Improving the Next Generation of Displays Through Pure Red LEDs
A team of electrical engineers at the King Abdullah University of Science and Technology (KAUST) has developed high-intensity, low-voltage red LEDs from nitride crystals.
Engineers can already make super-bright LEDs of various colors by using a variety of materials. However, these are no good for building the next generation of energy-efficient micro-LED displays and lighting with color tuning that is earmarked to follow current generation OLED displays.
Searching for a Suitable Material
Now, researchers from Saudi Arabia have reportedly succeeded in making pure red LEDs for the first time by using nitride crystals.
"Electrical engineers can already make bright LEDs using varying materials to produce different colors. But to improve display technologies, engineers must integrate the three primary color LEDs, red, green and blue, onto one chip," explains Daisuke Iida, an electrical engineer at KAUST.
To do this, they must find a material that is suitable for manufacturing all three colors onto a single chip and that is able to produce each color with high intensity. It should also have high-power output and use a relatively small amount of energy.
It is thought that the best candidate for generating LEDs with red, green, and blue colors are nitride semiconductors. These are crystals that contain nitrogen, and, in theory, they can be used to create LEDs that produce light with wavelengths between ultraviolet and infrared—the entire visible light spectrum.
Although gallium nitride (GaN) has been used to create blue and green LEDs, making bright red LEDs with it is challenging.
The machine used for metalorganic vapor-phase definition, which the researchers say is key to achieving bright red LEDs. Image used courtesy of KAUST
Creating Pure ‘Apple Red’ LEDs via a Crystal Growth System
"Red vision has been almost impossible--other groups have only really succeeded in making orange, not apple red," says group leader, Kazuhiro Ohkawa. "Now, we have developed a crystal growth system to realize pure red LEDs." The research team say that this is significant because producing red LEDs is almost impossible—red color is usually achieved by color conversion or based on different materials.
The Benefits of Pure Red LEDs
To produce the red LEDs, a reactor was created with extra indium vapor above the crystal’s surface. This process is known as a metalorganic vapor-phase deposition and when it is used, the added pressure prevents the indium in the nitride crystals from escaping.
This means that the crystals have a higher concentration of indium at the surface, which gives the desired red color. Without the metalorganic vapor-phase deposition process, the indium easily evaporates from the surface of the nitride crystals. By adding small aluminum atoms to the crystal, the strain on the crystal from indium’s larger atoms is reduced, resulting in fewer defects and a stronger red color.
Another benefit of pure red LEDs is that they use less energy by operating at about half the voltage of current LED technology. As a result, designers and engineers will be able to create devices with longer battery life.