Shuji Nakamura developed the first commercially available blue and green light emitting diodes and the first blue semiconductor laser based on GaN. GaN and its related compounds allow the fabrication of highly efficient light emitters and lasers ranging from red through yellow and green to blue in a single material. In this book the scientific basis of GaN light emitting devices and the physical concept and basic manufacturing technology of these new blue light emitting diodes and laser diodes are discussed. The breakthrough in GaN technology opens many new commercial applications for semiconductors, including displays, road and railway signalling, lighting, scanners, optical data storage, and much more. The new application field of power devices is also discussed. This second edition is not only updated but also significantly enlarged. The whole spectrum of GaN related materials, processing and application problems is contained, thus making this book the most comprehensive basic book in the field. It also tells the fascinating story of the extremely successful realization of Nakamura's research and development concept. The book will appeal to both researchers and engineers.