Light emitting diodes are made of semiconductors such as GaAs (Shen Huajia), GaP () and GaAsP (phosphorus and Shen Huajia), and their core is PN junction. Therefore, it has the I-N characteristics of general P-N junctions, i.e., forward conduction, reverse cut-off, and breakdown characteristics. In addition, under certain conditions, it also has luminescence characteristics. At the forward voltage, the electrons are injected into the P region from the N region, and the holes are injected into the N region by the P region. The minority carrier into the other area (minority) part and majority carrier (majority) composite light, assuming luminescence is occurred in the District of P in, then injected electrons and holes in the valence band direct composite and the light, or the first center of light capture, and hole composite luminescence. In addition to this light composite, some electrons are non luminescent center (the center between the conduction band, lies near the middle) capture, and then recombine with holes each release of energy is not, can not form a visible light. The greater the ratio of the composite amount of light to the amount of non luminescent compound, the higher the photon efficiency. Since the composite is light emitting in the minority diffusion region, light is generated only within a few m of the PN junction area.

Theory and practice have proved that the peak wavelength of light is related to the band gap Eg of the semiconductor material in the light emitting region

Lambda = 1240/Eg (mm)

The unit of Eg in the formula is electron volt (eV). If visible light can be produced (wavelength at 380nm violet to 780nm red light), the Eg of semiconductor material should be between 3.26 and 1.63eV. The light is longer than the red light. Use is not common.