A team of researchers, led by Kansas State University professor Hongxing Jiang and K-State associate professor Jingyu Lin, has created blue micro LEDs that are more efficient than conventional LEDs. Basically, putting hundreds of interconnected miniature LEDs in the same space one conventional LED used to take could boost the efficiency by 60 percent. "We can make very small images, Lin said. "The diameter we've made of an LED is as small as a human hair."
Conventional LEDs are used together to make up a variety of large lights and screens, including traffic signals, neon billboards and sports stadium screens. A very energy-efficient light source, LEDs don't emit heat and have a long duration. By comparison, a 15-watt LED stop light can last, on average, 20,000 hours, while a 100-watt house light bulb lasts only about 1,000 hours, Jiang said.
"Most microdisplays, like cell phone screens, are made of liquid crystal or LCDs, which require an external light source," Lin said. "What we've made is a miniature semi-conductor display. Basically, they are self-luminescent, resulting in both space and power saving." Blue LEDs, however, are not available at this time in micro-sizes, Lin said, making it virtually impossible to use in smaller items, such as heat-mounted microdisplays and cell phone displays.
Particular to this research is the creation of miniature blue LEDs. The researchers are able to make and fabricate these blue LEDs, Jiang said. The blue LEDs are created from laboratory-grown gallium nitride wafers, each two inches in diameter. Each wafer can produce about 10,000 conventional LEDs. "There are only a few universities that can get the light out," Lin said. "Some major companies can make the blue LEDs, but only a few universities have the technology to make these lights, especially micro-size lights."
"It's a very tiny LED," Jiang said. "What we can do with this is also display the image. By putting 100 tiny LEDs in a 0.5 millimeter by 0.5 millimeter space, we have turned each light on and off individually and displayed different images," he said. By combining red and green LEDs -- which are readily available -- with blue LEDs, semiconductor LEDs have paved the way for full-color displays and raised the possibility of mixing the three colors to create white light for general lighting applications.
"With white light, you can create so much," Jiang said. "If all household lights were replaced by these white LEDs, about $100 billion in energy costs a year could be saved worldwide, in addition to significant decreases in pollution and heat. We call this solid-state lighting technology," Jiang said. "In this technology, finding ways to enhance the efficiency of LEDs is one of the keys."
K-State's research is funded by the National Science Foundation, Department of Energy, Army Research Office, Ballistic Missile Defense Organization, the Office of Naval Research and the Defense Advanced Research Project Agency.
Jiang and Lin's current research team includes visiting professors Sixuan Jin and Guangde Chen; postdoctoral research associates Tom N. Oder and Zhaoyang Fan; research assistant Weiping Zhao; physics graduate students Jing Li, Kyoung Kim, Jagat Shakya, Ki-Bum Nam and Mim Nakarmi; and physics undergraduate students Chris Wyant and Zack Casey.
For more details, go to www.phys.ksu.edu/area/GaNgroup