Light-emitting diode into a lower energy level and releases energy in the form of a photon. The wavelength of the light emitted, and thus its color, depends on the band gap energy of the materials forming the "p-n junction". In silicon or germanium diodes, the electrons and holes usually recombine by a "non-radiative transition", which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible, or near-ultraviolet light. LED development began with infrared and red devices made with gallium arsenide. Advances in materials science
P–n diode P–n diode This article provides a more detailed explanation of p–n diode behavior than that found in the articles p–n junction or diode. A p–n diode is a type of semiconductor diode based upon the p–n junction. The diode conducts current in only one direction, and it is made by joining a "p"-type semiconducting layer to an "n"-type semiconducting layer. Semiconductor diodes have multiple uses including rectification of alternating current to direct current, detection of radio signals, emitting light and detecting light. The figure shows two of the many possible structures used for "p–n" semiconductor diodes, both adapted to increase