Drastic improvements in the crystal quality of GaN enabled the conductivity control of both p- and n-type nitride semiconductors. This led the production of the high-brightness GaN-based p–n junction blue-light-emitting diode (LED) and the high-performance violet/blue laser diode (LD). The development of blue LEDs has allowed us to complete the set of three primary light colors with semiconductors. Coupled with available high-brightness red LEDs, blue/green LEDs are leading to the development of completely solid-state, full-color displays, traffic lights, signage, and specialized lighting applications. White LEDs composed of nitride-based blue/ultraviolet LEDs are more efficient than fluorescent lamps, and, as such, white LEDs are now being used in TVs, cellular phones, and computer displays. Moreover, white LED lamps are heading toward use in general lighting applications in houses, offices, and factories. Blue LEDs, together with available red LEDs, are also being applied as agricultural lighting sources. Nitride-based violet LEDs are being used for reading/writing data in optical disc systems. These nitride-based devices are robust in harsh environments, enable us to save a significant amount of energy, and provide a route to avoid the use of hazardous materials. The use of these devices will be one of our major weapons in the fight against global warming.

A historical overview and recent trends in the research and development of nitride-based light emitters are presented. The growth of GaN using a low-temperature-deposited buffer layer conductivity control, and the use of GaInN alloys, by which nonradiative recombination centers in nitrides are screened, have been employed to fabricate high-efficiency blue and green light-emitting diodes. Today, luminous flux efficiency of up to 50 lm/W at a specific wavelength is available. Electrical pumping has realized commercial laser diodes in the violet and blue regions. Several milestones in the realization of these achievements are reviewed. Future prospects of the nitride-based light emitters are also discussed.

A review is presented of future issues on wide-bandgap group-III nitride materials and device technology for optoelectronic and high-temperature devices such as LEDs.