Solid-state lighting with wide band gap semiconductors

Abstract

Gallium nitride is currently the wide band gap semiconductor material from which almost all commercial LEDs for solid-state lighting are manufactured but in the future other promising materials, such as zinc oxide (ZnO), are also likely to play a leading role.• With further developments in LED technology, leading to cheaper luminaires, perhaps based on gallium nitride-on-silicon material, LED lamps will largely replace tungsten incandescent bulbs in the years to come. ABSTRACTLight-emitting diodes (LEDs) made from wide band gap semiconductors, such as gallium nitride, are undergoing rapid development.Solid-state lighting with these LEDs is transforming patterns of energy usage and lifestyle throughout the world.With solid-state lighting gradually taking over from incandescent and fluorescent lighting, light-emitting diodes (LEDs) are very much the focus of research nowadays. This compact review takes a look at LEDs for lighting applications made from wide band gap semiconductors.A very brief history of electric lighting is included for completeness, followed by a description of blue-emitting LEDs that serve as pump sources for all 'white' LEDs. This is followed by a discussion on techniques to extract more light from the confines of LED chips through surface patterning. The thermal management of LEDs is perhaps the most important consideration in designing and using LED-based luminaires.This topic is discussed with regard to recent studies on LED reliability. The very promising development of gallium nitride-on-silicon LEDs is examined next followed by a discussion on phosphors for color conversion in LEDs. LED lighting has positively infl uenced both upscale and downscale illumination markets worldwide. Its societal impact is examined, with the review concluding with a look at efforts to produce LEDs from zinc oxide -a material that holds much promise for the future of solid-state lighting.vacuum tube era with devices based on gas-fi lled incandescent and fl uorescent bulbs illuminating our homes and workplaces. It is only over the last two decades that solid-state light generating devices in the form of light-emitting diodes (LEDs) have become available as an alternative for lighting up living spaces. 1 , 2 This review takes a look at their development, current status, and future prospects. After a brief historical introduction, the development and structure of the blue LED at the heart of all white LEDs are examined. This is followed by a description of various techniques that have been explored to extract more light from LED chips. Such techniques make LEDs brighter without increasing their energy consumption and thus enhance their attractiveness as energy-effi cient light sources. The relatively recent development of a gallium nitride-on-silicon material for low cost, high performance LEDs is examined next, followed by a look at the phosphor technology for white LEDs.The societal impact of LED lighting is then described with this review ending by examining the still distant goal of making LEDs out of zinc ox...

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