ABSTRACT
That the demonstrations of red and infrared laser diodes (LDs) in the early 1960s were not quickly followed by the development of similar shorter wavelength devices was not due to a lack of desirability and commercial attractiveness but rather due to the difficult nature of the wide bandgap semiconductors. Despite early work on II-VI compounds, GaN and ZnO, the technology and quality of epitaxial structures composed from these materials lagged far behind that of narrower gap materials such as GaAs. High brightness blue light emitting diodes and lasers were not developed until the 1990s and followed major advances in the fabrication of group III-nitride (AlGaInN) structures. This chapter presents an outline of these developments and then proceeds to a description of the current status and performance of GaN-based blue LDs. The extension of the lasing wavelength in GaN-based lasers to both shorter (UV) and longer (blue/green) wavelengths is described along with the competing technologies: namely ZnO-based structures and frequency doubled systems for the blue and II-VI semiconductor structures for the green/yellow spectral region.
