The revised edition of this important book presents updated and expanded coverage of light emitting diodes (LEDs) based on heteroepitaxial GaN on Si substrates, and includes new chapters on tunnel junction LEDs, green/yellow LEDs, and ultraviolet LEDs. Over the last two decades, significant progress has been made in the growth, doping and processing technologies of III-nitride based semiconductors, leading to considerable expectations for nitride semiconductors across a wide range of applications. LEDs are already used in traffic signals, signage lighting, and automotive applications, with the ultimate goal of the global replacement of traditional incandescent and fluorescent lamps, thus reducing energy consumption and cutting down on carbon-dioxide emission. However, some critical issues must be addressed to allow the further improvements required for the large-scale realization of solid-state lighting, and this book aims to provide the readers with details of somecontemporary issues on which the performance of LEDs is seriously dependent. Most importantly, it describes why there must be a breakthrough in the growth of high-quality nitride semiconductor epitaxial layers with a low density of dislocations, in particular, in the growth of Al-rich and In-rich GaN-based semiconductors. The quality of materials is directly dependent on the substrates used, such as sapphire and Si, and the book discusses these as well as topics such as efficiency droop, growth in different orientations, polarization, and chip processing and packaging technologies. Offering an overview of the state of the art in III-Nitride LED science and technology, the book will be a core reference for researchers and engineers involved with the developments of solid state lighting, and required reading for students entering the field.