Lighting principle

LED light source LED is composed of Ⅲ-Ⅳ compounds, such as GaAs (gallium arsenide), GaP(gallium phosphide), GaAsP (phosphorus arsenide) and other semiconductor made of its core is PN junction. So it has the general P-N junction I-V characteristics, that is, forward conduction, reverse cut-off, breakdown characteristics. In addition, under certain conditions, it also has light-emitting characteristics. At the forward voltage, electrons are injected from the N region into the P region, and the holes are injected into the N region from the P region. A fraction of the minority carriers (minority) entering the other region recombines with the majority of carriers (polygons) and emits light.

Assuming that luminescence occurs in the P region, the injected electrons recombine directly with the valence band holes, or are first captured by the luminescent center and then recombined with the holes. In addition to this luminescent composite, some electrons are captured by non-luminescent centers (this center is near the middle of the conduction band and the tape), and then recombined with holes, each time the energy released is not visible and can not form visible light. The higher the ratio of the amount of luminescence to the amount of non-luminescent compound, the higher the photon efficiency. Since the recombination is glowing in the minority diffusion region, the light is generated only within a few μm of the PN junction.

The theory and practice show that the peak wavelength λ of the light is related to the bandgap Eg of the semiconductor material in the light emitting region, that is, λ ≈ 1240 / Eg (mm)

Where Eg is the unit of electron volts (eV). If the visible light (wavelength of 380nm purple ~ 780nm red light), the semiconductor material Eg should be between 3.26 ~ 1.63eV. The light longer than the red light is infrared light. There are infrared, red, yellow, green and blue light-emitting diodes, but the Blu-ray diode cost, the price is very high, the use is not common.