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Publisher Summary This chapter discusses visible light-emitting diodes (LEDs). Visible LEDs have been available commercially since the 1960s. The early LEDs utilized the gallium arsenide phosphide (GaAsP) materials system. They were direct energy-gap devices with near-band edge emission, which limited them to the red-spectral region with an emission wavelength of 650 nm because of the direct–indirect energy-gap transition at higher energies. These are indirect energy-gap devices, but the presence of the nitrogen trap, which is an efficient recombination center, enables them to achieve a surprisingly high level of luminous performance. To manufacture a practical visible LED, a number of basic materials properties must be well understood and technical challenges must be overcome, such as electron and hole transport, recombination mechanisms (radiative versus nonradiative), and the role of defects in these processes. An intermediate approach is to utilize a blue LED to pump a broadband yellow phosphor for indicator applications requiring white light. |
