gap) the gap of the main reason, but not at the same time proposes effective solutions.

LED droop refers to the higher current operation, the external quantum efficiency of the LED will decline. UCSB Kris DELaney, Patrick Rink and Chris Van deWalle calculations show that the decline in the efficiency of the culprit is Auger recombination, it is the composite behavior of a non radiation type, in 2.5eV (wavelength 0.5 m) reached the peak. This also explains the "green gap" - that is, the wavelength of the blue light into the green band, the quantum efficiency of LED will decline.

Earlier LED Lumileds manufacturer Philips according to the experimental results that the Auger recombination is the main cause of decline in efficiency at high current, non radiation recombination process involves three carrier interaction of this, which contains at least one electron and a hole. The calculation results of UCSB support this argument, unlike other theoretical research team believes that the Auger recombination effects on LED droop can be ignored, the difference lies in the different nitride band structure: the UCSB team found second band (conduction band), and included in the calculation.

The picture shows a different recombination process in a InGaN crystal

The Gan band structure of UCSB team is calculated by the density functional theory (density-functional theory) combined with theory (many-body perturbation). Then they used the Monte Carlo (Monte Carlo) method to calculate the statistical average of more than 40 million steps, only to get Auger recombination rate.

Results of first principles calculations of the UCSB research team

With the discovery of the mechanism of LED droop, the future research direction will focus on removing or reducing the loss caused by auger recombination. The UCSB team discussed three ways to reduce losses in the paper, but they all have drawbacks. One way is to grow into potassium nitride (zinc-blende) zinc blende lattice structure and general non wurtzite (wurtzite) structure, because it can be pushed to the second conduction band high energy position, but to grow high quality zinc blende structure is not easy. Other methods include the use of stress or change the ratio of InGaAlN to adjust the band structure, but the calculation shows that these changes will not significantly improve the performance of LED.