Recent development of high power light emitting diodes (LEDs) has enabled the fabrication of solid-state devices with efficiencies that that rival and in many cases exceed the capabilities of existing light sources utilized for illumination or display backlighting. A breakthrough in extraction efficiency of III-N light emitting diodes has been achieved through use of thin-film flip-chip and vertical injection devices. In addition a new phosphor plate technology enables much improved white color point targeting for phosphor converted white illumination. However, both drastic cost reduction and significant efficiency improvements are still necessary for solid state lighting to become the preferred choice over conventional light sources. It is especially the internal quantum efficiency at high current and at long wavelengths (green) that is the focus of III-nitride high power LED research and development. The complex AlInGaN heterostructures used in these devices consist of films with very different intrinsic lattice parameters, causing large strains and polarization effects to develop. These effects are larger for longer wavelength devices, i.e. more pronounced for green vs. blue, since these devices contain larger indium concentrations. In addition phase separation of high content InGaN layers may contribute to the reduced quantum efficiency of these films. The latest research in this area, recent device design and emerging applications for high power LEDs will be presented.
ANL Physics Division Colloquium Schedule