The semiconductor light emitting device includes a semiconductor light emitting diode ( LED ), a digital tube, a symbol tube, a meter tube, and a dot matrix display (referred to as a matrix tube). In fact, each of the digital tube, the symbol tube, the meter tube, and the matrix tube is a light emitting diode.
First, the working principle, characteristics and application of semiconductor light-emitting diodes
(1) Principle of LED illumination
The light-emitting diode is made of a III-IV compound such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP (phosphorus gallium arsenide) and the like, and its core is a PN junction. Therefore, it has the IN characteristic of a general PN junction, that is, forward conduction, reverse cutoff, and breakdown characteristics. In addition, it has luminescent properties under certain conditions. At the forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. A part of the minority carriers (small children) entering the other area is combined with the majority carriers (multiple sub-) to emit light, as shown in Fig. 1.
Assuming that luminescence occurs in the P region, the injected electrons directly composite with the valence band holes to emit light, or are first captured by the luminescent center and then condensed with the holes. In addition to this luminescent composite, some electrons are trapped by the non-luminous center (this center is near the middle of the conduction band and the intermediate band), and then recombined with the holes, and the energy released each time is not large, and visible light cannot be formed. The greater the ratio of the composite amount of luminescence to the non-luminous composite amount, the higher the photon efficiency. Since the recombination emits light in the minority carrier diffusion region, light is generated only within a few μm of the PN junction surface.
Theoretically and practically, the peak wavelength λ of light is related to the forbidden band width Eg of the semiconductor material in the light-emitting region, that is, the unit of Eg in the formula λ≈1240/Eg(mm) is electron volt (eV). If visible light (wavelength between 380 nm and 780 nm red) is produced, the Eg of the semiconductor material should be between 3.26 and 1.63 eV. Light longer than the wavelength of red light is infrared light. There are now infrared, red, yellow, green and blue light-emitting diodes, but the blue light diodes are expensive and expensive, and are not commonly used.
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