Team achieves highly efficient, independently controllable cascaded blue and green microLEDS

Inorganic micro-light-emitting diodes, which have an area smaller than 100 x 100 square micrometers, are an emerging technology with applications in the next generation of display technology, including augmented reality, virtual reality, and large area display. MicroLEDs offer advantages, such as lower power consumption, higher resolution, and higher thermal stability, when compared to the more established organic LEDs and liquid crystal displays.

While gallium nitride (GaN)-based microLEDs also allow fast modulation speed, their efficiency decreases as their area decreases. Li et al. demonstrate highly efficient GaN-based, cascaded blue/green microLEDs using tunnel junctions to improve performance. They grew the cascaded microLEDs with metalorganic chemical vapor deposition (MOCVD) instead of using the more common approach, molecular beam epitaxy, to evade the typical drop in efficiency.

The cascaded microLEDs consisted of blue and green microLEDs as well as tunnel junctions. The authors found the blue, green, and blue/green microLEDs can be controlled independently in the same device, and all exhibited exceptional electrical luminous performance. The peak external quantum efficiency was 42% for the blue microLEDs and 14% for the green microLEDs.

This work shows different colors of microLEDs can be vertically integrated in one device using tunnel junction technology grown with MOCVD, which could help realize a full color microLEDs display.

“This demonstration provides a promising technology for the realization of single chip microLED with arbitrarily colors mixing by controlling the independent junctions,” said author Hongjian Li. “This research could be a solution for full-color indium gallium nitride microLEDs display.”

Source: “Demonstration of high efficiency cascaded blue and green micro-light-emitting diodes with independent junction control,” by Panpan Li, Hongjian Li, Yifan Yao, Haojun Zhang, Cheyenne Lynsky, Kai Shek Qwah, James S. Speck, Shuji Nakamura, and Steven P. DenBaars, Applied Physics Letters (2021). The article can be accessed at https://aip.scitation.org/doi/full/10.1063/5.0054005 .