Color mixing, the process of combining different colors to create new ones, is crucial for the future of solid-state lighting. White light is achieved through phosphor down-conversion, but researchers are looking into LED color mixing as a more efficient alternative. LED color mixing has a higher theoretical maximum efficiency, essential for meeting the 2035 DOE energy efficiency goals. However, a significant challenge in this approach is the lack of suitable green LEDs, known as the “green gap.”

In a recent study, researchers at the University of Illinois Urbana-Champaign have significantly addressed this challenge. They have developed a green-emitting cubic III-nitride active layer with an internal quantum efficiency (IQE) of 32%, more than six times higher than conventional cubic active layers. This breakthrough could potentially triple the efficiency of today’s white light-emitting diodes, a goal that requires filling the green gap in the spectrum.

The most efficient white LEDs currently use blue light-emitting diodes with a rare-earth phosphor coating for down-conversion, which has inherent limitations. This down-conversion process is inefficient, leading to the generation of more heat than light output. Additionally, phosphors are chemically unstable and add significant raw material and packaging costs to the LED device. On the other hand, LED color mixing has a higher theoretical maximum luminous efficacy than phosphor-based lighting.

The researchers achieved this breakthrough by developing a cubic III-nitride system that enables highly efficient, droop-free green LEDs with a 32% IQE and only 16% indium content. This is a significant advancement considering that traditional hexagonal III-nitride materials require a much higher indium content and are plagued with efficiency droop at high current densities. The new cubic III-nitride system shows promise for overcoming these challenges and could pave the way for more efficient and cost-effective solid-state lighting solutions.

This research, recently published in Applied Physics Letters, demonstrates the potential of cubic III-nitride materials for addressing the green gap in LED technology. Developing high-quality, pure cubic III-nitride through innovative techniques opens up new possibilities for achieving energy-efficient and high-performance lighting systems.

References

• Lee, J., & Bayram, C. (2024). Green-emitting cubic GaN/In0.16Ga0.84N/GaN quantum well with 32% internal quantum efficiency at room temperature. Applied Physics Letters, 124(1), 011101. https://doi.org/10.1063/5.0179477

• Rose, A. & University of Illinois Grainger College of Engineering. (2024, January 23). Closing the green gap: A cubic III-nitride active layer with 32% internal quantum efficiency. Phys.Org; University of Illinois Grainger College of Engineering. https://phys.org/news/2024-01-green-gap-cubic-iii-nitride.html