Illumination accounts for much of world energy use, but the efficient production of light is notoriously challenging. Photons must be generated from semiconductor nanostructure layers and take a specific path away from their source to be extracted as light; otherwise, they are reflected back and dissipated as heat. Thus, the U.S. Department of Energy has launched a major initiative addressing solid state lighting technology.

Nelson Tansu, assistant professor of electrical and computer engineering, studies semiconductor nanostructures to increase the efficiency of solid state lighting and solar photovoltaic cells.

“Energy,” says Tansu, “is a driving force in modern society. To generate and use energy efficiently for lighting, we must rely on semiconductor nanotechnology as the enabling technology.”

Using metalorganic chemical vapor deposition (MOCVD), Tansu fabricates semiconductor nanostructures as active media with a precision of one or two planes of atoms for the efficient generation and absorption of light. He and his group have achieved highly efficient light generation from semiconductor nanostructure active regions used in lightemitting diodes (LEDs) for solid state lighting and medical applications. Their work has also led to greater wavelength extension and increased optical gain for efficient laser application. By enhancing the generation of photons, Tansu hopes, his group can develop efficient lasers and LEDs that are inexpensive to manufacture.

Tansu’s group is testing several novel approaches for enhancing the “wall plug” efficiency of nitride-based LEDs. In one project, Tansu is collaborating with James Gilchrist, assistant professor of chemical engineering, to investigate the potential for microlens arrays on LED surfaces to enhance the extraction of photons by increasing their ability to be refracted out.

NSF, the Department of Defense and the Pennsylvania Infrastructure Technology Alliance are funding Tansu’s work, which has been published in Applied Physics Letters, IEEE Photonics Technology Letters and elsewhere.