Daniel S. BurgessResearchers at Lumileds Lighting LLC in San Jose, Calif., Sandia National Laboratories in Albuquerque, N.M., and Agilent Technologies in Palo Alto, Calif., have reported improved far-field radiance from electrically operated InGaN/GaN LEDs that feature a photonic crystal structure in the top layer. With the development of a suitable manufacturing process for optimized designs, the work promises blue emitters with much higher extraction efficiencies than currently are available. Jonathan J. Wierer, senior scientist with Lumileds' advanced laboratories group, said that light extraction remains an issue in commercial GaN LEDs. The company's flip-chip design, for example, provides an estimated extraction efficiency of 50 percent. "There's still a factor of two there for improvement, and companies are looking at ways of doing that," he said...