= Light-emitting diode
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= LED
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{synonym}
A <light-emitting diode> is a <semiconductor> <diode> producing <electroluminescence> under <electric current>. <Forward bias> injects <Electrons> and <electron holes>; radiative <electron-hole recombination> emits <photons>. A <double heterostructure> uses <band offsets> to retain both <charge carriers> in an active layer. A sufficiently thin layer is a <quantum well>.https://journals.aps.org/rmp/pdf/10.1103/RevModPhys.87.1139[§I, p. 1139, Fig. 1; §IV.A, pp. 1143–1144: injection, active layer and quantum-well distinction]{ref}
The optical and electrical questions are different: <photon> <energy> sets a color scale, while <light-emitting diode efficiency> determines how much supplied <energy> escapes as <light>. The <blue light-emitting diode> made compact <white light-emitting diodes> and full-color displays practical. A modulated <light-emitting diode> can also supply the optical <signal> in a <chopped-light lock-in experiment>.
\Image[/blue-led-injection-structure-and-readout.png]
{title=<Blue light-emitting diode>: <carrier injection>, emitting structure and optical readout}
{description=Original functional schematic of a representative <indium gallium nitride> <quantum well> device on <sapphire>, not a reconstruction of the 1989 or 1994 devices. Layer thicknesses are schematic. Separate electrical and optical readings determine different properties: terminal <electric potential difference> and <electric current>, <spectrum>, and calibrated escaping optical <power>. The arrows represent routes through the device rather than a calculated <energy band> profile.}
{source=blue-led-injection-structure-and-readout.py}
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