Photonic crystals increase GaN LED output
Korean scientists have more than doubled the output power of GaN-based LEDs thanks to a holographic process that etches a two-dimensional photonic crystal (PC) into the device. The researchers say that their holographic method is a major improvement on previous work using electron-beam lithography, as the technique suits large area processing with high throughput. (Appl. Phys. Lett. 87 203508)
Typically, a large portion of the light generated by an LED is wasted because of internal reflection and lateral waveguiding. By integrating a PC lattice within the device structure, LED-makers have the opportunity to control photonic behaviour and improve light output.
Researchers from Seoul National University used a two-beam holography setup equipped with a He-Cd laser (325 nm) to write square-lattice PC patterns with periods of 300, 500 and 700 nm. LED wafers were provided by Samsung s Advanced Institute of Technology.
The team found that its 500 nm lattice design offered the best performance, with the device extracting 2.1 times more light than a conventional planar LED. "The only problem we noticed was a slight increase in operating voltage, but this can be solved in the future," Heonsu Jeon of Seoul National University told Optics.org
Computer simulation experts at Seoul s Korea University are now busy optimizing the structure of the PC-LED, which emits at around 400 nm. The next step for Jeon and his colleagues is to assess the device s commercial viability.
"Adding a photonic crystal pattern should not cause any significant increase in the cost of the LED," he said. "In the future, the laser holography method could [even] be replaced with a phase mask technique to suit a mass production environment."
Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.
