New Progress in wafer epitaxy technologies for high-brightness white LEDs

The concept of internal and external quantum efficiency of light emitting diodes (LEDs) and the basic ways to improve this are first introduced. The epitaxial structure and growth of LED wafers are then briefly described, with emphasis on the techniques to enhance the quantum efficiency. These include epitaxial structure optimization, lateral epitaxial overgrowth, growth on SiC or GaN substrates, growth of an AlInGaN active layer, epitaxy on non- or semi- polarized planes, growth of surface-roughening structures, regrowth on patterned templates, growth on patterned sapphire substrates, structural and composition designs to improve the injection efficiency into the active layer, and so on. Various novel epitaxial structures are discussed with regard to cost and reliability, and methods in growth to improve the reliability are introduced. Finally, we conclude that a breakthrough in semiconductor lighting can be achieved by a combination of non-polarized substrates, optimized epitaxial structures and photonic crystal technology.