Author: Anonymous repost from: Network Summary hits: 66
Light emitting diode (LED) is a forward biased PN junction diode made of semiconductor material. Its luminescence mechanism is that when a forward current is injected at both ends of the PN junction, the injected unbalanced carriers (electron-hole pairs) recombine to emit light in the diffusion process, which mainly corresponds to the spontaneous luminescence process of light. According to the position of light output, light emitting diodes can be divided into surface emitting type and edge emitting type. The most commonly used LED is InGaAsP/InP double heterojunction edge light emitting diode.
The light-emitting principle of light-emitting diodes can also be explained by the energy band structure of PN junction. The materials used for manufacturing semiconductor light emitting diodes are heavily doped. In thermal equilibrium, there are many electrons with high mobility in N region and more holes with low mobility in P region. Due to the limitation of PN junction barrier layer, the two can not naturally recombine under normal circumstances. When a DC voltage is applied to the PN junction, electrons in the conduction band of the channel region can escape from the barrier of the PN junction and enter the side of the p region. Therefore, near the PN junction, slightly to the side of P region, when electrons in high energy state encounter holes, luminescence recombination occurs. The light emitted by this luminescent recombination belongs to spontaneous radiation, and the wavelength of the radiated light depends on the band gap width Eg of the material, that is,
λ= 1.24μm？ ; Electric cars/electric cars
-Light-emitting diodes have obvious advantages such as high reliability, long continuous working time at room temperature, and good optical power-current linearity. And because this technology has developed quite maturely, the price is very cheap. Therefore, in the design of some simple optical fiber sensors, if LED is competent, choosing it as the light source can greatly reduce the cost of the whole sensor. However, the luminous mechanism of LED determines that it has many shortcomings, such as low output power, large emission angle, wide spectral line and slow response speed. Therefore, in some sensor designs that need light sources with high power, fast modulation rate and good monochromaticity, other light sources with higher performance have to be selected at the cost of increasing costs.
Because different materials have different band gaps, light emitting diodes of different materials can emit light with different wavelengths. In addition, some materials have different compositions and doping, for example, some materials have complex energy band structures and indirect transition radiation, so there are various light-emitting diodes.