Researchers developed micro-LEDs that can efficiently emit pure red light and enable development of full-color displays based on just a single semiconductor.
MicroLEDs are promising technology for future displays due to being energy efficient and very small. However, each microLED can emit a very narrow range of wavelengths or colors. A way to get around this issue is to combine many different LEDs, each emitting a different color. A full-colored display can be created by combining red, green and blue (RGB) micro-LEDs.
The color emitted by an LED is determined by the material properties of the semiconductor. For instance, nitride semiconductors are used to make blue and green micro-LEDs, whereas phosphide semiconductors are used for red light. In this way, the implementation is costly and the efficiency reduces as the chips get miniaturized further.
Indium gallium nitride can be created to emit red light by increasing the materials’ indium content. But this lowers the efficiency of the LED because there is a mismatch between the separation of atoms in the GaN and InGaN, which causes atomic-level imperfections. Now, researchers from King Abdullah University of Science and Technology have developed a more efficient red LED.
During the fabrication process of making InGaN micro-LED, sidewalls are damaged which makes the device less efficient. “But we have a chemical treatment to remove the damage and retain the high crystal quality of the InGaN and GaN sidewall interface,” explains Zhe Zhuang, first author of the study.
The team created a series of square devices with a side-length of 98 or 47 micrometers. These devices emitted light at a peak wavelength of 626 nanometers and exhibited an external quantum efficiency (the number of photons emitted from the LED per electron injected into the device) of up to around 0.87 percent. Moreover, the purity of the red color is close to primary red.
“The next step is to increase the efficiency of the red micro-LED with even smaller chip sizes, maybe below 20 micrometers,” says Zhuang. “Then we hope to integrate RGB nitride-based LEDs for full-color displays.”
The research has been published in the journal Optics Letters.